Photochemical degradation of an actual slaughterhouse wastewater by continuous UV/H2O2 photoreactor with recycle

•A novel slaughterhouse wastewater post-treatment by UV/H2O2 with recycle was evaluated.•Statistical models were developed to predict percent TOC removal and H2O2 residual.•Recycle ratio was significant in minimizing H2O2 residual and maximizing TOC removal.•Maximum TOC removal of 81% and minimum H2O2 residual of 1.4% were obtained.•Optimum conditions were 24 and 860 mg/L for TOCin and H2O2in, and 0.18 for recycle ratio.

ABSTRACTSlaughterhouse wastewater is treated using the UV/H2O2 process in a continuous photoreactor with recycle, in which the effect of the recycle ratio (the ratio of recycle flow rate to the main feed flow rate) on the photoreactor efficiency is investigated. A four-factor, five-level central composite design along with response surface methodology is used to maximize the total organic carbon removal from an actual slaughterhouse wastewater and minimize the H2O2 residual in the effluent. The effects of the flow rate and the influent concentrations of total organic carbon and H2O2 on the photodegradation of the actual slaughterhouse wastewater are also investigated. Statistical models are developed to predict both the total organic carbon removal and the H2O2 residual as response variables. The recycle ratio is found to be significant in minimizing the H2O2 residual and the cross-factor interactions of recycle ratio with other variables demonstrate a significant effect on both total organic carbon removal and H2O2 residual. A maximum total organic carbon removal of 81% and a minimum H2O2 residual of less than 2% are found at optimum operating conditions of 24 mg/L influent total organic carbon, 860 mg/L influent H2O2 concentration, 15 mL/min flow rate, and 0.18 recycle ratio. The model is validated under optimal operating conditions based on the experimental design results. The good agreement between model predictions and experimental values indicates that the proposed model could successfully describe the photochemical treatment of actual slaughterhouse wastewater by the continuous UV/H2O2 process with recycle and its applicability as a post-treatment method.