One of two proposed methods for disposing of McCall's treated sewage would allow something the city is currently banned from doing.
State regulations forbid the city from discharging its treated sewage into the North Fork of the Payette River. That is because the phosphorus in the treated water encourages algae growth downstream in Lake Cascade.
But the treatment now being considered by the city would take treatment to the next level and remove more phosphorus and nitrogen from the final product. That alternative would cost $70.2 million, according to current estimates.
"With a discharge to the North Fork of the Payette River, a primary treatment objective would be to remove as' much phosphorus as practicable to reduce the impact on the North Fork of the Payette River and Cascade Lake;" the city's draft wastewater facilities plan said.
"Although this alternative is developed to function by itself (complete treatment and discharge of all flows the River), it would be possible to combine the alternative with other effluent disposal alternatives to capture the use of the existing facilities to the extent practicable," the report said.
The city also can earn credits from the state if it takes action to keep phosphorus from getting into the river from other sources.
The best way to do that is to improve the way the city handles its storm water runoff or pay farmers in the valley to reduce phosphorus from their runoff, the report said.
New methods eyed
To allow discharge into the river, the city will need to use high-tech methods. One of these is called a membrane bioreactor, which would produce wastewater that is cleaner than the water currently coming out of the city's plant and used to irrigate land south of town.
Both biological and chemical processes would be used to remove nitrogen and phosphorus from wastewater.
The membrane bioreactor system is limited in its capacity if a large amount of storm water or spring runoff leaks into the plant.
The existing aerated lagoon system located off Deinhard Lane in southwest McCall would be used to equalize the flows prior to going into the bioreactor, Roberts said.
Features of this treatment system are:
• Total nitrogen reduction using anoxic selectors. Anoxic selectors are a biological treatment that uses organisms that eat nitrogen.
• Membranes will be used to filter solids, including those carrying phosphorus.
• Chemicals will be added to aid in the phosphorus removal.
• Digestion of sludge using aeration to reduce odor and dangerous bacteria.
• As the raw sewage enters the plant, it would be whirled into a vortex to remove sand
and rocks.
More information about the city's wastewater treatment planning process can be obtained on the city's Web site at www mccall.id.us.
