Abstract: A method of operating an immersed membrane filtration system includes a step of providing a liquid flow, for example a recirculation flow, past the surface of the membranes to clean, or help clean, the membrane surface. Since immersed outside-in membranes are effectively filtering out clean water from the effluent, they are also dewatering the effluent. To avoid solids concentration, most immersed membrane systems require that a certain amount of effluent liquid is recirculated back to an area upstream of the membranes. This is called a recirculation flow in general and is, for example, associated with the flow of return activated sludge (RAS) in a membrane bioreactor (MBR). In systems and methods described herein, we control a recirculating flow to have enough energy to scour the surface of the membranes, thus combining its use of providing liquid to the membranes and scouring their surfaces.

Abstract: In an immersed membrane system, the influent flows into an open membrane tank. The membrane tank can have multiple horizontally spaced immersed membrane units. The immersed membrane units may have flat sheet membrane elements within a membrane case. One or more ducts are provided in the tank for directing the flow of influent to the immersed membrane units. In some examples, the influent is divided into sub-streams that are fed through baffles to a corresponding immersed membrane unit, optionally in generally equal amounts, optionally in a single pass flow pattern. In a process of operating a membrane tank, the influent flow is directed across the bottom of the membrane tank and divided into multiple portions. Each of the multiple portions is fed directly to the bottom of a corresponding immersed membrane unit located in the tank. The influent may be mixed liquor in a membrane bioreactor (MBR).

Abstract: An immersed membranes uses aeration (air bubbles rising past the membranes) as a means to scour the membrane surface and keep it clean from solids, or foulants, allowing for continuous and effective operation. In a module of flat sheet membranes, fine bubble aeration is used to create and maintain space between the membrane sheets. The bubbles inhibit the sheets from touching and clogging together, thus reducing their surface area and their productivity. The aeration may be used for scouring, to supply oxygen to biomass and as a spacer to maintain the working surface area of immersed flat sheet membranes. The face-to-face spacing between the membrane sheets may be 4 mm or less. The bubbles may be less than twice the face-to-face spacing between the membrane sheets.