Effect of the anode material, applied current and reactor configuration on the atenolol toxicity during an electrooxidation process

Abstract

Atenolol (ATL) is a beta-blocker pharmaceutical product which is excreted mainly unchanged and may represent a long-term risk for organisms present in the sea and in fresh water. Due to its low biodegradation rate, electrochemical advanced oxidation processes (EAOPs) can be used to remove this compound. In this work, ATL ecotoxicity was analyzed in the presence of sodium sulfate (Na2SO4), which is widely used as supporting electrolyte in EAOPs. Ecotoxicity values were expressed as the pollutant concentration that leads to a 50% inhibition of the root elongation of Lactuca sativa seeds in relation to the control (EC50(5 days)). The obtained values for ATL showed an EC50(5 days) of 1377 mg L−1 towards Lactuca sativa. When Na2SO4 was added, the toxicity of the sample increased but no synergy was detected between both compounds. With 2 g L−1 Na2SO4, ATL showed an EC50(5 days) of 972 mg L−1; and with 4 g L−1 Na2SO4 and higher concentrations, EC50 value for ATL was 0 mg L−1. Statistical tools were used to obtain the zones of the [ATL]-[Na2SO4] plane which are toxic towards Lactuca sativa.Solutions containing ATL and Na2SO4 were treated by electrooxidation. Two anode materials (a boron-doped diamond electrode and a microporous Sb-doped SnO2 ceramic one); three operation currents (0.4, 0.6 and 1 A); and two reactor configurations (one-compartment reactor and two-compartment reactor separated by a cation exchange membrane) were used. Lactuca sativa seeds and Vibrio fischeri bacterium tests were employed to evaluate the toxicity of the solutions before and after applying the electrooxidation process. In all the tests, the ecotoxicity of the treated sample increased. This fact is owing to the persulfate presence in the solution due to the sulfate electrochemical oxidation. Nevertheless, none of the final samples were toxic towards Vibrio fischeri because ecotoxicity values were lower than 10 TU; and, in the case of the one-compartment reactor, practically all of them were also non-toxic towards Lactuca sativa. The toxicity of the treated samples increased when using the two-compartment reactor in the presence of the BDD anode, and when the operation current was increased. This is attributed to the highest formation of persulfates. Amongst all the tests performed in this work, the lowest toxicity value (i.e., 3 TU) together with the complete mineralization and degradation degrees was achieved with the two-compartment reactor using the BDD anode and operating at 0.6 A.