PERFORMANCE EVALUATION OF A HYBRID NATURAL WASTEWATER TREATMENT POND SYSTEM IN KIGALI, RWANDA

NHAPI I.¹, WALI U.G.², TWAGIRAYEZU B.³, KIMWAGA R.⁴, BANADDA N.^5
1School of Engineering, College of Science and Technology, University of Rwanda, Butare, Rwanda.
²School of Engineering, College of Science and Technology, University of Rwanda, Butare, Rwanda.
³School of Engineering, College of Science and Technology, University of Rwanda, Butare, Rwanda.
⁴Department of Water Resources Engineering, University of Dar-es-salaam, Dar Es Salaam, Tanzania.
⁵Department of Agricultural and Bio-Systems Engineering, Makerere University, Kampala, Uganda.

Received : 15-11-2013     Accepted : 12-12-2013     Published : 26-12-2013
Volume : 3     Issue : 1       Pages : 23 - 28
Bioinfo Environ Pollut 3.1 (2013):23-28

This study aimed at evaluating the performance of the Nyarutarama waste stablization ponds. The study was conducted from July to October 2008 with sampling done fortnightly. The parameters monitored were temperature, pH, conductivity, total suspended solids, dissolved oxygen, five-day biochemical oxygen demand, chemical oxygen demand, total nitrogen, total phosphorus, ammonium-nitrogen, nitrate-nitrogen, nitrite-nitrogen and faecal coliforms. The samples were collected at the inflow and outflow points of each pond and analysed according to standard methods. Parshall Flume was used for flow measurement. The Nyarutarama treatment ponds received about 355 m3/day of sewage with an estimated total hydraulic retention time of 45 days. The results showed that there is substantial reduction in pollutants in the system in terms of TSS, BOD5, COD, TN and TP, with high reductions observed in the second pond. Although there was about 96% removal of FC, the concentration in the final effluent was still very high (above 2,000 cfu/100ml) compared to WHO guidelines for irrigation water of 1,000/cfu/100ml. It was concluded that, there is scope for better results if the treatment system is properly managed in term of. This management includes optimal harvesting of macrophyte plants, control of open water zones, and protection of pond embankments.