Decolourizing distillery spent wash using fungal biotechnologies: from pollution to potential

Climate change and environmental pollution are among the most pressing global challenges today, with water pollution standing out as a particularly critical issue. Industrial wastewater discharge, especially from distilleries, significantly contributes to the degradation of aquatic and terrestrial ecosystems. Molasses-based distilleries are major perpetrators, producing vast quantities of dark brown effluent known as spent wash. This colouration is largely due to the presence of melanoidin, a recalcitrant compound formed via the Maillard reaction. Although many distilleries now utilize anaerobic digestion to convert this organic-rich waste into biogas, the resultant biomethanated spent wash remains highly coloured and environmentally hazardous. Direct discharge of untreated or partially treated spent wash into rivers, lakes, or soil severely disrupts ecological balance and poses risks to biodiversity. Existing disposal practices, such as lagoon storage or composting with press mud, offer limited solutions to the colour problem. Fungi, particularly those producing laccase and other oxidative enzymes, have demonstrated promising potential for decolourizing spent wash in laboratory studies. However, the enzymatic pathways involved in melanoidin degradation are still not fully understood. To address the persistant colour challenge, integrated treatment strategies combining fungal systems with complementary physical or chemical processes (eg, adsorption or advanced oxidation) may be required to achieve effective decolourisation. Such advancements are vital for creating effective, eco-friendly solutions to mitigate the environmental impact of the distillery industry and promote a circular bioeconomy.