A comparative study of tertiary wastewater treatment by physico-chemical-UV process and macrofiltration-ultrafiltration technologies

A comparative study was undertaken of the economic costs and quality of effluents obtained from physicochemical-UV and macrofiltration-ultrafiltration as municipal wastewater tertiary treatments. A physicochemical-UV urban wastewater treatment system was designed for the study. Pre-treatment to UV radiation disinfection consisted of coagulation with alumina (100 mg/L), sedimentation by sludge-blanket sedimentation tank (0.8 m(3)/m(2) h) and filtration by sand-pressure filter (5.0 m(3)/m(2) h). The ultrafiltration module was equipped with flat polyvinylidenefluoride membranes (0.05 mu m pore size), with pre-treatment carried out by a sand-pressure filter (8.0m(3)/m(2) h). Both systems obtained effluent of excellent physico-chemical quality (91% removal of suspended solids and 99% turbidity removal) and microbiological quality (total absence of nematode eggs, coliforms, E. coli and coliphages). However, while physico-chemical quality remained constant in both systems, microbiological quality of effluent from the UV-disinfection process was shown to depend on the quality of influent, particularly with regard to transmittance. By contrast, microbiological quality remained constant in the case of membrane technology. Other control parameters such as particulate analysis confirmed the higher quality of ultrafiltration effluent in comparison with the physico-chemical-UV process. With regard to costs, both technologies present similar variable costs, while fixed costs of the membrane installation are double those of the physico-chemical-UV process, owing particularly to the high cost of the installation itself.