Composting of plant waste. Composting waste - recommendations for forming a compost heap

The Art and Science of Composting

Introduction

The history of composting goes back centuries. The first written records of the use of compost in agriculture appeared 4,500 years ago in Mesopotamia, between the Tigris and Euphrates rivers (present-day Iraq). All civilizations on Earth have mastered the art of composting. The Romans, Egyptians, and Greeks actively practiced composting, which is reflected in the Talmud, the Bible and the Koran. Archaeological excavations confirm that the Mayan civilization also practiced composting 2,000 years ago.

Despite the fact that the art of composting has been known to gardeners since time immemorial, it was largely lost in the 19th century, when artificial mineral fertilizers became widespread. After the end of the Second World War, agriculture began to benefit from the results of scientific developments. Agricultural science recommended the use of chemical fertilizers and pesticides in all forms to increase productivity. Chemical fertilizers have replaced compost.

In 1962, Rachel Carson published Silent Spring, a book about the widespread abuse of chemical pesticides and other pollutants. This served as a signal for public protest and a ban on the production and use of dangerous products. Many have begun to rediscover the benefits of so-called organic farming.

One of the first publications in this aspect was Sir Albert Howard’s book “An Agricultural Testament,” published in 1943. The book sparked a huge interest in organic methods in agriculture and gardening. Today, every farmer recognizes the value of compost in stimulating plant growth and in restoring depleted and lifeless soil. It was as if this ancient agricultural art had been rediscovered.

Organic farming cannot be called a complete return to the old, since it has at its disposal all the achievements of modern science. All chemical and microbiological processes occurring in the compost heap have been studied thoroughly, and this makes it possible to consciously approach the preparation of compost, regulate and direct the process in the right direction.

Wastes that can be composted range from municipal waste, which is a mixture of organic and inorganic components, to more homogeneous substrates such as animal and crop waste, raw activated sludge and sewage. Under natural conditions, the process of biodegradation occurs slowly, on the surface of the earth, at ambient temperature and, mainly, under anaerobic conditions. Composting is a method of accelerating natural degradation under controlled conditions. Composting is the result of understanding the workings of these natural biological and chemical systems.

Composting is an art. This is how the exceptional importance of compost for the garden is now assessed. Unfortunately, we still pay very little attention to the proper preparation of compost. And properly prepared compost is the basis, the key to the future harvest.
There are well-established and proven general principles for preparing compost.

1. Theoretical basis of the composting process

The composting process involves a complex interaction between organic waste, microorganisms, moisture and oxygen. Waste usually has its own endogenous mixed microflora. Microbial activity increases when moisture content and oxygen concentration reach the required level. In addition to oxygen and water, microorganisms require sources of carbon, nitrogen, phosphorus, potassium and certain trace elements for growth and reproduction. These needs are often met by substances contained in waste.

By consuming organic waste as a food substrate, microorganisms multiply and produce water, carbon dioxide, organic compounds and energy. Part of the energy resulting from the biological oxidation of carbon is consumed in metabolic processes, the rest is released in the form of heat.

Compost, as the final product of composting, contains the most stable organic compounds, decomposition products, biomass of dead microorganisms, a certain amount of living microbes and products of the chemical interaction of these components.

1.1. Microbiological aspects of composting

Composting is a dynamic process that occurs due to the activity of a community of living organisms of various groups.

The main groups of organisms involved in composting:
microflora – bacteria, actinomycetes, fungi, yeast, algae;
microfauna – protozoa;
macroflora – higher fungi;
macrofauna - two-legged centipedes, mites, springtails, worms, ants, termites, spiders, beetles.

The composting process involves many species of bacteria (more than 2000) and at least 50 species of fungi. These species can be divided into groups according to the temperature ranges in which each of them is active. For psychrophiles, the preferred temperature is below 20 degrees Celsius, for mesophiles - 20-40 degrees Celsius and for thermophiles - above 40 degrees Celsius. The microorganisms that predominate in the final stage of composting are generally mesophilic.

Although the number of bacteria in compost is very high (10 million - 1 billion microbial biomass/g of wet compost), due to their small size they constitute less than half of the total microbial biomass.

Actinomycetes grow much more slowly than bacteria and fungi, and in the early stages of composting they do not compete with them. They are more noticeable at later stages of the process, when they become very numerous and a white or gray coating, typical of actinomycetes, is clearly visible at a depth of 10 cm from the surface of the composted mass. Their number is lower than the number of bacteria and is about 100 thousand - 10 million cells per gram of wet compost.

Fungi play an important role in cellulose degradation and the compostable mass must be controlled to optimize the activity of these microorganisms. Temperature is an important factor, as mushrooms die if it rises above 55 degrees Celsius. After a decrease in temperature, they again spread from colder zones throughout the entire volume.

Not only bacteria, fungi, actinomycetes, but also invertebrates take an active part in the composting process. These organisms coexist with microorganisms and are the basis of the “health” of the compost heap. The friendly team of composters includes ants, beetles, centipedes, fall armyworm caterpillars, false scorpions, fruit beetle larvae, centipedes, mites, nematodes, earthworms, earwigs, woodlice, springtails, spiders, harvest spiders, enchytriids (white worms), etc. .. Once the maximum temperature is reached, the compost, cooling, becomes accessible to a wide range of soil animals. Many soil animals contribute greatly to the recycling of compostable material through physical breakup. These animals also help mix the different components of the compost. In temperate climates, earthworms play a major role in the final stages of the composting process and the further incorporation of organic matter into the soil.

1.1.1. Composting stages
Composting is a complex, multi-stage process. Each stage is characterized by different consortia of organisms. The composting phases consist of (Figure 1):
1. lag phase,
2. mesophilic phase,
3. thermophilic phase,
4. maturation phase (final phase).

FIGURE 1. STAGES OF COMPOSTING.

Phase 1 (lag phase) begins immediately after adding fresh waste to the compost heap. During this phase, microorganisms adapt to the type of waste and living conditions in the compost heap. The decomposition of waste begins already at this stage, but the total size of the microbial population is still small and the temperature is low.

Phase 2 (mesophilic phase). During this phase, the process of substrate decomposition intensifies. The size of the microbial population increases mainly due to mesophilic organisms adapting to low and moderate temperatures. These organisms quickly degrade soluble, easily degradable components such as simple sugars and carbohydrates. The reserves of these substances are quickly depleted, and microbes begin to decompose more complex molecules such as cellulose, hemicellulose and proteins. After consuming these substances, microbes secrete a complex of organic acids, which serve as a source of food for other microorganisms. However, not all of the formed organic acids are absorbed, which leads to their excessive accumulation and, as a result, to a decrease in the pH of the environment. pH serves as an indicator of the end of the second stage of composting. But this phenomenon is temporary, since excess acids lead to the death of microorganisms.

Phase 3 (thermophilic phase). As a result of microbial growth and metabolism, temperature rises. When temperatures rise to 40 degrees Celsius and above, mesophilic microorganisms are replaced by microbes that are more resistant to high temperatures - thermophiles. When temperatures reach 55 degrees Celsius, most human and plant pathogens die. But if the temperature exceeds 65 degrees Celsius, the aerobic thermophiles in the compost heap will also die. Due to high temperature, there is an accelerated breakdown of proteins, fats and complex carbohydrates such as cellulose and hemicellulose - the main structural components of plants. As a result of the depletion of food resources, metabolic processes decline and the temperature gradually decreases.

Phase 4 (final phase). As the temperature drops to the mesophilic range, mesophilic microorganisms begin to dominate the compost heap. Temperature is the best indicator of the onset of the ripening stage. In this phase, the remaining organic substances form complexes. This complex of organic substances is resistant to further decomposition and is called humic acids or humus.

1.2. Biochemical aspects of composting

Composting is a biochemical process designed to convert solid organic waste into a stable, humus-like product. Simply put, composting refers to the biochemical breakdown of the organic constituents of organic waste under controlled conditions. The use of controls distinguishes composting from naturally occurring processes of rotting or decomposition.

The composting process depends on the activity of microorganisms, which require a carbon source for energy and cell matrix biosynthesis, as well as a nitrogen source for the synthesis of cellular proteins. To a lesser extent, microorganisms need phosphorus, potassium, calcium and other elements. Carbon, which makes up about 50% of the total mass of microbial cells, serves as a source of energy and building material for the cell. Nitrogen is a vital element in the cell's synthesis of proteins, nucleic acids, amino acids and enzymes necessary for the construction of cellular structures, growth and functioning. The need for carbon in microorganisms is 25 times higher than for nitrogen.

In most composting processes, these needs are met by the initial composition of the organic waste; only the carbon to nitrogen (C:N) ratio and, occasionally, the phosphorus level may need to be adjusted. Fresh and green substrates are rich in nitrogen (the so-called “green” substrates), while brown and dry substrates (the so-called “brown” substrates) are rich in carbon (Table 1).

TABLE 1.
RATIO OF CARBON AND NITROGEN IN SOME SUBSTRATES.

The carbon-nitrogen balance (C:N ratio) is of great importance for compost formation. The C:N ratio is the ratio of the weight of carbon (not the number of atoms!) to the weight of nitrogen. The amount of carbon needed significantly exceeds the amount of nitrogen. The reference value for this ratio for composting is 30:1 (30g carbon per 1g nitrogen). The optimal C:N ratio is 25:1. The more the carbon-nitrogen balance deviates from the optimal one, the slower the process proceeds.

