Microbial Cell Immobilized Biochar for Bioremediation of Metal Ions and Pesticide from Water and Soil

Abstract

The escalating water and soil contamination, due to industrialization and urbanization, poses significant threats to human health and ecological safety. Among various pollutants, pesticides and heavy metals, are alarming due to their potential to bioaccumulate in organisms, disrupting the food chain and exposing humans. Bioremediation with microbial cells is promising but faces challenges such as microbial loss or reduced survival due to high pollutant concentration, uneven growth, cell washout and prolonged process time. In recent years, microbial immobilization technology has rapidly advanced for pollutant removal, with a focus on lowcost carriers with high removal efficiency. Biochar stands out as an efficient carrier due to its high porosity and strong adsorption capabilities, providing a habitat for microorganisms. This work explores the potential of microbial cell-immobilized biochar in removing cadmium, nickel, and chlorpyrifos from contaminated water and soil. Different combinations of biochar and microbial cells were tested, with the most efficient biochar selected for further pollutant removal experiments. The effect of various operating conditions, pH, temperature, biocatalyst dosage, and initial metal ion concentration, on cadmium and nickel removal efficiency were examined. Pseudomonas stutzeri immobilized on rice husk biochar showed significant efficacy, removing up to 95% of cadmium and 92% of nickel. Moreover, efficiently remediated cadmium-contaminated soil, converting exchangeable cadmium to less bioavailable residual fractions. Other combinations of microbial cell-immobilized biochar, such as Pseudomonas stutzeri immobilized sawdust biochar, Bacillus sp immobilized rice husk biochar, and Pseudomonas stutzeri immobilized coconut shell biochar were also efficient in metal ion removal. Additionally, Aeromonas veronii immobilized on rice husk biochar effectively degraded chlorpyrifos, with a removal rate of 96.25% in water within 24 h and 92.4% in soil within 42 days. The mechanism of metal ion and pesticide removal involves biochar-mediated adsorption, microbial cell-mediated bioaccumulation for metal ions, and microbial metabolism and biochar-mediated adsorption for pesticides. This combined biochar and immobilized microbial cell approach presents an innovative, sustainable solution for remediating metal ions and pesticide-contaminated environments.