Recovery of Plant Nutrients from Food Residue by Microbial and Thermochemical Treatment

Recovery of plant nutrients from food residue is one of the most effective methods for resource recycling. To use food residue for hydroponics, the organic matters have to be mineralized and the nutrients have to be dissolved. Anaerobic digestion, biological oxidation, anaerobic digestion followed by biological oxidation, and wet oxidation are treatments to break down organic matter. The decomposition products of these processes are in liquid form and would be used as liquid fertilizer. The authors investigated the difference in the behaviour of nitrogen, potassium, and phosphorus in each treatment. Nitrogen was converted to ammonium by anaerobic digestion and wet oxidation, and to nitrate by biological oxidation. Potassium did not change significantly with treatment. The percentage of dissolved phosphorus in all treatments, especially in the microbial treatment, was smaller than in food residue. This is probably due to phosphorus binding to other ions and uptake by microorganisms during the treatment process.