If the solid waste contains a large amount of carbon in bound form, then the acceptable carbon-nitrogen ratio may be higher than 25/1. A higher value of this ratio results in the oxidation of excess carbon. If this indicator significantly exceeds the specified value, nitrogen availability decreases and microbial metabolism gradually fades. If the ratio is less than the optimum value, as is the case in activated sludge or manure, nitrogen will be removed as ammonia, often in large quantities. The loss of nitrogen due to ammonia volatilization can be partially compensated by the activity of nitrogen-fixing bacteria, which appear mainly under mesophilic conditions in the late stages of biodegradation.

The main detrimental effect of too low a C/N ratio is the loss of nitrogen due to the formation of ammonia and its subsequent volatilization. Meanwhile, nitrogen conservation is very important for compost formation. Ammonia loss becomes most noticeable during high-speed composting processes, when the degree of aeration increases, thermophilic conditions are created and the pH reaches 8 or more. This pH value favors the formation of ammonia, and high temperature accelerates its volatilization.

The uncertainty of the amount of nitrogen loss makes it difficult to accurately determine the required initial C:N value, but in practice it is recommended in the range of 25:1 – 30:1. At low values ​​of this ratio, the loss of nitrogen in the form of ammonia can be partially suppressed by the addition of excess phosphate (superphosphate).

During the composting process there is a significant reduction in the ratio from 30:1 to 20:1 in the final product. The C:N ratio is constantly decreasing because during the absorption of carbon by microbes, 2/3 of it is released into the atmosphere in the form of carbon dioxide. The remaining 1/3, together with nitrogen, is included in the microbial biomass.

Since weighing the substrate is not practiced when forming a compost heap, the mixture is prepared from equal parts of “green” and “brown” components. Regulation of the ratio of carbon and nitrogen is based on the quality and quantity of a particular type of waste that is used when laying the heap. Therefore, composting is considered both an art and a science.

Calculating the carbon to nitrogen ratio (C:N)

There are several ways to calculate the carbon to nitrogen ratio. We present the simplest one, using manure as a sample. The organic matter of semi-rotted and rotted manure contains approximately 50% carbon (C). Knowing this, as well as the ash content of manure and the total nitrogen content in it in terms of dry matter, we can determine the C:N ratio using the following formula:

C:N = ((100-A)*50)/(100*X)

Where A is the ash content of manure, %;
(100 – A) – content of organic matter, %;
X – total nitrogen content based on absolutely dry weight of manure, %.
For example, if ash content A = 30%, and total nitrogen content in manure = 2%, then

C:N = ((100-30)*50)/(100*2) = 17

1.3. Critical factors for composting

The process of natural decomposition of the substrate during composting can be accelerated by controlling not only the ratio of carbon and nitrogen, but also humidity, temperature, oxygen level, particle size, size and shape of the compost heap, and pH.

1.3.1. Nutrients and Supplements

In addition to the above substances necessary for the growth and reproduction of microorganisms - the main decomposers of organic waste, various chemical, plant and bacterial additives are used to increase the speed of composting. Except for the possible need for additional nitrogen, most waste contains all the necessary nutrients and a wide range of microorganisms, making it available for composting. Obviously, the onset of the thermophilic stage can be accelerated by returning some finished compost to the system.

Carriers (wood chips, straw, sawdust, etc.) are usually needed to maintain a structure that provides aeration when composting wastes such as raw activated sludge and manure.

1.3.2. pH

pH is the most important indicator of the “health” of a compote heap. As a rule, the pH of household waste in the second phase of composting reaches 5.5–6.0. In fact, these pH values ​​are an indicator that the composting process has begun, that is, has entered the lag phase. The pH level is determined by the activity of acid-forming bacteria, which decompose complex carbon-containing substrates (polysaccharides and cellulose) into simpler organic acids.

pH values ​​are also maintained by the growth of fungi and actinomycetes capable of decomposing lignin in an aerobic environment. Bacteria and other microorganisms (fungi and actinomycetes) are capable of decomposing hemicellulose and cellulose to varying degrees.

Microorganisms that produce acids can also utilize them as their only source of nutrition. The end result is a rise in pH to 7.5–9.0. Attempts to control pH with sulfur compounds are ineffective and impractical. Therefore, it is more important to manage aeration by controlling anaerobic conditions, recognizable by fermentation and putrid odor.

The role of pH in composting is determined by the fact that many microorganisms, like invertebrates, cannot survive in a very acidic environment. Fortunately, pH is usually controlled naturally (carbonate buffer system). One thing to keep in mind is that if you decide to adjust the pH by neutralizing an acid or alkali, this will result in the formation of salt, which can have a negative impact on the health of the pile. Composting occurs easily at pH values ​​of 5.5–9.0, but is most effective in the range of 6.5–9.0. An important requirement for all components involved in composting is weak acidity or weak alkalinity in the initial stage, but mature compost should have a pH in the range close to neutral pH values ​​(6.8–7.0). If the system becomes anaerobic, the accumulation of acid can lead to a sharp drop in pH to 4.5 and significantly limit microbial activity. In such situations, aeration becomes the lifeline that will return the pH to acceptable values.

The optimal pH range for most bacteria is between 6-7.5, while for fungi it can be between 5.5 and 8.

1.3.3. Aeration

Under normal conditions, composting is an aerobic process. This means that microbial metabolism and respiration require the presence of oxygen. Translated from Greek aero means air, and bios- life. Microbes use oxygen more often than other oxidizing agents, since with its participation reactions proceed 19 times more energetically. The ideal oxygen concentration is 16 - 18.5%. At the beginning of composting, the oxygen concentration in the pores is 15-20%, which is equivalent to its content in atmospheric air. The concentration of carbon dioxide varies in the range of 0.5-5.0%. During the composting process, the oxygen concentration decreases and the carbon dioxide concentration increases.

If the oxygen concentration drops below 5%, anaerobic conditions occur. Monitoring the oxygen content of the exhaust air is useful for adjusting the composting regime. The easiest way to do this is through smell, as decomposition odors indicate the onset of an anaerobic process. Since anaerobic activity is characterized by bad odors, small concentrations of bad-smelling substances are allowed. The compost heap acts as a biofilter that traps and neutralizes foul components.

Some compost systems are able to passively maintain adequate oxygen concentrations through natural diffusion and convection. Other systems require active aeration, provided by blowing air or turning and mixing the composting substrates. When composting wastes such as raw activated sludge and manure, carriers (wood chips, straw, sawdust, etc.) are typically used to maintain a structure that provides aeration.

Aeration can be carried out by the natural diffusion of oxygen into the composted mass by mixing the compost manually, using machinery or forced aeration. Aeration has other functions in the composting process. The air flow removes carbon dioxide and water formed during the life of microorganisms, and also removes heat due to evaporative heat transfer. Oxygen demand varies during the process: it is low during the mesophilic stage, increases to a maximum during the thermophilic stage, and drops to zero during the cooling and ripening stage.

With natural aeration, the central areas of the composted mass may find themselves in conditions of anaerobiosis, since the rate of oxygen diffusion is too low for the ongoing metabolic processes. If the composting material has anaerobic zones, butyric, acetic and propionic acids may occur. However, the acids are soon used by the bacteria as a substrate, and the pH level begins to rise with the formation of ammonia. In such cases, manual or mechanical agitation allows air to penetrate into anaerobic areas. Mixing also helps to disperse large fragments of raw materials, which increases the specific surface area required for biodegradation. Control of the mixing process ensures that most of the raw materials are processed under thermophilic conditions. Excessive mixing leads to cooling and drying of the composted mass, to ruptures in the mycelium of actinomycetes and fungi. Mixing compost in heaps can be prohibitively expensive in terms of machine and manual labor, and therefore frequency of mixing is a trade-off between economics and process needs. When using composting plants, it is recommended to alternate periods of active mixing with periods of no mixing.

1.3.4. Humidity

Compost microbes need water. Decomposition occurs much faster in thin liquid films formed on the surfaces of organic particles. 50–60% moisture is considered the optimal content for the composting process, but higher values ​​are possible when using carriers. Optimal humidity varies and depends on the nature and size of the particles. A moisture content of less than 30% inhibits bacterial activity. At a humidity of less than 30% of the total mass, the rate of biological processes drops sharply, and at a humidity of 20% they may stop altogether. Humidity above 65% prevents the diffusion of air into the pile, which significantly reduces degradation and is accompanied by stench. If the humidity is too high, the voids in the compost structure are filled with water, which limits the access of oxygen to microorganisms.

The presence of moisture is determined by touch when pressing a lump of compost. If 1-2 drops of water are released when pressed, then the compost has sufficient moisture. Straw-type materials are resistant to high humidity.

Water is formed during composting due to the activity of microorganisms and is lost due to evaporation. If forced aeration is used, water losses can be significant, and it becomes necessary to add additional water to the compost. This can be achieved by irrigation with water or the addition of activated sludge and other liquid wastes.

1.3.5. Temperature

Temperature is a good indicator of the composting process. The temperature in the compost heap begins to rise a few hours after laying the substrate and changes depending on the stages of composting: mesophilic, thermophilic, cooling, maturation.

