AWWA WQTC64142

Disinfection processes may be hindered by the presence of particles that can shield microorganisms.The main objective of this study was to determine to what extent turbidity and natural particulatematter can shield spores of aerobic spore forming bacteria (SASFB) from ultraviolet (UV) inactivation. Theextent of the protective shielding was assessed by comparing the inactivations in three waterfractions (untreated, dispersed and filtered on 8 µm membrane) of three water sources. Sampleswere either dispersed by a combination of high speed blending (8,000 rpm) and the addition of asurfactant (Zwittergent 3-12) before UV or after UV irradiation, or filtered on 8 µm prior toirradiation and then blended. Results were described by using a parallel Chick-Watson modelwhich allows for the definition of tailing. Inactivation results showed no tailing for the highquality water. Blending and filtration were shown to increase inactivation rates and decreasetailing levels for all water with higher turbidity and particle content. Filtration on 8 µm removedtailing on all samples on which tailing was observed. Levels of inactivation were then related tothe distribution and abundance of particles as measured by microflow imaging. Particle sizedistribution (PSD) analysis confirmed a statistically significant decrease of particles following thedispersion protocol and filtration. Required fluence to reach 1 log inactivation of ASFB sporeswas independent of particle concentration, whereas the fluence required to reach 2 log inactivationwas correlated with the concentration of particles over 8 µm (R² = 0.633). Results suggest thatnatural particulate matter can protect indigenous organisms from UV radiation in waters withelevated particle content while source water with low particle counts may not be subject to thisinterference. Includes 44 references, table, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2006

Number of Pages:

14

File Size:

1 file , 510 KB