New treatment system at ExxonMobil removes nitrates from wastewater, helping fight dead zone problem in Gulf of Mexico _lowres

Photo provided ExxonMobil -- Two of these tanks were added to the new ExxonMobil Refinery waste water treatment system in Baton Rouge to remove extra nitrates before the water is put into the Mississippi River. The new system allowed the facility to remove an extra 1.4 million pounds of nitrate last year, an 80 percent reduction over 2014.

When ExxonMobil started moving forward with a new wastewater treatment system for the Baton Rouge refinery, staff saw it as an opportunity to add some water quality lagniappe.

In 2009, the facility had started planning to transition its wastewater treatment from in-ground ponds to above-ground tanks, making it one of the largest systems of its kind.

“Nothing has ever been done on this scale before,” said Robert Berg, ExxonMobil’s regulatory adviser for Louisiana.

At the same time, staff at the facility thought this upgrade would be a perfect time to include an additional system to remove nitrates from the water beyond what is required by law.

Nitrogen is one of the components that contributes to the annual Gulf of Mexico low-oxygen dead zone every year. The nutrients, including nitrates, feed small plants, which use up oxygen in the water as they decompose, causing a large swath of low-oxygen water off the coast of Louisiana every summer.

According to the Louisiana Nutrient Management Strategy published in 2014, Louisiana accounts for 2 percent or less of the nutrients that flow into the Gulf of Mexico through the Atchafalaya and Mississippi rivers.

Even with this small contribution, Berg said the project was “the right thing to do because of the focus on the hypoxic (low-oxygen) zone.”

“We just like to get out in front of things,” Berg said.

The project recently was recognized by the state Department of Environmental Quality with an Environmental Leadership Award for reducing nitrates by 1.4 million pounds last year compared with 2014 — a more than 80 percent reduction.

The nitrate is removed through a two-step process as part of the overall new wastewater treatment system, said Junior Sanders, senior water adviser for the complex.

The wastewater first is pumped into a tank full of microorganisms in a low-oxygen environment. The organisms use up the oxygen, and the remaining nitrogen is released into the air.

From there, the wastewater goes into a second tank where microorganisms continue to break down the wastewater.

The wastewater is then recirculated back to step one, a process that is repeated about 10 times before the water gets discharged to the Mississippi River.

“The bugs are eating the organic material we don’t want to go into the river,” Berg said.

Previously, there was no separate system to take nitrates out of the water, although they could do some reductions by turning on or shutting off the aerators in the pond to allow different organisms to work on the material.

Planning for the whole wastewater treatment system started back in 2009, with construction running for two years from 2012 through 2014.

The project may not have been required, but after working with the state nutrient reduction committees and with a new call from DEQ Secretary Chuck Carr Brown for industry to look for ways to go beyond just regulations, it was a good fit, Berg said.

“It made sense for us to do this now,” Sanders said.

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