InvestIgatIon du lessIvage des stocks de boues d’épuratIon de nador : étude sur terraIn et apport de l’expérImentatIon Leaching investigation of sewage sludge stocks of Nador: Field study and experimental provision

The wastewater treatment plant (WTP) of Nador, using an activated sludge process, generates large quantities of sludge, which create a serious environmental problem. The sludge is stored near the Nador lagoon, without any measures to ensure protection of the environment. During the rainy period, the Lessivage des boues d’epuration de la ville de Nador 372 rain water seeps through the waste, extracting minerals and organic compounds and generating a leachate. Our study aimed to characterize the leachate from the stocked sludge and to explore experimentally, using a percolation test, the risk of contamination of water resources. The results of physicochemical analysis showed that the leachate is rich in total Kjeldhal nitrogen (TKN max = 1,440 mg•L-1), nitrate (NO3 max = 88.6 mg•L-1), total phosphorus (TP max = 88.8 mg•L-1) and orthophosphate (PO4 max = 20.9 mg•L -1). In addition, the leachate has high contents of SO4, Cl, Ca, Mg, Na and K. The leachate also contains heavy metals, mainly Cu and Zn. The percolation test indicates important levels of nitrogen and phosphorus leached from the sludge in comparison to the soil control. Furthermore, the quantities of NO3, NH4, TKN, PO4 and TP exported by leaching through the sludge are respectively, 8 fold, 21 fold, 35 fold, 3 fold and 18 fold higher than those leaching through soil. In addition, the levels of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) leached from sludge (0.07% of the initial load) are 2 fold higher than the levels leached from soil.