The reduction of chemical oxygen demand (COD) from vinasse using a sugar cane bagasse ash geopolymer

The aim of the study was to determine the use of sugarcane bagasse ash geopolymer (SCBAG) as an adsorbent for organic compounds to reduce the chemical oxygen demand (COD) from vinasse. The effect of solid loading, time and temperature was investigated for the batch adsorption whilst the effect of bed height and flow rate was investigated for the 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 studies could best be 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 3 cycles without significant loss in adsorption capacity.