Advanced disinfection processes (peracetic acid, UV irradiation and ozonation) 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 10mg/L peracetic acid at a 10min contact time, by UV radiation at 35mW.s/cm2 and by ozone at 5mg/L for 10min contact time. Higher doses are required for virus removal by UV and PAA and especially for highly 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 disinfection efficiency of ozone, UV and PAA depends on the criteria and methods employed. Standard method (plate count) results showed an important disinfection effect on culturability, while results from non-standard methods (respiratory activity and β-galactosidase activity assay) indicated less reduction of viable cells. Moreover, the results confirm that disinfectants act on bacteria in different ways. It has been clearly demonstrated that b-galactosidase activity is affected by PAA while UV treatment has no or very limited effect on the enzyme activity. Even without sunlight reactivation, bacterial regrowth in seawater was observed after disinfection of sewage effluents. This study also shows that the biodegradability of sewage effluent for an E coli strain was affected differently by the oxidative disinfectants ozone and PAA. Biodegradability should therefore be considered when evaluating the total disinfection efficiency.

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Bacteria which were β-d-galactosidase and β-d-glucuronidase positive or expressed only one of these enzymes were isolated from environmental water samples. The enzymatic activity of these bacteria was measured in 25-min assays by using the fluorogenic substrates 4-methylumbelliferyl-β-d-galactoside and 4-methylumbelliferyl-β-d-glucuronide. The enzyme activity, enzyme induction, and enzyme temperature characteristics of target and nontarget bacteria in assays aimed at detecting coliform bacteria and Escherichia coli were investigated. The potential interference of false-positive bacteria was evaluated. Several of the β-d-galactosidase-positive nontarget bacteria but none of the β-d-glucuronidase-positive nontarget bacteria contained unstable enzyme at 44.5°C. The activity of target bacteria was highly inducible. Nontarget bacteria were induced much less or were not induced by the inducers used. The results revealed large variations in the enzyme levels of different β-d-galactosidase- and β-d-glucuronidase-positive bacteria. The induced and noninduced β-d-glucuronidase activities ofBacillus spp. and Aerococcus viridans were approximately the same as the activities of induced E. coli. Except for some isolates identified asAeromonas spp., all of the induced and noninduced β-d-galactosidase-positive, noncoliform isolates exhibited at least 2 log units less mean β-d-galactosidase activity than induced E. coli. The noncoliform bacteria must be present in correspondingly higher concentrations than those of target bacteria to interfere in the rapid assay for detection of coliform bacteria.

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Three fluorogenic methylumbelliferone (MU) substrates were evaluated for rapid detection of total and fecal coliform bacteria (TC and FC) in drinking water. 4-MU-j0-D-galactoside, MU-heptanoate, and MU-glucuronide were used to determine enzyme activity as a surrogate measure of coliform concentration. Coliforms occurring in river water and in potable water artificially contaminated with raw sewage were tested. The initial rate of hydrolysis (AF) of MU-0-D-galactoside showed promise as an indicator of TC and FC within 15 min.