A conceptual framework for the sustainable management of wastewater in Harare, Zimbabwe I. Nhapi*, H.J. Gijzen** and M.A. Siebel** * Department of Civil Engineering, University of Zimbabwe, P.O. Box MP167, Mt. Pleasant, Harare, Zimbabwe (E-mail: nhapi@zimsite.com) ** IHE Delft, The Netherlands Abstract The aim of this study was to formulate an integrated wastewater management model for Harare, Zimbabwe, based on current thinking. This implies that wastewater is treated/disposed of as close to the source of generation as possible. Resource recovery and reuse in a local thriving urban agriculture are integrated into this model. Intervention strategies were considered for controlling water, nitrogen and phosphorus flows to the lake. In the formulation of strategies, Harare was divided into five major operational areas of high-, medium-, and low-density residential areas, and also commercial and industrial areas. Specific options were then considered to suit landuse, development constraints and socio-economic status for each area, within the overall criteria of limiting nutrient inflows into the downstream Lake Chivero. Flexible and differential solutions were developed in relation to built environment, population density, composition of users, ownership, future environmental demands, and technical, environmental, hygienic, social and organisational factors. Options considered include source control by the users (residents, industries, etc.), using various strategies like implementation of toilets with source separation, and natural methods of wastewater treatment. Other possible strategies are invoking better behaviour through fees and information, incentives for cleaner production, and user responsibility through education, legislative changes and stricter controls over industry. Keywords Decentralised; onsite; reuse; strategies; sustainability; wastewater Introduction Harare, the capital city of Zimbabwe, has systematically destroyed its major source of potable water supply, Lake Chivero. The lake is located about 35 km downstream of Harare as shown in Figure 1. It receives pollution from sewage effluent, agricultural, solid waste, industrial (un-sewered), and natural sources. Harare has a population of about 1,900,000 with the majority housed in 106,950 houses in 15 high-density suburbs. About 304,000 m 3 /d of sewage is produced in Harare with 43% of this directly discharged into the rivers after tertiary treatment (Nhapi et al., 2001c). The rest receives secondary treatment and is used for pasture irrigation. Overloading and numerous plant breakdowns often compro- mise the quality of effluent discharged to rivers. About 17,800 kg/d TN and 1,900 kg/d TP are generated and discharged to the two major sewage treatment works of Firle and Crowborough (Nhapi et al., 2001b). Urban agriculture is now a notable economic activity with about 16,000 hectares or 75% of the open spaces currently under cultivation. It is estimated that 2,800 and 480 metric tonnes of TN and TP respectively are used in Harare as commercial fertilisers mostly for maize production (Nhapi et al., 2001b). Some of the fertiliser applied eventually leaches into water courses. The central problem in Harare is that sewage effluent seems to be contributing significantly to eutrophication of Lake Chivero. With population increase, the Lake will increasingly receive a higher fraction of sewage effluent whilst raw water abstraction will also increase, further exacerbating the problem. Dry season nutrient levels in the Lake have been reported around 2.4 mg/l TN and 0.8 mg/l TP (Nhapi et al., 2001a). These are higher than the allowable limits of < 0.3 mg/l TN and < 0.01 mg/l TP for drinking water in lakes (JICA, Water Science and Technology Vol 47 No 7–8 pp 11–18 © IWA Publishing 2003 11