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Topic: Slow sand filter bed

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	Filter (water) - Wikipedia, the free encyclopedia
		A water filter is a device which removes impurities from water by means of a fine physical barrier and/or chemical processes.
		Filters are used to cleanse water for irrigation, drinking water, aquariums, and swimming pools.
		The physics of filters is based on sieving, ion exchanges and other processes.
	en.wikipedia.org /wiki/Filter_(water) (147 words)

	Slow sand filter bed - Wikipedia, the free encyclopedia
		Slow sand filters work through the formation of a gelatinous layer called the hypogeal layer or Schmutzdecke in the top few millimetres of the fine sand layer.
		Slow sand filters slowly lose their performance as the Schmutzdecke grows and thereby reduces the rate of flow through the filter.
		Slow sand filters are recognized by the World Health Organization, Oxfam, and the United States Environmental Protection Agency as being superior technology for the treatment of surface water sources.
	en.wikipedia.org /wiki/Slow_sand_filter_bed (672 words)

	Biosandfilter.org - The Bio-Sand Filter
		As a further distinction, slow sand filtration removes particles mainly at the surface of the sand bed.
		Rapid sand filters are suitable for large urban centers where land scarcity is an issue, whereas slow sand filters tend to be more suitable for areas where land is more available, since they need a much larger surface area to treat the same amount of water.
		Slow sand filtration is simpler to operate than rapid filtration, as frequent backwashing is not required and pumps are not always necessary.
	www.biosandfilter.org /biosandfilter/index.php/item/229 (1296 words)

	WT - Rapid Sand Filtration
		Rapid sand filtration is contrasted to slow sand filtration by increased flow rate, method of cleaning the filter bed.
		Rapid sand filters are cleaned often, usually daily, by reversing the flow of water through the entire filter bed, referred to as backwashing.
		Pressure filters are sand filters with the filter bed enclosed in a cylindrical steel or iron shell.
	ewr.cee.vt.edu /environmental/teach/wtprimer/rapid/rapid.html (1171 words)

	Slow Sand Filter
		A slow sand filter is comprised of a bed of graded sand which is supported by a layer of gravel.
		Slow sand filtration is well-suited to treat farm water supplies that have reasonable raw water quality.
		Further study of slow sand filtration is needed to address the treatment of nutrient-rich water and unusually turbid surface water; to investigate performance on manganese removal; and to assess long-term performance of the system.
	www.agr.gc.ca /pfra/water/slowsnd_e.htm (1245 words)

	WT - Slow Sand Filtration
		Slow sand filters in the United States are found primarily in smaller communities with fewer than 10,000 people, 45% of which serve fewer than 1,000 people (Sims).
		Slow sand filtration is a water purification process in which water is passed through a porous bed of filter medium.
		Slow sand filters are typically characterized by certain design components: the supernatant (water above the filter sand that provides hydraulic head for the process), filter sand varying in depth, the underdrain medium (usually consisting of graded gravel), and a set of control devices (Sims).
	ewr.cee.vt.edu /environmental/teach/wtprimer/slowsand/slowsand.html (1811 words)

	Slow Sand Filtration for Water Treatment
		Slow sand filtration was first developed to purify surface water sources for drinking purposes and became a legal requirement in Britain to assist in containing cholera epidemics.
		Sand is characterized by the diameter of the individual sand grains (eg 0.15-.35 mm) and the effective size of the composite sand, the ES or d10.
		Smaller particles of organic sediment left in the sand filter are eaten by microscopic organisms including bacteria and protozoans which 'stick' in the layers of slime that form around the sand particles and the clean water which passes through the filter is safe to drink.
	www.oasisdesign.net /water/treatment/slowsandfilter.htm (5012 words)

