废水处理系统中生物聚集体胞外多聚物研究进展

胞外多聚物(Extracellular polymeric substances,EPS)是废水生物处理系统中生物聚集体(包括絮体污泥、生物膜、颗粒污泥等)的重要组成部分,直接包裹于微生物细胞壁外,其理化性质及所处的特殊位置决定了它在生物聚集体中的重要作用.综述了EPS对废水生物处理系统污泥沉降性能、脱水性以及膜生物反应器膜污染影响的相关研究,分析认为EPS组成与结构特性改变污泥表面电位、疏水性等,进而影响污泥沉降与脱水性能、膜污染程度;以好氧颗粒污泥为典型的生物聚集体代表,总结了EPS组分含量与分布对颗粒污泥的形成与结构稳定性的影响,并在EPS提取方法标准化、现代理化技术与分子生物学技术综合分析等方面进行了展望,进一步的研究有望揭示生物絮凝体形成过程EPS的产生与调控机制.     

污泥制备活性炭的活化剂及活化机制研究进展

为探讨不同活化剂对污泥活性炭结构的影响,介绍了污泥制备活性炭过程中所用物理活化剂、化学活化剂和化学物理活化剂的研究现状,分别探讨了它们的活化机制和性能.从传统活性炭制备工艺的角度,提出了污泥活性炭的研究趋势和应用前景.分析认为利用剩余污泥制备活性炭,并将其用于污水厂恶臭气体的去除是避免造成二次污染、使之资源化利用的重要...     

pH调节对活性污泥混合液膜过滤性的影响

探讨了用NaOH调节pH值对膜-生物反应器混合液膜过滤性能的影响,并通过分析污泥混合液性质的变化研究其作用机理.试验表明,适当调节pH到碱性,可以使膜过滤性能得到改善.投加碱液使污泥胞外多聚物(EPS)减少,污泥容积指数(SVI)降低,但上清液中总有机碳(TOC)浓度增加.混合液膜过滤性能的改善与污泥SVI的降低密切相关.在碱性条件下,从细胞表面脱落下来的EPS对絮体颗粒的絮凝性有一定促进作用,但效果有限.推测碱液处理使细胞表面的LB-EPS脱落,从而使细胞表面疏水性增加,有利于絮体颗粒之间的絮凝,从而有利于混合液膜过滤性的改善.     

Cultivation of aerobic granular sludge in a conventional,continuous flow,completely mixed activated sludge system

Aerobic granules were formed in a conventional, continuous flow, completely mixed activated sludge system (CMAS). The reactor was inoculated with seed sludge containing few filaments and fed with synthetic municipal wastewater. The settling time of the sludge and the average dissolved oxygen (DO) of the reactor were 2 h and 4.2 mg·L^-1, respectively. The reactor was agitated by a stirrer, with a speed of 250 r·min^-1, to ensure good mixing．The granular sludge had good settleability, and the sludge volume index (SVI) was between 50 and 90 mL·g^-1. The laser particle analyzer showed the diameter of the granules to be between 0.18 and 1.25 mm. A scanning electron microscope (SEM) investigation revealed the predominance of sphere-like and rod-like bacteria, and only few filaments grew in the granules. The microbial community structure of the granules was also analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Sequencing analysis indicated the dominant species were α, β, and γ-Proteobacteria, Bacteroidetes, and Firmicutes. The data from the study suggested that aerobic granules could form, if provided with sufficient number of filaments and high shear force. It was also observed that a high height-to-diameter ratio of the reactor and short settling time were not essential for the formation of aerobic granular sludge.     

Simple model of sludge thickening process in secondary settlers

In wastewater treatment plants (WWTPs), a secondary settler acts as a clarifier, sludge thickener, and sludge storage tank during peak flows and therefore plays an important role in the performance of the activated sludge process. Sludge thickening occurs in the lower portions of secondary clarifiers during their operation. In this study, by detecting the hindered zone from the complete thickening process of activated sludge, a simple model for the sludge thickening velocity, u _s = aX ^b (a = 0.9925SSVI _3.5, b = 3.541ln(SSVI _3.5)+12.973), describing the potential and performance of activated sludge thickening in the hindered zone was developed. However, sludge thickening in the compression zone was not studied because sludge in the compression zone showed limited thickening. This empirical model was developed using batch settling data obtained from four WWTPs and validated using measured data from a fifth WWTP to better study sludge thickening. To explore different sludge settling and thickening mechanisms, the curves of sludge thickening and sludge settling were compared. Finally, it was found that several factors including temperature, stirring, initial depth, and polymer conditioning can lead to highly concentrated return sludge and biomass in a biologic reactor.     

