STRO / DTRO open-channel reverse osmosis
Reverse osmosis with the feed channel opened up. Disc-tube (DTRO) and net-tube (STRO) elements replace the narrow spacer of a spiral-wound module with a wide, hydraulically simple channel — so particulate matter passes through instead of lodging in the feed path, and scaling is easier to manage at high recovery.
Why the channel geometry matters
A spiral-wound element relies on a fine feed spacer to create turbulence. That spacer is also where particulate fouling and biological growth collect, and once it plugs, cleaning is limited and differential pressure climbs. An open-channel element removes that constraint: the feed path is wide enough that solids pass through rather than lodging, and the module can be opened and cleaned more thoroughly.
Consequence: open-channel RO tolerates feed conditions that would make a spiral-wound train uneconomic — at the cost of membrane area per unit volume.
DTRO and STRO
DTRO (disc-tube) stacks membrane discs and hydraulic flow plates on a central tie rod. STRO (net-tube) uses a tubular-net format with a comparable open-channel principle. Both are used where the concentrate stage of a train has to keep running on a feed that a spiral-wound element cannot handle.
Where open-channel RO is used
Landfill leachate
High organic and salinity load with variable composition, where spiral-wound fouling drives cleaning cost up.
Brine concentration
Concentrating the RO reject stream further, to reduce the volume that has to go to evaporation or disposal.
Zero liquid discharge
The membrane stage of a ZLD train, ahead of the evaporator, where scale and particulate load are the binding constraints.
Open-channel RO is normally the stage that handles the concentrate — the stream the earlier stages have already pushed to high salinity. That is why it usually appears together with upstream solids removal: tubular UF for solids and oil, TMF for hardness. Removing what the membrane cannot tolerate upstream is what lets the open-channel stage run at high recovery.
Specification
| Parameter | Value | Note |
|---|---|---|
| Formats | DTRO (disc-tube) and STRO (net-tube) | Both use an open feed channel |
| Feed channel | Open — no fine spacer | Particulate matter passes through rather than lodging |
| Duty | High salinity, high recovery | Concentrate stage of the train |
| Cleaning | Module can be opened and cleaned | Procedure confirmed per installation |
| Operating pressure | Confirmed per project | Set by feed salinity and target recovery |
| Recovery | Confirmed per project | Established during pilot work |
Pressure and recovery are not published as fixed values. They follow from your feed chemistry and the concentrate handling constraint.
Where does your concentrate have to go?
Tell us the feed salinity, the target recovery and what limits your concentrate handling. That is usually enough to say whether an open-channel stage is worth putting in.
Send your feed data