Cornel P, Wagner M, Krause S
Darmstadt University of Technology, Institute WAR, Wastewater Technology, Petersenstr. 13, 64287 Darmstadt, Germany.
Water Sci Technol. 2003;47(11):313-9.
In membrane bioreactors (MBRs) for wastewater treatment the secondary clarifier is replaced by a membrane filtration. The advantage of this process is a complete removal of solids from the effluent and a small footprint due to possible high biomass concentrations (MLSS). As oxygen supply counts for more than 70% of total energy cost in municipal WWTPs the design of the aeration system is vital for efficient operation. In this respect the alpha-value is an important influencing factor. The alpha-value depends on the MLSS-concentration as shown in various publications and confirmed by own measurements in two full scale municipal MBRs with MLSS ranging from 7 and 17 kg/m3. Furthermore it must be taken into account that alpha-values are not static values; they vary with loading rates, surfactant concentrations, air flow rates, MLSS concentrations, etc. The average alpha-value at typical 12 kg/m3 MLSS for municipal MBRs is about 0.6 +/- 0.1. As submerged configured MBRs are equipped with an additional coarse bubble "crossflow" aeration system for fouling control, supplementary energy is consumed. Therefore MBRs need more energy compared to conventional treatment plants. Measurements of both aeration systems show that the fine bubble aeration system is more efficient by a factor of three concerning oxygen supply compared to the coarse bubble system.
在用于污水处理的膜生物反应器（MBR）中，二次沉淀池被膜过滤所取代。该工艺的优点是能从废水中完全去除固体，并且由于可能存在的高生物量浓度（混合液悬浮固体，MLSS）而占地面积小。由于在城市污水处理厂中氧气供应占总能源成本的70%以上，曝气系统的设计对于高效运行至关重要。在这方面，α值是一个重要的影响因素。如各种出版物所示，并通过在两个全尺寸城市MBR中进行的自身测量得到证实，α值取决于MLSS浓度，这两个MBR的MLSS范围为7至17 kg/m³。此外，必须考虑到α值不是固定值；它们会随负荷率、表面活性剂浓度、空气流速、MLSS浓度等而变化。城市MBR在典型的12 kg/m³ MLSS时的平均α值约为0.6 +/- 0.1。由于浸没式MBR配备了用于防止膜污染的额外粗气泡“错流”曝气系统，会消耗额外的能量。因此，与传统处理厂相比，MBR需要更多能量。对两种曝气系统的测量表明，在氧气供应方面，细气泡曝气系统比粗气泡系统效率高三倍。
