Using sequentially coupled UV/H2O2-biologic systems to treat industrial wastewater with high carbon and nitrogen contents

[Display omitted] •The design and operation parameters of a UV/H2O2-biological system were established.•Nitrogen transformations were investigated throughout the UV/H2O2-biological process.•Hybrid process removed over than 60 % of persistent dissolved organic matter.•Biological denitrification stage has achieved more than 80 % of efficiency. This study evaluated the performance of a sequentially coupled UV/H2O2-anoxic system to treat industrial wastewater (IWW). Initial IWW characterization showed a high chemical oxygen demand (COD) load (13,261 mg L−1, 6,880 mg L−1 of total organic carbon (TOC), 569 mg L−1 of total nitrogen (TN), and an alkaline pH (9.1 ± 1.51). Using advanced oxidation processes (AOPs), removal efficiencies of 49.4 % of COD and 85 % of total organic carbon (TOC) were achieved after 60 min of UV-C irradiation (82 W m−2) using a H2O2/COD ratio of 0.78:1. Under these conditions, a 50 % transformation of TN into nitrites and nitrates (NO2+NO3)-N was also observed. After the AOP, the partially treated IWW was mixed with municipal wastewater (MWW) at ratio of 1:10, based on toxicity test results, and then used as the influent of the biological process. The biological process consisted of anoxic suspended and attached biomass coupled sequentially after the UV/H2O2 system. Both biological systems (attached and suspended biomass reactors) efficiently removed (NO2+NO3)-N, achieving 85 % removal of TN, 41.8 % removal of TOC, and 49.2 % removal of COD and denitrification process was found to occur after the AOP through the biological systems. In addition, pH values ranging from 6 to 7.6 were observed after the biological treatment, which suggests that the resulting effluent could be treated using conventional water treatment.