Treatment of 3,4,5-trimethoxybenzaldehyde and Di-bromo-aldehyde manufacturing wastewater by the coupled Fenton pretreatment and UASB reactor with emphasis on optimization and chemicals analysis

•Fenton optimization was studied by combined RSM and Convex optimization.•Convex optimization method can ensure global optimization.•Fenton effectively enhanced the biodegradability of wastewater treated.•Decomposition of organics was analyzed by GS-MS and FTIR.•The coupled Fenton-UASB can achieve significant COD removal efficiency.

An integrated Fenton-UASB was investigated for the treatment of 3,4,5-trimethoxybenzaldehyde (TMBA) and Di-bromo-aldehyde manufacturing wastewater. A quadratic model for describing the individual and interactive effects of three variables independent variables (pH, concentration of H2O2 and H2O2/Fe2+) affecting COD abatement in Fenton pretreatment was successfully developed by the response surface methodology. The model proposed was further interfaced with the convex optimization method to optimize the variables in that convex optimization method can guarantee global optimization. A substantial increase in the BOD5/COD ratio of the Fenton treated wastewater was observed, allowing sequent biological treatment feasible. The UASB reactor receiving treated effluent was operated continuously with an organic loading rate (OLR) from initial 3.0 g to 24.0 g COD/L/d with a stepwise reduction in hydraulic retention time (HRT) for 160 days. The degradation of organics in Fenton pretreatment and the anaerobic process was further revealed through GC–MS and FT-IR, respectively. The experimental results highlighted that the potential of integrated Fenton-UASB, providing 80.4% COD removal efficiency accompanied with 96.8% and 100% of TMBA and Di-bromo-aldehyde removal efficiency, respectively even when the applied OLR was up to 16.0 g COD/L/d.