A recent study explored how the composition of food waste anaerobic digestate affects the capacity of wood-derived biochar to adsorb ammonium (NH4+). The digestate, rich in NH4+, poses both environmental risks and agricultural value if managed correctly. Researchers examined how various components in digestate, such as organic particles and high pH levels, influence NH4+ adsorption on biochar.

They found that NH4+ adsorption is significantly higher in digestate solutions compared to pure NH4+ solutions. The presence of multiple cations in digestate generally reduced NH4+ adsorption due to competitive adsorption. However, the high pH and organic compounds in digestate enhanced NH4+ adsorption on biochar. Modified biochar with increased surface area and lower pH showed a greater capacity for NH4+ adsorption in high pH conditions compared to raw biochar. Surprisingly, the large organic particles in digestate only slightly decreased NH4+ adsorption on modified biochar.

The study also showed that more than 74% of adsorbed NH4+ could be desorbed using neutral salts, indicating that electrostatic attraction primarily drives NH4+ adsorption. This suggests that wood-derived biochar is effective for recovering NH4+ from digestate, which can then be used as a slow-release fertilizer in agriculture. These findings highlight the potential of using biochar to manage waste and recycle nutrients, supporting both environmental sustainability and agricultural productivity. Further research is needed to assess the bioavailability of NH4+ from digestate-loaded biochar in soil and plant systems.