Supercritical Water Gasification of Cassava Starch as a Model Component of Cassava Wastewater: Thermodynamic and Experimental Analysis

ABSTRACT

This work reports an alternative method for Cassava ( Manihot esculenta ) starch treatment, using starch as a model component for cassava wastewater (CWW) effluent. Supercritical water gasification (SCWG) was performed in a continuous flow reactor built in Inconel 625. The study had two complementary objectives: (1) to evaluate hydrogen‐rich gas production from the gasification process, and (2) to assess the decontamination efficiency of the liquid effluent. Experiments were conducted under constant pressure (240 bar) with a factoral design varying feed flow (5.00 to 10.00 g min ⁻¹ ), concentration (0.50 to 1.00 wt%) and temperature (600 to 800°C). Thermodynamic analysis were performed by Gibbs free energy minimization (at constant pressure and temperature) and entropy maximization (at constant pressure and enthalpy) methods with GAMS software. Simulations indicate that SCWG of cassava starch is attractive for hydrogen production (66.6% mol) under conditions of low feed concentration (0.50 wt%). Experimental results point out the maximum composition of hydrogen (65.7% mol) in the temperature of 800°C, flow of 10.00 g·min ⁻¹ and 1.00 wt% of starch in the feed. Regarding effluent treatment, the statistical analysis of the experimental data (ANOVA, p <0.05) showed that all factors were significant relating to COD reduction. The applied conditions enabled decreases in turbidity (98.97%), apparent color (99.95%) and COD (95.03%) of the liquid products. Therefore, the results obtained in this work suggest that SCWG is a promising option for simultaneous hydrogen production and treatment of starch industry effluents.