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A~2/O~2生物膜法处理焦化废水中试研究 【作者】赵义 【导师】李亚新

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A~2/O~2生物膜法处理焦化废水中试研究

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"bfT{5e1??1s9{0【作者】赵义 【导师】李亚新水利论文@)l0]#CJJ } R
【作者基本信息】太原理工大学,生物化工,2007年,博士

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【中文摘要】 焦化废水成分复杂,除含高浓度NH3-N外,还含大量难降解有机物。主要为芳香族有机物、杂环及多环芳烃有机物,可生化性较差。焦化废水的污染控制一直是我国工业废水污染控制的重大难题。大多数焦化厂面临的主要问题是经生物处理后COD和NH3-N浓度仍然不能达到污水综合排放标准(GB9878-1996)一级标准(即COD≤100mg/L,NH3-N≤15mg/L),或者要对生物处理系统进水用大量清水稀释后处理出水才能达到污水综合排放标准的一级标准。活性污泥法生物处理目前仍是大多数焦化厂主要的废水处理方法。国内两种比较流行的A/O(缺氧/好氧)和A2/O(厌氧/缺氧/好氧)活性污泥法焦化废水生物处理工艺存在的主要问题是生化处理出水COD和NH3-N浓度很难同时达标。不能同时达标的主要原因是:(1)由于好氧反应器进水COD浓度较高,活性污泥中硝化菌比例太低,而且废水中含有多种生物抑制性有机物,也抑制了硝化菌的活性,好氧反应器硝化效果差,使NH3-N很难达标;(2)由于焦化废水NH3-N浓度较高,进水中可生物降解COD浓度较低,缺氧反应器水力停留时间短,不能充分发挥缺氧反应器中反硝化菌对好...更多氧和厌氧条件下生物难降解有机物的缺氧降解作用,在缺氧反应器中反硝化碳源有机物严重不足。由于未能充分利用反硝化过程对COD的去除能力,反硝化效果差,使A/O和A2/O活性污泥法不能充分发挥全流程对COD的去除能力。论文以山西省临汾市同世达实业有限公司焦化厂废水处理系统气浮设备出水为实验废水水源,在中试规模上研究了生物膜法A2/O2工艺(厌氧/缺氧/好氧/好氧)处理焦化废水的工艺特性和效果。厌氧和缺氧反应器为以陶粒为填料的上流式滤池,第一级好氧反应器为以塑料空心球为填料的生物接触氧化池,第二级好氧反应器为以陶粒为填料的上流式曝气生物滤池。实验中生物膜法A2/O2工艺系统进水COD浓度多数在1000~2200mg/L范围内,进水NH3-N浓度大部分在200~400mg/L范围内。对中试系统和各反应器的主要研究结论如下:1.水解酸化(厌氧)反应器水解酸化菌在填料表面附着能力差,很难直接在填料上形成成熟的生物膜,因而生物膜法水解酸化工艺启动时间较长。在启动期间焦化废水COD和NH3-N浓度的剧烈变化,会影响水解酸化反应器的启动运行。以陶粒为填料的水解酸化反应器从挂膜启动到生物膜成熟约需半年时间。焦化废水水解酸化处理的目的是提高其可生化性,焦化废水中的含氮有机物的比例较大,含氮有机物水解酸化过程会释放出NH3-N。因此从工程上,可以很方便的用水解酸化反应器进出水BOD/COD比值的变化和进出水NH3-N浓度的变化来判断水解酸化反应器挂膜启动成熟程度和运行效果。水解酸化反应器对焦化废水COD和BOD都有一定的去除作用。对于中试的水质条件水解酸化时间以20h为最好。当HRT为20h,进水COD容积负荷为1.61~2.65kgCOD/(m3·d)时,在进水BOD/COD比值为0.05~0.17的情况下,出水BOD/COD比值为0.16~0.48,平均提高了175%左右,出水BOD/COD比值最高可提高至0.48,提高了336.4%左右,大大改善了水解酸化反应器出水的可生化性。焦化废水水质浓度变化大,可以用水力停留时间作为水解酸化反应器的设计参数。以陶粒为填料的水解酸化反应器生物量(以SS计)高达8960mg/L,挥发性固体含量(VSS)高达7420mg/L。由于生物量高,以陶粒为填料的水解酸化反应器对进水pH值、温度和进水水质变化有很强的适应性。处理焦化废水水解酸化反应器的优势微生物主要为兼性菌,有芽孢杆菌属、气单胞菌属、黄杆菌属及副球菌属等。以陶粒为填料的水解酸化反应器泥龄长,剩余污泥产率很低,在两年的运行中水解酸化反应器未进行反冲洗,不影响水解酸化反应器的运行效果。2.缺氧反应器挂膜启动期间由于生物膜尚不完全成熟,反硝化能力差,应采用较小的回流比。缺氧反应器的回流以300%为宜。当回流比为300%时,NO3-N的平均还原率略高于90%。为使反硝化反应正常进行,缺氧反应器的水温必须保持在20℃以上。焦化废水经水解酸化处理后,进入缺氧反应器的废水pH值一般在6~8之间,可以满足缺氧反应器对于pH值的要求。缺氧反硝化对去除焦化废水中COD有重要作用。反硝化菌可以利用一些好氧微生物和厌氧微生物都难以降解的焦化废水中的有机物作碳源进行反硝化。因此,缺氧反应器中硝态氮的反硝化有促进焦化废水中难降解有机物降解的作用,从而可以提高系统的COD去除效果,反硝化反应器可以去除进水中的40%的COD。所以,在A2/O2焦化废水处理工艺中,缺氧反应器的合理设计对保证系统出水COD浓度达标至关重要。只要充分发挥反硝化菌对焦化废水中难降解有机物的缺氧降解作用,对焦化废水缺氧反硝化而言,碳源还是相对充足的,不需要补充外加碳源。缺氧反硝化进水C/N比在5以上就可以基本上满足反硝化对于碳源的需求。由于生物膜法A2/O2焦化废水处理工艺中,反硝化菌可利用的碳源除水解酸化反应器出水中容易生物降解的有机物外,还需要利用厌氧和好氧作用难于生物降解的有机物和内源碳作碳源。因此,反硝化速率相对于城市污水反硝化要低得多。反硝化反应器的NO3-N容积负荷也相对较低。中试中稳定运行状况下的NO3-N容积负荷不大于0.24kgNO3-N/(m3·d)。缺氧反应器的水力停留时间不小于24h。以陶粒为填料上向流生物膜缺氧反应器中生物量(以SS计)从下到上逐渐减小,平均生物量(以SS计)为4.16g/L,挥发性固体含量(VSS)为3.24g/L。当填料粒径为3~6mm时,生物膜反硝化反应器由于回流比较大,填料中的上向流速也较大,可以使反硝化产生的氮气自然逸出,不需要考虑释氮循环,也不需要对填料进行定期反冲洗。处理焦化废水缺氧反应器的优势微生物主要为产碱杆菌属、施氏假单胞菌属、黄杆菌属等。尽管二级好氧生物反应器中的溶解氧浓度较高(4~5mg/L),由于缺氧反应器中水流推流式上升,反应器底部的微生物可以尽快的消耗回流硝化液带到反应器中的溶解氧,大大减少了回流硝化液中溶解氧对反硝化的抑制作用。