污水处理的英文文献翻译(1)

Nutrient removal in an A2O-MBR reactor with sludge
reduction
ABSTRACT
In 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; TMP
1. Introduction
Excess 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 (Wen
et 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 phosphorous
concentration 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. Methods
2.1. Wastewater
The 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-MBR
The 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 in
aerobic 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 pump
was 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 sludge
Mixed 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-chemically
digested sludge was amenable to further anaerobic bio-degradation (Vlyssides and Karlis, 2004), so it was sent to theanaerobic basin of the MBR
2.4. Phosphorus recovery
Lime 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 analysis
COD, 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 discussion
Fig. 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 COD
reported 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 the
first 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%.。

From the results it can be concluded that PAO organisms were not affected by thermo chemical pretreatment and TP in the effluent was found to be less than 1 mg/L throughout the study period.
Fig.3 presents data on phosphorus profile of the sludge during the thermo chemical digestion. In the process of thermo chemical digestion, the bound phosphorous in the biosolids was solubilised and released into the solution. The phosphorous solubilisation was found to be in the range of 45-50%. The alkali increases the pH of the digested mixed liquor and was in the range of 9.2-9.8. This high pH range was favorable for phosphorous removal using calcium salt. The phosphorous removal in the supernatant was carried out using lime at a mole ratio of 2.1:1.
4. Conclusions
Stable operation of MBR process was possible without significant accumulation of biomass when a part of the biological solids were disintegrated with alkali at pH 11 and temperature 75℃.Thermo chemical sludge digestion favors the recovery of phosphorous in the
supernatant using calcium salts. The system can run for a long period of time with any further detoriation in TP removal efficiency. Further studies focusing on fate of disintegrated sludge are in progress. References
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在一个A2O-MBR反应器中实现污泥的脱氮除磷技术
摘要
在目前的研究中,一种先进的污水处理工艺研制出了在A2O-MBR过程合并减少剩余污泥和回收磷的技术。

A2O-MBR反应器在17LMH流量下连续运行210天。

然后在两周内逐步提高设计流量。

这座反应器运行在两种不同的MLSS范围。

热化学消化污泥运行在一个固定的pH值(11)和温度(75℃)下，可溶解的COD 含量为25%。

释放出的磷通过沉淀，转化为有机物等过程被送回厌氧罐。

污泥的厌氧消化对COD和总磷的去除没有任何影响。

反应器在210天的运行中,MBR通过膜过滤压差保持相对稳定。

研究结果表明,所提出的流程配置在不降低处理水水质的情况下，有可能减少剩余污泥的产生。

关键词：A2O反应器；MBR；脱氮除磷技术；TMP
1.引言
剩余污泥的减少和脱氮除磷是污水处理厂两个相关的重要课题。

MBR过程由于具有更长的污泥龄，所以处理程度更高,污泥的产量相对较低(Wen et al., 2004)。

在MBR反应器内污泥的产量大概降低28-68%，这取决于所用的污泥龄(Xia et al.,2008)。

然而，通过减少污泥龄来降低污泥产量是受到限制的，因为生物膜上聚集太多的MLSS可能会有潜在的危害(Yoon et al., 2004)。

在MBR 反应器内这个问题可以通过引进污泥分解技术来解决。

据报道，污泥分解技术可以提高污泥的可生化性能(Vlyssides and Karlis, 2004)。

总体来说，污泥的消化分解和生化处理是污泥减量化处理的基础。

最新的技术提供了一些很有前途的污泥分解技术，包括：超声波分解(Guo et al., 2008)、脉冲动力分解(Choi et al.,2006)、臭氧氧化(Weemaes et al., 2000)、热分解(Kim et al., 2003)、碱催化分解(Li et al., 2008)、酸催化分解(Kim et al., 2003)、热化学分解
(Vlyssides and Karlis, 2004)。

在这些分解技术中，热化学分解法被认为是最简单而且最有效的方法(Weemaes and Verstraete, 1998)，在热化学分解法中，氢氧化钠水解法又被认为是最为有效的方法，(Rocker et al., 1999).。

