Enhanced Biological Nutrients Removal in Modified Step-feed Anaerobic_Anoxic_Oxic Process
污水处理的英文文献翻译(1)
Nutrient removal in an A2O-MBR reactor with sludgereductionABSTRACTIn the present study, an advanced sewage treatment process has been developed by incorporating excess sludge reduction and phosphorous recovery in an A2O-MBR process. The A2O-MBR reactor was operated at a flux of 77 LMH over a period of 270 days. The designed flux was increased stepwise over a period of two weeks. The reactor was operated at two different MLSS range. Thermo chemical digestion of sludge was carried out at a fixed pH (11)and temperature (75℃) for 25% COD solubilisation. The released pbospborous was recovered by precipitation process and the organics was sent back to anoxic tank. The sludge digestion did not have any impact on COD and TP removal efficiency of the reactor. During the 270 days of reactor operation, the MBR maintained relatively constant transmembrane pressure. The results based on the study indicated that the proposed process configuration has potential to reduce the excess sludge production as well as it didn't detonated the treated water quality.Keywords: A2O reactor; MBR; Nutrient removal; TMP1. IntroductionExcess sludge reduction and nutrients removal are the two important problems associated with wastewater treatment plant. MBR process has been known as a process with relatively high decay rate and less sludge production due to much longer sludge age in the reactor (Wenet al., 2004). Sludge production in MBR is reduced by 28-68%, depending on the sludge age used (Xia et al.,2008). However, minimizing the sludge production by increasing sludge age is limited due to the potential adverse effect of high MLSS concentrations on membrane (Yoon et al., 2004). This problem can be solved by introducing sludge disintegration technique in MBR (Young et al., 2007). Sludge disintegration techniques have been reported to enhance the biodegradability of excess sludge (Vlyssides and Karlis, 2004). In overall, the basis for sludge reduction processes is effective combination of the methods for sludge disintegration and biodegradation of treated sludge. Advances in sludge disintegration techniques offer a few promising options including ultrasound (Guo et al., 2008), pulse power (Choi et al.,2006), ozone (Weemaes et al., 2000), thermal (Kim et al., 2003), alkaline (Li et al., 2008) acid (Kim et al., 2003) and thermo chemical(Vlyssides and Karlis, 2004). Among the various disintegration techniques, thermo chemical was reported to be simple and cost effective (Weemaes and Verstraete, 1998). In thermal-chemical hydrolysis, alkali sodium hydroxide was found to be the most effective agent in inducing cell lysis (Rocker et al., 1999). Conventionally, the nutrient removal was carried out in an A2O process. It has advantage of achieving, nutrient removal along with organic compound oxidation in a single sludge configuration using linked reactors in series (Tchobanoglous et al., 2003). The phosphoroes removal happens by subjecting phosphorous accumulating organisms (PAO) bacteria under aerobic and anaerobic conditions (Akin and Ugurlu, 2004). These operating procedures enhance predominance PAO, which are able to uptake phosphorous in excess. During the sludge pretreatment processes the bound phosphorous was solubilised and it increases the phosphorousconcentration in the effluent stream (Nishimura, 2001).So, it is necessary to remove the solubilised phosphorus before it enters into main stream. Besides, there is a growing demand for the sustainable phosphorous resources in the industrialized world. In many developed countries, researches are currently underway to recover the phosphoroes bound in the sludge's of enhanced biological phosphorus removal system (EBPR). The released phosphorous can be recovered in usable products using calcium salts precipitation method. Keeping this fact in mind, in the present study, a new advanced wastewater treatment process is developed by integrating three processes, which are: (a) thermo chemical pretreatment in MBR for excess sludge reduction (b) A2O process for biological nutrient removal (c) P recovery through calcium salt precipitation. The experimental data obtained were then used to evaluate the performance of this integrated system.2. Methods2.1. WastewaterThe synthetic domestic wastewater was used as the experimental influent. It was basically composed of a mixed carbon source, macro nutrients (N and P), an alkalinity control (NaHCO3) and a microelement solution. The composition contained (/L) 210 mg glucose, 200 mg NH4C1, 220 mg NaHCO3, 22一34 mg KH2PO4, microelement solution (0.19 mg MnCl2 4H20, 0.0018 mg ZnCl22H2O,0.022 mg CuCl22H2O, 5.6 mg MgSO47H2O, 0.88 mg FeCl36H2O,1.3 mg CaCl2·2H2O). The synthetic wastewater was prepared three times a week with concentrations of 210±1.5 mg/L chemical oxygen demand (COD), 40±1 mg/L total nitrogen (TN) and 5.5 mg/L total phosphorus (TP).2.2. A2O-MBRThe working volume of the A2O-MBR was 83.4 L. A baffle was placed inside the reactor to divide it into anaerobic (8.4 L) anoxic (25 L) and aerobic basin (50 L). The synthetic wastewater was feed into the reactor at a flow rate of 8.4 L/h (Q) using a feed pump. A liquid level sensor, planted in aerobic basin of A2O-MBR controlled the flow of influent. The HRT of anaerobic, anoxic and aerobic basins were 1, 3 and 6 h, respectively. In order to facilitate nutrient removal, the reactor was provided with two internal recycle (1R). IRl (Q= 1)connects anoxic and anaerobic and IR 2 (Q=3) was between aerobic and anoxic. Anaerobic and anoxic basins were provided with low speed mixer to keep the mixed liquid suspended solids (MLSS) in suspension. In the aerobic zone, diffusers were used to generate air bubbles for oxidation of organics and ammonia. Dissolved oxygen (DO) concentration in the aerobic basin was maintained at 3.5 mg/1 and was monitored continuously through online DO meter. The solid liquid separation happens inaerobic basin with the help of five flat sheet membranes having a pore size of 0.23 pm. The area of each membrane was 0.1 m2. They were connected together by a common tube. A peristaltic pumpwas connected in the common tube to generate suction pressure. In the common tube provision was made to accommodate pressure gauge to measure transmembrane pressure (TMP) during suction. The suction pump was operated in sequence of timing, which consists of 10 min switch on, and 2 min switch off.2.3. Thermo chemical digestion of sludgeMixed liquor from aerobic basin of MBR was withdrawn at the ratio of 1.5% of Q/day and subjected to thermo chemical digestion. Thermo chemical digestion was carried out at a fixed pH of 11(NaOH) and temperature of 75℃for 3 h. After thermo chemical digestion the supernatant and sludge were separated. The thermo-chemicallydigested sludge was amenable to further anaerobic bio-degradation (Vlyssides and Karlis, 2004), so it was sent to theanaerobic basin of the MBR2.4. Phosphorus recoveryLime was used as a precipitant to recover the phosphorous in the supernatant. After the recovery of precipitant the content was sent back to anoxic tank as a carbon source and alkalinity supelement for denitrification.2.5. Chemical analysisCOD, MLSS, TP, TN of the raw and treated wastewater were analyzed following methods detailed in (APHA, 2003). The influent and effluent ammonia concentration was measured using an ion-selective electrode (Thereto Orion, Model: 95一12). Nitrate in the sample was analyzed using cadmium reduction method (APHA, 2003).3. Results and discussionFig. 