Some clogging occurs in most MBR systems regardless of membrane module type or geometry. Prevention or control measures are typically considered at the system design level and during operation. Examples include fine screening of raw wastewater and rescreening of mixed liquor. But even with adequate pre-treatment, clogging can still occur and require remediation protocols and/or specialist equipment.
Features - Membrane operation
The integrated fixed-film activated sludge membrane bioreactor (IFAS-MBR): comparison with a regular MBR for nutrient removal
The IFAS-MBR process is less well explored than the MBBR-MBR configuration. It is of interest to establish the performance of the IFAS-MBR when challenged with a variable influent C/N ratio, since this affects both nutrient removal and the emission of N2O – a highly active greenhouse gas (GHG).
Ragging is a type of clogging, where clogging relates to agglomeration of solids in the membrane tank. In the case of ragging, the filament solids from textile materials join together to form long rags or braids. These rags, which may contain filaments no more than a few mm in length, are mechanically stable in the mixed liquor and can block the inlet channels of the membrane module and/or wrap themselves around the infrastructure of the membrane tank – including the aerators.
The arguments surrounding the precise target sludge (or mixed liquor suspended solids, MLSS) concentration to use when running an MBR are pretty well developed but what is it that ultimately sets the solids concentration range?
It is most often assumed that the main cost associated with operating a membrane separation plant relates to the energy consumption, followed by the membrane replacement. Consequently, considerable efforts have been devoted to fouling control and mitigation, with more than one fifth of all MBR research literature publications devoted to this topic (Judd, 2017).
Clogging can take place within MBR module channels as a thick deposit which fills the channel (‘sludging’ or ‘localised dewatering’). Sometimes long rags or braids can develop in the tank itself which wrap around the membrane tank infrastructure (‘ragging’ or ‘braiding’). Chemical cleans are largely ineffective since they can only attack the foulants on the membrane surface, so leaving the clogged material filling the membrane channels largely unaltered. Cranfield University and Qatar University have completed work on this largely neglected research area.