PERACETIC ACID (PAA) AS A DISINFECTANT FOR MUNICIPAL WASTEWATERS: ENCOURAGING PERFORMANCE RESULTS FROM PHYSICOCHEMICAL AS WELL AS BIOLOGICAL EFFLUENTS

Peracetic acid (PAA) was assessed as a potential disinfectant for municipal wastewaters. Effluents from four plants in Quebec (Canada) were subjected to batch tests; two were physicochemical (using ferric and/or alum) and two were biological (activated sludge). A recently developed colourimetric method, using horseradish peroxidase and ABTS as the key reagents, was used to measure the PAA residuals (as mM peroxycompounds). UV is arguably the most popular disinfection process for new or retrofitted wastewater treatment plants, hence it was also assessed in the current study as a comparison, via collimated beam tests.For an arbitrary target fecal coliform (FC) level of 1,000 CFU/100 mL, and contact times of 30 – 120 minutes, PAA doses ranged from 2 to >6 mg/L for the physicochemical effluents, and from 0.6 to 4 mg/L for the biological effluents. PAA consumption rates varied from 0.065 to 0.356 mM for the physicochemical effluents, and almost all the PAA was consumed after 120 minutes; for the biological effluents the consumption rates were lower and steadier at 0.02 to 0.05 mM, and only 30% of the PAA was consumed.UV disinfection performance was also affected by the type of effluent, requiring 7 to 15 mJ/m2 to reach the FC target for the physicochemical effluents, versus 5 to 7.5 mJ/m2 for the biological effluents. These differences would be exacerbated in terms of required full-scale plant capacity, due to the lower UV transmittances of the physicochemical effluents.Thus PAA has been shown to be a viable disinfectant for municipal wastewaters, and especially for those effluents having been treated by biological processes. Applications would be favoured particularly in those situations requiring flexible operation and low capital costs.