Separate volume reduction from chemical enrichment
For a batch with no new inputs, VCF = initial volume / final retentate volume. Volumetric permeate recovery is permeate volume / initial volume. If there are no losses or other volumes, VCF = 1/(1 − recovery). State whether piping, tank and module hold-up are included in the final retained inventory.
In an ideal example, a 10 m³ batch produces 8 m³ permeate and leaves 2 m³ retentate. Recovery is 80% and VCF is 5. This does not mean any ceramic membrane can reach that concentration with any stream. Include samples, drains and added water where they occur in the real trial.
Balance each constituent that matters
A completely retained substance with no deposition could reach five times its initial concentration in that example on a consistent volume basis. Passage into permeate changes that result. Where density changes materially or concentrations are expressed by mass, use solution mass and concentration on the same basis.
Measure feed, composite permeate and final retentate. A single early permeate sample may not represent the full 8 m³ produced. Salts, organic compounds and solids can have different retention. Permeate turbidity cannot establish the fate of all dissolved compounds or demonstrate destruction of the contaminant mass.
Identify operating limits before the endpoint
Concentration can increase viscosity, polarisation, precipitation and deposit formation. Temperature and composition influence these effects. More TMP does not guarantee recovered flux and may increase resistance. Record pressures, circulation and power to determine whether the constraint lies in separation, pumping or transport near the surface.
The pilot should reach the intended concentration factor and repeat operating and cleaning cycles. Compare cumulative production and total time to the endpoint, not just instantaneous flow. A laboratory endpoint may be unattractive if removing the final water takes excessive time or produces retentate that cannot readily be pumped.
Define destinations and acceptance metrics
Specify whether retentate must be pumped, stored, fed to an evaporator or used for component recovery. Each destination adds viscosity, solids and stability constraints. The project is not complete once volume falls: both resulting streams need suitable quality and a feasible route for use or management.
Request useful recovered volume, actual target-component concentration, campaign duration, energy and cleaning residuals when comparing quotations. Agree how final equipment inventory will be measured. Provide representative samples, analysis and stream destinations to convert the desired VCF into a measurable concentration-trial objective.
Common questions
Does VCF 5 mean five times the salt concentration?
No. It describes volume reduction only. Each component needs a balance accounting for permeate passage, deposits and other exits.
Is greater recovery always more economical?
No. The final part of a campaign can disproportionately increase time, energy, cleaning and concentrate-handling difficulty.