Innovative utilization of coal bottom ash for bioremediation of toxic organic pollutants

•We examined coal bottom ash, gravel and tuff for Cupriavidus basilensis biofilm growth.•Massive biofilm was developed on coal bottom ash which was further utilized for bioremediation.•Phenol degradation by the biofilm was faster than the degradation by the plankton bacterial cells.•Phenol degradation also occurred under conditions of relatively extreme pH and temperature.

Cupriavidus basilensis cells were grown on coal bottom ash, tuff and gravel in a medium containing phenol. Confocal scanning laser microscope analysis demonstrated a live biofilm on the coal bottom ash, but not on the tuff or gravel. Measurement of the dehydrogenase activity in the biofilm showed an absorbance of 0.697 ± 0.04 at 540 nm when the biofilm was grown on coal bottom ash, and only about 0.002 on tuff and gravel.Planktonic bacterial cells and biofilm which were grown on coal bottom ash degraded 400 mg l−1 phenol within 47 ± 2.5 h and 28 ± 1.7 h, respectively. Optimal phenol degradation occurred between pH 6 and pH 8. Degradation by the biofilm was slower at lower or higher pH values, whereas no degradation was observed by the planktonic bacterial cells at these pH values.The optimum temperature for biodegradation was observed at 28 °C. At 37 °C and 15 °C degradation by the biofilm was slower, whereas no degradation was observed by the biofilm. Repeated biodegradation of the biofilm was carried out for 200 h. The biofilm on the coal bottom ash exhibited a developed network of appendages connecting the bacterial cells to each other. To the best of our knowledge, this study is the first to evaluate coal bottom ash for biodegradation of toxic organic pollutants.