活性污泥系统微型动物群落特征及其与水温、溶氧的关系

于2002年7月至2003年7月对保定市银定庄污水处理厂活性污泥混合液中的微型动物群落做了为期1a的研究.共采集了49个水样,发现纤毛虫89种,其中自由游泳型纤毛虫12种,匍匐型纤毛虫13种,附着型纤毛虫38种,肉食型纤毛虫26种;鉴定到变形虫23种,其中有壳肉足虫5种,裸肉足虫18种;大型鞭毛虫共记录有8种;记录到的后生动物有轮虫、线虫和腹毛虫.附着型纤毛虫的密度占纤毛虫总密度的42.7%,匍匐型纤毛虫的密度占纤毛虫总密度的31.7%,肉食型纤毛虫的密度占纤毛虫总密度的21.2%,自由游泳型纤毛虫的密度占纤毛虫总密度的4.4%.附着型纤毛虫和匍匐型纤毛虫密度合计占纤毛虫总密度的74.4%,为纤毛虫中的优势类群.相关分析表明,锐利楯纤虫与水温呈非常显著的负相关,因此可作为低水温的指示生物;集盖虫与DO呈非常显著的负相关,可作为低DO的指示生物.表2参20     

Control of sludge settleability and nitrogen removal under low dissolved oxygen condition

Low dissolved oxygen (DO) is an energy-saving condition in activated sludge process. To investigate the possible application of limited filamentous bulking (LFB) in sequencing batch reactor (SBR), two lab-scale SBRs were used to treat synthetic domestic wastewater and real municipal wastewater, respectively. The results showed that prolonging low DO aeration duration and setting pre-anoxic (anaerobic) phase were effective strategies to induce and inhibit filamentous sludge bulking, respectively. According to the sludge settleability, LFB could be maintained steadily by adjusting operation patterns. Filamentous bacteria content and sludge volume index (SVI) were likely correlated. SVI fluctuated dramatically within a few cycles when around 200 mL·g^-1, where altering operation pattern could change sludge settleability in spite of the unstable status of activated sludge system. Energy consumption by aeration reduced under low DO LFB condition, whereas the nitrification performance deteriorated. However, short-cut nitrification and simultaneous nitrification denitrification (SND) were prone to take place under such conditions. When the cycle time kept constant, the anoxic (anaerobic) to aerobic time ratio was determining factor to the SND efficiency. Similarity keeping aerobic time as constant, the variation trends of SND efficiency and specific SND rate were uniform. SBR is a promising reactor to apply the LFB process in practice.     

Transport of Sewage Sludge in a Mixed Water Column

Sewage sludge from four publicly-owned treatment works was sampled and characterized in terms of parameters affecting transport at the 106-mile deep ocean disposal site as part of the US Environmental Protection Agency's site monitoring programme. Samples from treatment plants in Passaic Valley, Rahway, and Elizabeth, New Jersey and New York City were characterized in terms of dynamic size distribution, suspended solids and density. the transport characteristics of sludge particles were measured using a 2 metre computer-interfaced laboratory settling column. Experiments were conducted at constant salinity (35 ppt) while varying hydrodynamic mixing, sludge type and concentration using a modified factorial experimental design. Hydrodynamic power dissipation was varied so that the vertical dispersion and rms fluid shear rate ranged between 0-6 cm²S^-1 and 0-30s^-1 respectively. Results indicate that at least 80% of suspended sludge particles will eventually settle under mixed conditions. the average settling velocities ranged between 0.05-4.05 × 10^-3 cm ^s-1. Shear rates above 15 s^-1 inhibited sludge settling due to aggregate breakup and boundary effects, but at a lower shear rate, differential settling and fluid shear were the dominant transport mechanisms. Sludge dilution (1/500-1/5000) had a limited effect on the settling rate. Results from this study can be used to calibrate particle transport models to determine the fate of sludge disposed at an ocean disposal site.     

