OCCURRENCE AND REMOVAL OF ASCARIS SP OVA BY WASTE STABILIZATION PONDSIN KENYA

A study was conducted to determine the occurrence of Ascaris sp. ova i n municipal wastewater and their removal by a variety of waste stabili sation pond systems in the republic of Kenya. A total of 52 wastewater samples were examined for the presence of ova, comprising 10 raw wast ewater and 42 pond effluent samples over a two month period during 199 0. Ascaris sp. ova were detected in 6 out of 10 designated pond system s examined. In raw wastewater, ova concentrations ranged from 17.5 to 133.3 ova/l and in pond effluents from 0.7 to 88.9 ova/l. Although the majority of ova were removed in primary ponds that received raw waste water, ova were detected in pond effluents with estimated hydraulic re tention times far in excess of estimated settling rates for Ascaris. T he occurrence of ova in pond effluent samples suggested that in these multi-pond systems, estimated cumulative retention periods of 12.4 (El doret), 26.2 (Dandora) and 17.8 (Nakuru) days, respectively, were requ ired to achieve an effluent free of Ascaris sp. ova. Laboratory experi ments were performed to assess physico-chemical and microbiological pa rameters to provide an indication of pond performance. Copyright (C) 1 996 IAWQ. Published by Elsevier Science Ltd