1 presents data of MLSS and yield observed during the operational period of the reactor. One of the advantages of MBR reactor was it can be operated in high MLSS concentration. The reactor was seeded with EBPR sludge from the Kiheung, sewage treatment plant, Korea. The reactor was startup with the MLSS concentration of 5700 mg/L. It starts to increase steadily with increase in period of reactor operation and reached a value of 8100 mg/L on day 38. From then onwards, MLSS concentration was maintained in the range of 7500 mg/L by withdrawing excess sludge produced and called run I. The observed yields (Yobs) for experiments without sludge digestion (run I) and with sludge digestion were calculated and given in Fig. 1. The Yobs for run I was found to be 0.12 gMLSS/g COD. It was comparatively lower than a value of 0.4 gMLSS/g CODreported for the conventional activated sludge processes (Tchoba-noglous et al., 2003). The difference in observed yield of these two systems is attributed to their working MLSS concentration. At high MLSS concentration the yield observed was found to be low (Visva-nathan et al., 2000). As a result of that MBR generated less sludge.The presently used MLSS ranges (7.5一10.5 g/L) are selected on the basis of the recommendation by Rosenberger et al. (2002). In their study, they reported that the general trend of MLSS increase on fouling in municipal applications seems to result in no impact at medium MLSS concentrations (7一12 g/L).It is evident from the data that the COD removal efficiency of A2O system remains unaffected before and after the introduction of sludge digestion practices. A test analysis showed that the differences between the period without sludge digestion (run I) and with sludge digestion (run II and III) are not statistically significant.However, it has been reported that, in wastewater treatment processes including disintegration-induced sludge degradation, the effluent water quality is slightly detonated due to the release of nondegradable substances such as soluble microbial products (Ya-sui and Shibata, 1994; Salcai et al., 1997; Yoon et al., 2004). During the study period, COD concentration in the aerobic basin of MBR was in the range of 18-38 mg/L and corresponding organic concentration in the effluent was varied from 4 to 12 mg/L. From this data it can be concluded that the membrane separation played an important role in providing the excellent and stable effluent quality.Phosphorus is the primary nutrient responsible for algal bloom and it is necessary to reduce the concentration of phosphorus in treated wastewater to prevent the algal bloom. Fortunately its growth can be inhibited at the levels of TP well below 1 mg/L (Mer-vat and Logan, 1996).Fig. 2 depicts TP removal efficiency of the A2O-MBR system during the period of study. It is clearly evident from the figure that the TP removal efficiency of A/O system was remains unaffected after the introduction of sludge reduction. In the present study, the solubilised phosphorous was recovered in the form of calcium phosphate before it enters into main stream. So, the possibility of phosphorus increase in the effluent due to sludge reduction practices has been eliminated. The influent TP concentration was in the range of 5.5 mg/L. During thefirst four weeks of operation the TP removal efficiency of the system was not efficient as the TP concentration in the effluent exceeds over 2.5 mg/L. The lower TP removal efficiency during the initial period was due to the slow growing nature of PAO organisms and other operational factors such as anaerobic condition and internal recycling. After the initial period, the TP removal efficiency in the effluent starts to increase with increase in period of operation. TP removal in A2O process is mainly through PAO organisms. These organisms are slow growing in nature and susceptible to various physicochemical factors (Carlos et al., 2008). During the study period TP removal efficiency of the system remains unaffected and was in the range of 74-82%.。
温度对生物除磷颗粒污泥形成的影响
温度对生物除磷颗粒污泥形成的影响王然登;李硕;郭安;彭永臻【摘要】为考察温度对生物除磷颗粒污泥形成的影响,采用三个实验室小试SBR反应器考察了不同温度下生物除磷系统中颗粒污泥的形成情况、颗粒特性及磷酸盐的去除情况.结果表明,在温度条件为8、23和31℃的反应器中,PO43--p的去除率分为99％、98.8％和20.9％.其中,在8和23℃的系统中形成了生物除磷颗粒污泥,污泥的平均粒径为230和465 μm,颗粒中聚磷菌占全菌比例为95.7％和97.3％;在温度为31℃的系统中,污泥以絮状体为主,平均粒径为133μm.随着温度的升高,污泥中的胞外聚合物(EPS)的含量逐渐降低,颗粒状的形成与EPS中蛋白质/多糖的比值有关.【期刊名称】《黑龙江大学自然科学学报》【年(卷),期】2015(032)004【总页数】6页(P513-518)【关键词】生物除磷;颗粒污泥;温度;EPS【作者】王然登;李硕;郭安;彭永臻【作者单位】哈尔滨工业大学城市水资源与水环境国家重点实验室,哈尔滨150090;哈尔滨工业大学城市水资源与水环境国家重点实验室,哈尔滨150090;哈尔滨工业大学城市水资源与水环境国家重点实验室,哈尔滨150090;哈尔滨工业大学城市水资源与水环境国家重点实验室,哈尔滨150090;北京工业大学北京市水质科学与水环境恢复工程重点实验室北京市污水脱氮除磷处理与过程控制工程技术研究中心,北京100124【正文语种】中文【中图分类】X703.1磷是引起湖泊、水库水体富营养化的主要元素,为去除污水中的磷,以聚磷菌超量吸磷为基础的生物除磷技术在污水处理厂得到了广泛的应用[1]。
温度是影响生物除磷系统的一个重要因素。
有研究表明,高温(30 ℃)不利于生物除磷,而在常温和低温条件下,生物除磷系统的运行效果良好[2-3]。
Whang等[4]考察了20和30 ℃时两个生物除磷系统的除磷效果,发现20 ℃条件下系统的除磷效果要明显高于30 ℃。
聚磷菌在不同碳源下的反硝化研究_李夕耀
wastewater treatment1209 (2)
Pin Point floc
• • • • Low filamentous organisms Weak, small floc Turbid supernatant High SVI
Secondary Treatment Sequencing Batch Reactor （序列间歇反应器）
• Suspended growth system • Completely mixed mode; batch mode with discontinuous flow
Settled, Digested sludge
Wastewater Treatment
Digester gas
Digestion
Separation
Complete mix, or high-rate, anaerobic digester
Sludge Treatment and Disposal Anaerobic Digestion
Advantages • High degree of waste stabilization at high organic loading rates • Very little sludge production (< 5% of biodegradable organic matter being converted to cell material) (10% of aerobic sludge production) • Easy dewatering of the excess sludge • No aeration equipment • Methane production – very low energy input (if the methane gas is used to heat the digester) • Long preservation of adapted sludge without feeding for more than a year
qcl-sodp硫自养脱氮技术在废水脱氮中的应用
Vol. 2 No. 1Jan. 2020第2卷第1期2020年1月环境生态学Environmental EcologyQCL-SODP 硫自养脱氮技术在废水脱氮中的应用刘波文*，刘济忠，石井裕之（广东省东莞市台腾环保材料科技有限公司，广东东莞523586）摘要:近年来，自养反硝化脱氮技术颇受重视,与传统异养反硝化脱氮相比，自养反硝化因无需外加碳源，节约运行成本，颇具 优势。
针对传统污水处理好氧生化后低碳氮比水体、生物脱氮效率低的问题，通过研究自主开发QCL-SODP 载体硫自养脱氮 技术，载体在高温改性条件下处理包埋了脱氮硫杆菌所必备的营养源，生化系统脱氮滤池采用升流式设计，反应过程中无需 补充任何有机碳源。
采用污水处理厂剩余污泥进行接种，成功驯化后，表面富集的脱氮硫杆菌可以利用总氮中的硝态氮和亚 硝态氮作电子受体，利用载体里营养源（S 、P 、Ca 等）做电子供体，将硝态氮转变为氮气进而降解总氮中的硝态氮，反应过程中无需调整pH 、补充碱度。
目前韩国80%污水厂采用该工艺脱氮，国内暂时停留在理论研究阶段，本公司国内完成中试应用，同 时逐步开始工程化应用。
关键词：硫自养脱氮;脱氮硫杆菌；QCL-SODP 载体;异养反硝化中图分类号：X703 文献标识码：A 文章编号：2096-6830（2020）01-0085-04Application of QCL-SODP sulfur auto-oxidation denitrification technology in wastewater denitrification ・ LIU Bo-wen * ,LIU Ji-zhong,Hiroyuki Ishii ( Guangdong Dongguan taiteng environmental protection material technology Co. , Ltd , Dongguan 523586, China). Environmental Ecology , 2020,2( 1) ,85-88.Abstract : In recent years , the technology of autotrophic denitrification has been attracted a lot of attention. Compared with conventionalheterotrophic denitrification , autotrophic den 让rification has a lot of advantages because it doesn' t need additional carbon source and saves operation cost. Aims at the low C/N water quality and low biological nitrogen removal efficiency , the sulfur self-oxygendenitrification technology of QCL-SODP carrier was researched and developed. The carrier has embedded the essential nutrient source ofthio-bacillus denitrification , and the up-flow denitrification filter was used , so there is no need to add any organic carbon source in the whole reaction process. Using inoculated sludge from sewage treatment plant,after successful domesticated ,the thiobacillus of the carrier surface can make use of the nitrate nitrogen in total nitrogen as electron acceptor,and use the nutrients in carrier,such as S,P,Ca etc,as electron donor. The TN is degraded without adjusting pH in the process of reaction , because that he thiobacillus can change nitrate nitrogen into the nitrogen. At present , 80% of sewage plants in South Korea adopt this technology , which is still in the stage of theoretical research in China. Our company has completed the pilot application in China,and gradually started the promotion in engineering.Key words :sulfur autoxidation denitrification ； thiobacillus denitrification ; QCL-SODP carrier ； heterotrophic denitrification1硫自养脱氮技术开发的意义氨氮是水体富营养化的主要污染物之一，废水 中氨氮的去除有物理法、化学法和生物法，其中生物 法作为一种经济、高效的脱氮方法被广泛应用。
