(23g) Factors Influencing Nutrient Solubilization from Biomass during Hydrothermal Carbonization

Hydrothermal carbonization (HTC) has attracted researchers to study primarily its potential to produce solid fuels from different kind of waste streams, including agricultural biomass, food waste, and sludge. However, application of HTC to recover nutrients and other valuable chemicals also shows great potential. The objective of this study is to identify HTC conditions to recover nitrogen and phosphorous in the aqueous phase. An experimental project was undertaken, and HTC was performed on cow manure in a batch reactor. Reaction conditions studied include temperature, time, and addition of acid. The experiments were carried out at 170 ËšC, 200 ËšC and 230 ËšC, and reaction times are 5 min, 30 min, and 120 min. Effects on nutrient recovery of adding hydrochloric acid and citric acid at concentrations of 0.1M, 0.3M and 0.5m were studied. Aqueous concentrations of nitrogen and phosphorous were analyzed by spectrophotometric technique. Solid content of nitrogen was measured by elemental analysis and phosphorous was measured by ICP after acid digestion. A partial factorial experimental design was designed, and the resulting data went through a rigorous statistical analysis including Tukey HSD test. These results suggest that the effect of time on solubilization of both P and N is not significant, as is the effect of temperature on the recovery of the Nitrogen. HTC temperature has a significant influence on P solubilization, with lower temperatures favoring high P solubilization. Acid addition plays a major role in solubilizing P. Both HCl and citric acid substantially enhance solubilization of phosphorous, but have little impact on nitrogen recovery. The concentration of acid addition was shown to be important on phosphorous solubilization. Increasing concentration from 0.1M to 0.3M improves the recovery substantially; however further increasing the concentration from 0.3M to 0.5M has only a modest effect.

With analysis of the content of both P and N in the solid phase, a mass balance was performed on both elements, and the mass balances were closed within ± 25%. We discuss potential for production of liquid and solid fertilizers from the solubilized nutrients, and indicate future research directions.