During the cooling stage, which follows the temperature maximum, the pH slowly drops but remains alkaline. Thermophilic fungi from colder zones recapture the entire volume and, together with actinomycetes, consume polysaccharides, hemicellulose and cellulose, breaking them down to monosaccharides, which can subsequently be utilized by a wide range of microorganisms. The rate of heat release becomes very low and the temperature drops to ambient values.
The first three stages of composting occur relatively quickly (in days or weeks) depending on the type of composting system used. The final stage of composting - maturation, during which weight loss and heat generation are small - lasts several months. At this stage, complex reactions occur between lignin residues from waste and proteins of dead microorganisms, leading to the formation of humic acids. Compost does not heat up, anaerobic processes do not occur in it during storage, and it does not remove nitrogen from the soil when added to it (the process of nitrogen immobilization by microorganisms). The final pH value is slightly alkaline.

High temperature is often considered a prerequisite for successful composting. In fact, when the temperature is too high, the biodegradation process is suppressed due to the inhibition of microbial growth; very few species remain active at temperatures above 70 degrees Celsius. The threshold for suppression occurs is around 60 degrees Celsius, and therefore high temperatures over a long period should be avoided in rapid composting. However, temperatures around 60 degrees Celsius are useful for controlling heat-sensitive pathogens. Therefore, it is necessary to maintain conditions under which, on the one hand, pathogenic microflora will die, and on the other, microorganisms responsible for degradation will develop. For these purposes, the recommended optimum temperature is 55 degrees Celsius. Temperature control can be achieved by using forced ventilation during composting. Heat removal is carried out using an evaporative cooling system.

The main factors in the destruction of pathogenic organisms in the process of compost formation are heat and antibiotics produced by destructor microorganisms. The high temperature lasts long enough to kill the pathogens.

The best conditions for compost formation are mesophilic and thermophilic temperature limits. Due to the many groups of organisms involved in the process of compost formation, the range of optimal temperatures for this process as a whole is very wide - 35-55 degrees Celsius.

1.3.6. Particle dispersion

The main microbial activity occurs on the surface of organic particles. Consequently, a decrease in particle size leads to an increase in surface area, and this, in turn, would seem to be accompanied by an increase in microbial activity and decomposition rate. However, when the particles are too small, they stick tightly together, impairing air circulation in the pile. This reduces the supply of oxygen and significantly reduces microbial activity. Particle size also affects the availability of carbon and nitrogen. Acceptable particle size is in the range of 0.3–5 cm, but varies depending on the nature of the raw material, heap size and weather conditions. An optimum particle size is required. For mechanized installations with mixing and forced aeration, the particles can have a size after grinding of 12.5 mm. For stationary heaps with natural aeration, the best particle size is about 50 mm.
It is also desirable that the composting material contains a maximum of organic material and a minimum of inorganic residues (glass, metal, plastic, etc.).

1.3.7. Compost pile size and shape

Various organic compounds present in the compostable mass have different calorific values. Proteins, carbohydrates and lipids have a calorific value of 9-40 kJ. The amount of heat released during composting is very significant, so that when composting large masses temperatures of about 80-90 degrees Celsius can be reached. These temperatures are well above the optimum of 55 degrees Celsius and in such cases evaporative cooling through evaporative aeration may be necessary. Small quantities of compostable material have a high surface to volume ratio.

The compost pile must be of sufficient size to prevent rapid loss of heat and moisture and to ensure effective aeration throughout. When composting material in heaps under natural aeration conditions, they should not be stacked more than 1.5 m in height and 2.5 m in width, otherwise the diffusion of oxygen to the center of the heap will be difficult. In this case, the heap can be stretched into a compost row of any length. The minimum heap size is about one cubic meter. The maximum acceptable heap size is 1.5m x 1.5m for any length.

The stack can be any length, but its height has a certain meaning. If the stack is stacked too high, the material will be compressed by its own weight, there will be no pores in the mixture, and an anaerobic process will begin. A low compost pile loses heat too quickly and cannot be maintained at the optimum temperature for thermophilic organisms. In addition, due to the large loss of moisture, the degree of compost formation slows down. The most acceptable heights of compost piles for all types of waste have been established experimentally.

Uniform decomposition is ensured by mixing the outer edges towards the center of the compost pile. This exposes any insect larvae, pathogenic microbes or insect eggs to the lethal temperatures inside the compost pile. If there is excess moisture, frequent stirring is recommended.

1.3.8. Free volume

The compostable mass can be simplified to be considered as a three-phase system, which includes solid, liquid and gas phases. The structure of compost is a network of solid particles, which contains voids of various sizes. The voids between the particles are filled with gas (mainly oxygen, nitrogen, carbon dioxide), water or a gas-liquid mixture. If the voids are completely filled with water, this greatly complicates the transfer of oxygen. Compost porosity is defined as the ratio of free volume to total volume, and free gas space is defined as the ratio of gas volume to total volume. The minimum free gas space should be about 30%.

The optimal moisture content of the composted mass varies and depends on the nature and dispersion of the material. Different materials can have different moisture contents as long as the appropriate volume of free gas space is maintained.

1.3.9. Compost maturation time

The time required for compost to mature depends on the factors listed above. A shorter ripening period is associated with optimal moisture content, C:N ratio and aeration frequency. The process is slowed down by insufficient substrate moisture, low temperatures, high C:N ratios, large substrate particle sizes, high wood content and inadequate aeration.
The process of composting raw materials proceeds much faster if all the conditions necessary for the growth of microorganisms are met. Optimal conditions for the composting process are presented in Table 2.

TABLE 2
OPTIMAL CONDITIONS FOR COMPOSTING PROCESS

The challenge is to implement a set of these parameters into low-cost but reliable composting systems.

The required duration of the compost formation process also depends on environmental conditions. In the literature you can find different values ​​for the duration of composting: from several weeks to 1-2 years. This time ranges from 10-11 days (formation of compost from garden waste) to 21 days (waste with a high C/N ratio of 78:1). With the help of special equipment, the duration of this process is reduced to 3 days. With active composting, the process duration is 2–9 months (depending on composting methods and the nature of the substrate), but a shorter period is possible: 1–4 months.

During composting, the physical structure of the material undergoes changes. It takes on the dark color associated with compost. Noteworthy is the change in the odor of the composted material from fetid to the “smell of earth” caused by geosmin and 2-methylisoborneol, waste products of actinomycetes.

The end result of the composting stage is the stabilization of organic matter. The degree of stabilization is relative, since the final stabilization of organic matter is associated with the formation of CO2, H2O and mineral ash.

The desired degree of stability is one at which there are no problems when storing the product even when wet. The difficulty is to determine this moment. The dark color typical of compost may appear long before the desired degree of stabilization is achieved. The same can be said about the “smell of the soil.”

In addition to appearance and odor, stability parameters are: final temperature drop, degree of self-heating, amount of decomposed and stable substance, increase in redox potential, oxygen absorption, growth of filamentous fungi, starch test.

Unambiguous criteria have not yet been developed to assess acceptable levels of stability and “maturity” of compost. Composting potential can be determined by assessing the rate of conversion of organic compounds into soil constituents and humus, which increase soil fertility.

Humus formation (humification) is a certain set of all processes involved in the transformation of fresh organic matter into humus. Determining the rate of this conversion is a complex task and, in turn, an important tool for the scientific study of the composting process.

From a number of works carried out by various researchers in this field, it is clear that the parameters that can be used as indicators of the rate of humification, maturity and stability of composts fall into two categories. The first category indicators - pH, total organic carbon (TOC), humification index (HI) and carbon to nitrogen ratio (C/N) - decrease during the composting period. Other chemical indicators and parameters of humification - total nitrogen content (TON), total extractable carbon (TEC) and humic acids (HA), ratio of humic acids to fulvic acids (HA:PhA), degree of humification (DH), humification rate (HR) , maturity index (MI), humification index (IHP) - increase over time, and the quality of the composts stabilizes.

Among the chemical parameters analyzed, the ratio of humic acids to fulvic acids, rate of humification, degree of humification, humification index, maturity index, humification index, carbon to nitrogen ratio have so far been considered key parameters for assessing the rate and degree of conversion of organic waste during composting.

S.M. Tiquia proposed a simpler approach to assessing the degree of “maturity” of compost based on pig manure, the processing of which into a complete and safe organic fertilizer is an important agricultural and environmental problem. The universality of this approach should be emphasized. With its help, you can evaluate not only the composting process that naturally occurs in nature, but also that carried out using biotechnological methods. The latter category includes vermicomposting with the help of dung worms, as well as the use of special microbial “starters”.

Since composting is carried out due to the vital activity of the microbial community of manure, microbiological indicators were taken as indicators of the “maturity” of compost. Of the six microbiological indicators studied, the test of dehydrogenase activity turned out to be the most informative and adequate. Compared to other criteria, it turned out to be a simpler, faster and cheaper method for monitoring the stability and readiness of compost. Once the material is determined to be stable enough for storage, it is sorted into fractions by sieving.

Making compost. Anaerobic and aerobic types of decomposition. The ratio of carbon and nitrogen. How to properly start a compost heap.

Compost is a fertilizer obtained from the microbial decomposition of organic matter.

Almost all gardeners use compost, regardless of what agricultural technology they follow, whether they dig the soil, or just loosen it, use mineral fertilizers, or do without them.

Almost every garden has a heap, or pit, for recycling kitchen waste and yard waste. For composting, someone builds all kinds of boxes, barriers, using metal mesh, boards, slate - any material that encloses a place suitable for composting organic waste.

The resulting compost has a loose, breathable structure and is enriched with all the nutrients necessary for plants. In fact, composting in the garden is a very good thing!

