Isolating and Identifying Chromium-Reducing Fungus from Pistachio Shells: Investigation on Capacity of Dead and Live Fungi for Cr(VI) Removal

Hexavalent chromium represents a potent toxicant that poses significant health risks in the living environment, necessitating its reduction or removal below allowable limits before environmental discharge. This research investigates the elimination of hexavalent chromium from wastewater using three different fungal strains: Aspergillus niger NCIM548, A. fumigatus UB2 60˚, and A. niger isolated from a pistachio shell identified through ITS sequencing. In a brief interaction period within a mixing reactor, both strains of Aspergillus niger successfully eliminated Cr(VI) from an initial concentration of 50 mg/L. The study assessed Cr(VI) removal using live and dead A. niger biomass from pistachio shells at Cr(VI) concentrations of 50 to 800 mg/L. The study examined the impact of pH, temperature, and Copper(II) and Nickel(II) on Cr(VI) removal. At 30 °C and pH 3, live biomass (5 g dry cell/L) removed 97% of Cr(VI) (up to 400 mg/L) within 48 hours. Dead biomass nearly fully removed Cr(VI) (800 mg/L) at 45 °C and pH 2 within 24 hours. Higher biomass concentrations improved removal efficiency, but Cu(II) and Ni(II) reduced it. The primary mechanism in live biomass was metabolic Cr(VI)-to-Cr(III) reduction, while dead biomass relied on redox reactions and biosorption. SEM-EDX confirmed Cr(VI) reduction and biosorption.