Regulating phosphorus bioavailability and dissolved organic matter dynamics through deep eutectic solvent addition in distillery waste composting

The efficient use of phosphorus (P) through organic waste composting is a sustainable strategy for fertilizer production. This research investigated how two choline chloride-based deep eutectic solvents (DES) (ethylene glycol/citric acid) affected P fraction transformation, dissolved organic matter (DOM) characteristics, and microbial communities during co-composting of dewatered sludge and distiller's grains from a Baijiu winery, compared to DES-free controls. After 30 days of composting, the P bioavailability of compost was increased in all cases, 49.46 % in the control group and 99.49 % and 67.17 % in the experimental group after addition of DES. DES treatment enhanced P bioavailability and promoted the conversion of organic P to inorganic P. Mental tested the significant positive correlation between Proteobacteria, Firmicutes in the bacterial community and NaHCO₃-P, NaOH-P. Partial least squares path modeling analysis revealed that DES improved P bioavailability through both direct effects and indirect regulation of compost physicochemical properties and microbial activity. In addition, the addition of DES does not affect the relevant characteristics of DOM, whose humic-like components may be associated with P release, and the produced compost all meets the requirements of the maturity standards. Therefore, the addition of DES to compost provides a waste-resource solution to utilize the potential of P in the long term.