Composting of Municipal Solid Waste (MSW) Caitriona Gaffney Deirdre Mulchrone Teresa Conway

Transcription

1 Composting of Municipal Solid Waste (MSW) Caitriona Gaffney Deirdre Mulchrone Teresa Conway

2 Overview INTRODUCTION - CAITRIONA GAFFNEY Definition, Sources, Characterisation, End Products INTERMEDIATE - TERESA CONWAY Waste Hierarchy, Legislation, Microbiology, Site Selection, Types of Systems CONCLUSIONS - DEIRDRE MULCHRONE Environmental Factors, Problems, Economics

3 Introduction Caitriona Gaffney Definition of MSW & Irish Facts Sources Composting & Classification Compost Grades End Uses Who Benefits

4 What is Municipal Solid Waste? Mixed waste from Residential, Commercial & Industrial sources Compostable potential of 60-90% Composition includes: paper, glass, wood, plastics, soils, chemicals, food waste, plant debris, metals, textiles, street cleaning & OM Organic material makes up 50-70% of MSW The fewer the non-compostable materials in feedstock the better the finished compost material.

5 Components of MSW Recycling Composting Combustion Landfilling

6 Municipal Waste Management in EU Countries

7 Irish Facts The national recovery rate of MSW was 9% with 91% going to landfill Waste Management: Changing our Ways published targets to be achieved over 15 year period; a diversion of 50% of household waste from landfill, recycling of 35% of MW rationalisation of municipal waste landfills 20 state of the art facilities incorporating energy recovery & enviro protection reduce methane emission from landfill by 80%.

8 Irish Facts Changes in waste composition between the years 1995, 1998 & 2001

9 Irish Facts ,704,035 tonnes MW produced, 4% of the total waste generated % landfilled & 13.3% recycled ,723,739 tonnes MW produced - Landfill of MW decreased by 5% ,001,016 tonnes MW produced - EPA carried out survey on waste generation & management. - Recycling increased by 46% - 69% of the recyclable waste was recycled abroad - Export of hazardous waste increased by 56% % of municipal waste was consigned to landfill - Landfill capacity will still be used up within the next 10 years

10 Irish Facts Provisional data from 6 surveys carried out in Waterford Coco & Galway City in November 2004 and March 2005

11 Composting & Classification Definition:- Composting is the biological decomposition of the organic constituents of wastes under controlled conditions to a state sufficiently stable for nuisance-free storage and utilization. Performed either by households or in large centralised units Compost systems can be classified on three general bases: 1. Oxygen usage (aerobic & anaerobic) 2. Temperature (Mesophilic O C & Thermophilic O C) 3. Technological approach (static pile or windrow, and mechanical or "enclosed" composting)

12 Grades of Compost Premium Grade - agricultural and horticultural use - home use, turf, pot plants - can be freely traded - regulations may control the application of nitrogen to land Regulated Grade - remediation, restoration, agriculture, forestry and non food crops - specialist expertise necessary in trading and its use - regulation of the application - biological, chemical or physical hazards remain a concern Engineering Grade - access to composts is strictly limited - other risk management measures in place for e.g. uses such as daily cover, or as engineering fill material - in bunds and sound barriers, or as pollution control measures such as biofilters.

13 End Uses of Compost Soil Improvement - soil structure, condition and fertility Growing media - component of mixes used to grow crops in containers Mulches - suppress weed growth, conserves water and also to maintain soil temperatures. Mulching also protects plants from frost. Restoration - used for soil forming and soil improvement Landfill Applications - improvement of landfill covers soil formation

14 Those Who Benefit from the End Uses Local Authorities Landfill companies Waste and sewage companies

15 Overview Teresa Conway Waste Hierarchy Process Options for Organic Waste Why Biologically Treat Waste Legislation & Targets Physical Processing of MSW Biological Process of Composting Biology Site Selection Types of Systems

16 Waste Hierarchy Composting can be considered a component of Integrated Waste Management (IWM) Options near top are more desirable than those at the bottom

17 Process Options for Organic Waste Process Options Landfill Incineration Biological Processing Direct Land Disposal Anaerobic Digestion Composting Specialised Methods Marketable Products

