The bright-blue cylinders roar day and night, and their powerful motors make the floor tremble as unseen parts spin inside. The two centrifuges have been hard at work at the city sewage treatment plant since it was built in 1983, separating solids from the millions of gallons of wastewater that’s piped to the plant each day.
After 20 years of service, these workhorses of the treatment plant, as well as other parts of the city sewer system, are feeling the effects of growth.
An $18.5 million bond issue approved by voters in November included $1.3 million to add two centrifuges, a purchase that’s been put on hold while consultants conduct a stem-to-stern evaluation of the city system and decide whether to expand the existing plant or build one at another location.
Black & Veatch, an engineering firm, is expected to deliver a final report in August about its $843,654 study of the sewerage system that’s designed to chart the future of one of the city’s most important utilities.
“This is a master plan report, which looks at a wider perspective, as far as 20 years down the line,” sewer utility manager Terry Hennkens said.
Each centrifuge was designed to process 125 gallons of wastewater per minute, separating solids, or sludge, that are eventually used as fertilizer and soil conditioner on city-owned and private farmland. But a growing city means more sewage, and Hennkens said the new centrifuges will likely have a capacity of processing 300 gallons a minute. The older centrifuges are still operating efficiently, Hennkens said, and will be kept in service.
The ongoing study will examine population growth and distribution, current and future regulations and evaluate three alternatives:
n Upgrading the existing plant on the west side of Columbia off Gillespie Bridge Road with additional treatment capacity.
n Replacing the existing plant on the same site or at a different location.
n Upgrading the existing facility and building a second plant at a different location.
Plant superintendent Joel Gambill said the study also involves monitoring the flow of water in the sewer lines throughout the city. The goal is to better match the present and future needs of the city.
Gambill said a plant expansion is the most likely outcome of the evaluation along with the purchase of centrifuges with a larger capacity.
“The plant cost the city nearly $25 million when it was first built,” he said, and a new plant would cost at least $60 million, “which won’t be probably worth it since all the pipelines already come here.”
Hennkens said the current centrifuges are in operation 24/7, so emergency repairs must be performed quickly.
“We can’t afford stopping for too long, because a continuous influx of material builds up,” he said.
Hennkens hopes to be able to purchase at least one new centrifuge by October.
“In this way, while we carry out repair work, the larger machine can be kept running for both smaller ones,” he said.
Gambill said this was the intent of having two of the machines when the plant first opened. But as the city has expanded, the plant has needed to keep both centrifuges in operation.