Milwaukee might be known for having the second best team in NL central right now, but the home of the Brewers is also known for exclusively producing the microbe-based fertilizer Milorganite. Microbes are used in the aeration part of the wastewater recovery process. There, they are coaxed by bubbles and lots of nutrients (aka waste) to eat, grow, and reproduce. I had the pleasure of visiting the Milwaukee Metropolitan Sewerage District wastewater reclamation facility not long ago and got these close-up pictures of Milorganite-making that I thought I’d share with you all.
I passed up on touching the fertilizer even though it had been heated to 480-650 degrees Celsius. Milwaukee’s wastewater recovery plant is smart with its business model for the fertilizer – they make the same amount of product each year. This guarantees there will always be customers who buy their product when it’s ready, and they have a consistent profit margin that goes back into running the plant. It’s more about producing useful byproducts of the treatment process than growing into a Milorganite company for them. That is cool.
“Although some major cities like New York City and Philadelphia have combined sewer [overflow] systems, most communities with combined sewer problems have fewer than 10,000 people, according to the EPA report.” -John Tibbetts, Env. Health Perspectives
If other municipalities could have a wastewater recovery facility like Milwaukee’s, some of them might. Limitations in infrastructure such as outdated combined sewer systems must be overcome with money, though, and not every city has enough members to pay the taxes to make that possible. Wastewater treatment facilities need to consider environmental issues relevant to their area. For example, wastewater treatment plants that discharge into bodies of water with temperature-sensitive native fish species should perform temperature corrections on their effluent. Newer plants are also more able to adapt new designs, while older plants are dependent on equipment that will work with their setup.
Milwaukee’s wastewater treatment plant is so large that even a depiction of the process takes up an entire wall. The Archimedes screw, bars, mesh, and coarse screening with grit removal at the start of the process are all underground. The primary and secondary clarifiers and aeration tanks following that are outdoors, but the rest continues underground where tourists can’t wander. Placing the enormous middle part of the process outside doesn’t change the efficiency of the process. Mostly, it saves money on building materials.
Although there are some natural micro-organisms in wastewater, specific micro-organisms can be selected, purchased, and introduced to the system in order to biologically clean the water at a much quicker pace. A part of the process not included in the drawing above is the part where micro-organisms are recycled out of the aeration tank. When the micro-organism population starts to grow too large, a fraction is drained and becomes the base product for Milorganite. In the Milorganite plant, the product is pressed to remove any excess water, and heated to super high temperatures for cleaning. The end result looks a lot like dirt and is packaged up and sold.
The biggest nuisance at the plant which clogs up the mesh and screens is flushable wipes. Believe it or not, toilet paper and human waste breaks apart by the time it gets to the treatment plant, but flushable wipes are still fully intact and will stop up the machinery. The workers there ask that if flushable wipes are used, they go into the trash after use! The treatment plant removes all garbage found in their system, however, too much trash in the screen requires them to halt the process and sometimes even remove all the wipes with a rake. Flushable wipes aren’t flushable.
Milwaukee Metropolitan Sewerage District truly seeks to help address environmental issues in the area. One such example is their push for organizations to implement green roofs. Green roofs help to reduce flooding, which then causes pressure on combined sewer overflow systems. Some barriers to implementing green roofs are that existing buildings may not be able to support the weight, and of course, the cost. Although I advocate for green roofs, I saw so much potential for a natural landscape at the wastewater treatment plant itself. Everywhere I looked there was a never-ending expanse of concrete that could be turned into a field of wildflowers or tall grass, or planted with shrubs or saplings. Not only this, but there wasn’t a ton of green roof at the plant. I’m sure this is largely due to the fact that trucks need to access the plant in order to remove grit and Milorganite. Maybe there’s something small and experimental they could try, like solar roads or permeable pavement. Hopefully MMSD is able to implement innovative green practices at their plant in the future.
Hope you enjoyed learning about Milorganite! Have a great rest of your Sunday, Jess 🙂