Tracers for investigating pathogen fate and removal mechanisms in mesocosms

The purpose of the present investigation has been to develop a tracer suite that has application in in-situ assessment and optimization of physical and biological removal and elimination mechanisms of pathogens within laboratory scale biological treatment systems. The tracer suite includes three pathogen indicators, namely, a conserved non-viable particle (fluorescently labelled microspheres, FLM), a non-conserved non-viable particle (fluorescently labelled bioparticles, FLB), and a non-conserved viable particle (Nalidixic acid resistant E. coli, NAREC). The tracer triplet principles were developed with practical experiments on planted, and unplanted subsurface flow wetland mesocosms treating a synthetic domestic wastewater. The tracers monitor for physical removal mechanisms (FLM), elimination activity (FLB), and removal thresholds (NAREC). FLM enumeration was simplified by calibration of particle concentration with respect to acetone-extractable fluorescence. Similarly, FLB elimination was assessed by bulk fluorescence using two characteristic excitation–emission wavelength pairs: 494/519 and 220/319 nm. NAREC results indicated that first order removal kinetics may only proceed down to limiting threshold concentrations.