Synthesis of Hydrogel-Encapsulated Nanofertilizers from Biogas Digestate for Controlled Nutrient Release

Natural fertilizers offer a more sustainable alternative to conventional mineral fertilizers by reducing energy-intensive production and minimizing nutrient runoff and chemical residues. In this study, a hydrogel-encapsulated nanofertilizer (HENF) was developed using biogas digestate, a waste-derived nutrient source, to regulate nutrient release and reduce environmental losses. Biogas digestate nanofertilizer (BDNF) was encapsulated within a cellulose-based hydrogel synthesized from sodium carboxymethyl cellulose (NaCMC) and xanthan gum (XG), with citric acid serving as a chemical crosslinker to enhance structural stability and water retention. The resulting HENF exhibited a moderated yet substantial swelling capacity (350.94%), indicating effective water uptake while maintaining diffusion control. Nutrient release behavior was evaluated in deionized water, with electrical conductivity as an integrated indicator of ionic release. Compared with non-encapsulated BDNF, HENF showed a pronounced suppression of early-stage release and sustained nutrient diffusion over time. Kinetic modeling using the Korsmeyer–Peppas equation revealed a non-Fickian, relaxation-controlled transport mechanism ( n  = 0.9789, R ²  = 0.9079), while lag-phase analysis using the Richards model indicated a hydration-controlled delay of approximately five days. Soil column leaching simulations further demonstrated reduced ionic transport for HENF relative to BDNF, indicating effective mitigation of nutrient leaching under repeated wetting conditions. Hence, the results establish a structure-property-function relationship linking hydrogel network design to regulated nutrient release, supporting the potential of waste-derived hydrogel nanofertilizers for environmentally responsive nutrient management.