Separation of oily sludge and glycerol from biodiesel processing waste by coagulation

Raw waste glycerol is a by-product of biodiesel production from transesterification, which is high in salt, and has a highpH value (more than 9.6). The purpose of this research is to reduce the water pollution from waste glycerol by using acoagulation process and discussing the possibility of waste glycerol reuse. The commercial coagulant (2% by weight), whichwas composed by cationic polyamine (PA) 6% and poly-aluminium chloride (PACl) 94% (w/w), was used as coagulant totreat waste glycerol. The results showed that after acidification and coagulation process, most of the chemical oxygen demand(COD), biochemical oxygen demand (BOD5), total suspended solids (TSS), and oily sludge (such as fatty acid, methyl ester,methanol and soap) in raw waste glycerol were removed, except glycerol. The removal efficiencies of COD, BOD5, TSS, soapand methanol were 96.2%, 93.3%, 98.1%, 100%, and 85.8%, respectively, but the removal efficiency of glycerol was only65.4%. There was still a certain amount of glycerol (about 147.5g/L) in the solution, which is separated from oily sludge