一般来说，在A2O工艺过程中既可以脱氮也可以除磷。

同时，这对在一个构筑物内，通过一系列的工艺，同步去除有机物也是很有利的(Tchobanoglous et al., 2003).。

磷的去除主要是在有氧与缺氧交替的情况下通过聚磷微生物的过度摄取而达到的。

在污泥的预处理中，一定量的可溶解磷将被投加，它可以增加磷在污水中的聚合度(Nishimura, 2001)。

所以，在这些可溶解磷进入河流之前一定要去除掉。

此外，工业化对磷资源的需求在不断地增长，在许多发达国家，一些研究已经开始着手从剩余污泥中提取磷资源，释放的磷通过钙盐沉淀析出的方法提取。

考虑到这种情况，在最近的研究中，一些新式的处理工艺已经将三个过程整合在一起：一：在MBR工艺中进行热化学分解以进行污泥减量化处理；二：A2O工艺进行生物脱氮除磷；三：通过钙盐沉淀析出提取磷。

取得的数据然后用来评价这种混合系统的性能。

2.方法
2.1 废水
经过预处理的废水作为原水流入。

这种进水中含有混合碳源、大量的营养元素、一个碱度控制系统(NaHCO3)和一些微量元素，主要成分包括：(/L)210毫克葡萄糖、200毫克NH4C1、220毫克NaHCO3,22～34毫克KH2PO4。

微量元素包括：0.19 mg MnCl2·4H2O, 0.0018 mg ZnCl2·2H2O, 0.022 mg CuCl2·2H2O, 5.6 mg MgSO4·7H2O, 0.88 mg FeCl3·6H2O, 1.3 mg CaCl2·2H2O。

这种混合污水每周准备三次，并且化学需氧量(COD)为210 ±1.5 mg/L, 总氮(TN)为40±1 mg/L和总磷(TP)为 5.5 mg/L。

2.2 A2O-MBR处理器
A2O-MBR处理器，好氧部分的工作容积是83.4L，用一个挡板将它分为三部分，其中厌氧部分8.4L，缺氧部分25L，好氧部分50L，混合的污水通过泵吸的方式以一定的流速流入处理器中。

一个流速传感器被安置在好氧池的底部来控制进水的流速。

厌氧池、缺氧池、好氧池的水力停留时间分别是1h、3h、6h.为了更好地脱氮除磷，该装置设置了两种内循环，循环一是在厌氧段与缺氧段中进行，循环二是在好氧段与缺氧段中进行，厌氧段与缺氧段以较低的转速混合，以保证混合物中的悬浮固体始终处于悬浮状态。

在好氧区域，曝气头被用来提供氧气以使有机物得到氧化和氨化，好氧池中的氧气浓度维持在3.5 mg/1，并通过溶解氧在线检测仪来控制。

在五块大小为0.23pm的滤膜作用下，好氧池中发生固液分离。

每块滤膜的工作面积为0.1m2。

它们通过普通的管道被连在一起。

一个真空泵连在管上以提供负压。

在通常的管道中安装压力测量仪表来测定管内压力。

泵的工作时间自动控制，每启动10分钟后自动关闭2分钟，如此循环。

2.3 热化学分解污泥
从MBR的好氧段流出的混合液体每日约有1.5%的流量被截留然后进入热化学消化系统，热化学消解反应运行在一个固定的pH 11(氢氧化钠)和温度为75℃，运行时间为3小时。

经过热化学消解反应后悬浮物与污泥分离，经过消解的污泥可用于后续的厌氧生物化学反应(Vlyssides and Karlis, 2004)。

所以这些污泥会被送入MBR反应器的厌氧段。

2.4 磷的回收
生石灰被用来做沉淀剂以回收浮在表面的含磷化合物，经过回收处理后的悬浮物被送回缺氧池用作碳源和氮源。

2.5 化学分解
对废水中的COD, MLSS, TP, TN应进行详细的分析(详见APHA方法,2003)，进水和出水中的氨氮含量通过离子选择性电极来测定(Thereto Orion, Model: 95一12)。

