Scrubber washwater discharges to sea


A scrubber system needs to be approved by IMO, and the system has to be included in the vessel´s IAPP certificates. IMO has set limits to the emissions to air and discharges to the sea.

Values are monitored 24/7 and records must be kept available to prove the vessel´s compliance at any time. In addition, rules require detailed chemical washwater sampling and analysis.

Regulations apply to vessels at port, and the norm is seawater should retain PH>6.5 when sampled four meters from the ship´s hull. Operation in US waters require PH>6 over board. Verification of this sampling procedure is a part of the certification process for the ship.

PAH, Turbidity and PH values are being measured 24/7. Whenever the scrubber operates, logs should be available for inspection.

Press reports

Three-party water analyses have been carried out as part of Solvang´s scrubber operation on six vessels. There are good reasons to believe that the uncertainty created in the press recently, arises from cases with poor water sampling and analytical procedures. When sampling is erroneous, results may get significantly misleading, even if they are published with IMO or other legitimate fora.

As an example of methodological weakness, there was made no distinction between exhaust gas cleaning systems with and without water treatment in open loop. The following gauging results show lower out-values than intake values of a series of substances, which if correct implies that the scrubber acts as a water purifier. Still, the official conclusion to the report is the opposite. Link to IMO report.

Corroborated figures

Washwater from Solvang´s scrubbers has been sampled and analysed as part of a Norwegian state-sponsored research program, requiring scientific procedures.

Evaluations follow the (PEC/PNEC) criteria and the Norwegian criteria for coastal seawater. The washwater is being checked for 9 potential metals, arsen, 16 different PAH components, hydrocarbon C10-C40, nitrate/nitrite, turbidity and PH, in total 35 different components.

The corroborated results confirm very low levels of ∆PAH, less than 10 percent of the requirements, PAH carcinogene is close to detection level (below in 5 of 6 tests), and nitrates close to zero. ∆Turbidity is also less than 10 percent of the max level.

PH levels come close to those in coffee, the washwater is rated as non-toxic for all components in the analysis, and better than good for 19 of the components. The values for (PAHs) fenantren, fluoranten and pyren is higher than in water of good quality, but far below poor quality.

Nickel and vanadium

Metals nickel and vanadium are the main components in the fuel which need to be considered in more detail.

Vanadium is an ordinary part of seawater in concentrations 0.9-2.5 µg/l. Vanadium is constantly being fed to the nature in the range 0.6 mill tonnes/year from decomposed bedrock, and is not a prioritised pollution metal due to low toxicity.

The amount of vanadium released from HFO operation in ships can be estimated to 0.045 million tonnes (225 milliion tonnes of HFO, average 200 mg/kg fuel, a conservative estimate, while total seawater is 1,368,000,000 km3 in the ocean), which gives a yearly supply of 0.000033 µg vanadium/l seawater. Upholding this feeding rate for one hundred years will add 0.1-0.4 percent to the current concentration.

Nickel is also a normal part of seawater in concentrations around 1.7 µg/l, as nickel is constantly fed into the seawater from decomposed rocks. If we estimate an average of 50 mg nickel/kg HFO the calculation shows an average supply of 0.0000082 µg/l, which in 100 years may increase the nickel concentrations in the ocean by 0.05 percent.

No pollution

A PEC/PNEC analysis near the scrubber discharge outlet combined with simulation (se figure below) shows that the washwater has the same PEC/PNEC as the surrounding water at a distance between 3-6 meters from the outlet. Meaning that washwater discharge does not affect the surroundings beyond this distance. The water treatment plant reduces all components except from nickel and vanadium, typically 50 percent in PEC/PNEC.

Washwater concentration around Clipper Harald, in scale (150 meter vessel).

The results above are in line with the conclusion from the recent official Danish Environmental project 1431, Assessments of possible effect of scrubber water discharge on the marine environment.

An obvious conclusion to the above, if there is doubt about the water quality in a specific sensitive harbour area with high traffic, is that detailed analyses could be done to evaluate water quality implications from ships running on HFO.

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