Abstract
Food waste digestate is difficult to dewater due to high salinity and residual oil. This study evaluated an amphiphilic ethylene oxide-propylene oxide (EO-PO) demulsifier for dewatering of food waste digestate by comparing with other methods (e.g., polyacrylamide (PAM), polyaluminium chloride (PAC), Fe(II)-Oxone, and polyethylene oxide (PEO)). EO-PO conditioning showed the highest improvement in filterability, with 87% reduction of capillary suction time (CST) and 93% reduction of specific resistance to filtration (SRF) compared with raw sample (RS). In contrast, PAM, PAC, Fe(II)-Oxone, and PEO showed limited CST and SRF reduction efficiencies. The superiority of EO-PO in dewatering was further testified by results of bound water, median particle size, zeta potential, compressibility, filtrate mass, water content of dewatered cake, and rheological properties. Moreover, the addition of EO-PO shifted the predominant organic component from hydrophilic substances to hydrophobic acidic organic matter. It also increased the proportion of C–CH3 (nonpolar carbon groups) and decreased the proportion of C–OH (hydrophilic hydroxyl groups). The second minimum value and Lewis acid-base interaction energy of the EO-PO treated digestate were markedly larger than those of other conditioning methods, indicating a stronger tendency for digestate particles to aggregate. EO-PO transformed the filter cake from isolated pores into a connected pore network, increasing total porosity from 1.36% of RS to 13.54% and reducing tortuosity from 1.46 of RS to 1.04. Further analysis indicated EO-PO demulsifier as a dewatering agent was economically feasible and environmentally friendly. This study proposed a novel EO-PO demulsifier method for enhancing digestate dewatering.