PAH stands for polycyclic aromatic hydrocarbons. They are hydrocarbon compounds linked to fuel and combustion, and scrubber washwater can pick them up from the exhaust gas. PAH is one of the parameters that washwater must be monitored for under the scrubber guidelines.
The Rivertrace exhaust scrubber washwater discharge page lists the limit as a maximum of 50 µg/l above the inlet water level, measured as phenanthrene equivalent. This article explains what that means.
What are PAHs?
PAHs are a group of hydrocarbon compounds. Their presence in washwater is a sign that fuel related hydrocarbons have been carried into the water, which is why the guidelines use PAH as the hydrocarbon indicator for scrubber discharge.
What does “above inlet level” mean?
The limit is not an absolute value. It is the increase between the clean seawater going in and the washwater going out. The monitor therefore needs a baseline reading. See where should scrubber washwater be sampled.
| Key point: The PAH limit is a difference measurement. Without a reliable inlet reading, the discharge reading has no reference. |
What does “phenanthrene equivalent” mean?
Phenanthrene is a reference PAH compound. The result is expressed as the concentration of phenanthrene that would give the same response, so different monitors report on the same basis.
How does the SMART ESM measure PAH?
The SMART ESM measures PAH by UV fluorescence, using a 254 nm excitation wavelength in a measuring cassette. The range is 0 to 4500 µg/L with accuracy of 5% of reading. Details are in the SMART ESM technical overview and the SMART ESM library page.
| Item | Detail |
|---|---|
| Technology | UV fluorescence, 254 nm excitation |
| Range | 0 to 4500 µg/L |
| Accuracy | 5% of reading |
| Limit (per Rivertrace page) | 50 µg/l above inlet, phenanthrene equivalent |
What helps PAH readings stay reliable?
- A steady sample flow within the stated range.
- A debubbler to remove most air from the sample.
- A pump that raises pressure and homogenises the sample where the line pressure is low.
- Regular checks of the PAH cassette using the calibration check kit.
Frequently asked questions
What is PAH in scrubber washwater?
PAH means polycyclic aromatic hydrocarbons, hydrocarbon compounds linked to fuel and combustion. Scrubber guidelines use PAH as the hydrocarbon indicator for washwater.
What is the PAH limit for scrubber washwater?
The Rivertrace scrubber page states a maximum of 50 µg/l above the inlet water level, measured as phenanthrene equivalent.
How is PAH measured in washwater?
The SMART ESM uses UV fluorescence with 254 nm excitation. The range is 0 to 4500 µg/L.
Why is PAH measured at the inlet as well?
The limit is the increase above the inlet level, so the inlet reading is the baseline.
Which Rivertrace products are relevant?
| Product | Technology and use |
|---|---|
| SMART ESM | Washwater monitor for PAH, turbidity, pH and temperature. Open loop, closed loop and hybrid scrubbers |
| Calibration Check Kits | Used to check the PAH and turbidity readings onboard |