And almost every gardener considers himself an expert in this matter, but some simply don’t think that compost can be prepared in various ways: “What’s so difficult? I threw weeds and grass into the pile, dumped kitchen waste in there, watered it, and wait until it all rots!”

In general, that's correct. But I would like to understand in a little more detail the biological processes that occur during the decomposition of organic matter, so that composting in the garden does not occur spontaneously, but according to a planned scenario.

Anaerobic

It is also called “cold” and occurs at temperatures of 15–35°C, with the participation of anaerobic microorganisms that receive energy in the absence of oxygen.

During this type of composting, the compost heap is compacted, covered with film, or placed in pits. But it is better to abandon this composting method. Why?

A significant disadvantage of this method is the slow decomposition of organic matter, and the process of decay itself, with a lack of oxygen, can take a direction harmful to plants, provoking the development of fungi, including pathogenic ones.

In anaerobic fermentation, the carbon present in the fermenting materials is converted not into carbon dioxide, as in aerobic fermentation, but into methane. Hence the unpleasant smell. In nature, this process occurs at the bottom of swamps, and in compost heaps it can occur when the compost humidity is high.

Aerobic

Faster, occurs at higher temperatures, without an unpleasant odor. Most gardeners prefer aerobic composting, that is, with air access.

Although it must be admitted that in a compost heap both aerobic and anaerobic processes occur simultaneously. If there is more oxygen (air) in the upper layers of the compost heap, then aerobic composting will predominate there.

Aerobic fermentation occurs on a large scale in nature and is the dominant method by which waste from fields and forests is converted into humus that is beneficial to soils and their inhabitants.
Therefore, gardeners most often strive to use this particular method, systematically mixing (shifting) decomposing organic matter in a heap to provide it with air.

It happens that the compost mass sometimes heats up to 70 ° C, as if it “burns out”. Should we be happy about these temperatures or not?

There is an opinion that hot composting leads to the destruction of pathogenic organisms, and also to the fact that weed seeds that fall into the compost heap lose their germination.

As experiments have shown, seeds that have undergone heat treatment in a compost heap still partially germinate, so when laying grass for composting, you should avoid collecting weeds after they bloom.

Learn more about the composting process itself

In the first stage, all microbes present take part in waste processing. At the same time, an intensive oxidation process is underway, that is, interaction with oxygen, which releases heat.
The most striking and fastest example of oxidation as a chemical process is combustion. As for the decomposition of organic matter, this oxidation is slow, and heat (energy) is released slowly during this process.

But what happens to microorganisms at this time? They will die from the elevated temperature.? The fact is that there are a number of so-called thermophilic bacteria that develop at high temperatures (above 50, up to 90 ° C, depending on the species).

The cell wall of thermophiles is resistant to temperature. This is due to its structure and chemical composition. It is these bacteria that continue their work, it is they who heat the compost heap to a critical temperature at which other microorganisms stop their activity.

Some microorganisms die, and some go into an inactive form (cysts) in order to survive as a species. Cyst (from the Greek kystis - bubble), a temporary form of existence of many single-celled plants and animals. It has a protective shell, which is also called a cyst.

Some protozoa can exist in unfavorable conditions in the form of a cyst for several years.
Later, the activity of thermophiles will decrease, as will the temperature in the compost heap itself. Bacteria that have fallen asleep in the cysts will come to life and continue their work. If temperature and humidity are favorable, new microorganisms will colonize the compost and continue the process of decomposition of the components of the compost heap.
From the above it follows that high temperatures, indeed, can partially destroy certain types of microorganisms - both harmful and beneficial.

But pathogenic microbes tolerate unfavorable conditions better, so the claim that hot composting disinfects compost is not entirely justified.
Many experienced gardeners make compost heaps small and low so that the heating in them is not so strong. Such heaps are more quickly populated by worms, which in turn leads to more valuable and nutritious compost.
When adding organic matter for composting, it is worth considering one more circumstance.

Organics are nothing more than a combination of various chemical elements with carbon.

In addition to carbon, nitrogen is of great importance in nature - an important building material for amino acids, proteins, nucleic acids and other compounds.
And the organic materials we use for composting contain both carbon and nitrogen and are characterized by the ratio of these chemical elements.
So, for example, in sawdust the approximate ratio of carbon to nitrogen is: C/N = 500/1
in straw C/N =100/1
in foliage C/N = 50/1;
in lawn grass C/N = 15/1
in vegetable waste C/N = 13/1
manure compost C/N =10/1
This means that compost obtained as a result of the decomposition of grass will be more saturated with nitrogen than compost obtained with a predominance of sawdust.

Therefore, when laying a compost heap, you should alternate or mix nitrogenous components with carbon components.

That is, it’s a good idea to mix sawdust with manure, and transfer vegetable waste with dry leaves, etc. Tree branches should be chopped, and grass should be chopped, if possible.

The smaller the components, the faster the decomposition process will occur.

What usually goes into a compost heap?

Kitchen waste: vegetable peelings, eggshells, offal and fish bones. And also shavings, sawdust, paper, weeds, grass cut from lawns, leaves collected from under trees, straw, brushwood.

It is advisable to sprinkle the layers of components with wood ash, then the compost will be more nutritious.
After a layer of 25-35 centimeters, add a little soil “for fermentation”.
It is advisable to spray each layer with an EM preparation; this will significantly speed up the composting process. After 5–10 days, the pile is mixed, if possible, and when dry, moistened.
If EO preparations are not available to the gardener, to speed up composting you need to add some ready-made compost saturated with microorganisms. If this is not possible, you should use a starter made from grass, manure, or soil from the garden. Well, you can add nothing, using the “And so it will do!” rule, but then mature compost will be obtained at a later date.

Composting allows you to obtain valuable organic fertilizer and dispose of waste, which becomes harmless to the environment.

“Quick preparation of compost. Compost is made in one season by larvae" -

The sharp increase in consumption in recent decades around the world has led to a significant increase in the generation of municipal solid waste (MSW). Currently, the mass of solid waste entering the biosphere annually has reached an almost geological scale and is about 400 million. Considering that existing landfills are overfilled, it is necessary to find new ways to combat solid waste. Currently, solid waste processing technologies implemented in world practice have a number of disadvantages, the main one of which is their unsatisfactory environmental...

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Introduction………………………………………………………………………………3

1. Composting………………………………………………………………………………….5
   1.1 Composting process…………………............................................ ..........6
2. Various composting technologies……………………………………..7
   2.1 Field composting.................................................... ...............................8
3. Composting of municipal solid waste……………………...................14
   1. Aerobic composting in industrial conditions………..…………16
   2. Anaerobic composting of municipal solid waste……………………19

Conclusion………………………………………………………………………………….21
List of references………………………………………………………......22

Introduction

Human life is associated with the emergence of a huge amount of various waste. The sharp increase in consumption in recent decades around the world has led to a significant increase in the generation of municipal solid waste (MSW). Currently, the mass of solid waste flowing annually into the biosphere has reached an almost geological scale and amounts to about 400 million tons per year.

Solid industrial and household waste (IW and BO) litter and litter the natural landscape around us, and are also a source of harmful chemical, biological and biochemical preparations into the natural environment. This creates a certain threat to the health and life of the population of the village, city and region, and entire areas, as well as future generations. That is, these TPs and BOs upset the ecological balance. On the other hand, TP and BO should be considered as technogenic formations that need to be characterized in an industrially significant manner by the content in them of a number of ferrous, non-ferrous metals and other materials suitable for use in metallurgy, mechanical engineering, energy, agriculture and forestry.

It is impossible to make production waste-free, just as it is impossible to make consumption waste-free. Due to changes in industrial production, changes in the standard of living of the population, and an increase in market services, the qualitative and quantitative composition of waste has changed significantly. Stocks of some low-liquidity waste, even with the current decline in production in Russia, continue to accumulate, worsening the environmental situation of cities and regions.

Solving the problem of processing TP and BO has become of paramount importance in recent years. In addition, in connection with the upcoming gradual depletion of natural sources of raw materials (oil, coal, ores for non-ferrous and ferrous metals), the full use of all types of industrial and household waste is of particular importance for all sectors of the national economy. Many developed countries are almost completely and successfully solving all these problems. This is especially true for Japan, the USA, Germany, France, the Baltic countries and many others. In a market economy, researchers, industrialists and municipal authorities face the need to ensure the maximum possible safety of technological processes and the full use of all production waste, that is, to come closer to the creation of waste-free technologies. The complexity of solving all these problems of recycling solid industrial and household waste (IW and BO) is explained by the lack of their clear scientifically based classification, the need to use complex capital-intensive equipment and the lack of economic justification for each specific solution.

In all developed countries of the world, the consumer has long been “dictating” to the manufacturer this or that type of packaging, which makes it possible to establish waste-free circulation of their production.

In 2001, a sociological survey was conducted which showed that 64% of the country's citizens are ready to separate waste collection without any conditions. Given that existing landfills are overfilled, it is necessary to find new ways to combat solid waste. These methods should be very different from incineration, since incinerators are extremely dangerous.

Currently, the solid waste processing technologies implemented in world practice have a number of disadvantages, the main one of which is their unsatisfactory environmental performance associated with the formation of secondary waste containing highly toxic organic compounds and the high cost of processing. This is mainly associated with waste containing organochlorine substances and releasing highly toxic organic compounds (dioxins, etc.). Dioxin-forming components of solid waste include materials such as cardboard, newspapers, plastics, polyvinyl chloride products, etc. Let's consider one of the processes for processing solid household waste.

