Investigation of biosorption and bioaccumulation properties of some textile dyes with penicillium funiculosum

The extensive use of synthetic dyes in the textile industry continues to pose a severe and persistent threat to aquatic ecosystems and overall water quality. These dyes are characterized by their high chemical stability, complex aromatic structures, resistance to biodegradation, and, in many cases, inherent toxicity. Once discharged into natural water bodies without proper treatment, they can cause significant environmental issues, such as eutrophication, reduction in sunlight penetration, and disruption of aquatic photosynthesis. This leads to oxygen depletion, negatively affecting aquatic flora and fauna, and ultimately disturbing ecological balance. Among the numerous dyes used in textile processes, Acid Violet 90 (AV90) and Direct Blue 86 (DB86) stand out due to their widespread application, strong chromophoric properties, and recalcitrant nature. Their persistent presence in wastewater makes them difficult to remove using conventional treatment technologies. AV90 and DB86 belong to the azo dye group, which is structurally composed of one or more azo (-N=N-) linkages attached to aromatic systems, conferring intense coloration and high stability. These properties, while beneficial for textile applications, render the dyes resistant to photodegradation, microbial attack, and chemical breakdown under standard wastewater treatment conditions. Conventional remediation methods such as coagulation-flocculation, chemical oxidation (e.g., using ozone or hydrogen peroxide), adsorption onto activated carbon, and membrane filtration have been employed to remove synthetic dyes from aqueous environments. However, these approaches often suffer from critical drawbacks including high operational and maintenance costs, production of hazardous sludge or secondary pollutants, and limited effectiveness under varying effluent compositions. Additionally, energy consumption and chemical usage in these methods raise environmental and economic concerns, especially for small to medium-sized textile enterprises. In light of these challenges, there is an increasing interest in developing sustainable, environmentally benign, and economically feasible alternatives for dye removal. Biological treatment methods, particularly those utilizing microbial systems, have emerged as promising tools due to their low energy requirements, adaptability to variable effluent characteristics, and minimal generation of toxic byproducts. Among microbial candidates, fungi have attracted significant attention because of their robust enzymatic systems, ability to grow under extreme conditions, and large surface area facilitated by filamentous morphology. This study aims to explore the dual mechanisms of biosorption and bioaccumulation for the removal of AV90 and DB86 dyes using the filamentous fungus Penicillium funiculosum. This fungal species is known for its high surface-to-volume ratio, metabolic versatility, and capacity to bind and internalize various pollutants. The biosorption process involves the passive adhesion of dye molecules onto the fungal cell wall via functional groups such as carboxyl, hydroxyl, amino, and phosphate moieties. It does not require energy input, making it a cost-effective approach for the initial phase of dye removal. Conversely, bioaccumulation is an active, energy-dependent process in which live fungal cells uptake dye molecules into their intracellular compartments through specific transport systems. To evaluate the efficiency of these mechanisms, a series of controlled batch experiments were conducted under varying operational parameters including pH (ranging from acidic to neutral), temperature (20–50 °C), initial dye concentration (25–200 mg/L), contact time (up to 120 minutes), agitation speed (50–200 rpm), and biomass dosage. The objective was to determine the optimal conditions under which maximum dye removal could be achieved. Analytical techniques such as Fourier Transform Infrared (FTIR) spectroscopy were utilized to identify changes in the functional groups on the fungal surface following dye exposure. Additionally, optical and electron microscopy provided insights into morphological transformations and the extent of surface binding or internalization of dye particles. These analyses confirmed that the fungal biomass exhibited strong dye-binding capacities, with removal efficiencies reaching up to 99% for AV90 and 98% for DB86 under optimized biosorption conditions. Notably, the removal of AV90 was more effective at lower pH values, suggesting that electrostatic attractions between the positively charged dye molecules and negatively charged functional groups on the fungal surface played a critical role. Further, desorption studies were carried out to assess the reusability and regeneration potential of the biosorbent. Acidic solutions (e.g., 0.1 M HCl) demonstrated higher desorption efficiencies compared to basic and alcoholic media, indicating the feasibility of repeated biosorption-desorption cycles with minimal performance loss. This highlights the economic and environmental benefits of employing such fungal systems in industrial-scale wastewater treatment. Kinetic modeling of the dye removal process revealed that both AV90 and DB86 followed the pseudo-second-order kinetic model, suggesting that chemisorption involving valence forces or electron sharing was the rate-limiting step. Equilibrium data were best described by the Langmuir isotherm model, indicating that dye molecules formed a monolayer on the fungal surface with finite, homogeneous sorption sites. This is consistent with the hypothesis that biosorption occurs predominantly through specific, localized chemical interactions rather than non-specific physical adsorption. In the bioaccumulation phase, experiments were performed using metabolically active P. funiculosum cultures under the previously determined optimal conditions: pH 6.7, temperature 28 °C, and agitation at 160 rpm. The results showed substantial dye removal, with efficiencies exceeding 97% for both dyes. Interestingly, AV90 consistently demonstrated more stable and reproducible removal across multiple trials, implying a higher affinity for metabolic uptake, better transport across the cell membrane, or more effective sequestration within intracellular compartments. These findings underscore the dual utility of P. funiculosum as both a biosorbent and a bioaccumulator, offering an integrative solution for textile dye remediation. Its ability to function effectively under mild and non-extreme environmental conditions, coupled with high dye removal efficiency and the potential for regeneration, makes it a suitable candidate for practical wastewater treatment applications. Moreover, utilizing a single fungal species capable of performing both mechanisms can simplify the operational process, reduce treatment time, and minimize costs associated with the use of multiple microbial strains or treatment stages. Beyond laboratory-scale experimentation, the implications of this study extend to the design and implementation of scalable, hybrid treatment systems. These could integrate fungal-based biosorption-bioaccumulation units with other biological or physico-chemical methods to achieve complete dye mineralization or further detoxification of wastewater. Additionally, future studies may explore enhancements such as fungal biomass immobilization on solid supports, genetic modification to improve dye degradation pathways, and continuous flow systems to simulate real-world industrial settings. In conclusion, this comprehensive investigation demonstrates the high efficacy and practical potential of P. funiculosum in the removal of recalcitrant textile dyes AV90 and DB86 via combined biosorption and bioaccumulation. The fungus exhibited superior performance in acidic environments, confirmed by high removal rates, reusability, and favorable kinetic and equilibrium profiles. These results strongly support the feasibility of adopting fungal-based systems as low-cost, sustainable, and eco-friendly alternatives to conventional wastewater treatment technologies, contributing to the broader goal of mitigating industrial pollution and protecting aquatic ecosystems.