Effect of steel slag in recycling waste activated sludge to produce anaerobic granular sludge.

The amount of waste activated sludge (WAS) has grown dramatically in China. WAS is considered as a problematic and hazardous waste, which should be disposed in a safe and sustainable manner. In order to recycle WAS to an anaerobic granular sludge (AnGS) process for anaerobic digestion, Fe powder and steel slags (rusty and clean slags) were used to enhance the granulation process. The results demonstrated that both rusty and clean slags encouraged the development of granular sludge. Adding 10 g/L clean slags could increase AnGS granulation rate by 37%. In the presence of clean slags, extracellular polymeric substances (EPS) concentration in granules increased noticeably to 715 mg/g mixed liquor suspended solids (MLSS). High throughput sequencing analysis exhibited more diversity and higher abundance of functional microbial communities in the batch bottle with 10 g/L clean slags. This study suggested that adding clean slags at 10 g/L dosage was a sustainable and effective method for the sludge granulation.