A new immersed membrane for pretreatment to reverse osmosis

Ultrafiltration is an ideal pretreatment method for reverse osmosis because it allows removing suspended solids and colloidal materials completely and reliably without chemicals. This paper introduces the ZeeWeed® 1000 immersed membrane and its application for seawater ultrafiltration. ZeeWeed® 1000 is a new version of the ZeeWeed® immersed membrane designed to minimize life cycle costs. The building blocks of a ZeeWeed® 1000 filtration system are parallelepiped membrane elements. Cassettes are built by assembling elements in the vertical and horizontal dimensions to fill tanks of various depths and sizes. This lead to the construction of very small footprint plants. The ZeeWeed® 1000 system is operated as a simple semi-batch process where filtration and backwash alternate in sequence. In filtration mode, permeate is drawn through the membranes as a result of the negative pressure applied to the permeate network. Filtration is direct (dead-end), without aeration. All particulate materials rejected by the membrane are left behind in the tank, and accumulate near the membrane surface. In backwash mode, the membrane is back-pulsed with permeate while air and feed water are injected to aid in dislodging the rejected particulate materials from the membrane surface. This process is efficient in de-concentrating the membranes without emptying the tank. The ZeeWeed® 1000 was evaluated in several pilot studies on different types of water. Typical results on an open seawater will be presented.