Keep the fraction of feed becoming permeate separate from how strongly the permeate concentration differs from feed.
Define the Interface or Transport Basis
Applied Membranes' glossary distinguishes recovery from solute rejection. For a defined single-pass steady comparison, recovery=permeate flow/feed flow. Concentration-based rejection is 1−permeate concentration/feed concentration for the named solute. These ratios have different denominators and answer different questions.
Review a Hypothetical Comparison
Suppose a fictional single-pass feed is 20 L/h and its permeate is 5 L/h. Recovery is 25%. If feed concentration is 10 g/L and permeate concentration is 0.2 g/L for one specified solute, concentration-based rejection is 98%. Feed solute flow is 200 g/h while permeate carries 1 g/h. Thus 98% concentration rejection is not the same as saying 2% of feed solute mass went into this permeate stream: that mass fraction is 0.5%.
Keep the Evidence with the Decision
Draw feed, permeate and concentrate boundaries and identify whether recycled flow crosses them. Pair concentrations sampled in the same state with the relevant flows. Distinguish a single element, a membrane pass and the whole system before comparing recovery. Retain a mass balance if the decision concerns recovered product rather than only permeate concentration.
This arithmetic describes invented steady streams. It predicts no real membrane performance and does not set a recovery target or identify which stream must be the desired product.
Which mass-flow and concentration basis supports each reported membrane result?
This blank worksheet is for your own project. It contains no H M machine trial result.
| Review field | Reference or result | Responsible person |
|---|---|---|
| Single-pass or system flow boundary | To complete | To complete |
| Matched feed and permeate flows | To complete | To complete |
| Named-solute concentrations at the same state | To complete | To complete |
| Concentration ratio and solute-flow balance | To complete | To complete |
Customer Questions
Does 98% rejection mean 98% of feed water was recovered?
No. Water recovery and solute concentration rejection are different ratios.
Is solute mass passage equal to 1−rejection?
Not generally; include the permeate/feed flow ratio when comparing solute mass flows.
Can internal recycle be counted as new system feed?
Define the system boundary first; internal circulation is not automatically external feed.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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