分析样品中硝态氮减少量使用镉分析的方法(APHA,2003。

3.结果与讨论
图一数据记录了运行过程中反应器内MLSS的浓度，MBR反应器的一个优点是它可以在高浓度的MLSS下正常运行，反应器所用的EBPR污泥来自韩国的Kiheung污水处理厂。

反应器开始运行的MLSS浓度是5700 mg/L，并随着时间的增加逐渐增加MLSS的浓度，到第38天时MLSS的浓度已经达到8100 mg/L。

从此时起，通过回收剩余污泥来使MLSS的浓
度维持在7500 mg/L，这个过程叫做步骤一。

在表一中对缺少
污泥消化（步骤一）与具备污泥消化所得数据进行了对比，具
备污泥消化的试验负荷为0.12 gMLSS/gCOD.，与传统的活性
污泥法0.4 gMLSS/gCOD相比相对低些(Tchoba-noglous et al., 2003)。

在高浓度MLSS下处理量较低(Visva-nathan et al., 2000)，因此MBR工艺的处理能力应该小些。

Rosenberger et al.
等人建议采用MLSS的浓度范围(7.5一10.5 g/L)作为判断的指标。

在他们的研究中，他们指出，通常情况下，在中等浓度(7
一12 g/L).的MLSS浓度下，MLSS的增加对处理结果并没有
影响。

从这些数据可以看出，即便是引入污泥消化预处理，A2O的脱氮除磷效率也并没得到改变。

一个实验分析显示，这些显示经过污泥消化和不经过污泥消化处理的试验数据并没有达到统计上的显著水平。

然而，在污水处理过程中，包括污泥消化过程，出水的水质会越来越坏，这是因为一些可溶但不可降解的微生物产物的释放(Ya-sui and Shibata, 1994; Salcai et al., 1997; Yoon et al., 2004)。

在研究期间，溶解性化学需氧量在18-38 mg/L的水平上，对应出水中有机物的含量为4-12mg/L.。

这些数据证明，在保证良好的和稳定的出水水质方面，膜法隔离起着重要的作用。

磷元素是引起海洋赤潮的主要营养元素，因此减少出水中磷元素的含量十分必要。

幸运的是磷元素的总含量一直维持在 1 mg/L(Mer-vat and Logan, 1996)。

图二数据显示在该研究中，A2O-MBR处理系统对磷的去除效率。

即便是引入了污泥消化处理，A/O工艺对磷的去除效果也并不理想。

在最新的研究中，通过生石灰吸收的方式使可溶性的磷元素变成磷酸盐沉淀，并在处理水流入河流之前被回收，所以由于污泥减量化处理而使出水中磷元素含量升高的可能性被大大减小。

进水的磷元素浓度在5.5 mg/L左右，经过四周的处理，出水中磷元素的含量已经降到2.5 mg/L。

开始磷的去除率比较低是因为聚磷微生物的生长率比较低，并且一些像缺氧这样的运行环境
也不具备。

经过最初一段时间，磷的去除效率逐渐提高。

在A2O 工艺中磷的去除主要靠聚磷微生物的过量摄取，这些微生物生长缓慢，并且易受外界环境的影响(Carlos et al., 2008)。

在整个研究中，磷的去除率基本不受影响，一直处在74-82%。

从实验的结果来看，热化学预处理对聚磷微生物基本无影响，在研究中，出水中磷的浓度一直维持在1 mg/L以下。

图表三揭示热化学分解中磷元素的状况。

在热化学分解过程中，生物体中固定的磷被溶解并被释放到溶液中。

被溶解的磷大概占到45-50%。

碱性物质被投加以增加溶液的PH使其保持在9.2-9.8.，这样的PH有利于形成磷酸盐以除去磷元素。

溶液表面的磷可以通过投加生石灰吸收来除去，投加的比例为摩尔比2.1:1。

4.结论
在PH为11和温度为75℃的条件下，当一部分固体微生物用碱进行消解时，MBR工艺仍能够稳定的运行。

热化学消解法中可以用钙盐来回收浮在表面的磷元素。

这个系统可以在保证除磷效率的情况下长期运行。

关于污泥消化的进一步研究正在进行中。

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