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

摘要

Introduction The Lusaka Water and Sewerage Company (LWSC) produces ~800–1,000?kg of treated sewage sludge per day at its Manchinchi wastewater treatment plant (WWTP). The biosolids are used for land application purposes although the contaminant and pathogen composition and quality of the biosolids have been unknown until this study. Zambia does not have legal standards and guidelines for biosolids management or application. The Manchinchi plant in Lusaka suffers from constant breakdowns such that the effectiveness of the plant to produce quality grade biosolids for land application use is questionable. In peri-urban areas, the problem of poor sanitation is being addressed using different technologies including urine diversion ecosan toilets. The effectiveness of ecosan toilets to stabilize faecal sludge has not been assessed in Zambia. The purpose of this study was to stabilize and characterize the biosolids from Manchinchi plant and ecosan toilets. Stabilization was done by use of drying beds and irradiation. The parametres that were used for characterization were microbiological, parasitological and heavy metals. Results Biosolids from the Manchinchi WWTP sun drying bed, ecosan toilets and from an experimental plastic-covered drying bed were found to contain different pathogenic microorganisms and contaminant levels. A radiation dose and time-related declining trend in pathogens loads in biosolids were observed. By the third week, no viable Ascaris eggs were detected. Based on controlled conditions, the biosolids quality was found to be within the internationally acceptable standards for restricted use. Conclusions Both the untreated LWSC biosolids and ecosan sludge contained pathogen levels with the potential to cause environmental and public health hazards if used for agriculture purposes. Under plastic-covered drying beds, viable Ascaris eggs were not detected by the fourth week of treatment and the biosolids were stabilized to levels equivalent to Class C of the Australian standards for restricted land application. Covered drying beds can be considered as cost effective stabilization treatment technology for biosolids in developing countries. The technology has potential benefits for improving public health and reducing environmental pollution in Zambia, especially during the rainy season when biosolids are directly discharged into the environment.