Understanding the pathway of phosphorus metabolism in urban household consumption system: A case study of Dar es Salaam, Tanzania

Phosphorus discharge in urban household consumption system has an important impact on the urban ecological environment, especially the surface water environment. In this study, a framework and its accounting model of phosphorus flow analysis in urban household consumption system by means of SFA (substance flow analysis) was constructed. Based on the accounting model, the flow of phosphorus in the urban household consumption system of Dar es Salaam was described quantitatively, and the results demonstrated: (1) the total phosphorus input, stock and output of urban household consumption system in Dar es Salaam were 4874t of P, 59t of P and 4815t of P, respectively. In terms of system input of phosphorus, residents’ food consumption had a decisive impact on the system’s phosphorus input (4765t of P, 97.76%), while the contribution of detergent to the phosphorus input of the system was small. In terms of system phosphorus output, human feces and urine phosphorus output accounted for the majority of the total system phosphorus output (2313t of P, 48.04%). The total phosphorus output of domestic garbage, wastewater and food processing loss were 1464t of P (30.41%), 561t of P (11.65%), 477t of P (9.90%), respectively. (2) There were 2314t of P discharged into surface water through human feces and urine and domestic wastewater, which had a negative impact on the prevention and control of surface water pollution. 34t of P came from scattered garbage storage and 315t of P came from centralized garbage storage due to limited treatment capacity of waste treatment plant. Centralized storage and decentralized storage increased the risk of further phosphate loss. (3) Accelerated urbanization, rapid economic development and low sewage treatment capacity would cause more phosphorus loss, and Dar es Salaam faced great challenges in P discharge reduction and pollution control. Finally, we proposed policy recommendations for P discharge reduction including the guidance to the reasonable dietary structure with low phosphorus, the promotion of cleaning products with less phosphorus and no phosphorus, and the construction of garbage treatment and sewage treatment infrastructure.