A thesis submitted in partial fulfilment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1990

A laboratory study was conducted to investigate the immobilization of the laboratory waste s ludge, mainly from chemical oxygen demand {COD) waste , using cementitious binders. The binders were Ordinary Portland Cement {OPC), and lime - Rice Husk Ash (RHA) cement. The sludges were mixed with cement - sand mortar having a cement to sand ratio of 0.5, and water to cemen t ratio of 0.5 for OPC mortar and 0.9 for lime - RHA ceme nt mortar, respectively. Physical properties lik e compressive strength and leachability were studied to assess the effectiveness of the binders in containing the waste sl udg es within their matrix . Leachability was determined by the US EPA Extraction Procedure. The leachability was found to be proportional to the sludge/ cement ratios and inversely proportional to the curing time. The compressive strength of OPC mortar was found to be proportional to the curing time and inversely proportional to the sludge/ cement ratios. On the contrary , the compressive strength of lime - RHA cement mortar was found to be proportional to the sludge/ cement ratios and a pyramidal trend was observed to curing time. The compressive strength of OPC mortar was found to be greater than that of lime - RHA cement mortar. On the other hand , leachabili ty of lime - RHA cement mortar was invariably much less than that of OPC mort ar in all the tests. In this way , lime - RHA cement was found to be a better immobilizer than OPC. Economic evaluation was done for three different kinds of cementitious binders, namely, OPC, Portland Rice Husk Ash Cement {PRHAC ) which contain ed rice hu sk ash 50 percent by dry weight, and lime - RHA cement. The result showed that lime - RHA cement was cheapest. The applicability of Freundlich' s desorption isotherm was studi ed to assess the l eachability of sludges. The leachability of both cement mortars were found to follow the desorption isotherms. From this study , it is concluded that lime - RHA cement , which is cheaper than OPC, can be used as a cementitious binder to solidify heavy metal sludge with much less leachability than that of OPC, and its compressive strength s are high enough for landfill disposal. Moreover , it is expected that lime - RHA cement can be a solution to rice husk disposal problem .