BACKGROUNDAlkaline fermentation of waste activated sludge (WAS) is feasible to recover carbon for biological nutrients removal. However, it is difficult to abstract the soluble organics from the fermented mixture since sludge dewaterability is deteriorated after fermentation. In this study, a novel system consisting of complete mixing fermentation, water elutriation and settling reactor was developed to produce and abstract short chain fatty acids (SCFAs) from waste activated sludge through an alkaline fermentation process. RESULTSFor the novel system, 57% of sludge solubilization and 327mg COD g(-1) VS of SCFAs production were achieved in the fermentation zone, resulting in a sludge reduction of 54%. In the elutriation zone, nearly 70% of soluble organics was recovered when the water exchange ratio was 33.3%. Moreover, mass balance of the system was calculated and the results showed that C, N, and P element were converted into the liquors phase in the fermentation process with proportions of 54%, 30%, and 16%, respectively. CONCLUSIONThis work successfully developed a novel process for wasted sludge fermentation and soluble organic carbon separation. Effective results were obtained in the system, indicating it is favorable for pilot and full scale application. (c) 2017 Society of Chemical Industry