Application of in-line coagulation/ultrafiltration process in water treatment

An in-line coagulation (without sedimentation step)/ultrafiltration process was investigated. An attempt to establish the influence of aluminium-type coagulant and its dose as well as the membrane type and water pH on permeate flux and final water quality was undertaken. Three aluminium-based coagulants, i.e., alum, polyaluminium chloride and sodium aluminate, were tested on 30 kDa ultrafiltration membranes made of regenerated cellulose and polyethersulfone. In the process investigated, alum or polyaluminium chloride used as coagulants proved to be more efficient in the removal of NOM (natural organic matter) from treated water and in reduction of membrane fouling, compared to ultrafiltration. When coagulation was carried out in the conditions of charge neutralisation (low pH) the membrane susceptibility to fouling was lower than that in conditions of sweep flocculation. In alkaline solution, both membranes tested were strongly blocked by NOM particles and anionic products of coagulant hydrolysis.