15 SEPTEMBER 1999
REMOVAL OF PARTICLE-ASSOCIATED BACTERIA BY PREFILTRATION AND ULTRAVIOLET IRRADIATION
H. Liltved, S.J. Cripps-1999
Aquaculture Research, 30: 445-450
Abstract:
The combined effect of prefiltration and ultraviolet (UV) irradiation on the removal of bacteria associated with plankton fragments was investigated in an experimental flowthrough system. The system was supplied by sea water containing fragments of Artemia nauplii in the size range 10-240 micro m diameter (mean = 66 micro m), as determined by particle size analysis. By applying an UV dose of 10 mJ/cm^2, the number of colony-forming units (CFU) was reduced from 7.4 x 10^5 per 100 mL to 2.0 x 10^3 per 100 mL. Increasing the dose to 13 or 22mJ/cm^2 did not result in any further reduction, suggesting that bacteria associated with Artemia fragments were protected. This protection hypothesis was supported by improved overall bacterial removal efficiency by prefiltration. At the highest dose (22 mJ/cm^2), more than 5 log10 units total reduction was obtained by prefiltration using 50 micro m mesh sizes. The reduction relative to the unfiltered sample were 1.4, 2.4 and 3.0 log10 units using mesh sizes of 355, 80 and 50 micro m respectively. It is concluded that sea water for aquacultural purposes should be filtered to remove particles before UV disinfection, thereby improving the overall bacterial removal efficiency and reducing the risk of introducing UV-shielded bacteria.
(Norwegian Institute for Water Research, Southern Branch, Televn. 3, N-4879, Grimstad, Norway)