Nutrient Removal in Wastewater Treatment
Nutrient Removal in Wastewater Treatment Wastewater treatment is a crucial process that ensures the removal of contaminants from sewage before it is released into the environment. One of the most important aspects of wastewater treatment is the removal of nutrients such as nitrogen and phosphorus. The presence of excess nutrients in water bodies can lead to eutrophication, which can have devastating effects on aquatic ecosystems. In this response, we will explore the importance of nutrient removal in wastewater treatment from various perspectives.From an environmental perspective, nutrient removal in wastewater treatment is crucial to protect aquatic ecosystems. Nitrogen and phosphorus are essential nutrients for plant growth, and their presence in water bodies can lead to excessive growth of algae and other aquatic plants. This can cause a range of problems, including reduced oxygen levels, increased water turbidity, and the death of fish and other aquatic animals. By removing excess nutrients from wastewater before it is released into the environment, we can help to prevent these negative impacts and maintain healthy aquatic ecosystems.From a public health perspective, nutrient removal in wastewater treatment is also important. Excess nutrients in water bodies can lead to the growth of harmful bacteria and other pathogens, which can pose a risk to human health. By removing these nutrients from wastewater, we can reduce the risk of waterborne illnesses and other health problems associated with contaminated water.From an economic perspective, nutrient removal in wastewater treatment can be costly. The process of removing nutrients from wastewater requires specialized equipment and expertise, and can consume significant amounts of energy and resources. However, the cost of not removing nutrients from wastewater can be even greater, in terms of the negative impacts on the environment and public health. In addition, there are potential economic benefits associated with nutrient removal, such as the recovery of nutrients for use in agriculture or other industries.From a technological perspective, there are a variety of methods that can be used to remove nutrients from wastewater. These include biological processes such as activatedsludge and trickling filters, as well as physical and chemical processes like sedimentation and chemical precipitation. Each method has its own advantages and disadvantages, and the choice of method will depend on factors such as the characteristics of the wastewater, the desired level of nutrient removal, and the available resources.From a regulatory perspective, nutrient removal in wastewater treatment is often required by law. Many countries have regulations in place that limit the amount of nutrients that can be discharged into water bodies, and wastewater treatment plants are required to meet these standards. Failure to comply with these regulations can result in fines and other penalties, as well as damage to the environment and public health.In conclusion, nutrient removal in wastewater treatment is a crucial process that serves a variety of important purposes. From protecting the environment and public health to complying with regulations and potentially generating economic benefits, there are many reasons why nutrient removal is essential. By utilizing a variety of technological methods and approaches, we can ensure that wastewater is properly treated and that excess nutrients are removed before they can cause harm to the environment and human health.。
11.8号托福阅读真题答案解析
11.8号托福阅读真题答案解析本文关于2017年11月18日阅读真题回忆，有利于考生备考复习。
让我们回忆一下最近考试的内容：环境类，生物类，词汇题等，请考生们要认真的阅读哦，来店铺会给你不一样的精彩内容，店铺会在考试后第一时间更新。
11.8号托福阅读答案解析阅读部分考试回忆如下：1. Preventing Overgrowth among Tree Branchesshedding剪枝的意义。
一个是因为有些树枝消耗掉的碳物质比生产的多，另一个原因是有时候气候很干，剪枝减少水的消耗。
词汇题补充：exposed = unprotectedwith no warning = without any indication beforehandcongestion = overcrowding2. Crown of Thorns Starfish and Coral Reefs冠状棘海星，话题重复2011.01.08珊瑚的消失和一种海星的数量猛增有关系，主要说的是导致猛增的原因(环境+人)词汇题补充：outbreak = sudden increaseaccompany = occur along withconverge = come togetherseverity = seriousness原题重现：The crown of thorns starfish, Acanthaster Tlanci, is large, twenty-five to thirty-five centimeters in diameter, and has seven to twenty-one arms that are covered in spines. It feeds primarily on coral and is found from the Indian Ocean to the west coast of Central America, usually at quite low population densities. Sincethe mid-1950s, population outbreaks at densities four to six times greater than normal have occurred at the same time in places such as Hawaii, Tahiti, Panama, and the Great Barrier Reef. The result has often been the loss of a fifty percent to nearly one hundred percent of the coral cover over large areas.A single Acanthaster can consume five to six square meters of coral polyps per year, and dense populations can destroy up to six square kilometers per year and move on rapidly. Acanthasters show a preference for branching corals, especially Acroporids. After an outbreak in a particular area, it is common to find that Acroporids have been selectively removed, leaving a mosaic of living and dead corals. In places where Acroporids previously dominated the community devastation can be almost complete, and local areas of reefs have collapsed.Areas of dead coral are usually colonized rapidly by algae and often are later colonized by sponges and soft corals. Increases in abundance of plant-eating fish and decreases in abundance of coral-feeding fish accompany these changes. Coral larvae settle among the algae and eventually establish flourishing coral colonies. In ten to fifteen years the reefs often return to about the same percentage of coral cover as before. Development of a four-species diversity takes about twenty years.Two schools of thought exist concerning the cause of these outbreaks. One group holds that they are natural phenomena that have occurred many times in the past, citing old men's recollections of earlier outbreaks and evidence from traditional cultures. The other group maintains that recent human activities ranging from physical coral destruction through pollution to predator removal have triggered these events.One theory, the adult aggregation hypothesis, maintains thatmost species is more abundant than we realize when a storm destroys coral and causes a food shortage. The adult Acanthasters converge on remaining portions of healthy coral and feed hungrily. Certainly there have been outbreaks of Acanthaster following large storms, but there is little evidence that the storms have caused the enough reef damage to create a food shortage for these starfish.Two other hypotheses attempt to explain the increased abundance of Acanthaster after episodes of high terrestrial runoff following storms. The first hypothesis is that low salinity and high temperatures favor the survival of the starfish larvae. The second hypothesis emphasizes the food web aspect, suggesting that strong fresh water runoff brings additional nutrients to the coastal waters, stimulating phytoplankton production and promoting more rapid development and better survival of the starfish larvae.Those favoring anthropogenic (human influenced) causes have pointed to the large proportion of outbreaks that have been near centers of human populations. It has been suggested that coral polyps are the main predators of the starfish larvae. Destruction of coral by blasting and other bad land use practices would reduce predation on the starfish larvae and cause a feedback in which increases in Acanthaster populations cause still further coral destruction. Unfortunately, there are too few documented instances of physical destruction of coral being followed by outbreaks of Acanthaster for these hypotheses to be fully supported.Another group of hypothesis focuses on removal of Acanthaster's predators. Some have suggested that the predators might have been killed off by pollution whereas othershave suggested that the harvesting of vertebrate and invertebrate predators of Acanthaster could have reduced mortality and caused increased abundance of adults. The problem with this group of hypothesis is that it is difficult to understand how reduced predation would lead to sudden increases in Acanthaster numbers in several places at the same time in specific years. It seems probable that there is no single explanation but that there are elements of the truth in several of the hypotheses. That is there are natural processes that have led to outbreaks in the past, but human impact has increased the frequency and severity of the outbreaks.3.Dorset Culture格林兰岛Dorset Culture的起源，首先是由于气候变冷，一部分人迁走了，另一部分留下来的人创立了文明。
