Characterisation of the behaviour of particles in biofilters for pre-treatment of drinking water.
Biofiltration of surface water was examined using granular activated carbon (GAC) and expanded clay (EC). Particle removal was 60-90%, measured by flow cytometry, which enabled discrimination between total- and autofluorescent particles (microalgae) in size ranges of 0.4-1 and 1-15 microm, and measured by on-line particle counting. Total particles were removed at a higher degree than autofluorescent particles. The biofilters were also challenged with 1 microm fluorescent microspheres with hydrophobic and hydrophilic surface characteristics and bacteriophages (Salmonella typhimurium 28B). Added microspheres were removed at 97-99% (hydrophobic) and 85-89% (hydrophilic) after 5 hydraulic residence times (HRT) and microspheres retained in the biofilter media were slowly detaching into the filtrate for a long time after the addition. Removal of bacteriophages (5 HRT) was considerably lower at 40-59%, and no long-lasting detachment was observed. A comparison of experimental data with theoretical predictions for removal of particles in clean granular media filters revealed a similar or higher removal of particles around 1 microm in size than predicted, while bacteriophages were removed at a similar or lesser extent than predicted. The results highlight the selectivity and dynamic behaviour of the particle removal processes and have implications for operation and microbial risk assessment of a treatment train with biofilters as pre-treatment.
Persson
Frank
F
CMB, Microbiology, Göteborg University, Box 462, 405 30 Göteborg, Sweden. frank.persson@gmm.gu.se
Långmark
Jonas
J
Heinicke
Gerald
G
Hedberg
Torsten
T
Tobiason
John
J
Stenström
Thor-Axel
TA
Hermansson
Malte
M
D000538:Aluminum Silicates; D001435:Bacteriophages / Q000302:isolation & purification; D002244:Carbon; D000077215:Clay; D056890:Eukaryota / Q000302:isolation & purification; D005374:Filtration; D005434:Flow Cytometry; D008863:Microspheres; D010316:Particle Size; D018570:Risk Assessment; D014871:Water Microbiology; D014872:Water Movements; D018508:Water Purification / Q000379:methods*
D000538:Aluminum Silicates; D002244:Carbon; D000077215:Clay