Combined anaerobic baffled reactor and UV/H2O2 process for the treatment of synthetic slaughterhouse wastewater

Abstract

A laboratory scale for the combined processes of a biological anaerobic baffled reactor (ABR) and a UV/hydrogen peroxide (H2O2) was used to investigate the treatment of a synthetic slaughterhouse wastewater with various influent concentrations and various hydraulic retention times (HRT) at room temperature in this study. The results showed that the removal efficiencies of total organic carbon (TOC), chemical oxygen demand (COD), and 5-day carbonaceous biochemical oxygen demand (CBOD5) of the wastewater with an influent concentration of 973 mgTOC/L and a HRT of 3.8 days reached 89.9, 97.7, and 96.6%, respectively, in the ABR process, whilst the removal efficiency of TOC in the UV/H₂O₂ process reached 50.8% at a HRT of 3.6 h and H2O2 dosage of 1371 mgH2O2/L, leading to 95.0% of overall TOC removal of the combined processes. For comparison, the removal efficiencies of TOC, COD, and CBOD5 of the synthetic wastewater with an influent concentration of 158 mgTOC/L reached 64.9, 81.9, and 84.3% respectively, at an HRT of 2.5 h and a H2O2 dosage of 1371 mgH2O2/L in UV/H2O2 process alone. An optimum value of hydrogen peroxide was found to be 3.5 (mgH2O2/L)/(mgTOCin/L.h). After the ABR treatment, the ration of CBOD5/COD of the untreated wastewater changed from 0.4 to 0.6 and 0.5 to 0.2, and the ratio of COD/TOC of the wastewater decreased from 2.4 to 0.5 and 2.2 to 2.0, at the HRT of 3.8 and 0.9 days, respectively, indicating that the biodegradability of the wastewater was enhanced at a longer HRT in the ABR process. Afer the UV/H2O2 process treatment, the ratios of CBOC5/COD of the untreated and the ABR treated wastewater increased from 0.4 to 0.6 and 0.3 to 0.5, and the ratios of COD/TOC of the wastewaters decreased from 2.3 to 0.6 and 1.8 to 0.9, respectively, at the HRT of 2.5 h, indicating that the UV/H2O2 process had the ability to enhance the biodegradability of the wastewater. A kinetic model for the ABR process was obtained and used to evaluate the experimental findings. The parameters of the kinetic model for the ABR process were determined to be 3.1X10⁻2 for refractory coefficient, 0.4 for kinetic coefficient, 2.0 mg/L for half-saturation constant for hydrolyzed substrate, and 1.9 day⁻1 for the maximum specific growth rate of organism, respectively. The optimum HRT and the minimum total electricity cost were determined to be 78.9 h and $11.45 /kg of TOC removed for the ABR process, with 1000 mgTOC/L of the wastewater influent concentration, leading to 100.0 mgTOC/L of the effluent concentration which met the disposal level in Canada.