Nitrogen spike inundates sewer
Overwhelmed treatment bugs on way to
recovery at Bellevue
By MATT FURBER
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
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)
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,
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."