Treatment of Pharmaceutical Wastewater by Electrochemical Method: Optimization of Operating Parameters by Response Surface Methodology

Abstract

The treatment of a high-strength pharmaceutical wastewater (PW) has been carried out using two different electrochemical processes [i.e., electrocoagulation (EC) using aluminium and electrooxidation (EO) using carbon electrodes]. For EC, the main object was to study the adsorption capacity of electroflocs using the Freundlich isotherm (R2=0.8) and the kinetics of adsorption by (Lagergren model) first-order (R2=0.88) and second-order (R2=0.83) kinetic models. For the EO process, the effect of current density (CD) in a range from 40 to 120 A/m2 and initial pH from 3 to 11 on the treatment efficiency was studied. Under identical operating conditions (CD 80 A/m2; pH 7.2), EC resulted in 24% after 25 min, whereas the EO yielded 35.6% chemical oxygen demand (COD) removal after 90 min of treatment. The kinetics of COD removal for EO was described by a two-stage, first-order kinetic model. Based on the cyclic voltammetric studies, the presence of chlorides was found to have an influence, resulting in indirect oxidation by the generation of chloride/hypochlorite oxidants. Response surface methodology (RSM) was found to be an effective optimization tool, which shows the optimum pH/CD/electrolysis time to be 6.56/76.06 A/m−2/86.89 min for achieving 30.89% COD removal by the EO process. The study has shown that electrooxidation treatment can be more effectively used as pre treatment to improve the biocompatibility of PW than as a direct biological treatment of PW.