Efficient Wastewater Treatment With Membrane Bioreactors
Technical Know-How Improves Performance
Industrial areas are often limited in space and room for expansion. By implementing the membrane as a secure ”shield” against all particles, the actual load of total solids in the activated sludge can be increased to 10 to 12 g/l (conventional plants operate with 3-5 g/l). This in turn results in a much smaller filtration chamber—often times up to 2-3 times smaller than a conventional WWTP.
Besides using an MBR as a space-saving technology, MBRs also represent an important feature of wastewater treatment plants when treating very complex wastewater, for example containing micro-pollutants. The biological treatment process of such highly polluted wastewater does not remove all micro-pollutants. Further treatment steps are required. By applying an MBR and therefore providing particle-free wastewater, the following treatment steps with ozone and/or activated carbon can be sized and operated much more efficiently. The treatment with ozone will break up the dissolved micro-pollutants. The activated carbon can absorb the micro-pollutants. Both options become more economic when an MBR is included. The chemical and pharmaceutical industry as well as the farming industry will benefit comparably from such systems.
In order to further improve these systems the cleaning strategy for the membrane and energy efficiency of an MBR are of importance. A clean membrane allows for a higher flux, which in turn results in lower energy consumption for the same amount of wastewater. The recently developed mechanical cleaning process for submerged membranes (MCP: mechanical cleaning process) is the latest innovation in the wastewater treatment sector. It was specifically developed for the above mentioned modules that use laminated membranes which are backwashable.
When applying MCP, polymeric granules are added to the wastewater to mechanically clean the membrane surface. The aforementioned cross flow aeration will move the beads along the membrane surface. The contact of the beads with the membrane surface will break up the layer on the membrane and the cross flow aeration will move it away from the membrane. The result is a very clean membrane throughout the entire operating cycle.
By applying MCP to the MBR process a multitude of advantages can be observed. Not only is the need for chemical cleaning decreased to almost zero, but the average flux is increased by approximately 25%. This results in less membrane area needed and therefore smaller filtration chambers. If less membrane area is needed for the same amount of wastewater, then overall energy consumption is reduced.
In summary, MBR plants overall have a lot to offer to the operator. The capacity of existing WWTPs can be increased. Small ecological footprint allows for efficient wastewater treatment even if space is limited. The high quality of the effluent allows for a range of potential re-use applications. In combination with other treatment processes, even very complex wastewater streams can be treated efficiently.