Urban wastewater treatment by infiltration-percolation with sand and coconut media after an anaerobic pond under tropical climate
In Burkina Faso, one of the major problems is the management of waste water in the cities. Biological processes for the small and middle-size communities exist, for example the infiltration-percolation approach that is particularly adapted to tropical climatic conditions. The efficiency of two filtration media (sand and coconut fiber) was tested in pilot systems downstream from an anaerobic pond acting as a primary treatment. The results show increasing efficiencies of COD removal, from 93% to 95%, and BOD5 removal efficiency reaches 99%, with the progressive colonization of the sand filter by the biomass. The filtration media composed of crushed coconut exhibited COD removal efficiencies of 15% and 51% for low (20 L•m-2•d-1) and high (60 L•m-2•d-1) hydraulic loads respectively, because of the progressive extraction of phenolic compounds from the coconut material during the first leachings. However, the coconut media gave almost the same efficiency as the sand with respect to the removal of biodegradable pollution. Nitrogen removal was also investigated, and both media transformed Kjeldahl nitrogen efficiently (75% and 84%). However, the coconut media gave the lowest concentration of nitrate (7 mg•L-1) because of tannins. The nitrate concentrations in the effluent of the sand filters reached 40 mg•L-1. This behavior of coconut media can be attributed to complexes formed between nitrogenous compounds and tannins coming from this material.