Biochar biofilms help microbes clean dye wastewater more efficiently
image: Enhancement of the anaerobic biodegradation efficiency of azo dye by anthraquinone-loaded biochar biofilm: factors affecting biofilm formation and the enhancement mechanism
Credit: Guangyuan Wang, Chenhao Cui, Yuqian Wang, Jiwei Pang, Shanshan Yang, Chuandong Wu, Rui Fang, Luyan Zhang, Nanqi Ren & Jie Ding
A study shows how a modified form of biochar can help microbial biofilms break down stubborn dye pollutants in wastewater, offering a promising strategy for cleaner and more stable anaerobic treatment systems.
Azo dyes are widely used in textile printing and dyeing, but they are also a major source of highly colored industrial wastewater. These dyes can be difficult to remove because their complex chemical structures resist degradation and can inhibit microbial activity during anaerobic treatment. Researchers have long explored ways to improve anaerobic digestion, a low-energy and environmentally friendly process, but the role of biofilms growing on carbon-based carrier materials has remained unclear.
In a study published in Biochar, researchers investigated a biofilm system formed on anthraquinone-2-sulfonate-loaded biochar, known as AQS-BC. Anthraquinone compounds can act as redox mediators, helping shuttle electrons during microbial reactions. By immobilizing AQS on biochar, the team aimed to improve electron transfer while avoiding the cost and instability associated with repeatedly adding soluble mediators to treatment systems.
The study focused on Reactive Red 2, a model azo dye. The researchers found that the AQS-BC biofilm system achieved high and stable anaerobic decolorization performance. After 48 hours, the AQS-BC biofilm removed 92.36% of Reactive Red 2, compared with 73.95% for ordinary biochar biofilm. In contrast, biochar materials without biofilms removed less than 20% of the dye, showing that microbial biofilms were the main drivers of decolorization.
“Our results show that biochar is not only a passive carrier for microorganisms,” said the study’s corresponding author. “When biochar is modified with an electron-shuttling compound, it can create a more active microenvironment for biofilms and accelerate the biodegradation of dye pollutants.”
The team also found that AQS-BC biofilms maintained strong performance during repeated treatment cycles. Biofilms grown on AQS-BC had greater biomass, thicker structure, higher extracellular polymeric substance content, and stronger electron transfer system activity than biofilms on unmodified biochar. These characteristics helped the microbial community remain stable and metabolically active under dye stress.
The modified biofilm system also influenced anaerobic fermentation. Reactive Red 2 caused volatile fatty acids to accumulate and inhibited methane production, but the presence of AQS helped relieve this inhibition. In dye-containing systems, the AQS-BC biofilm produced slightly more methane than the ordinary biochar biofilm, suggesting that the modified carrier helped support microbial metabolism during pollutant removal.
Microbial community analysis further showed that AQS loading increased microbial diversity and enriched groups associated with organic pollutant degradation, electron transfer, volatile fatty acid production, and biofilm stability. These included Proteobacteria, Firmicutes, Actinobacteriota, Desulfobacterota, Brachymonas, Desulfovibrio, Dechloromonas, and other functional microorganisms.
The researchers also examined how inoculation conditions affected biofilm formation. Contact time, sludge concentration, glucose concentration, and dye concentration all influenced how quickly the biofilm matured. Under the tested conditions, suitable biofilm formation was promoted by a 24-hour contact time, 1 g VSS/L sludge concentration, 1000 mg/L glucose, and relatively low initial dye concentrations.
“This work provides a clearer picture of how engineered biochar biofilms function in anaerobic wastewater treatment,” the author said. “By improving electron transfer, microbial attachment, and community stability, AQS-loaded biochar could help develop more efficient treatment technologies for dye-contaminated wastewater.”
The findings suggest that engineered biochar-based biofilms may offer a practical route for strengthening anaerobic treatment of industrial wastewater, especially where toxic or persistent organic pollutants limit microbial activity.
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Journal Reference: Wang, G., Cui, C., Wang, Y. et al. Enhancement of the anaerobic biodegradation efficiency of azo dye by anthraquinone-loaded biochar biofilm: factors affecting biofilm formation and the enhancement mechanism. Biochar 6, 95 (2024).
https://doi.org/10.1007/s42773-024-00384-5
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.