外文翻译---DE型氧化沟生物脱氮除磷工艺
外文资料DE-oxidation ditch biological nitrogenand phosphorus removal process1、DE-oxidation ditch biological nitrogen removal processNitrogen is a plant growth essential nutrients, but if the chlorine content in water too high, it will produce eutrophication so that the dissolved oxygen content to reduce, the proliferation of algae growth, accelerate the aging process of natural water bodies. In addition to the nitrate form of chlorine is considered a cause of infant leukemia temporary high-speed railway on January 1 of the root causes of hemoglobin. Therefore, drinking water sources will Liuren the oxidation ditch water is necessary dechlorination.Oxidation Ditch biological nitrogen removal is the first by the self-support of aerobic microbes in the aerobic state, the use of dissolved oxygen in the mixture through nitrification will be for the effect of nitrate oxide, and then from heterotrophic microorganisms in the state in the anti-anoxia The role of nitrifying bacteria, the use of nitrates in the role nitrification oxygen to produce anti-nitrate nitrogen into the release of chlorine out.Nitrification-as：Nitrifying bacteriaNH4+1.86+O21.985+HCO3 0.021C5H7O2N+1.044H2O+1,881H2CO3+0.98NO3-D enitrification-as：Denitrifying bacteriaNO3-+1.08CH3OH+0.24H2CO30.056C5H7O2N+0.47N2 +1.68H2O+HCO3-Denitrifying bacteriaNO3-+0.67CH3OH+0.53H2CO30.04C5H7O2N+0.48N2 +1.23H2O+HCO3-DE-oxidation ditch the dechlorination role through a special operation mode, in turn create two Gounei nitrification and nitrification conditions. Nitrogen and purpose of reach.Operation to the following four stages of operation (Figure 1).Stage A: Well distribution of the sewage ditch into the Ditch I, interim ditch running low brush, only to maintain the activated sludge mixture of suspended state; dissolved oxygen concentration of less than 0.5 mg/l, in a state of hypoxia, so that the former An aerobic phase of the nitrate to raw sewage as carbon source for denitrification.At this point, I ditch behind the overflow weir open, muddy mixtureinto this two-person pool for precipitation separation, and in the ditch II to the high-speed brush aeration, into one of the previous phase of the sewage in Amoy good Oxygen state (D0> 2mg/l) for nitrification. Stages of the run-time for 15 min.Phase B: the distribution of sewage are still people well into the groove I,DitchI, II maintained ditch on the stage of the anti-nitrification, nitrification state. But the water from the ditch I read the Amoy II, guarantee people into the ditch II of the sewage pollution in the organic material is fully degradable. The stage for the run-time 105 min.Stage C: Well into the distribution of the sewage ditch II. At this point ditch II interim low brush then pushed into the flow of denitrifying state. To the water. I ditch and high-speed transit brush aeration, nitrification. The stage for the running time 15min.Stage D: D stage of the operation and status similar to stage B, only Ditch I, iI into the ditch, the water situation in the opposite. The stage of the running time for 105 minProcess in the course of the operation. Well distribution, Brush, overflow weir by the pre-set time control operation. In addition, Brush also be installed in each groove of dissolved oxygen analyzer control.Figure 1 Biological nitrogen removal opertation mode2、DE-oxidation ditch biological phosphorus removal processPhosphorus is essential microbial metabolism of nutrients, microbial cells is composed of part, by ADP and adenosine triphosphate (ATP) of each other to provide energy to achieve conversion of synthesis.Rely mainly on the removal of phosphorus-phosphate of energy exchange in the process of absorbing phosphorus, and polymerization in the form of phosphorus in thebody. Anaerobic state,These bacteria will be in polymerization of phosphorus to PO43--P in the form of a release in aerobic or oxygen sha state, the P-Han and respiration through the absorption of sewage in the PO43--P, a polymerization of phosphorus in the form of Synthesis of the cell.DE-oxidation ditch the biological phosphorus removal is the basis of this mechanism, set up in the oxidation ditch before anaerobic pond, Thus forming anaerobic January 1 January 1 hypoxia aerobic processes (Figure 2), and created a conducive to the best of phosphorus operating conditions.The system of anaerobic pond by the three ditches group. HRT for lh. Diving pool installed blender, sewage sludge and returning well-mixed.- P because of the need to completely anaerobic conditions can be fully in the polymerization of phosphorus released, if the pool NO3-,containing excessive, it will affect the efficiency of phosphorus, in the first Gounei contain NO3-，the Return to the use of sewage sludge as carbon source for a more through response to the denitrification to ensure that phosphorus in the second, three in the Amoy been fully released. The distribution of sewage into the wells after the people oxidation ditch, In the aerobic and anoxic conditions (aerobic state of maximum efficiency of absorption), the release of phosphorus has been activated sludge absorption, and then people into the sedimentation tank precipitation, Sheng after the remaining sludge from, in addition to this The purpose of phosphorus.Figure 2 Bilogical phosphours remonal process中文译文DE型氧化沟生物脱氮除磷工艺1、DE型氧化沟生物脱氮工艺氮是植物生长的一种必不可少的营养成分，但是如果水体中氮的含量过高，就会产生富营养化，使溶解氧含量降低，藻类生长泛滥，加速水体天然老化过程。
bmr污水处理工艺流程
bmr污水处理工艺流程下载温馨提示:该文档是我店铺精心编制而成，希望大家下载以后，能够帮助大家解决实际的问题。
文档下载后可定制随意修改，请根据实际需要进行相应的调整和使用，谢谢!并且，本店铺为大家提供各种各样类型的实用资料，如教育随笔、日记赏析、句子摘抄、古诗大全、经典美文、话题作文、工作总结、词语解析、文案摘录、其他资料等等，如想了解不同资料格式和写法，敬请关注!Download tips: This document is carefully compiled by theeditor.I hope that after you download them,they can help yousolve practical problems. The document can be customized andmodified after downloading,please adjust and use it according toactual needs, thank you!In addition, our shop provides you with various types ofpractical materials,such as educational essays, diaryappreciation,sentence excerpts,ancient poems,classic articles,topic composition,work summary,word parsing,copy excerpts,other materials and so on,want to know different data formats andwriting methods,please pay attention!深入解析：BMR污水处理工艺流程在环保领域，高效的污水处理技术对于保护水资源和环境至关重要。
混合营养脱氮在低C
化工进展Chemical Industry and Engineering Progress2023 年第 42 卷第 12 期混合营养脱氮在低C/N 工业废水处理中的研究进展鄢子鹏1，2，郑梦启1，2，王成业1，2，陈国炜1，2，王伟1，2，袁守军1，2，苏馈足1，2（1 合肥工业大学土木与水利工程学院，安徽 合肥 230009；2 安徽省农村水环境治理与水资源利用工程实验室，安徽 合肥 230009）摘要：富氮工业废水中难降解的氮杂环化合物加剧了碳氮比失衡，抑制了生物脱氮工艺中硝化反硝化过程，因而探究新型处理工艺是高效处理低C/N 工业废水的必由之路。
混合营养脱氮技术结合异养脱氮和自养脱氮的代谢路径，优化低C/N 工业废水脱氮性能，进而实现低C/N 工业废水处理提质增效。
