Close water and solute balances before choosing recovery
At steady state, feed equals permeate plus concentrate. For each conservative species, mass entering must leave in the two outlets unless precipitation, reaction or accumulation is demonstrated. Water recovery therefore is not contaminant destruction: a smaller reject stream is generally more concentrated.
Sample representative feed states and estimate the recovery range for each scenario. Analyse salinity, hardness, silica, metals, relevant organics and pretreatment chemicals; characterise spent cleaning liquors too. Conductivity alone may miss the constituent that prevents a management route.
| Potential outlet | Feasibility questions |
|---|---|
| Discharge or transfer to treatment | Is capacity, permission and chemical compatibility available? |
| Specific reuse or beneficial use | Does quality suit that use without transferring a risk? |
| Additional membrane recovery | What scaling and energy limits are reached? |
| Evaporation or crystallisation | Is energy, suitable material and final solids management available? |
Compare routes at the same system boundary
The Bureau of Reclamation groups approaches as disposal, beneficial use and high-recovery processing. The list is a framework; actual availability depends on site and applicable approval. An existing discharge may fail because of one constituent; a high-recovery option may shift cost into energy and final solids.
Include pipes, tanks, transport, analyses, emergency operation and spent cleaning liquor. If concentrate returns to the head of the same works, model salt accumulation; recycling flow does not remove mass. Compare scenarios per cubic metre of useful water and per mass of final residue, not only nominal recovery.
- Define the response if the reject destination is temporarily unavailable.
- Confirm discharge constraints with the competent operator or authority before fixing design.
- Test scaling and second-pass permeate quality if further recovery is proposed.
Decision point
Identify a feasible concentrate destination first; then optimise RO recovery within that boundary. If no technical and lawful reject route exists, adding membrane area does not make the project viable.
Common questions
Does high-recovery RO eliminate concentrate?
No. It reduces water volume while retained salts and other constituents remain in a more concentrated outlet or subsequent solid residue.