Bio-elimination of Chromium Using Bacillus Cereus Strains Isolated from Activated Sludge

Industrial activities have intensified heavy metal pollution, with chromium-particularly hexavalent chromium [Cr(VI)]-recognized as one of the most toxic and carcinogenic pollutants. Heavy-metal-resistant bacteria are promising, eco-friendly, and cost-effective bioremediators that can efficiently remediate heavy metal pollution as an alternative to traditional techniques. This study investigates chromium-resistant bacteria isolated from activated sludge to evaluate their Cr(VI) detoxification mechanisms, as well as their chromium accumulation and reduction efficiency. The effects of environmental factors (pH, metal concentration, and contact time) on bioaccumulation and reduction were examined, and bacterial characteristics were analyzed using TEM, EDX, and FTIR. Three Bacillus cereus strains (A, B, and C) were isolated from activated sludge, with a maximum inhibitory concentration (MIC) of 800 mg/L of Cr(VI). These isolates were evaluated for Cr(VI) detoxification. Strain A showed the highest Cr(VI) accumulation (48.8%) and overall detoxification efficiency (69.81%), while strain B exhibited the greatest reduction efficiency (24% within 30 min). Detoxification performance was strongly influenced by pH, with bioaccumulation being optimal at pH 7 and reduction favored under acidic conditions. FTIR and TEM analyses revealed strain-specific mechanisms, with strains A and B showing surface functional group interactions, while strain C employed enhanced intracellular and spore-associated sequestration.