本文综述了混合营养脱氮工艺中铁介导生物脱氮、硫介导生物脱氮和菌藻共生脱氮工艺的作用机理、研究进展与影响因素，阐述了三种工艺特点及不同类型低C/N 工业废水的适用性，并就三种混合营养脱氮工艺中存在的问题并结合当前研究方向，从优化电子供受体和代谢路径的角度提出增大电子容量、提高电子转移速率，结合电化学体系与Fe-S 耦合增强协同代谢从而提升污染物代谢性能的建议。
关键词：低C/N ；工业废水；氮杂环化合物；混合营养中图分类号：X52 文献标志码：A 文章编号：1000-6613（2023）12-6567-09Research progress of mixotrophic system in industrial wastewater oflow C/N ratioYAN Zipeng 1，2，ZHENG Mengqi 1，2，WANG Chengye 1，2，CHEN Guowei 1，2，WANG Wei 1，2，YUAN Shoujun 1，2，SU Kuizu 1，2(1 School of Civil Engineering, Hefei University of Technology, Hefei 230009, Anhui, China; 2 Anhui Provincial EngineeringLaboratory for Rural Water Environment and Resources, Hefei 230009, Anhui, China)Abstract: Since refractory nitrogen heterocyclic compounds in nitrogen-rich industrial wastewater aggravates the imbalance of carbon to nitrogen ratio and inhibits the nitrification and denitrification process in biological nitrogen removal process, exploring a new treatment process has become theinevitable course to efficiently treat low C/N industrial wastewater. Mixotrophic technology combines the metabolic pathways of heterotrophic and autotrophic nitrogen removal to optimize the nitrogen removal performance of low C/N industrial wastewater and further realizes the quality and efficiency improvement of low C/N industrial wastewater treatment. This paper reviews the mechanism, advance and influencing factors of Fe-mediated biological nitrogen removal, sulfur-mediated biological nitrogen removal and bacteria-algal symbiosis processes in mixotrophic nitrogen removal processes, and expounds thecharacteristics of the three processes and the applicability of different types of low C/N industrial综述与专论DOI ：10.16085/j.issn.1000-6613.2023-1037收稿日期：2023-06-25；修改稿日期：2023-08-14。
- 1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
- 2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
- 3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。
BIOTECHNOLOGY AND BIOENGINEERINGChinese Journal of Chemical Engineering, 17(5) 840ü848 (2009)Enhanced Biological Nutrients Removal in Modified Step-feedAnaerobic/Anoxic/Oxic Process*W ANG Wei ( )1, W ANG Shuying ( )1,**, PENG Y ongzhen ( )1, ZHANG Shanfeng ( )2 and YIN Fangfang ( )11 Key Laboratory of Beijing for Water Quality Science and Water Environmental Recovery Engineering, BeijingUniversity of Technology, Beijing 100124, China2 Beijing Municipal Engineering Professional Design Institute Co. Ltd, Beijing 100037, ChinaAbstract In order to enhance phosphorus removal in traditional step-feed anoxic/oxic nitrogen removal process, a modified pilot-scale step-feed anaerobic/anoxic/oxic (SFA2/O) system was developed, which combined a reactor similar to UCT-type configuration and two-stage anoxic/oxic process. The simultaneous nitrogen and phosphorus removal capacities and the potential of denitrifying phosphorus removal, in particular, were investigated with four different feeding patterns using real municipal wastewater. The results showed that the feeding ratios (Q1) in the first stage determined the nutrient removal performance in the SFA2/O system. The average phosphorus removal ef-ficiency increased from 19.17% to 96.25% as Q1 was gradually increased from run 1 to run 4, but the nitrogen re-moval efficiency exhibited a different tendency, which attained a maximum 73.61% in run 3 and then decreased to59.62% in run 4. As a compromise between nitrogen and phosphorus removal, run 3 (Q10.45Q total) was identifiedas the optimal and stable case with the maximum anoxic phosphorus uptake rate of 1.58 mg·(g MLSS)ˉ1·hˉ1. The results of batch tests showed that ratio of the anoxic phosphate uptake capacity to the aerobic phosphate uptake capacity increased from 11.96% to 36.85% with the optimal influent feeding ratio to the system in run 3, which demon-strated that the denitrifying polyP accumulating organisms could be accumulated and contributed more to the total phosphorus removal by optimizing the inflow ratio distribution. However, the nitrate recirculation to anoxic zone and influent feeding ratios should be carefully controlled for carbon source saving.Keywords nutrients removal, nitrogen, phosphorus, anaerobic/anoxic/oxic, step-feed1 INTRODUCTIONTo prevent the eutrophication in enclosed water system, biological nitrogen and phosphorus removal from wastewater has been extensively investigated and employed [1 3]. For simultaneous nitrogen and phosphorus removal, wastewater treatment system is designed to provide anaerobic, anoxic and aerobic environment for phosphorus release, denitrification and nitrification/phosphorus uptake, respectively [4]. In principle, oxygen is used as an electron acceptor for phosphorus uptake and nitrification in these processes. Nitrate, the product of nitrification and the electron acceptor for denitrification, is generally recognized as an inhibiting component for the biological phosphorus removal process [5, 6]. However, many studies have verified that in the absence of any exogenous carbon sources in the anaerobic zone, phosphorus removal may occur in the presence of nitrate [7 10]. It is pre-sumed that the denitrifying polyP accumulating or-ganisms (DNPAOs) use intracellular storage com-pounds poly-hydroxyl-alkanoates (PHA) as carbon and energy sources to assimilate P and synthesize polyP, as polyP accumulating organisms (PAOs) do, and use nitrate as terminal electron acceptor [11]. If the DNPAOs take up and store phosphate using nitrate as electron acceptor, then the organic carbon substrate can be used simultaneously for both phosphorus and nitrogen removal. This is of significance since organic carbon content in most municipal wastewater is often limited for phosphorus and nitrogen removal. The ac-cumulation of DNPAOs has been investigated exten-sively in laboratory scale reactors and it has been shown that phosphorus removal by DNPAOs has similar capacities and characteristics as PAOs in an-aerobic processes [9]. The main advantages of apply-ing denitrifying phosphorus removal are energy saving [aeration and external carbon source] and less sludge production [12]. It has been demonstrated that numer-ous treatment processes, such as dephanox process, the anaerobic-anoxic-oxic (A2/O) process and the University of Cape Town (UCT) process developed for simultaneous nitrogen and phosphorus removal, are well suitable for denitrifying phosphorus removal [13 15].The step-feed anoxic/oxic activated sludge proc-ess is characterized by multi-stages of anoxic/oxic (A/O) reactor in series, which eliminates the need for internal recycling and optimizes organic carbon utili-zation for denitrification [16, 17]. A pilot-scale step-feed A/O nitrogen removal system has been used to treat low COD/TN municipal wastewater with deep nitrogen removal by making full use of carbon source in raw wastewater, but it is unfavorable for optimal phosphorus removal. To accumulate the phosphorus removing organisms, especially the DNPAOs, a modified step-feed A/O system, defined as SFA2/O (step-feed anaerobic/anoxic/oxic), is developed and adopted inReceived 2008-12-23, accepted 2009-05-16.* Supported by the Project of Beijing Science and Technology Committee (D07050601500000) and the National Key Science and Technology Special Projects (2008ZX07317-007-105).