Peracetic acid (PAA), a well known powerful antimicrobial agent in hospitals and in agribusiness (Fraser, 1986), has recently been used to disinfect urban effluents. It appears to be highly competitive against chlorine (Audic, 1990; Baldry, French, Slater and Desprez, 1990; Giodani, Iacoponi, Polidori, 1989), the most widely used disinfectant for sewage disposal. As PAA is a new biocide, not much quantitative data is available on its action against the faecal indicator bacteria and viruses. An on-site experimental study investigated the disinfectant action of PAA against these indicator bacteria and viruses as well as against Salmonella and enterovirus. To complete this study we will test its action on suspended solids to find out whether there is regrowth of the microorganisms after treatment. Multi-factor analysis in terms of criteria like inactivation efficiency, safety environmental impact, and cost will be used to compare PAA to chlorination and ozonation, the most commonly used techniques.

The simultaneous removal of carbonaceous and nitrogenous pollution by the activated sludge process is becoming common in industrial and municipal wastewater treatment plants. An oxygenation monitoring process has been developed, which is based on the dynamic analysis of ORP and DO signals and allows the detection of specific characteristic points at the end of the biological nitrification and denitrification. The aim of this study is to validate this process in a food-processing industry WWTP (slaughterhouse) having large variations of carbonaceous and nitrogenous loads. In order to treat during the peak period, pure oxygen is used. The first part of the study provides a precise diagnosis of the WWTP operation by the analysis of the ORP and DO signals. It is particularly easy to estimate the level of nitrogen treatment actually achieved and the oxygen requirements, and to detect the over- or under-oxygenated phases. Thanks to the monitoring process, the aerobic period of each cycle is reduced to the optimal duration, providing a reduction of 30% on the energy consumption compared to a traditional schedule. We have demonstrated that the use of pure oxygen associated with the existing air system is particularly relevant for the peak period. The revamping of an existing plant to simultaneously treat the carbon and the ammonia in the same basin is now technically feasible.

A new agitation system, called Turboxal, used for the oxygenation and the mixing of wastewater biological treatment tanks has been studied. The interactions between the shell and the three impellers which compose the Turboxal have been analyzed by single‐phase flow patterns. The pumping capacity and the power consumption have also been measured. In addition, the gas dispersion regimes have been analyzed in the tank and in the shell. Finally, the effect of the interaction and the effect of the position of the different agitators on the limit of the flooding regime have been determined.