A novel ethylene oxide-propylene oxide demulsifier for dewatering of food waste digestate

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–CH 3 (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.