No Trouble Removing Oil From Water

The Extended Gravity Oil Water Separation (EGOWS) concept is animprovement on the industry-standard American Petroleum Institute (API)gravity separator that has been widely used for the last 60 years.

The API separator, originally designed for oil refineries, isnot designed to reduce the oil content of water below about 100 partsper million and is not suitable for releasing water directly to theenvironment.

Regulatory requirements for the release of oil-contaminatedwater to the environment are becoming stricter worldwide. It is commonfor environmental protection authorities to impose a limit of 10 partsof oil per million of effluent water, and increasingly for there to beno visible sheen on the receiving water.

Although other systems can achieve low effluent oil contents,they tend to be more energy intensive and incur higher costs,particularly for ongoing maintenance, says David Tolmie, who developedEGOWS with colleague Peter Stone from the University's Water ResearchLaboratory in the School of Civil and Environmental Engineering.

"EGOWS can removes oil down to below 10 parts per million,requires no power and is most useful in situations that areunattended," says Mr Tolmie. "Most of the EGOWS installations to datein Australia have been in electricity substations to eliminate thesmall but potentially disastrous risk of a major spill of oil to theenvironment."

The system's secret lies in its ability to take episodicinflows of oily water and extend the time it spends in the separatortank.

Because oil is less dense, it rises to the surface of thewater. The more time given to effluent water in the separator, the moreoil that can be separated. EGOWS achieves a separation time of days inthe tank as opposed to 20 or 30 minutes in an API separator.

This is achieved by arranging for the separator to be in apartially emptied state before the arrival of episodic inflows of oilywater. When the separator is full, water is released automaticallyusing a siphon that involves no mechanical devices or powerrequirements.

Oily water inflows are accumulated progressively, with norelease of water until it reaches a siphon priming level. APIseparators and other separators that operate full of water , releaseequal quantities of water as soon as there is an episodic inflow ofoily water, creating the risk that oil droplets can escape into theseparator outlet.

Tolmie and Stone began researching their concept back in thelate 1990s when Energy Australia asked them to review their oilseparator systems.

"We were looking for a simpler way of doing things," saysTolmie. "One way is to make the tank bigger -- and that works -- but werealised we could use the existing API separators more productively.The beauty of our concept is that existing systems can be retrofittedwith relative ease."

New South Innovations, the commercialisation arm of UNSW, hassince patented the concept and successfully licensed it to Australiancompanies. . Energy Australia estimates their EGOWS system could savethe company $18 million in 10 years. Caltex Australia has installed twoEGOWS units which they describe as innovative and highly effectivesolutions to their stormwater treatment requirements.

New South Innovations has obtained patents in America, Europe,New Zealand and parts of Asia and is actively looking for potentialinternational licensees.

"The cost of an oil spill clean up can be many times the costof a separator which will contain the oil spill automatically," saidTolmie.

EGOWS is suitable for use with episodic inflows of oil or oilywater in such places as electricity substations, oil storages,transport and container terminals, highways and ports.