【作者】 陈永志；

【导师】 彭永臻；

【作者基本信息】 北京工业大学 ， 环境工程， 2012， 博士

【摘要】 控制与治理水体富营养化是十分棘手、代价昂贵的世界性难题，被称为生态癌症。人类对引起水体富营养化的根本原因已经达成共识，即氮磷等营养元素的过量排放是最关键因素。因此，只有切断污染源，才能根治富营养化，实现经济和社会的可持续发展。A~2/O作为最简单的同步脱氮除磷工艺被广泛应用于国内外大型城市污水处理厂，然而，A~2/O工艺的固有缺欠就是硝化菌、反硝化菌和聚磷菌(PolyphosphateAccumalating Oganisms, PAO)在污泥龄（Sludge Retention Time, SRT）、碳源需求以及回流污泥中携带的硝酸盐影响聚磷菌厌氧释磷等，很难在单一系统中同时获得氮磷的高效去除。A~2/O–BAF系统将活性污泥法和生物膜法结合起来，通过缩短A~2/O的污泥龄，将硝化过程从A~2/O中分离出去，用BAF实现硝化，A~2/O在短污泥龄条件下运行，以除磷和反硝化为目的，而BAF在长污泥龄条件下运行，主要完成硝化。另一方面，从BAF回流来的硝酸盐为A~2/O的缺氧段提供了充足的电子受体，为反硝化除磷创造了条件。同时，由于A~2/O不硝化，回流污泥中不含硝酸盐，为厌氧段提供了绝对的厌氧环境，有利于聚磷菌厌氧释磷。本研究采用连续流双污泥A~2/O–BAF系统处理实际城市生活污水。系统由A~2/O反应器、二沉池和BAF组成。A~2/O为推流式，均分9个格室，有效容积30L；二沉池为竖流式，有效容积20L；BAF为圆柱形，采用上向流，填料层高度H=1.67m，有效容积13L。系统稳定运行后，考察了A~2/O的厌氧、缺氧和好氧段的容积比对脱氮除磷的影响。结果表明，在污泥龄为10d、污泥回流比(Sludge Return Ratio, r)为100%、硝化液回流比(Nitrate Recycling Ratio, R)为300%、总悬浮固体（Total SuspendedSolids, TSS）为3.0g/L时，A~2/O的厌氧、缺氧和好氧段容积比为1:6:2时，既能保证聚磷菌的优势增值又能有效地抑制硝化细菌的繁殖，系统的脱氮除磷效率最佳，总氮（Total Nitrogen, TN）和总磷（Total Phosphorus, TP）的去除率分别达到67.4%和98.6%。微生物的增值对TN去除率的贡献约为30%，反硝化脱氮是生物脱氮的主体。对于前置反硝化系统，从BAF回流来的硝化液为A~2/O的缺氧段提供电子受体，回流比越大，脱氮效果越好。另一方面，在缺氧条件下反硝化聚磷菌（DenitrifyingPhosphorus Removing Organisms, DAPO）与反硝化菌争夺有限的电子供体，如果硝酸盐氮浓度有限，DAPO将被淘洗，反之，DPAO将成为优势菌种，种群结构得到优化。研究结果表明，硝化液回流比与COD、TP和NH＋4-N的去除没有明显相关性，TN的去除率随硝化液回流比的增大呈现升高趋势，但升高幅度呈递减规律，缺氧反硝化能力和反硝化吸磷量随硝化液回流比的增大而提高。低温使硝化菌的活性降低，是生物脱氮的瓶颈。BAF中的活性生物填料为硝化菌的生长提供了天然的生存环境，低C/N和较高的溶解氧（Dissolved Oxygen,DO）均有利于硝化菌成为优势菌种。在平均进水温度为14.2℃、COD为369.5mg/L、TN为76.8mg/L的条件下，平均出水TN与TP分别为13.21mg/L和0.23mg/L，满足国家一级A排放标准(GB18918-2002)。硝化液回流为A~2/O的缺氧段提供硝酸盐氮的同时，也携带一定量的溶解氧，兼性异养菌优先利用溶解氧，消耗有机碳源，因此，在较低的C/N比条件下（C/N=3.0），增大硝化液回流比，TN去除率下降。提高C/N比为4.0时，硝化液回流比从100%升高到400%时，TN去除率呈上升趋势，硝化液回流比增大到500%时，TN去除率不升反降，继续增大到600%时，TN去除率恶化。当C/N比为5.5、硝化液回流比从100%升高到600%时，TN去除率呈现上升趋势。C/N比为3.0和4.0时，硝化液回流比对TP去除率影响较小；当C/N比为5.5时，二沉池释磷，出水磷浓度超标，硝化液回流比增大可以缓解“二次释磷”。BAF存在临界进水氨氮浓度。BAF对磷的去除主要基于填料层中的悬浮物质的短期截流及吸附作用。聚磷菌厌氧释磷速率与主体溶液中磷浓度呈零次方关系，与挥发性脂肪酸（Volatile FaticAcid, VAF）的浓度呈正相关；碳源对厌氧释磷速率和好氧/缺氧摄磷速率均有影响。分子氧、硝酸盐氮和亚硝酸盐氮均可作为电子受体，亚硝酸盐氮浓度过高致使聚磷菌“中毒”，破坏细胞壁，导致“磷泄露”。更多还原

【Abstract】 Eutrophication, the most urgent and troublesome problem in the world, hasgained significant attention worldwide. Once the eutrophication occurred, it isdifficult to control and handle. Simultaneous biological nutrients (particularlynitrogen and phosphorus) removal from wastewater is essential to preventeutrophication and achieve sustainable development.The anaerobic/anoxic/oxic (A~2/O) process is most commonly used in existingwastewater treatment plants (WWTPs) in the world. However, there are three mainoperational problems existing in A~2/O process, which are summarized as follows:Firstly, the confliction problem between sludge retention time （SRT） ofnitrifiers (long SRT) and polyphosphate accumulating organisms (PAO)(short SRT)can not be solved. So the SRT in the A~2/O process must maintain in a narrow rangefor removal of nitrogen (N) and phosphorus (P).Secondly, shortage of organic carbon sources in low strength wastewater is oftena rate-limiting factor to simultaneous N and P removal. Sufficient carbon source isnecessary for denitrification, in contrst, synthesis of poly-hydroxy-alkanoate (PHA)and glycogen degradation are the foundation of P removal. In A~2/O