Transport of Sewage Sludge in a Mixed Water Column

Abstract

Sewage sludge from four publicly-owned treatment works was sampled and characterized in terms of parameters affecting transport at the 106-mile deep ocean disposal site as part of the US Environmental Protection Agency's site monitoring programme. Samples from treatment plants in Passaic Valley, Rahway, and Elizabeth, New Jersey and New York City were characterized in terms of dynamic size distribution, suspended solids and density. the transport characteristics of sludge particles were measured using a 2 metre computer-interfaced laboratory settling column. Experiments were conducted at constant salinity (35 ppt) while varying hydrodynamic mixing, sludge type and concentration using a modified factorial experimental design. Hydrodynamic power dissipation was varied so that the vertical dispersion and rms fluid shear rate ranged between 0-6 cm²S^?1 and 0-30s^?1 respectively. Results indicate that at least 80% of suspended sludge particles will eventually settle under mixed conditions. the average settling velocities ranged between 0.05-4.05 × 10^-3 cm ^s-1. Shear rates above 15 s^?1 inhibited sludge settling due to aggregate breakup and boundary effects, but at a lower shear rate, differential settling and fluid shear were the dominant transport mechanisms. Sludge dilution (1/500-1/5000) had a limited effect on the settling rate. Results from this study can be used to calibrate particle transport models to determine the fate of sludge disposed at an ocean disposal site.     

Acid mine-drainage toxicity testing

The BOD inhibition test, the activated sludge respiration inhibition test, and the Microtox® Bioassay procedure were examined for their potential as rapid toxicity screening methods for acid mine drainage (AMD) and for setting toxicity threshold levels in receiving waters. The BOD inhibition test proved to be unsuitable due to the high chemical oxygen demand of the toxicant. The long incubation time (minimum 5 d at 20°C) allowed growth of chemo-autotrophic bacteria and resulted in excessive flocculation and precipitation of metals, making accurate and meaningful measurements of inhibition impossible. The activated sludge respiration inhibition test was successful in measuring AMD toxicity, and for deriving toxicity threshold levels for the basic heterotrophic community in surface waters. However, it is a very time-consuming technique and is not sensitive enough to be used as a routine screening technique. The variability in toxicity was found to be due to the availability of metals as well as the effect of pH on metabolism. Simple linear models were derived to estimate inhibition within surface waters. Prediction of the inhibition caused by AMD can be made as long as the pH of the river water after mixing and the dilution of the AMD are known. Most accurate predictions are made using equations for specific pH ranges, but a useful estimation of inhibition can be obtained using the general equation: inhibition (%) = -2.34 pH + 6.41 AMD (%) + 22.1. The Microtox® Bioassay method, although expensive, was rapid and simple to use. It was the most sensitive test of the three, with the toxic response of marine bacteria increasing notably from 5 to 15 min due to the presence of bivalent metals in the toxicant. The problem of repeatability and reproducibility encountered with the activated sludge inhibition test was overcome with the highly standardised Microtox® method, making it an ideal screening method for AMD. However, the advantage of the activated sludge inhibition test is that the types of heterotrophic micro-organisms found in activated sludge are similar to those found in receiving waters such as the Avoca River and so more meaningful toxicity threshold values can be obtained.     

活性炭辅助微波热解污泥反应条件的试验研究

针对微波不能直接实现原污水污泥高温热解的问题,采用活性炭作为微波能吸收物质辅助污泥热解。对影响污泥热解效能的3个主要因素：污泥样品量、活性炭掺杂量和微波辐射功率,各做了3个水平的考察,得到了试验条件下的最优方案：污泥样品量30g、活性炭掺杂量6g、微波辐射功率1200W。结果表明：在最优试验方案下,污泥能在7min内升至920℃的高温,实现污泥快速、高效热解。通过分析3个因素对污泥热解效能的影响,进一步对最优试验方案下的固体产物吸收微波的性能及用其作为掺杂物辅助微波热解污水污泥的可行性进行了研究,结果表明：固体残渣吸收微波性能良好,可以代替活性炭作为更经济、高效的污泥微波热解辅助材料。     

Evaluation of activated sludge properties’ changes in industrial-wastewater pre-treatment: role of residual aluminum hydrolyzed species with different polymerization degree

