Nordic microalgae immobilized to a sulfur-cooking oil copolymer form a highly efficient, sustainable and reusable sorbent to remove heavy metals from complex mixtures

Abstract

Heavy metal contamination is of highest concern for the environment. Bioremediation, using microorganisms to adsorb and enrich heavy metals, offers an outstanding solution, especially when the pollutants appear at concentrations where physical/chemical methods are not efficient. This study presents a sustainable approach to heavy metal removal through the development of a microalgae-based sorbent supported on a copolymer produced entirely from recycled waste streams. The copolymer was synthesized by inverse vulcanization using sulfur recovered from petrochemical waste and waste cooking oil, demonstrating a circular use of industrial and household by-products. This sustainable, biobased sorbent was highly efficient in removing the heavy metals copper, cadmium and lead in a multi-element mixture at concentrations of industrial relevance. Kinetics and equilibrium parameters and even adsorption capacities improved drastically after immobilization of microalgae to the copolymer, compared to free-swimming microalgae or copolymer alone. The green microalga Chlorella vulgaris (13-1) immobilized to the copolymer removed more than 95% of the total Cu²⁺ and Cd²⁺ and 50% of the total Pb²⁺ within 8 h. Additionally, this sorbent is reusable; a desorption and regeneration step with 0.1M EDTA and CaCl₂ allowed up to 98% recovery of the concentrated, bound heavy metals. Reusing the microalgal-copolymer sorbent in a second removal cycle resulted in removal rates of 75–99% of the initial ones. This novel sorbent allows not only sustainable and efficient removal of heavy metal mixtures from industrial wastewaters but also can be used in subsequent rounds during wastewater purification.