process, COD wasprimarily utilized by PAO in the anaerobic zone in which approximately70%of CODwas consumed, and around10%COD was consumed by denitrifiers in the followinganoxic zones. This leads to deterioration of N removal due to insufficient externalcarbon source.Finally, NO3–-N in return sludge is an inhibiting factor to the P release inanaerobic zone where denitrifiers will compete with PAO for external carbon source,and net P release won’t occur until denitrification is completed. This leads todeterioration of P removal in anoxic and/or aerobic zone. Therefore, how to resolvethe contradictions between removal N and P in the traditional processes is a crucialissue.The novel system integrating A~2/O-biological aerated filter (BAF) had substantialadvantages to solve the above mentioned problems. In this system, the A~2/O wasmainly used for P removal and denitrification, and the BAF was used for nitrification.Short SRT was applied in A~2/O and relatively longer SRT was applied in BAF toenrich nitrifiers, which not only benefited PAO, but also nitrifiers. In the same time,NO3–-N was recycled from BAF to the A~2/O’s anoxic zone rather than its anaerobiczone to provide an extremely strict anaerobic environment for phosphate release. Inaddition, influent with lower C/N ratio also stimulated the growth of denitrifyingphosphorus removing organisms （DPAO）, which were capable to use NO3–-N as electron acceptors in simultaneous removal of N and P from wastewater. Furthermore,large amount of COD was consumed in the anaerobic zone of A~2/O and reduced theC/N ratio of supernatant that flowing into the BAF, which was favorable to the growthof nitrifiers in the biofilm and enhanced nitrification. Furthermore, the sufficientnitrate from BAF was recycled into the anoxic zones of A~2/O which benefits thedenitrifying phosphorus removal.A laboratory-scaled A~2/O-BAF system, for treating domestic wastewater, wasconsisted of an influent tank, an A~2/O reactor, a secondary settler and a BAF reactor.The transparent Plexiglas A~2/O reactor had nine compartments with a working volumeof30L. The mixed liquor from A~2/O reactor was settled in a cylindrical settler with aworking volume of20L. The media’s depth of up-flow BAF was167cm and theworking volume of the BAF reactor was13L.After stable operation of the A~2/O-BAF system, the effect of volume ratio in theA~2/O on the N and P removal was discussed. The volume ratio ofanaerobic/anoxic/aerobic zone was1:6:2and the major operating parameters were:SRT10d, sludge recycle ratio (r)100%, nitrate recycling ratio (R)300%, TSS3.0g/L.The results showed that the A~2/O-BAF system has potential for the domesticwastewater treatment and67.4%of TN and98.6%of TP were removed. This canguarantee the advantage of PAO growth and effectively restrain nitrifiers, and thesystem’s N and P removal efficiency is the highest.Cell assimilation was estimated to remove about30%of the TN concentrationpresent in the influent domestic wastewater, and the nitrification-denitrificationcontributed significant amount of the overall TN removal efficiency. High nitraterecycling stream would bring more nitrates back to the anoxic zone for denitrificationand prevent