Industrial and Municipal Waste
Industrial Waste
Some industrial wastes containing organic substances can be used as organic fertilizers, achieving:
- increased crop yields;
- industrial production becomes more cost-effective and avoids the costs of storing and disposing of waste.
Industrial organic wastes used as fertilizer are divided into three groups:
1. Wastes requiring composting. This group includes wastes hazardous in sanitary-helminthological, entomological, and phytosanitary respects, for example, feather and down wastes, seed husks of oil crops, cranberry and apple press cake, grape pomace, and wine lees.
2. Wastes requiring early application to the soil, for example, pulp and marc, grape-seed meal, wastes from bristle factories, sweepings from wool shops, cuttings from felt products, wool wastes, and wool dust. Often these are wastes with a wide carbon to ammonium nitrogen ratio (C:NH4). When applied directly to the soil before sowing, temporary biological immobilization of available soil nitrogen by microorganisms occurs, leading to nitrogen starvation of plants and reduced yields. Therefore, they are applied well before sowing — under primary tillage; before sowing, nitrogen fertilizers are applied.
3. Wastes suitable for fertilization without restrictions. For example, pig and cattle sludge, raw fish wastes, fleshings, glue production wastes, horn and galalith shavings, silkworm pupa, silk floss, silkworm excreta, tobacco and makhorka dust, tobacco leaves after nicotine extraction, castor meal, and castor, cotton, camelina, rapeseed, and colza oil cakes.
Maximum application rates of industrial wastes to soil are generally 80–100 kg of total nitrogen. Up to 6 t/ha can be applied with manure spreaders or as mixtures with manure and composts.
Tree Bark and Sawdust
Tree bark can serve as an organic fertilizer; it accounts for 10–20% of the total volume of a tree and accumulates at wood-processing plants. Tree bark and sawdust are used for mulching and as fertilizer, for preparing artificial soil for greenhouse and hotbed farms, and as litter on poultry farms and poultry plants with subsequent use as fertilizer.
Reserves of woody greenery in the Russian Federation exceed 20 million t per year, of which less than 10% is used. Tree bark contains the main nutrient elements, which become available to plants during mineralization. It has good humus-forming potential; during mineralization, carbon dioxide is released, thereby improving air nutrition of plants.
Tree bark contains 33–35% cellulose, 22–30% lignin, 5.3–12 mg/100 g potassium, and insignificant amounts of phosphorus. The strength, elasticity, and high filtration capacity of bark help improve the water-physical properties of soil; its difficult-to-decompose part enriches the soil with lignin and tannins involved in humus formation. The disadvantage of bark as a fertilizer is that it does not contain plant-available nitrogen. The carbon-to-nitrogen ratio is 140:1. The ash content of pine bark is 2.8%, of spruce bark 3.1–5.9%. Acidity — pH 4.8–5.7. Bark is biologically active: it contains large numbers of bacteria and molds.
Tree bark is plowed into the soil to a shallow depth. When 125 m3/ha is applied, soil structure improves and water-holding capacity increases. When uncomposted bark is applied, additional nitrogen fertilizers are required for the normal activity of microorganisms that promote bark decomposition. Decomposition of coniferous bark crushed to 5 cm takes about 2 years.
Other ways of using tree bark include composting with mineral and organic additives, as well as use as biofuel, mulch, and substrates in protected ground.
Methods of preparing composts: layered, focal, and platform methods.
Optimal conditions for bark composting are created when windrows are formed with a base width of 3.0–4.0 m, a height of 1.5–2 m, and a length of at least 4.0 m. When composting in winter, to avoid freezing, the stack height is increased to 2–5 m and the length to 10 m. The mass of the stack is 100–120 t, since with a mass of less than 60 t the stack freezes. The temperature during composting reaches 40–60 °C.
