不同高级氧化工艺处理焦化废水二级生化工艺出水研究

Treatment of the secondary biochemical effluent from coking wastewater by different advanced oxidation processes

针对焦化废水二级生化处理工艺出水化学需氧量(COD)难以达标的问题,采用实际焦化废水,通过开展半连续实验室小试试验,对比研究了单独臭氧氧化、O3/H2O2氧化和UV-Fenton氧化3种工艺深度处理焦化废水的效果,并对不同工艺出水的UV254、BOD5/COD、发光细菌毒性、三维荧光光谱进行分析,研究不同高级氧化工艺对出水水质的影响规律。结果表明:增加臭氧投加量和添加H2O2能显著提高焦化废水二级生化工艺出水中有机物的去除效果。进水COD为(200±10)mg/L、O3投加量为30mg/L时,反应120min后单独臭氧氧化对COD的去除率仅为36%;而对于UV-Fenton氧化,进水COD为(200±10)mg/L、H2O2(30%)投加浓度为2g/L、Fe2+与H2O2摩尔比为1∶10时,COD的去除率为50%;单独臭氧氧化和UV-Fenton均不能满足排放标准。进水COD为(200±10)mg/L、O3投加量为30mg/L、H2O2(30%)投加浓度为2g/L,反应120min后COD去除率达到63%,O3/H2O2氧化工艺出水COD达到74mg/L,满足GB16171—2012《炼焦化学工业污染物排放标准》的要求。3种工艺中,O3/H2O2氧化的COD去除效果最好,这主要归因于O3和H2O2协同产生强氧化性自由基,但当H2O2浓度过高时,体系中产生的·OH反而与H2O2反应,从而导致O3/H2O2体系的氧化能力下降。3种工艺都能有效降低出水毒性,出水发光细菌急性毒性试验显示,单独O3氧化、O3/H2O2氧化处理15min后,相对发光度分别上升到90%和87%,UV-Fenton氧化处理30min后,出水的相对发光度上升到71.57%。与单独臭氧氧化和O3/H2O2氧化工艺相比,UV-Fenton工艺处理出水急性毒性相对较高,可能与臭氧的消毒作用有关。3种工艺对废水可生化性的提高程度不明显,BOD5/COD从0.02最大提升到0.1左右。UV254和三维荧光光谱的对比分析表明,3种工艺对出水中芳香族化合物和荧光物质具有明显的分解作用。单独O3氧化可优先降解废水中腐植酸类物质中的共轭双键结构,而O3/H2O2氧化工艺对环状共轭污染物的氧化效果更显著。随着UV-Fenton氧化处理,焦化废水中大分子的类腐植酸以及紫外区类富里酸优先被氧化降解,最终转化为可见区类富里酸和类蛋白质,而类蛋白质和可见区类富里酸物质在出水中仍存在较高浓度,UV-Fenton氧化工艺对荧光物质去除能力最差。

The COD of the effluent from the secondary biological treatment process of coking wastewater couldn't meet the standard.In order to resolve the problem,the effects of advanced treatment of coking wastewater by single ozonation,O3/H2O2 oxidation and UV-Fenton processes respectively,were investigated through laboratory test,which were carried out in semi-continuous mode.The quality of effluent from the different processes were analyzed,where UV254,BOD5/COD,the luminescent bacteria toxicity,three-dimensional fluorescence spectrum were evaluated.The influence of different advanced oxidation processes on effluent quality was explored.The results show that the increase of ozone dosage and addition of H2O2 can significantly enhance the removal of organic compounds in the secondary biochemical effluent from coking wastewater.When the COD of the influent is(200±10) mg/L,the average COD removal rate for 120 min reaction in single ozonation process is 36% with the ozone dosage of 30 mg/L.When the COD of the influent is(200±10) mg/L,the average COD removal rate for 120 min reaction in UV-Fenton process is 50% with the H2O2 dosage of 2 g/L and the molar ratio of Fe2+ and H2O2 of 1∶10.When the COD of the influent is (200±10) mg/L,the average COD removal rate for 120 min reaction in O3/H2O2 oxidation process is 63% with the ozone dosage of 30 mg/L and H2O2 dosage of 2 g/L,which meets the Emission Standard of Pollutants for Coking Chemical Industry,China(GB 16171-2012).Among the three processes,the O3/H2O2 oxidation process is the most effective for organic compounds removal.This is mainly attributed to the synergistic production of strong oxidizing radicals by O3 and H2O2.However,when the concentration of H2O2 is too high,·OH produced in the system reacts with H2O2 instead,resulting in the decline of oxidation capacity of O3/H2O2 system.All the three processes can reduce its toxicity.The results of acute toxicity test of with luminescent bacteria shows that the relative luminosity of effluent after single ozonation and O3/H2O2 oxidation for 15 min increaseto 90% and 87%,respectively.After UV-Fenton oxidation for 30 min,the relative luminescence of effluent increases to 71.57%.Compared with single ozonation and O3/H2O2 oxidation process,the effluent of UV-Fenton treatment has relatively higher acute toxicity,which may be related to the disinfection effect of ozone.The three processes can hardly improve its biodegradability,while BOD5/COD only increases from 0.02 to about 0.1.The comparative analysis of UV254 and EEM (Excitation-emission Matrix) show that the three processes have obvious decomposition effect on aromatic compounds and fluorescent substances in the secondary biochemical effluent.The conjugated double-bond substances of humic acid-like substances in wastewater can be preferentially degraded in single ozonation process,while O3/H2O2 oxidation process has more significant oxidation effect on cyclic conjugated pollutants.In the UV-Fenton process,humic acid-like substances and UV-fulvic acid-like in coking wastewater are oxidized preferentially,and eventually converted into visible fulvic acid-like and protein-like,which still have relatively high concentration in the effluent.Among the three oxidation processes,the removal of fluorescent substances by UV-Fenton oxidation process is the worst.