Comprehensive treatment scheme for distillery wastewater targeting recovery of water, antioxidant compounds and biogas

Abstract

This work integrates forward osmosis (FO) and adsorption to recover water and antioxidant compounds (melanoidins and polyphenols) from sugarcane molasses distillery wastewater prior to biogas generation by conventional anaerobic digestion (AD). FO enables water recovery with simultaneous concentration of the antioxidant compounds in the wastewater feed; the adsorption-desorption step permits recovery of the antioxidant compounds. The FO step was optimized in earlier studies and a flow rate of 1 L/min and draw solution concentration of 3 M MgCl2.6H2O was chosen. Column adsorption with XAD16 resin was tested at different flow rates and the maximum adsorption yield of 66 % melanoidins and 71 % polyphenols was obtained at 1 mL/min. While polyphenols were readily desorbed (86 % desorption with water-acidified ethanol-water), melanoidins desorption was comparatively lower (46 %). Four different treatment schemes were investigated viz. ADS1 (FO + AD), ADS2 (adsorption + AD), ADS3 (FO + adsorption + AD) and ADS4 (adsorption + FO + AD). Among these, ADS4 showed the best results with recovery of 91 % polyphenols, 72 % melanoidins, 72 % water and methane yield of 189 mL/gVSin after 37 days. While the integrated FO-adsorption process is promising and can be readily incorporated in the overall Zero Liquid Discharge (ZLD) schemes conventionally practiced in Indian distilleries, there are several aspects of the FO and adsorption steps that need further investigation.