Estimation of Dissolved Organic Foulant during Direct Treatment of Sewage by Forward Osmosis

Abstract

 Direct treatment of sewage by forward osmosis (FO) using polyamide FO membrane was examined, and the dissolved organic foulant in the sewage was estimated. Filtrated sewage and 3 M sodium chloride solution were used as feed solution (FS) and draw solution, respectively. The permeate flux decreased from 18.7 L/m²/h to 9.9 L/m²/h during 14 h of FO treatment owing to the membrane fouling, whereas the FO membrane rejected 98 % of dissolved organic carbon in FS. The dissolved orgnic matter was partially accumulated in the fouling layer. Analysis using liquid chromatography–organic carbon detection revealed that biopolymer fraction was dominant organic matter in the fouing layer. Although the accumulation of fraction of humic substances, building blocks, and low-molecular weight acids was only 1–2 %, that of biopolymer fraction was above 15 %. The biopolymer fraction is therefore estimated as a key dissolved organic foulant.