Study of the flocculation of anaerobically digested residue and filtration properties of bentonite based mineral conditioners

• The use of high porosity materials increases dewatering performance for digestate.
• The use of bentonite-based materials decreases polyelectrolyte dosage to 19 mg/g TS.
• Water retention capacity was defined and used as an indicator for dewatering.

The turbidimetric and capillary suction time (CST) methods were used for the assessment of some properties (e.g., filtration process, water uptake etc.) of diatomite–bentonite based conditioners for dewatering of effluents from digestate of a biogas plant. These physical conditioners were prepared based on natural porous highly dispersible systems such as bentonite and diatomaceous earth. A characterization of the materials was performed by scanning electron microscopy (SEM) and fluorescence of X-rays spectrometry (XRF). A cationic polyacrylamide polymer (ZETAG® 9014) was added prior to the dewatering process of the anaerobic digestion residue and an optimal dose of the mineral conditioner and the polymer was determined. It was suggested the formula, by means of which the amount of separated water was identified as water retention capacity (WRC). A favorable filterability region was determined with WRC between 1.5 and 4.4 (high level of WRC) and 1.5 and 2.9 (low level of WRC) in terms of the percentage of polymer in the dry cake.