| At present,the production of polyvinylchloride?PVC?is based on calcium carbide method.Acetylene purification wastewater?APW?is one of the main sources of wastewater generated during the production of acetylene in PVC plant.The APW contains complicated compounds and has large quantity,especially,the high concentration of ammonia nitrogen?NH4-N?in the APW can make adverse effects on the treatment efficiency of the bio-treatment subsequently.However,there are few researches on the treatment of APW.Therefore,proper methods should be used to remove the NH4-N in the APW.To study the removal of NH4-N from the APW has great effects on the pollution control and emission reduction.In this study,source of the NH4-N in the APW was investigated,and some techniques,such as struvite precipitation method,air stripping method and sodium hypochlorite?NaClO?oxidation method,were employed to remove NH4-N from the APW.Energy dispersive spectroscopy?EDS?and X-ray diffraction?XRD?were applied to analyze the calcium carbide.The EDS analysis results indicated that elements in the calcium carbide contained C,O,Al,Si,S and Ca.The XRD analysis results showed that the compositions of the calcium carbide were complex,which consisted of Ca C2,Ca?OH?2,Ca CO3,Ca3N2,Ca?CN?2 and Ca CN2.According to the results and some relative literatures,Ca3N2,Ca?CN?2 and Ca CN2 were the main sources of NH4-N from the APW.Struvite precipitation method was used to remove NH4-N from the APW,and the effects of some factors on NH4-N removal efficiency were investigated.The NH4-N could be effectively removed at an optimum initial APW p H of 10.00,Na2HPO4·12H2O and Mg SO4·7H2O were applied to NH4-N at ratios of 1.1 and 1.2,respectively,stirring rate of 150 r/min,reaction time of 10 min and wastewatertemperature of 20 °C.Under these conditions,the concentration of NH4-N could be removed from 114.4 mg/L to 23.8 mg/L,which could meet the Discharge Standard for Integrated Wastewater in China for NH4-N?second grade?.The precipitate generated under the optimal conditions was a white crystalline powder.Scanning electron microscopy?SEM?analysis of the precipitates showed a typical morphology of stick-like and prismatic crystals with coarse surface.EDS analysis showed that the precipitates contained a great deal of O,Mg and P,and trace of Ca,Al and Si.XRD,Fourier transform infrared spectroscopy?FTIR?and elemental analysis of the precipitates indicated that the precipitates were dominated by struvite.The kinetics experiment indicated that the removal of NH4-N followed first order kinetic model,and its kinetics rate constant was 0.0052 /s.Air stripping method was used to remove NH4-N from the APW,and the effects of some factors on NH4-N removal efficiency were investigated.The NH4-N could be effectively removed at an optimum initial APW p H of 12.00,air flow rate of 0.500m3/?h·L?,wastewater temperature of 60 °C,packing height of 6 cm and reaction time of 150 min.Under these conditions,the concentration of NH4-N could be removed from 126.3 mg/L to 23.8 mg/L,which could meet the Discharge Standard for Integrated Wastewater in China for NH4-N?first grade?.One volume of H2SO4solution?1 %?could absorb about 93.1 % of the NH3 stripped from 54 volume of the APW,correspond to 1 mol of H2SO4 could absorb 1.8 mol of the stripped NH3.NaClO oxidation method was used to remove NH4-N from the APW,and the effects of some factors on NH4-N removal efficiency were investigated.The NH4-N could be effectively removed at an optimum initial APW p H of 8.00,wastewater temperature of 50 °C,NaClO solution dosage of 30.0 ml/L and reaction time of 3 min.Under these conditions,the concentration of NH4-N could be removed from 120.0mg/L to 0.3 mg/L,which could meet the Discharge Standard for Integrated Wastewater in China for NH4-N?first grade?.The kinetics experiment indicated that the removal of NH4-N followed first order kinetic model,and its kinetics rate constant was 0.0317 /s.The NH4-N in the APW could be removed efficiency by struvite precipitation,airstripping and NaClO oxidation.Analyzed from the view of economy,the costs of the three methods increased in the order of struvite precipitation,air stripping and NaClO oxidation,their costs were 2.2 Yuan,6.6 Yuan and 12.4 Yuan,respectively,to treat 1ton of the APW.While the cost of NaClO oxidation could be reduced to 0.6 Yuan when used liquid chlorine as reagent.Analyzed from the view of NH4-N residual concentration,the NH4-N removal efficiencies by the three methods decreased in the order of NaClO oxidation,air stripping and struvite precipitation.After treated by the three methods,the residual concentrations of NH4-N were 0.3 mg/L,1.4 mg/L and23.8 mg/L.Analyzed from the view of operating conditions,the flexible of the three methods operation conditions were increased in the order of struvite precipitation,air stripping and NaClO oxidation. |
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