Pulsatile flow may increase performance of ultrafiltration
Treatment of stormwater with a pulsatile liquid flow on ultrafiltration membranes may improve purification properties.
Today, stormwater treatment becomes increasingly important. From the environmental aspect, it is vital to remove the pollutants before releasing stormwater to the water bodies. In addition, in dry and semi dry regions, stormwater treatment is important prior to water re-use. Membrane processes have gained a lot of attention especially in water and wastewater treatment industries due to their high removal efficiency. Why not use these processes in stormwater treatment? One of the challenges of membranes is fouling. To postpone fouling, it is necessary to have a suitable pre-treatment. In addition, periodical membrane cleaning is recommended.
“Currently, I am putting the pieces of the puzzle together including appropriate pre-treatment and cleaning methods that are compatible with the properties of the stormwater to be treated. The stormwater consists of melted snow in these experiments. Also, I am assessing a polymeric ultrafiltration membrane and the quality of the produced water,” Saida Kaykhaii, PhD candidate in Urban Water Engineering, explains.
To postpone fouling as much as possible, pulsatile fluid flow will be used to help cleaning the membrane. The mechanism of pulsatile flow is thinning the boundary layer on the membrane, shooting particles to bulk flow and preventing them to stick to the membrane surface. In addition, sedimentation will be used as pre-treatment (see figure below for experiments schematic).
Preliminary results from my first experiments have shown that after ultrafiltration the process turbidity and TSS content of melted snow decreased to zero showing good efficiency of the membranes. In addition, the results indicate that the ultrafiltration membrane process has good ability to remove TOC, total as well as dissolved metals.
In comparison to steady flow, using pulsatile flow with a pulse frequency of 4 Hz increased the productability – the volume of permeate water - of membrane and time of the experiment more than twice which means using pulsatile flow may postpone fouling. The pressure measurements showed that using pulsatile flow moderates the transmembrane pressure variation. TOC was reduced more efficiently with pulsatile flow compared to steady flow. Most important, when pulsatile flow was used rather than steady flow, flux declines slower which indicates that pulsatile flow may support removing particles from the membrane surface.
