Sammendrag
Membrane filtration of surface water for removal of turbidity and natural organic matter (NOM) is becoming increasingly widespread. In view of proposed regulations addressing the removal of precursors to disinfection by-products, membrane filtration is an economic alternative to conventional processes for drinking water production. Furthermore, membranes are physical barriers to various microorganisms and the filtered water quality is very consistent. Ultrafiltration (UF) and microfiltration (MF) processes achieve complete removal of suspended solids (including bacteria, algae, and protozoa) at lower operating pressures and higher permeate fluxes than nanofiltration. However, UF removes dissolved compounds such as NOM only to a certain extend depending on the pore size of the membrane. MF does not remove dissolved compounds unless they are adsorbed to particles. Chemical pretreatment by coagulation/flocculation enhances the separation efficiency of UF and MF membranes with respect to dissolved pollutants and controls membrane fouling. Consequently, high permeate fluxes can be achieved at lower transmembrane pressures without a major deterioration of the permeate quality. Conversely, the advantages of chemical addition and MF or UF treatment can be offset by cost for chemicals and sludge treatment. Special attention will be given to chitosan, an organic biopolymer derived from chitin. Experiments will be carried out on a pilot-scale unit using a immersed hollow-fiber membrane module provided by Zenon Environmental Inc. The module is operated in outside-in mode and equipped with a set of diffusors in the bottom end. Aeration creates turbulence in the vicinity of the fibers to control concentration polarisation and fouling.
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