GMP-compliant multimedia pre-treatment for purified water and WFI production trains. 316L electropolished stainless steel vessels, hot-water sanitisable design, food-grade certified silica sand, full validation package (URS/FAT/SAT/IQ/OQ). Worked example: 8 m³/hr purified water system for oral solid dosage manufacturing.
A pharmaceutical contract manufacturing organisation (CMO) producing oral solid dosage (OSD) forms requires a new purified water (PW) generation system with a peak demand of 8 m³/hr. The feed water is UK chlorinated mains supply. The purified water system must meet the Ph. Eur. 2.2.3 specification (conductivity ≤ 4.3 μS/cm at 20 °C, TOC ≤ 500 ppb). Multimedia filtration is the first stage of the pre-treatment train, removing suspended solids that would otherwise foul the downstream activated carbon filter and reverse osmosis membranes. All wetted components must comply with GMP material requirements for pharmaceutical water contact. A validation package (URS, FAT, SAT, IQ/OQ) is required for regulatory submission.
Why multimedia filtration is the first stage: Mains water contains chlorine (0.2–0.5 mg/L) and typically low but variable suspended solids. The multimedia filter removes suspended solids before the activated carbon (AC) filter, protecting the AC bed from premature blinding and extending its service life. Chlorine removal is the primary duty of the AC stage; the multimedia stage ensures the AC is not fouled before it can accomplish this.
UK mains water enters the pre-treatment skid at the site water meter. A manual isolation valve and a 100 μm self-cleaning strainer provide the first protection against particulate ingress. A flow transmitter records daily consumption for the pharmaceutical water system logbook, a GMP record requirement.
A single 316L stainless steel pressure vessel (electropolished internal surface, Ra ≤ 0.8 μm) charged with food-grade silica sand (certified to confirm no heavy metal contamination, with CoA supplied) removes suspended solids and turbidity. SLR of 10 m/h at peak flow gives a vessel cross-section of 0.8 m² (1,010 mm diameter). Backwash with purified water reject from the downstream RO or a dedicated backwash supply. Differential pressure transmitter triggers automatic backwash at 0.3 bar. All elastomers (seals, diaphragms) are food-grade EPDM or silicone, traceable to batch certificates.
A 316L SS activated carbon filter removes chlorine and chloramine from the mains water to protect the downstream RO membranes (chlorine attacks polyamide membranes irreversibly at concentrations > 0.05 mg/L). Foodsafe activated carbon (coconut shell or coal-based, certified to ANSI/NSF 61 or equivalent) is specified. The AC media is replaced on a service-life schedule (typically 3–5 years) and all media changes are documented in the site change control system.
Dual-vessel duplex softener (one duty, one regenerating) removes calcium and magnesium hardness, preventing scale formation on the downstream RO membranes. Regeneration with pharmaceutical-grade NaCl brine. Hardness breakthrough monitoring on each vessel outlet; automatic changeover on exhaustion. Conductivity monitoring confirms effective regeneration before return to service.
A double-pass RO system (two stages in series) produces a permeate meeting the Ph. Eur. conductivity specification ≤ 4.3 μS/cm at 20 °C. First pass removes > 97% of dissolved salts; second pass polishes to specification. Rejection membranes (polyamide thin-film composite) monitored continuously by conductivity transmitters on permeate and concentrate lines. System recovery typically 75% on first pass; reject water routed to drain or recycle.
RO permeate is stored in a 316L SS electropolished storage vessel (with HEPA-filtered pressure vent) and continuously recirculated around the distribution loop at a velocity of ≥ 1.5 m/s to suppress biofilm. UV disinfection on the return leg provides a continuous bio-burden reduction step. Total organic carbon (TOC) and conductivity are monitored continuously on the loop; microbial counts are sampled weekly at point-of-use. All monitoring data is stored in the site’s validated data acquisition system.
Wetted parts in 316L stainless steel (UNS S31603). Internal surfaces electropolished to Ra ≤ 0.8 μm (product-contact finish). External surfaces pickled and passivated. All welds continuous, full-penetration, internally smooth — no crevices. Passivation certificate supplied with the vessel. EPDM or silicone seals with food-grade approval; no natural rubber.
User Requirements Specification (URS) drafted and approved before manufacture. Factory Acceptance Test (FAT) witnessed at the fabricator’s works — pressure test, internal inspection, media certification review. Site Acceptance Test (SAT) after installation — performance run at design flow, backwash cycle, DP alarm test. Installation Qualification (IQ) and Operational Qualification (OQ) protocols completed, with executed reports retained as GMP batch records.
The vessel, pipework, and valves are designed for hot-water sanitisation at 80 °C circulated through the system for a minimum of 30 minutes. All instrument connections use tri-clamp fittings (3-A or equivalent) to allow removal and cleaning. Sanitary-pattern diaphragm valves are used throughout (no ball valves in the process wetted path). A sanitisation cycle is performed quarterly or following any media change, documented in the site change control system.
Differential pressure transmitter (4–20 mA) across the vessel for backwash trigger and performance trending. Pressure gauges on inlet and outlet (calibrated to UKAS-traceable standards; calibration records in the site instrument calibration system). All instruments tagged on the P&ID. Calibration frequency documented in the equipment qualification plan. No sight glasses in the process line (biofilm risk).
Media options, duplex arrangements and worked application examples
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View ExampleGMP-compliant multimedia pre-treatment for purified water systems. 316L SS, sanitisable, validated.
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