An Updated Review on Tannery Waste Treatment with Emphasis on Fungal Mediated Applications

Abstract

Current estimates state that the global leather industry produces 600 million m³ of effluent annually. Since tannery effluents are toxic with high salinity, and contain several recalcitrant organics, they cannot be broken down by conventional biological treatment methods. Biological treatment options are more sustainable, cost-effective, and environmentally friendly, as they rely on microorganisms. Recently, fungi have garnered attention from the research community for their potential use in the remediation of wastes and wastewaters. A number of filamentous fungi are found naturally in wastewater treatment systems as spores or vegetative cells which metabolize organic substances, e.g., Phanerochaete chrysosporium, Trametes versicolor, etc., which produce key enzymes like lignin peroxidase (LiP), manganese peroxidase (MnP), and laccase. These enzymes break down persistent organic pollutants, including polyaromatic hydrocarbons (PAHs), dyes, and pesticides. Other fungi like Aspergillus spp., Irpex lacteus, and Fusarium spp. bioaccumulate heavy metals and degrade complex organic compounds. Tannins represent one of the least biodegradable substances in tannery wastewaters, with high recalcitrant compounds. Further, several biophysical, enzymatic, cellular, and metabolic advantages of fungi have advantages in tannery effluent treatment. The current review with an introduction on tannery treatment delves into the fungal bioremediation in detail. The recent developments in this area are also covered to update the readers on the developments in genomics and proteomics. Additional methods, viz., enzymatic treatment, strain improvement, scale-up biological processes, and microalgae applications, can enhance the quality and efficacy of the treatment.