Reverse Osmosis & High-Purity Water Consulting

Every RO performance problem traces back to one of four fouling mechanisms, and correct diagnosis determines the fix. Colloidal fouling — fine particulate and silt deposited across the lead membrane elements — is best predicted and tracked through Silt Density Index (SDI) testing on feedwater; a rising SDI ahead of RO is an early warning that pretreatment (media filtration, ultrafiltration) is losing capacity before flux decline shows up. Organic fouling from natural organic matter or oil traces forms a different signature, often concentrated on lead elements with a slower, sticky differential-pressure rise. Biofouling is distinct again — biofilm growth accelerates once a nutrient source and warm feedwater combine, showing up as a differential-pressure rise that responds to a chlorine-dechlorination-based pretreatment gap or a lapsed CIP schedule rather than to particulate control. Scale formation — calcium carbonate, calcium sulphate, barium/strontium sulphate, or silica — occurs on the concentrate-side, tail-end elements where the reject stream has concentrated dissolved salts closest to their solubility limit.

Antiscalant selection and dosing are only as good as the saturation-index calculation behind them. We evaluate Langelier Saturation Index (LSI) for calcium carbonate scaling tendency and Stiff & Davis Stability Index (S&DSI) where high-TDS or seawater-influenced feedwater makes LSI less reliable, then check whether the antiscalant dose and recovery setpoint are consistent with the actual saturation risk at the tail element — not a generic percentage. Recovery optimisation is the central lever: pushing recovery too high concentrates the reject stream into scaling territory and accelerates fouling; running recovery too conservatively wastes permeate yield and inflates energy cost per unit product. CIP programme design and frequency are reviewed against actual fouling type (acid cleans for scale, high-pH/detergent cleans for organics and biofilm) — a CIP programme built for the wrong fouling mechanism can accelerate membrane degradation rather than restore performance.

Beyond the RO train itself, high-purity polishing for boiler feedwater or process use draws on electrodeionisation (EDI) or mixed-bed ion exchange to reach the resistivity or silica specification RO alone cannot achieve. We assess whether RO product water quality is consistently within the design envelope for the downstream polisher, since RO upsets (a fouled or damaged element, a seal failure) show up immediately as reduced polisher run length or resin exhaustion — often misdiagnosed as a demineraliser problem when the root cause sits upstream in the RO train.