Advanced wastewater disinfection technologies: Short and long term efficiency

Advanced disinfection processes (peracetic acid, UV irradiation and ozonati on) have been tested and evaluated through bench and pilot scale studies. 3 log removals of total coliforms, faecal coliforms and faecal streptococci were achieved by 10 mg/L peracetic acid at a 10 min contact time, by UV rad iation at 35 mW.s/cm(2) and by ozone at 5 mg/L for 10 min contact time. Hig her doses are required for virus removal by UV and PAA and especially for h ighly resistant viruses such as F-specific bacteriophage MS2. Ozonation has the advantage of having a strong effect on all types of bacteriophages and , protozoa cysts even when low treatment doses and short contact times are applied. The results of this study demonstrated that evaluation of disinfec tion efficiency of ozone, UV and PAA depends on the criteria and methods em ployed. Standard method (plate count) results showed an important disinfect ion effect on culturability, while results from nonstandard methods (respir atory activity and beta-galactosidase activity assay) indicated less reduct ion of viable cells. Moreover, the results confirm that disinfectants act o n bacteria in different ways. It has been clearly demonstrated that b-galac tosidase activity is affected by PAA while UV treatment has no or very limi ted effect on the enzyme activity. Even without sunlight reactivation, bact erial regrowth in seawater was observed after disinfection of sewage efflue nts. This study also shows that the biodegradability of sewage effluent for an E coli strain was affected differently by the oxidative disinfectants o zone and PAA. Biodegradability should therefore be considered when evaluati ng the total disinfection efficiency. (C) 1998 IAWQ Published by Elsevier S cience Ltd. All rights reserved.