Oil contamination continues to be a very hot topic, due largely in part to recent catastrophic events with shipping tankers in open waters. The coastal contamination off Spain, the Valdez in Alaska, accidents off California, refinery spills in Brazil (11), and dozens of other countries have all provided much insight into the damage that can be caused when gross amounts of oil are suddenly released into the environment.
While it is the large volume spills close to land that draw attention; it is the continuous low concentration release of hydrocarbons that is the issue with industrial separator discharge, stormwater run-off, water cooling and produced water. This spans the complete industrial sector from manufacturing factories, electrical generation plants, oil production and refining, and municipal wastewater facilities. This paper will address the low concentration contamination of water by hydrocarbons. A brief look into the history of oil will give some perspective.
A review of the hydrocarbon compound will help to recognize the difficult task presented to authorities in defining the actual contaminants and at what levels they may become harmful. Once defined, industry must be diligent in monitoring for these contaminants. This introduces even further issues related to the private and public sector that must understand, maintain, interpret and report the data.
Instrument manufacturers are also a variable, and necessary to this equation. The manufacturers strive to provide products to meet the demands of the application while providing data that is valuable to both the authorities and the industrial user. Oil may have been used for thousands of years but it is only in the last century that oil has played such as dramatic role in society and industrial development. As a valuable source of energy, oil has helped to shape the world and provide a solid standard of living. This, of course, does not come without it's potential damaging affects if not monitored and controlled effectively.
Petroleum oils are a natural resource of Earth that occurred millions of years ago through the decomposition of natural plant and aquatic life (19). History suggests that as plant and animal life decayed, it became trapped beneath sediment. The lack of oxygen resulted in the absence of a support mechanism for bacteria, which halted decay (18). At this point the decaying plants had been reduced to mostly carbon and hydrogen. Through temperature and pressure, a transformation took place resulting in oil. These hydrocarbon mixtures have worked their way into various deposits around the globe as they migrated and became trapped beneath the earth's surface.
This has been a totally natural process for millions of years and this process continues today. It is also natural for hydrocarbons to further degrade and return into the ecosystem. When oil is released from the deposits, either naturally or with the help of man, the compounds will eventually breakdown. When this loading on the environment is kept to a minimal release rate, the affects are also usually minimal and recovery can take place.
The source of damaging contamination is due from the careless handling of the oils and from the production and refining of hydrocarbons into new chemical structures that are not able to breakdown as naturally. The hydrocarbon contamination that can result from the fuel burning emissions can concentrate into marine and plant life, resulting in the breakdown of the natural ecosystem.
Investigation into hydrocarbon compounds reveals that certain compounds are more harmful than others, and therefore are targeted to be monitored more closely.
3. Hydrocarbons Revealed
Hydrocarbons are a common and natural occurrence in the environment and varying concentrations in stormwater and effluent water are not unusual. Hydrocarbons in water can be found as free floating, emulsified, dissolved, or adsorbed to suspended solids. The category that a hydrocarbon molecule finds itself is typically dictated by it’s size. The larger structures tend to be more buoyant and are free. This are readily separated from water by natural separation or enhanced through oil/water separators such as dissolved air floatation (DAFs) or coalescing systems. The smaller molecules tend to emulsify with the water and are more difficult to remove from industrial water prior to discharge.
Microbes in the soils and water have a natural ability to breakdown many of these compounds and any hydrocarbon that is exposed to the air will also have an affinity to volatilize. As well, reactions including photochemistry, and the various transformations of the hydrocarbon through these reactions can enhance the hydrocarbon decomposition. Industrial processes and man-induced activities often result in the increased loading of hydrocarbons in water. The natural abilities of the water to decompose the hydrocarbons become overwhelmed and the resulting affect on the environment includes, but is not limited to:
- Oils can affect respiration of fish by adhering to the gills
- Oils adhere to and destroy algae and plankton
- Feeding and reproduction of water life (plant, insect, and fish) is affected
- Aesthetics is affected by sheens
- Micro-organisms needed for plant nutrition is redirected to oil degradation
Typical sources of man-induced hydrocarbons include the refining processes of crude oil into gasoline, lubricating oils, kerosenes, etc. As well, the resulting commercial products find their way into the environment through stormwater run-off and spills from road asphalts, fueling depots (i.e. airports, maintenance facilities), transportation and haulage, cooling water systems, manufacturing facilities such as automotive, plastics and steel production, and wood distillation industries. Understanding hydrocarbons and the techniques to monitor for them is an important part in the assessment of filters and separators, and the associated productivity and environmental impacts they can have.
4. Hydrocarbons Defined
A hydrocarbon, by definition, is one of a group of chemical compounds composed only of hydrogen and carbon. Typically, hydrocarbons are broken down into three main classes; aliphatic, alicyclic, and aromatics. Further sub-classes can also be defined. Simply stated though, hydrocarbons are organic compounds made up of hydrogen and carbon. Of course, the chemistry involved can be a lot more complicated than this. In fact, there could be thousands of individual organic compounds in one sample of conventional or synthetic crude oil.
There can be many confusing references to hydrocarbon contamination water. Terminology such as:
- PAH’s (polycyclic aromatic hydrocarbons)
- BTEX (benzene, ethyl benzene, toluene, xylene)
- TPH (total petroleum hydrocarbons)
- TRPH (total recoverable petroleum hydrocarbons)
- TOG (total oil and grease)
- Organic vs. Inorganic
all contribute to this confusion.
Generally, hydrocarbon contamination in water is discussed in parts per million (ppm) levels of the hydrocarbon in water. For example, a hydrocarbon level of 30 ppm in water could contain any number of compounds that total this 30 ppm; including compounds found in jet fuels, diesels, lubricating oils, etc.. In other words, the source of the hydrocarbon and the specific compound is not particularly targeted.
It is the overall total of hydrocarbon compounds that is typically of interest. A hydrocarbon can refer to a vast array of compounds, but a determination of a contaminating hydrocarbon will help to define this scope. As well, acceptable and available measurement techniques may define a contaminating hydrocarbon even further.
The 3 main classes of hydrocarbons are defined as follows. This definition uses the physical chemical structure to determine the grouping. The aliphatics are straight chain compounds. The following aliphatic example is named acetylene. One atom joins to the next in a linear fashion and the last in the chain is left open. These compounds can become quite large and can extend in multiple branch chains with many open ends.