A low kWh/m³ figure is meaningful only when the numerator, denominator and operating conditions are defined. One supplier may report the high-pressure membrane train while another includes intake pumps, pretreatment, post-treatment and product delivery. Build a common energy schedule before comparing equipment or operating-cost claims.
1. Define the meter boundary and denominator
Mark every electrical meter and motor included in the quoted figure. List intake and transfer pumps, screening, coagulation, media or membrane pretreatment, cartridge filtration, high-pressure and booster pumps, energy-recovery auxiliaries, chemical dosing, flushing, CIP, post-treatment, ventilation, controls, concentrate discharge and product delivery. State which loads are excluded and who supplies them.
Use net compliant product water delivered at an agreed point as the denominator. Declare whether startup water, flushing, off-spec permeate, backwash and cleaning downtime are included in the reporting period. The DOE bandwidth study evaluates intake, pretreatment, desalination, post-treatment and concentrate management as separate unit operations, illustrating why a membrane-train number cannot automatically represent the whole plant.
2. Hold feed and operating conditions constant
Record seawater salinity and temperature range, intake type, SDI or turbidity basis, required product salinity and boron target, recovery, design flow and operating hours. Add intake elevation, pipe length, total dynamic head, concentrate outfall head and product delivery pressure. These conditions affect osmotic pressure, pump duty and auxiliary consumption, so comparisons need one agreed design case and seasonal cases.
Identify energy-recovery device type, stated efficiency basis, high-pressure pump and motor efficiency, variable-speed operation and any circulation or booster pump. DuPont explains that pressurized seawater concentrate can return energy to the process, but a percentage-saving statement still needs its reference system. Ask for an electrical load list and calculated duty point for every major motor rather than a single headline value.
3. Compare guarantees and measured results on one method
Request both design-point power and expected annual specific energy. The annual estimate should show production schedule, standby loads, seasonal water conditions, membrane aging allowance, planned cleaning and availability. Separate guaranteed maximum input power from forecast average consumption. Do not transfer a published value from a large facility to a small plant without matching capacity, salinity, recovery, product quality and hydraulic boundary.
For acceptance, agree meter class, calibration, sampling interval, steady-state duration, treatment of pauses and formula: total included kWh divided by net accepted product m³. Record feed, permeate and concentrate flows, pressures, conductivity, temperature and recovery during the test. The existing SWRO-3 reference identifies a BOKAWATER product family, but it does not establish an energy promise; only the project quotation and agreed test can do that.
Data to collect before comparing proposals
| Parameter / interface | Unit / format | Why it matters |
|---|---|---|
| Energy numerator | Included meters and kWh | List every included and excluded motor. |
| Water denominator | Net accepted product m³ | Exclude or declare off-spec and internal water. |
| Intake | Type, head, distance and variability | Include pumping and screening boundary. |
| Pretreatment | Process, backwash and pressure loss | Include pumps, air and chemical auxiliaries. |
| RO train | Feed conditions, recovery and pressure | State pump, motor and membrane design case. |
| Energy recovery | Device and efficiency basis | Name the reference case for any savings claim. |
| Post-treatment | Remineralization and disinfection | Include dosing, mixing and pumping as agreed. |
| Concentrate / delivery | Outfall and product head | Declare both terminal connection points. |
| Acceptance test | Meters, duration and formula | Measure flows, conditions and net compliant water. |
Technical references
- US Department of Energy — Seawater Desalination Energy Bandwidth Study ↗Source checked:
Evidence scope — original English record
Separates energy for intake, pretreatment, RO desalination, post-treatment and concentrate management and attaches comparisons to salinity, recovery, product quality, capacity and pumping head.
- DuPont FilmTec — RO System Components Technical Manual Excerpt ↗Source checked:
Evidence scope — original English record
Explains high-pressure pumping and recovery of pressure energy from seawater concentrate; actual savings depend on the selected system and operating conditions.
- US Department of Energy — Desalination Basics ↗Source checked:
Evidence scope — original English record
Explains pressure-driven membrane desalination and the relationship between feed salinity, pressure and concentrated brine production.
- BOKAWATER — Small desalination plant reference ↗Source checked:
Evidence scope — original English record
Existing BOKAWATER desalination product-family reference only; this comparison method does not add a model energy rating or guarantee.