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.
Keywords
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Introduction
Tannery effluent contains heavy loads of tannins, chromium, and sulfides, alongside over 175 other chemicals used in leather processing. This highly toxic, dark-brown wastewater requires complex physical, chemical, and biological treatments to prevent severe soil and aquatic pollution. Because tannery effluents are high in salinity, toxicity, and recalcitrant organics, conventional biological treatment methods (like activated sludge) struggle to break them down. Advanced methods like electrocoagulation, membrane filtration, and advanced oxidation processes (AOPs) are required to target recalcitrant compounds like tannins and toxic metals. Biological treatment options are generally considered more sustainable, cost-effective, and environmentally friendly, as they rely on microorganisms to break down pollutants. 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. Using fungi in tannery effluent treatment provides an eco-friendly, highly efficient biological alternative to conventional chemical methods. Fungi excel at breaking down complex organic pollutants and capturing toxic heavy metals, making them a sustainable solution for leather industry wastewater
Conclusion
This review has comprehensively examined the current state of tannery wastewater treatment, with a particular focus on fungal-mediated bioremediation. Tannery effluents represent a significant environmental challenge due to their high toxicity, salinity, and recalcitrant organic content. While conventional physical-chemical and biological treatment methods have been employed, they often fall short of achieving complete remediation. Fungi, particularly white-rot fungi and tannin-degrading species, offer a promising, sustainable, and cost-effective alternative for the treatment of tannery wastewater. Their ability to produce non-specific extracellular enzymes (LiP, MnP, laccase, tannase) enables the degradation of a wide range of recalcitrant compounds, while their cell walls facilitate the biosorption of heavy metals.
Recent developments in genomics, metagenomics, enzyme immobilization, and microbial consortia have further enhanced the potential of fungal bioremediation. The integration of AI and machine learning for process optimization, coupled with the development of hybrid treatment systems combining fungal treatment with other methods, represents a promising direction for future research. However, challenges remain, including the need for optimized process conditions, stability in non-sterile environments, and scalability for industrial applications.
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