EWT Water Technology – Water Treatment

EWT Water Technology

Sand Filter

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Within the scope of water treatment, filtration ist a mainly physical process for removal of suspended solids from liquids. The liquid to be filtrated flows through a filter medium, which results in the suspended solids being retained by this filter medium. A sand filter ist a vessel for filtration, with a filter bed consisting of silica sand serving as filter medium.

With increasing service life, the differential pressure between the filter inlet and out increases for a given volume flow, as more solids are being retained within the filter medium. Eventually, the filter medium needs to be either backwashed or replaced.

A sand filter requires periodic backwash, either with water only, or with both air and water. During backwash, waste water needs to be discharged.

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Design Example:

sand filter

Sand filter plant, two lines, fully automated backwash with air and water.

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Technical Data:

filtrate volume flow available from approx. 1.5 up to 120 m³/h for each line
amount of lines usually 2x50%
smaller plants also 1x100% or 2x100%
larger plants also 3x33% or 4x25%
filtration grade approx. 10 ... 25 μm, without flocculation
approx. 0.5 ... 5 μm, with flocculation
filtrate quality turbidity ≤ 0.1 ... 1 NTU
total suspended solids (TSS) ≤ 0.5 ... 1 mg/L
differential pressure at nominal flow rate usually ≤ 0.5 bar
operating temperature usuually 5 ... 40 °C
backwash intervals usually 12 ... 72 h
backwash duration approx. 15 minutes, for water backwash
approx. 5 ... 10 minutes, for air and water backwash
backwash water volume flow usually operating volume flow × 2 ... 4
waste water approx. 2 ... 80 L for each 1 m³ filtrate
recommended raw water quality total suspended solids (TSS) ≤ 20 mg/L
filter medium silica sand
total service life of the filter medium usually ≫ 10 years
material options pressure vessel • glass-reinforced plastic (GRP)
• carbon steel (e.g. S235JR, P265GH)
• stainless steel (e.g. 1.4301, 1.4404)
pipelines • polyvinyl chloride (PVC)
• polypropylene (PP)
• stainless steel (e.g. 1.4541)
valves • polyvinyl chloride (PVC)
• polypropylene (PP)
• stainless steel (e.g. 1.4408)
gaskets • etyhlene propylene diene monomer rubber (EPDM)
• polytetrafluorethylene (PTFE)
• NBR composite
control options differential pressure monitoring • local display
• remote measurement
filtrate quality monitoring • manual sampling and analysis
• continuous turbidity measurement
line change-over • manually
• fully automated
backwash • manually
• fully automated

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further downloads

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2018-05-05 • water treatment made in GermanyCompany InformationPrivacy