The paper summarizes the results of a bench‐scale study to evaluate the feasibility of using peracetic acid (PAA) as a substitute for sodium hypochlorite both for discharge into surface water and for agricultural reuse. Trials were carried out with increasing doses (1, 2, 3, 5, 10, and 15 mg/L) and contact times (6, 12, 18, 36, 42, and 54 minutes) to study disinfectant decay and bacterial removal and regrowth, using fecal coliform and Escherichia coli (E. coli) as process efficiency indicators. Peracetic acid decay kinetics was evaluated in tap water and wastewater; in both cases, PAA decays according to first‐order kinetics with respect to time, and a correlation was found between PAA oxidative initial consumption and wastewater characteristics. 
 
 The PAA disinfection efficiency was correlated with operating parameters (active concentration and contact time), testing different kinetic models. Two data groups displaying a different behavior on the basis of initial active concentration ranges (1 to 2 mg/L and 5 to 15 mg/L, respectively) can be outlined. Both groups had a “tailing‐off” inactivation curve with respect to time, but the second one showed a greater inactivation rate. Moreover, the effect of contact time was greater at the lower doses.
 
 Hom's model, used separately for the two data groups, was found to best fit experimental data, and the disinfectant active concentration appears to be the main factor affecting log‐survival ratios. Moreover, the S‐model better explains the initial resistance of E. coli, especially at low active concentrations (<2 mg/L) and short contact times (<12 minutes). 
 
 Microbial counts, performed by both traditional methods and flow cytometry, immediately and 5 hours after sample collection (both with or without residual PAA inactivation), showed that no appreciable regrowth took place after 5 hours, neither for coliform group bacteria, nor for total heterotrophic bacteria.

Lake Iseo is undergoing a progressive deterioration in water quality, mainly due to eutrophication. This paper, based on measurements performed on the main tributaries and the outflow, considers the phosphorus, nitrogen and silica budget of the lake, related to its trophic evolution. The chief conclusion of the study is that the significant reduction in P load over the last few years following the construction of treatment plants is not enough to reverse the trend to eutrophication and the progressive deterioration in water quality. An attempt to use the OECD statistical approach to quantify the relationships between P load and the trophic condition of the lake yielded poor results, because the characteristics of the lake did not fulfil the hypothesis of the model. The reduced tendency to a complete overturn of the water is one of the most important aspects, leading to hypolimnion anoxia and P release from the sediments

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The paper summarizes the results of a bench-scale study to evaluate the long-term disinfection efficiency of peracetic acid (PAA). Bacterial counts were repeated 5, 24, and 29 h after the end of the disinfection test, to simulate real re-growth conditions (no residual quenching) and, for the 5 h interval, the potential re-growth (quenching of residual PAA). Fecal coliforms, Escherichia coli, and total heterotrophic bacteria (THB) were enumerated by traditional plate count technique; THB were also enumerated by cytometry. After disinfection, the residual PAA concentration became negligible in about 5 to 11 h, depending on the tested doses. Microbial counts showed that no appreciable re-growth took place after 29 h for coliform group bacteria. For THB, the previously cited enumeration techniques gave different results in re-growth tests, especially for the lowest PAA doses. Indeed plate count technique evaluates the ability to form colonies, while cytometry enumerates intact membrane cells. No regrowth took place, even when no residual disinfectant was present, suggesting that bacteria are unable, even at the lowest doses, to repair damage caused by the PAA disinfecting action. PAA was found to be an efficient disinfecting agent, not only as a bacteriostatic, but also as a bactericide.

Disinfection tests were carried out at pilot scale to compare the disinfection efficiency of ozone, sodium hypochlorite (NaOCl), peracetic acid (PAA), and UV irradiation. Total coliforms, fecal coliforms, and Escherichia coli were monitored as reference microorganisms. Total heterotrophic bacteria (THB) were also enumerated by cytometry. At similar doses, NaOCl was more effective than PAA, and its action was less affected by contact time. The results obtained by ozonation were comparable for total coliforms, fecal coliforms, and E. coli. On the contrary, some differences among the three indicators were observed for NaOCl, PAA, and UV. Differences increased with increasing values of the disinfectant concentration times contact time (CÁt) and were probably the result of different initial counts, as total coliforms include fecal coliforms, which include E. coli. The UV irradiation lead to complete E. coli removals, even at low doses (10 to 20 mJ/cm 2 ). Total heterotrophic bacteria appeared to be too wide a group to be a good disinfection indicator; no correlation was found among THB inactivation, dose, and contact time. Water Environ. Res., 79, 2373Res., 79, (2007.