3.好氧反应器二级好氧生物反应器曝气生物滤池的启动挂膜应在气温较高的夏天进行,可以缩短挂膜启动的时间;挂膜期间尽量限制NH3-N负荷,二级好氧反应器的进水NH3-N浓度最好不高于60mg/L,防止对还不成熟的硝化菌生物膜产生抑制作用,影响挂膜启动;挂膜期间,可适当增加稀释水,以降低焦化废水中有机物的毒性;挂膜初期最好采用较小的气水比,防止对尚未成熟的生物膜冲刷作用过强。一级好氧反应器对COD有较好的去除效果。当容积负荷不大于2.79kgCOD/(m3·d)日寸,COD去除率不低于80%。二级好氧反应器进水中COD浓度小于200mg/L时,对NH3-N的去除影响不大;当水中COD浓度超过200mg/L时,NH3-N的去除率有所下降。当二级好氧反应器进水COD负荷≤0.67kg/(m3·d)NH3-N负荷≤0.49kg/(m3·d)时,可以得到良好的硝化效果。当水解酸化时间为20h,缺氧反应器HRT为24h,对系统进水不进行稀释,一级好氧反应器和二级好氧反应器HRT为48h,一级好氧反应器DO为5~6mg/L,COD容积负荷为0.40kg/(m3·d),NH3-N容积负荷为0.128kg/(m3·d);二级好氧反应器DO为4~5mg/L,COD容积负荷为0.07kg/(m3·d),NH3-N容积负荷为0.022kg/(m3·d)时,系统出水COD和NH3-N浓度都可以达到国家《污水综合排放标准》(GB8978-1996)中的一级标准。由于焦化废水COD和NH3-N浓度高,并且含有大量生物难降解有机物和对生物有毒有害物质,有机物好氧生物降解速率和氨氮硝化速率相对于城市污水来说要低得多。因此,焦化废水生物处理时以去除COD为主要功能的一级好氧反应器和以NH3-N硝化为主要功能的二级好氧反应器应该采用较低的容积负荷和较长的水力停留时间,以保证在系统进水不进行稀释的条件下,系统出水COD和NH3-N浓度同时达到国家《污水综合排放标准》(GB8978-1996)中的一级标准。一级好氧反应器生物量(以SS计)为7.44g/L,二级好氧反应器生物量(以SS计)为3.87g/L。活性污泥法单独硝化工艺中MLSS很难超过2g/L,实验中,曝气生物滤池中生物量(以SS计)为3.87g/L,比活性污泥法单独硝化工艺中的MLSS值高得多。由于生物膜法构筑物用于硝化处理时,可以保持较高的生物量,因此,当采用单独硝化工艺时,宜采用生物膜法构筑物。一级好氧反应器主要优势菌为异养菌,主要菌属为芽抱杆菌属、动胶菌属、黄杆菌属、诺卡菌属及产碱杆菌属;二级好氧反应器优势菌为硝化菌,主要菌属为硝化杆菌、硝化球菌、亚硝化单细胞及亚硝化球菌。异养菌为一级好氧反应器的优势菌,亚硝化菌和硝化菌为二级好氧反应器的优势菌。有机物浓度、溶解氧浓度、温度、pH值、碱度等都对二级好氧反应器硝化作用有影响。最佳条件是:溶解氧浓度在5mg/L左右,温度保持在25℃左右,pH值控制在7.0~7.8之间,维持出水碱度在150mg/L以上。二级好氧反应器曝气生物滤池不仅用于去除COD和NH3-N,反应器内的填料还有截留悬浮物的过滤作用,系统经过5个月的运行后才在曝气生物滤池出水检出很低的SS浓度。有利于降低出水中微生物固体的COD量,对降低出水COD浓度有一定作用。焦化废水由于COD和NH3-N浓度都很高,应采用两级好氧工艺。第一级好氧构筑物以去除COD为目标,第二级好氧构筑物以NH3-N硝化为目标。由于去除COD和NH3-N硝化在不同的构筑物中完成,应针对两个不同阶段进行各自优化管理。采用单独的硝化工艺,由于进水中碳源有机物浓度低,易于形成硝化菌为优势菌的生物相。特别是在第一级好氧反应器中,由于生物降解作用大大减少了对二级好氧反应器中硝化菌有害和有毒物质浓度,减轻了对第二级好氧构筑物中硝化菌的抑制和毒性作用,大大提高了硝化构筑物的硝化效率和运行的稳定性。研究结果表明,系统进水COD浓度在1000~2200mg/L范围内,进水NH3-N浓度在200~400mg/L范围内,对系统进水不进行稀释的条件下,水解酸化反应器HRT为20h,缺氧反应器HRT为24h,一级好氧反应器和二级好氧反应器HRT均为48h,二级好氧反应器硝化液回流比为3时,生物膜法厌氧/缺氧/好氧/好氧(A2/O2)处理出水COD≤100mg/L,NH3-N≤15mg/L,COD和NH3-N浓度可以同时达到《污水综合排放标准》(GB8978-1996)中的一级排放标准。本研究在焦化废水的生物处理技术上取得如下的创新性成果:(1)提出生物膜法厌氧/缺氧/好氧/好氧(A2/O2)处理焦化废水工艺。厌氧和缺氧反应器为以陶粒为填料的上流式滤池,第一级好氧反应器为以塑料空心球为填料的生物接触氧化池,第二级好氧反应器为以陶粒为填料的上流式曝气生物滤池。(2)中试规模研究了生物膜法A2/O2工艺处理焦化废水的工艺参数,为生产工艺的设计提供了技术参数。(3)焦化废水经隔油和气浮预处理后,在不对焦化废水进行稀释的条件下,采用生物膜法A2/O2工艺,处理出水COD和NH3-N浓度可以同时达到国家《污水综合排放标准》(GB8978-1996)中的一级标准(即COD≤100mg/L,NH3-N≤15mg/L)。(4)强调了缺氧反硝化在处理流程中对COD去除的重要作用。缺氧反应器的合理设计对保证系统出水COD浓度达标至关重要。只要充分发挥反硝化菌对焦化废水中难降解有机物的缺氧降解作用,对焦化废水缺氧反硝化而言,碳源还是相对充足的,不需要补充外加碳源。研究结果表明,缺氧反硝化进水C/N比在5以上就可以基本上满足反硝  还原水利论文(x^/M t4X`.L;r6]

8i5axU(B@'i"j0【英文摘要】 Coking wastewater is complicated in compositions and is characterized by a high NH4+ concentration and slowly degradable organics such as aromatic compounds, heterocyclic and polycyclic aromatic hydrocarbons (PAHs) which are very slow in degradation. Pollution control of coking wastewater is a tough topic in the pollution control of industrial wastewater in China. A popular problem faced in most of coking plants is that effluent COD and NH4+ concentrations