Page 465 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

420 Fundamentals of Water Treatment Unit Processes: Physical, Chemical, and Biological

Preozonation: Oxidation of the raw water prior to filtration. the flow in a given time increment to particles
Reservoir: The filter box zone above the filter media; the approaching collectors that have crossed the
location of the headwater or supernatant water. same area and plane within the same time increment.
Ripening: (1) The process whereby a diverse biological com- See Chapter 12.
munity develops within a filter bed. (2) The sense of Turbidity: Cloudiness of the water due to small particles.
the term is that a biofilm develops on the sand surfaces Underdrain: A system of perforated pipes in the gravel sup-
that may then serve as for ‘‘attachment’’ of microor- port that serves to collect filtered water and channel it
ganisms that are transported to the surface. out of the filter box to an overflow weir.
Roughing filter: A pretreatment consisting of a series of Uniformity coefficient, UC, d 60 =d 10 : The ratio of the sieve
chambers of coarse media which serve to reduce size through which 60% of the sand will pass to the
raw water turbidity. size through which 10% will pass.
Run length: The period of time between filter startup and UVA: Ultraviolet absorbance. Term relates to instrumental
terminal headloss. method to measure dissolved organic carbon.
Sand bed: The filter media. Weir: A plate or other device that serves as for overflow of
Schmutzdecke: A German word which translates literally as water and which may function to control the water
‘‘dirty layer,’’ and adopted early in American prac- elevation and to measure the flow.
tice. The schmutzedecke is defined here as a layer of
material deposited on the top of the filter bed which
causes headloss disproportionate to its thickness. As REFERENCES
stated by van de Vloed (1955, p. 568) the term Alagarsamy, S. R. and Gandhirajan, M., Package and water treat-
was used by Piefke in 1880 (there is no further ment plants for rural and isolated communities, Journal of
citation available), which is useful to date the rec- Indian Water Works Association, 13(1):73–80, 1981.
ognition of the phenomenon as well as the German Arix, A Professional Corporation, Project manual for water system
involvement. improvements—Filter plant, Town of Empire, CO, Project No.
83206.00, February 1984.
Scour: Disturbance of the filter media, usually caused by
Babbitt, H. E. and Doland, J. J., Water Supply Engineering, 3rd edn.,
high-velocity discharge of water into the filter.
McGraw-Hill, Inc., New York, 1939.
Scraping: Removing the schmutzdecke from the surface of Baker, M. N., The Quest for Pure Water, The American Water
the filter bed by manual raking. The depth of removal Works Association, New York, 1948.
ranges from about 5 mm in the case of Empire to Barrett, J. M., Improvement of slow sand filtration of warm water by
perhaps 10–20 mm in other installations. using coarse sand, PhD dissertation, Department of Civil,
Sedimentation: Settling. Environmental, and Architectural Engineering, University of
Colorado, Denver, CO, 1989.
Small community: There is no strict definition but probably a
Beer, C. R. and Dice, J. C., Denver’s slow-sand filters, in: Research
small community would have a population of
News, No. 38, AWWA Research Foundation, Denver, CO,
5000, but more likely 1000 and it is likely that November 1982.
one person has several jobs, for example, operation Bellamy, W. D., Slow sand filtration of Giardia Lamblia and other
of plants for drinking water and wastewater plants, substances, PhD dissertation, Department of Civil Engineer-
water mains, street maintenance, animal control, etc. ing, Colorado State University, Fort Collins, CO, 1984.
Usually public enterprises are limited by money to a Bellamy, W. D., G. P. Silverman, and D. W. Hendricks, Filtration of
Giardia Cysts and Other Substances, Volume 2: Slow Sand
greater extent than in larger communities.
Filtration. Project Summary, Report No. EPA-600=S2-85=026,
Supernatant water: Headwater; the raw water in the
Water Engineering Research Laboratory, USEPA, Cincinnati,
reservoir. OH, May 1985a (NTIS Report No. PB85-191633=AS).
SWTR: Surface water treatment rule. A federal regulation Bellamy, W. D., Silverman, G. P., and Hendricks, D. W., Removing
adopted by the USEPA pursuant to the 1994 Safe Giardia cysts with slow sand filtration, Journal of the
Drinking Water Act (PL93-523). In general, the American Water Works Association, 77:52–60, February
SWTR requires a three-log inactivation of Giardia 1985b.
Brink, D. R. and Parks, S., Update on slow sand=advanced biological
lamblia cysts and a four-log removal of viruses. The
filtration research, in: Graham, N. J. D. (Ed.), Slow Sand
regulation requires filtration of surface waters, with
Filtration: Recent Developments in Water Treatment Technol-
exceptions. As applied to slow sand the turbidity ogy, John Wiley & Sons, Chichester, England, 1996.
limit was set at 1 NTU. (USEPA, 1989; Pontius, Bryck, J., Giardia removal by slow sand filtration—Pilot to full
1990, p. 41). scale, in: Proceedings Sunday Seminar on Coagulation and
Tailwater: The filtered water that emerges from the filter Filtration: Pilot to Full Scale, Annual Conference of the
underdrain system and flows over a weir. The eleva- American Water Works Association, Kansas City, MO,
June 14, 1987.
tion of the weir, along with the headwater elevation,
Bryck, J., Personal communication, September 20, 1990.
controls the pressure gradient in the filter bed.
Bryck, J., Walker, B., and Hendricks, D. W., Slow Sand Filtration at
THMFP: Trihalomethane formation potential. 100 Mile House, British Columbia, Supply and Services Can-
Transport coefficient, h: Ratio of particles striking collector ada Contract ISV84-00286, Dayton & Knight, Ltd., Consult-
surfaces in a given unit area in a plane normal to ing Engineers, West Vancouver, BC, June 1987.