Performance of Sand and Wood Fibres in Tertiary Treatment of Effluent Discharged by Lagoons

Abstract

In Burkina Faso, as in most developing countries, access to water and sanitation remains a challenge. This justifies the reuse of wastewater to provide additional quantities of water for different uses to reduce water deficits. In this context, the wastewater from the city of Ouagadougou is treated by lagoons for its reuse on gardening plots downstream the station. Since several years these plots have been disaffected and abandoned due to the quality of the discharged water. This work aims at experimenting complementary treatments to improve water quality for agricultural reuse. Indeed, pilots of infiltration-percolation on sand and on wood fibres have been implemented during 3 months in the Institute of Research in Applied Sciences and Technologies. A comparative analysis of the treated waters according to the ISO and AFNOR standards indicated that the various filters gave satisfactory purification efficiencies which are in agreement with the quality objectives imposed by the national standards for parameters such as Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD 5 ), nitrogen and faecal coliforms. The respective removals of COD by the sand filter (FS) and the wood fibres filter (FC) were 94% and 91%, while BOD 5 was eliminated with efficiencies of 84% and 64% respectively. Regarding nutrients such as ammonium and nitrate, the station gave the effluents contents conform to the discharge standards but the filters have made it possible to improve their quality. FS and FC gave satisfactory efficiencies of 97% and 92% for the faecal coliforms removal. Concerning faecal streptococci and Bacillus cereus , it is noted non-negligible with respective efficiencies of 84 and 93% with the wood fibres while the sand allowed efficiencies of 79 and 88% for the same parameters. In general, the additional treatment by the pilots has made it possible to improve the quality of the water coming from the station.