Mechanical influence of PAC particles on membrane processes

Nanofiltration cross-flow experiments have been performed with powdered activated carbon (PAC) suspended in a solution of 1 g/l MgSO4 in water. Depending on the shear rate of the experiments PAC causes either a decrease in permeate flux and rejection or a decrease of rejection and an increase of permeate flux. The first can be explained by the formation of a particle layer which hinders the back transport of solutes, the second by membrane abrasion. The transition from hindered back transport to membrane abrasion is in the region of 12,000–20,000 s−1. This result is independent of feed pressure, orientation of the test cell and distance from the entrance of the test cell. The rate of membrane abrasion seems to increase with distance from the entrance of the test cell.