18 Why Biologically Treat MSW? Reduces waste going to landfill Estimated to be 10 years remaining landfill capacity available for municipal waste (Nationally in 2004) Could be the first step in Ireland meeting its waste challenge

19 % MSW that is biodegradable 80% 70% 60% 60% 50% 40% 35% 30% 25% 20% 10% 0% Paper & Cardboard Food & Garden Waste Total Biodegradable MSW (EEA,2003 )

20 Number of authorised Landfills remaining in Ireland No. of Landfills

21 Legislation & Targets Taking the Landfill Directive as a framework the following National Landfill Diversion targets were outlined in 1998 in the Policy statement Changing Our Ways. -The statement includes a number of targets to be achieved over a 15 year time period. Some of these include:

22 Legislation & Targets a diversion of 50% of household waste from landfill by 2013 a minimum 65% reduction in biodegradable waste consigned to landfill the development of waste recovery facilities, including the development of composting and other feasible biological treatment facilities capable of treating up to 300,000 tonnes/year

23 Legislation & Targets The primary statute law on waste management is contained in Waste Management Act, 1996 & 2001 and Regulations made under the Act EPA Act 1992 and Regulations under the Act Regulations made under the European Communities Act, 1972 in relation to waste management Landfill Directive 99/31/EC

24 Biological Process of Composting Microorganisms + OM > H 2 O + CO 2 + Heat + Humus 3 phases under optimal conditions (1) Mesophilic - lasts couple of days (~40 o C) (2) Thermophilic can last a few dys to several mts ( 55 o C 65 o C) (3) Several-month cooling and maturation phase

25 Biological Process of Composting Abundance and variety of microbes indigenous to wastes are sufficient to compost the wastes Microbes active in the compost process are: Bacteria (mesophyllic and thermophyllic) Actinomycetes Fungi Protoza Rotifers

26 Food Web of a Compost pile Tertiary Consumers centipedes, mites, beetles Secondary Consumers nematodes, protozoa, rotifera, Primary Consumers bacteria, fungi, actinomycetes Organic Residue

27 Site Selection for MW Processing Large enough to receive projected waste volumes & for technology used Adequate buffer zone from neighbours with a prevailing wind that blows away from neighbours A nearly level surface, 2-3% grade A high soil percolation rate to avoid standing water but an impermeable surface as a base

28 Site Selection for MW Processing A low water table to prevent site flooding A central accessible location with good traffic flow A water source for wetting compost piles & fire protection Arrangements for leachate to be collected and treated Windrows need shelter in regions of moderate to heavy rainfall

29 Physical Processing Quantity and characteristics of the feedstock is collected and determined MSW differs from other feedstocks Nonbiodegradable and biodegradable separated through: Separation (Recovery) Manual Separation Mechanical Separation Size Reduction Air Classification Screening Trommel Magnetic Separation Drying and Densification

30 Biological Processing Options 1) Turned Windrow 2) Static Aerated Pile 3) In-Vessel -Horizontal Units -Vertical Units -Rotating Drums NOTE: Design and management of technical options must be based on the needs of microorganisms

31 Turned Windrows

32 Windrows Composting Sites Natural Air Circulation in a Compost Windrow

33 Turned Windrow Systems Most preferred method used in Ireland Commonly used for rapid composting of yard wastes Windrows are aerated regularly by turning Constructed to be 6 to 10 ft high, 10 to 20 ft wide The center of the pile insulated so that composting can continue when outdoor temperatures are below freezing Finished compost can be made between 3 mts - 2 yrs Rate of composting is generally directly proportional to frequency of turning

34 Typical 18 month schedule using Turned Windrow system Autumn Windrows formed Using a front end loader Summer Windrows turned monthly Winter Windrows turned monthly Autumn Windrows dismantled Room made for new incoming material Spring Windrows turned monthly Next 6 Months Compost screened Moved to curing pile Stabilised & yields N March/April Finished Compost Peak Demand

35 Static Aerated Pile Does not employ turning static Air is drawn or blown through a network of perforated plastic pipes under the windrows Faster than windrow systems Used where aeration and temperature control are crucial, (i.e. sludge or food processing wastes) Works best with a material that is relatively uniform in particle size ( not > 1.5 to 2 in. in any dimension)