1. Composting

Compostingis a waste recycling technology based on their natural biodegradation. Composting is most widely used to process waste of organic - primarily plant - origin, such as leaves, leaves and grass clippings.

Worldwide, composting of solid waste, manure, manure and organic waste is the most common method of treating livestock waste. And there are good reasons for this, because this method of waste processing can solve problems such as unpleasant odors, the accumulation of insects and reducing the number of pathogens, improve soil fertility, reclaim landfills, etc.

In Russia, composting using compost pits is often used by the population in individual homes or in garden plots. At the same time, the composting process can be centralized and carried out at special sites. There are several composting technologies, varying in cost and complexity. Simpler and cheaper technologies require more space and the composting process takes longer.

The main components for composting are: peat, manure, slurry, bird droppings, fallen leaves, weeds, stubble, food waste, vegetable waste, sawdust, municipal solid waste: paper, sawdust, rags, sewage waste.

1.1 Composting process

Composting waste consists of increasing the content of nutrients available to plants in the organic mass (nitrogen, phosphorus, potassium and others), neutralizing pathogenic microflora and helminth eggs, and reducing the amount of cellulose, hemicellulose and pectin substances. In addition, as a result of composting, the fertilizer becomes free-flowing, which makes it easier to apply it to the soil. At the same time, in terms of its fertilizing properties, compost is in no way inferior to manure, and some types of compost are even superior to it.

Thus, composting waste allows you not only to get rid of feces and waste in a timely manner and without unnecessary headaches, but at the same time to obtain high-quality fertilizer from them.

It is important to remember that hospital waste, offal from veterinary laboratories, admixtures of pesticides, radioactive, disinfectants and other toxic substances are not subject to composting.

Composting of waste can be accelerated using advanced composting technologies and equipment. At the same time, devices for composting waste must meet fairly high modern environmental requirements. ABONO Group specialists design composting sites, develop technologies and supply a complete set of composting equipment.

2. Various composting technologies

Minimal technology.Compost heaps 4 meters high and 6 meters wide. Turn over once a year. The composting process takes one to three years depending on the climate. A relatively large sanitary area is required.

Low level technology. Compost heaps are 2 meters high and 3-4 meters wide. The heaps turn over for the first time after a month. The next turning over and the formation of a new heap after 10-11 months. Composting takes 16-18 months.

Mid-level technology.The piles are turned over daily. Compost is ready in 4-6 months. Capital and operating costs are higher.

High level technology. Special aeration of compost heaps is required. Compost is ready in 2-10 weeks.

High level technology. Special aeration of compost heaps is required. Compost is ready in 2-10 weeks.

The end product of composting is compost, which can have various applications in urban and agricultural applications.

Possible markets for compost: garden plots; enterprises; nurseries; greenhouses; cemeteries; agricultural enterprises; landscape construction; public parks; roadside strips; land reclamation; landfill covering; mining reclamation; reclamation of urban wastelands.

Composting, used in Russia at mechanized waste processing plants, for example, in St. Petersburg, is a process of fermentation in bioreactors of the entire volume of solid waste, and not just its organic component. Although the characteristics of the final product can be significantly improved by extracting metal, plastic, etc. from waste, it is still a rather dangerous product and has very limited use (in the West, such “compost” is used only for covering landfills).

2.1 Field composting of solid waste

The simplest and cheapest method of solid waste disposal is field composting. It is advisable to use it in cities with a population of over 50 thousand inhabitants. Properly organized field composting protects the soil, atmosphere, ground and surface waters from solid waste contamination. Field composting technology allows for the joint neutralization and processing of solid waste with dewatered sewage sludge (in a ratio of 3:7), the resulting compost contains more nitrogen and phosphorus.

There are two basic schemes for field composting:

With preliminary crushing of solid waste;

Without preliminary crushing.

When using a scheme with preliminary crushing of solid waste, special crushers are used to crush the waste.

In the second case (without preliminary crushing), grinding occurs due to repeated shoveling of the composted material. Uncrushed fractions are separated on a control screen.

Field composting plants equipped with crushers for preliminary crushing of solid waste provide greater compost yield and produce less production waste. Solid waste is crushed using hammer crushers or small biothermal drums (drum rotation speed 3.5 min1). The drum provides sufficient crushing of solid waste in 8001200 revolutions (46 hours). After such processing, 60-70% of the material passes through the drum shell sieve with holes with a diameter of 38 mm.

Field composting facilities and equipment must ensure the reception and preliminary preparation of solid waste, biothermal neutralization and final processing of compost. Solid waste is unloaded into a receiving buffer or onto a leveled area. Using a bulldozer, a grab crane or special equipment, stacks are formed in which aerobic biothermal composting processes take place.

The height of the stacks depends on the method of aeration of the material and when using forced aeration it can exceed 2.5 m. The width of the stack at the top is at least 2 m, the length is 10 50 m, the slope angle is 45°. Passages 36 m wide are left between the stacks.

To prevent the dispersal of paper, the breeding of flies, and eliminate odor, the surface of the stack is covered with an insulating layer of peat, mature compost or earth 20 cm thick. The heat released under the influence of the vital activity of thermophilic microorganisms leads to “self-heating” of the composted material. At the same time, the outer layers of material in the stack serve as heat insulators and themselves heat up less, and therefore, in order to reliably neutralize the entire mass of material, the stacks must be shoveled. In addition, shoveling promotes better aeration of the entire mass of composted material. The duration of solid waste disposal at composting sites is 1 - 6 months. depending on the equipment used, the technology adopted and the season of laying the stacks.

When placing uncrushed solid waste in the spring and summer, the temperature in the shatbel of composted material rises to 60-70 °C after 5 days and is maintained at this level for two to three weeks, then drops to 40-50 °C. Over the next 34 months. the temperature in the shatbel decreases to 30-35 °C.

Shovelling helps to activate the composting process; 4-6 days after shoveling, the temperature rises again to 60-65 °C for several days.

During autumn-winter stacking, the temperature during the first month rises only in individual pockets, and then, as self-heating occurs (1.5-2 months), the temperature of the stack reaches 50 60 ° C and remains at this level for two weeks. Then, for 2 3 months, the temperature in the stack is kept at 20 30 ° C, and with the onset of summer it rises to 30 40 ° C.

During the composting process, the moisture content of the material is actively reduced, therefore, in order to speed up the biothermal process, in addition to shoveling and forced aeration, it is necessary to moisten the material.

Schematic diagrams of structures for field composting of solid waste are shown in Fig. 2.5.

In Fig. 1, a, b, c, d shows schemes with preliminary grinding of solid waste, and in Fig. 1, d processing was moved to the end of the production line. In Fig. 1, a, b, c solid waste is unloaded into receiving bins equipped with an apron feeder, in Fig. 1, g into trenches and then removing them with a grab crane. In Fig. 1, a, b, d shredding of solid waste is carried out in a crusher with a vertical shaft, in Fig. 1, c - in a horizontal rotating biodrum.

In Fig. 1, and crushed solid waste is mixed with dewatered sewage sludge and then sent to piles, where they remain for several months. During composting, the material is shoveled several times.

The technological scheme of composting in two stages is shown in Fig. 1, b. During the first ten days, the biothermal process takes place in a closed room, divided into compartments by retaining longitudinal walls. The composted material is reloaded every two days with a special mobile unit from one compartment to another. To activate the biothermal process, forced aeration of the composted material is carried out through holes located at the base of the compartments.

After screening, the composted material is transferred from closed compartments to an open area, where it matures in piles for 2 to 3 months.

The diagram shown in Fig. 1, c, differs from the others in that it uses a biodrum as a crusher.

In the diagram shown in Fig. 1, d, double screening of the material is used. During primary screening, the material crushed in the crusher is divided into two fractions: large, sent for combustion, and small, sent for composting. Composting is carried out in a tray located in an open area. The tray is divided into sections by longitudinal walls and equipped with an installation for reloading compostable material into adjacent sections. Mature compost is subjected to repeated (control) screening, after which it is sent to the consumer.

In the absence of a crusher for solid waste, the scheme shown in Fig. 1, d, in which screening, crushing and magnetic separation occur at the end of the technological cycle.

The simplest and most common solid waste disposal facilities are landfills. Modern solid waste landfills are complex environmental structures designed for the neutralization and disposal of waste. Landfills must provide protection from waste pollution of atmospheric air, soil, surface and ground water, and prevent the spread of rodents, insects and pathogens.

Fig. 1 schematic diagrams of field composting facilities for solid waste:

a) joint processing of solid waste and sludge water

b) two-stage composting of solid waste

c) scheme with pre-treatment of solid waste in a drum

d) scheme with composting in open compartments and preliminary screening of solid waste

e) composting of uncrushed solid waste

1 receiving hopper with apron feeder; 2 crusher for solid waste; 3 suspended electromagnetic separator; 4 supply of sewage sludge; 5 mixer; 6 stacks; 7 grab crane; 8 closed room for the first stage of composting; 9 mobile installation for shoveling and reloading compost; 10 longitudinal retaining walls; 11 aerators; 12 control screen for composter; 13 biodrum; 14 primary screen for crushed solid waste; 15 cylindrical control screen; 16 compost crusher.

Rice. 2 schematic diagram of the construction of a solid waste landfill.

