Evolution of phosphorus with the promotion of KOH in supercritical water gasification of dewatered cyanobacteria from ion perspective

Abstract

Phosphorus is a very important resource, and dewatered cyanobacteria contains a large amount of it. Basic additives, such as KOH, are often used to promote hydrogen production during supercritical water gasification (SCWG) of biomass, but their effects phosphorus transformation have rarely been investigated. In this study, SCWG of dewatered cyanobacteria with potassium salt and KOH was conducted in autoclave at 400 °C for 10 min, to investigate the effect of K+ on the transformation of phosphorus under neutral and alkaline conditions. Results showed that K+ increased the proportion of phosphorus in the solid phase from 88.4% to 90.8–98.3%. Furthermore, K+ could promote the transformation of iron-combined phosphorus to calcium-combined phosphorus and occluded phosphate. Only when the reaction environment was alkaline, the proportion of phosphorus in the solid phase was significantly reduced to a minimum of 26.1%. When the amount of OH− was sufficient, can this part of phosphorus and organic phosphorus, which was decomposed and transformed by the promotion of OH−, be transferred to the liquid products. Results from this study laid a foundation simultaneously for hydrogen production and phosphorus recovery more environmentally and high-effectively.