EWT Water Technology

Sand Filter

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Summary:

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

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Applications:

Removal of suspended solids from well water or surface water.
Removal of iron and manganese from well water, with upstream oxidation stage.
Removal of organic compounds (TOC) from surface water, with upstream flocculation stage.
As →side stream filter in →open circuit cooling systems, for limiting the concentration of suspended solids in the recirculating cooling 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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Downloads:

→further downloads

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2018-05-05 • water treatment made in Germany • Company Information • Privacy