	2.5 Filtration systems
		The filter can be cleaned by either scraping off the surface layer of sand and replacing it with washed sand stored after previous cleanings (periodic re-sanding of the bed), or washing the sand in place with a washer that travels over the sand bed.
		Slow sand filters were constructed in Ecuador at a cost of $132.30 with an estimated operation and maintenance cost of 25% of the construction cost.
		The slow sand filters are very effective in removing bacteria; in general, their effectiveness in removing bacteriological contaminants ranges between 80% and 99%, depending on the initial level of contaminants and the number and design of the filtration units.
	www.oas.org /USDE/publications/Unit/oea59e/ch24.htm (3883 words)

	Sand filtration notes
		A "slow sand filter" is 1 to 1.5 meters thick.
		A "rapid sand filter" is less deep; half a meter to one meter is a typical thickness.
		Filter aids combat cake compaction, and intelligent application of pressure can optimize rates by using low driving force when the cake could be crushed and more head later when you might as well get what you can.
	www.rpi.edu /dept/chem-eng/Biotech-Environ/FILTRATION/sand.htm (907 words)

	Slow Sand Filtration of Secondary Effluent (Site not responding. Last check: 2007-10-13)
		The filter was operated at sand depths of 135, 105, and 55 cm, respectively, for each size of the sand, to determine the operational range of the sand depth.
		It was observed that the use of coarse sand resulted in longer duration of filter operation as compared to the fine sand for similar removal of turbidity and coliform, i.e., 84 days in the case of coarse sand compared to a maximum of 26 days for the finer sand.
		The development of the head loss in the sand media was extremely small during the initial period of the operation, which later increased exponentially with most of the head loss occurring in the top dirty surface of the filter, known as schumtzdecke in German.
	www.pubs.asce.org /WWWdisplay.cgi?9303951 (241 words)

	Lesson 3: Treatment Well
		Slow sand filters have been used for the treatment of relatively clear water when there is a possibility of the water becoming turbid. This filtration method can be used to treat spring or well water that is relatively safe from contamination, but should not be used to treat surface water (lakes, ponds, etc.)
		Filters are cleaned by backwashing. The influent valve is closed and a waste line is opened. Treated water from the system is pumped upward through the filter bed. The water pumped upward has the velocity and volume to agitate the sand and carry away the foreign matter that has collected there.
		The slow sand filter is similar in design to a rapid sand filter and a pressure filter, except that the sand is usually 36 inches in depth and the filter cannot be backwashed.
	water.me.vccs.edu /courses/ENV115/LESSON_3g.htm (490 words)

	biology - Slow sand filter bed
		In the base of each bed are a series of herring-bone drains which are covered with a layer of pebbles which in turn is covered with coarse gravel.
		Slow sand filters work through the formation of a gelatinous layer called the hypogeal layer or Schmutzedecke in the top few millimetres of the fine sand layer.
		Slow sand filters slowly lose their performance as the Schmutzedecke grows and this reduces the rate of flow through the filter.
	www.biologydaily.com /biology/Slow_sand_filter_bed (444 words)

	Filter Process Removes Cryptosporidial Oocysts From Water Supplies
		During the operation of the filters, not only are removal efficiencies low at start-up, but later in the cycle flow surges can also cause sloughing off from the medium, resulting in a breakthrough of the infected particles.
		Slow sand filters are more efficient in retaining oocysts than rapid gravity units, largely because of the formation of a 'schmutzdecke' layer.
		A vacuum is drawn from outside the filter element using a liquid ring pump to maintain the vessel at the precise pressure.
	www.waterinfocenter.com /wwd/index.cfm/powergrid/rfah=\|cfap=/CFID/2607134/CFTOKEN/81939736/fuseaction/showArticle/articleID/811 (1083 words)

	Ronald L. Shimek, Ph.D. - The Why's and How's of Sand Beds - Sept. 6th 1998 - www.reefs.org (Site not responding. Last check: 2007-10-13)
		The sand is aragonitic sand, a mixture of oolitic sand, live sand and general goo...
		Sand is a harsh environment, and generally the animals are pretty rugged.
		I have done some calculations (for an upcoming sand bed article) that show the normal activities of the worms in my tank are sufficient to turn all the sediment over every two days.
	www.reefs.org /library/talklog/r_shimek_090698.html (3732 words)

