Reverse-pressure back-flush in pilot scale, dead-end ultrafiltration of surface water

A simple protocol that makes use of the inertia of water to generate a rapid negative pressure differential across capillary ultrafiltration membranes is reported. This short-interval back-flush technique, preceded by cross-flow forward flush, was evaluated as an alternative to conventional back-flush to maintain membrane flux productivity in a pilot dead-end filtration application. Intermittent back-flush conditions are created when a reverse-pressure pulse, during which product is drawn in the reverse direction through the membrane wall, is introduced. The duration of the negative pressure-pulse peak is very short (1–2 s), after which it subsides and levels out in accordance with the net positive suction head of the centrifugal pump used to recirculate the feed. Reverse-pressure spikes of up to −90 kPa, which subside after only a few second to −40 kPa, were generated. The combined effect of reverse-pressure pulsation sequence of events is that of (i) a short back-flush (direct result of negative trans-membrane pressure conditions that are introduced) and (ii) flow destabilisation (sudden retardation and start-up of lumen-flow) during a forward flush that precedes the reverse-pressure pulse event. The reverse-pressure pulse technique was evaluated in a dead-end filtration pilot study producing potable water from a surface resource without the addition of chemicals. The membranes suffered no adverse effects and their flux performance was maintained reasonably well, even though the feed water turbidity reached values as high as 90 NTU during the exercise.