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

## TL;DR

This paper shows how biochar-modified hydrogels can efficiently recover and slowly release nutrients from wastewater, improving soil fertility and plant growth.

## Contribution

The novel use of biochar-modified hydrogels to enhance nutrient binding through electron transfer at heterointerfaces is introduced.

## Key findings

- MCDI recovered 76.89% of ammonia and 78.94% of phosphate from wastewater.
- Biochar-modified hydrogels prolonged nutrient release rates significantly compared to unmodified hydrogels.
- Modified hydrogels improved lettuce growth and altered rhizosphere microbial composition.

## Abstract

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.

Enhancing the utilization efficiency of nutrients recovered from wastewater is achieved through hydrogel modification by biochar. The strategy improves nutrient binding to hydrogels via electron transfer at heterointerfaces, thereby reducing nutrient release rate. Consequently, biochar‐modified hydrogels facilitate vegetable growth by enhancing soil fertility and altering the microbial composition within the rhizosphere of the host.