from biological treatment processes cannot meet the needs of the General Wastewater Discharge Standards I (GB9878-1996:COD≤100 mg/L, NH4+≤15 mg N/L), ifinfluent is not diluted by tap water.Coking wastewater is usually treated by activated sludge processes such as A/O and/or A2/O, however, which are difficult to realize simultaneous removals for both COD and NH4+ to the standards mentioned above. The reasons are analyzed for: (1) depressed nitrifying bacteria by high influent COD concentrations and bacteria-inhibited organics...更多 in influent; (2) a small part of degradable COD, a short HRT and less carbon source in anoxic reactor. As the capacity of COD removal by denitrification is not fully utilized, the effect of denitrification is poor so that the A/O and/or A2/O processes cannot make use of the whole process for COD removal.In this thesis, a pilot-scale biofilm A2/O2 (anaerobic/anoxic/oxic/oxic) process was studied for its process performance and results, based on the coking wastewater from an air-flotation equipment at a coking plant of Tongshida Co. Ltd. Linfen,, Shanxi. Ceramic pellets were packed in the anaerobic and anoxic reactors with an upflow-filter mode. Hollow plastic balls were packed in the first aerobic reactor, and ceramic pellets were packed in the second aerobic reactor. During the trial of the biofilm A2/O2 process, the influent COD varied between 1000 and 2200 mg/L, and the influent NH4+ concentration fluctuated between 200 and 400 mg N/L.The key points about every reactor in the A2/O2 biofilm system are concluded as follows:1. Hydrolysis-acidification (anaerobic) reactorThe bacteria responsible for hydrolysis-acidification were poor in adherence and difficult to grow on the surface of packing materials, so that the hydrolysis- acidification reactor took longer time to start up. Violent changes on the influent COD and NH4+ concentrations seriously affected the start-up and operation of the hydrolysis-acidification reactor. The hydrolysis-acidification reactor with ceramic pellets packed took half a year from the start-up to the normal operation with ripe biofilm. Hydrolysis-acidifcation was used for improving the degradability of coking wastewater. During hydrolysis-acidification, much NH4+ was released due to a high ratio of nitrogen-containing organics. Therefore, it was very easy to judge the status of biofilm growth and the operational performance by the change of in fluent-effluent BOD/COD ratio and NH4+ concentration. Both COD and BOD could be removed in the hydrolysis-acidification reactor to a certain extent. Under the conditions of the on-site experiment, 20 hrs (HRT) was found to be optimal for hydrolysis-acidification. At HRT=20hrs, CODload=1.61~2.65kgCOD/(m3·d) and BOD/CODin=0.05~0.17, BOD/COD(eff) was calculated at 0.16~0.48, which meant a great improved degradability of organics