November 17, 2005 at 6:18 a.m.

Wastewater plant showcased for member officials after several week shakedown operations

Wastewater plant showcased for member officials after several week shakedown operations
Wastewater plant showcased for member officials after several week shakedown operations

The new multi-million dollar Chisago Lakes Joint Sewage Treatment Commission’s sewer treatment plant is operational. The project was built within original cost estimates and the word is that everything’s looking A-okay.

The wastewater in-flow was switched over to the new facility a few weeks ago and unless you are a CLJSTC employee-- you wouldn’t have noticed the change.

The CLJSTC built the new plant which is based on a sewage treatment process called Sequencing Batch Reactor or SBR.

The commissioners selected SBR for cost-effectiveness. The new plant is built for a capacity of almost 2.5 million gallons per day. It is currently running at about three-quarters of one million; but Wyoming and Stacy haven’t begun to pipe their influent yet. Stacy is still laying connecting line to hook-up to the Chisago City line at a point just south of the plant, and it was reported the Stacy connection should be charged up by mid- December. Wyoming was awaiting electric power to a lift station for its new line. Both those cities still have all or a portion of their old systems operating until the connections are complete.

CLJSTC project engineer Steve Alm explained that the plant is designed to add a third SBR tank which, depending on population growth, expansion could be required in 10 years.

In SBR the sewage rushes into a pre-treatment building, through a 36 inch diameter pipe. Sewage is collected through a vast network of pipes and over 50 lift stations linking member communities.

Communities are basically billed for plant operations based on their own flow and debt service on the $13.4 million loan is also apportioned out.

In the pre-treatment structure the really smelly influent is screened and grit drops into a chamber. This debris is washed and inspected for anything toxic, etc. Eventually this is trucked away to a special landfill.

The slightly-less-solid influent is then pumped into a concrete tank filled with what the plant supervisor Mark Nelson calls “bugs.”

“Our job is to keep the bugs happy,” Nelson declared.

The bugs, or protozoa, breakdown the “food” in the wastewater. Aeration devices also help and settling is another part of the treatment process.

The technologically-advanced plant has a computer-controlled “cycle” for each SBR tank.

The cycles are calibrated to flow levels.

There’s 10 cycles daily at the plant now, in two tanks, at approximately five hours per cycle. This is basically a 24-hour operation with only about 15 minutes of “idle time” in a tank.

The current flow requires about two and a half hours to fill the tank to a depth of about 16 feet. (As flows of wastewater grow each tank can go to 21 feet deep.)

You do not want to fall into one of these.

While every aspect of this processing system is based on science, the art to operating this plant is constant monitoring of the protozoa populations. The lab technician and staff keep close watch on which species are thriving or declining and generally how all the “bugs” are faring. The trick is balancing the micro-organism colonies-- some digest certain elemnets only,certain species live at certain depths and some eat other protozoa.

Samples used by the on-site laboratory are gathered at a variety of automatic testing stations erected along the system, that fill sample bottles and store them for collection.

The lab is set up for measuring pH levels, ammonia and similar tests. The end product that comes out of this plant has to meet state restrictions on levels of dissolved oxygen, bio-solids and phosphorus-- which is a new state restriction and one of the reasons the aging former plant was replaced.

Nelson explained experienced staff can eyeball the tank contents and judge pretty well how the micro-organism breakdown is going. Color, smell, turbidity of the water and other observations are invaluable.

The cleaner upper level of the SBR tank is “decanted” into a post-aeration tank that’s smaller than the SBRs. A chlorine contact tank is used for chlorination and de-chlorination in summer months.

The state requires this for recreational considerations, swimming and fishing, as the treated water becomes effluent and is discharged from the pkant to go on its merry way into a tributary of the Sunrise River.

Engineer Alm noted there’s been “good readings” on the discharge.

As for the “bio-solids” that the system shed early in the process, the plant has an activated sludge tank and two digester tanks. Come spring the commission will plant huge reed beds that will grow in the accumulated sludge taking up the water and dehydrating the material. There are five reed bed cells proposed.

Imbeded into the sprawling plant complex are an office, computer nerve center, emergency diesel engine generator and underground pipes, plus blowers and system engines of a size that entire buildings were constructed just for them.

Much of the plant is built well underground because the whole thing utilizes gravity. The pre-treatment building is on the highest elevation with discharge at the lowest point.

Back at headquarters....

The regular monthly CLJSTC meeting was held following last week’s tour.

With Wyoming representative Ted Phillips absent the commissioners heard an update on the spill that occured several weeks ago.

Nelson reports there have been samples taken weekly at and around the lift station and everything is back to what would be considered normal levels in the wetland and channel-pond near the North Meadows subdivision.

Commission clerk Lou Carpenter will send a final mailing to nearby property owners summarizing the follow-up.

Stacy sent engineer Chuck Schwartz to talk about the Stacy forcemain and how that will be tied into the holdings of the commission. There may need to be legal restructuring of the original agreement due to outside financing for the Stacy line and requirements within the loan about “ownership” of the asset.

The commission set up a special meeting for November 23 at 2:30 at Lindstrom City Hall to discuss the line.


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