Green strategies for chromium detoxification in tannery effluents: Adsorption and bioconversion with Portieria hornemannii

Hexavalent chromium (Cr (VI)) is a toxic heavy metal contaminant that poses significant risks to living organisms. Notably, the red algae Portieria hornemannii has demonstrated the ability to adsorb and reduce chromium in aqueous environments. This study focuses on the effective on-site adsorption and bioconversion of Cr (VI) to Cr (III) using organized dead algal biomass enriched with active phytochemicals. The biomass's structural characteristics, surface morphology, functional groups, elemental composition, surface area, and porosity were thoroughly analyzed. Physiochemical parameters were optimized to enhance adsorption efficiency. Various adsorption isotherm models, including Langmuir, Freundlich, and Temkin, and kinetic models (pseudo-first-order and pseudo-second-order) were employed to analyze the adsorption process. The algal biosorbent achieved a maximum removal efficiency of 96.4 % at pH 2.0, with an adsorbate concentration of 300 ppm, an adsorbent dosage of 6 g/L, a temperature of 40 °C, and a contact time of 200 minutes. This study also investigated chromium levels in water released from chrome-tanning processes at tanneries and employed an optimized algal remediation technique. The evaluation of phytotoxic effects and growth metrics for Vigna mungo in the treated tannery water indicated a decrease in phytotoxicity, dropping from 80 % to 35 %. This research highlights the potential of utilizing dead algal biosorbents as an innovative and eco-friendly method for continuous industrial and environmental monitoring to protect groundwater resources. • Portieria hornemannii , a readily available waste resource, efficiently converts hazardous Cr 6+ to non-hazardous Cr 3+ . • The biomass removed 92.7 % of chromium in standard solutions and 83.7 % in real samples, resulting in visible color change. • Dead algal biosorbents provide an economical way to remove toxic chromium from tanneries, reducing labor needs