** To whom correspondence should be addressed. E-mail: wsy@; wang_wei2005@Chin. J. Chem. Eng., Vol. 17, No. 5, October 2009841this study. An anaerobic zone is introduced before the first anoxic zone for phosphorus release. The returned activated sludge from the settler is recirculated to the beginning of the anoxic zone of first stage, and the mixed liquor in this anoxic zone is recirculated to the beginning of the anaerobic zone. The first stage is simi-lar to the UCT-type configuration, which is recognized as an alternative denitrifying phosphorus removal process with single sludge [13, 18]. The modified process combines the advantages of pre-denitrifying UCT-type system and the step-feed A/O system. It is expected to enhance the phosphorus removal and use the carbon source to a best extent. Due to the coexis-tence and/or competition behavior between microor-ganisms in the simultaneous nitrogen and phosphorus removal process, however, the operation of this sys-tem is complicated especially when the step-feed con-trol strategy is adopted. The stability of the system and effective N and P removal are affected by several fac-tors, such as the internal recycling ratio, influent flow distribution, C/N and C/P. To make use of the avail-able organic substrate for N and P removal in low COD/N municipal wastewater treatment system, the optimization of feeding ratios is a key issue in the step-feed A2/O system.In this study, the technical feasibility of simulta-neous phosphorus and nitrogen removal is investi-gated in the modified step-feed nutrients removal sys-tem, SFA2/O. The objectives are as follows. (1) En-hance the phosphorus removal by introducing the an-aerobic reactor and reduce the external carbon source dosage by strategic step-feed scenario. (2) Investigate the effects of influent flow distribution ratio on opera-tion and provide the optimal feeding ratio for N and P removal in municipal wastewater, especially at low C/N ratio. (3) Evaluate the possibility of denitrifying phosphorus removal and the contribution of denitrify-ing dephosphatation to the phosphorus removal. Based on the operation of the pilot-scale step-feed A2/O sys-tem, we expect to provide some fundamental data for upgrading the existing wastewater treatment plants and solve the conflictive problems in the operation of conventional nutrient removal process.2 MATERIALS AND METHODS2.1 Pilot-scale step-feed A2/O system2.1.1Experimental conditions and setupFigure 1 shows the schematic diagram of the pilot-scale SFA2/O system. The notations A, D i(i1,2,3) and N ij(i1,2,3; j1,2,3) indicate the anaerobic zone, anoxic zone of stage i, and aerobic zone j of stage i, respectively. The total influent flow (Q total) from the primary settler is divided into three streams: Q1, Q2 and Q3, which are the feeding flows into the anaerobic zone (A), the second anoxic zone D2, and the third one D3, respectively. Two recycle flows compose the recirculation system: one is the returned activated sludge Q r (Q r0.6Q total) from the secondary settler to the beginning of the first anoxic zone (D1) and the other is the internal recycle flow Q c(Q c0.3Q total) from the end of first anoxic zone (D1) to the begin-ning of the anaerobic zone (A). The total working volume is 320 L in the reactor. The effective volumes of the anaerobic reactor, anoxic1, aerobic1, anoxic2, aerobic2, anoxic3 and aerobic3 are 32 L, 32 L, 64 L, 32 L, 64 L, 32 L and 64 L, respectively.The stream Q1 provides the necessary substrate for phosphorus release in the anaerobic zone. The in-tracellular PHA accumulated by phosphorus removal organisms may, thus, serve as a carbon source for de-nitrification and phosphorus uptake when nitrate is available in the subsequent anoxic zone (D1). Resid-ual phosphorus is absorbed in the subsequent aerobic zone (N11 N13). It is assumed that no phosphorus is released in the anoxic zone D2 and D3 with a low C/N feeding influent.During the start-up period of this study, the dis-solved oxygen (DO) concentration in aerobic zones was controlled at above 2.5 mg·Lˉ1 so that the nitri-fying bacteria grew prosperously. In order to evaluate the effect of feeding ratio on nitrogen and phosphorus removal, once the steady-state condition was achieved, the influent flow distribution ratio was changed to 0.2Ή0.3Ή0.5 (run 1), 0.3Ή0.4Ή0.3 (run 2), 0.45Ή0.35Ή0.2 (run 3) and 0.6Ή0.25Ή0.15 (run 4). Each experi-mental circle lasted for 20 or 30 days (i.e, 2 or 3 times of solid retention time, SRT) for data collection. The influent flow rate and hydraulic retention time (HRT) of each stage under different runs are shown in Table 1. The other operational parameters of A2/O step-feed process are shown in Table 2.2.1.2Wastewater and sludgeThe wastewater used in this study was collected from the sewers of campus residential area. The char-acteristics of the wastewater are summarized in Table 3. The activated sludge was seeded from a full-scale wastewater treatment plant in Beijing, China (200000 m3·dˉ1), with regular operation and nutrient removal. The sludge was fed to an anaerobic/aerobic operating sequencing batch reactor (SBR) to accumulate phospho-rus removal organisms. After the operation for one month, a maximum specific P release rate 10.98 mg·gˉ1·hˉ1 and uptake rate 12.94 mg·gˉ1·hˉ1 were achieved with 100% P removal. Then the sludge was inoculated to the pilot-scale SFA2/O system and different operating conditions were carried out.2.2 Batch test for sludge characterization assayTo evaluate the sludge performance on phospho-rus release and uptake when the system was operated at different feeding patterns, batch experiments were carried out at the same time. The activated sludge at the end of anaerobic stage was transferred to three paralleled SBR reactors, each with a volume of 10 L. The temperature was kept at 20q C. NaAc and K2HPO4 were fed and the initial COD and 34PO -P concentra-tion were maintained at 200 mg·Lˉ1 and 6 mg·Lˉ1,Chin. J. Chem. Eng., Vol. 17, No. 5, October 2009842respectively. The anaerobic condition was controlled at 180 min for complete P release and adequate PHB (poly-ȕ-hydroxybutyrate) synthesis in the sludge. The aerobic or anoxic condition was kept for 300 min for full phosphorus uptake. Samples were collected at 30 min interval. 2.3 AnalysesSamples for dynamic studies were collected regularly from different zones of the reactors. Theconventional parameters including 4NH -N, 2NO-N, 3NO -N, COD, BOD 5, MLSS (mixed liquid sus-pended solids) and SVI (sludge volume index) were routinely analyzed according to the Standard Method [19]. Multi-3000 N/C analyzer (jena, Germany) was used for TN analysis. DO, pH and temperature were determined on-line using pH/Oxi 340i sensors (WTW, Germany).3 RESULTS AND DISCUSSION3.1 Phosphorus removal: P release and P uptake In the modified step-feed A 2/O system, P release and P uptake mainly occurred in the first stage. The factors influencing P removal were evaluated for the optimal operation of the first stage. Figs. 2 and 3 show the TP removal efficiency of runs 1 4 and the concen-trations of phosphorus and nitrate in different phases, respectively. During the first period (run 1), P removal efficiency is only 19.17% even though the PAOs are enriched in the seeding sludge. The poor phosphorus removal efficiency mainly results from the lower in-fluent feeding ratio of Q 1. Less organic compounds in Q 1 has a negative effect on the PHA synthesis [20], decreasing the phosphorus release in the anaerobic zone. In the absence of any exogenous carbon source or intracellular compounds (PHA) in the aerobic zone, PAOs will not grow aerobically and polyP synthesis efficiency will be decreased greatly. As a result, obviously excessive P uptake phenomenon is not observed in theaerobic zone. In addition, due to the higher nitrate inFigure 1 Schematic diagram of the modified SFA 2/O processTable 1 The influent flow rate and hydraulic retention time under different runsHydraulic retention time (HRT)/hRun Time/dQ 1ΉQ 2ΉQ 3A D1 N11 N13 D2 N21 N23 D3 N31 N331 0 20 0.2Ή0.3Ή0.5 4.0 4.0 8.0 2.67 5.33 1.6 3.2 2 20 50 0.3Ή0.4Ή0.3 2.67 2.67 5.33 2.0 4.0 2.67 5.33 3 51 80 0.45Ή0.35Ή0.2 1.78 1.78 3.56 2.29 4.58 4.08.04 81 99 0.6Ή0.25Ή0.15 1.33 1.332.663.26.45.33 10.67Table 2 The operational parameters of SFA 2/O processQ total /L·d ˉ1Q r /L·d ˉ1Q c /L·d ˉ1 SRT/d T /q C pH DO/mg·L ˉ1 MLSS ave /g·L ˉ1960 576 288 10 20±1 7.14 7.67 2.2 4.16 3.8Figure 2 TP removal