Iron-carbon Coupled Fenton-Denitrification Filter Process For The Advanced Treatment Of Coking Wastewater

The discharge standards of coking wastewater have become increasingly strict and traditional treatment processes can't make it achieve the standards, therefore, the research of advanced treatment technology is of great significance. Treatment of the bio-treated coking wastewater by iron-carbon and Fenton assisted denitrification filter process was studied in this paper. A comparative study was made between iron-carbon seriesed Fenton and iron-carbon coupled Fenton through pilot test with COD and chroma as the monitoring indicators, the main influencing factors and treatment efficiency was investigated and analyzed, and the optimal combined technique was decided. With NO3--N and COD as the monitoring indicators, the influencing factors and treatment efficiency of glucose, sodium acetate and methanol as external carbon source of denitrification was investigated and compared, and decided the optimal external carbon source. The treatment effect and cost of the optimal combined process was investigated. The main conclusions are as follows:1. For the iron-carbon seriesed Fenton process:(1) The optimum condition of iron-carbon is that the inlet p H is 3, mass ratio of iron versus carbon is 2, flux ratio of gas versus water is 3, HRT(Hydraulic Retention Time) is 1.5h. At the optimal operating conditions, the average removal rate of COD and chroma is 46% and 53%.(2)The optimum condition of Fenton oxidation is that the inlet p H is 5, amount of substance ratio of H2O2 versus Fe2+ is 2, dosage of H2O2 is 1.0 ml/L, dosage of Fe SO4?7H2O is 1.36g/L, reaction time is 1h. At the optimal operating conditions, the average removal rate of COD and chroma is 39% and 70%.(3)With the adding of Fe SO4?7H2O is 1.36g/L, the treatment effect of Fenton oxidation can be effectly promoted, the removal rate of COD is 16%higher than no adding of Fe SO4?7H2O and can reach 39%.(4)The effluent p H of iron-carbon micro-electrolysis is between 4.85~5.20, and the optimal inlet p H of Fenton oxidation is 5, thus it can be directly Fenton oxidated without regulating p H.(5) At the optimal operating conditions of the iron-carbon seriesed Fenton oxidation process, the everage removal rate of COD and chroma is 66% and 86% respectively, the effluent p H is4.60~4.80 and the dosage of sodium hydroxide in neutralization sedimentation tank is0.15g/L.2. For the iron-carbon coupled Fenton process: The optimum condition of iron-carbon coupled Fenton oxidation is that the p H is 3, dosage of H2O2 is 1.2 ml/L, mass ratio of ironIV versus carbon is 3 and HRT is 1.5h. At the optimal operating conditions, the average removal rate of COD and chroma is 70% and 91%, the effluent p H is between 4.60~4.80 and the dosage of sodium hydroxide in neutralization sedimentation tank is 0.155g/L.3. At the optimal operating conditions:(1)The cost of iron-carbon seriesed Fenton oxidation process is 2.62 yuan per ton of water and B/C is 0.21, while the cost of iron-carbon coupled Fenton oxidation process is 1.85 yuan per ton of water and B/C is 0.30,and the treatment efficiency is better, HRT is shorter, the operation is easier, also the organic carbon source it can provide for denitrification is more.(2) The optimized advanced oxidation technology is iron-carbon coupled Fenton oxidation, and its effluent is more suitable to be used as the influent of denitrification filter.4. For the denitrification filter process:(1)The optimum denitrification condition of glucose as external carbon source is that dosage of glucose is 0.262g/L, and HRT is 1.71 h.At the optimal operating conditions, the average removal rate of NO3--N and COD is92.2% and 74%.(2)The optimum denitrification condition of sodium acetate as external carbon source is that dosage of sodium acetate is 0.43g/L, and HRT is 1.29 h. At the optimal operating conditions, the average removal rate of NO3--N and COD is 91.9% and69%.(3)The optimum denitrification condition of methanol as external carbon source is that dosage of methanol is 0.168 m L/L, and HRT is 1.29 h. At the optimal operating conditions, the average removal rate of NO3--N and COD is 89.5% and 68%.(4)The cost of glucose, sodium acetate and methanol as external carbon source is 1.05 yuan per ton of water, 0.99 yuan per ton of water and 0.42 yuan per ton of water respectively, the HRT is1.71 h, 1.29 h and 1.29 h respectively, and the concentration of NO3--N in the effluent is4.5mg/L, 4.4mg/L, 5.6mg/L. Take treatment efficiency, cost of per ton of water and HRT into consideration, the optimal external carbon source is methanol.5. With methanol as external carbon source, at the optimal operating conditions of iron-carbon coupled Fenton oxidation- denitrification filter process, the average removal rate of COD, NO3--N and chroma is 70%, 89.5% and 92%. The concentration of COD, TN,NH4 +- N in the effluent is 96mg/L?14 mg/L and 5.6 mg/L, p H of the effluent is between7.5~8.5, COD in the effluent can meet the direct discharge limits of Emission Standard of Pollutants for Coking Chemical Industry(GB16171-2012)setted for existing enterprises,TN, NH4 +- N and p H in the effluent can meet the direct discharge limits of Emission Standard of Pollutants for Coking Chemical Industry(GB16171-2012) setted for newly-built enterprises. The cost of the optimum combined process is 2.27 yuan per ton of water.