ELYRIA’S WASTEWATER SYSTEM
Wastewater comes into the plant through large interceptor sanitary sewers throughout the City:
- East Side: There is one 27-inch diameter interceptor sewer and one 48-inch diameter interceptor sewer servicing the East Side. We are in the process of constructing another very large 78-inch diameter interceptor sewer, known as the East Side Relief Sewer, which will convey both sanitary and storm water to the plant during rain events.
- West Side: There is one 72-inch diameter interceptor sewer that services the West Side.
- South Side: The City just completed construction of a new relief sewer on East Avenue, consisting of twin, side-by-side 72-inch sewers between 4th Street and 6th Street. South of there, the sewer slowly reduces in size. Known as the East Avenue Relief Sewer, it transports sanitary flows to the plant during dry weather and also stores and conveys excess stormwater to the plant during rain events. This sewer allows the City to control the combined sewer overflows (CSOs) in that area of town. Additionally, there are miles of smaller sanitary sewers that run down every street in Elyria. These smaller sanitary sewers tie into the larger interceptor sanitary sewers that come to the Wastewater Plant. In total, there are 163 miles of sanitary sewers in Elyria.
Elyria also has 108 miles of storm sewers which convey rain water from the streets to the Black River. Surprise!! These storm sewers do not come to the Wastewater Plant – they go directly to the Black River. So, whatever gets dumped into the storm grates goes straight to the fish. The storm grates are for rain water only.
Elyria has 8 miles of combined sewers in the oldest parts of downtown. These “combo” sewers convey both sanitary sewage and storm water to the Wastewater Plant for treatment. However, if a rain event is extreme, some of these combined sewers may overflow to the river. These overflows volumes contain mostly storm water and small amounts of sanitary water. Although EPA has allowed these overflows to occur during rain events in the past, the City is working on several projects similar to the East Avenue Relief Sewer to control these overflows to comply with newer regulations. In the meantime, it is best to avoid bodily contact with the river water during and immediately after a rain event.
The water that comes to the Wastewater Plant is cleaned at the plant by flowing through several treatment processes in the following order:
- Preliminary Treatment
- Primary Treatment
- Secondary Biological Treatment
- Final Clarification
- Discharge to the Black River
As water flows through these treatment processes, the cleanliness of the water is evaluated after each process. You would be amazed at the difference each step makes.
Preliminary Treatment: Starts with the wastewater passing through bar screens that remove larger items, such as paper, twigs and pop bottles that come in from the combined sewers. These items are removed, washed, dried and compacted into dumpsters that go to the landfill. The bar screens also remove wipes and other sanitary solids. All of these solids are collected, washed and compacted into dumpsters and taken to the landfill. The landfill charges a fee per ton to dispose of these materials.
After the bar screens, the wastewater flows through square grit tanks. In the grit tanks, the flow of the wastewater slows down just enough to allow heavy solids like road grit, coffee grounds, corn kernels, egg shells, and other solids from garbage disposals, etc. to drop to the bottom of the grit tank. There is a collector mechanism on the bottom of the tank that collects the grit to a sump where it is pumped to a grit concentrator to be washed, dried and placed into a dumpster that goes to the landfill.
Primary Treatment: Makes use of primary clarifiers, which are large rectangular tanks (41’W x 148’L x 10’D) that hold 454,00 gallons each. In these clarifiers, the flow of the wastewater REALLY slows down to allow fine solids to settle to the bottoms of the clarifier tanks and lighter-than-water items (cooking grease, etc.) to float to the top. Cooking grease and other such items are removed, dewatered, and placed into a dumpster to be sent to the landfill.
Solids that settle to the bottom of a clarifier tank are called a sludge. All sludges are collected by a mechanism in the clarifier to a sump and pumped to anaerobic digesters where the sludges are stabilized by anaerobic bacteria in the digesters. To stabilize the sludge, the bacteria will absorb anything that is organic in the sludge and use it for food. The bacteria in the anaerobic digesters are from the domain Archae and, as such, do not use oxygen to break down their food. In fact, oxygen is toxic to these bacteria. Some of these anaerobic bacteria, called methanogens, produce methane gas as a metabolic byproduct. The methane gas is collected and piped to large boilers that heat the digesters to 95 degrees F. With the organic materials gone, the stabilized sludge, now called biosolids, will be dewatered to produce a dry sludge cake and sent to a landfill. At the end of Primary Treatment, the wastewater is much cleaner because the fine solids and floatable materials have now been removed.
Secondary Biological Treatment: As its name implies, everything that happens in this section to clean the water happens biologically. The plant has many specialized tanks called aeration basins where aerobic bacteria are grown that will use any pollutant that is dissolved in the wastewater as food. These “pollutants” can include bath soaps, laundry detergents, car wash soaps, part-washer solutions from industrial processes, and other household, commercial and industrial chemicals.
