In Mexico City, drinking water is mainly produced from groundwater (70%). This practice has caused collateral problems such as Mexico City's soil sinking (5-30 cm/year). One of the most viable alternatives to palliate this problem is the treatment of wastewater for reuse in either irrigation or for groundwater artificial recharge. This paper presents the evaluation of two physicochemical pretreatment systems to treat the wastewater from the metropolitan area of the Mexican Valley that are conducted by two main sewage systems called Great Canal and Churubusco River. In this research two treatment processes were studied: 1) coagulation-flocculation and, 2) Fenton's reagent. For each one of these processes suggested, tests were performed with wastewater samples of the Great Canal and the Churubusco River mixed in a volume ratio of 1:1. In the case of the coagulation-flocculation process, additional experiments were performed to determine the optimal conditions by applying an experimental design technique. In this experimental design, six coagulant agents were considered (alum, ferric chloride, three coagulant reagents of polymeric kind with aluminium and a coagulant reagent of natural origin), and three flocculant agents (an anionic, a cationic, and a non ionic polymers). Concerning the application of the Fenton's reagent (Fe2+:H2O2), the experimental variables were the weight ratio of the ferrous iron and the hydrogen peroxide and the concentrations of these reagents. The pH value was controlled to be near to 4. For the best experimental conditions, the effluent of the Fenton's method showed similar physicochemical characteristics to the wastewater treated by coagulation-flocculation. Nevertheless, Fenton's reagent showed two very important advantages compared to the coagulation-flocculation process: a disinfecting effect and a lower production of residual sludges.

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