Impacts of process upsets and transient water quality events on UV disinfection performance at Ontario water treatment facilities

The effectiveness of UV disinfection at two Ontario drinking water facilities during sub-optimum water quality conditions was studied. The disinfection performance of a pilot-scale low pressure UV reactor, delivering a reduction equivalent dose of 60--90 mJ/cm2, was not negatively impacted by either pre- and post-filter water quality conditions experienced at the two treatment facilities. Enmeshment of coliforms within particles, resulting in reduced inactivation levels did occur in samples of raw water from one facility that were coagulated with alum and alum+polymer at turbidities >6 NTU and exposed to low UV dosages (≤10 mJ/cm2). No evidence of coliform enmeshment was observed in tests that examined raw water coagulation with STERNPACRTM/activated silica/sand/LT27A. No conclusive evidence was observed that would relate changes in inactivation efficiency as a result of bacterial enmeshment to turbidity or particle count data.