● Medium poly Al salts dominated the PAC residual salts with a rational dosage. ● Settlement flocculation effect under medium poly Al salts showed a better trend. ● Complex of medium poly Al salts and enzymes promoted cell activity. ● Medium poly Al salts were beneficial to the effluent indexes. With the widespread introduction of pre-coagulation prior to the biological unit in various industrial wastewater treatments, it is noteworthy that long-term accumulation of residual coagulants has certains effect on both micro and macro characteristics of activated sludge (AS). In this study, the morphology distributions of residual aluminum salts (RAS) and their effects on the removal efficiency of AS were investigated under different PAC concentrations. The results showed that the dominance of medium polymeric RAS, formed under an appropriate PAC dose of 20 mg/L enhanced the hydrophobicity, flocculation, and sedimentation performances of AS, as well as the enzymatic activity in cells in the sludge system, improving the main pollutants removal efficiency of the treatment system. Comparatively the species composition with monomer and dimer / high polymer RAS as the overwhelming parts under an over-dosed PAC concentration of 55 mg/L resulted in excessive secretion of EPS with loose flocs structure and conspicuous inhibition of cellular activity, leading to the deterioration of physico-chemical and biological properties of AS. Based on these findings, this study can shed light on the role of the RAS hydrolyzed species distributions, closely relevant to Al dosage, in affecting the comprehensive properties of AS and provide a theoretical reference for coagulants dosage precise control in the pretreatment of industrial wastewater.     

施用城市污泥对土壤生态系统影响的研究进展

城市污泥的合理处置已成为目前环境科学研究领域中的重要课题。因污泥富含有机质和有效营养成分,对土壤改良有积极的促进作用,所以污泥的土地利用普遍被认为是一种积极、有效的处置方式。鉴于此,本文就国内外施用城市污泥对土壤生态系统的．影响及相关的过程和机理进行了综述。结果显示,施用污泥可改善土壤理化性质,提高土壤有机质和氮、磷等养分元素的含量,其改良作用因污泥类型而异。污泥对土壤重金属的积累有所影响,特别是在酸雨频发地区或者长期施用污泥,可能会带来重金属Gu污染的环境风险。污泥普遍有利于提高土壤酶活性,譬如土壤淀粉酶、脲酶和蔗糖酶活性,但污泥施用过量或时间延长,则会抑制多酚氧化酶和磷酸酶的活性,而污泥对过氧化氢酶的影响则不大。污泥对土壤微生物特性短期内有积极的影响,但长期则有负面作用。施用污泥可导致土壤动物活性的增加,但也会对一些土壤动物产生毒性,譬如异壳介虫属和弹尾目昆虫,而且污泥毒性不仅取决于污泥用量,土壤类型也起着重要作用。基于上述分析和评述,提出了未来研究展望如下：（1）针对污泥施用后土壤生态系统生物、物理和化学过程和机理进行系统、综合的基础研究;（2）对污泥土地利用进行长期的系统定位试验和环境监测,并对之进行环境风险评价;（3）对污泥稳定化处理技术的创新及其应用研究。     

AB工艺减少污泥重金属的效果

在AB工艺中,利用A段活性吸附去除重金属从而降低B段污泥中重金属含量,使其达到农用标准（GB4284-84酸性土壤控制标准）。利用小型污水处理实验场,模拟研究了AB工艺A段中重金属的去除情况,对AB运行控制参数进行优化探讨,以使A段能有效去除大部分重金属,并尽可能降低有毒有害污泥产量。结果表明：溶解氧质量浓度控制在0.5mg·L-1,污泥质量浓度调节为约500mg·L-1时,Cu2＋去除率可达87.6%,Zn2＋的去除率为78.7%,Ni2＋去除率为51%。当污泥质量浓度在1000～1500mg·L-1时,A段处理后污泥沉降性能好转,对重金属离子的去除有较好的效果,且不过多截留污水中的有机物。且B段剩余污泥中的Cu2＋、Zn2＋、Ni2＋含量都基本达到酸性土壤污泥农用控制标准。因此,适当控制AB工艺相关参数条件,利用A段活性污泥去除大部分重金属,降低B段产泥中重金属含量,达到农业控制标准是可行的,污泥经处理后进行土地资源化利用可成为我国污泥处置与利用的一种有效途径。     

Effects of Al3+ on pollutant removal and extracellular polymeric substances (EPS) under anaerobic,anoxic and oxic conditions