Landfills are built according to designs in accordance with SNiP. A diagram of the structural elements of the landfill is shown in Fig. 2

The bottom of the landfill is equipped with an anti-filtration screen and a substrate. It consists of clay and other waterproof layers (bitumen soil, latex) and prevents leachate from entering groundwater. Leachate is a liquid contained in waste that flows down to the bottom of the landfill and can seep through its sides. Filtrate mineralized liquid containing harmful substances. The filtrate is collected using drainage pipes and discharged into a tank for neutralization. Every day at the end of the working day, the waste is covered with special material and layers of soil, and then compacted with rollers. After a section of the landfill is filled, the waste is covered with a top cover.

The product of anaerobic decomposition of organic waste is biogas, which is mainly a mixture of methane and carbon dioxide. The biogas collection system consists of several rows of vertical wells or horizontal trenches. The latter are filled with sand or crushed stone and perforated pipes.

All work at landfills for storage, compaction, isolation of solid waste and subsequent reclamation of the site must be fully mechanized.

Solid waste landfills must ensure environmental protection according to six hazard indicators:

1. The organoleptic indicator of harmfulness characterizes the change in the smell, taste and nutritional value of phytotest plants in adjacent areas of the existing landfill and the territories of the closed landfill, as well as the smell of atmospheric air, taste, color and smell of ground and surface waters.

2. The general sanitary indicator reflects the processes of change in biological activity and self-purification indicators of the soil in adjacent areas.

3. The phytoaccumulation (translocation) indicator characterizes the process of migration of chemicals from the soil of nearby areas and the territory of reclaimed landfills into cultivated plants used as food and fodder (into the marketable mass).

4. The migration-water indicator of harmfulness reveals the processes of migration of chemical substances from solid waste leachate into surface and groundwater.

5. The air migration indicator reflects the processes of emissions entering the atmospheric air with dust, vapors and gases.

6. The sanitary-toxicological indicator summarizes the effect of the influence of factors acting in combination.

The disadvantage of this method of waste disposal is that, along with the leachate formed in the depth of the landfill, which is the main pollutant of the natural environment, toxic gases enter the atmosphere, which not only pollute the air space near the landfill, but also negatively affects the ozone layer of the earth. In addition, when buried in landfills, all valuable substances and components of solid waste are lost.

1. Composting of municipal solid waste (MSW)

The main purpose of composting is disinfection of solid waste (as a result of self-heating to 60-70 O C pathogens are destroyed) and processed into fertilizer compost due to the biochemical decomposition of the organic part of solid waste by microorganisms. The use of compost as a fertilizer in agriculture can increase the yield of crops, improve the structure of the soil and increase the humus content in it. It is also very significant that during composting, a smaller amount of “greenhouse” gases (primarily carbon dioxide) is released into the atmosphere than when burned or disposed of in landfills. The main disadvantage of composthigh content of heavy metals and other toxic substances

Optimal composting conditions are: pH from 6 to 8, humidity 40-60%, but the previously used composting time of 25-50 hours turned out to be insufficient. Currently, composting is carried out in special indoor pools or tunnels for a month

Processing of solid waste into compost on a small scale (1-3% of the total mass of waste) is carried out in a number of countries (Netherlands, Sweden, Germany, France, Italy, Spain, etc.). The organic part separated from solid waste, which is less contaminated with non-ferrous metals than all waste, is often composted. Composting of solid waste was most widespread in France, where in 1980 there were 50 composting plants and 40 combined incineration and composting plants. In the United States, composting is practically not widespread. In Japan, about 1.5% of solid waste is recycled using this method. A number of plants for composting solid waste in biodrums were built in the USSR (in Moscow, Leningrad, Minsk, Tashkent, Alma-Ata). Most of them are no longer functioning.
A combined (composting and pyrolysis) plant for processing solid waste in the Leningrad region worked well. The plant complex consisted of a receiving, biothermal and crushing-sorting departments, a warehouse for finished products and an installation for pyrolysis of the non-compostable part of the waste.
The technological scheme provided for the unloading of garbage trucks into receiving bins, from which the waste was fed onto belt conveyors using apron feeders or grab cranes, and then into rotating biothermal drums

In biodrums, with a constant supply of air, the vital activity of microorganisms was stimulated, which resulted in an active biothermal process. During this process, the temperature of the waste increased to 60 O C, which contributed to the death of pathogenic bacteria.
Compost was a loose, odorless product. On a dry matter basis, the compost contained 0.5-1% nitrogen, 0.3% potassium and phosphorus, and 75% organic humic matter.

The sifted compost underwent magnetic separation and was sent to crushers to grind mineral components, and then transported to the finished product warehouse. The separated metal was pressed. The screened non-compostable part of solid waste (leather, rubber, wood, plastic, textiles, etc.) was sent to a pyrolysis unit.

The technological scheme of this installation provided for the supply of non-compostable waste to a storage hopper, from which it was sent to the loading hopper of the drying drum. After drying, the waste entered the pyrolysis furnace, in which, without air access, its thermal decomposition occurred. As a result, a vapor-gas mixture and a solid carbonaceous residue, pyrocarbon, were obtained. The vapor-gas mixture was sent to the thermomechanical part of the installation for cooling and separation, and pyrocarbon was sent for cooling and further processing. The final products of pyrolysis were pyrocarbon, tar and gas. Pyrocarbon was used in metallurgical and some other industries, gas and resin as fuel.

In general, the scheme for sanitary cleaning of the city is presented in Fig. 3

Rice. 3. Sanitary cleaning of the city

3.1 Aerobic biothermal composting of municipal solid waste in industrial conditions

The method of mechanical biothermal composting began to be used in world practice in the twenties of the last century. The biothermal drums developed at that time turned aerobic biothermal composting into a widely used industrial technology for the neutralization and recycling of solid waste. Using a set of technological measures, it is possible to normalize the content of microelements in compost, including heavy metal salts. Ferrous and non-ferrous metals are extracted from solid waste.

To build a plant for the mechanical processing of solid waste into compost, the following optimal conditions are necessary: ​​the presence of guaranteed consumers of compost within a radius of 20-50 km and the location of the plant near the city border at a distance of up to 15-20 km from the solid waste collection center with a population of at least 300 thousand served. people.

About 25-30% of waste is not compostable. This part of the waste is either burned in compost plants, or subjected to pyrolysis to produce pyrocarbon, or taken to a solid waste landfill for disposal. Household waste is delivered to the plant by garbage trucks, which are unloaded into receiving bins. Waste from the bunker is unloaded onto belt containers, through which they are sent to a sorting building equipped with screens, electromagnetic and aerodynamic separators. Sorted waste intended for composting is conveyed through conveyors into the loading devices of biothermal drums in the form of rotating cylinders (Fig. 4).

The biothermal process of waste neutralization occurs due to the active growth of thermophilic microorganisms under aerobic conditions. The mass of waste itself warms up to a temperature of 60°C, at which pathogenic microorganisms, helminth eggs, larvae and pupae of flies die, and the mass of waste is neutralized. Under the influence of microflora, fast-rotting organic matter decomposes, forming compost. To ensure forced aeration, fans are installed on the body of the biodrum, which supply air into the thickness of the waste. The amount of supplied air is adjusted depending on humidity and material temperature. The optimal humidity to speed up the composting process is 40-45%. The outside of the biodrum is covered with a layer of heat-insulating material to maintain the required temperature conditions.

The biodrums are unloaded onto belt conveyors, which deliver the compost to the sorting building. Here the material flies into a double funnel, divided by a partition into two compartments. Heavy particles (glass, stones), which have greater inertia, fly into the far compartment, and light fractions (compost) are poured into the near one. Next, the compost will fall on a fine sieve, after which the compost is finally cleared of ballast fractions. Glass and fine ballast are poured into carts, and the compost is transported through a conveyor system to storage areas. Most of the territory allocated for the location of the waste processing plant (WRP) is occupied by storage areas for compost maturation and storage. The approximate ripening time for compost in storage is usually at least 2 months.

The compost produced at the MPZ has the following composition: organic matter by dry weight of at least 40%, N 0.7%, P2O5 0.5%, content of ballast inclusions (stones, metal, rubber) 2%, environmental reaction (pH of salt extract) not less than 6.0. As practice shows, with proper organization of solid waste collection, the content of heavy metal salts in compost does not exceed the maximum permissible concentrations.

Emissions into the atmosphere of MPZ during compost production contain ammonia, hydrocarbons, carbon oxides, nitrogen oxides, non-toxic dust and more.

