Physical Modeling oftheComposting Ecosystemt

ratio. Inthephysical model, conductive flux(rate ofheat flowthrough chambersurfaces) was madeconstant andslight through a combination ofinsulation and temperature control ofthesurrounding air. Thiscontrol was basedon theinstantaneous conductive flux, as calculated fromtemperature differentials viaaconductive heatflowmodel.Anexperiment wasperformed over a 10-day period inwhichcontrol ofthecomposting processwas basedon ventilative heatremovalinreference toamicrobially favorable temperature ceiling (temperature feedback). Byusing theconduction control system (surrounding airtemperature controlled), 2.4%ofthetotal heatevolved fromthechamberwas through conduction, whereas theremainder was through theventilative mechanisms ofthelatent heatofvaporization andthesensible temperature increase ofair.Bycomparison, withinsulation alone(theconduction control system was notused) conduction accounted for33.5%ofthetotal heatevolved. Thisdifference inconduction resulted insubstantial behavioral differences withrespect tothetemperature ofthecomposting matrixandthe amountofwaterremoved. Byemphasizing theslight conduction system (2.4%oftotal heatflow) asbeing a better representative offield conditions, a comparison was madebetweencomposting system behavior inthe laboratory physical modelandfield-scale piles described inearlier reports. Numerousbehavioral patterns were qualitatively similar inthelaboratory andfield (e.g., temperature gradient, 02 content, andwaterremoval). Itwas concluded thatfield-scale composting systembehavior can besimulated reasonably faithfully inthe physical model. Composting isasolid-phase process whichexploits the phenomenon ofmicrobial self-heating (14). Thematerial being composted serves asitsownmatrix, permitting gas exchange, andprovides itsownsource ofnutrients, water, andanindigenous, diverse inoculum. Italsoserves asits ownwastesink andthermal insulation. Hence, metabolically generated heatisconserved within thesystem, elevating its temperature. Current interests incomposting range fromthetraditional tothenovel. Traditional, product-oriented usesoftheprocessinclude theconversion ofagricultural wastestoa stabilized organic soil amendment (compost) or,inanincreasingly competitive industry, toasubstrate fortheproduction ofedible mushrooms (mushroom compost) (5). A nontraditional, process-oriented useofcomposting isasa treatment technology forwastewater sludges orfractions of municipal solid waste, possibly incombination (4,9).Inthis context themaingoalistostabilize anddrythewasteto render itenvironmentally acceptable forfinal disposition, preferably involving someformofuseoftheprocess residue.Thus, composting isnotseenprimarily asameansof producing anyparticular product, butrather asatreatment component ofanoverall wastemanagement plan. A novel areaofinterest isintheuseofcomposting intheremediation ofsoil contaminated withrelatively lowlevels ofbiodegradablehazardous wastes (7). Composting experimentation inthefield iscostly and difficult tocontrol, anditessentially excludes certain aspects ofquantification. Thisindicates a needfora laboratory