重力出流式膜生物反应器污泥浓度的优化控制

Optimization of Mixed Liquid Suspended Solids Concentration in a Membrane Bioreactor with Gravitational Draining

采用重力出流式膜生物反应器(MembraneBioreactor,MBR)工艺对生活污水进行了实验研究.重力出流式MBR是利用液位水头重力驱动出水,整个系统结构紧凑,操作简便.结果表明,随着污泥浓度增大(3.9～18.4g/L),同样的曝气强度对膜表面滤饼层的剪切能力降低,膜通量下降;污泥粘度从5.4mPa-s上升到680mPa-s,相应的污泥中的传氧系数与清水中的传氧系数之比α从0.89降到0.10.因此,从提高膜通量、氧传递速率和降低能耗的角度出发,将MBR的污泥浓度控制在适当范围是非常必要的.此外,当污泥浓度大于4.8g/L,污泥浓度的提高对有机物的去除、硝化以及反硝化速率的提高没有明显的贡献.因此,从MBR的处理能力和运行能耗的双重影响确定MBR的最佳处理污泥浓度值为4～6g/L,在该浓度区间,生物反应器系统对冲击负荷有较好的抵御能力,同时系统的运行能耗也较低.

In comparison with the conventional activated sludge process, membrane bioreactor （MBR） offers the advantages of a smaller footprint due to higher biomass concentrations and a complete removal of solids from the effluent. As aeration system for fouling control and oxygen supply counts for more than 90% of total energy cost in MBR, it is important for the design of the aeration system. Generally operational cost and mixed liquid suspended solids （MLSS） concentration were inversely proportional to each other, which means that membrane flux and a value are minimized when MLSS concentration is maximized and vice versa. Therefore, MLSS concentration was considered to be a key parameter for the operation of MBR. In order to achieve the optimum MLSS concentration, the relationship between these parameters （including membrane flux, a value and pollutant removal rate） and MLSS （3.9-18.4 g/L） were investigated in the study. It clearly showed that viscosity of sludge increased with higher MLSS. The viscosity of sludge increased from 5.4 mPa.s at MLSS of 4.8 g/L to 680 mPa.s at MLSS of 18.4 g/L. The relationship between viscosity of sludge and MLSS Can be indicated with the equation η=e^0.1635c＋0.055. The a value, which defines the relation of oxygen transfer in pure water to oxygen transfer in activated sludge, decreased from 0.89 at MLSS of 4.8 g/L to 0.10 at MLSS of 18.4 g/L. However, the MLSS concentration had no impact on pollutant removal rate of COD, NH4^＋-N and TN when MLSS exceeded 4.8 g/L. Therefore, optimum MLSS concentration was turned out to be 4 g/L to 6 g/L in the case of typical municipal wastewater.