Single and combined electrochemical oxidation driven processes for the treatment of slaughterhouse wastewater

Abstract

Electrochemical oxidation (EO) and EO related processes, either alone or in combination with pre-ozonation, were investigated as a polishing step for slaughterhouse wastewater treatment. The wastewater had previously been subjected to grit removal, degreasing, biological treatment and settling, but failed to comply with European emission limits for treated urban wastewaters in regards to organic compounds, suspended solids and colour. Besides EO alone, the following processes were applied: EO with hydrogen peroxide (EO/H2O2), EO with ultraviolet C light (EO/UVC) and EO with ultraviolet C light and hydrogen peroxide (EO/UVC/H2O2). Without pre-ozonation, electrochemical processes could be arranged in the following order according to their ability to mineralisation and colour removal: EO < EO/H2O2 < EO/UVC < EO/UVC/H2O2. To reach a colour of 25 mg Pt-Co/L, it took more than 480 min for EO, ῀400 min for EO/H2O2, ῀260 min for EO/UVC and ῀120 min for EO/UVC/H2O2. At this treatment time, chemical oxygen demand and suspended solids were below the European emission limit values. The pre-ozonation step improved organics removal by EO and all related processes by converting the original organic compounds into easily oxidisable compounds. Beyond that, ozonation itself led to suspended solids and colour abatement to values in agreement with the legislated/permissible discharge limits.