Precommissioning studies of proposed outfalls along the north coast of Spain included in situ and laboratory determinations of T90 values directed at the development of a local-specific inactivation model.
The effect of salinity, light intensity, temperature and depredation on inactivation (T90) of Escherichia coli, was studied in unifactorial experiments carried out in the laboratory. The values of T90 obtained fitted the exponential model of die-off for the first three variables (salinity, light, temperature: R > 0.93). Light intensity showed the greatest bactericidal effect, with T90 values near or lower than 1 hour, when light radiation was greater than 120 Wm−2. The logarithm of T90 showed a linear relationship with each one of these three factors. Nevertheless, the global relationship which best fits the values obtained was not linear in its coefficients.
The values of T90 estimated from experiments in situ, carried out in summer (33.6 min) and winter (116.8 min), reflected the seasonal differences in the environmental conditions in this zone, mainly from light intensity. Differences between these values and those obtained applying the model pointed out the need to study in depth the effect of light on the bacterial die-off in natural systems.