Physical, chemical and bacteriological characterization of two principal Mexico City wastewater flows are reported. COD and TSS variations were in the ranges of 290 to 680 mg/l and of 50 to 380 mg/l, respectively. The wastewater was strongly alkaline with marked bacteriological characteristics. High concentrations of chlorides, sulfates, Na, K, Ca, Mg and Si were found. Ascaris counts were between 24 and 84 eggs/l. Zeta Potential was from -20 mV to -40 mV. Conventional bench-scale tests were done to study the treatability of the wastewater by coagulation-flocculation with FeCl3 and polymers. The tests of FeCl3 performance showed that at a dosage of 80 to 100 mg/l, TSS and COD removals of between 60 to 68% can be obtained. Best performing flocculants were the cationic acrylamid copolymers, but good results were obtained with some anionic flocculants, too. The removal rates achieved with 20-30 mg/l of FeCl3 and a series of anionic polymers at doses 0.2 to 1.5 mg/l were 74 to 84% for TSS, 48-55% for COD and up to 77% for turbidity and color. Coliforms were not removed, however helminth eggs could be removed completely with low reagent doses. Copyright (C) 1996 IAWQ. Published by Elsevier Science Ltd.
