Keeping it clean
Despite what people think, oil and water do mix. Not for long, mind, and it is not always an amicable separation. In commercial and operational terms, dealing with wastewater at tank farms is sometimes a major hazard, often an expensive process, and almost always a hassle
Where there is oil, there is contamination, and contaminated wastewater is a big issue in the energy sector. A potentially huge environmental problem if released into the sea or other watercourse, wastewater needs channelling, collecting, storing, treating, and often transporting and finally disposal of, somehow and somewhere.
This necessary level of care applies to all wastewater, whether its origin is tank draining, tank cleaning, or the sky. According to cleaning and waste treatment practitioners, there is evidence around the world of breaches of environmental legislation covering the disposal of hazardous waste, including contaminated water. This is often because tank cleaning and responsible wastewater handling perhaps do not flag up on the average tank owner’s priority radar as highly as inspection, for example, and not least due to the high costs of treatment, transportation and disposal. Tank farms and terminals end up with large volumes of associated wastewater for a number of reasons. A large proportion results from tank bottom draining as part of normal operations. Rainwater infiltration, condensation and any water present in the product upon delivery at a site can all contribute to water presence inside a tank. When this water separates and settles on a tank bottom, it can contribute to corrosion in some types of tank and also eventually reduces the space available to store product.
A certain volume comes from storm water run off, and from secondary containment areas around the tanks. These are designed to hold leaks and spills to prevent release into the surrounding soil, and so water gathering in these areas will be contaminated in the event of such a release. Contaminated firewater is of course also a high volume cause of wastewater at a terminal, and the issues post-Buncefield have been well documented. Other sources of contaminated water at terminals are tanker and railcar washing, if these activities occur onsite, and water from certain vapour recovery processes that may sometimes be applied. But probably the greatest volume of contaminated wastewater produced at tank farms and terminals, and often needing to be stored until treatment, results directly from tank cleaning activities. These might mean regular tank cleaning because of product change, cleaning prior to a full in-tank inspection or repairs that require the tank to be taken out of service, and cleaning of decommissioned tank sections before removal from the site. Due to the nature of the products stored in them and necessity for purity, chemical tanks generally need more frequent cleaning than petroleum.
Cleaning needs vary from site to site, but minimising actual cleaning costs, water used and the resultant waste are high on the list for terminal managers contracting cleaning services. In fact, many of those surveyed cite waste minimisation as the most desirable, and yet most challenging, aspect of tank cleaning procurement, not in the least part due to the high costs of treatment and disposal.
