Treatment of Wastewater by Natural Lagoon for its Reuse in Irrigation

The process of natural lagoon consists in purifying the waste water by simple flow of the effluent in not very deep ponds where proliferate bacteria, algae and other living organisms, under a surrounding air and in the presence of a solar radiation. For this study, which is spread out over 3 years (2004-2006) and which still continues, we chose the Beni Messous plant of purification by natural lagoon, to locate in Algiers. The parameters considered were: The biological oxygen demand (BOD₅), the Chemical Oxygen Demand (COD), nitrites (NO₂^-), orthophosphates (PO₄^{3 -}), Suspended Solid (SS), pH and variation of the chlorophyll concentration. This lasts which made it possible to test the efficiency of this process for a possible reuse of the treated water, for the irrigation. The concentrations of the various parameters obtained after treatment the waste water by natural lagoon are as follows: 10 mg L^-1 of BOD₅, 12 mg L^-1 of COD, 0.2 mg L^-1 of nitrites, 1.4 mg L^-1 of orthophophates, 75 mg L^-1 of SS, 0.075 mg L^-1 of Chlorophyll, the pH reaches values superior to 7 testifies to alkaline environment lagoon. These concentrations are generally lower than the standards irrigation.