Direct sewage filtration by forward osmosis (FO) was investigated with the aim of concentrating organic matters in sewage into a small volume of energy source. The results showed that chemical oxidation demand (COD) in the feed sewage solution was concentrated by more than 300%. Although a gradual decline in membrane flux with filtration time occurred, a flux of 3-7.4 L m(-2) h(-1) was still produced satisfactorily. The membrane flux decline was caused by both membrane fouling and the decline of osmotic driving force due to the salinity change in both feed solution and draw solution. The membrane fouling analysis indicated that the fouling was mainly attributed to the formation of cake layer on the membrane surface in both membrane orientation, the active layer facing the feed side (AL-FS) and the active layer facing the draw solution side (AL-DS). However, AL-FS outperformed AL-DS in terms of membrane flux and fouling. This study may offer new insight into the development of low-energy wastewater treatment processes and energy recovery. (C) 2014 Elsevier B.V. All rights reserved.