Chennai oil spill: Disposing of toxic chocolate mousse scooped in buckets, safely

A lot of oil sludge that hit Chennai’s coast in 2017 awaits bioremediation

Updated - December 01, 2021 06:27 am IST

Published - December 23, 2017 10:00 pm IST - Chennai

Tarnished shores:  The Coast Guard’s  team tackles the oil spill at Ernavoor in north Chennai on January 29, 2017.

Tarnished shores: The Coast Guard’s team tackles the oil spill at Ernavoor in north Chennai on January 29, 2017.

Eleven months after two ships collided off the coast of Chennai on January 28, resulting in an oil spill, officials of the Indian Oil Corporation (IOC) say they have succeeded in biologically decomposing a portion of the oil mixture that was collected from the coast into harmless components. Some independent experts and officials of Central agencies, however, recommend a thorough review of the results as well as testing by third parties for validation.

When the oil was being removed after the collision, trolls on social media coined a term for it — bucket technology. Their derisive coinage was describing how, well into the 21st century, the only devices that could successfully remove the dirty “chocolate mousse” that had washed on to the Chennai coast from the ship Dawn Kancheepuram were hand-held buckets.

Chocolate mousse may sound delicious but the nearly 250 tonnes of heavy fuel oil that spilled from the ship, when acted on by sea water, became a thick, toxic sludge that was life-threatening. Volunteers and government staff carried bucketfuls of the oily mixture that was being washed ashore on to large tanks. Tar balls that marred the beach sands were removed too.


In all, some 187 tonnes of oil sludge, 109 kilolitres of oil mixed with water, and 81.5 tonnes of oil mixed with sand were collected. And these had to be safely disposed of.

Nearly 10 days of mass action using ‘bucket technology’ was followed by more than two months of professionals scrubbing out the final traces of oil. The rags, absorbent booms and normal booms they used for the clean-up and the gloves and other protective gear had to be disposed of too, along with the oil sludge.

“Not knowing what to do with the recovered oil was a learning from the accident,” said R. Rajeevan, Assistant Commandant, Coast Guard, while speaking at a seminar on the collision and the clean-up held recently at the Seafarers Club in Chennai. The Coast Guard is the recognised nodal agency for fighting marine oil pollution.

Officials then decided that they would try biodegradation of the waste. “Indian Oil Corporation was asked by the Ministry of Petroleum to carry out bioremediation of the oil mixture since we have been successfully implementing this technology,” says S. K. Puri, Chief General Manager for Bio-Energy at the IOC R&D Centre, Faridabad.

Bacterial cultures

In bioremediation, specific bacterial cultures are introduced that feed on the oil and break it down into largely carbon dioxide and water, says Banwari Lal, a microbiologist and senior director at The Energy and Research Institute (TERI), New Delhi.

While some experts are critical of biodegradation, saying it is too time-consuming, leaves out other toxic elements, has to be done in a controlled manner, and requires maintenance for it to be successful, others have argued that alternatives, such as incineration, are not only more expensive but also create secondary pollutants.

Bioremediation is safe, clean and well established, says Mr. Puri. “Further, additional energy would have been needed in the form of, say, diesel to burn all the oily waste we recovered,” he adds. The waste from the clean-up was taken inside Kamarajar Port, where a pit of 20 m by 50 m and 1 foot deep was dug. The 187 tonnes of oily sludge was mixed with soil and deposited. Underneath the mixture was a sheet of plastic liner to contain leaching. The rest of the oily waste has been lying in tanks inside the port, awaiting disposal.


“We started on February 6, 2017. In 230 days, the total petroleum hydrocarbons has come down from a high of 8.8% to a safe level of 0.4% at the site. We can bioremediate the remaining 81.5 tonnes of oil-sand mixture if we are asked,” says Mr. Puri.

Independent researchers are, however, calling for a study of the results before taking up more bioremediation. One researcher, who has been associated with the clean-up, says the oil levels are not uniformly low across the site and bioremediation guidelines laid down by the Central Pollution Control Board (CPCB) were not followed fully. As a result, at one time, unremediated oil had flowed away with rainwater run-off, the researcher said. Experts are also calling for a review of a variety of parameters, and how they changed over a period of time.

The authorisation given to IOC by Tamil Nadu Pollution Control Board for bioremediation says that soil samples from the site should be sent to TNPCB for tests every 15 days, and the agency would validate the results. TNPCB officials, however, refused to give information on the results.

“When we visited the site earlier this year after bioremediation started, we advised that a kerb should be laid around the site and monitoring wells dug to draw samples. We asked TNPCB to test at a third-party lab parameters, including volatile organic compounds, total petroleum hydrocarbons and diesel range organics, since we don’t have test facilities. In November, we lifted samples but we have received no analysis,” says H.D. Varalaxmi, a scientist at the CPCB in Bengaluru. IOC officials say the kerb was indeed laid, and test wells were dug.

Ms. Varalaxmi adds that bioremediation of a contaminated site is happening for the first time in the south and, if successful, the Ennore process can be a template. IOC officials are confident. Mr. Puri says there were variations in the levels through the year since the performance of the bacteria is affected by temperature but it is now time to declare the effort a success.” IOC officials say bioremediation is routinely done at their facilities on sludge left over in tanks. “It’s a patented product,” says K. S. Rao, Chief General Manager for Operations at IOC, Chennai.

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