Metropolitan Council

Transcription

Have you ever wondered what happens after you flush? Or how water goes from this to this? That's where Metropolitan Council Environmental Services comes in. MCES, as it's better known, collects and treats wastewater in the seven-county Twin Cities region. A process that takes place mostly underground, wastewater treatment is literally “out of sight, out of mind” for most people. Today, the Mississippi River is beautiful and full of life. But it wasn't too long ago that it looked like this. It looked bad… and it smelled bad. Back in the early 1900s, the first sewers carried sewage, or wastewater, directly into the Mississippi River. There was no wastewater treatment as we know it today. The river naturally cleaned the wastewater, but as the population rapidly grew, so did pollution, which overburdened the river. Sometime in the 1920s or early 1930s, the State of Minnesota did a survey of the Mississippi River from the Twin Cities all the way to Hastings, and in that entire stretch, they only found three live fish. In 1926, the Minnesota State Board of Health declared the Mississippi River a public-health nuisance. As a result, in 1938, the Metropolitan Wastewater Treatment Plant was built in St. Paul. It was the first treatment plant in the Twin Cities and on the entire Mississippi River. Over the next decade, the river’s water quality steadily improved, a direct result of the Metro Plant. During the 1950s and ‘60s, a number of local communities built treatment plants of their own. In 1969, the Minnesota Legislature created the Metropolitan Sewer Board, which centralized wastewater treatment and inherited 33 municipal treatment plants. Of the 33 plants, only four were capable of meeting state and federal wastewater treatment standards. By the late 1970s, 21 of the 33 plants were closed and four new, more efficient plants were built. And the Sewer Board changed its name to the Metropolitan Waste Control Commission. In 1994, the Waste Control Commission merged with the Metropolitan Council and became a division of the Council called Metropolitan Council Environmental Services. Today, MCES as it’s known, operates and maintains the regional wastewater collection and treatment system. The system includes more than 600 miles of regional sewer pipes, more than 60 lift stations, and seven wastewater treatment plants. The regional system processes nearly 260 million gallons of wastewater every day. You get the idea of how much that is when you consider that kind of volume would easily fill the Empire State Building. So, after you turn on the faucets, use the bathroom or do the dishes, what does happen to that wastewater? Most people would say that after you flush, the wastewater goes to the sewer, and they’re mostly right. Wastewater first travels into local community sewer pipes. These community pipes then connect to MCES “interceptor sewers,” which “intercept” wastewater and direct it to one of seven treatment plants. Interceptor sewers range in size from 7 inches in diameter to 14 feet which is big enough to drive a car through. The network of interceptor pipes in the metro area is huge. MCES operates more than 600 miles of these underground pipes. 600 miles would be like driving from St. Paul to Duluth and back… Twice. To help move wastewater towards treatment plants, lift stations pump wastewater to a higher point, and let gravity do the work for the rest of the journey. Lift stations are monitored frequently by MCES crews. Some of the higher-volume lift stations are maintained daily. We travel throughout the seven-county metro area with our crews to check all our different pumping stations and different facilities throughout the area. To prevent damage to the sewer pipes and pumps, lift stations are equipped with bar screens that remove large items like rags, sticks and other debris from the wastewater. After flowing through interceptor sewers. wastewater ends up at one of seven treatment plants. The regional system processes the wastewater of 105 communities in the seven-county metro area, but the Metro Plant is the workhorse of the system, treating more than 70% of the wastewater in the Twin Cities region. Here's how the wastewater is treated at the Metro Plant, one of the largest plants in the nation. The wastewater treatment process is essentially the same at all MCES treatment plants. On its most basic level, wastewater treatment is the separation of solids from liquids. Let’s follow the liquids process first. When wastewater enters the plant, it passes through bar screens like those at lift stations. Screened material is removed and placed in a dumpster. Next, wastewater travels to a large tank, or “grit chamber.” As it comes into the treatment plants, wastewater travels at around two miles an hour. Inside the plant, it moves even slower, to allow heavier material, like sand and gravel, to settle. At that point, there are these scrapers that come along the bottom and push the sand into, basically, a hole or a sump. That material is then pumped out and loaded into landfill-bound trucks. Next, the wastewater travels into “primary treatment.” In primary treatment tanks, the floatable material, like grease and oil, rise to the top of the water. Heavier material, again, sinks to the bottom. Both floatable material and sinkable material are removed from the liquids and treated separately, which we’ll talk about in a bit. From here, wastewater moves on to “secondary treatment.” By looking at it, you probably wouldn't guess that half of the original pollutants have already been removed. The brown color of the wastewater actually comes from bacteria, often called “bugs,” introduced into the tanks. These bugs feast on pollutants, like nitrogen and other organic material. When they [the bugs] are full, they sink to the bottom of the settling tanks. When these guys settle out in our final clarifiers. If you give them a minute, they’ll settle out to a layer on the bottom and we remove those through our solids treatment stream and clear water goes out the top. Bubbles in the tanks come from oxygen pumped in through stone diffusers, like those in fish tanks but on a much larger scale. The bugs are either recycled back through the tanks or disposed of with the solids. At this point, more than 95% of the original pollutants are gone. Wastewater now goes from the final settling tanks to the last stage of the treatment