The type of coagulant has been identified as a significant factor
influencing the fouling in ultrafiltration. Kabsch-Korbutowicz [41]
used three types of coagulants in a constant pressure in-line
coagulation-UF (dead end filtration) system and found that alum
and polyaluminum chloride can increase the removal of organic
matter and bring a considerable membrane fouling reduction, with no
effect for sodium aluminates. However, different reagents may need
different optimum conditions, because coagulation may produce
different floc with distinct characteristics in different ways due to the
various working conditions. Kim et al. [42] compared different mixing
conditions for chemical coagulation and found that back-mixing with
an in-line coagulation is useful for NOM fouling reduction.
Optimized dosage of coagulant in a classic coagulation process
may not be the best for UF. Howe et al. [43] found that under-dose of
coagulant usually had an adverse effect on the fouling of ultrafiltration,
while over-dose was always effective for fouling reduction.
Coagulation is the most promising pretreatment for UF, and more
researches are needed to optimize and establish a particular coagulation
way directly aiming at better ultrafiltration