A $3 million expansion of Tooele City's Wastewater Treatment Plant that began last month will increase the current plant's capacity by 60 percent and update its inner workings.

The expansion of the seven-year-old plant will take about a year.

Currently, the plant can process 2 million gallons of wastewater per day. When the expansion is completed next fall, the plant will have a processing capacity of 3.2 million gallons a day. The expansion will be paid for by a combination of impact fees and sewer revenue funds.

According to Tooele City Engineer Paul Hansen, this expansion is only the first of several phases in the longer-term expansion of the plant.

"We are thinking, 'What are we going to do 50 years out?'" Hansen said.

The Bountiful-based firm Aqua Engineering has been working on the plan for about two years, Hansen said.

The current wastewater treatment system is still one of the most advanced in the state, according to Hansen. The plant treats wastewater in four different stages, and is clean enough to be used as reclaimed water for non-agricultural land.

The treatment plant's current capacity is adequate for the residents and businesses of Tooele City, as well as Deseret Peak and Miller Motorsports Park. This expansion is designed to handle current growth, with additional expansions to be scheduled on an "as needed" basis.

The current expansion includes replacing the headworks screens, adding blowers and diffusers to the aeration ditches, and adding control structures to fix hydraulic issues. In addition, pipe sizes will be changed to allow more water to flow through the plant.

Wastewater comes into the plant at the headworks building. Here all of the foreign objects -- from 2-by-4 planks of wood to clothing -- are filtered out. Next is the aeration stage where aerobic bacteria digest the biological waste. This happens in two large rectangular pools where air is forced into tanks and an ecosystem of microbes digests the solid waste.

"I'm part wildlife manager too," said Wastewater Superintendent Dan Olson, adding that it takes some skill keeping the naturally occurring bacteria alive.

The organic cleansing is where the system is the most vulnerable, Olson added. Petroleum products, paint, an excessive amount of bleach and other toxic chemicals can kill the bacteria, requiring plant operators to culture more.

Any undigested solids are processed and used as fertilizer, and the filtered water is piped into clarifying pools. There are currently two pools, and one more will be added as part of the first phase of expansion.

Most wastewater treatment plants stop with the clarifying process, but Tooele's plant adds two more steps. The water is piped into a separate building where it is filtered again and sodium hypochlorite (1 percent bleach solution) is added. The water is tested before it is released and used to water the Oquirrh Hills Golf Course. There is also a re-use facility in Overlake, Olson said, but it is currently not in operation.