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Selectors were operated at four full-scale activated sludge plants to control bulking and foaming problems due to filamentous microorganisms. Selector effectiveness was not related to reduction of biodegradable organic matter in the contact zone, but was related to soluble COD levels in selector effluent. Significant reductions in the numbers of filamentous m icroorganisms were reported.

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.