摘要
膜-生物反应器作为一种新型、高效的污水处理技术,具有诸多传统生物处理工艺所无法比拟的优点,在近年来已经广泛应用于城市生活污水以及工业废水的处理。目前,在国际膜-生物反应器市场上主要是平板膜-生物反应器和中空纤维膜-生物反应器两种。平板膜与中空纤维膜相比,具有水力学条件易于控制、通量高、抗污染能力强和清洗更换方便等特点,能够在更高污泥浓度条件下保持高通量稳定运行。但是,我国的平板膜-生物反应器的研究明显滞后,且平板膜-生物反应器的应用比例远远小于中空纤维膜-生物反应器,而在国际的膜-生物反应器市场上,平板膜-生物反应器的应用比例达到了68%(截止至2006年)。因此,加大平板膜-生物反应器的研发力度,构建我国膜-生物反应器的合理结构和布局,促进膜-生物反应器在我国的均衡发展,对膜-生物反应器技术的发展及其在水污染控制和污水资源化的应用具有重要的意义。
本论文主要借助于400m~3/d规模的平板膜-生物反应器和几套小试膜-生物反应器,跟踪研究平板膜-生物反应器在工程化应用中的主要问题。研究结论对平板膜-生物反应器在工程化应用中的设计及运行具有一定的借鉴和参考价值。
建设了400m~3/d的平板膜-生物反应器中水回用工程,并正常运行了一年半。该工程出水达到了《城市污水中水回用—杂排水水质标准GB18920-2002》中的水质要求,可以回用做厂区绿化、洗车用水;技术经济分析表明,采用中水回用代替自来水,可年节约自来水费用15.94万元;本工程的吨水能耗、清洗费用达到了国际同类产品的相同水平,膜价格更是具有很大的优势。
对平板膜-生物反应器的出水进行了长期跟踪,发现无论进水如何变化,出水COD、氨氮和SS均较为稳定;通过计算污泥的动力学系数表明,该工程的污泥净产率系数Y=0.225kgMLVSS/kgCOD,内源代谢系数K_d为0.0045 d~(-1)。
开发了膜组件边侧固定技术、自动在线清洗设备、可清洗式曝气管、事故紧急处理系统等工程化应用中的关键技术,并在本工程上得到了成功的应用,,大大提高了工程的稳定运行能力,方便了操作管理。
通过长期跟踪膜污染规律发现,在20L/m~2·h的通量下,正常运行TMP不超过20kPa,TMP增长到30kPa时就应进行在线化学清洗;处理化学一级强化处理后的城市污水时,平板膜的清洗周期比处理普通生活污水要短;对于不同水泵抽吸的上下支架,在上、下支架通量之比为1.15:1的条件下,可以实现两个支架TMP增长基本一致。
针对典型的城市合流污水,平均COD/TN为8.0,利用AO膜-生物反应器,出水COD、氨氮和TN去除率分别可以达到97%、99%和77.6%,出水能够稳定达到《城镇污水处理厂污染物排放标准GB18918-2002》中的一级A标准;
缺氧段HRT和硝化液回流比是TN去除的关键影响因素;在缺氧段HRT<3h条件下,增加缺氧段HRT能够显著提高TN去除率,而在缺氧段HRT>3h条件下,增加缺氧段HRT对于总氮去除无影响;在回流比r<100%条件下,增加r能够显著提高TN去除率,而在r>100%条件下,增加r对于TN去除无明显影响。
Membrane bioreactor (MBR) process has emerged as a new and efficient technology for wastewater treatment. Compared with conventional activated sludge (CAS) system, MBR process has many advantages. Therefore, MBR has been increasingly popular for the treatment of municipal and industrial wastewater in recent years. Nowdays, hollow-fiber membrane and flat-sheet membrane are the two major membrane types in MBRs. In international MBR market, flat-sheet membrane has been intensively studied and widely used due to its high flux, anti-fouling capability and easily-controlled hydraulic conditions. According to related statistics, flat-sheet MBRs accounted for 68% of the total full-scale MBRs throughout the world by the end of 2006; however, the research on flat-sheet MBR in China obviously lagged behind. Thus, intensive efforts must be dedicated to the research of flat-sheet MBR in our country in order to better promote the development of MBR technology and its engineering application on water pollution control and wastewater reuse in China.
The objective of this thesis is to study the key problems of flat-sheet membrane bioreactor for the engineering application by employing a full-scale MBR of 400m3/d under long-term operation and several lab-scale MBRs. The results were expected to provide a sound understanding of the design and operation of full-scale flat-sheet MBRs.
A 400m~3/d flat-sheet MBR used for reclaimed water reuse is established and works for one and a half years. The effluent water quality of this MBR including COD, ammonia, turbidity and pH was superior to that of the standard "water quality requirements for water resource reuse generated by municipal wastewater" (GB/T 18920-2002), and can be used for green watering and car washing. Based on economic assessment, MBR technology for water resource ruse could save 159.4 thousand Yuan per year. Comapared with international membrane companies, the energy consumption and cleaning costs of this application are quite close, and the costs of membrane replacement are much lower.
It was found that the MBR could bear the shocking load and effluent at low level of COD, ammonia and suspendend solid could be achieved though the influent water quality fluctuated. The net yield coefficient (Y) and endogeneous decay coefficient (Kd) of the pilot-scale MBR for municipal wastewater treatment was about 0.225 kgMLVSS/kgCOD and 0.0045 d~(-1), respectively.
The edge-side-fixing of the flat-sheet membrane module, the automatic chemical cleaing of MBR, the washable aeration tube and the emergency responsing system were established and had great effect in engineering application. The stability of MBR is improved and the operation is simplified.
Under the membrane flux of 20L/m~2·h, the operating TMP should not be more than 20kPa, and chemical cleaning must be carried out when the TMP was at 30kPa. When treating effluent of chemical primary enhance treatment, the cleaning period of flat-sheet membrane was much shorter. At the operating flux of 1.15:1, the TMP growth of the upper and lower membrane unit could be the same.
In the treatment of typical municipal wastewater, when the COD/TN was 8.0, The performance of a lab-scale AO-MBR showed that the effluent water quality including COD, ammonia and TN can achieve the I-A criteria specified in the "Pollutant Discharge Standard of Municipal Wastewater Treatment Plant" (GB/T 18918-2002).
The HRT_(anoxic) and the recycling ratio are the main factors influencing the TN removal efficiency. When HRT_(anoxic)<3h, the raise of HRT_(anoxic) can obviously improve the TN removal efficiency; and when HRT_(anoxic) >3h, the the raise of HRT_(anoxic) can hardly improve the TN removal efficiency. When recycling ratio r<100%, the increase of r can obviously improve the TN removal efficiency; and when HRT anoxic >3h, the the raise of HRT anoxic can hardly improve the TN removal efficiency.
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