Rice. 4 Technological scheme of continuous anaerobic composting with aerobic oxidation of organic waste in a rotating drum:

1 overhead crane with grab bucket; 2 garbage truck; 3 waste receiving bin; 4 dosing hopper; 5 apron feeder; 6 crane with magnetic washer for loading scrap metal packages; 7 roller conveyor; 8 magnetic separator; 9 scrap metal bunker; 10 baling press; 11 rotating biothermal drum; 12 fan; 13 boiler room or pyrolysis plant; 14 exhaust fan; 15 stacks of compost at the ripening and finished product sites; 16 compost grinder; 17 roar; 18 trailer for collecting screenings from the screen

In small cities (50 thousand inhabitants or more), if there are free areas near the city, field composting of solid waste is used (Fig. 4). In this case, the waste is composted in open piles. The duration of waste processing increases from 2-4 days to several months, and accordingly the area allocated for composting increases. In world practice, two schemes for field composting are used: with and without preliminary crushing of solid waste. In the first case, the waste is crushed with special crushers, in the second, grinding occurs due to natural destruction during repeated “shovelling” of the composted material. During field composting, solid waste is unloaded into a receiving bin or onto a prepared site. A bulldozer or special machines form piles in which aerobic biothermal composting processes take place. To prevent the dispersion of light fractions of garbage, intensive breeding of flies and eliminate unpleasant odors, the surface of the stack is covered with a layer of peat, mature compost or soil about 0.2 m thick. The heat released under the influence of the vital activity of microorganisms leads to “self-heating” of the composted waste in the stack. In this case, the outer layers heat up less than the inner ones and serve as thermal insulation for the internal self-heating layers of waste. To neutralize the entire mass of material in the stack, it is “shoveled”, as a result of which the outer layers are inside the stack, and the inner ones are outside. In addition, this promotes better aeration of the entire compost mass. Also, to increase the activity of the biothermal process, the stacks are moistened. Before being sent to the consumer, the finished compost is sent to a screen, where it is cleaned of large ballast fractions. In field composting, waste is sometimes separated into fractions before composting. Field composting sites are placed on waterproof soils and periodic backfilling of the surface of freshly formed piles with inert material protects the soil, atmosphere and groundwater from contamination.

1. Anaerobic composting of municipal solid waste

Anaerobic composting of solid waste involves the processing of the organic part of waste by fermenting it in bioreactors, resulting in the formation of biogas and compost. The scheme for processing solid waste under anaerobic conditions is as follows (Fig. 5).

Rice. 5 Scheme for processing solid waste using anaerobic composting

1 receiving hopper; 2 overhead grab crane; 3 crusher; 4 magnetic separator; 5 pump mixer; 6 digester; 7 screw press; 8 ripper; 9 container for collecting spin; 10 cylindrical screen; 11 packaging machine; 12 large screening; 13 fertilizer warehouse; 14 gas holder; 15 compressor; 16 equalization chamber; I direction of waste movement; II directions of gas movement

Solid waste is unloaded into a receiving hopper, from where it is fed by a grab crane into a cone crusher with a vertical shaft. The crushed waste is passed under an electromagnetic separator, where scrap metal is extracted from it. Next, the waste enters the digester, where it is kept in anaerobic conditions for 10-16 days at a temperature of 25°C in order to neutralize it. As a result, from each ton of waste about 120-140 m3 of biogas containing 65% methane, 470 kg of organic fertilizers with a moisture content of 30%, 50 kg of scrap metal and ballast fractions, 250 kg of large screenings and 170 kg of gas losses and filtrate are obtained. The spent solid fraction is unloaded and then fed into a screw press for partial dewatering. Then the dehydrated solid fraction enters the disintegrant and from there into a cylindrical screen, in which the material is separated into mass used as organic fertilizers and coarse screenings.

Anaerobic composting of solid waste is used in cases where there is a practical need for biogas.

Conclusion

In Russia, the processing industry has been forgotten, a system for collecting secondary resources is not organized, places for collecting secondary resources (metal) are not equipped in populated areas, a system for removing generated waste is not established everywhere, and there is weak control over its formation. This entails deterioration of the environment and a negative impact on human health.

It is obvious that no technology by itself will solve the problem of solid waste. Both incinerators and landfills are sources of emissions of polyaromatic hydrocarbons, dioxins and other hazardous substances. The effectiveness of technologies can only be considered in the overall life cycle chain of consumer goods waste. MSZ projects, which public environmental organizations have spent a lot of effort fighting, may remain projects for a long time in the current economic situation.

Landfills will remain the main method of disposal (processing) of solid waste in Russia for a long time. The main task is to develop existing landfills, extend their life, and reduce their harmful effects. Only in large and major cities is it effective to build incineration plants (or waste processing plants with pre-sorting of solid waste). It is realistic to operate small incinerators for burning specific waste, hospital waste, for example. This involves diversifying both waste processing technologies and their collection and transportation. Different parts of the city can and should use their own methods of solid waste disposal. This is due to the type of development, income level of the population, and other socio-economic factors.

Bibliography

1) Bobovich B.B. and Devyatkin V.V., “Processing of production and consumption waste”, M2000.

2) “Solid waste disposal”, ed. A.P. Tsygankova. M.: Stroyizdat, 1982.

3) Mazur I.I. et al., “Engineering ecology, T1: Theoretical foundations of engineering ecology”, 1996.

4) Akimova T.A., Khaskin T.V. Ecology: Textbook for universities. M.: UNITY. -1999

5) www.ecolin e. ru

6) www. ecology. ru

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Composting (biothermal method) is a method of biological neutralization of the raw organic part of waste under the influence of aerobic bacteria. Household, some industrial and agricultural waste can be composted. Waste from hospitals, clinics, veterinary laboratories, and fecal matter cannot be composted. Before composting, substances that affect biological decomposition processes, such as pesticides, radioactive and toxic substances, must be eliminated.

The essence of the process is that various aerobic microorganisms actively grow and develop in the thickness of the garbage, causing a fermentation process with the release of heat, resulting in self-heating of the waste to 60°C (not lower than 50°C, can reach 70°C). At this temperature, pathogenic and pathogenic microorganisms, helminth eggs and fly larvae die, and higher rates of decomposition of solid organic pollutants in household waste are achieved, releasing carbon dioxide and water. This reaction continues until a relatively stable material (compost) is obtained, similar to humus, harmless in sanitary terms and a good fertilizer. The mechanism of the main composting reactions is the same as during the decomposition of any organic substances: more complex compounds decompose and turn into simpler ones.

Important for the life of microorganisms is the ratio of carbon and nitrogen, as well as the dispersion of the material, which provides access to oxygen. Dense wastes with a high moisture content (such as manure, wet activated sludge and many plant wastes) that have a low carbon to nitrogen ratio must be mixed with a solid material that absorbs excess moisture and provides the missing carbon and the mixture structure necessary for aeration.

The main indicators characterizing waste as a material for composting include: organic matter content; ash content; content of total nitrogen, calcium, carbon. In table 6.11 shows the types of waste in accordance with the possibility of composting them.

Table 6.11

Suitability of different types of waste for composting

In practice the following are used industrial composting methods -.

• composting in piles without forced aeration;
• composting in piles with forced aeration;
• composting in facilities with controlled conditions (composting in drums, pond composting, tunnel composting, etc.);
• mixed systems.

The choice of composting methods is determined by the optimal combination of the cost of the process and the achieved effect of recycling composted waste. It must be remembered that the use of specialized equipment increases the cost of composting, which can reach significant values. However, the annual increase in the amount of waste stimulates the development of accelerated, mechanized methods for their processing and leads to an expansion of their use.

In any case, to apply composting methods, special waste processing plants are built, where a complete waste disposal cycle is carried out, consisting of three technological stages:

• reception, preliminary preparation of organic waste;
• the actual biothermal process of neutralization and composting;
• compost processing and storage.

The most common and simple biothermal process is composting in piles without forced aeration. Waste neutralization takes a period of 6 to 14 months, while organic waste is delivered to special composting sites, where it is formed in piles- embankments in the form of trapezoids (can be in the form of shafts). The width of the base of the trapezoids is 3 m, the height is 2 m (in the northern regions the height is up to 2.5 m), the length is 10-25 m, the distance between parallel rows of trapezoids is 3 m. The bottom layer of the compost mass should be above the groundwater level at least 1 m. The surface of the piles is covered with a layer of earth or peat at least 15-20 cm thick, which prevents the spread of odor, the breeding of flies and retains the heat necessary for the high-quality decomposition of the biomaterial.

Application composting in piles with forced aeration allows you to increase the intensity of biothermal processes in the composted mass, significantly increase the self-heating temperature and significantly reduce the time for compost preparation (up to 1.5-2 months). In this case, aeration of the piles is ensured by a special installation that allows air to be supplied to the internal layers of stored waste, for example, using a fan, supply pipe and air distribution device.

In connection with the increasing demand for soils and organic fertilizers, attention has increased to the separation of organic waste with its subsequent composting, and therefore the creation of various technical devices intended for composting has become relevant. Thus, it is carried out composting in controlled facilities. Currently, the most common industrial composting methods are drum composting, pond composting, and tunnel composting. All these methods are based on the use of specially designed units to carry out a biothermal process in them. The waste remains in them for different periods of time, and the resulting materials have significant differences. So, composting in drums requires the waste to remain in the installations for about two days, during which time the decomposition process is just beginning, and then the material is placed in open areas for ripening. Composting in a holding pond takes 46 weeks and results in a stabilized finished product. If used tunnel composting, then after 7-10 days the material, in which decomposition processes are still actively occurring, contains a sufficient amount of carbon and nitrogen and is suitable for further processing processes, such as combustion or gasification. The main conditions for choosing the optimal composting method or developing a device for this process are the efficiency of its use and the possibility of using the resulting compost in the future.

In general, a composting device is a complex technical complex that meets the necessary environmental requirements. Annual waste processing in such a device can currently vary from 5,000 to 50,000 tons. The process of processing organic waste in special devices can be implemented in two ways:

• a) a large centralized device;
• b) a complex of devices with many decentralized units.

In practice, there is a tendency to build and operate

namely centralized composting devices. Firstly, despite the significant investment costs during the construction phase, the running costs of centralized devices are significantly lower. Secondly, composting devices must meet fairly high modern environmental requirements, which require the use of expensive technical and technological developments. These measures, such as solving the odor problem, can be implemented in centralized devices at significantly lower costs compared to decentralized ones.

