Composting of Municipal Solid Waste (MSW)

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Composting of Municipal Solid Waste (MSW). Caitriona Gaffney Deirdre Mulchrone Teresa Conway. Overview. INTRODUCTION - CAITRIONA GAFFNEY Definition, Sources, Characterisation, End Products INTERMEDIATE - TERESA CONWAY - PowerPoint PPT Presentation


<ul><li><p>Composting of Municipal Solid Waste(MSW)Caitriona Gaffney Deirdre Mulchrone Teresa Conway </p></li><li><p>OverviewINTRODUCTION - CAITRIONA GAFFNEYDefinition, Sources, Characterisation, End Products INTERMEDIATE - TERESA CONWAYWaste Hierarchy, Legislation, Microbiology, Site Selection, Types of Systems </p><p>CONCLUSIONS - DEIRDRE MULCHRONEEnvironmental Factors, Problems, Economics</p></li><li><p>Introduction Caitriona GaffneyDefinition of MSW &amp; Irish FactsSourcesComposting &amp; ClassificationCompost Grades End UsesWho Benefits</p></li><li><p>What is Municipal Solid Waste?Mixed waste from Residential, Commercial &amp; Industrial sourcesCompostable potential of 60-90%Composition includes: paper, glass, wood, plastics, soils, chemicals, food waste, plant debris, metals, textiles, street cleaning &amp; OMOrganic material makes up 50-70% of MSW The fewer the non-compostable materials in feedstock the better the finished compost material.</p></li><li><p>Components of MSW</p><p>RecyclingCompostingCombustionLandfilling</p></li><li><p>Municipal Waste Management in EU Countries</p></li><li><p>Irish Facts 1998-20051998 The national recovery rate of MSW was 9% with 91% going to landfill</p><p>Waste Management: Changing our Ways published targets to be achieved over 15 year period; </p><p>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 &amp; enviro protectionreduce methane emission from landfill by 80%.</p></li><li><p>Irish Facts 1998-2005Changes in waste composition between the years 1995, 1998 &amp; 2001</p></li><li><p>Irish Facts 1998-20052001 - 2,704,035 tonnes MW produced, 4% of the total waste generated - 86.7% landfilled &amp; 13.3% recycled</p><p>2002 - 2,723,739 tonnes MW produced - Landfill of MW decreased by 5%</p><p>2003 - 3,001,016 tonnes MW produced - EPA carried out survey on waste generation &amp; management. - Recycling increased by 46% - 69% of the recyclable waste was recycled abroad - Export of hazardous waste increased by 56%</p><p>2004 - 72% of municipal waste was consigned to landfill - Landfill capacity will still be used up within the next 10 years</p></li><li><p>Irish Facts 1998-2005Provisional data from 6 surveys carried out in Waterford Coco &amp; Galway City in November 2004 and March 2005 </p></li><li><p>Composting &amp; ClassificationDefinition:- 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. </p><p>Performed either by households or in large centralised units </p><p>Compost systems can be classified on three general bases: 1. Oxygen usage (aerobic &amp; anaerobic)2. Temperature (Mesophilic 15-40OC &amp; Thermophilic 45-65 OC)3. Technological approach (static pile or windrow, and mechanical or "enclosed" composting)</p></li><li><p>Grades of CompostPremium Grade- agricultural and horticultural use- home use, turf, pot plants - can be freely traded - regulations may control the application of nitrogen to landRegulated 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 concernEngineering 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. </p></li><li><p>End Uses of CompostSoil 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 improvementLandfill Applications- improvement of landfill covers soil formation </p></li><li><p>Those Who Benefit from the End UsesLocal AuthoritiesLandfill companiesWaste and sewage companies</p></li><li><p>Overview Teresa ConwayWaste Hierarchy Process Options for Organic WasteWhy Biologically Treat WasteLegislation &amp; Targets Physical Processing of MSWBiological Process of CompostingBiologySite SelectionTypes of Systems</p></li><li><p>Waste HierarchyComposting can be considered a component of Integrated Waste Management (IWM)</p><p>Options near top are more desirable than those at the bottom</p></li><li><p>Process Options for Organic Waste</p></li><li><p>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</p></li><li><p>% MSW