Full Permeability Recovery of Dewatered MBR Membranes

Submerged membranes are subjected to unique fouling mechanisms that occur at the microscopic level and at generally controllable rates. However, in some cases, fouling can occur at the macroscopic level in the form of localized caking or dewatering of solids. Dewatered sludge can result in reduced performance, flux decline, high energy consumption (1) and require mechanical or manual cleaning to remove. The phenomenon of localized dewatering is not unique to one technology and generally results from a combination of poor screening, unequal flow splitting and insufficient air scouring at elevated MLSS concentrations.The effects of dewatering (also called sludging or plugging) are fairly well documented for hollow-fiber membrane technology but not as well understood for flat-plate membrane equipment. Based on a survey of 130 North American facilities using flatplate membrane equipment, dewatering has been observed in 21 plants and generally occurs during the first year of operation only. Dewatering is usually isolated to specific reactors (not the whole plant) and its affects are short-lived. It is estimated that combined plant performance was impacted less than 0.6% of the time in service for plants surveyed. New chemical cleaning and mechanical cleaning methods are presented for addressing localized dewatering.