It is beyond the scope of this note to outline the national and international rules on cargo-related discharges, in particular for petcoke. However, a brief note on the rules in the UK and US, as well as those promulgated through the IMO, may be useful for understanding the issues at hand.
Table 2. Summary of MARPOL discharge provisions for petcoke wash water (modified to include oily mixtures)
Further, any hydrocarbon “sheen” produced by discharged tank wash water would constitute a violation under MARPOL Annex 1 (concerning oil pollution). Discharge from bilge tanks in areas where permitted must pass through an oily water separator and monitoring system, plus the oil content of the discharge must not exceed 15ppm.
Legislation in the United States, such as the Clean Water Act (CWA), the Act to Prevent Pollution from Ships (APPS) and several Coast Guard regulations, implement the standards imposed by MARPOL and prohibit discharge of oily residues or MARPOL defined garbage within 12 nautical miles from shore. On the other hand, in its guidance on the at-sea disposal of cargo tank washings and hatch washings, the UK Maritime and Coastguard Agency (MCA) states that:
“.... after unloading some bulk cargoes many ships will wash their holds or decks to remove this excess or spilt material as it could contaminate the next cargo. In such cases this material can be disposed of at sea so long as it is inert, has been minimised by removing as much cargo residue as possible and any disposal complies with the 2008 Regulations and any other relevant legislation. If the material is a marine pollutant, a hazardous or noxious material, or a material that could cause secondary pollution on contact with the sea (such as petcoke, which if disposed of at sea, can cause a sheen on the surface, which will put the ship in contravention of Annex 1 of MARPOL 73/78), then any washings should be disposed of on shore through appropriate reception facilities.”
Although petcoke is not officially classed as harmful to the marine environment and it could in theory be discharged while a vessel is en route and at least 12 nautical miles from the nearest land, petcoke cargo residue and wash water can contain a number of harmful components such as residual hydrocarbons, heavy metals, cleaning agents or dust suppressants. The presence of such components in sufficient quantity could therefore result in a particular cargo residue being considered as harmful to the marine environment.
Generally, the impacts of a discharge of petcoke residue and cleaning products within hold wash water will depend on the volume and the location of the discharge. However, the most likely impact is that an oily sheen may be visible on the water surface for a short time in the immediate vicinity of the discharge, with a localised and short-term increase in the pH of the seawater. If the discharge is undertaken in sufficient depth of seawater with currents allowing a good water exchange, it is likely that any residues will quickly dissipate and that no environmental effects will be observed.
Finally, it is worth noting that the legislation regarding the discharge of any hold wash water from vessels is complicated, whether nationally or internationally. The minimum requirements worldwide tend to be in line with the MARPOL recommendations (for example as outlined in Table 2) but may be more stringent in certain locations. As a result, operators are finding it ever more prudent to transfer tank wash water to shore side facilities for processing rather than discharge at sea in order to avoid potential environmental issues and possible litigation or fines. This is also true for petcoke wash water.
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2Edwards, L. The history and future challenges of calcined petroleum coke production and use in aluminium smelting. J. Miner. 67, (2015).
3Lee, J. M.; Baker, J. J.; Murray, D.; Llerena, R.; Rolle, J. G. . Quality analysis of petroleum cokes and coals for export specifications required in use of specialty products and utility fuels. in 214th National Meeting, American Chemical Society, Division of Fuel Chemistry (1997).
4Puttaswamy, N., Turcotte, D. & Liber, K. Variation in toxicity response of Ceriodaphnia dubia to Athabasca oil sands coke leachates. Chemosphere 80, 489–497 (2010).
(This article is for informational purposes only.)
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