Finished compost must contain at least 80% organic matter on a dry-mass basis with moisture not exceeding 60%, 10–15% humic acids of the total organic matter, pH of the aqueous extract — not less than 5.5, C:N ratio — not more than 30:1, and nitrogen, phosphorus, and potassium — respectively 3.0%, 0.1%, and 0.1% of dry mass. Density — 0.18–0.3 g/cm3, crumbly structure, and water-holding capacity 250–350 g of water per 100 g of dry matter. Due to its calcium content, the compost is an ameliorant for acidic soils. Compost helps reduce the incidence of root rot and suppresses nematode development.
The use of composts based on tree bark can provide greenhouse and hotbed farms with high-quality soils.
Sawdust finds similar use in agriculture. All types of sawdust help improve the physical properties of soils, increase porosity and water-holding capacity, and reduce the density of heavy clay soils. Like tree bark, sawdust contains little nitrogen, so the most effective way to use it is composting with nitrogen fertilizers.
Hydrolytic Lignin
Hydrolytic lignin is the main waste of the hydrolysis industry, accounting for up to 40% of the mass of the raw material. When unloaded from a hydrolysis apparatus, it retains the shape of particles of the raw material with a dark brown color. Chemically, it is a complex of substances, the bulk of which are products of condensation and polymerization of natural lignin. Non-hydrolyzable polysaccharides, unwashed sugars, humic substances, organic acids, sulfuric acid, and ash elements are also present. The first two — lignin and polysaccharides — account for 84–91% of the mass of hydrolytic lignin. Polysaccharides account for 24–45%, lignin for 39–70%. Lignin has an acidic reaction; moisture content is 63–75%.
Table. Agrochemical parameters of hydrolytic lignin (calculated on a dry basis) (Tsurkan M. A., Russu A. P., 1980).
| Parameter | Hydrolytic lignin | Hydrolytic sludge |
|---|---|---|
| Moisture, % | 63.1–75.1 | 61.9–89.6 |
| Ash content, % | 3.5–14.7 | 4.2–72.5 |
| Total carbon, % | 42.9–50.8 | 12.5–53.0 |
| Humic acid carbon, % | 3.4–6.4 | 5.2–18.4 |
| Fulvic acid carbon, % | 3.7–7.7 | 3.0–6.4 |
| Total nitrogen, % | 0.34–0.54 | 0.62–2.32 |
| Nitrate nitrogen, mg/100 g | 0.1–0.7 | 0.5–2.5 |
| Ammonium nitrogen, mg/100 g | 2.2–7.6 | 133–389 |
| Easily hydrolyzable nitrogen, mg/100 g | 40–79 | 183–1470 |
| Total phosphorus, % P2O5 | 0.01–0.16 | 0.39–2.46 |
| Total potassium, % K2O | 0.01–0.22 | 0.14–0.33 |
| Total calcium, % CaO | 0.20–1.19 | 0.16–4.07 |
| Total sulfur, % SO4 | 0.41–2.23 | 0.64–9.28 |
| pHwater | 1.9–4.7 | 3.0–4.6 |
Among nutrient elements, it contains large amounts of sulfur and calcium. Phosphorus and potassium average 0.06% and 0.09% of dry matter, respectively. The total nitrogen content in hydrolytic lignin is 0.34–0.39%, 14% of which is hydrolyzable. The C:N ratio ranges from 75:1 to 117:1.
Returning lignin organic matter to the biological cycle helps protect the environment from pollution and increases the total production of local fertilizers.
The disadvantages of using lignin as a fertilizer are associated with its acidity and low content of nitrogen, phosphorus, and potassium. The positive aspects are: improvement of air permeability, porosity, structure, and physicochemical properties of the soil. It has the ability to adsorb nitrogen from mobile nitrogen-containing fertilizers, enter into a chemical bond with it, thereby reducing nitrogen leaching from the upper soil layers and increasing its utilization coefficient by plants.
