Biological short-chain fatty acids (SCFAs) production from waste-activated sludge affected by surfactant

Short-chain fatty acids (SCFAs), the preferred carbon sources for biological nutrient removal, are the important intermediate products in sludge anaerobic fermentation. Sodium dodecylbenzene sulfonate (SDBS) is a widespread used surfactant, which can be easily found in waste-activated sludge (WAS). In this investigation, the effect of SDBS on SCFAs production from WAS was investigated, and the potential of using fermentative SCFAs to promote enhanced biological phosphorus removal (EBPR) was tested. Results showed that the total SCFAs production increased significantly in the presence of SDBS at room temperature. At fermentation time of 6 days, the maximum SCFAs was 2599.1 mg chemical oxygen demand (COD)/L in the presence of SDBS 0.02 g/g, whereas it was only 339.1 mg (COD)/L in the absence of SDBS. The SCFAs produced in the case of SDBS 0.02 g/g and fermentation time 6 days consisted of acetic acid (27.1%), propionic acid (22.8%), iso-valeric acid (20.1%), iso-butyric acid (11.9%), n-butyric acid (10.4%) and n-valeric acid (7.7%). It was found that during sludge anaerobic fermentation, the solubilization of sludge particulate organic-carbon and hydrolysis of solubilized substrate as well as acidification of hydrolyzed products were all increased in the presence of SDBS, while the methane formation was decreased, the SCFAs production was therefore remarkably improved. Further investigation showed that the production of SCFAs enhanced by SDBS was caused mainly by biological effects, rather than by chemical effects and SDBS decomposition. With the fermentative SCFAs as the main carbon source, the EBPR maintained high phosphorus removal efficiency (∼97%).