What a scrubber has to neutralise, how flow rate and inlet concentration set the model, why the exhaust fan is the part most often undersized, and the commissioning paperwork a Department of Environment certificate depends on.
Every laboratory fume hood, semiconductor wet bench and industrial process tool that handles acids, alkalis or toxic gases generates an exhaust stream that must be treated before it reaches the atmosphere. In Bangladesh, the Department of Environment (DoE) enforces emission standards under the Environment Conservation Rules 2023, and international accreditation bodies (ISO 17025, IEB/BAETE) increasingly require documented exhaust treatment as part of laboratory safety management. Vvon Technologies Limited supplies Semian SBW-series wet gas scrubbers, compact, high-efficiency units designed specifically for laboratory and light-industrial exhaust treatment.
A scrubber is a chemistry problem before it is a mechanical one. Write down every gas the extract will ever carry, with the worst-case concentration and how often it occurs, and the model largely selects itself. Acid gases and alkali mists both scrub well in water with a reagent. Solvent vapours, non-polar organics and some hydrides do not, and a wet scrubber specified for them will pass them straight through while its pH controller reports that everything is fine.
Two failure modes come out of skipping this step. The first is a laboratory that buys one scrubber for a shared extract carrying both acid and alkali streams, and finds the reagent neutralising itself. The second is a department that adds a new process two years later, sends an unlisted gas up an existing stack, and discovers at the next emission test that the abatement it paid for does nothing for the compound the inspector measured.
A wet gas scrubber passes the contaminated exhaust stream through a packed tower or spray chamber where it contacts a liquid reagent, typically water, dilute NaOH (for acid gases) or dilute H₂SO₄ (for alkali gases). The pollutant dissolves into the liquid phase and is neutralised, producing a safe aqueous effluent that can be discharged to drain after pH adjustment. Semian's MIDAS series uses a counter-current packed-bed design with polypropylene packing media, achieving removal efficiencies above 99% for HCl, HF, HNO₃, H₂SO₄, NH₃ and NaOH mists at typical laboratory concentrations.
A note that saves confusion on site. Semian's MIDAS scrubbers and Honeywell's Midas gas detectors share a name and nothing else. If your project carries both, put the manufacturer in front of the model on every drawing and every purchase order, or the wrong item will reach the wrong contractor at least once.
| Model | Airflow capacity | Inlet concentration | Key feature |
|---|---|---|---|
| MIDAS-I | Up to 500 m³/h | Up to 500 ppm | Single-stage and compact, ideal for a single fume hood |
| MIDAS-II | Up to 1,500 m³/h | Up to 2,000 ppm | Two-stage packed bed for multi-hood or process tool exhaust |
| SBW 200-CE | Up to 2,000 m³/h | Up to 5,000 ppm | CE-certified, recirculating reagent for industrial exhaust |
| SBW 200-C | Up to 2,000 m³/h | Up to 5,000 ppm | Continuous reagent feed for high-load industrial applications |
Those four cover the majority of laboratory and light-industrial duties, but they are not the whole range. The Semian catalogue extends to fifteen units, adding the SBW 200-K, the SSW 200-E and SSW 200-K, the SSD 100-S and SBD 200-S, the SBW III_202_S, and the ENVIRO-MATRIX family (Trinity, Infinity, Cyrus, Sentinel and Altair). Selection across the wider range turns on the same three inputs: the gas list, the extract flow rate, and whether the load is continuous or intermittent. Send those three and the shortlist comes back short.
Size on the extract flow the ventilation design actually delivers, not on the number of hoods. A hood at full sash draws considerably more than the same hood at working sash height, and a shared duct serving six hoods is sized against a diversity assumption someone made on a drawing. Get the commissioned flow figure from the ventilation contractor, in m³/h, at the point where the scrubber will sit, before selecting anything.
Where sizing is argued, err upward on flow and downward on optimism about concentration. A scrubber running below its rated flow simply uses less reagent. A scrubber running above it loses contact time, and contact time is what the removal efficiency depends on.
Semian scrubbers are supplied as complete packaged units with integral sump, recirculation pump, level control and pH probe connection. Installation requires a concrete plinth or steel frame, a drain connection for sump blowdown, a mains water supply for reagent make-up, and an exhaust fan sized to overcome the scrubber pressure drop (typically 100 to 300 Pa). Vvon Technologies provides the full installation scope including ductwork design, fan selection, civil works specification and commissioning. We also supply pH controllers and chemical dosing systems for automated reagent management.
The fan is the item most often got wrong. A scrubber added to an existing extract system inserts a pressure drop the original fan was never selected for, and the result is a hood that no longer meets its face velocity. If the scrubber is a retrofit, the fan is part of the scope, and the face velocity at every hood on that system should be measured before and after.
Vvon Technologies provides a commissioning report including stack emission test results, scrubber efficiency data and a maintenance schedule, the documentation package required for DoE environmental compliance certificates and ISO 17025 or ABET laboratory accreditation audits. Annual service contracts include packed-bed inspection and replacement, pump overhaul, pH probe calibration and reagent system cleaning.
Keep that commissioning report with the laboratory safety file rather than with the estates department. When an inspector or an accreditation assessor asks how the extract is treated, the useful answer is a measured efficiency figure with a date on it, not a model number.