Hydrothermal carbonization of food waste digestate solids: Effect of temperature and time on products characteristic and environmental evaluation

Food waste digestate solids (FWDS) is the by-product of anaerobic digestion and it contains high moisture. Hydrothermal carbonization (HTC) has the ability to convert wet bio-waste to hydrochar, which is a potential technology for handling FWDS. This study investigates the effect of reaction temperature and residence time on solid and liquid products from HTC process of FWDS. The solid product was named as hydrochars, and their physicochemical characters were tested and compared. The results showed that temperature had a more significant effect on hydrochar properties, compared to residence time. The higher heating value of hydrochar was 15.46 MJ/kg and the yield was 49%, under reaction conditions of 260 degrees C and 60 min. It was also found that hydrochar generated at higher temperature had a more stable combustion, higher ignition temperature, higher burnout temperature. For liquid product, the main organic matter are pyridine derivatives, pyrazine derivatives, indole derivatives, cyclopentene derivatives and phenolic compounds. It was also discovered that the increase of temperature can significantly reduce the concentrations of Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) in liquid product. When reaction temperature increased from 220 degrees C to 260 degrees C, the COD decreased from 23,357 mg/L to 19,658 mg/L, TOC decreased from 9827 mg/L to 6352 mg/L, respectively. After HTC under the conditions of 260.C and 60 min, 67% of nitrogen in solid feedstock e migrated from to liquid product, and N-contained compounds decomposed into ammonia, while phosphorus was mainly remained in the solid phase (>90%), which mainly existed in the form of apatite.

Automated summary

This study investigates the effect of reaction temperature and residence time on solid and liquid products from the hydrothermal carbonization (HTC) process of food waste digestate solids (FWDS). The results show that temperature has a more significant effect on the properties of hydrochar, while the effect on the liquid product is relatively small. It is also discovered that the increase of temperature can significantly reduce the concentrations of COD and TOC in the liquid product.