The highest removal efficiencies of COD and TN were achieved under 10 mg/L of Al³⁺. The highest TP removal efficiency occurred under 30 mg/L of Al³⁺. EPS, PS and PN concentrations increased with the addition of Al³⁺. Sludge properties significantly changed with the addition of Al³⁺. Aluminum ions produced by aluminum mining, electrolytic industry and aluminum-based coagulants can enter wastewater treatment plants and interact with activated sludge. They can subsequently contribute to the removal of suspended solids and affect activated sludge flocculation, as well as nitrogen and phosphorus removal. In this study, the effects of Al³⁺ on pollutant removal, sludge flocculation and the composition and structure of extracellular polymeric substances (EPS) were investigated under anaerobic, anoxic and oxic conditions. Results demonstrated that the highest chemical oxygen demand (COD) and total nitrogen (TN) removal efficiencies were detected for an Al³⁺ concentration of 10 mg/L. In addition, the maximal dehydrogenase activity and sludge flocculation were also observed at this level of Al³⁺. The highest removal efficiency of total phosphorus (TP) was achieved at an Al³⁺ concentration of 30 mg/L. The flocculability of sludge in the anoxic zone was consistently higher than that in the anaerobic and oxic zones. The addition of Al³⁺ promoted the secretion of EPS. Tryptophan-like fluorescence peaks were detected in each EPS layer in the absence of Al³⁺. At the Al³⁺ concentration of 10 mg/L, fulvic acid and tryptophan fluorescence peaks began to appear, while the majority of protein species and the highest microbial activity were also detected. Low Al³⁺ concentrations (<10 mg/L) could promote the removal efficiencies of COD and TN, yet excessive Al³⁺ levels (>10 mg/L) weakened microbial activity. Higher Al³⁺ concentrations (>30 mg/L) also inhibited the release of phosphorus in the anaerobic zone by reacting with PO₄^3-.     

长江三角洲地区城市污泥的综合生物毒性研究

运用发光细菌法对我国长江三角洲地区16个城市中54个污泥样品的综合急性生物毒性进行了测定，并以毒性较为稳定的HgCl2作为参比毒物，以发光细菌抑光率、相当标准毒物HgCl2质量浓度及百分数等级比较法毒性划分标准评价城市污泥的毒性。结果表明，供试的不需稀释测定毒性的城市污泥中，有13个是剧毒的，占样品总数30．95％；需稀释测定毒性的城市污泥中，毒性等级为Ⅰ级的8个，占样品总数66．67％。长江三角洲地区城市污泥大部分有较高的综合急性生物毒性，这与含多种高量的有毒重金属有关。城市污泥对发光细菌毒性的大小与城市污泥来源、污水处理工艺及污泥类型等因素有关。上海地区的污泥毒性大于江苏和浙江地区；42个毒性较小的污泥中，大部分氧化沟处理的城市污泥的毒性要大于A^2／O（厌氧-缺氧／好氧）处理的，12个毒性较大的污泥中处理工艺多为活性污泥处理与A^2／O处理；大部分以生活污水和混流污水为主的城市污泥毒性要高于以工业污水为主的城市污泥。     

Modification of the activated sludge model for chemical dosage

Full-scale experiments have been carried out to adapt the activated sludge model ASM2d to include the influence of metal dosage (Fe³⁺ and Al³⁺) for phosphorus removal. Phosphorus removal rates, nitrification rates, as well as pH and sludge settling performance, were evaluated as functions of the metal dosages. Furthermore, models relating certain parameters to the dosage of chemicals have been derived. Corresponding parameters in the ASM2d and the secondary settler models, included in the Benchmark Simulation Model No 1 (BSM1), have been modified to take the metal influence into consideration. Based on the effluent limits and penalty policy of China, an equivalent evaluation method was derived for the total cost assessment. A large number of 300-day steady-state and 14-day open-loop dynamic simulations were performed to demonstrate the difference in behavior between the original and the modified BSM1. The results show that 1) both in low and high mole concentrations, Fe³⁺ addition results in a higher phosphorus removal rate than Al³⁺; 2) the sludge settling velocity will increase due to the metal addition; 3) the respiration rate of the activated sludge is decreased more by the dosage of Al³⁺ than Fe³⁺; 4) the inhibition of Al³⁺ on the nitrification rate is stronger than that of Fe³⁺; 5) the total operating cost will reach the minimum point for smaller dosages of Fe³⁺, but always increase with Al³⁺ addition.     