	Testing and Certification of
		A field test was performed to examine the potential for using finely processed recycled glass sand as a filtration medium in high-rate sand filtration.
		An anomaly in filter pressure differentials was found during the data analysis phase.
		Filters used for this evaluation were "Triton" TR series filters manufactured by PacFab, Inc. These filters are common in the swimming pool industry, with an estimated 5,000 to 7,000 filter vessels located on the West Coast of the United States.
	www.cwc.org /glass/gl_htm/gl981rpt.htm (4964 words)

	MSF-USA: Refugee Camp Project - Learn More: Water (slow sand filter) (Site not responding. Last check: 2007-10-13)
		Slow sand filtration allows a highly effective microbiological purification of water in addition to mechanical purification by the sand.
		Open the inlet valve (not too much, to avoid putting the pre-filter sand into suspension); when the filter is full, open the outlet valve so as to have an outflow of about 1 L/min.
		If the needs are greater, several filters may be built in parallel (this also avoids having to cut the supply during maintenance).
	www.refugeecamp.org /learnmore/water/slow_sand_filter.htm (658 words)

	[No title] (Site not responding. Last check: 2007-10-13)
		To diminish negative impact during the scraping of the filter, it is necessary to carry out this operation in one day, thus preventing the death of the beneficial microorganisms in the sand layer that will remain in the filter, and shortening the subsequent ripening period.
		Concentration of nutrients: The rate of development of the biological formation in the filter depends on the concentration of nutrients in the water, because this is the feeding source of the microorganisms.
		The problem is that they generate sludge on the surface of the filter, reducing the filter’s capacity for removal of the biological formation and dramatically reducing the duration of the filter run.
	www.cepis.ops-oms.org /eswww/caliagua/simposio/enwww/ponencia/ponen12.doc (1393 words)

	MSF-USA: Refugee Camp Project - Learn More: Water (simple water treatment) (Site not responding. Last check: 2007-10-13)
		Under certain conditions, in passing water through a bed of sand, particularly effective filtration is achieved by biological purification in addition to the mechanical action of the filter.
		Slow sand filtration is the only procedure which achieves such an improvement of water quality in a single operation.
		A slow sand filter can operate for weeks or even months without maintenance (which consists of the removing of a thin layer of sand when the filtration rate becomes too low).
	www.refugeecamp.org /learnmore/water/simple_water_treatment.htm (798 words)

	Detailed Information for the Water Treatment Technology Center
		The former involves a constructed filter bed in which water passes through the sand medium slowly while the latter involves the same removal principles as the former except the filter bed is naturally configured from the native river bank.
		The schmutzedecke of the slow sand filter will be monitored by periodic core sampling of the slow sand filter surface, and hydraulic head measurements at piezometer points installed in the sand filter.
		The river bed material will also be periodically sampled at times similar to the slow sand filter, to evaluate the build-up of particulate matter across the contributing riverbed area.
	www.unh.edu /wttac/details.html (3646 words)

	J Water SRT - Aqua 52 (2003) 109-118 - A. J.Peters et. al. - Control of nuisance chironomid midge swarms from a slow ...
		The hydrodynamics of the slow sand filter were studied using a chemical tracer, and mesocosm experiments were undertaken to examine the effects of permethrin on the filter bed micro-fauna community.
		Permethrin rapidly dispersed in the water and accumulated in the surface layer (the ‘schmutzdecke’) of the filter, attaining mean maximum average concentrations of 8.3 µg/l in water and 2.3 µg/g in the schmutzdecke after 1 and 6 h, respectively.
		The single treatment was effective in eliminating chironomid midge emergences from the filter bed for a period of 1 month.
	www.iwaponline.com /jws/052/jws0520109.htm (356 words)

