Feasibility of an electrochemical pre-treatment prior to a biological treatment for tetracycline removal

The purpose of this work was to examine biodegradability improvement of tetracycline-containing solutions after an electrochemical pre-treatment, since about 70% of the applied drugs are not metabolized and hence can be found in wastewaters. Cyclic voltammetry with a vitreous carbon electrode revealed a significant electrochemical activity of tetracycline. Electrochemical treatment was therefore performed in a home-made flow cell. The effect of some operating conditions, tetracycline concentration, flow rate and the applied potential was investigated. Optimal conditions led to more than 99% conversion yield of tetracycline in oxidation and reduction, using a neutral salt as supporting electrolyte.TOC analyses of the electrolyzed solution revealed that the level of mineralization remained low, underlying the interest of a combined electrochemical and biological treatment. The biodegradability, based on the BOD5 on COD ratio, increased with the oxidation potential from 0.13 to 0.39, namely a biodegradable solution, for 1.0 and 1.6 V/SCE, respectively. None of the electrolyzed solutions in reduction was biodegradable even if it was not toxic for the activated sludge. If the reduction is combined with a subsequent oxidation, BOD5/COD ratio reached a value of 0.39 when the oxidation at 1.0 V/SCE was preceded by a reduction at −1.3 V/SCE.

► Relevance of an electrochemical pre-treatment to improve biodegradability of tetracycline containing solutions.
► Cyclic voltammetry revealed a significant electrochemical activity of tetracycline.
► Optimal conditions led to more than 99% conversion yield of tetracycline, while the mineralization remained low.
► The biodegradability, based on the BOD5 on COD ratio, increased to 0.39 for 1.6 V/SCE.