Critical evaluation of the factors affecting Escherichia coli environmental decay for outfall plume models

Abstract

The Escherichia coli T₉₀ parameter is widely employed in outfall plume hydrodynamic models. Although there is a great deal of academic literature estimating T₉₀, no standard methodology has been validated so far. Estimation of die-off rates should consider many other biological, chemical and physical processes. Over the last three decades, while a great deal of new knowledge about microbial biology and ecology has become available, it has not been fully incorporated into the overall research. Consequently, hydrodynamic models of sewage plumes lack consistency with environmental dynamics and frequently do not fully reproduce processes. This article scrutinized the relevant works that could improve T₉₀ assessment using the most robust and realistic approaches. The most important related literature since the 1990s was considered, together with earlier relevant works. The research focused on techniques and methodologies, especially their ecologic and cellular biology aspects. A brief discussion of the methods applied to evaluate the T₉₀ of bacteria examined aspects like representativeness of incubation, incubation scale, measurement procedures and models’ representations of bacterial decay. The factors affecting population decay, such as solar radiation, salinity and interaction with solids, were considered in the light of the very large literature registry. Finally, biological aspects affecting decay, like predation and genetic resistance, were also analyzed. The resulting updated understanding of T₉₀ may contribute to better managerial procedures that could improve water quality in freshwater and coastal systems, and consequently improve human health outcomes.