ABSTRACT
The current membrane bioreactor (MBR) technology based on submerged membranes technology is the product of numerous trials and errors throughout the last two or three decades. Many misunderstandings, underexpectations and overexpectations, and misguidances have been corrected. The following are some of the remarkable findings during this time:
• The necessity for fine screens to remove debris was often underestimated in the early days. This was partly because membranes were erroneously considered compatible with debris. The clogging/ragging of membranes by fibrous materials is detrimental for the membrane system. The debris caught by hollow fiber bundles can only be removed manually after disassembling the cassette. The sludge cake plugging the channels in flat sheet membranes can be removed by mechanical surface scraping after taking all membrane panels out from the cassette. As discussed in Section 6.2, membrane system operation can be hampered by debris when mechanical prescreens do not function properly regardless of the membrane type. Although prescreens with 1 to 3 mm mesh size have been routinely used, this problem is still one of the most common issue along with excessive membrane fouling due to the selection of improper screen types, improper installation that allows leaking debris, inherent limitation of screens in removing fibrous materials, etc. (Stefanski et al. 2011).
