Fate and Survival of Fecal Coliform through Centrifuge Dewatering and Role of Centrate in Growth Inhibition

Recent studies have reported significant increases in fecal coliform counts in anaerobically digested and centrifugally dewatered sludge. The reasons behind the observed increases are not yet understood, and this study investigated the role of inhibitor substances on the reactivation and regrowth of sludge bacteria, and the effect of storage time and temperature on their growth behaviour. The study consisted of full-scale and lab-scale testing, and quantified the microbiological and chemical characteristics of sludge, cake, and centrate samples under different temperatures and aging times. The results showed that the regrowth phenomenon is not observed for all sludges, and differences in sludge characteristics and treatment processes may play a role in determining the reactivation and regrowth behaviour of sludge. Centrate collected from one of the treatment plants had an inhibitory effect on the growth of fecal coliform, and was four times more toxic than cake. Chemical analyses of the centrate identified sulphide as one of the possible inhibitory compounds. The results also indicate that fecal coliform have different growth and survival behaviour compared to other sludge bacteria, and may not be a good indicator for biosafety of digested sludge.