Turning screened seawater into membrane-ready feed — DAF, media and ultrafiltration pre-treatment engineered to deliver a consistently low Silt Density Index (SDI) that protects SWRO membranes and maximises their life.
SWRO membranes foul when the feed carries colloidal and particulate matter — quantified by the Silt Density Index (SDI). Most membrane warranties require SDI₅ < 5, and good practice targets <3 for long element life. The job of intake pre-treatment is to take screened seawater — with its variable turbidity, algae, organics and the occasional bloom — and deliver that low, stable SDI every hour of every day. Reynolds & Bauhm designs the pre-treatment train (coagulation, DAF where needed, media or ultrafiltration, and cartridge polishing) sized for the worst-case raw water, not the average.
| Stage | Role | Typical outcome |
|---|---|---|
| Coagulation | Ferric dosing destabilises colloids | Enables solids capture |
| DAF (bloom/oil sites) | Floats algae, oil & light flocs | Bloom & FOG resilience |
| Media / multimedia filtration | Removes the bulk turbidity | SDI typically to < 4–5 |
| Ultrafiltration (UF) | Absolute barrier to particles | SDI consistently < 3 |
| Cartridge filtration | 5 µm guard before HP pumps | Final membrane protection |
| Dechlorination | Removes free chlorine (SBS/carbon) | Protects polyamide membranes |
Dual/multimedia pressure or gravity filtration with coagulation — robust and economical where raw turbidity is moderate and stable, delivering SDI typically below 4–5.
Multimedia FiltersDissolved air flotation ahead of filtration handles algal blooms, oil and low-density solids that blind media filters — essential resilience on bloom-prone coasts.
DAF Pre-TreatmentUF provides an absolute particle barrier and a consistently very low SDI regardless of raw-water swings — increasingly the standard for new SWRO pre-treatment.
Online turbidity and routine SDI testing close the loop on filter performance and trigger backwash and coagulant trim before the membranes ever see a problem.
Intake MonitoringFlow-paced ferric dosing tuned by jar testing and online turbidity gets the most from every filtration stage without over-dosing or carry-over to the membranes.
Intake DosingThe cartridge guard and dechlorination are the last line before the high-pressure pumps and membranes — specified for absolute reliability.
RO ProtectionShare the raw seawater quality, the bloom profile and the SWRO requirement — we’ll design the pre-treatment train to hold a low, stable SDI to the membranes.
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