Upgrades to South Sewage Treatment Plant (SSTP) have proven to be more successful and cost efficient than originally predicted, saving the City of Castlegar approximately $125,000 per year.
“From a staff perspective, we are excited that the upgrades have created better than anticipated results,” said director of transportation and civic works Chris Barlow. “The cost savings are nice to see long term.”
In 2004, the SSTP was upgraded when its capacity was doubled and a second activated sludge plant was installed. It was then identified that the process was performing almost complete nitrification, resulting in plant effluent with a pH of 4.5 to 5.5 — this was a problem as the city’s permit requires pH to be between six and nine.
In order to raise the pH, staff began adding dry hydrated lime to the process. It did the job raising the pH, but was hard to inject into the wastewater stream, resulting in large pH swings in the influent.
Liquid caustic soda was then added to the influent at the rate of approximately four gallons per hour; this was successful, but costly, costing the city between $85,000 and $125,000 per year. So the city then hired a consultant to look into ways to incorporate an anoxic zone into the wastewater system in order to control the pH biologically, instead of chemically. This resulted in plans for upgrades to the SSTP in 2016.
The anoxic zone is an area within the treatment process that is not aerated. It allows for a biological and chemical process to happen that frees up dissolved oxygen and allows for changes in pH.
Projections were that the anoxic zone would reduce the use of the caustic soda by 90 per cent. They also identified that a reduction in aeration would occur, resulting in energy cost savings.
In early 2016, the design, tender and construction process began and the new system was activated in November. Since then, the need for caustic soda has actually been eliminated and the aeration blower speed reduced by half, resulting in the larger than anticipated savings.
During the upgrade process, staff also noticed that there was an increased energy efficiency in the south aeration cell over the north aeration cell so all influent flows have now been diverted to the south cell and the north cell is being drained and washed down in preparation for not being used. This also means that now only one 60-horse-power blower is being used, instead of three.
The budget for the project was $480,000, so the cost savings will pay for the project in less than four years.
“It has been very satisfying internally that a lot of the ground work and the testing was done by internal crews — and a lot of the ideas,” said Barlow. “To see it come through to fruition is very complimentary to the treatment crews that we have and the utilities manager.”
The city will now start small incremental repairs and upgrades on the north aeration cell in preparation for the time when an increase in development or a significant increase in influent to the SSTP occurs, providing the city with reserve capacity for many years of development.