Physico-chemical, chemical and biological characterization of wastewater treatment plant of Oujda (Eastern Morocco) and possibility of reuse in irrigation

Abstract

The wastewater treatment plants (WWTP), in particular those using aerated lagoons, can be subject to failures that limit the reliability of treatment performance over the operating period. This is observed at the wastewater treatment plant of the city of Oujda, object of our study, the objective of which is to verify the purification performance from the diagnosis of the WWTP. To do this, we diagnosed the functioning of the different treatment stages during one year of operation (2020) by determining the physico-chemical, chemical, parasitological and bacteriological (biological) characteristics of the treated wastewater, throughout their treatment process, in comparison with the standards for reuse in irrigation and the Moroccan standards for direct liquid discharge into the natural environment.Data analysis showed that the efficiency of the combined system reached 79 %, 85 % and 84 % of suspended solids (SS), chemical demand in oxygen (COD) and biochemical oxygen demand (BOD5) respectively. With pollutant loads at the WWTP inlet of 13 306.45 Kg/d of suspended solids, 32 407.39 kg/d of COD and 20 752.29 kg/d of BOD5 and polluting loads at the WWTP outlet of 3 379.80 kg/d of suspended solids, 4 949.08 kg/d of COD and 3 261.93 Kg/d of BOD5.The bacteriological analysis shows faecal pollution of human origin, which is of the average order of 3.2 E + 07 at WWTP entry and 4.4 E + 03 at WWTP exit, with an abatement yield of 99.99 %.The analysis of the purified effluent at the WWTP outlet revealed that the discharge standards for the flows at the outlet of the station in terms of physico-chemical and parasitological parameters, in particular the BOD5, COD, SS, salmonella and cholera vibrios are well respected. While, the system shows signs of imbalance that is expressed in the non-compliance of fecal coliforms (FC).