Survival kinetics of faecal bacterial indicators in spent broiler litter composting

The objective of this study was to deduce and analyse equations that best describe the behaviour of faecal bacterial indicators and two decomposition parameters during broiler litter composting. Mathematical models were fitted and the order of rate equations were identified.

The Levenburg-Marquardt algorithm was used to fit nonlinear mathematical models to total coliforms (TC), faecal coliforms (FC), Escherichia coli (EC), faecal enterococci (FE), organic-C and volatile solids reduction, VS Red, by the least squares procedure. The rate equations showed that TC, FC and EC reductions were expressed by second-order decay kinetics. FE reduction followed first-order decay. Temperature dependency of decomposition rate was effectively verified by applying empirically derived rate equations.

The governing mathematical models critically compare the inactivation kinetics of faecal indicators. TC, FC and EC were rapidly destroyed while FE was more resistant. Temperature elevation, organic-C and VS Red dynamics provide an accurate understanding of composting-induced decomposition of the broiler litter.

The conservative performance of FE with respect to the other indicators has been established. Hence, FE presents better opportunities to encompass the totality of the composting process in terms of attainment of hygiene efficacy compared with EC.