Experimental assessment of RSF, UF, RSF-O₃ and RSF-H₂O₂/UV for unrestricted agricultural wastewater reuse in Italy

In this paper, tertiary treatment processes aimed at achieving a wastewater quality suitable for reuse in agriculture in Italy have been investigated, with experimental results generated by means of pilot and bench scale tests. Studies were conducted to assess the removal of mineral oil, total surfactants, total coliforms, Escherichia coli and Salmonella using the following treatment options: rapid sand filtration (RSF), hollow fiber ultrafiltration (UF), RSF followed by ozonation (RSF-O₃) and RSF followed by hydrogen peroxide combined with UV radiation (RSF-H₂O₂/UV). Mineral oil concentration, evaluated by means of the hydrocarbon oil index measurement, indicated an effluent concentration consistently below 0.05 mg/L for all processes studied. While total surfactants in the secondary effluent never exceeded the applicable limit of 0.5 mg/L during the studies, the degree of removal measured in studied treatments ranged from moderate to low, with the greatest removal observed using RSF-O₃ (24%) and RSF-H₂O₂/UV (30%) under applied conditions. Overall, the optimal treatment performances were achieved by the RSF-H₂O₂/UV combined process using ≥1.5 mg/L H₂O₂ and UV dose ≥45 mJ/cm², which provided adequate mineral oil and total surfactants removal, complete removal of measurable total suspended solids (TSS) and Salmonella, and greater than 4-log reduction in total coliforms and Escherichia coli.