Compost is the final product of organic waste processing and must be epidemiologically safe. The quality of the finished compost is one of the main criteria for production efficiency, but it is also important to take into account the quality of the feedstock. To calculate the quality of composting, an indicator such as the degree of decomposition is traditionally used, which is based on a standardized comparison of temperature during biological self-heating of the composted material.

The use of compost from solid waste is limited, since it should not be used either in agriculture or forestry, due to the possible content of heavy metals or other hazardous components that, through herbs, berries, vegetables, and milk, can cause harm to human health. For the same reason, the systematic use of such material in city squares and parks is impractical, so this material is used mainly as covering soil in landfills or when closing mine workings. However, if hazardous components are excluded from the initial waste at the collection stage, then compost from municipal solid waste can be used as an organic fertilizer, and its safety indicators are the data given in Table. 6.12.

Table 6.12

Compost safety indicators

The main disadvantage of composting is the need to store and neutralize non-compostable waste components, the volume of which can constitute a significant part of the total volume of waste. In addition, the composting process produces substances that have an unpleasant odor and create a burden on the environment. Minimizing these contaminants can be carried out quite successfully using a biofilter, but it requires significant costs, especially considering that odors are formed not only during the decomposition process, but also during the delivery and preparation of waste, as well as during the subsequent processing of the finished compost.

The benefit of composting is that it reduces organic-heavy landfills and produces usable material.

Foreign experience

In Germany, the use of compost from solid waste as a fertilizer is prohibited by law due to the excess content of heavy metals.

Compost is a universal fertilizer that gives plants everything they need for full growth and development. Fertilizing has only one drawback - the long ripening process. This problem can be solved by using a compost accelerator.

The considered feeding has the following variations:

• Peat manure mixture is a combination of manure and peat in equal parts.
• Slurry is liquid mullein with sawdust or peat. The proportion is 50:50. This fertilizer ripens within a month.
• Fecal-peat - a combination of peat and toilet waste in equal parts.
• A mixture of universal composition - fallen leaves, tree shoots, non-aggressive weeds. Ripening period is about 12 months. For better effect, the pile is shifted from place to place several times.
• Manure-soil mixture - earth and manure in a percentage ratio of 40/60. Most of this proportion is occupied by manure. Layout is carried out in the spring and is ready for use on the site in the fall.

Pig waste contains a lot of nitrogen. This is not the best fertilizer option for the soil.

How to make compost?

Laying a compost pit begins with making a box. You can buy a plastic one, make a wooden one yourself, or dig a regular hole. In the latter case, the place is equipped with wooden logs. The material is placed in layers. You can also place them in any order. The main thing is to ensure oxygen access from the top and sides of the compost heap.

It is possible to place the “compost” on the surface of the earth. A recess is first dug for the bayonet of the shovel. Branches of bushes or trees are laid at the bottom. Next comes the compostable material. The pile is surrounded with boards or netting to give it shape. The top of the structure is covered with earth.

The formation of a compost pit occurs as follows:

1. Hard raw materials are crushed into smaller parts. The soft is mixed with the hard to achieve the necessary looseness.
2. The thickness of each layer varies within 15 cm. Thicker rows will make it difficult for air to penetrate inside.
3. Very dry raw materials are first wetted with water.
4. 700 grams of lime are poured onto the top of the next layer. It would not be superfluous to add 300 g of ammonium sulfate and 150 g of superphosphate to each row. The first component can be replaced with bird droppings at the rate of 4.5 kg of the latter instead of 450 g of sulfate. Wood ash replaces lime. Urea will add value to the final rotting result.
5. The normal size of a compost heap is approximately 1.5 m2. With such proportions, the optimal ratio of temperature and humidity inside is maintained.
6. When the heap reaches a height of 1.5 m, it is covered with earth to a level of approximately 5 cm.
7. The laid layers are covered with film or other waterproof material.

It is necessary to ensure that the compost heap is moderately moist.

How to choose a place for a “compost”?

A shady area that does not receive direct sunlight is an ideal location for the compost bin. In such conditions, the required humidity is easily maintained. Moisture promotes a large accumulation of worms and woodlice: the presence of beneficial insects ensures a uniform decomposition process.

It is better if there is not one, but two or three heaps on the site. You should not arrange a place next to trees: powerful roots will draw out all the useful substances from the future fertilizer.

Composition of the compost pit

The basis of any “compost” is mowed grass, leaves without signs of diseases or the presence of pests. Rotting food waste, paper without paint, leftover tea and coffee, egg shells, vegetable and fruit peels, and seed husks are suitable. The more diverse the composition, the more useful elements the future fertilizer will contain.

You need to be very careful when choosing individual types of grass. Aggressive perennial weeds can germinate and colonize inside the compost heap. They should be folded separately and covered tightly with film. In a separate pile, the chances of germination of such weeds are significantly lower.

It is not advisable to send meat, animal fat, potato peelings, or plants with pests or diseases for processing. It is unacceptable to introduce materials that cannot rot.

You should not put citrus peels, the remains of coniferous trees and animal bones in a pile: such waste rots for a very long time and disrupts the conditions for normal compost maturation.

Maintaining a moisture balance is a guarantee of rapid and high-quality decomposition. If there is an excess of moisture, stir the contents; if there is a lack, water it. Turning is also necessary for oxygen to enter the heap.

How to speed up compost maturation?

In the natural environment, the ripening of the organic fertilizer in question occurs very slowly. You can reduce the composting time of the mass with the help of manure: it is a rich source of nitrogen, and this is a necessary condition for a high rate of decay.

Regular yeast is also used. Dilute 1 tbsp per liter of water. sugar and add 1 tbsp. l. dry yeast. The resulting solution is poured into small depressions in the compost heap.

A quick process is facilitated by constant stirring of the contents with a pitchfork and timely moistening. The speed at which humus is produced is affected by the size of the “compost”: the smaller it is, the faster the ripening.

The main stages of rotting of a compost pit

Stages of obtaining organic fertilizer:

1. In the first 7-10 days, decomposition and fermentation of the material begins. The temperature inside the heap reaches 68 °C.
2. Over the next two weeks, heat levels drop significantly. Intensive gas formation occurs and fungi multiply.
3. After the previous 14 days the temperature is around 20°C. The active work of earthworms begins. Their vital activity completely completes the process of organic matter formation. Humus forms inside the compost bin.
4. Reaching the temperature of the compost mass to the appropriate environmental values ​​means the completion of decomposition. The composition is ready for use.

Application of biodestructors

Biodestructor is a new generation microbiological agent for compost. The drug is saturated with living microorganisms necessary for rapid decomposition.

They are able to multiply quickly inside a compost heap. During their life, microbes release substances that accelerate the process of decay. The resulting compost is well absorbed by any plants. The product is based on inorganic additives, vitamins and various amino acids.

The benefits of using biodestructors are more than obvious:

• Waste is disposed of in an environmentally friendly way.
• Compost bacteria are aggressive and kill all other harmful organisms.
• The process of humus formation occurs much faster than in the natural environment.
• When using a biodestructor, the disposed waste does not emit an unpleasant odor.

The resulting organic fertilizer has high fertility. The soil fertilized with it increases its nutritional value several times, and the yield increases by 10-20%. This allows you to significantly save on the purchase of inorganic fertilizers.

Preparations for accelerating compost maturation

Often environmental conditions greatly slow down the time it takes to produce compost. EM drugs are used to speed things up. The abbreviation stands for “effective microorganisms.” Such biological products contain bacteria, in the presence of which the composition decomposes faster. EM concentrates have different names. There are many of them on the market:

• Tamir - reduces the compost readiness period to 2 - 3 weeks. The solution is prepared in a ratio of 1:100. Every 20 cm of compost heap is processed. 1 m3 requires 5 liters of solution. With “Tamir” you don’t have to make one big pile: you can make two small ones, which is much more convenient if you don’t have much space in your dacha. With the use of the drug, the final material is especially nutritious.
• BIOTEL-compost is a safe, effective product. A package weighing 150 grams processes 3 m³ of waste. The product processes plant and food waste equally well. Add 2.5 g of product to 10 liters of water. The resulting liquid is poured into a pile, then the mass is carefully mixed with a pitchfork.
• Baikal EM – contains stamps of beneficial microorganisms for compost and is widely used. Used for the production of humus, pre-sowing treatment of seeds and soil. Diluted in different proportions depending on the task.

How do you know when the compost is ripe?

As it rots, the composition and appearance of the “compost” changes. The decomposed mass becomes loose and friable. The color changes to black and the smell becomes earthy. There are still small undecayed inclusions in it, but there are very few of them.

The main problems that arise during the compost maturation process.

The biological process does not always go smoothly. The following difficulties may arise:

1. There are ants inside the compost heap. This is a sure sign of lack of moisture - you should water the mass.
2. The compost heap smells unpleasant. The phenomenon occurs due to the fact that a significant amount of soft elements is embedded. It is necessary to turn over the compost pile and add straw, paper or dry leaves.
3. There are too many midges hovering over the compost heap. The problem arises due to excess moisture - the mass must be dried. To do this, it is left open for several days.
4. There are no processes observed inside the compost bin. In this case, there is not enough moisture or moist elements. The pile should be shed or green grass should be added.

Compost is a valuable organic fertilizer. In order for it to rot correctly and bring maximum benefits, you need to know the features of its preparation and feeding.