that is biodegradable(EEA,2003 )</p></li><li><p>Number of authorised Landfills remaining in Ireland </p></li><li><p>Legislation &amp; TargetsTaking 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:</p></li><li><p>Legislation &amp; Targetsa diversion of 50% of household waste from landfill by 2013a minimum 65% reduction in biodegradable waste consigned to landfillthe 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</p></li><li><p>Legislation &amp; TargetsThe primary statute law on waste management is contained in </p><p>Waste Management Act, 1996 &amp; 2001 and Regulations made under the Act EPA Act 1992 and Regulations under the ActRegulations made under the European Communities Act, 1972 in relation to waste managementLandfill Directive 99/31/EC</p></li><li><p>Biological Process of Composting Microorganisms + OM -------&gt; H2O + CO2 + Heat + Humus</p><p> 3 phases under optimal conditions(1) Mesophilic - lasts couple of days (~40oC)(2) Thermophilic can last a few dys to several mts ( 55oC65oC)(3) Several-month cooling and maturation phase</p></li><li><p>Biological Process of CompostingAbundance and variety of microbes indigenous to wastes are sufficient to compost the wastes </p><p>Microbes active in the compost process are:Bacteria (mesophyllic and thermophyllic)ActinomycetesFungiProtozaRotifers </p></li><li><p> Food Web of a Compost pile Organic ResiduePrimary Consumersbacteria, fungi, actinomycetes Secondary Consumersnematodes, protozoa, rotifera, Tertiary Consumerscentipedes, mites, beetles</p></li><li><p>Site Selection for MW ProcessingLarge enough to receive projected waste volumes &amp; for technology usedAdequate 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</p></li><li><p>Site Selection for MW ProcessingA low water table to prevent site floodingA central accessible location with good traffic flowA water source for wetting compost piles &amp; fire protectionArrangements for leachate to be collected and treated Windrows need shelter in regions of moderate to heavy rainfall</p></li><li><p>Physical ProcessingQuantity and characteristics of the feedstock is collected and determined MSW differs from other feedstocks</p><p>Nonbiodegradable and biodegradable separated through:Separation (Recovery)Manual SeparationMechanical SeparationSize Reduction Air ClassificationScreening Trommel Magnetic SeparationDrying and Densification</p></li><li><p>Biological Processing Options1)Turned Windrow2)Static Aerated Pile3)In-Vessel -Horizontal Units-Vertical Units-Rotating DrumsNOTE:Design and management of technical options must be based on the needs of microorganisms</p></li><li><p>Turned Windrows</p></li><li><p>Turned Windrow SystemsMost preferred method used in IrelandCommonly used for rapid composting of yard wastesWindrows 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 freezingFinished compost can be made between 3 mts - 2 yrs Rate of composting is generally directly proportional to frequency of turning</p></li><li><p>Typical 18 month schedule using Turned Windrow system</p></li><li><p>Static Aerated PileDoes not employ turning staticAir is drawn or blown through a network of perforated plastic pipes under the windrowsFaster than windrow systemsUsed 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 &gt; 1.5 to 2 in. in any dimension) </p></li><li><p>This blower forces air into a static compost pile.</p></li><li><p>Forced aeration in a bin type system Passively Aerated Windrow System (PAWS)</p></li><li><p>Permanent air outlets in the pad for an aerated static pile at a site in Washington </p></li><li><p>In-Vessel SystemsAlso referred to as -Contained systems-Reactor-BioreactorComputer provides greater control of composting process Raw waste is placed in a large container, with built-in aeration and mechanical mixing equipment </p></li><li>In-Vessel SystemsProtected from severe weather and odour containmentLow retention time (RT) (often </li><li><p>Types of In-Vessel SystemsHorizontal UnitsVertical UnitsRotating Drums</p></li><li><p>Horizontal UnitsMaterial contained and aerated in a long, horizontal reactor, usually build of concreteMaterial may be moved in and out by:A front end loader or conveyor systemPlug