Disinfection of filtered and unfiltered secondary effluent in two ozone contactors

the objective of this study was to evaluate the effect of filtration of secondary effluent on the mass transfer and disinfection efficiencies of two ozone contactors. The two contactors used in the comparison were a multicolumn bubble diffuser and a stirred tank reactor. The approach chosen was based on a type of statistical experimental design used in a previous contactor comparison. The design made it possible to compare the ozone transfer and coliform reduction efficiencies of the two contactors with respect to applied dose, while at the same time comparing filtered and unfiltered effluent. Results indicated that better mass transfer efficiency and, consequently, better coliform reduction efficiency occurred in the bubble diffuser, and the differences between contactors increased with dose. Mass transfer in both contactors was higher in unfiltered effluent than in filtered effluent. The most significant factors affecting the fecal coliform numbers in the treated secondary effluent were total chemical oxygen demand (COD) and absorbed ozone dose. Regression equations were developed to predict final coliform numbers as a function of COD and absorbed ozone dose.