RESUMEN
AIM: This study investigates differences in bacterial growth response in broth amended with compost-substrate extracts periodically bypassed during broiler litter composting. METHODS AND RESULTS: Compost samples, suspended in diluent were mixed with double strength broth into which ampicillin selective (0.3 g l(-1)) Escherichia coli and E. faecalis were separately seeded. Growth was measured by viable cell count. The Levenberg-Marquardt algorithm was applied to obtain a four-parameter sigmoidal function that best described the diminishing height transitions of the curves for extracts of increasing composting age. The time course of the growth rate followed a unimodal bell-shaped curve. The Microfit application was run to generate information of direct microbiological interest: increasing lambda and decreasing mu(max) for both bacteria with time. CONCLUSION: More than the curve-fitting process, the Unified model option of the Microfit application has confirmed the significant differences (P < 0.05) in the growth curve behaviour with more stabilized substrate extracts. The study demonstrates further scopes for characterization of the sanitization potential and indirectly, the impact of indigenous microbial competitive exclusion effects on enteric bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: A different outlook to understanding faecal bacterial growth dynamics in compost has been presented, using predictive microbiology concepts. Further structured studies are needed to fine-tune the generality of the findings for model development.
Asunto(s)
Enterococcus faecalis/crecimiento & desarrollo , Escherichia coli/crecimiento & desarrollo , Suelo , Algoritmos , Animales , Biodegradación Ambiental , Pollos , Recuento de Colonia Microbiana/métodos , Heces/microbiología , Matemática , Viabilidad Microbiana , Modelos BiológicosRESUMEN
AIMS: 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. METHODS AND RESULTS: 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. CONCLUSIONS: 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. SIGNIFICANCE AND IMPACT OF THE STUDY: 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.