Investigation Of Applying Pre-oxidation And Biological Process For Typical Refractory Organic Pollutants Treatment In Wastewater From A Chemical Industry Park

The wastewater generated from chemical industry parks is usually complex in composition with high toxicity and fluctuated quality and quantity,which has been a key issue for wastewater treatment in China.The objective of this research is to investigate the performance of different pre-oxidation-biological treatments of wastewater from a chemical industry park in Hubei,and two typical refractory organic pollutants in wastewater,namely sulfamethoxazole（SMX）and glyphosate（Gly）were selected as the characteristic pollutants.Firstly,Fenton and sodium hypochlorite oxidations are conducted to evaluate their degradation effects and the biological toxicity of organic pollutants after pre-oxidation treatment.Secondly,a pre-oxidation-sequence batch bioreactor（SBR）system was established to examine the treatment mechanism of simulated SMX and Gly wastewaters and the impacts of the pre-oxidation process on the microbial community in the SBR.Finally,the pre-oxidation-SBR system was used for treating real wastewater collected from the chemical park to reveal the synergistic effects of the pre-oxidation unit on the biological treatment unit,and the evolution of key microorganisms in the SBR was analyzed.The main results are summarized as follows:（1）For SMX and Gly,the degradation rates of Fenton and Na Cl O oxidation can reach 99%and 50%,80%and 70%,respectively.The corresponding mineralization rate（TOC removal rate）is only 22%and 37%,5.6%and 23%,respectively,indicating that pre-oxidation can effectively degrade the two pollutants,but complete mineralization is neither economical nor necessary.Combining the calculation results of the ECOSAR software and the toxicity test results of cabbage seeds suggests that the pre-oxidation treatment can significantly reduce the biological toxicity,and Fenton can significantly reduce the toxicity by comparison.（2）SMX and Gly have limited effects on the COD removal rate of SBR,but obviously inhibit the removal of NH₄⁺-N and TN,while the pre-oxidation can significantly improve the nitrification and denitrification processes in the SBR.High-Throughput Sequencing showed that SMX and Gly inhibited the growth of denitrifying bacteria,such as Firmicutes,Chloroflexi,Proteobacteria,and Chloroflexi,thereby inhibiting denitrification.The Fenton pre-oxidation process increased the abundance of Anaerolineae,Actinobacteria,Acidimicrobiia,and Chloroflexia in the sludge,while the Na Cl O pre-oxidation increases the abundance of KD4-96 and Saccharimonadia,thereby improving denitrification in the two SBR.（3）The combined process of the Fenton-SBR system for treating real wastewater in the chemical park can effectively degrade refractory organic pollutants,thereby improving the removal efficiency of COD,NH₄⁺-N and TN.The Na Cl O pre-oxidation of real wastewater could produce organic intermediates that inhibit the microbial activity,interfering with the SBR operation,resulting in the sludge decomposition and the deteriorated effluent quality.High-Throughput Sequencing showed that the abundance of EPS-producing bacteria in the Fenton-SBR combined process increased from 16.58%to 28.23%at genus level,and the microbial community structure was effectively improved.The contents of nitrifying bacteria and denitrifying bacteria increased from 5.49%and 2.08%to 7.11%and 8.31%,respectively,which was beneficial for nitrogen removal.The contents of aromatic organic matter decomposition bacteria,glycogen bacteria,and phosphorus accumulating bacteria increased from 6.04%and 8.08%to 16.40%and 16.49%,respectively,which effectively improved the removal of refractory COD.The contents of EPS-producing bacteria and denitrifying bacteria structure in Na Cl O-SBR were significantly reduced,weakening the microbial community activity.The results show that the combined process of the Fenton-SBR system has good potential in treating wastewater with complex components and high toxicity treatment in chemical parks.