The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) dictates that for a drinking water treatment plant
(DWTP) to receive credit for ultraviolet (UV) inactivation of chlorine resistant pathogens such as
Cryptosporidium and Giardia, validation testing must be performed to demonstrate that the
UV reactor equipment delivers the required dose. This paper summarizes an extensive
bioassay validation program undertaken at the DVGW testing center in Germany with the
objective to evaluate the performance of two closed-vessel UV reactors for the disinfection
of drinking water. A cross-flow in-line reactor and an axial-flow bottom-through-top reactor
operating with 4-kWatt medium pressure lamps were tested using the UV intensity set-point
method and Bacillus subtilis spores as a pathogen indicator. The paper reviews the impact of
key design parameters on the disinfection performance as measured during bioassay
validation testing. Key design parameters evaluated include sensor to sleeve distance,
approach hydraulics, reactor inlet and outlet configuration and doped versus non-doped
sleeves. It was determined that optimization of sensor to sleeve distance is vital to yielding
maximum reactor performance. Increasing the initial sensor to sleeve distance produced
beneficial results. Under conditions where the inlet pipe diameter was smaller than the
diameter of the cross-flow reactor, the resulting approach hydraulics yielded a high inlet
velocity, described as a core jet, and subsequent degradation of performance. The
implementation of a stilling plate restored performance to some extent particularly with low
flow conditions. No significant impact on reactor performance was observed by using doped
versus non-doped sleeves. Careful consideration and optimization of the design parameters
outlined herein is a vital component of any reactor validation program, ensuring that UV
reactors can deliver the proper UV dose over a wide range of water quality and flow
conditions experienced at water treatment facilities. Includes 4 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 16 |
| Published : | 11/15/2004 |
