Phosphorus recovery from hydrothermal carbonization of organic waste: a review

Background: This review sheds light on the topic of phosphorus (P) recovery from hydrothermal carbonization (HTC) of organic waste. The paper focuses on the rising need for securing alternative P sources for the increasing demand, in addition to the development of HTC as a thermochemical technique for waste valorization. Results: This article studies the definition of P-recovery from HTC, while introducing the notion of availability, which is a significant factor for studying the efficiency of P-recovery. A brief comparison between different treatment techniques for P-recovery from waste streams is presented, and the advantages of HTC are highlighted among different thermochemical techniques. Furthermore, the mechanisms of P-transformation during HTC reactions are studied, and the effect of various parameters on P-destination and recovery is emphasized. Finally, applications of P-recovery from HTC products on the laboratory and industrial scales are studied to assess the feasibility of the application. Conclusion: In short, the paper offers a detailed insight into the definition, mechanism, and potential feasibility of P-recovery from HTC of organic wastes within the scopes of resource management, waste valorization, and fertilizer production. Even though HTC for P-recovery from organic waste has been applied on laboratory and industrial scales, several challenges persist towards optimizing this process. The paper concludes that adopting P-availability as a criterion for efficiency is necessary to optimize HTC conditions for P-recovery. Further studies on P-transformation during later-stage reactions of HTC are recommended, as well.