efficiency in different phases × influent; + effluent; Ʒ removal efficiencyChin. J. Chem. Eng., Vol. 17, No. 5, October 2009 843Q r and lower organic substrate in feeding flows (Q 1),nitrate concentration is higher, up to 10.36 mg·L ˉ1 in the effluent of anoxic zone (D1) (see Fig. 3). Nitrate is introduced to the “anaerobic” zone with internal recy-cling flow (Q r ), results in the competition between denitrifying bacteria and PAOs for available substrate, so that P release is inhibited [6, 21, 22]. Therefore, onlyan average phosphorus concentration 8.95 mg·L ˉ1 anda maximum specific P release rate 0.28 mg·g ˉ1·h ˉ1 (see Fig. 3) are obtained in the anaerobic zone. How-ever, in runs 2, 3 and 4, P release and uptake rate in-crease as Q 1 is increased to 0.6(Q 1/Q total ), phosphorusconcentration in effluent is lower than 0.5 mg·L ˉ1, and 96.25% TP removal efficiency is obtained in run 4, indicating that the complete P removal is achieved. Fig. 3 shows that when feeding ratio Q 1 increases (from run 1 to run 4), the specific maximum P releaseincreases from 0.28 to 7.35 mg·g ˉ1·h ˉ1. In runs 3 and 4, higher P release rates are obtained. The maximumphosphorus release rates are 5.29 and 7.35 mg·g ˉ1·h ˉ1 and the average phosphorus concentrations in the an-aerobic zone are 24.01 and 27.9 mg·L ˉ1, accordingly. In run 4, however, the P release rate is not improved compared with run 3, which mainly ascribes to the higher carbon source concentration induced by influ-ent in run 4, so that the PAOs do not have enough an-aerobic time to take all organic substrate.P uptake in the anoxic reactor and aerobic zone was evaluated. Fig. 4 shows the specific P uptake rate for different feeding ratios. Similar to P release rate in anaerobic zone, aerobic P uptake in the first stage and the average P uptake of the whole system increase significantly from run 1 to run 4. The average phos-phorus concentration in aerobic zone (N13) is 5.45,5.08, 5.14 and 1.84 mg·L ˉ1, and the average P uptakeof the system is 0.22, 0.72, 2.08 and 3.39 mg·g ˉ1·h ˉ1 (see Table 4). A general view is that, under anaerobic conditions, PAOs assimilate organic substrate rapidly to synthesize PHA using polyP stored in cells as en-ergy source, and the orthophosphate generated from polyP degradation is released into the bulk liquid. In the absence of any organic compound in the aerobic zone, organisms with PHA stored are able to use the endogentic carbon as energy source to grow and as-similate phosphate to synthesize polyP. Therefore, the P uptake rate is decided by the energy source of PHA stored in the anaerobic zone. On the other hand, the P uptake has significant effect on P release. The more phosphorus is untaken, the more poly-P is stored, and the P release in the anaerobic zone will be furtherTable 3 The characteristics of feeding wastewater (mg·L ˉ1)COD BOD 54NH -N TN 2NO -N3NO -NTP Alkalinitymin/max 228.5/307.6 110.7/150.5 53.42/70.7 56.37/74.87 0.08/0.19 0.05/1.42 5.14/7.30 289/376 average 273.37 124.30 62.13 65.58 0.14 0.74 6.74 341.5Table 4 Summary of P removal in the different phasesRun 1 Run 2 Run 3 Run 4average TP removal efficiency/%19.17 50.41 89.81 96.25 specific anaerobic P release rate of anaerobic zone/mg·g ˉ1·h ˉ1 0.13 0.49 2.26 3.6specific anoxic P uptake rate of stage 1/mg·g ˉ1·h ˉ10.19 0.93 1.58 0.36 specific aerobic P uptake of stage 1/mg·g ˉ1·h ˉ10.23 0.62 2.32 4.91 specific P uptake rate of system/mg·g ˉ1·h ˉ10.22 0.72 2.08 3.39Figure 3 Concentration of phosphorus and nitrate in dif-ferent phases ƻ anoxic (D1) effluent P; Ʒ aerobic (N13) effluent P; ƹ anaerobic (A) effluent P; ƺ anoxic (D1) effluent nitrateFigure 4 Comparison of specific anoxic and aerobicP-uptake rate ƹ anoxic (D1) P uptake; Ʒ aerobic (first stage) P uptake; ƻ average P uptake rate of systemChin. J. Chem. Eng., Vol. 17, No. 5, October 2009844promoted. In this study, it seems reasonable that the P removal efficiency of the system shows the same ten-dency with anaerobic P release rate because different Q 1 results in different PHA content of phosphorus re-moval organisms. In addition, P uptake is not com-plete in N13 until the end of system, which is typical in runs 3 and 4 (see Table 5). It suggests that the an-oxic and aerobic retention time in the first stage is not enough for P uptake, and the intracellular storage compounds PHA may be used in the following stages to finish the P uptake.Denitrifying phosphorus removal was also stud-ied for different feeding ratios. Compared to the aero-bic P uptake, the curve of specific anoxic P uptake rate is different. Fig. 4 shows that the maximum anoxic Puptake rate (q a ) of 1.58 mg·g ˉ1·h ˉ1 occurs in run 3 with 0.45Q total fed to the anaerobic zone, and the ratio of specific anoxic P uptake rate (q a ) to aerobic P uptake rate (q o ) is 0.68 accordingly. The higher q a /q o ratio is resulted from the UCT-type configuration, in which lots of PHA (COD) are available in the anoxic reactor for denitrifying before entering the aerobic reactor, so the anoxic P uptake rate is kept at a higher level and denitrifying P removal is enhanced gradually. The lower COD concentration of anaerobic effluent en-sures the intracellular compounds, like PHA, as a car-bon source with reducing power to assimilate P and synthesize polyP, at the same time, using nitrate as terminal electron acceptor. This reducing power provided by intracellular compounds guarantees the DNPAOs a dominative position in the competition with ordinary heterotrophic denitrifying bacteria. When Q 1 is in-creased from 0.45Q total to 0.60Q total , q a decreases from1.58 to 0.36 mg·g ˉ1·h ˉ1 (see Table 5). It suggests that more exogenous carbon sources in anaerobic effluent in run 4 stimulate the ordinary heterotrophic organ-isms (OHOs) to use nitrate as electron acceptor for heterotrophic denitrification in the anoxic zone, and anoxic phosphorus uptake occurs after available ex-ogenous carbon sources is depleted. However, due to the limited returned activated sludge, nitrate becomes a limiting factor for anoxic P uptake. The lower nitrate concentration in the anoxic zone (D1), below 0.4mg·L ˉ1 (Fig. 3), verifies the above analysis further-more. Summarize the above results, it is noted that the extent of anoxic phosphorus uptake is closely related to the presence of nitrate in the anoxic zone. If the system is operated such that the nitrate loading in the anoxic zone exceeds its denitrification potential, an-oxic phosphorus uptake will be enhanced and aerobic P uptake is reduced correspondingly in the aerobic zone, and vice versa , when returned nitrate is not suf-ficient. In the further investigations on denitrifying P removal in SFA 2/O systems, the effect of nitrate loadingTable 5 Summary of nutrient and organic substrate removal in different phasesStage 1Stage 2Stage 3Parameters InfluentA D1 N11 N12 N13D2N21N22N23D3N31N32 N33EffluentRemovalefficiency/%Run 1 TN 74.427.75 26.52 25.06 25.40 25.729.8426.6025.7727.9530.3429.9027.82 26.95 27.09 63.49 TP6.47 8.95 6.38 6.10 5.66 5.456.796.075.76 5.45 5.96 5.67 5.55 5.35 5.23 19.17 4NH -N 73.222.88 16.17 10.07 7.02 1.8320.1310.68 6.414.8827.2617.3910.04 5.88 5.94 91.893NO -N1.22 4.87 10.36 15.00 18.38 23.879.7115.9319.3623.072.5912.5217.78 21.07 21.15COD 253 79.8 31.58 35.59 31.08 25.5839.4230.5828.5930.5860.4642.1331.58 25.59 24.64 90.26 Run 2TN68.7 40.34 29.87 29.10 29.80 29.0029.3627.7827.4727.3319.0819.3818.74 18.35 19.00 72.35TP 6.19 11.24 6.88 6.04 5.66 5.08 6.784.144.08 3.98 3.36 3.02 3.06 3.18 3.07 50.41 4NH -N 67.739.98 25.41 12.07 4.68 1.6919.2611.366.122.3510.057.51 4.98 1.33 1.34 98.01 3NO -N 1.02 0.36 4.46 17.03 25.12 27.3110.1016.4221.3524.989.0311.8713.76 17.02 17.66COD 259 109.8 47.58 39.12 30.08 36.5942.1335.5828.7625.5835.5828.5630.08 27.58 31.58 87.80 Run 3TN61.8 44.46 31.51 27.44 28.59 