Filtration of super compactible materials is characterized by little or no effect of pressure on either filtrate flow rate or % cake solids when pressure is increased beyond a critical value. Application of mechanical forces on the cake surface to change solid stress distribution has been considered effective for filtration of the very highly compactible materials. Another efficient method for filtration of the material is to decrease cake compactibility by addition of incompactible or little compactible filter aids. Rice Hull Ash containing 92-95% of amorphous SiO2 is selected as the filter aid. Filtration of a super compactible biosludge with and without filter aids addition, under “cake filtration” and “cake filtration followed by expression” methods are involved in the study. Experimental results and fundamental explanations of the reduction of cake compactibility and improvement of filtration with addition of the filter aid will be given in the paper.

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