Hydrothermal carbonization of wet biomass from nitrogen and phosphorus approach: A review

With increasing energy and resource consumption due to population growth, the biorefinery concept is becoming popular. This concept aims to harness all the properties of biomass by producing energy and recovering useful chemical products. Nutrients such as nitrogen and phosphorus play a key role in the world’s food production because they are the main elements used in fertilizer production. Hydrothermal carbonization (HTC) has been presented as a suitable option for energy recovery that can also be used as a pre-treatment for enhanced nutrient recovery. During the HTC process, part of the nitrogen and phosphorus are solubilized into the process water and the other part remains within the hydrochar. Hydrochars are mainly used as soil amendments due to their high content of phosphorus and nitrogen, but in this process, water still contains a considerable concentration of these compounds making it a potential source for their recovery. Therefore, HTC may boost the nutrient recovery strategy by extraction (process water) or densification (hydrochar) from biomass if it is coupled with another nutrient recovery process. This review presents an overview of the phosphorus and nitrogen fate during the HTC process from a perspective of nutrient recovery, presenting existing technologies and future trends.