36 This blower forces air into a static compost pile.

37 Forced aeration in a bin type system Passively Aerated Windrow System (PAWS)

38 Permanent air outlets in the pad for an aerated static pile at a site in Washington

39 In-Vessel Systems Also referred to as -Contained systems -Reactor -Bioreactor Computer provides greater control of composting process Raw waste is placed in a large container, with builtin aeration and mechanical mixing equipment

40 In-Vessel Systems Protected from severe weather and odour containment Low retention time (RT) (often <14 days) Requires further compost processing - low RT is insufficient for thermophilic composting stage Expensive to build and operate

41 Types of In-Vessel Systems Horizontal Units Vertical Units Rotating Drums

42 Horizontal Units Material contained and aerated in a long, horizontal reactor, usually build of concrete Material may be moved in and out by: A front end loader or conveyor system Plug flow system hydraulic ram Moving floor system

43 Horizontal Bed Reactor

44 Vertical Units Small land area Enclosed and aerated in a vertical reactor known as silos or towers. Compaction of material at the base reactor - impedes aeration - anaerobic regions developing Good for Sludge composting industry but not MSW

45 A vertical in-reactor composting system

46 Rotating Drums Most common in-vessel composting approach Combined with aeration in static piles or turned windrow Feedstock introduced into one end of slowly rotating drum, inclined at about 5 degrees from horizontal RT varies from 4-6 hours to 2-3 days Drum allows homogenisation and screening of materials

47 A large-scale, Rotating Drum Composting Vessel

48 Some Biological Treatment Locations in Ireland Facility Capacity Feedstock Technology Tralee Composting site 3,000 Household Organics Windrow Limerick Composting Site 2,000 Household Organics In-Vessel and Windrow Galway Corporation Depot 5,000 Household Organics Aerated Pile (VAR System) Lucan Green Waste Composting 5,000 Green Waste Windrow Aran Island Recycling Scheme 500 Household Organics In-Vessel (Biosal Unit) Ballinasloe Composting Site 4,000 Household Organics In-Vessel and Aerated Pile (Celtic Composting) Silliot Hill, Kildare 5,200 Commercial and Green Waste VCU In-Vessel Kildare Sludge Plant 5,200 Municipal Sludge TEG In-Vessel CTO Middleton 3,000 Commercial Organics Windrow Kinsale Road Facility 2,000 Green Waste Windrow Keady Composting Facility (Armagh) 65,000 Organic and Green Waste Enclosed Aerated and Windrows McGill Facility (Cork) 10,000 Commercial Sludges Enclosed Aerated Enviro Grind Ltd. 3,000 Green Waste Windrow Shannon Vermicomposting 1,000 Household Organics/ Municipal Sludge Windrow Robert Delaney 10,000 Green Waste Windrow Down District Council Composting Site 1,800 Household Organics Windrow SimproIreland Ltd. 4,000 Green Waste Windrow Organic Gold 3,000 Municipal Sludge, Cattle Manure Windrow

49 Problems associated with Composting of Municipal Waste 1. Leachate Odours Vector for organisms supports the proliferation of insects 2. Odour & VOC s Feedstock Enhanced under anaerobic conditions 3. Dust Agitation of composting materials Bioaerosols

50 Problems associated with Composting of Municipal Waste 4. Vermin, Birds & Insects -Nuisance Problems -Pathogens in Final Product 5. Bioaerosols and other Health Risks Hazard pathogenic organisms in feedstock. Pathway ingestion of materials (for example from unwashed hands). Receptor compost site workers. 6. Fire -Stored in bulk

51 Environmental Factors Affecting Composting 1. Temperature Thermophilic ( C) and Mesophillic ( C). Above this temperature spores produced (Resting Stage). Microorganisms inactivated or die off. Affected by its climatic surroundings and method of aeration. In a windrow highest temperature reached in centre, lower at edges.

