Mineralization of synthetic and industrial pharmaceutical effluent containing trimethoprim by combining electro-Fenton and activated sludge treatment

Abstract

A combined process coupling of an electro-Fenton and a biological degradation was investigated in order to mineralize synthetic and industrial pharmaceutical effluent containing trimethoprim, a bacteriostatic antibiotic. Electro-Fenton degradation of trimethoprim was optimized by means of a Doehlert experimental design, showing that 0.69 mM Fe2+, 466 mA and 30 min electrolysis time were optimal, leading to total trimethoprim removal, while mineralization remained limited, 12% for 30 min electrolysis times. The aromatic and aliphatic by-products were identified and a plausible degradation pathway was proposed. Biodegradability was improved, since the BOD5/COD ratio increased from 0.11 initially to 0.32 and 0.52 after 30 and 60 min electrolysis times respectively, confirmed by activated sludge culture, 47 and 59% mineralization of the byproducts from electrolysis.The relevance of the proposed combined process was then confirmed on an industrial pharmaceutical effluent. Its electrolysis under the above conditions showed an almost total removal of trimethoprim after 180 min of electrolysis, while TOC removal remained low, 14 and 16% for 180 and 300 min reaction times, respectively. Overall removal yields of the industrial effluent during the combined process were therefore 80 and 89% for 180 and 300 min of effluent pretreatment followed by 15 days activated sludge culture, respectively.