Physico-chemical and bacteriological characterization of wastewater from Mexico City

Abstract

This study was designed to characterize the behavior of the wastewater produced by Mexico City after being subjected to a physico-chemical treatment of Al₂(SO₄)₃ and FeCl₃ in a jar test simulation of an Advanced Primary Treatment (APT). Special attention was paid to the evaluation of the removal efficiency of suspended solids and of helminth eggs. The effluent thus obtained was first subjected to a simulated filtration process (through a fiberglass filter paper with an opening of 11 μm) and then it was disinfected with the use of two chemicals: sodium hypochlorite (NaOCl) and copper sulphate (CuSO₄).

The use of both the Al₂(SO₄)₃ (dose ranging from 25 to 40 mg/L) and the FeCl₃ (varying from 20 to 40 mg/L) in combination with the filtration process proved to be quite effective in what refers to the removal mechanisms of helminth eggs. The concentrations recorded in each of the effluents fell always below the international regulations for irrigation reuse (<1 org/L as helminth eggs). The removal rates achieved for both coagulants were close to 99%.

In what refers to the disinfection accomplished with the use of NaOCl (from 4 to 17 mg/L as Cl₂) and CuSO₄ (from 3 to 5 mg/L as Cu), it was found to be an excellent supplementary process because less than 1000 CFU/100 mL were recorded and this value satisfies the international recommendations. The treatment as a whole showed removal efficiencies of 45% as COD, 73% SST, 99% helminth eggs, 99.99% faecal coliforms and from 7 to 87% in heavy metals.