Organic composting

courtesy : 3. Composting: • The process of breakdown of biodegradable organic waste to produce stable, nutrient rich compost through the natural, exothermic process of aerobic decomposition.
4. Composting: – natural biological process, but for rapid composting and consistent quality, environmental conditions must be controlled – end product (compost) bears little resemblance to original wastes from which the compost was made – typically dark brown to black in colour, with crumbly texture and earthy odour
5. ORGANIC WASTE COMPOST
6. Finished compost – humus-like, resembling rich topsoil – resistant to further microbial decomposition
8. What can be composted? • any waste material with a high organic matter content is a potential candidate • used more recently for: – sewage sludges – industrial wastes (e.g. food, pulp & paper) – yard and garden wastes – municipal solid wastes (up to 70% organic matter by weight)
9. Compost Preparation • waste collection • sorting into organic and inorganic • reduce size if necessary • adjust moisture content • starters/additives • adjust C:N ratio
10. Compost preparation • place prepared waste in piles, windrows, chamber or bins • turn the compost regularly or arrange other ways to aerate the waste • regularly monitor temperature & moisture
11. Temperature during composting process
12. Controlling composting To achieve maximum composting for any organic material, certain environmental conditions must be maintained in the compost pile may be classified into interdependent • biological conditions • physical conditions • chemical conditions
13. THE BIOLOGICAL ENVIRONMENT Key organisms: • bacteria • fungi • Actinomycetes – play active role in decomposing organic matter
14. THE BIOLOGICAL ENVIRONMENT Secondary organisms: –earthworms –insects –other soil invertebrates • play a less significant role in decomposition process compared to microorganisms • more important in mechanical breakdown of wastes (chewing, burrowing, movement, aeration)
15. Fate of organic matter in compost • Carbon-containing compounds are consumed by microorganisms and converted to: –microbial tissues –carbon dioxide –water –humicbreakdown products – Heat is released as a result of microbial metabolic activity => temperature in pile increases
16. • Humic breakdown products resulting from one type of microbial activity may be used as a food and energy source by another generation or type of microbes • Chain of succession continues until there is little decomposable organic material remaining COMPOST
17. COMPOST Stable end product composed of: • living and dead microbial cells and cell fragments • byproducts of microbial decomposition • undecomposed particles (organic and inorganic)
18. Microbial succession in compost piles • A wide variety of microorganisms naturally present in most nontoxic agricultural wastes, yard wastes, or mixed municipal wastes • ==> number and type of available organisms generally not a limiting factor • Depending upon environmental conditions, certain microbial groups may predominate at certain stages in the decomposition process
19. THE CHEMICAL ENVIRONMENT • determined largely by the composition of the waste materials to be composted Important factors influencing the chemical environment for composting: – adequate food / energy sources for microorganisms – balanced amount of nutrients – adequate water content – adequate oxygen – acceptable pH range – lack of toxic substances that could inhibit microbial activity
20. Food / energy sources for compost microbes • microbes rely on organic carbon compounds to meet energy needs • Carbon in natural or synthetic organic substances varies in degradability, e.g.: • sugars easily metabolized by most microbes • lignins in wood or paper degraded more slowly, by fewer groups • plastic very resistant to breakdown
21. Food / energy sources for compost microbes As degradable organic compounds are decomposed: • small portion of the carbon goes into microbial cells • large portion of carbon converted to CO2 and lost to the atmosphere => reduction in weight and volume of waste
22. Food / energy sources for compost microbes • More resistant carbon compounds form the matrix for the physical structure of finished compost. • Most municipal, yard, and agricultural wastes have adequate biodegradable carbon to support microbial activity
23. Nutrients for compost microbes • nitrogen, phosphorus, and potassium are most important nutrients • nitrogen is usually the limiting nutrient CARBON to NITROGEN (C:N) RATIO IS CRITICAL IN DETERMINING THE RATE OF DECOMPOSITION.
24. • C:N ratio established on the basis of decomposable rather than total carbon • ratio lower than 30:1 is desirable • higher ratios result in slower decomposition rates adjusted by co-composting with different materials
25. Typical C:N ratios for waste products: Manure – 15:1 to 20:1 Yard wastes – 20:1 to 80:1 Municipal wastes – 40:1 to 100:1 Wood chips – 400:1 to 700:1
26. Moisture in compost piles • ideal moisture: 50% to 60% by weight • most wastes do not contain enough moisture => composting process slowed down unless water is added • excess water causes problems in compost piles: leachate generation, anaerobic conditions, rotting, and obnoxious odours • loss of moisture occurs through evaporation => controlled by adjusting the size and shape of the compost pile
27. Oxygen in compost piles • aerobic decomposition is required for odour- free, rapid composting • pile should have enough void space to allow gas exchange with the atmosphere • 5% to 15% oxygen concentration is considered adequate • piles aerated by mechanical turning, air injection
28. pH in compost piles • pH of 6 – 8 considered ideal Level of acidity / alkalinity affects: –nutrient availability –solubility of (potentially toxic) heavy metals – overall metabolic activity of microbes
29. pH in compost piles • pH may be adjusted upwards by the addition of lime (calcium carbonate), but most organic substances are naturally well-buffered with regard to pH change • slight tendency towards acidification as compost matures, due to production of carbonic acid
30. THE PHYSICAL ENVIRONMENT Includes factors such as: • particle size • temperature • mixing • pile size and shape

Organic composting

courtesy : 3. Composting: • The process of breakdown of biodegradable organic waste to produce stable, nutrient rich compost through the natural, exothermic process of aerobic decomposition.

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