Study On Treatment Of Refractory Organic Compounds In Electroplating By Fenton-like A/O Combined Process

With the development of modern industrialization,electroplating technology has also been widely used in various fields,but it resulted wastewater discharge has also increased sharply.Electroplating wastewater is also listed as one of the three major industrial pollutants due to its complex composition,strong toxicity,poor biodegradability,large quantities of emission and other characteristics.At present,the monitoring of wastewater discharge in electroplating enterprises only focuses on heavy metals in wastewater,while ignoring the damage caused by organic pollution in electroplating wastewater.Therefore,with the aggravation of environmental pollution and the implementation of new standards for discharge of electroplating wastewater,the upgrading of treatment technology for electroplating organic wastewater has become an urgent environmental problem to be solved.Due to the poor biodegradability of electroplating organic wastewater,single treatment method can not reach the discharge standard.This paper takes the actual degreasing wastewater of an electroplating plant in Shenzhen as the experimental target,and explores the removal effect of organic matter in wastewater by the combined process of persulfate pre-oxidation and biological treatment.The main water quality indicators of the test wastewater are as follows:pH value is 13.2¹3.6,the concentration of suspended solids is about 12 mg/L,COD concentration is between 950¹150 mg/L,and B/C is 0.20⁰.22.In this paper,we first studied the activation of persulfate by ferrous sulfate to produce SO₄^-·with strong oxidizing property and used to pretreat wastewater.The experimental results show that the treatment of wastewater by adding ferrous iron alone and persulfate alone is general.When the pH value of Fe²⁺-S₂O₈^2-system was7.0,and the dosage of sodium persulfate is 4 g/L,n(Fe²⁺):n(S₂O₈^2-)is equal to 1.0,the reaction time was 20 min,the COD concentration of wastewater is reduced to 310mg/L,biodegradability also increased from raw water of 0.21 to 0.40.In order to improve the utilization efficiency of activator and oxidant and solve the anion problem caused by ferrous iron,this paper continues to use zero-valent iron as an indirect source of iron to provide activated molecule ferrous iron,and investigated the influence of persulfate dosage,zero-valent iron dosage,initial pH value,time and other factors on the wastewater treatment effect at room temperature.The experimental results show that the pretreatment effect increases first and then decreases with the increase of the amount of zero-valent iron,when the dosage of zero-valent iron was 0.8 g/L in Fe⁰-Na₂S₂O₈ system,the COD removal rate of waste water after 60 minutes of reaction reached 65%,and the biodegradability also increased to 0.37,meeting the basic requirements of subsequent biological treatment.Comprehensive consideration of the treatment effect?economy and utilization of the two activation modes,zero-valent iron activated persulfate was selected as the pretreatment method for subsequent biological treatment.The optimum operating conditions for the treatment of pre-treated wastewater by A/O bioreactor are as follows:the HRT is 9 h,nitrification liquid reflux ratio is 200%,and dissolved oxygen is controlled at 2⁴ mg/L.Under this operating condition,The final effluent COD concentration and total nitrogen concentration of the A/O bioreactor were 43.8 mg/L and 13.2 mg/L,respectively,which meet the requirements for electroplating wastewater discharge in table 2 of the?Electroplating Pollutant Emission Standard?.