Impact of coagulation conditions on the in-line coagulation/UF process for drinking water production

An in-line coagulation (without settling)/UF process has been studied to improve membrane performance and water quality for surface water treatment. Using coagulation before UF increases permeate quality; the extent of dissolved organic matter removal is controlled by the coagulation step. Efficient coagulation conditions for a coagulation/settling process can be applied for the in-line coagulation/UF process and membrane fouling is reduced. Floc cake resistance is lower than resistance due to the unsettled floc and the uncoagulated organics. For an insideout hollow-fiber system, the impact of coagulation dose depends on filtration mode: for instance, in cross-flow with a feed-and-bleed configuration, a reduction of coagulant dose induces an increase of the mass transfer resistance even in quasi-stable hydrodynamic operating conditions.

In-line coagulation/UF process can be used to treat poor quality surface water: permeate quality is increased and membrane fouling is reduced. Coagulation conditions determined by jar-test experiments are efficient to good performance in line coagulation/UF process. The permeate quality remains controlled by coagulation efficiency and the impact of physical-chemical coagulation conditions depends on the filtration process. It can be noted the fraction of interstitial fluid which contents the uncoagulated water (and/or the smallest floc) may induce a higher fouling than floc cake.