with an average increase of 175% and/or a top increase of 336.4% on BOD/COD.Due to fluctuating characteristics of coking wastewater, HRT is proposed as a parameter of process design for hydrolysis-acidification. The biomass concentration in the hydrolysis-acidification reactor was measured up to 8960 mg/L on the basis of SS (VSS=7420 mg/L). For this reason, the hydrolysis-acidification reactor had a good adaptability to fluctuating pH, temperature and wastewater quality. The dominant bacteria in the hydrolysis-acidification reactor were facultative bacteria, such as Bacillus sp., Aeromonas sp., Flavobacterium sp. and Paracoccus sp. Further, the sludge production in the hydrolytic acidification reactor was low. The hydrolysis-acidification reactor had a long SRT and resulted in a low sludge production. Although backwashing was not done during the two-year's experiment, the performance of the reactor was not affected at all.2. Anoxic reactorDuring the start-up, biofilm was under growth and denitrification capacity was poor so that a low recirculation ratio should be applied. The optimal recirculation ratio for the anoxic reactor was 300%, at which an average NO3- -N reduction efficiency was maintained at>90%. Normal denitrification in the anoxic reactor occurred above 20℃. After hydrolysis-acidification, pH in the influent to the anoxic reactor was between 6 and 8 and could meet the needs of the anoxic reactor. Denitrification played a very important role in removing COD from coking wastewater. Denitrifying bacteria could use some slowly degradable organics for denitrification, which had not been degraded by aerobic and anaerobic microorganisms. Therefore, nitrate in the anoxic reactor was helpful for sturdy COD removal, which could remove COD up to 40% in the anoxic rector and further increased the total COD removal efficiency of the system. So, the reasonable design for anoxic reactor in the A2/O2 biofilm process is critical to assure the effluent COD standard. For denitrification of coking wastewater, carbon source was relatively enough and no external carbon was needed if denitrifying bacteria could be fully used to degrade slowly degradable organics in the anoxic reactor. An influent C/N ratio above 5 was enough of carbon needed for denitrifying in the anoxic reactor. Because denitrifying bacteria in the A2/O2 biofilm process used not only degradable COD bu also slowly degradable COD and even endogenous carbon, the denitrifying rate of coking wastewater was lower than that of municipal wastewater. The volumetric load of NO3- -N in the anoxic reactor was relatively low, which was lower than 0.24 kgNO3- -N/m3·d under the stable operation. HRT in the anoxic reactor should be longer than 24 hrs. The biomass amount (SS) decreased from the bottom to the top, with an average SS of 4160 mg/L and an average VSS of 3240 mg/L. When