Competitive exclusion as a means to reduce E. coli regrowth in digested sludge cake
Williams, T.1, Le, M.S.2, Miller, K.2 Tyrrel, S.F.1 and Harris, J.A.1, 1Cranfield University, UK, 2United Utilities, UK
(free)
Sewage sludge treatment processes are intended to reduce the numbers of pathogens to acceptable levels. However, it has been reported that Escherichia coli (E. coli) numbers can increase significantly following the dewatering step of cake manufacture, particularly where high shearing forces are involved such as in centrifugation.
E. coli is used as an indicator of the microbiological quality of sludge-derived products destined for agricultural recycling. The re-growth phenomenon is of concern because of the potential for additional treatment requirement, ensuing higher disposal costs and loss of consumer confidence associated with a compliance failure.
In this paper we report on an investigation into the use of the competitive exclusion principle to control E. coli re-growth in digested cake. Competitive exclusion relies on the principle that two or more species competing for the same resources cannot co-exist if other ecological factors are constant. The technique has seen widespread implementation and success in other industries. The paper presents the latest results on laboratory-scale competition experiments performed in sludge-derived liquid broth with candidate competitive organisms and describes the direction of planned work.
Keywords: scherichia coli, regrowth, competitive exclusion, sludge cake.
