Posts Tagged: filtration
Pressure, Energy and Sand Media Filters
Sand media filters are commonly used in agricultural microirrigation systems. They have the advantages of simplicity and large capacities and are favored by many farmers and designers over other filtration hardware when there is a lot of organic matter in the water. The Irrigation Training and Research Center (ITRC) at Cal Poly San Luis looked at sand filters to see if it were possible to use lower-than-accepted backflush pressure and thereby reduce the total pressure required for irrigation systems. By lowering backflush pressure it would be possible to design a system that could run at an overall lower pressure and hence cost. The various components of microirrigation systems run at lower pressures than the backflush pressures recommended for most sand media filters.
The conclusions are:
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There are substantial pressure differences amongst different models and designs during backflush and filtration
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The main pressure loss is at the backflush valves
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If designed right large backflush flow rates can be accomplished at low backflush pressures (this is critical for proper detritus removal).
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There are substantial differences among underdrains of various models which affects pressure requirements
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No large intimal high pressure was necessary to break up the media bed, a common practice.
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Different underdrain designs create different patterns of cleaning the media.
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There were substantial differences among models in the amount of sand discharged from the system at backflow rate of 190 GPM. Sand discharge should actually be avoided since it's an indication of preferential flow and poor cleaning.
These are some new ideas, and even though they are meant to reduce pressure and energy use, they are also good management suggestions.
If this strikes your fancy, read more at http://www.itrc.org/reports/mediafilters.htm
sand filter
Wood Chips as an Air Filtration Media
One of the more unusual uses for woody biomass is in bio-filtration. In this example the wood chips are used to form a bed and malodorous air is fed through to remove the offensive smell. Facilities that need this kind of filtration include sewage treatment plants and waste processing facilities. There are a number of examples in California including the facility pictured that processes municipal solid waste.
How does it work?
For this type of filtration, material from a grinder (followed by screening) is best as the stringy nature of the particles allows for air flow through the bed. The chip specification is important to avoid restriction of air flow or forced air channeling in any part of the filtration bed. Particles in the 3-6 inch range are optimal and no 1 inch minus material is acceptable. The material typically comes from forestry sources (pine and fir) or orchard removals (citrus and nut). No recycled wood is allowed and species such as redwood and eucalyptus are not appropriate as they would inhibit the growth of the bacteria. Facilities may pay $40 per cubic yard delivered. For a 50,000 cubic yard filter this represents an investment of $2m. So although they last for 5 years and have quite a tight specification it could represent a potential source of income for a business that had other markets for materials from a grinding operation.
Typical filter material