Comparison between PAA/UV and H₂O₂/UV disinfection for wastewater reuse

The effect of peracetic acid (PAA) on indicator bacteria in secondary sewage effluent has shown PAA to be a viable alternative to other biocides. The synergy between UV/PAA and UV/H₂O₂ in laboratory experiments and at a pilot plant fed by the secondary effluent of two civil wastewater treatment plant has been investigated. This experiment is part of a larger research project on advanced treatment for municipal wastewater reuse in agriculture. A very high level of disinfection is necessary because of Italy's strict limits on unrestricted wastewater reuse in agriculture (2 CFU Total Coliform/100 ml). We found out that a combined treatment is satisfactory and that it is more efficient when chemical products such as PAA or H₂O₂ are introduced before UV irradiation, taking advantage of the hydroxyl radicals formation due to photolysis. At a cost parity PAA/UV advanced oxidation process shows the same disinfectant action as H₂O₂/UV while at a dose (amount) and cost parity, PAA shows a significantly better disinfectant action than H₂O₂.