Living adsorbent for Congo red removal and value-added product recovery via synergistic integration of photosynthetic bacteria and bacterial cellulose

Conventional adsorbents for Congo red (CR) removal pose economic and environmental challenges owing to high energy consumption and secondary pollution from waste adsorbent residues, highlighting a critical need for developing ecofriendly alternatives. This study reports a fully bio-based adsorbent comprising photosynthetic bacteria immobilized within a bacterial cellulose matrix, termed photosynthetic bacteria–bacterial cellulose (PSB–BC), for CR removal in batch and continuous systems. The PSB–BC biosorbent achieved a CR removal efficiency of 97% within 3 days and demonstrated a high cell immobilization efficiency of 472% under shaking for 120 h relative to the initial inoculum concentration. The immobilized cells exhibited enhanced production of value-added compounds after the removal process compared to the free-cell system, indicating 1.75-fold higher biomass, 1.86-fold higher carotenoid, and 2.39-fold higher bacteriochlorophyll a production. Cost-effective CR removal (96%) was achieved with minimal nutrient supplementation (0.2% yeast extract), and the biosorbent retained its activity after 20 days of storage at 4°C. A fixed-bed column study confirmed the continuous CR removal capability of the PSB–BC biosorbent, with dynamic adsorption behavior successfully described by the Thomas and Yoon–Nelson models. The Thomas model showed a maximum adsorption capacity of 468.88 mg/g, while the Yoon–Nelson model determined a 50% breakthrough time of 164.99 min and provided the best fit to the data, reflecting the synergistic adsorption–biodegradation behavior of the biosorbent. This study introduces a cost-effective, biodegradable biosorbent with high CR removal efficiency and storage stability, offering a scalable and environmentally responsible solution for treating dye-contaminated wastewater.