Environmental Studies Field Trips: Wastewater Treatment Plant

CGEE Student Voice
by Jenni Abere


This week, Hamline Environmental Studies students got a special "Metro After Dark" tour of the Wastewater Treatment Plant. This plant covers a lot of land: I guess I expected it to be much more compact. This plant is also very old, so many of the buildings are no longer used. As we travelled from building to building, following the path of wastewater, the sun set and it was dark when we reached the final stage. At this point, the water was heading back into the Mississippi. It smelled like river water, and it looked black in the darkness.

This old-fashioned gauge was at one point the only way they could monitor flow.
Although it is still hooked up to monitors today, it's mostly decorative. 

The process

This plant treats an average of 160 million gallons of wastewater per day. The total used to be much higher when storm-water was also treated, but these two water streams have been separated. Storm water goes directly into the river without treatment.

Wastewater will also return to the river once treated, and much cleaner than typical river water.

1. Removing grit

Sand, rocks, and "grit" is first removed to prevent damage to the machinery.

2. Settling and skimming

This is done to remove solids, both things that float, by skimming the surface, and things that sink, by allowing them to settle to the bottom.

"Screen and Grit" building

3. Micro-organisms

A variety of bacteria, affectionately called "bugs," perform their natural process, only much faster. Different bugs consume organic matter, phosphorous, and other pollutants. Some tanks are aerated and others are not, depending on the type of bacteria. 

4. Disinfection with bleach (seasonal)

During the warmer months when the river is used recreationally, the final stage is disinfection with bleach. Bleach is applied and then removed. This costly process is only required by the EPA six months of the year.

5. Solids 

Once solid waste has been removed, gravity and centrifuges are utilized to remove as much water as possible. This makes incineration more efficient. The solids are incinerated at incredibly high temperatures. The plant captures the heat (enough to heat the plant all winter long) and has steam turbines as well, providing 20% of the plant's energy needs.

The fine ash produced is then landfilled. They would prefer to find a use for this product. It used to be made into cement, until concerns about heavy metals ended this.

Threats to water quality

1. Anti-bacterial soap and hand-sanitizer 

I've always avoided anti-bacterial soap and hand-sanitizer because it can produce anti-biotic-immune bacteria. However, I had never considered the impact on water treatment. Bacteria are vital to water treatment, so we don't want things going down the drain that will kill bacteria.

Use alcohol-based hand-sanitizers instead because these break down. 

2. Micro-plastics

Minnesota recently banned the used of plastic micro-beads in personal care products such as soaps and toothpaste. However, this hasn't solved the problem entirely. Tons of micro-plastics enter the water stream through washing machines: synthetic fibers come off clothing with every wash and go down the drain. 

There is currently no way to remove these in water treatment. 

The Rozalia Project is currently working on a filter that people can use at their home washing machines to collect the plastic fibers before they go down the drain. Landfilling these plastic fibers is not nearly as harmful. However, the best solution (if an impractical one) is to buy clothing with no synthetic fibers. 

3. Pharmaceuticals 

Pharmaceuticals should be disposed of through Household Hazardous Waste programs, so they can be incinerated. Do not flush medicine! Endocrine disruptors, such as from birth control, are especially harmful to amphibians. 

To learn more about this wastewater treatment plant, watch the Metropolitan Council's video below: