Pre-coagulation in the UF system is generally categorized into
standard coagulation and in-line coagulation in accordance to the
presence and absence of the sedimentation.
Standard coagulation can remove destabilized pollutants or their
aggregates. Coagulant hydrolytes/precipitates can also partly be
eliminated during the sedimentation process. Liang et al. [37]
compared coagulation, coagulation–sedimentation, and coagulation–
sedimentation–filtration prior to ultrafiltration applied in drinking
water production from algae-rich reservoir water, and found that
coagulation–sedimentation was the most effective; however, filter
presented an adverse effect. Dong et al. [38] presented an opposing
view that in-line coagulation could form an initial floc cake layer on the
membrane surface for adsorption of the contribution parts of NOM.
The phenomenon suggests that there is probably a kind of aggregate
benefiting the following ultrafiltration, which can be settled or filtered
during the subsequent conventional process. And Kimura et al. [39]
studied the efficacy of pre-coagulation/sedimentation on the control of
irreversible fouling in a polysulfone ultrafiltration membrane by a pilot
scale experiment in a drinking water production plant, and found that
pre-coagulation/sedimentation could not remove fractions of organic
substances (such as polysaccharides and protein), which accounted for
the irreversible fouling in UF in the experiment.