DEVELOPMENT OF DESIGN PARAMETERS FOR AN INCLINED STEP-GRATE COMPOST VESSEL TO TREAT URBAN SOLID WASTES

Abstract

There are several methods and systems of managing urban solid wastes. Aerobie systemsor managing wastes arc less expensive and the composition of wastes in most Sri Lankancities is conducive to compost making since the biodegradable component is high,The total quantity of organic matter generated in the urban centres if used as compost willstill not satisfy the demand for it. These basic problems could he solved by makingcompost [rom biodegradable urban wastes. facilitating the management of these wastes andalso providing organic matter for long awaited sustained and assured agriculturalproduction in Sri Lanka.The development of a feasible system or compost making was the challenge taken up by theDcpnruucnt or Agricultural Engineering. A series of studies were undertaken to determinesome of the major parameters to rcalise the concept of an inclined step-grate compostmakingvessel.The studies indicate that (l.'i% moisture content should be maintained for optimumconditions for compost making, The bulk density increases with time and It is inverselyproportional to mass, Within the first 20 days of degradation or mixed wastes. most of thevolatile solids react producing largely carbon dioxide and water, The generated heat fromthis reaction actuates the process or evaporating excess moisture. The reduction in massand increase in density can be expressed mathematically.A calculation or heat and mass balances was obtained for a 3-meter pile of wastes, Thesecalculations were based on data obtained from an Engineering Model. Several or the majorparameters such as the retention time. suction. heating and cooling system for moisturecontrol were developed to design a versatile bio-reactor to produce compost for treatingwastes aerobically.