	Sand Filter Design
		In Case 1 the filter is preceded by an extended detention basin.
		In Case 2 the filter is preceded by a retention pond with a surcharge extended detention above the permanent pool.
		This relationship for a sand filter (i.e., Figure 3) appears to be not sensitive to the hydraulic surcharge on the filter's surface and can be expressed by Equation 6.
	www.udfcd.org /fhn97/sand97.htm (2521 words)

	Water Supply 2:5-6 (2002) 387-394 - H.-B. Jun et al. - Removal of particulates, natural organic matters, and ...
		Removal characteristics of particulates, natural organic matters, and microorganisms with six slow sand filter units were measured with a diameter of 50 mm and packed with sand to a depth of 50, 150, 300, 600, and two 700 mm, respectively.
		One of the 700 mm depth filters was amended by covering the surface of the filter bed with a prefilter.
		Turbidity removal in the 700 mm depth filter with prefilter was similar to that without the prefilter, however, the removal of particles smaller than 2 mm was improved with the prefilter.
	www.iwaponline.com /ws/00205/ws002050387.htm (348 words)

	Enhanced Ripening of Slow Sand Filters (Site not responding. Last check: 2007-10-13)
		While successful in removing turbidity and pathogens from drinking water, slow sand filters require ripening periods at the beginning of each filter run.
		The premise of this research was that it should be possible to enhance the ripening of slow sand filters.
		Most turbidity removal in the treated filter occurred in the schmutzdecke rather than within the depth of the filter bed.
	www.pubs.asce.org /WWWdisplay.cgi?0004048 (212 words)

	CLEANIndia
		Jal-TARA Slow Sand Filter is designed to treat drinking water using slow sand filtration technique as per the specifications of World Health Organisation (WHO).
		Jal-TARA filter is a biological filter merged with advanced technique of fabric protection to improve and simplify the traditional process of slow sand filtration.
		Filter can be maintained by the members of the community thus creating livelihood options.
	www.cleanindia.org /jalpur_system1.htm (407 words)

	[No title] (Site not responding. Last check: 2007-10-13)
		Essentially a slow sand filter put to work as a waste treatment mechanism.
		Water stream is spread over a sand bed; water infiltrates and is filtered at the surface of the bed.
		Filter must be taken out of use and dried on a regular basis to allow aeration of the organic layer (failure to do this has apparently given intermittent filters a bad reputation)
	www.uwsp.edu /water/espangen/Water382/lec3-2d.htm (446 words)

	[No title]
		The sand bed filter is connected to the low rate biogas plant and receive directly the discharged fermented slurry from the plant.
		The solid waste from the Slow Sand Bed Filter can be dried further or composted and sold as organic fertilizer to crop farms.
		The bulk of waste water with a high soluble organic matter content is treated in the UASB reactor together with filtered water from the sand bed filter.
	chmai.loxinfo.co.th /~bau/biogas.html (1013 words)

	Lake and Water Word Glossary - F (Site not responding. Last check: 2007-10-13)
		FILTER BED—A layer of sand or gravel on the bottom of a reservoir or tank, used to filter water or sewage.
		FILTER CAKE—(1) The solids or semisolids deposited on a filter as a fluid is moved through it.
		FILTER ZONE (of a Dam)—A band or zone of granular material that is incorporated into a dam and is graded (either naturally or by selection) so as to allow seepage to flow across or down the filter without causing the migration of material from zones adjacent to the filter zone.
	www.nalms.org /glossary/lkword_f.htm (10891 words)

	Hayward Pools / Troubleshooting / Filters (Site not responding. Last check: 2007-10-13)
		The sand bed may be clogged with mineral deposits that will not backwash away.
		The sand you are using could be too small, which will go through the filter system, then back into the pool.
		The filter elements may be clogged because of an accumulation of chemical deposits.
	www.haywardnet.com /owners/troubleshooting/filters.html (1594 words)

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