Novel Fenton-biological combined process at neutral pH by virtue of endogenous acidification and fungal degradation: Performance and cost analysis in the lab-scale study

•A novel cost-effective Fenton-biological combined process was proposed and its treatment cost was evaluated.•By virtue of acidic intermediates, Fenton was performed at initial neutral pH without acidification by adding acid.•Acidic Fenton effluent was treated by a specially screened fungi consortium without pre-neutralization.•The novel combined process could reduce the operational cost by at least 20% compared to classical operation. In this study, a novel cost-effective Fenton-biological combined process performing at initial neutral pH was proposed to avoid or reduce the chemicals for acidification and neutralization, its performance and preliminary operational cost were evaluated in the lab-scale. By virtue of acidic intermediates, Fenton oxidation was performed at initial neutral pH without acidification by adding acid. After removing the dissolved Fe by ion exchange resins, acidic Fenton effluent was treated by a fungal consortium without pre-neutralization. Our results demonstrate that several phenolic compounds, representing target pollutants, could be effectively oxidized by Fenton at initial neutral pH through endogenous acidification by formed carboxylic acids; in some cases, phenolic complexation with Fe3+ also played an important role. When Fenton treatment was conducted in a continuous-flow reactor similar to anaerobic baffled reactor (ABR), the effect of H2O2 dosage in terms of COD removal efficiency, H2O2 utilization efficiency, acidity and BOD5/COD was assessed. From an economic perspective, the optimal H2O2 dosage was in the range of 0.6 to 0.7 times the theoretical H2O2 dosage. Additionally, the acidic Fenton effluent was further purified in a biofilm reactor inoculated with a specially screened fungal consortium, and effective COD removal and pH increase to near neutral were achieved. This novel Fenton-biological combined process was further validated by treatment of real tannery wastewater. By comparison with classical Fenton-biological combined process, this novel technology could reduce the operational cost by at least 20%, showing a significant economic advantage.