process… Disinfection. Each treatment plant does disinfection in one of two ways. Some plants use ultraviolet lights to disinfect the water. At the Metro Plant, disinfection is done with liquid chlorine. Once the water is sufficiently clean the chlorine is removed. Finally, after 15 hours of processing at the Metro Plant, the clean water is discharged back into the Mississippi River. The water that we put back into those rivers is much cleaner than the water it’s going into, than that river water. And we do that consistently, day in and day out. Clean water that’s discharged into the river must meet strict regulations of the U.S. Environmental Protection Agency and Minnesota Pollution Control Agency. These regulations insure that harmful amounts of chemicals, like mercury and phosphorus, are not being reintroduced into the environment. MCES takes these regulations very seriously and partners with both environmental agencies as well as entities like the University of Minnesota, to monitor pollutant levels in the region's waters. Water samples are taken from the final treatment stage at each plant and tested daily at the MCES laboratory. The lab processes more than 100,000 samples a year. In the early days of the Clean Water Act we were primarily concerned with much more conventional pollutants and it took about 20 years for us to get our treatment plants to the point where we were routinely passing these permit limits. In the last 10 years, we've seen the emergence of concern for newer, more exotic pollutants such as endocrine disruptors. Now we are concerned with things like PFCs. These are the efforts that we spend our time on these days looking at new technologies and new instrumentation. Now that the liquids have been treated, what happens to the solids removed earlier in the process? Some solids, like the rags scraped off of the bar screens, have no recyclable use so they're sent to a landfill. Other solids, like floatable and sinkable material collected earlier, pass through an incinerator like this one. Burning at over 1,400 degrees Fahrenheit, the solids instantly combust into a fine ash. A state-of-the-art air emission control system removes virtually all remaining pollutants. Finally, the ash is collected and landfilled. Once the incinerator is running, incoming solids act as a fuel, keeping the incinerator going 24/7. As part of the incineration process, we take the hot gasses, we run them through a waste heat boiler. In the waste heat boiler, we create steam. In the winter time, we use that steam to heat the plant buildings. In the summertime, when there isn’t that heating demand, we take that steam and we run a steam turbine and we can produce up to 20% of our electrical needs here. So in a good month, we can be saving $150,000 or more off of our electrical bill. Not all seven treatment plants have incinerators, however. Some need to transport their solids to the Metro Plant for processing. Other treatment plants like the Empire Plant in Empire Township treat solids onsite. By removing bacteria from the solids, the remaining material can be reused as fertilizer on farm land. Metropolitan Council Environmental Services consistently wins awards and commendations for its successes in protecting the environment and public health. As mentioned previously, treatment plants must have their treated wastewater tested daily to meet strict pollution control requirements. Since February 2007, all MCES plants have been in full compliance with clean water discharge regulations. That's no small feat when you consider these regulations require tests for more than 130 different types of contaminants. The National Association of Clean Water Agencies recognizes wastewater treatment plants that have maintained full compliance for the past year. Several MCES treatment plants have received this award consecutively for more than a decade. The recognition is really nice, but it’s not why we do the work we do. We’re passionate about protecting public health and the environment. We’re also very committed to keeping our costs among the lowest in the nation. Bottom line for the homeowners is a wastewater rate that's 40% below the national average. MCES’s award-winning operation is a national and international model of efficiency and innovation. In addition to being a model, MCES is also a resource, partnering with more than 800 local industries to insure the wastewater they put down the drain is as pollutant-free as possible. We are working with the industries to regulate and control the type of waste that they discharge into the sewer system and that allows the treatment plants to function properly and meet the standards that they have to meet at the plants. One such partnership is with the Minnesota Dental Association to prevent area dental offices from discarding mercury- containing material, like fillings, in their wastewater. Mercury is a heavy metal that can build up in fish. People or other animals that eat those fish can get mercury poisoning. As a result of the partnership, MCES has tracked a 50% decrease of mercury in the incoming wastewater. Addressing another pollutant of concern in area rivers, new technology was introduced into the treatment process to reduce the amount of phosphorus being released. Phosphorus is an essential element for life, but too much causes algae to overgrow in water. Phosphorus is necessary for life; we all have phosphorus in our system. Every living thing has phosphorus in it but if it exceeds the limits, then it becomes… Like everything else, too much of it is no good. MCES also partners with the public, providing tours of the treatment plants and participating in community events. As the population in the Twin Cities increases growth planning will play a critical role in the region's continued success. In addition to maintaining and expanding its network of interceptor sewers, MCES will also work to identify locations for possible treatment plants. As wastewater discharge restrictions increase, MCES will continue to ensure the water discharged back into the environment is clean and safe. The mission of Metropolitan Council Environmental Services is to provide wastewater services that protect the public health and environment while supporting regional growth. It's a service that's critical to the quality of life in a growing, thriving Twin Cities area. For more information, please visit the Metropolitan Council website at www.metrocouncil.org