Filtration of natural organic matter using ultrafiltration membranes for drinking water purposes: circular cross-flow compared with stirred dead end flow

Application of ultrafiltration membranes for removal of humic acids is investigated below. Membrane filtration processes were compared using two different set-ups: circular flow and stirred dead end flow. The transmembrane pressure, temperature, feed concentration, pH, ionic strength and shear stresses applied on the membrane surfaces were kept constant whilst the permeate flux and solute rejection were measured during the experiments with both set-ups. It was shown that the rejection (both the observed and the true rejection) in the case of circular flow was higher than in the case of dead end flow. The mass transfer coefficients were determined for both set-ups. In the case of stirred dead end, it ranged in from 2.14 to 4.72 × 10−6 m/s; however, for circular cross flow system, the mass transfer coefficients were found in the range 2.24–3.22 × 10−5 m/s. Comparison of the mass transfer coefficients obtained for both systems showed that it was significantly higher for circular flow systems as compared with stirred dead end system at similar operating conditions. Energy consumed per volume of purified water by circular flow system (0.345 kW) was found to be much lower when by stirred dead end system (0.955 kW). This proved that the performance of circular flow system was more efficient in terms of rejection, mass transfer coefficient and energy consumption.