Pilot Plant Investigation of Ozone Disinfection of Physico- Chemically Treated Municipal Wastewater

An ozonation pilot plant was installed at the Montréal Urban Community Wastewater Treatment Plant (MUCWTP) to assess the feasibility of employing a full scale ozone disinfection system. Wastewater characteristics such as turbidity, COD, TOC, BOD, pH, ORP and suspended solids were monitored to assess their effect on ozone disinfection. Fecal conforms (FC) were used as indicators to measure disinfection performance. Ozone disinfection was capable of reducing the fecal conform counts from typical 0.4 4 million CFU/100 ml to thousands, hundreds or tens per 100 ml depending on the dose applied. None of the parameters monitored could be correlated with the ozone dose required to achieve particular disinfection efficiency. Pilot tests showed that an ozone dose of 17 mg/l reduced the percentage of cases (observed in this study) for which the concentration of FC in the effluent was higher than 5000 CFU/100 ml (as required by the Quebec Ministry of the Environment) to 10%. A dose of 20 mg/l reduced the number of occurrences to 2%. An integrated CT value (ozone residual x detention time) of 0.15 mg-min/l was needed to achieve a FC survival ratio of 3.1x10 (i.e. to reach the target FC value). Results of a comparison study showed that when alum was substituted for FeCl3 as a coagulant in the treatment process at the MUCWTP, ozone disinfection efficiency was enhanced. No additional toxicity in the wastewater could be attributed to ozonation. An increase in the biodegradability of the wastewater following ozonation was observed.