Skeletal Structure-Based Conditioning for Improved Deep-Dewatering Efficiency of High-Salinity Food Waste Digestate

The solid–liquid separation of food waste anaerobic digestate residue (FD) is a crucial step in maximizing the efficiency and sustainability of anaerobic digestion processes. However, the high salinity and organic content of FD significantly hinder conventional dewatering methods, making deep-dewatering particularly challenging. This study introduces a composite conditioning strategy using basic aluminum chloride (BAC) and a complex quaternary ammonium salt surfactant (G agent) to enhance the digestate's drainage performance and dewatering efficiency by constructing a skeletal structure within it. Experimental results showed that BAC+G composite conditioning significantly reduced the water content of the digestate from 90.69 ± 0.36 to 54.19 ± 0.16%, achieving deep dewatering that was unattainable with BAC or G agent alone. On a macroscopic scale, the BAC+G treatment enhanced floc strength and increased flocculated particle size to 469.07 ± 0.73 μm, approximately 18 times larger than untreated digestate, which significantly mitigated clogging and improved the permeability coefficient from 2.40 × 10–6 to 9.79 × 10–6 cm/s, ensuring smooth water discharge. Microscopically, the treatment increased effective porosity by 34.90%, reduced tortuosity to 1.45, and improved overall permeability (4.41), accelerating water discharge and further enhancing the dewatering performance. Additionally, BAC+G composite conditioning transformed floc particles to hydrophobic, lowered the interfacial free energy, and formed stable structures, further enhancing dewatering performance. These findings demonstrate that combining flocculation with skeletal structure formation is critical for achieving deep-dewatering of a high-salinity food waste digestate. This research provides a promising approach for improving digestate management and could have broader implications for the sustainable treatment of high-moisture organic waste streams.