Humic acids removal by aerated spiral-wound ultrafiltration membrane combined with coagulation–hydraulic flocculation

An aerated spiral-wound ultrafiltration membrane system (ASWUF) combined with coagulation–hydraulic flocculation was tested with a view to evaluating its efficiency as a system for removing humic acids (HA). The tests were carried out at pilot scale, using FeCl3 as a coagulant. The ASWUF was equipped with polyethersulphone membranes (molecular weight cut-off of 50 kDa). The system was fed with reservoir water, to which different concentrations of HA (1–30 mg/l) were added. HA removal capacity of the ASWUF varied according to the molecular weight (MW) of the HA, and performance never exceeded 41% as dissolved organic carbon (DOC). However, coagulation–flocculation combined with ASWUF achieved results of approximately 90% for HA concentrations of up to 30 mg/l. Coagulation–flocculation as pretreatment for ASWUF makes it possible to remove HA with a low MW, without having to modify the pH of the water. This efficiency led to a decline in the specific UV absorbance (SUVA) of the effluent, which therefore presented a lower risk of trihalomethane (THM) generation after post-chlorination. Final effluent HA concentration was the main conditioning factor for THM generation. However, it was noted that the fraction of HA persisting after treatment generated a higher concentration of THM per unit of DOC.