Sewage sludge disposal on land – impacts on surface water quality
Basic principles of sewage treatment and sludge disposal options, common for the region have been presented, together with regulatory aspects for a safe practical application. A case study of digested sludge and effluent mixture, disposed beneficially for pasture irrigation on Crowborough farm in Harare, has been investigated during 1998 – 1999, in terms of loading rates and the impacts of such type of disposal method on surface water after 30 years of operation. Results show considerable adverse impacts on natural streams, draining the pasture, with respect to TP, TKN, nitrate and Ni, with pronounced seasonal variation. TKN and TP impacts were pronounced during the dry season, while nitrates impacts were pronounced throughout the year with higher impacts during the wet season. Recommendations with respect to the future operation of the pasture have been made.