Study On The Key Problems Of Flat-sheet Membrane Bioreactor For Engineering Application

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 400m³/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/m²·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.