Pressure vessels charged with a single grade of washed silica sand for turbidity and suspended solids removal ahead of reverse osmosis. The simplest, most efficient pre-filtration option where SDI < 5 is acceptable and raw water turbidity is low.
A single-media pressure filter contains a deep bed of uniform silica sand, typically 0.4–1.2 mm effective size (ES), graded to achieve 90–95% turbidity removal from low-turbidity feed water. Water flows downwards under inlet pressure through the sand bed; particles larger than the pore spaces between sand grains are physically strained and adsorbed onto grain surfaces.
Sand specification for RO pre-filtration: Effective size 0.45–0.55 mm, uniformity coefficient < 1.6 (tight grading gives fewer fine grains that migrate and block under-drains). Silica content > 95%. Acid solubility < 2%. A graded support gravel layer (2–32 mm in 3–4 grades) sits beneath the sand bed on the underdrain laterals to prevent media loss during backwash.
Single media charge, single vessel, minimal complexity. Lower capital outlay than dual or triple-media systems for the same flow rate, with straightforward media replacement at end of life (typically 5–10 years).
Mains water, low-turbidity boreholes (< 1 NTU), and pre-settled surface water. Raw water SDI typically reduced from 8–15 to 4–6. Not recommended where SDI < 3 is required without coagulant addition upstream.
Single-media filter runs on low-turbidity feed: 8–16 hours between backwashes at 10–12 m/h SLR. Run length is primarily governed by differential pressure rising to 0.5–0.8 bar across the filter bed, not by turbidity breakthrough.
Upflow backwash at 25–35 m/h for 10–15 minutes using filtered product water or towns mains water. Air scour (6–8 m/h for 3–5 minutes preceding the water backwash) significantly improves media cleaning and extends run length, particularly in higher-turbidity duties.
| Flow (m³/hr) | Vessel Dia. | Vessel Height (s/s) | Connections | Media Volume |
|---|---|---|---|---|
| 5–8 | 900 mm | 1,800 mm | DN65 | ~0.55 m³ |
| 8–15 | 1,200 mm | 2,000 mm | DN80 | ~1.0 m³ |
| 15–25 | 1,600 mm | 2,200 mm | DN100 | ~1.8 m³ |
| 25–40 | 2,000 mm | 2,400 mm | DN125 | ~2.8 m³ |
| 40–65 | 2,500 mm | 2,600 mm | DN150 | ~4.4 m³ |
| 65–100 | 3,200 mm | 2,800 mm | DN200 | ~7.2 m³ |
Dimensions are indicative at 10 m/h SLR. Exact sizing by enquiry. s/s = straight-side (excluding dished ends).
Media options, duplex arrangements and a worked pre-RO example
Technology selection, SDI targets, hydraulic design, and backwash sizing for multimedia pre-RO filtration.
View OverviewSingle-grade sand filtration for lower-turbidity feeds where SDI < 5 is acceptable without multi-layer grading.
View PageAnthracite over sand for improved particle capture, higher flux, and longer filter runs between backwashes.
View PageAnthracite / sand / garnet for the best SDI reduction — the standard pre-RO media configuration.
View PageParallel vessel pairs for uninterrupted 24/7 operation where backwash must not cut the downstream supply.
View PageWorked example: borehole → duplex multimedia → RO → steam boiler feed at 24 m³/hr.
View ExampleOur process engineers will review your raw water analysis, flow rate, SDI targets, and downstream RO membrane specification to recommend the optimum media type, vessel size, backwash regime, and control philosophy.
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