Comprehensive review on treatment of high-strength distillery wastewater in advanced physico-chemical and biological degradation pathways

Fermentation distilleries produce a considerable volume of high-strength wastewater, known as stillage, having unconvertible organic fractions, lower pH and high percentage of dissolved organic and inorganic matters. Molasses stillage comprises higher level of chemical oxygen demand of 80-140 g/l, biochemical oxygen demand of 40-65g/l, inorganic impurities and dark brown colour. Grain stillage contains comparatively lower chemical oxygen demand of 40-60g/l. This stillage is acidic in nature (pH of 3.4-4.1) and exhibits considerable pollution potential upon discharge of untreated or partially treated wastewater into water body. Physical, chemical, biological and integrated processes for treatment of distillery stillage, which have been established by several researchers, are discussed in this review article. These treatment methods are discussed with focus on process details and current challenges, prospect and opportunities of future research and development. By utilizing distillery stillage as substrate in microbial fuel cell or integrated or combined fungal aerobic treatment followed by microbial fuel cell system, encouraging observations are demonstrated recently in terms of achieving the required treatment efficiency to meet the discharge standards, simultaneous bioelectricity generation and value-added products recovery. Such treatment system can offer a suitable solution for treatment of distillery wastewater in coming days.