Changes in thermophilic bacteria population and diversity during composting of coal fly ash and sewage sludge

The thermophilic bacteria in compost made from coal fly ash-amended sewage sludge were isolated and identified using the Biolog system to investigate the effect of coal fly ash on the thermophilic decomposition of sewage sludge during composting. A total of 8 species of Bacillus were isolated from the compost and Bacillus brevis was the dominant species during the entire composting process. The present results demonstrate that the Biolog system is a fast and simple method for identifying bacterial species in compost, provided that optimum conditions could be achieved for the Bacillus culture. Adding coal fly ash as an amendment did not change the dominant bacteria species during composting, but decreased the population and diversity of thermophilic bacteria species due to the high alkalinity and salinity. Fewer thermophilic bacteria were detected in ash-amended sewage sludge compost than in sludge compost. There was also reduced metabolic activity observed in the ash-amended sludge compost from the data of CO₂ evolution and weight loss. Although ash amendment demonstrated a negative effect on the population and diversity during thermophilic phase, it did not cause any significant effect on compost maturity.