the size of ceramic pellet packed in the anoxic reactor fell in 3~6mm, the upflow velocity was so high due to a high recirculation ratio that release of dinitrogen gas produced in the denitrifying process could naturally occur and that a recirculation for releasing dinitrogen gas and backwashing for the reactor was not needed. The dominant bacteria in the anoxic reactor were Alcaligenes sp., Pseudomonas stutzeri UP1, Flavobacterium, etc. Though the DO level in the second aerobic reactor was high (4~5 mg/L), denitrifying in the anoxic reactor was not disturbed as the oxygen introduced by the recirculation flow from the aerobic reactor was consumed by denitrifying bacteria at the bottom of the anoxic reactor.3. Aerobic reactorThe start-up of the second aerated biological filter reactor was good in the summer, which could shorten the time of biofilm growth. During the period of biofilm growth, the influent NH4+ concentration should be limited below 60 mg N/L in order to avoid the effect on young biofilm. A high dilution ratio was proposed for a low toxicity of organics from coking wastewater during biofilm growth. A low gas-liquid ratio was also proposed to avoid washing out young biofilm during biofilm growth. The COD removal efficiency in the first aerobic reactor was good and was maintained above 80% if the COD volumetric load was lower than 2.79 kg COD/(m3·d). The nitrifying process in the second aerobic reactor was good at CODin<200mg/L and became poor at CODin>200mg/L. A good performance of nitrifcation could be realized at CODVL<0.67 kgCOD/(m3·d) and NH4+VL<0.49 kg N/(m3·d). Without any dilution, both the effluent COD and NH4+ of the system could meet the needs of the General Wastewater Discharge Standards I, at HRT=20, 24, 48 and 48 hrs respectively in the anaerobic, anoxic, first aerobic and second aerobic reactors, and at DO=5~6mg/L and 4~5mg/L, CODVL=0.40 and 0.07 kg COD/m3·d and NH4+VL=0.128 and 0.022 kg N/m3·d in the first aerobic and second aerobic reactors respectively. Aerobic organic conversion rate and denitrifying rate of coking wastewater were lower than those of municipal wastewater, as COD and NH4+ concentrations of coking wastewater were quite high and there were a lot of slowly degradable and detrimental organics. Therefore, low volumetric loads and long HRTs were proposed for both the first aerobic and second reactors to reach the discharge standards (GB8978-1996). The amounts of biomass were 7440 and 3870 mg/L (SS) in the first and second aerobic reactors respectively, which were much higher than that in conventional nitrifying activated sludge process (about 2000 mg N/L). For this reason, a biofilm process is proposed for single nitrifying process. Heterotrophic bacteria were the dominant microorganisms in the first aerobic reactor, such as Bacillus sp., Zoogloea