The rejection of untreated waste water in the nature decreases groundwater quality. Waste water treatment plants like activated sludge plant and stabilization pond plant built in Benin show their limits. Due to these problems, reed beds have to be experimented to bring a durable solution to waste water treatment problems in Benin. Compare to activated sludge plant and to stabilization pond plant, reed beds are the cheapest based on the technical and economical point of view. On addition to that, reed beds are easy to build and to maintain. The experiment plant is composed of four basins. The first basin is unplanted. The second basin is planted with Echinochloa pyramidalis. The third basin is planted with Panicum maximum and the last basin is planted with Typha domingensis. Each basin is a 1 m3 tank with drilled drain pipes. Three differentl ayers of gravel have been put on drilled drain pipes. Treated water analysis showed that the Typha domingensis basin has the best purfiying performances with final concentrations : 0 mg/L ; 21,10 mg/L ; 10 mg/L ; 0 mg/L et 12,20 mg/L respectively for TSS, COD, BOD5, TKN and TP. These final concentrations reached the discharge standards for municipal wastewater treatment plant in Benin. Consequently, Typha domingensis beds can be popularized by the beninese government to solve waste water treatment problems.
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