flow system hydraulic ramMoving floor system</p></li><li><p>Horizontal Bed Reactor </p></li><li><p>Vertical UnitsSmall land areaEnclosed and aerated in a vertical reactor known as silos or towers.Compaction of material at the base reactor - impedes aeration - anaerobic regions developingGood for Sludge composting industry but not MSW</p></li><li><p>A vertical in-reactor composting system </p></li><li><p>Rotating DrumsMost common in-vessel composting approachCombined with aeration in static piles or turned windrow Feedstock introduced into one end of slowly rotating drum, inclined at about 5 degrees from horizontalRT varies from 4-6 hours to 2-3 daysDrum allows homogenisation and screening of materials </p></li><li><p>A large-scale, Rotating Drum Composting Vessel </p></li><li><p>Some Biological Treatment Locations in Ireland</p></li><li><p>Problems associated with Composting of Municipal Waste 1. LeachateOdoursVector for organisms supports the proliferation of insects 2. Odour &amp; VOCsFeedstockEnhanced under anaerobic conditions3. DustAgitation of composting materialsBioaerosols</p></li><li><p>Problems associated with Composting of Municipal Waste4. Vermin, Birds &amp; Insects-Nuisance Problems-Pathogens in Final Product5. Bioaerosols and other Health RisksHazard pathogenic organisms in feedstock. Pathway ingestion of materials (for example from unwashed hands). Receptor compost site workers.6. Fire-Stored in bulk</p></li><li><p>Environmental Factors Affecting Composting 1. TemperatureThermophilic (45 650C) and Mesophillic (15-400C).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.</p></li><li><p>Environmental Factors Affecting Composting 2. pHAnaerobic 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. </p></li><li><p>Environmental Factors Affecting Composting 3. Aeration(Anaerobic &amp; Aerobic)Anaerobic: Advantagesa) minimisation of the loss of nitrogenb) less costlyDisadvantages include:a) Slowness of decompositionb) Absence of high temperaturesc) The presence of un-decomposed intermediatesd) The un-pre-processed appearance of the product </p></li><li><p>Environmental Factors Affecting Composting AerobicAerobic composting benefits from:a) A rapid rate of degradationb) Elevated temperature levelsc) Absence of putrefactive </p><p>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).</p></li><li><p>Environmental Factors Affecting Composting 4. Moisture ContentMoisture 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%. </p></li><li><p> Factors affecting Composting5. SubstrateThe waste (referred to as the substrate) should contain all necessary nutrients.MacronutrientsMicronutrientsCarbon (C)Cobalt (Co)Nitrogen (N)Manganese (Mn)Phosphorous (P)Manganese (Mg)Potassium (K)Copper (Cu)</p></li><li><p> Factors affecting CompostingSubstrate (cont.)</p><p>only available if they are in a form that can be assimilated by the microbes. </p><p>Certain groups of microbes have an enzymatic complex that permits them to attack, degrade and utilise the organic matter found in freshly generated waste.</p><p>Others can only utilize decomposition products (intermediates) as a source of nutrients.</p></li><li><p>Factors affecting CompostingCarbon: Nitrogen Ratio (C: N) </p><p>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. </p></li><li>C: N (continued) (CAST STUDIES)Galway City CouncilAt the Galway City Council composting site -no clear cut method of establishing a C: N ratio for the material. -done by visual assessment and theexperience of the operative -Food waste is estimated at a C: N ratio of15:1. -Woodchip is added at the assessment ofthe operative-Less woodchip is required if there isadequate shrub prunings in the incomingwaste.-More woodchip is added if there is a lot ofgrass in the incoming material as there isin summerCeltic Composting-The C: N of source separated bio-waste is typically measured using the total nitrogen and volatile solids content of a sample screened to </li><li><p>Economic FactorsThe 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.</p></li><li><p>ConclusionFrom an environmental perspective, composting not only reduces the problems associated with landfills and incinerators, but t...</p></li></ul>