Activation of persulfate using copper oxide nanoparticles for the degradation of Rhodamine B containing effluents: Degradation efficiency and ecotoxicological studies

The development and implementation of advanced oxidation processes (AOP) are intended to assist in the treatment of effluents produced during anthropogenic activities, reducing the release of chemicals to the environment and consequently their potential toxicity to the environment. The present work is intended to assess the chemical and ecotoxicological efficiency of an AOP that uses copper oxide nanoparticles (CuO-NP) and persulfate (PS, as an oxidation agent) for the removal of Rhodamine B (RhB) from an aqueous solution. For this, CuO-NPs were prepared and used as a sole catalyst or combined with thermal treatment to activate PS for the degradation of RhB (in distilled water, DI, and in ASTM medium). Kinetic and mechanistic studies were employed to understand the performance of the system. The lethal ecotoxicity of the untreated and treated RhB solution was characterized using rotifer species Brachionus calyciflorus. Complete removal of RhB was achieved at [RhB]0 = 50 mg/L, [PS]0 = 1 mM, CuO = 0.5 g/L under pH = 7.5 at 45 degrees C for DI and ASTM. Brachionus calyciflorus mortality pointed to a very high ecotoxicity of the effluent before and after the AOP treatment; the former was less toxic than the latter: LC50,24h = 44.3% and 8.24%, respectively. Mortality observed in the treated effluent was most probably due to the presence of reaction products (e.g., activated PS) rather than RhB, since CuO/PS system was able to remove >90% of RhB. The obtained results demonstrated that although the proposed method is applicable to deal with high concentrations of recalcitrant organic compounds, the treated effluents can cause high ecotoxicity when released into the environment.