Enhancing Binding by Electron Transfer at Heterointerfaces of Biochar‐Modified Hydrogel to Improve Utilization Efficiency of Wastewater Recovered Nutrients

Here, this work combines membrane capacitive deionization (MCDI) technology with biochar-modified hydrogel production to recycle nutrients from wastewater efficiently. MCDI selectively recovered 76.89 ± 5.12% of ammonia and 78.94 ± 3.84% of phosphate from municipal wastewater. The biochar formed layered linear arrays within the hydrogel matrix, and enhanced hydrogen bonding led to the formation of a nanoscale hydrogel coating, creating the distinct heterointerfaces. Interestingly, biochar mediated the enhanced nutrient binding to hydrogel through electron transfer at heterointerfaces, thereby confining the nutrients in nanoscale hydrogel coating and mitigating their release rate. Therefore, the release period of nitrate, ammonia, phosphate, and potassium was prolonged by times of 0.8 to 7.3, 1 to 5.2, 0.1 to 9.1, and 4.7 to 5.7 compared to the unmodified hydrogel. The application of biochar-modified hydrogel improved soil fertility, which in turn affected the host rhizosphere microbial composition. Furthermore, it resulted in increased lettuce fresh and dry weight compared to fertilization with nutrient-enriched liquid and the unmodified hydrogel, respectively. This work paves the way towards sustainable nutrient utilization.