Overcoming Deep-Dewatering Challenges in Food Waste Digestate with Polyethylene Oxide as an Innovative Conditioning Agent

Abstract

The effective treatment of food waste digestate is critical for reducing environmental pollution and mitigating carbon emissions, with deep dewatering playing a pivotal role. Conventional dewatering agents such as polyaluminum chloride (PAC) and polyacrylamide (PAM), commonly employed in municipal sludge treatment, exhibit limited efficacy when applied to food waste digestate due to the latter's high salinity and advanced fermentation stages. This study introduces polyethylene oxide (PEO) as a novel conditioning agent and investigates its dewatering performance in comparison to PAC and PAM, elucidating the underlying mechanism. PEO conditioning markedly improves deep-dewatering, reducing digestate moisture content from 93.11% to 56.71% and lowering specific resistance to filtration (SRF) by 90.3%. In contrast, PAM, PAC, and their combination achieve moisture reductions to 81.18%, 84.49%, and 87.07%, respectively, with significantly lower SRF improvements. PEO promotes the release of bound water by weakening solid-liquid binding energy, facilitating the transition of bound water to free water and enhancing overall water mobility. Moreover, compressibility coefficient analyses and X-ray computed tomography (X-CT) reveal that PEO treatment significantly increases filter cake porosity, with an effective porosity rate of 56.65%, resulting in superior drainage performance. The enhanced dewatering efficiency of PEO stems from its ability to improve water permeability within the filter cake during compression, distinguishing its mechanism from traditional flocculation (PAM) and coagulation (PAC) approaches. This work highlights the potential of PEO as a highly effective solution for food waste digestate treatment in solid waste management, with its salt-resistant properties further extending its applicability to high-salinity waste streams.