Abstract
Ultraviolet (UV) disinfection is now widely implemented as a tertiary treatment for wastewater reclamation. The negative impact of suspended particles on UV disinfection efficiency has been established. The aim of this study was to provide plant operators with a simple way to predict water quality degradation. To this end, simple correlations between indicators of suspended particles contamination and UV disinfection efficiency of activated-sludge effluents were explored using effluents from a wastewater treatment plant (WWTP) in the South of France. Three groups of microorganisms were considered: coliforms, Escherichia coli and enterococci. To test activated-sludge effluents of varying quality, secondary effluent was blended with different volumes of mixed liquor from the aeration tank of the WWTP. The number of particle greater than 25 μm was found to be well-correlated with total suspended solids (TSS) (R2 = 0.88), turbidity (R2 = 0.94) and UV transmittance at 254 nm (UVT254) (R2 = 0.81). Large particles were shown to impact UV disinfection at two main levels: they scattered UV light and they shielded bacteria inside their compact cores. Linear correlations were determined in this study between indicators of suspended particles presence and 1) inactivation constant of the UV-susceptible fraction of the microorganisms studied, 2) residual bacterial counts after exposition to high UV fluence (tailing potential). These correlations are intended to be used by the wastewater reclamation plant operator to predict the effect of secondary effluent quality degradation on the UV disinfection treatment process.
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