Wastewater reclamation by advanced treatment of secondary effluents

The objectives of this study were the investigation of the performance of an advanced treatment system, for the reclamation of secondary municipal effluents, and the study of the environmental quality of treated effluents. The secondary effluents from a conventional activated sludge process were fed to an advanced wastewater treatment system, consisting of a moving-bed sand filter, a granular activated carbon adsorption bed and ozone disinfection. The performance of this plant was evaluated by measuring the physicochemical, microbiological and ecotoxicological characteristics of reclaimed water. Sand filtration resulted in about 45% turbidity removal, while carbon adsorption enhanced mainly the removal of organic content, i.e. the total organic carbon removal exceeded 80%. The quality of treated effluents, obtained after ozonation by an ozone dosage of 26.7 mg/L, was found to comply with the respective US EPA proposed guidelines for urban reuse, food crop irrigation and recreational impoundments. However, a high ozone dose caused adverse effects on bacterium V. fischeri, possibly due to the formation of secondary oxidation byproducts. The annual cost of overall tertiary treatment process was evaluated to 0.24 €/m3, indicating the relatively high cost of these processes. Nevertheless, such processes are required in order to produce an effluent, with a high reuse potential.