A proposal for managing wastewater in Harare, Zimbabwe

Abstract

This paper deals with wastewater management in Harare, in the Lake Chivero catchment area of Zimbabwe. It aims at developing a sustainable system for managing water and nutrients and is based on the literature and a water quality monitoring study conducted from June 2000 to December 2001. This study has shown serious water pollution problems due to urbanisation in the catchment. A 'three-step strategic approach' to urban (waste)water management was used as a basis for formulating solutions. The short-term solutions include reduction of wastewater volume in industries and households, reducing wastewater flows by 24% and total phosphorus by 5%. The medium-term solutions involve treating wastewater to high standards, resource recovery and reuse, and controlling upstream sources of pollution, and thus would reduce the lake total nitrogen and total phosphorus levels to about 0.4 and 0.07 mg/L, respectively. A long-term solution was suggested based on pollution prevention and direct reuse, treatment at onsite and decentralised levels followed by reuse, and minimal disposal of the remaining effluents combined with the stimulation of the self-purification capacity of the receiving rivers. It was concluded that it is feasible to reduce pollution levels in the catchment by applying these phased developments.

Phosphorus transport and retention in a channel draining an urban, tropical catchment with informal settlements

“…In fact, most parts in the city of Kampala (> 90 %) as well as other urban areas in SSA (> 70 %) are largely unsewered (Nyenje et al, 2010) implying that most people living in these areas rely on on-site sanitation for wastewater disposal. However, due to poor on-site sanitation systems especially in slum areas (Kulabako et al, 2007;Nyenje et al, 2013a;Isunju et al, 2011;Katukiza et al, 2010), most wastewater generated in the catchment ends up into the drainage system hence introducing a number of pollutants and nutrients to downstream ecosystems.…”

“…Zhang et al (2007) found a TP flux of only 0.034 kg km −2 d −1 in nutrient runoff from forested watershed in central Japan. Nhapi et al (2006) showed that the TP flux for the two major river inflows to the eutrophic Lake Chievero in the city of Harare (Zimbabwe) ranged between 0.1 and 0.35 kg km −2 d −1 . Although these rivers were heavily polluted by on-site sanitation and sewage overflows from treatment plants, the TP fluxes were still low when compared to those in our study.…”

“…Sediments were analysed for geo-available metals (Fe, Ca, Mg and K), pH, organic matter (OM), organic carbon (OC), available phosphorus and grain size distribution. Geo-available metals were extracted with 0.43 M HNO 3 (Rauret, 1998;Novozamsky et al, 1993) and analysed using an ICP spectrophotometer (Perkin Elmer Optima 3000). Al and Si were not determined due to analytical limitations.…”

“…Phosphorus (P) derived from urban catchments in subSaharan Africa (SSA) is increasingly becoming a major cause of eutrophication of urban fresh water bodies (Nhapi et al, 2002;Nyenje et al, 2010). This is primarily attributed to the increasing release of untreated or partially treated wastewater into the environment especially in the informal settlements or slums.…”

“…However, these two systems could have contrasting mechanisms controlling P transport due to differences in climate, land use and geology. Hence, the fate of P in urban tropical catchments with informal settlements remains unknown (Nyenje et al, 2010). Chua et al (2009) presented a case study of P transport in a tropical environment but they only focused on P transport dynamics during high and low flows without providing insights into the chemical processes regulating P transport.…”