This presentation outlines a sustainable approach to improve nutrient recovery from food waste anaerobic digestate, tackling global waste challenges while boosting soil fertility in sandy soils. Globally, 1.3 billion tons of food waste are generated annually, posing significant environmental issues. Anaerobic digestion converts this waste into biomethane for energy and digestate, a nutrient-rich by-product with reduced phytotoxicity compared to raw waste, making it a promising agricultural resource. However, its adoption is hindered by high costs, low biogas value, and digestate management challenges.
Our research developed acidified digestates by treating liquid digestate with sulphuric, nitric, or phosphoric acid, followed by evaporation to produce solid ammonium salts: ammonium sulphate, ammonium nitrate, and monoammonium phosphate. These were analysed using FTIR, XRD, and SEM-EDS for composition and tested against liquid digestate, unacidified solid digestate, and urea ammonium nitrate (UAN) for their impact on sandy soil chemistry, kikuyu grass and wheat growth, and rhizosphere bacterial communities.
Findings revealed full ammonium retention, with acid additions enhancing nutrient content through sulphate, nitrate, and phosphate anions. Acidified digestate rivalled conventional fertilisers in promoting wheat and ryegrass growth, surpassing controls and unacidified digestate. It also improved soil organic carbon and beneficially altered bacterial communities, positioning it as a sustainable alternative to synthetic fertilisers while easing storage and handling issues at digestion facilities.
The next stage proposes blending acidified digestate with a nitrogen inhibitor to reduce nitrogen loss and granulating the material for improved storage and application. This step aims to optimise its effectiveness as a fertiliser in sandy soils, where nutrient retention is vital. By transforming food waste into a valuable resource, this method supports sustainable waste management and agriculture.