Municipal Solid Waste Composting

Transcription

1 JICA Ex Participants Association of Solid Waste Management One day workshop, Colombo, 18 th February 2016 Municipal Solid Waste Composting Dr Anurudda Karunarathna Senior Lecturer in Environmental Engineering Department of Agricultural Engineering University of Peradeniya

2 Definition of composting process Decomposition of heterogeneous organic matter by a mixed microbial population in a moist, warm, aerobic environment to a state sufficiently stable for nuisancefree storage and utilization (Gray & Biddlestone, 1974). Compost systems can be classified on three general bases: 1. Oxygen status (aerobic & anaerobic) 2. Temperature (Mesophilic O C & Thermophilic O C) 3. Technological approach (static pile or windrow, and mechanical or "enclosed" composting)

3 Rapidly degradable organic matter (carbohydrate, protein, lipids, etc. + chemical energy) Slowly degradable organic matter (cellulose, lignin, wax etc. + chemical energy) Water Microorganisms (decomposers/ saprotrophs, pathogens, worms) W V Water Heat CO 2 Composting process O 2 O 2 Organic matter (carbon, humus) Slowly degradable organic matter Minerals (N, P, K, S, etc.) Water Microorganisms (dead, live) ~0.2W ~0.5V Feedstock Compost

4 Feedstock characteristics - physical 1) Moisture 2) Density (porosity) 3) Physical state; solid, semi-solid, liquid & gases 4) Mechanical properties e.g. shear strength 5) Particle size, shape, size distribution 6) Physical composition of wastes: Categories Sub-classes

5 Moisture content For most organic waste, it will vary from 60 to 80%, depending on the composition of the wastes, the season of the year, and the humidity and weather conditions Ash Dry matter Biodegradable/ combustible Moisture

6 Moiature Content (W/W) Change of MC & FC during composting Available MC % MC at Field Capacity Days

7 Particle size and size distribution

8 Chemical properties Proximate analysis: determination of combustible components of waste includes analysis of moisture content, volatile combustible matter, fixed carbon and ash. Ultimate analysis: involves the determination of the percent of C, H, O, N, S, ash and halogens. to characterize the chemical composition of the organic matter in waste to define the proper mix of waste materials to achieve suitable C/N ratios for biological conversion processes. 8

9 Biodegradability The principal organic waste components in MSW are often classified as rapidly and slowly decomposable Component Volatile solids (VS) % of total solids (TS) Lignin content (LC) % of VS Biodegradabl e fraction (BF) Food wastes Paper Newsprint Office paper Cardboard Yard wastes

10 VS (%) Biodegradation- Volatile solid (VS) Days

11 Solid biodegradability- measurement In Germany, the biodegradability is defined either with the respiration activity (AT4) or gas formation potential (GB21). 11

12 The Relative Microbiological Breakdown Rates Organic Material Group I Sugars Starches, glycogen, pectin, fatty acids and glycerol Lipids, fats, and phospholipids Amino acids Nucleic acids Protein Group II Hemicellulose and cellulose Chitin Low molecular weight Aromatics and aliphatics Group III Lignocellulose Lignin Breakdown Rate Readily degradable Slower to degrade (more relevant during maturation) Usually resistant

13 Parameters governing the composting 1) ph 2) Moisture content 3) Aeration (oxygen consumption) rates 4) Temperature & Heat evolution evaporative cooling, etc., are governed by biochemical properties of the substrate and the type of microbial activities taking place during the degradation processes. 5) Degradation processes, which in turn depend on particle size and pile height. 6) Permeability 7) Composition

14 Biological Aspects of Composting Combined activities of a rapid succession of microbial populations, each suited to a particular environment for a relatively limited duration of time and being active in the degradation process Food of one Web particular of a Compost type or pile group of organic material. Bacteria (mesophyllic and thermophyllic) Actinomycetes Fungi Protoza Rotifers Tertiary Consumers centipedes, mites, beetles Secondary Consumers nematodes, protozoa, rotifera, Primary Consumers bacteria, fungi, actinomycetes Organic Residue

15 Nutrients required for micro-organisms Nitrogen Phosphorous Potassium Magnesium Sulphur Calcium Other elements

16 Carbon: Nitrogen ratio The ideal C/N ratio for composting of MSW generally falls in the range of 20:1 to 25:1 The experimental values obtained in the Sri Lankan studies varied between 20-33:1 Feedstock, gradually reducing to between 9-10:1 after 60 days of composting C/N ratio of 10 to be ideal for mature compost

17 ph ph D ay s Typical Values of ph Variation with Time

18 Aeration Rates Experiment conducted on an engineering model, a vertical reactor obtained values of 0.36 to 0.39 m 3 of air per day per kg of volatile solids Natural Air Circulation in a Compost Windrow

19 Temperature 0 C The Temperature time Pattern in relation to Biological Activities 60 a b c d Time in days Temperature Variations with Time with Indicating the Stages of the Composting Process

20 Phases 1. Psychrophilic-mesophilic-- Microbes multiply exponentially; give off heat; pile warms up. 2. Thermophilic or hot phase -- Bacteria consume easy food; pile heats rapidly; H 2 O, heat, CO 2 given off in large amounts. 3. Cool-down Microbes run out of food and/or oxygen; pile cools; may be re-activated by turning, introducing air, and/or adding water. 4. Curing At ambient temps; actinomycetes and fungi multiply; slow breakdown of cellulose & lignins. Humic compounds form. Mineralization of N to NO 3.

