Ecotoxicity characterization assisted performance assessment of electro-bioremediation reactors for nitrate and arsenite elimination

The performance of combined reduction of nitrate (NO3-) to dinitrogen gas (N2) and oxidation of arsenite (As[III]) to arsenate (As[V]) by a bioelectrochemical system was assessed, supported by ecotoxicity characterization. For the comprehensive toxicity characterization of the untreated model groundwater and the treated reactor effluents, a problem-specific ecotoxicity test battery was established. The performance of the applied technology in terms of toxicity and target pollutant elimination was compared and analyzed. The highest toxicity attenuation was achieved under continuous flow mode with hydraulic retention time (HRT) = 7.5 h, with 95%, nitrate removal rate and complete oxidation of arsenite to arsenate. Daphnia magna proved to be the most sensitive test organism. The results of the D. magna lethality test supported the choice of the ideal operational conditions based on chemical data analysis. The outcomes of the study demonstrated that the applied technology was able to improve the groundwater quality in terms of both chemical and ecotoxicological characteristics. The importance of ecotoxicity evaluation was also highlighted, given that significant target contaminant elimination did not necessarily lower the environmental impact of the initial, untreated medium, in addition, anomalies might occur during the technology operational process which in some instances, could result in elevated toxicity levels. High efficiency of electro-bioremediation for nitrate and arsenite elimination was demonstrated under continuous flow mode (hydraulic retention time [HRT] = 7.5) with a nitrate removal of 95% and complete oxidation of the arsenite to arsenate was achieved. The importance of ecotoxicity testing in the electro-bioremediation system performance assessment was highlighted: Daphnia magna proved to be the most sensitive ecotoxicity test organism.image