Rice Hull Ash (RHA) generated from suspension burning process is highly porous silica base particles with irregular particle shapes, low bulk density and high filter cake permeability, which enables the RHA to perform as an efficient filter aid product. RHA filter aid products have been successfully applied to many areas including chemical, water, waste water and swimming pool industries. Application of the RHA filter aids in bio-sludge dewatering will be discussed in this paper.

Effects of RHA, Diatomaceous Earth (DE), paper fiber and spent coffee grounds on dewatering rate, cake volume, cake moisture content and quality of filtrate were investigated on laboratory filtration followed by expression tests on nine activated sludge samples from three City of Houston's waste water treatment plants (WWTP). Test results on the nine samples consistently indicated that RHA increased not only sludge deliquoring rate, but also cake solid content, and filtrate quality. On an UB sludge sample (2-18-06), compared to dewatering without any filter aids addition, a MaxfloTM RHA filter aid dosed at 50% of sludge solids, increased dewatering rate by 37%, decreased cake thickness by 33% improved Cake Water to Cake Sludge Solid Ratio to 41%, and improved filtrate color by 57.7%.