Electrochemical advanced oxidation combined with a biological treatment to remove the pharmaceutical hydrochlorothiazide: Influence of operating conditions in batch and continuous reactors

Improving the mineralization of concentrated pharmaceutical effluents by combining an electrochemical advanced oxidation process (EAOP) pre-treatment with a biological process is gaining interest. In this context, the objective of this study was to better understand how the conditions applied in the EAOP (anodic oxidation and electro-Fenton) pre-treatment influence the biological process in order to optimize the synergism. EAOP pretreatment was applied in batch condition at lab -scale and in continuous mode in a bench -scale prototype. The presence in the solution of the pharmaceutic hydrochlorothiazide (HCT) at 10 to 100 ppm level and aromatic intermediates formed by its oxidation inhibited the activity of microorganisms. To perform an efficient combined treatment, it was evidenced that some specific operating conditions for the EAOP pre-treatment should be applied with the aim of (i) degrading the pollutant HCT while reaching a low mineralization degree, (ii) reducing the concentration of aromatic intermediates and (iii) promoting the formation of biodegradable compounds like carboxylic acids. The combined treatment was then applied using these optimal conditions. In the lab -scale batch reactor using a BDD anode, the mineralization yield reached 66 % including 38 % by the biotreatment whereas using Pt anode, the mineralization yield reached 85 % including 50 % by the biotreatment. The same strategy was then applied to the continuous prototype EAOP reactor with BDD anode and a mineralization yield of 91 % was reached including 31 % by the biotreatment.