Treatment of cattle slaughterhouse wastewater by sequential coagulation-flocculation/electrooxidation process

Abstract

This study aimed to investigate the applicability and efficiency of sequential coagulation-flocculation (CF) and electrooxidation (EO) processes for cattle slaughterhouse wastewater by evaluating treatment efficiency and total operating cost values together. The effect of two different coagulant dosages (FeCl3 and alum) in the CF process and operating parameters such as current density (5 to 30 mA/cm2), wastewater flow rate (0.9 to 3.6 L/h), and supporting electrolyte concentration (1 to 3 g NaCl/L) in the EO process on chemical oxygen demand (COD) and turbidity removal were investigated. During the first part of the study, the FeCl3 coagulant dosage worked better than other coagulants, eliminating 50% of the COD and 68% of the turbidity. Due to the insufficient removal efficiencies of COD and turbidity, a secondary treatment was required. In the second part of the study, a boron-doped diamond (BDD) electrode was used to treat the coagulated effluent in a continuous EO reactor. The COD and turbidity removal efficiency under optimum treatment conditions (j = 30 mA/cm2, Q = 0.9 L/h, pH = 8.5, SE = 3.0 g NaCl/L, and hydraulic retention time = 1 hour) were calculated as 97.2% and 99.9%, respectively. At these optimum conditions, the energy consumption and total operating cost were calculated as 91.1 kWh/m3 (73.5 kWh/kg COD) and 3.50 US $/m3 (1.5 US $/kg COD), respectively. As a result, combined coagulation-flocculation and electrooxidation processes have proven to be very successful and cost-efficient for treating cattle slaughterhouse wastewater.