Calcium alginate-biochar composite immobilized A. ferrooxidans effectively removes sulfate and ferric iron from acid mine drainage.

Bioremediation has been applied in the treatment of acid mine drainage (AMD), but high levels of sulfate (SO₄^2-) and ferric iron (Fe³⁺) in AMD often affect microbial activity. A novel biochar-microorganism composite (I-CMR600) was developed by alginate gel-embedding method to improve the tolerance of microorganisms and the removal effects of SO₄^2- and Fe³⁺ in AMD, and its removal mechanism and biological behavior were explored in this study. The removal performance of I-CMR600 under different influencing factors was studied by batch adsorption experiments. The removal mechanisms and biotransformation of SO₄^2- and Fe³⁺ were explored through different adsorption models combined with physicochemical characterizations. The results showed that A. ferroxidans secreted extracellular polymers to enhance the removal of contaminants, and high concentrations (>400 mg/L) of SO₄^2- and Fe³⁺ inhibited the activity of microorganisms. The Langmuir maximum adsorption capacities of I-CMR600 for SO₄^2- and Fe³⁺ were 32.85 and 63.53 mg/g, respectively. The effects of A. ferroxidans on SO₄^2- and Fe³⁺ were mainly through promoting their biotransformation, the adhesion of A. ferroxidans, and the complexation of secreted extracellular polymers with pollutants. I-CMR600 showed good reusability and promising potential for practical application in actual AMD. This study demonstrates that I-CMR600 is a promising biosorbent, providing a new avenue for removing SO₄^2- and Fe³⁺ from AMD.