Waste-water from Ben Sergao (Morocco) is treated by a process using infiltration on sand which includes an anaerobic lagoon (1500 m3) in which waste-water has a retention time of 1.4 days followed by 5 infiltration basins (1500 m2 each). Each basin comprises by a 2 meter thick sand dune layer. The basins are drained at their base through a network of gravel-embedded drains. Three 350 m3 batches are performed daily. These are received in 3 separate basins. Each basin receives one batch a day during 3 days and is then left to rest for 2 days before carrying out a new cycle. It has been estimated that the treatment induced a decrease of 99.93 % for the fecal coliforms and 99.98 % for the fecal streptococci. Concerning the parasitology, neither nematode eggs nor cestode eggs were found in treated sewage even though their number in raw waste-water could be estimated respectively to be 139 and 75 per liter. As for physicochemical parameters, no significant difference appears between raw and treated sewage for K, P and conductivity, but there is a very significant increase of parameters NO2 and NO3 and a very important decrease of COD and total suspended matter after treatment. This treatment process seems to be very well adapted for the treatment of sewage and the reuse of treated water in rural areas.

The wastewater treatment by infiltration-percolation plant at Ben Sergao (a suburb of Agadir, Morocco) foreshadows the installation which will be able to be built for Greater Agadir (first fraction: 40,000 m3/d). The present plant treats 1,000 m3/d of highly concentrated raw effluents which after being decanted in an anaerobic stabilization pond are infiltrated into 5 infiltration basins of 1,500 m2 each, constituted by a bed 2 metres thick of eolian sand drained at its base. The decanted water infiltrates at the rate of one metre per day. With this process 100 % of the suspended matter, and 95 % of the chemical oxygen demand are removed, 85 % of the nitrogen is oxidized. The parasites are entirely eliminated and the number of fecal coliforms and streptococci is made 10,000 to 100,000 times smaller. A series of experiments of irrigation by the treated effluents is under way.

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