Physico-chemical, microbiological and ecotoxicological evaluation of a septic tank/Fenton reaction combination for the treatment of hospital wastewaters.

Hospital wastewater is considered a complex mixture populated with pathogenic microorganisms. The genetic constitution of these microorganisms can be changed through the direct and indirect effects of hospital wastewater constituents, leading to the appearance of antibiotic multi-resistant bacteria. To avoid environmental contamination hospital wastewaters must be treated. The objective of this study was to evaluate the efficiency of hospital wastewater treated by a combined process of biological degradation (septic tank) and the Fenton reaction. Thus, after septic tank biodegradation, batch Fenton reaction experiments were performed in a laboratory-scale reactor and the effectiveness of this sequential treatment was evaluated by a physico-chemical/microbiological time-course analysis of COD, BOD(5), and thermotolerant and total coliforms. The results showed that after 120min of Fenton treatment BOD(5) and COD values decreased by 90.6% and 91.0%, respectively. The BOD(5)/COD ratio changed from 0.46 to 0.48 after 120min of treatment. Bacterial removal efficiency reached 100%, while biotests carried out with Scenedesmus subspicatus and Daphnia magna showed a significant decrease in the ecotoxicity of hospital wastewater after the sequential treatment. The use of this combined system would ensure that neither multi-resistant bacteria nor ecotoxic substances are released to the environment through hospital wastewater discharge.