suggested that the copy number of the 16S rRNA gene is 4 per cell for bacteria, and 2.5 per cell for (methanogenic) archaea. Using these figures to calculate cell counts from absolute 16S rRNA gene copy numbers, the bacterial cell count in the current study was estimated to be circa 6.25 times that of the archaeal cell count throughout the monitoring period in the thermophilic
process, and 0.2 to 8.5 times that of archaeal cell count in the mesophilic process