Safety of treated water for re-use purposes--comparison of filtration and disinfection processes.

A study was conducted on the distribution of pollutants in treated wastewater and the its safety for re-use purposes. Based on the results of a series of tertiary treatment experiments, the effects of three filtration processes, i.e. coagulation-filtration, ozonation-biological activated carbon filtration (O3-BAC) and ultrafiltration (UF), and two chemical disinfection processes, i.e. chlorination and ozonation, on the safety of water re-use were evaluated. It was found that the concentrations of the main pollutants in the secondary effluent and further filtered water follow a log-normal distribution and, therefore, a log-normal probabilistic function can be used to evaluate the suitability of the treated water for re-use purposes. Among the three filtration processes evaluated, UF is the most effective in turbidity removal but less effective in colour and COD removal, while coagulation-filtration and O3-BAC can ensure a good removal of all these pollutants. Regarding chemical disinfection, although chlorine is very effective in inactivation of coliform bacteria, it can not achieve a substantial decrease in viruses. As ozone is applied, effective virus removal can be achieved.

Application of a virological tracer method for the assessment of pathogen removal by physicochemical treatment and chemical disinfection.

Coxsackie B3 (CoxB3) virus was used as a virological tracer for an assessment of the efficiency of pathogen removal by several typical physicochemical treatment and chemical disinfection processes, such as coagulation-filtration, ultra-filtration, and disinfection using chlorine and ozone, with regard to the pathogenic quality of the treated domestic wastewater for reuse purposes. The CoxB3 virus was seeded to sterilized secondary effluent to make a raw water of known pathogenic level. After applying the raw water to each treatment or disinfection process, the residual virus in the finished water was concentrated, and virus assay was carried out by the Tissue Culture Infectious Dose technique. TCID50 was used as an indicative parameter of CoxB3 virus in the raw and treated water. Parallel experiments were also conducted to evaluate the effectiveness of each process for the removal of coliform bacteria. It was noticed from the experiment that both coagulation-filtration and ultrafiltration could achieve substantial removal of TCID50 at about the same level (2-log removal). However, the effect of the two processes on the removal of coliform bacteria was much different: 2-log removal by coagulation-filtration and 4 to 5-log removal by ultrafiltration. The TCID50 removal correlates more closely with the removal of turbidity than that of coliform bacteria. Chlorine was found to be effective in coliform removal but almost had no effect on TCID50. As ozone was applied, a high removal of both coliform bacteria and TCID50 could be obtained.