The objective of this work was to find an alternative wastewater treatment technology to that of waste stabilization ponds which was capable of producing an effluent safe for reuse in irrigation, but which did not require the large land areas of such a system. Single-stage lime treatment of raw domestic wastewater in a continuous-flow pilot-plant produced an effluent suitable for reuse in unrestricted irrigation by attaining the Engelberg/WHO guidelines of ≤ 1 intestinal nematode egg per litre and ≤ 1000 faecal coliforms per 100 ml. Such treatment was achieved for a mean hydraulic retention time in the sedimentation tank of less than nine hours. The principal mechanism of bacterial removal was physical entrapment and sedimentation to the sludge layer: high pH was only a secondary mechanism for faecal coliform destruction. Faecal coliforms acted as good indicators of the removal of salmonellae in the lime flocculation-sedimentation system, but intestinal nematode eggs were not reliable indicators of the removal of protozoan cysts.

Coagulation, flocculation, sedimentation, lime, faecal coliforms, helminths, pathogens, reuse
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© IWA Publishing 1992
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