The effect of process water recycle on hydrothermal treatment of yard long bean (Vigna unguiculata ssp. sesquipedalis) and water spinach (Ipomoea reptans) seeds

Abstract

Hydrothermal treatment is one of thermal biomass conversion method that the solid product can be used as fuel. The main problem of hydrothermal system is the liquid product that usually become waste. The water requirements of hydrothermal treatment need to be assessed to determine commercial feasibility. This research aims to study the influence of reusing liquid product to become process waster in hydrothermal treatment of yard long bean and water spinach seed with temperature variation of 180, 200 and 220 °C, biomass and water ratio of 1:5, and residence time of 40 minutes. Solid product was characterized in terms of mass yield and heating value (HHV). It is found that the solid yield value increased 8% from the first to the sixth process using recycle water. The biggest HHV of solid product was the hydrothermal process with temperature of 220°C using the 5th recycle liquid at 5499 cal/g for water spinach seed and 5466 cal/g for long bean seed.