Combining submerged membrane technology with anaerobic and ...

Introductionof water. Energy savings can be achieved by injecting air into the base of the verticalmembrane modules, obtaining an airlift effect and avoiding the use of a pump (reaching1.2 kWh·m -3 of purified water).The first systems developed were small-scale and industrial scale applications,treating small volumes of wastewater streams with high organic loads. In any case,operational costs remained high, with special emphasis on the modules and the powerconsumption, limiting the competitiveness of the technology compared to conventionalprocesses.In the eighties started the development of filtration membranes on a larger scale,especially on three fronts: North America, Japan and Europe. Many types of membraneswere then developed specifically for the food industry. Nevertheless, the ease with whichthe modules rupture occurred generated distrust and uncertainty.In the early nineties, the membrane modules were optimized, developing newmodels more robust and reliable. The Japanese government launched an ambitious R&Dproject which led to the most important technological and industrial advance of the MBRprocess, with the development of submerged membrane modules, resulting in thesubmerged MBR membrane (figure 1.5B). In these systems the membrane module issubmerged in the aeration tank, in contact with the mixed liquor. Therefore it was possibleto suppress the pump that was used to drive the sludge and replace it for another pumpthat suck the filtered effluent or permeate from the membrane module. Thus there was asignificant reduction in investment and operation costs due to the reduction andsimplification of equipment and energy saving was needed to pump the sludge. Energyconsumption associated with water treatment by submerged MBR is between 0.55-1.5kWh·m -3 depending on configuration and membrane technology (Judd, 2011) and is higherthan that observed in well operated CAS reactors (0.38 to 0.48 kWh·m -3 , Evans andLaughton, 1994). Similarly, the costs and the operational problems decreased, emergingnew markets as well as pharmaceutical and food industries.In most of the first submerged MBR membrane modules were installed in the sametank where the influent was received. However there is a tendency today to remove themembrane from the influent inlet using an additional chamber to immerse membranemodules. This external submerged MBR configuration (figure 1.5C) significantly reducesmembrane fouling.35