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22 Gas Emissions During composting MSW 300 components were evaluated and classified and 18 chemicals were found to be of special importance and thus well-suited as control parameters in emissions. Methane Ammonia Benzene Xylole Trichlorethene Tetrachorethene limonene and Ethanol

23 Type of emmisions Highest emissions occur during the self-heating stage in the first days of the rotting process. At this stage, the waste gas emits a range of volatile pollutants taking about two weeks to complete. During the whole composting process, readily degradable carbon compounds such as alkanes, aldehydes, alcohols, etc., are present in the waste air. These are volatile metabolites, which can be removed through biological air filters. Referring to its efficiency, a comparison of the content of the pollutants before and after the bio-filters indicate a reduction of about 60% as a mean value with cleaning efficiencies varying between 0% and 100% depending on the substance. Dioxine and most heavy metals are in the concentration range of the natural environment.

24 Compost production Aspect Preferred condition Remarks MSW characteristics Organic fraction of MSW Kitchen waste, food waste, garden waste, paper and small amount of non-degradable/ long-term degradable materials may present Particle size mm for optimum results Smaller particles increases the density thus reduce the air disintegrate and decompose C:N ratio 25 to 50 C:N ratio above the limit prolong the decomposition and very low ammonia leaching Blending & seeding 1-5 % Addition of partly decomposed matter accelerate the garden waste Moisture content 55% (optimum) Higher moisture increases leachate generation and reduces aeration, dryness ceases the decomposition Windrow size Mixing/turning 2 m width and 1.5 m height and 3 m long 4-5 days (optimum) Weekly (recommended) Maturing/curing Weekly mixing/turning (optimum) Wide and tall windrows restrict the air movement inside the pile Low turning frequency reduces the aeration, mixing and disintegration and slower the decomposition Continue pile mixing/turning until temperature drops to 40 C or less, and add water while mixing/turning

25 Compost production- Operation Aspect Preferred condition Remarks Monitoring parameters Temperature C for first few days C for reminder period Temperature below 50 C during the composting caused by low C:N ratio, excessive moisture, dryness, compaction due to large pile size and toxins ph (optimum) Not above 8.5 to minimize nitrogen losses via ammonia volatilization, very low ph at early stages indicates excessive, fast decomposable carbohydrates in feedstock Maturity indices Stability Toxicity assessment (Phytotoxicity) Simple tests C:N ratio <25 Self heating test Advance tests Specific O 2 uptake rate CO 2 evolution NH 4 -N:NO 3 -N ratio, Compost bioassays Simple tests are cheap and easy but low accuracy Advance test are more accurate but requires special equipments and skills to perform Caused by the presence of organic chemicals such as lactic and acetic acid, herbicides, heavy metals, and pathogens

26 Small scale on-site composting - pit/heap method Advantages; Easy to construct and minimum operation & maintenance requirement No or minimum cost of construction Disadvantages: Requires relatively large area Use of meat & fish waste is not recommended Requires relatively long time to decompose

27 Small scale on-site composting - Jeewakotuwa Advantages; Easy to construct and minimum operation & maintenance requirement Relatively low cost of construction Disadvantages: Requires relatively large area Use of meat & fish waste is not recommended

28 Small scale on-site composting - Bin Advantages; Composters are available at subsidized price & in markets Small land area requirement Disadvantages: Purchasing and transport cost Requires basic skills to operate Difficult to fabricate in-house

29 MSW composting

30 Aims 1. Dry matter/volume reduction ~ 50% 2. Cheaper transportation 3. Land apply at farmer s convenience 4. Reduced odor 5. Reduces fly and disease problems 6. Environmental conservation 7. Prolong landfill life

31 Composting feedstock High-nitrogen material [ greens ] Manure Dairy, beef, horse, poultry, swine Hatchery waste shells, washing, rejects Food processing waste (vegetable or fruit) Fish processing waste High carbon material [ browns ]--- Yard trimmings, leaves, woodchips Sawdust, shavings, straw, old hay, seed cleaning waste Shredded Paper and Un-waxed Cardboard

32 Windrow method

33 Windrow composting- indoor Composting under roof Continuous turning, Supersoils, NC

34 Passive aeration - Static piles Passive aeration, Vermont

35 Forced aeration

36 Active aeration- Composting reactors

37 Active aeration- Composting reactors

38 Is a few days enough?

39 Odor management- Filters Odor

40 Municipal Solid Waste Composting - University research

41 Open Windrow Construction with Dome Aeration Equipment

42 * Heterogeneous MSW 1. Sorted quickly to remove hazardous non-degradable components 2. Sorted waste was mixed well and used for the experiment * SP and SG were heaped up to 3m and 2.5m respectively SP -3m (height) SG - 2.5m(height),1m (width) Appearance after filling with MSW 6 Appearance after filling with MSW

43 Schematic Diagram of Aerated Static Pile Composting System (Source: Tchobanoglous et al., 1993)

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45 Inclined Step-Grate (ISG)

46 Solar Aeration Chimney Composting System Ventilator Chimney 6"height panel WASTE PILE 4"dia PVC pipe Plastic coated wire mesh & porous pipe concreted floor

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49 Cone shaped mesh cage inside the waste pile

50 MSW composting- Local Authorities

51 Waste receiving and unloading

52 Waste sorting

53 Making windrow piles

54 Windrow piles

55 Leachate control and treatment

56 Turning and maturing windrow piles

57 Sieving and processing

58 Final Product Compost Fertilizer

59 Material flow in windrow composting (20TPD of MSW) Volatile losses Raw waste 2% Recyclables % Sorting Screening Compost 49% Pre- Rejects 49% % Post- Rejects 16% Water Leachate 700 L/D

60 END