52 Environmental Factors Affecting Composting 2. ph Anaerobic digestion the ph level covers a narrow range (ph 6.5 to 7.5) Aerobic- ph so broad difficulties rarely encountered with too high or too low ph in composting. During the early stages the ph usually drops (down to about ph 5.0) because of organic acid formation. An exception which can reduce the ph is fruit wastes which can reduce the ph to 4.5. calcium hydroxide (lime) can be used as a buffer but it also lead to a loss in ammonium nitrogen.

53 Environmental Factors Affecting Composting 3. Aeration (Anaerobic & Aerobic) Anaerobic: Advantages a) minimisation of the loss of nitrogen b) less costly Disadvantages include: a) Slowness of decomposition b) Absence of high temperatures c) The presence of un-decomposed intermediates d) The un-pre-processed appearance of the product

54 Environmental Factors Affecting Composting Aerobic Aerobic composting benefits from: a) A rapid rate of degradation b) Elevated temperature levels c) Absence of putrefactive Oxygen uptake reflects intensity of microbial activity. Theoretically the amount of oxygen required is determined by the amount of carbon to be oxidised (Chrometzka, 1968).

55 Environmental Factors Affecting Composting 4. Moisture Content Moisture content and oxygen availability are closely related If the moisture content of the mass is so high as to displace the air from the interstices (voids between particles) anaerobic conditions will develop within the mass. The maximum permissible moisture content is a function of the structural strength of the particles of the material to be composted i.e. the degree of resistance of individual particles to compression. Woodchips, straw and hay can be as high as 75 to 80% whereas paper (upon becoming wet, collapses and forms mats) has a permissible moisture content of 55 to 60%.

56 Factors affecting Composting 5. Substrate The waste (referred to as the substrate) should contain all necessary nutrients. Macronutrients Micronutrients Carbon (C) Cobalt (Co) Nitrogen (N) Manganese (Mn) Phosphorous (P) Manganese (Mg) Potassium (K) Copper (Cu)

57 Factors affecting Composting Substrate (cont.) only available if they are in a form that can be assimilated by the microbes. Certain groups of microbes have an enzymatic complex that permits them to attack, degrade and utilise the organic matter found in freshly generated waste. Others can only utilize decomposition products (intermediates) as a source of nutrients.

58 Factors affecting Composting Carbon: Nitrogen Ratio (C: N) The C: N ratio of the waste to be composted is the most important factor that requires attention. A large percentage of the carbon is oxidised to carbon dioxide by the microbes in their metabolic activities. The major consumption of nitrogen is in the synthesis of protoplasm consequently much more carbon is required. The C: N of the substrate should fall within the range of 20-25:1. Mmicroorganisms such as bacteria and fungi grow best with the proper level of Carbon and Nitrogen.

59 C: N (continued) (CAST STUDIES) Galway City Council At the Galway City Council composting site -no clear cut method of establishing a C: N ratio for the material. -done by visual assessment and the experience of the operative -Food waste is estimated at a C: N ratio of 15:1. -Woodchip is added at the assessment of the operative - Less woodchip is required if there is adequate shrub prunings in the incoming waste. -More woodchip is added if there is a lot of grass in the incoming material as there is in summer Celtic Composting -The C: N of source separated biowaste is typically measured using the total nitrogen and volatile solids content of a sample screened to <10mm. -Inclusion of large amounts of unavailable carbon from woody bulking materials will give a false high carbon reading. - Normally bio-waste with high green waste content is fine. -However, winter deliveries with little green waste needs nitrogen supplementation. -In the UK, it is typical to include a lot of paper and cardboard in the bio-bins and this needs nitrogen additions also. Similarly mixed waste composting often suffers from low nitrogen

60 Economic Factors The costs of a composting facility include land, labour and equipment. It will divert waste that would otherwise need costly disposal. If the compost site is closer than the other disposal site, there will be savings in transport costs. The finished compost can be used as a substitute for purchased mulch or topsoil in municipal landscaping. If sold commercially, compost can generate revenues, which help defray processing costs.

61 Conclusion From an environmental perspective, composting not only reduces the problems associated with landfills and incinerators, but the finished compost adds beneficial humus and nutrients to soil. Composting is a waste management solution, which can benefit municipalities and benefit the environment at the same time.

62 Questions?