MODELING FECAL-COLIFORM BACTERIA .1. FIELD AND LABORATORY DETERMINATION OF LOSS KINETICS

Contamination of surface waters through the discharge of fecal material in surface run-off, combined sewer overflows and point source discharges is an important water quality problem in many urban environments. Field and laboratory studies were conducted to develop and verify the kinetic expressions and attendant coefficients required to simulate the loss of fecal coliform bacteria in lakes due to death [as mediated by irradiance (light) and temperature] and sedimentation. The dark death rate coefficient at 20-degrees-C (k(d) = 0.73 d-1) was established in laboratory experiments utilizing raw sewage diluted with filtered lake water. No consistent relationship was observed between the dark death rate coefficient and temperature (theta = 1). The irradiance-mediated death rate (k(i)) was shown to be proportional to irradiance (I) in water column incubations of raw sewage using a dialysis tube technique: k(i) = alphaI; alpha = 0.00824 cm2 cal-1. The settling loss rate (1.38 m d-1) was quantified by determining the association of fecal coliform bacteria with particles of various size classes and measuring the sedimentation rate for those particle classes using sediment traps. Individual loss terms are combined into a single predictive expression which may be used to simulate fecal coliform bacteria dynamics in lakes.