sp., Flavobacterium, Nocardia, Alkaligenes, etc.; nitrifying bacteria were dominant microorganisms in the second aerobic reactor, such as Nitrobacter, Nitrosococcus sp. Environmental factors such as organic concentration, DO, temperature, pH had effects on the nitrifying process in the second aerobic reactor and the optimal condition was at DO=5 mg/L, T=25℃, pH=7.0~7.8 and ALKeff≥150 mg/L. The aerobic filters were also helpful to remove SS, and low levels of SS were measured in the effluents of the aerobic filters after the operation for 5 months, which served the function of lowering effluent biomass COD. Two-stage aerobic reactors were proposed for coking wastewater treatment: the first aerobic reactor for COD removal and the second for ammonium removal. Because of different operational conditions, process optimization should be taken for each rector. A single nitrifying reactor was helpful to have more nitrifying bacteria as high and detrimental COD concentrations were decreased in the first aerobic reactorThe experimental research showed that the effluent of the A2/O2 biofilm system could reach the discharge standards: (COD≤100 mg/L, NH4+≤15 mg N/L (GB8978-1996) with CODin=1000~2000 mg/L and NH4+in=200~400mg N/L and without any dilution, at HRT=20, 24, 48 and 48 hrs respectively in the anaerobic, anoxic, first aerobic and second aerobic reactors and at a nitrifying recirculation ratio of 3.Creative results obtained in this research were as follows:The A2/O2 biofilm process was proposed for coking water treatment. Ceramic pellets were used in the upflow anaerobic and anoxic filters and in the second upflow aerated filter; hollow plastic balls were employed in the first upflow aerated filter. The pilot-scale experiment of the A2/O2 biofilm process obtained some useful technical parameters for process design.The A2/O2 biofilm process could meet the needs of the general wastewater discharge standards I (GB8978-1996: COD≤100mg/L, NH4+≤15mg/L) without any dilution, after coking wastewater was pretreated for oil removal by isolating and flotating.COD removal during the anoxic denitrifying process was enhanced. A reasonable process design for the anoxic reactor was critical for a low COD effluent. Carbon source was relatively enough and no external carbon was needed if denitrifying bacteria could be fully used to degrade slowly degradable organics in the anoxic reactor. An influent C/N ratio above 5 was enough of carbon needed for denitrifying in the anoxic reactor.  还原

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$k5vn/v:T3p*[ d}0【中文关键词】 焦化废水; 生物膜法; 厌氧-缺氧-好氧-好氧; 水解酸化; 曝气生物滤池; 反硝化; 中试
FXq*lN"c%d0【英文关键词】 Coking wastewater; biofilm process; anaerobic-anoxic-oxic-oxic(A2/O2 ); hydrolysis-acidification; biological aerated filter (BAF); denitrification; pilot-scale experiment水利论文 ?i5H)t$gy8A

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