农用污泥中铜的生态安全阈值研究

本论文采用污泥和土壤外源铜的活性差异系数法研究了农用污泥中铜的生态安全阈值。首先通过比较确定不同土壤条件下污泥中铜和水溶性铜的活性差异的系数,然后利用系数法得到相应土壤条件下污泥铜HC5值(即能够保护95%物种的浓度),并建立了土壤理化性质参数与污泥铜HC5值的量化关系和预测模型。最后与我国现行污泥农用标准值进行了比较,提出了修改建议。结果表明,土壤中来源污泥的铜活性均值约为来源水溶性盐的40%左右。土壤阳离子交换量(CEC)是影响土壤中污泥源铜的毒性的主控因子,可影响污泥铜HC5值变异的84.6%,而土壤pH值和有机碳含量(OC)分别可影响污泥铜HC5值变异的8.4%和1.8%。基于土壤pH、OC和CEC的三因子模型进行预测优于基于土壤pH和CEC的两因子模型,其相关性达到94.8%。与模型预测值相比,我国现行污泥农用标准GB4284-84与CJ/T309-2009中对铜限值的规定均存在着不同程度的保护不足或保护过度问题。     

Transport of Sewage Sludge From the 106-Mile Site - Results From an October Survey

Approximately 8 million tons of sewage sludge were disposed of annually at the 106-Mile Deepwater Municipal Sludge Dump Site (106-Mile Site) between 1987 and 1990. Beginning in 1988 and continuing to the present, the focus of monitoring at the 106-Mile Site moved towards improved understanding of the fate of the sludge. A survey conducted in October 1989 was designed to (1) detect the presence of any sludge particles that settle rapidly following disposal, (2) determine if sludge could be detected in the surface waters at locations away from the immediate disposal site, and (3) determine if water quality was degraded, by assessing whether the Environmental Protection Agency's marine water quality criteria were being exceeded.

The survey showed that the sludge does have a rapidly settling component composed of organic floc. mineral grains, and other heavy, gritlike particles, all of which are relatively large. These particles may settle at rates of between 8 and 180 m h^-1 and may reach the sea floor within 1 to 13 days following disposal. Even though a rapidly settling component is present in the sludge, a significant fraction of the sludge was detectable in the form of intact sludge plumes in the upper 35 m of the water column at least 15 km from the Site. in addition, unique tracers of sludge such as xylem tracheids and Clostridium perfringens plus elevated total suspended solids and trace metals concentrations, were found at locations up to 40 km from the Site. the presence of these tracers correspond with in situ transmissometry data suggesting that a fraction of the sludge was remaining in the near-surface waters above the seasonal pycnocline. Concentrations of metals were below EPA chronic marine water quality criteria, which indicates that the water quality downstream of the Site was not impaired. the detection of sludge downstream of the 106-Mile Site is consistent with the southwestward movement of the surface water mass during the survey, as recorded by satellite-tracked surface drifters and current vectors derived from a current meter moored at 100-m depth immediately west of the Site. Near-surface transport was generally towards the southwest at a speed of approximately 22 cm s^-1*.     

Effects of shear force on formation and properties of anoxic granular sludge in SBR

This paper reports the effects of shear force on anoxic granular sludge in sequencing batch reactors （SBR）. The study was carried out in two SBRs （SBR1 and SBR2） in which sodium acetate （200mg COD·L^-1） was used as the sole substrate and sodium nitrate （40 mgNO3-N·L^-1） was employed as the electron acceptor. The preliminary objective of this study was to cultivate anoxic granules in the SBR in order to investigate the effects of shear force on the formation of anoxic granular sludge and to compare the properties of anoxic sludge in the SBR. This study reports new results for the values of average velocity gradient, a measure of the applied shear force, which was varied in the two SBRs （3.79 s^-1 and 9.76 s^-1 for SBR1 and SBR2 respectively）. The important findings of this research highlight the dual effects of shear force on anoxic granules. A low shear force can produce large anoxic granules with high activity and poor settling ability, whereas higher shear forces produce smaller granules with better settling ability and lower activity. The results of this study show that the anoxic granulation is closely related to the strength of the shear force. For high shear force, this research demonstrated that： 1） granules with smaller diameters, high density and good settling ability were formed in the reactor, and 2） granular sludge formed faster than it did in the low shear force reactor （41days versus 76 days）. Once a steady-state has been achieved, the nitrate and COD removal rates were found to be 98% and 80%, respectively. For low shear force, such as was applied in SBR1, this research demonstrated that： 1） the activity of anoxic granular sludge in low shear force was higher than that in high shear force, 2） higher amount of soluble microbial products （SMPs） were produced, and 3） large pores were observed inside the larger granules,which are beneficial for nitrogen gas diffusion. Electron microscopic examination of the anoxic granules in both reactors showed that the morphology of the granules was ellipsoidal with a clear outline. Coccus and rod-shaped bacteria were wrapped by filamentous bacteria on the surface of granule.