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Friday, June 18, 2004


Nitrogen spike inundates sewer

Overwhelmed treatment bugs on way to recovery at Bellevue

Express Staff Writer

Microorganisms at the Bellevue sewage treatment plant gorged themselves on a nitrogen feast last week. The bugs, essential to the consumption of the potential groundwater contaminate, are still recovering.

Bellevue Water and Sewer Superintendent Brian Whipple said he noticed the nitrogen spike when the treatment ponds south of the city turned a darker brown and tests showed diminished levels of dissolved oxygen in the wastewater.

Clearing more duckweed from the lagoons at the Bellevue sewage treatment facility, Bellevue Water and Sewer Superintendent Brian Whipple said the sewer department has been diligently working to maximize the efficiency of a treatment system that is working at capacity. Express photo by David N. Seelig

"We test for dissolved oxygen and pH everyday," he said. "If the bugs are not working right, the dissolved (oxygen) goes down."

The event sent nitrogen levels of the influent to the treatment plant soaring to 101 parts per million.

The city has a state permit for land discharge of treated water from its lagoon treatment system at a nitrogen level of 20 parts per million.

Whipple said that, although the spike overwhelmed the bugs, the nitrogen bloom was diluted in the treatment ponds, and that microorganism activity is once again increasing.

"Things are smoothing out," he said.

Whipple added that wastewater is detained in the lagoons for about a month to be treated.

Typically, most of the nitrogen is broken down by the microorganisms in the treatment ponds and is safe to spread over farmland during the growing season or discharge into the ground during the rest of the year.

Bellevue had other nitrogen spikes in the past year, especially during winter months, when microorganism activity slows. But the city is about to embark on a study, which will help city leaders decide how best to upgrade the treatment system.

Rapid growth in the city has shortened the life expectancy of the city’s wastewater treatment system by about 10 years, Whipple said.

The source of last week’s nitrogen discharge was a heavy flushing of proteins and amino acids, components of food and fecal matter.

Barring a repeat of the event, the dinoflagellates and other bugs that work to break down the nitrogen-rich influent should be able to recover from the feast, said Department of Environmental Quality Manager for Engineering Dave Anderson

Fortunately, the bloom occurred at a time when the city applies its treated wastewater to crops of hay and feed grain for cattle, which are capable of absorbing the energy source, he said.

This amounts to more fertilizer going out in the field, he said.

Nonetheless, Anderson added that getting wastewater within permitted levels for nitrogen is important to avoid groundwater contamination after treated water is released to the ground.

Whipple said he does not yet know the source of the nitrogen, but he said the city is investigating the matter.

"It was one big flush," he said. "We don’t know how it got into our system. It may have come in through a drain or a manhole. We’re trying to track it."


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