In-line coagulation with low-pressure membrane filtration.

The objectives were to investigate the effects of in-line coagulation on removal of natural organic matter (NOM) and turbidity and on fouling of membranes during ultrafiltration (UF). Coagulants were added prior to UF, without intermediate use of conventional processes for removal of particles. Synthetic and natural raw waters were examined. Charge neutralization, sweep floc, and under-dose conditions (with respect to conventional treatment) were all effective for removal of NOM and turbidity by UF. Most coagulation conditions resulted in decreased resistance to filtration and improved hydraulic removal of filter cake, including conditions that would be ineffective prior to conventional settling and rapid-filtration. Flocs that were produced under charge neutralization conditions and acidic under-dose conditions produced lower hydraulic resistance and were less compressible than for sweep floc conditions.