An industrial method has been developed for composting lignin with mineral fertilizers and treating the compost with ammonia solution before application to the soil. To prepare composts, lignin is preliminarily neutralized with dolomite flour at a rate of 30–35 kg per ton of fertilizer. The most effective are lignin-manure composts with a manure-to-lignin ratio of 1:1. To prepare 100 t of compost, 48.2–48.5 t of lignin with a moisture content of 60%, 1.5–1.75 t of dolomite flour, and 50 t of manure are used. To accelerate maturation, windrows are made up to 1.5 m high, and the mixture is thoroughly mixed. The wet mass of the compost contains: N — 0.36%, P2O5 — 0.32%, K2O — 0.34%, pH 5.7. In effectiveness, lignin-manure compost is not inferior to peat-manure compost.
Domestic Waste
Domestic waste and municipal refuse, for example, kitchen waste, paper, rags, dirt, dust, and ash, can be comparable in nutrient content and fertilizing qualities to bedding manure. The rate of their mineralization in soil depends on the amounts and ratio of components. With a large amount of food waste and dust, refuse decomposes quickly; it can be applied as fertilizer without composting. When paper and rags predominate, the decomposition rate is lower, so composting is more effective.
Domestic waste amounts to 0.15–0.25 t/year per resident of Russia. They often include up to 30–40% organic food components and 20–30% paper. The chemical composition of domestic waste varies greatly. On average, they contain 40–70% organic matter, 28–30% ash, 23–37% carbon, 0.75–1.15% nitrogen, and 2.0–5.5% calcium. On a dry-mass basis: 0.6–0.7% N, 0.5–0.6% P2O5, and 0.6–0.8% K2O.
Domestic waste is characterized by high biological contamination, can pose an epidemiological hazard, and requires disinfection. This problem is solved by disinfection at landfills, incineration, and biothermal disinfection during compost production in factory installations.
Disinfection of refuse by long-term composting at landfills, although common, is unpromising from a sanitary-hygienic standpoint. Composted refuse disinfected at landfills, without removal of impurities, is unsuitable for use as fertilizer. The use of such refuse leads to clogging of fields with metal, glass, brick, plastics, polyethylene film, and other wastes.
A more advanced method of disinfection and processing of domestic waste is field composting.
Currently, methods of industrial biothermal disinfection and processing of domestic waste into compost and biofuel are becoming widespread.
Domestic waste entering the plant undergoes separation: ferrous metals are extracted by electromagnetic belt separators, then the refuse is treated with air and water at a temperature above +40 °C. The refuse self-heats to 60–70 °C and is disinfected within 3 days.
The resulting compost contains 40–52% organic matter of dry mass, 1.0–1.3% nitrogen, 0.8–0.7% phosphorus, and 0.4–0.6% potassium. The presence of up to 3% glass with a particle size of not more than 15 mm and 4% foreign inclusions is allowed. Moisture content is 30–40%, pH — 7.8.
Industrial compost from municipal solid waste can be applied under fruit crops at 50–150 t/ha, grapes — 20 t/ha, cereals — 20–50 t/ha, sunflower, maize — 30–100 t/ha. The yield increase, depending on crop and soil, is 10–50%. The compost is safe in sanitary-hygienic, helminthological, and entomological respects. Autumn application is preferable. Due to the content of lead and zinc in the compost, its use under vegetable crops is prohibited.
As a pre-sowing fertilizer under primary tillage, refuse without preliminary composting can be applied under various crops at rates of 20–60 t/ha. In protected ground, it is effective in hotbeds and greenhouses as biofuel, after which it becomes a homogeneous, crumbly, and decomposed organic fertilizer for open ground. After composting or use in hotbeds, the decomposed homogeneous refuse is applied under crops at rates up to 20 t/ha.
References
1. Mineev V. G., Sychev V. G., Gamzikov G. P., et al. (2017). Agrochemistry. Textbook. Edited by Mineev V. G. Moscow: Publishing House of the VNIIA named after D. N. Pryanishnikov.
2. Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Edited by B. A. Yagodin. Moscow: Kolos.
