Operational costs in MBRs are marginally higher than those of conventional activated sludge (CAS). Firstly, permeating water through a membrane demands energy. In the case of the immersed technologies (iMBRs) this means that the overall specific aeration demand (SAD) is higher, since air is needed both for maintaining the process biology in the aeration tank and scouring the immersed membrane.
Features - Membrane operation
In autumn 2015, after two years of research and development, Pentair brought to market its new ‘Helix’ product. An enhancement to X-Flow tubular membrane technology, Helix features a helically-winding ridge on the inside of the membrane which is designed to tackle cake build-up and enhance flux. The technology has so far been tested on both industrial effluents and municipal wastewater.
Key facets to take into account when selecting a screen for your MBR design include the screenings capture ratio, screen apertures, screening flow velocity, ancillary processes and coarse suspended solids, and screen maintenance. The screenings capture ratio (SCR) represents the amount of solids removed by the screen as a proportion of the total coarse solids load, and as such is analogous to membrane rejection.
The importance of screening upstream of a membrane bioreactor remains a key concern for MBR practitioners. Screening protects the membrane from mechanical damage from sharp or abrasive particles and from clogging from hair and matted cotton fibre. While any screen is better than no screen at all, it is critically important to have a properly designed and sized screening system.
While most scientific articles about MBR systems suggest membrane surface fouling as being the main operational limitation for the technology, it is widely recognised by practitioners that clogging phenomena – possibly related to inefficient pre-treatment – are at least as important. It is also recognised that clogging takes different forms...
There is little doubt that, of the challenges faced in MBR operation, recovery of permeability is arguably the most critical. When the routine maintenance membrane clean fails to achieve the required recovery and more aggressive recovery cleans are also found wanting, then ex-situ cleaning becomes necessary. This invariably incurs extensive manual intervention, not always with guaranteed success.