the nitrates from escaping out with the effluent. On the other hand, themajor factor influencing the occurrence of DAPO and associated anoxic P-uptake wasthe nitrate load in the anoxic zones, only if the nitrate load was high enough orexceeding the denitrification potential of ordinary heterotrophic organisms (OHO), i.e.non-PAO organisms in the anoxic zones, could it be possible to stimulate DPAO inthe system because the specific denitrification rate of OHO was significantly largerthan that of DPAO. There was no distinct relationship between the nitrate recyclingratio and the removal efficiencies of COD, TP and ammonia nitrogen. However, theremoval efficiencies of TN increased with the increasing of the nitrate recycling ratio,the rising rate was descending. Both the capacity of denitrifying and phosphorusremoval in anoxic zone increased simultaneously with the increasing of the nitraterecycling ratio.Also, the performance of A~2/O-BAF system was investigated when treatingdomestic wastewater with low C/N ratio at low temperature. Under the conditions of average temperature of14.2℃and C/N ratio of4.81, enhanced N and P removal wasachieved. Average effluent TN and TP concentrations were13.21mg/L and0.23mg/L, respectively，which could satisfy the class A discharge standards (Integratedwastewater discharge standard, GB18918-2002, China).Denitrifiers are facultative bacteria that energetically prefer oxygen to nitrate asthe terminal electron acceptor. A high nitrate recycling stream, typically required foreffective denitrification operation, will also bring a large amount of DO from the BAFto the anoxic zone of the A~2/O that, in turn, would inevitably deteriorate the TNremoval efficiency. This is especially crucial when the organic matters present in theinfluent wastewater are insufficient to deplete the high DO concentration present inthe nitrate recycling stream (C/N ratio of3.0). When the C/N ratio was4.0, TNremoval efficiency declined when R was above400%due to insufficient carbonsource and oxygen intrusion in the anoxic zone of the A~2/O. Highest C/N ratio of5.5improved the TN removal efficiencies when increasing R. The P removal efficiencyexhibited an upward trend with increasing of R. The lower C/N ratios of3.0and4.0had little influence on P removal. In contrast, the highest C/N ratio of5.5resulted in Prelease in settler due to the observed residual carbon source present, led to a decreasein P removal efficiency, although the higher R can relieve this conflicting influence.There is a critical ammonia concentration in the BAF. The removal ofphosphorus in BAF is due to the closure and adsorption by the suspended materials.The phosphorus release rate of PAO was not related to the phosphate concentration inmain solution but was positively related with the concentration to volatile fatic acid(VFA). The carbon source not only affected the rate of phosphorus release of PAO,but also the rate phosphorus uptake in oxic/anoxic conditions. Oxygen, nitrate andnitrite could be used as the electron acceptor for phosphorus uptake. However, therewas a nitrite threshold concentration because it would cause phosphorus release due todetriment to anoxic phosphate uptake.更多还原