Ecotoxicological assessment of industrial effluents treated by the activation of persulfate using CuO nanomaterials

• Main Author: Davarazar, Mahsa
• Publication Date: 2021
• Format: Master thesis
• Language: eng
• Source: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Download full: http://hdl.handle.net/10773/31919
• topic: Wastewater treatment; Ecotoxicity; Advanced oxidation processes; Rhodamine B; Cladocera; Rotifers

Wastewaters originated from industrial activities can cause severe toxic effects to the biota inhabiting the receiving environment. Hence, there is a need for efficient treatment technologies to a) removing the contaminants, and b) providing good quality water resources. In this context, the present thesis main goal is to assess the efficiency of advanced oxidation process (AOP) in the treatment of industrial effluents. To attain this main goal, first a scientometric study was performed to identify the main gaps in the application of various AOps, namely regarding a) optimization of AOPs for the treatment of recalcitrant organic compounds, and b) the need for ecotoxicity characterization after effluent treatment to ensure the good quality of the final treated effluents. Secondly, the efficiency of an AOP, by the activation of persulfate (PS) using CuO nanomaterials, in the treatment of an artificial effluent (with 50 mg/L Rhodamine B) was assessed. For this, different treatment designs were tested in the artificial effluent done in distilled water. The obtained results identified the treatment using 0.5 g/L of CuO, 5 mM of PS to exhibit the highest the effectiveness as it removed 100% of RhB after 120 minutes of reaction. The mentioned treatment conditions were then applied to the artificial effluent performed in ASTM medium (an artificial medium simulating freshwater; [RhB]0=50 mg/L). A drop was observed in RhB removal efficiency to 29% after 30 min, and 57% after 60 min due to the complexity of the medium. Hence, integration of catalytic and thermal activation was adopted under the same experimental condition but with an elevated temperature to 45 °C. As a result, complete degradation of RhB was observed within 60 min of reaction. The lethal toxicity of the artificial effluent to Daphnia magna was assessed before and after the AOP treatment. The toxicity of CuO and PS was also assessed. The results indicated that the treated effluent was still highly toxic to D. magna and that PS was probably the main cause for such high toxicity. Following these results, a complementary set of experiments was performed by treating the effluent with the same conditions except for the PS concentration used that was reduced to 1 mM. After 60 min of the reaction time, complete degradation of RhB was observed. The lethal toxicity of the effluent before and after the AOP treatment was then assessed for the rotifer Brachionus calyciflorus, by exposing these organisms to serial dilutions of the effluents (6.25%, 12.5%, 25%, 50%, 100%). The median lethal concentration of the effluent before treatment was 44.3% while that for the treated effluent was 8.24%, suggesting a much higher lethal toxicity of the treated effluent. It is hypothesised that such high toxicity is due to the PS, since both D. magna and B. calyciflorus exposed to this chemical alone showed 100% mortality. Adding to this, the formation of intermediate compounds during the AOP treatment, may have also contributed to the increased toxicity of the treated effluent. Overall, the obtained results suggested that other oxidant compounds should be considered to be used in AOPs to treat (waste)water effluents, as well the concentrations of CuO must be adjusted or the removal of these nanoparticles and metallic ions should be improved to allow obtaining a treated effluent with no to low environmental toxicity.