Phosphate adsorption using biochar derived from solid digestate

Abstract

Anaerobic co-digestion of food waste and manure is an increasingly common waste management strategy. However, current disposal alternatives for the resulting effluent, “digestate”, can lead to nutrient run-off and cause surface and groundwater contamination. Biochar made from the solid fraction of digestate was used to recover nutrients present in the liquid fraction of the same effluent stream. Biochar produced from solid digestate at three different temperatures (500, 800 and 1000 °C) was characterized and evaluated for adsorption of phosphate in solution and from liquid digestate. Pyrolysis temperature was negatively related to yield. However, higher processing temperatures (800 °C–1000 °C) are preferred due to better soil stability and phosphate adsorption capacity. Additional analysis to determine the potential to replicate this process at scale concluded that the amount of solid digestate biochar produced is sufficient to adsorb approximately 20% of the total phosphate present in the liquid fraction of the digestate.