Abhatoo - Centre Nationale de Documentation

Samples of raw, decanted, and purified waters were taken off during five months (in 2004-2005) from a wastewater treatment plant using infiltration-percolation and eleven physicochemical parameters were analyzed to determine the performances of this purification system under an arid climate. Compared to raw and decanted waters, the values of chemical and biochemical oxygen demands, NH₄⁺, total phosphorus and PO₄^2- in the purified water were significantly decreased. In contrast, the contents of nitrites and nitrates in the purified water were 56 and 177 times greater (a mean of 0.11 g/L for N-NO₂ and 5.5 g/L for N-NO₃). Using a principal component analysis, chemical and biochemical oxygen demands, NH₄⁺, total phosphorus and PO₄^2- were correlated with the raw water, while the purified water was correlated with nitrites, nitrates and electric conductivity. The huge increase of nitrites and nitrates noted in the purified water would be due to a malfunction of the system, probably in reason of an organic material overload which accumulated in sand filters during water alimentation of basins. Owing the nitrite and nitrate concentrations in the purified water, its reuse in agriculture poses a real problem for soil and vegetation so that an additional treatment is necessary for eliminating these both salts from the purified water.