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.
Operational experience at La Center WWTP in Washington, USA indicates that the cost of MBR technology may be lower than that of a conventional biological treatment process, despite the higher energy demand. La Center is a small city in Clark County, Washington, USA, with a population of 3,100. The wastewater treatment works at the town was originally constructed in 1967
Municipal wastewater usually contains between 4 and 12 mg/L total phosphorus (TP) concentrations in the range 4−12 mg/L. A conventional activated sludge process (CAS) can take this down to 2−4 mg/L, or 0.5−1 mg/L if an enhanced biological phosphorus removal (BPR) process is used. To achieve the levels required to suppress eutrophication, however, demands P levels of 0.01−0.3 mg/L
There has been a recent surge of interest in anaerobic MBRs. The technology provides the potential for removing COD with a net energy benefit from the methane generated, albeit without nutrient removal. Interest within academia is evidenced by the publication of five independent reviews of the subject in various learned journals in 2012 alone.