Characterization of biosolids and evaluating the effectiveness of plastic-covered sun drying beds as a biosolids stabilization method in Lusaka, Zambia

Introduction The Lusaka Water and Sewerage Company(LWSC) produces *800–1,000 kg of treated sewagesludge per day at its Manchinchi wastewater treatmentplant (WWTP). The biosolids are used for land applicationpurposes although the contaminant and pathogen compositionand quality of the biosolids have been unknown untilthis study. Zambia does not have legal standards andguidelines for biosolids management or application. TheManchinchi plant in Lusaka suffers from constant breakdownssuch that the effectiveness of the plant to producequality grade biosolids for land application use is questionable.In peri-urban areas, the problem of poor sanitationis being addressed using different technologies includingurine diversion ecosan toilets. The effectiveness of ecosantoilets to stabilize faecal sludge has not been assessed inZambia. The purpose of this study was to stabilize andcharacterize the biosolids from Manchinchi plant andecosan toilets. Stabilization was done by use of drying bedsand irradiation. The parametres that were used for characterizationwere microbiological, parasitological andheavy metals.Results Biosolids from the Manchinchi WWTP sun dryingbed, ecosan toilets and from an experimental plasticcovereddrying bed were found to contain different pathogenicmicroorganisms and contaminant levels. A radiationdose and time-related declining trend in pathogens loads inbiosolids were observed. By the third week, no viableAscaris eggs were detected. Based on controlled conditions,the biosolids quality was found to be within theinternationally acceptable standards for restricted use.Conclusions Both the untreated LWSC biosolids andecosan sludge contained pathogen levels with the potentialto cause environmental and public health hazards if usedfor agriculture purposes. Under plastic-covered dryingbeds, viable Ascaris eggs were not detected by the fourthweek of treatment and the biosolids were stabilized tolevels equivalent to Class C of the Australian standards forrestricted land application. Covered drying beds can beconsidered as cost effective stabilization treatment technologyfor biosolids in developing countries. The technologyhas potential benefits for improving public healthand reducing environmental pollution in Zambia, especiallyduring the rainy season when biosolids are directlydischarged into the environment.