Reduction of chemical oxygen demand of vinasse using sugar cane bagasse ash geopolymer

The aim of this study was to determine the use of sugar cane bagasse ash geopolymer (SCBAG) as an adsorbent for organic compounds to reduce the chemical oxygen demand (COD) of vinasse. The effects of solid loading, time and temperature on batch adsorption were investigated, while the effects of bed height and flow rate were investigated through column studies. The adsorption of organic compounds onto SCBAG could be modelled well using the Langmuir isotherm and pseudo-second-order kinetics. The maximum batch adsorption capacity was 738 mg/g at 298.15 K after 5 h of adsorption. The column studies showed that the highest COD reduction of 81% could be achieved using a flow rate of 2.5 ml/min and a bed height of 13 cm. These conditions gave a dynamic uptake of 107 458 g and a breakthrough time of 600 min. The column adsorption could be best described using the Bohart–Adams model, giving a correlation coefficient of 0.98, a Bohart–Adams rate constant of 3.05 × 10⁻⁸ l/(mg min) and a saturation concentration of 6.93 × 10⁷ g/l. The SCBAG could be regenerated and be used as an adsorbent in three cycles without significant loss in adsorption capacity.