Combinative treatment of phenol-rich retting-pond wastewater by a hybrid upflow anaerobic sludge blanket reactor and solar photofenton process

Abstract

In this study, recalcitrant rich retting-pond wastewater was treated primarily by anaerobic treatment and subsequently treated with a solar photofenton process to remove phenol and organics. The anaerobic treatment was carried out in a granulated laboratory scale hybrid upflow anaerobic sludge blanket reactor (HUASBR) with a working volume of 5.9 L. It was operated at different hydraulic retention times (HRT) from 40 to 20 h over a period of 140 days. The optimum HRT of the anaerobic reactor was found to be 30 h, with corresponding chemical oxygen demand (COD) and phenol removal of 60% and 47%, respectively. Primary anaerobically treated wastewater was subjected to secondary solar photofenton treatment which was carried out at pH 3.5. Response surface methodology (RSM) was used to design and optimize the performance of the solar photofenton process. Regression quadratic model describing COD removal efficiency of the solar photofenton process was developed and confirmed by analysis of variance (ANOVA). Optimum parameters of the solar photofenton process were found to be: 4 g/L of fenton as catalysts, 25 mL of hydrogen peroxide, and 30 min of reaction time. After the primary anaerobic treatment, solar photofenton oxidation process removed 94% and 96.58% of COD and phenol, respectively. Integration of anaerobic and solar photofenton treatment resulted in 97.5% and 98.4% removal of COD and phenol, respectively, from retting-pond wastewater.