Study And Application Of Zero Valent Iron Fenton Like-Immobilized Microorganism Process In The Treatment Of Pesticide Wastewater

Pesticide wastewater is characterized by complex pollutant composition,high organic concentration,poor biochemical properties and fluctuating water quality and quantity,making it difficult to treat.The existing treatment processes are generally complex in operation and low in efficiency,and some of them cannot be applied in engineering due to high costs.In this paper,the zero valent iron Fenton like-immobilized microorganism process was used to treat the wastewater of a pesticide company in Jiangsu Province.By conducting small-scale experiments,the operating conditions were determined with the removal of COD（Chemical Oxygen Demand）as the index,and high-throughput sequencing was used to study the diversity and community composition of the immobilized microorganisms.The main conclusions include:Zero valent iron Fenton-like was used for pretreatment of the wastewater to remove the difficult organic matter and improve the biochemical properties.Using iron filings as a source of Fe⁰ for the oxidation reaction with H₂O₂,the optimum operating conditions were obtained as follows:initial pH 3.0,reaction time 1.5 h,iron filings（Fe⁰）dosing 45 g/L and H₂O₂ dosing 10 mL/L.In the continuous influent test under optimal conditions,the COD removal rate of the wastewater reached 27.11%～39.05%and the BOD₅/COD（BOD₅,five-day Biochemical Oxygen Demand）increased from 0.11 to about 0.35,creating favourable conditions for subsequent biochemical treatment.The effect of pH,HRT and DO on the removal of COD was investigated after activation of domesticated microorganisms using porous polyurethane foam as a carrier,and the pH of the anaerobic unit was determined to be 7.0～7.2 with an HRT of 72 h.The DO of the aerobic unit was 5.0 mg/L with an HRT of 63 h.Under the optimal conditions of continuous The COD removal rate of the wastewater reached 95.41%～97.13%in the continuous water inlet test.After the commissioning operation of the process,the COD of wastewater is within the range of 10120～25000 mg/L,the COD removal rate of the zero valent iron Fenton-like system reached 22.98%～53.26%and the COD removal rate of the immobilized microbial system reached 93.15%～97.30%.The process is working well and the effluent COD is 195～447 mg/L,which meets the nets standards of the park where the company is located（COD≤500 mg/L）.High-throughput sequencing was used to cluster the microbial diversity and community structure,the distribution of bacteria had great stability.The main aerobic bacteria were Proteobacteria,Firmicute,Deinococcota,Chloroflexi,and Actinobacteriota.The diversity of aerobic microbial groups was high,and the abundance accounted for a relatively high Deinococcota and the unnamed Norank＿norank＿SBR1031 genus of special function bacteria were found.The experimental analysis and engineering operation results prove that the zero valent iron Fenton like-immobilized microorganism treats high concentration pesticide wastewater with high treatment efficiency and stable operation effect,so the research of this process provides a new process idea and engineering application parameters for pesticide wastewater treatment.