The aerobic bacteria will absorb these pollutants and metabolize them, breaking them down to carbon dioxide and water. Ammonia is a special pollutant that is very toxic to the aquatic life in the river. Ammonia is found in many household and commercial cleaners and also in human urine. So, in addition to the other aerobic bacteria in the aeration basins, populations of special aerobic bacteria called nitrifiers are also grown. These nitrifiers have the ability to oxidize ammonia (NH3) first to nitrite (NO2) and then further to nitrate (NO3). While ammonia is toxic to aquatic life, nitrate is not. All of these aerobic bacteria need a lot of oxygen in order to work efficiently, so we pump a lot of oxygen into the basins using 400 horsepower air blowers. When you look at the aeration basins, you will notice that the color of the wastewater is similar to a light chocolate brown. This brown coloration is due to the extremely large amounts of bacteria growing in the basins. You will also notice the air bubbles percolating through the basins as the oxygen is supplied to the bacteria, so they can purify the water. When the work of the bacteria in the aeration basins is done, the wastewater continues flowing to the next stage: Final Clarification.
Final Clarification: The water and bacteria mixture from the aeration basins flows next to the final clarifiers, which are large round settling tanks. On the way there, since phosphorus can cause algae to bloom in the river, ferric chloride is added to the water to remove phosphorus. The ferric chloride reacts with the phosphorus to form ferric phosphate, which will precipitate out of the water in the final clarifiers. In the final clarifiers, the bacteria from the aeration basins settle out of the water to the bottoms of the clarifiers and are pumped back into the aeration basins, so they can keep on working for us. The bacteria-free water will flow out of the top of the final clarifiers and head to the next step — disinfection.
At this stage, our wastewater is now simply “water.” The water is clean, with all types of pollutants removed (paper, twigs, pop cans, grit, fine solids, floatable cooking grease and other materials, dissolved chemicals, ammonia, phosphorus, etc.) Currently, one of the three final clarifiers is empty and out of service. This clarifier is in the process of being completely taken apart and reconstructed with a much more efficient design. There is no cause for alarm, however. The plant was designed to function optimally using only two of the three clarifiers, so this will have no negative effect on the purity of the water leaving the plant. One of these clarifiers has already gone through this process. Over the next year, the other two clarifiers will be completed, one at a time. These, and other projects at the plant, are being done to increase the wet weather design flow through the plant from 30 million gallons per day (30 MGD) to 40 MGD.
Disinfection: Now that the bacteria have been removed and are safely back at work in the aeration basins, the water looks like the drinking water from your faucet. However, during the recreational season on the river (May 1st through October 31st) it needs to be disinfected before it can be released into the Black River. Ultraviolet light (UV light) is used for disinfection. The water passes through several banks of UV lamps. The lamps give off a UV light with a wavelength of 254 nanometers (nm), which just happen to be the wavelength that destroys DNA and RNA, the molecules that make up the genetic materials of bacteria and viruses. When bacteria or viruses pass through the UV light, their genetic material is irreversibly destroyed and they can no longer cause environmental or human health issues. The water leaving the plant is tested daily to make sure the UV process is working effectively. Upon exiting the UV process, the water spills down a series of cascading steps which adds dissolved oxygen back into the water (which the fish love). The water then heads out to the Black River, and ultimately to Lake Erie. When you take a close look at the water as it cascades down the steps, you can see how clean it is. It looks just like the water that comes out of your faucet — only it isn’t. Our drinking water comes from Lake Erie and is cleaned up again at the City of Elyria Water Treatment Plant in Lorain before it gets to your house via the water mains.
Of course, the above is a simplified version of everything that is happening here at the Elyria Wastewater Plant. We have 58 highly skilled employees who do their part to keep the plant running well. Many have degrees in Biology, Chemistry, Environmental Science and certifications in Mechanical Trades. We are also certified by Ohio EPA as Wastewater Plant Operators. Our Operator Certifications need to be renewed every two years and we have to document hours of continuing education in the field to obtain certification renewal. We also need to keep up to date in our degreed areas of expertise because these fields are advancing at warp speed. We have a full-service environmental laboratory with three full-time lab technicians who do all of the testing on the samples collected throughout the plant on a daily basis. We also have an Industrial Pretreatment Division that is responsible for inspecting and sampling the commercial and industrial facilities in the city. Highly skilled Operations and Maintenance teams are responsible for all of the process equipment at the plant and out in the sanitary and storm sewer collection systems.
Clean water is a very hot topic. As global warming continues, droughts and extreme storms will become more frequent. Water conservation, water reclamation, water reuse, storm water drainage, and other such issues will only become more important — from both an engineering and operational perspective. Those who have an inclination towards math and science might want to consider a career in an environmental field.
Everything we do here is overseen by the Federal and State EPA. Ohio EPA has issued a National Pollutant Discharge Elimination System (NPDES) permit to the City that allows us to operate this plant and to discharge the clean water back to the Black River and, ultimately, to Lake Erie. In the permit are many requirements which we have to abide by, which include sampling and testing frequencies for a variety of parameters on the wastewater coming into the plant, the water going out of the plant to the Black River, and many other requirements. We provide paper and electronic reports to Ohio EPA on a monthly, quarterly and annual basis. We also file reports with the US EPA, when requested. We are in constant contact with Ohio EPA’s Northeast District Office in Twinsburg to keep them up to date with our operations here.