Nutrient recovery from biogas slurry via hydrothermal carbonization with different agricultural and forestry residue

Abstract

Hydrothermal carbonization (HTC) of various agricultural and forestry waste (yellow bamboo, green bamboo, peanut shell, wood meal, peanut straw, wheat straw, rice husk, corn straw) with biogas slurry (BS) was studied, with the goal of recovering nutrients from BS. The ideal biomass material for nitrogen recovery was green bamboo, where 46.64 % of N was recovered after HTC at 250 °C for 3 h. The best one for phosphorus recovery was peanut straw, where P in liquid residue was not detectable post HTC. However, with all types of biomass tested, HTC failed recovering potassium from BS. Nitrogen recovery performance was positively correlated to the total cellulosic content of biomass as C-N active binding site for the formation of aliphatic amine were mainly provided by cellulose and hemicellulose. Increased metal salt concentration in biomass feedstock promoted phosphorus recovery as the mechanism was formation of metal phosphate precipitates. The hydrochars obtained from different biomass samples resulted in a wide range of pore sizes, which was critical for nutrient slow-release characteristics and plant growth promoting microorganism immobilization. Pot experiment further confirmed corn straw hydrochar had significant advantages over chemical fertilizer in water and nutrient retaining, which was critical for the enhancement of long-term soil fertility.