Characterise the intake and its variation
Identify an open intake or a well intake and describe the changes observed throughout the year. Gather temperature, salinity, turbidity, solids, organic matter and relevant algal events. Add information on storms, port activity, nearby discharges and intake shutdowns where these form part of the project conditions. Describe any existing upstream treatment before taking the membrane feed sample.
Analysis should represent the conditions that govern supply. Calm winter water and a seasonal algal event can call for different pretreatment responses. Define which variations the selection data must cover and which conditions need a process trial. Base sampling and trial planning on the actual intake water and the production duty required by the installation.
Define what UF must deliver to RO
Set net flow, delivery pressure, design temperature and water quality at the RO feed point. UF controls the fraction retained by its membrane; salts and part of the dissolved organic matter remain in the water. Separate the objectives assigned to each stage and retain the controls required by the desalination elements. Define the interface in a shared process specification.
Use turbidity, SDI and organic-matter measurements relevant to the treatment objective. Each indicator observes a different aspect of feed water. Where storage separates UF and RO, include its operating arrangement and sample at its outlet. The high-pressure plant needs the specified quality at its actual inlet, after storage, conditioning and any blending rather than only at the UF filtrate connection.
| Decision | Supporting information |
|---|---|
| UF module and area | Representative water, minimum temperature and required net output |
| Additional pretreatment | Algae, solids, organic matter and intake variation |
| RO feed | Flow, pressure and quality at the actual RO inlet |
| Cleaning and dosing | Both membrane procedures and circuit isolation |
| Availability | Cleaning, maintenance, storage and response to seasonal events |
Close the balance using net recoveries
Consider an illustrative example: RO receives a net 100 m³/h and operates at 45% recovery, producing 45 m³/h of permeate and 55 m³/h of concentrate. If upstream UF delivers that 100 m³/h at an assumed net recovery of 90%, it requires 100 / 0.90 = 111.1 m³/h of raw water. The net difference through UF is 11.1 m³/h.
Overall recovery in this example is 45 / 111.1 = 40.5%. The 90% and 45% values are assumptions rather than product performance. A project balance needs to identify cleaning, internal water use and returns. Where the 90% net figure already includes a consumption, count it once. Then check operating hours and storage capacity against the need to keep the RO system supplied.
Coordinate chemistry, materials and circuits
Module selection includes wetted materials, seals and connections exposed to seawater and cleaning chemicals. Review the frame, manifolds, valves and instrumentation against their intended service conditions as well. Define the interfaces between module supply, skid fabrication and installation so every component has a traceable specification. Include both normal service and cleaning conditions in the materials review.
Separate the UF cleaning sequence from conditioning of water entering RO. Check each dosed chemical for compatibility with both stages, and establish isolation, rinsing and return-to-production criteria. Where oxidants are used, verification of the water condition before RO must follow the requirements of the installed elements and the complete process. The control description should make those transitions and release checks explicit.
Compare proposals for normal and seasonal duty
Compare offers on the same net output, design water and availability basis. Include modules, prescreening, pumps, backwash, air where applicable, instruments and controls within the agreed scope. A change in cleaning frequency can affect both utility consumption and productive hours. The comparison schedule should show what happens during the intake event used as the demanding design condition.
To start selection, provide RO flow and process arrangement, seasonal intake data, available space and existing pretreatment. For replacement work, add installed module models and quantity, pressure trends and cleaning records. This information supports assessment of membrane-only supply or a complete skid, together with the checks needed to turn the selection into a defined technical and commercial proposal.
Common questions
Does UF reduce seawater salinity?
UF serves here as a barrier to particles and colloids. Salt reduction belongs to reverse osmosis or another desalination stage.
Can UF always replace the remaining pretreatment?
Review the intake and the RO feed requirements. The project defines the protection, conditioning and additional treatment needed before and after UF.
Should this application use PES or PVDF?
Compare the complete model: admissible feed, performance on representative water, cleaning, materials and interfaces. The polymer name alone does not complete the selection.