Sustainable microalgal bioremediation of heavy metals and dyes from synthetic wastewater: Progressing towards United Nations Sustainable Development Goals

Abstract

Current research investigates the sustainable bioremediation of heavy metals (cadmium and chromium) and dyes (methyl orange and crystal violet) from synthetic wastewater while simultaneously facilitating CO₂ sequestration for microalgal growth enrichment. The study is motivated by the urgent need for environmentally benign approaches to wastewater treatment, utilizing acclimatized microalgae species (Arthrospira platensis and Spirulina sp.) to continuously remove hazardous pollutants. The primary objective is to achieve effective bioremediation of heavy metals (up to 100 mg/L) and dyes (up to 10 mg/L) through biosorption, bioaccumulation, and degradation under optimized light conditions, including natural sunlight and red illumination. Sunlight is naturally existing whereas red illumination provides better growth and chloroplast activity. Gradual acclimatization of microalgae to increasing concentrations of contaminants enabled optimal removal efficiencies. Mechanisms for biosorption and bioaccumulation of heavy metals as well as degradation and utilization of dyes, is well elucidated by acclimatized microalgae under sunlight and red illumination. Results indicate complete removal of cadmium and chromium, with partial removal of methyl orange and higher efficiency for crystal violet degradation. Acclimatized Spirulina sp. achieved 100 % removal of heavy metals within 24 h of fermentation under controlled pH, temperature, and red illumination (45,000 Lux). The findings support the scalability of this bioremediation process for industrial wastewater treatment, highlighting its potential as an effective and sustainable solution for mitigating environmental contamination.