A Guide to Oil in Water Monitoring for Environmental Compliance

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Courtesy of Arjay Engineering Ltd.

Applications for industrial oil in water monitoring can vary greatly.

In upstream and midstream oil and gas production applications, monitoring separation efficiencies is key to optimize production rates, preventative maintenance, chemical use, flow, and environmental compliance. Separated water from the oil is called produced water and it must be cleaned of oil before disposal or re-injection.

In downstream applications and for end-users of fuels and oils, environmental compliance becomes key for stormwater management and spill protection. Refineries, power stations, airports, steel plants, pulp and paper, and basically any industry or facility that could have oil contamination in their stormwater run-off would also have an interest to monitor for trace oil in water contamination in their effluents.

Where water is used in heat exchanger applications, monitoring for oils is important to warn of impending water contamination through pin-holes leaks or other breaches into the cooling water.

Shipboard applications of ballast and bilge water discharges to open waters must be monitored for compliance.

De-salination and water purification plants need to monitor for possible oils in their raw water sources due to the detrimental affects of oil to Reverse Osmosis (RO) and other filtration media.

These are just a few of the many applications for oil in water monitoring. Anywhere oil is being separated from water or where oil can come into contact with water, there could be monitoring needs for efficiency or compliance.

Trace Oil in Water Discharges
Trace oil in water typically refers to ppm and mg/l concentrations of oil in water. While ppm and mg/l do not correlate directly, industry has generally accepted the two as equals for discussion purposes.

When water is released back into the environment or to a treatment facility, allowable concentration levels are usually regulated by an environmental authority. Allowable discharge concentrations vary by country and region. Typically, 30 mg/l (29 mg/l in Gulf of Mexico) is a guideline for produced water in open bodies of seawater. Land based applications for water discharge tend to be about 15 mg/l. The shipping industry regulates ballast and bilge water discharge concentrations at 15 ppm as guided by the IMO (International Maritime Organization) and some countries adopt inland water ship discharges as low as 5 mg/l.

Re-injection or effluents headed to a treatment facility may allow higher concentrations.

Oil Spill and Containment
Industrial applications that store fuel or use oils in transformers, heat exchangers and manufacturing may not have trace oil in water concerns. Sumps and separators are a common approach to contain water effluents as a final catch for any gradual accumulation of oils or spills.

In these applications, the oil is contained and not monitored as trace contamination in the effluent water. Alarms and monitors are available to alert operators of a spill situation or when the oil accumulation has reached a defined amount that requires action for disposal.

Oil/Water Interface

In process operations such as oil production and recycling facilities, oil is intentionally separated from water by mechanical or chemical means. Alarms and monitors are used to track the oil/water interface levels and rag (emulsion) layers and provide valuable data to the operators for process control decisions.

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