29.0425.1625.7324.1624.0619.1617.6716.66 16.24 16.31 73.61TP 6.86 24.01 11.74 7.5 6.43 5.14 2.041.931.49 1.29 1.860.920.93 0.98 0.63 89.81 4NH -N 61.1 43.71 31.11 24.10 15.86 7.6218.6014.339.464.2711.287.02 4.80 0.92 1.22 98.0 3NO -N 0.79 0.75 0.40 3.34 12.73 21.416.5611.3914.7019.797.8710.6611.87 15.32 15.09COD 267 132.5 46.73 41.98 37.58 35.5845.1435.5825.7628.5837.5828.8628.58 27.76 35.74 86.59 Run 4 TN 71.1 57.18 43.74 41.00 37.65 35.9737.6433.9231.8929.2428.0927.7428.55 28.03 28.73 59.62 TP5.86 27.9 18.84 10.29 5.14 1.841.330.800.620.480.430.360.29 0.24 0.22 96.25 4NH -N 70.256.73 43.62 28.89 22.27 15.8628.0617.6910.37 6.7114.0310.078.85 3.66 2.8695.92 3NO -N 0.99 0.45 0.12 11.1 15.39 19.209.5816.2321.5222.5314.0617.6719.71 22.21 22.59COD 254 158.9 66.68 46.52 39.12 35.5839.5831.0835.5829.1230.0825.5624.08 22.08 25.26 90.05Chin. J. Chem. Eng., Vol. 17, No. 5, October 2009 845on anoxic P removal will be further substantiated in more detail.3.2 Characterization analysis of sludgeTo further investigate the effect of feeding pat-terns on the accumulation of PAOs and DNPAOs, batch tests were carried out in this study. Phosphate uptake rates under anoxic and aerobic conditions were measured in separate batch reactors. The activated sludge samples were obtained from the pilot scale SF A 2/O system when the system had been operated for 70 days. After confirming the complete phosphorous release in anaerobic phase, the anaerobic sludge was removed and divided into two parts equally. One was exposed to anoxic condition, and the other to aerobic condition. The results are compared to that from the seeding sludge (day 0), as showed in Fig. 5. The rates of anoxic (q a ) and aerobic phosphate uptake (q o ) onday 0 are 1.51 and 12.62 mg·g ˉ1·h ˉ1, respectively, and q a /q o is 11.96%. Based on the method provided by Wachtmeister et al . [21], in which the contribution of DNPAOs to the total phosphorus removal is calculated from the ratio q a /q o . It is estimated that the proportion of DNPAOs is 11.96% of total PAOs in the seeding sludge, though no anoxic time is provided for the cul-ture of seeding sludge. With the modified SFA 2/O system, the effect on the accumulation of PAOs and DNPAOs is expected to be different because of a changed biomass distribution in the system, and proved by the results on day 70. In Fig. 5 (b), the an-oxic and aerobic phosphate uptake rates are 5.24 and14.22 mg·g ˉ1·h ˉ1, respectively. The proportion of DNPAOs is increased from 11.96% to 36.85% of the total PAOs. Therefore, it is concluded that the DNPAOs are accumulated and enriched gradually in the modified step-feed A 2/O nutrient removal process, which presents a satisfactory performance for denitri-fying phosphorus removal.3.3 Nitrogen removal: Nitrification and denitrifi-cationFigure 6 shows the total N-removal of the system with different influent flow distribution ratios. Theinfluent TN concentration is 56.37 to 74.87mg·L ˉ1 and C/N is 3.23 to 5.17, which represents the charac-teristics of municipal wastewater in China. The aver-age ammonia removal efficiency from run 1 to run 4 is 91.89%, 98.01%, 98.0% and 95.92%. The higher ef-fluent ammonia of run1 may be due to the higher in-fluent flow rate of Q 3 (0.5Q total ) with the optimal coef-ficient method developed by Wang et al [23]. Nitrifica-tion is affected by influent ammonia loading signifi-cantly when the optimal coefficient is applied to treat low C/N sewage, which leads to a relatively short hy-draulic retention time in the third stage (3.2 h) and induces an incomplete ammonia removal. In Fig. 7 (a), the ammonia concentration in effluent of run 1 is 5.94mg·L ˉ1. In other three runs, higher oxygen concentra-tion with the descending influent distribution in each stage results in lower effluent ammonia, usually below1.0 mg·L ˉ1. However, due to the constant nitrification capacity of each stage, incomplete nitrification occurs frequently in stage 1 or stage 2 when Q 1 is higher, such as the situations in runs 3 and 4, shown in Figs. 7 (c) and 7 (d). The change of ammonia concentrationsuggests the importance of the feeding ratios to the(a) Day 0(b) Day 70Figure 5 Phosphate uptake tests under aerobic and anoxicconditions with the activated sludge from the A 2/O step-feedsystem on day 0 and day 70 Ʒaerobic;anoxicFigure 6 N removal with different influent flow distribu-tion ratios× influent TN; + effluent ammonia; ƺ effluent nitrate;efflu-ent TN; Ʒ ammonia removal efficiency; TN removal effi-ciencyChin. J. Chem. Eng., Vol. 17, No. 5, October 2009846nitrification process. The nitrification should be con-sidered when different influent feeding ratios are ap-plied especially in wastewater treatment systems with high ammonia loading and low C/N ratio.Figure 6 also shows that TN removal efficiencies is 63.49%, 72.35%, 73.61% and 59.62% from run 1 to run 4. Run 3 is more effective for TN removal since more nitrate is removed in anoxic zone (D1), which serves as electron acceptor for denitrifying phosphorus removal. As a result, more carbon source is saved for denitrification in the subsequent stages. In addition, the low concentration nitrate transferred into the an-aerobic zone reduces the competition of carbon source between ordinary heterotrophic denitrifying bacteria (OHOs) and phosphorus removing organisms, which enhances the phosphorus release significantly. More influent feeding to the anaerobic zone provides suffi-cient organic substrate for phosphorus release and more PHA is stored as intracellular compounds, which serves as the carbon source for phosphorus uptake in the anoxic or aerobic zone and improves the phospho-rus removal. When Q 1 is increased to 0.6Q total in run 4, however, the TN removal efficiency is the lowest, 59.62%. The higher COD concentration of anaerobic effluent and a little nitrate in anoxic zone, shown in Fig. 7 (a), suggests that the nitrate returned with acti-vated sludge to the anoxic zone, as terminal electron acceptor, is not enough for denitrifying phosphorus uptake or heterotrophic denitrification. As a result, the carbon source is wasted and denitrification rate is de-creased significantly.It is concluded from above results that higher Q 1 feeding rates supply sufficient organic compounds for sufficient phosphorus release and improve phosphorus removal, but the carbon source may be wasted and N-removal efficiency may decrease to a large extent. To avoid this situation, another internal nitrate recy-cling flow is suggested from the end of system to D1 as an alternate choice. To ensure stable operation, keep the nitrate at a lower but non-zero level in anoxic zone via real-time control of returned activated sludge and internal recycling flow would to be a feasible strategy.3.4 Removal of organic compoundsThe COD concentrations of the influent, anaero-bic effluent (A), anoxic effluents (D1), aerobic efflu-ent (N13) and final effluent are shown in Fig. 8. The effluent COD concentrations are maintained although the influent flow distribution ratios are different and the COD removal efficiency is 90.26%, 87.80%, 86.59% and 90.05% from run 1 to run 4. The COD profiles of anaerobic zone shows that the average COD concentration in run 1 is the lowest and it is the highest in run 4, fed with 0.15Q and 0.60Q , respec-tively. With the higher nitrate concentration and deni-trification rate in the anaerobic zone, the COD con-centrations in the anoxic zone are not different sig-nificantly in runs 1, 2 and 3. However, the anoxic ef-fluent COD concentration in run 4 is relatively high,66.68 mg·L ˉ1, which may be due to a lower Q r , so that the electron acceptors are not sufficient for denitrifica-tion in this zone.(a) Run 1(b) Run 2(c) Run 3(d) Run 4Figure 7 Concentration of ammonia and nitrate in dif-ferent reactor in each runƽ 4NH -N ; 3NO -N。