Immobilised native bacterial consortia for algal toxin removal: Towards sustainable in-situ remediation

This study proposes a novel in-situ bioremediation strategy for the removal of highly toxic algal metabolites released during Harmful Algal Blooms (HABs). The target algal toxins are Microcystin-LR (MC-LR) and Anatoxin-a (Atx-a) as they are acutely toxic, environmentally stable, evade conventional treatment processes and contribute to disinfection by-products formation. Native bacterial consortia isolated from lakes with recurrent algal blooms were immobilised on three matrices: polyethylene (PE), polyurethane (PU), and cellulose sponge (CS). Suspended systems achieved 90.4 % (MC-LR) and 92.5 % (Atx-a) removal at 50 μg/L, but efficiencies declined to 77.8 % and 80.0 %, respectively, at 250 μg/L. In contrast, immobilised systems maintained high removal efficiencies even at an initial toxin concentration as high as 250 μg/L, achieving 100 % toxin removal with PU and CS and over 90 % with PE. Although CS showed complete removal, its biodegradable nature limits long-term use. PU emerged as the most durable and effective carrier, ensuring stable microbial activity and negligible sorption. Microbial degradation was confirmed as the dominant mechanism, with Burkholderia sp. identified as the key degrader. This study also provides insight on Atx-a attenuation by identifying degradation products and proposing a potential co-metabolic biodegradation pathway. Microplastic analysis revealed minor particle release from PU, which can be further mitigated by enclosing the immobilised matrices in permeable barrier during field deployment to prevent secondary contamination. Present study highlights the promise of combining native consortia with immobilised systems as a scalable and environmentally compatible strategy for in-situ algal toxin remediation.