Wastewater System Infrastructure Improvements
FREQUENTLY ASKED QUESTIONS
1. Why is it called a regional P.O.T.W. plant?
The P.O.T.W. stands for Publically Owned Treatment Works. We are a regional P.O.T.W. in that we serve 5 communities. Besides East Moline, we also receive wastewater from Hampton, Rapid City, Silvis, and Carbon Cliff.
2. What is the capacity?
Our design average flow (DAF) is 11.1 MGD (million gallons per day.) The design maximum flow (DMF) is 27.8 MGD. We have the capacity for additional flow to our plant. See the next FAQ.
3. What is the typical flow?
The annual average flow for 1999 was 5.79 MGD. Flow is definitely weather related. When it has been really wet, the flow reflects that through infiltration. The more the ground gets saturated, water begins to seek empty space and seeps into the sewer collection lines.
4. What type of treatment plant is it?
We are a secondary treatment plant using activated sludge and anaerobic digestion. We also have aerobic digesters, but they are not in use.
5. How are the wastes treated?
Approximately 20-35% of the solids that come into the plant, settle in the primary clarifiers. From there, they are pumped to the anaerobic digesters. In the absence of oxygen (anaerobic) along with other important factors such as temperature, pH, and a combination of acid and methane producing bacteria, the solids are reduced in volume. A usuable byproduct of this process is methane gas, which we use for heating the digesters and the plant. The secondary treatment comes after primary clarification. Any suspended solids that did not settle in the primary clarifiers are carried over into the second stage of treatment. This stage is called activated sludge. This process has been around for more than 100 years. It uses bacteria that need air, in an aeration (oxygenated) basin. It basically speeds up Nature's natural process of decomposition. The suspended and dissolved solid waste is food for the bacteria. This food becomes broken down through adsorption and absorption. After a mix and digestion period, the next step is gravity separation of the solids and the liquid in the secondary clarifiers. The solids are pumped off the bottom, and returned to the aeration basins, where they become the seed stock for the newly arriving flow to receive the same digestion process. To keep the bacteria hungry, we keep them at a certain level in their growth cycle by removing a portion of the solids. So, part of the return activated sludge (RAS) is removed and becomes waste activated sludge (WAS.) This WAS is sent to the anaerobic digesters for storage and further digestion.
6. Can you dump anything down the drain?
No. Because the bacteria (bugs, to us) can be harmed and not do their work, the waste can pass through without complete treatment and cause fish kill in the river or worse. It could also impair the water that is used for drinking water downstream. We have a Sewer Use Ordinance that spells out what is and is not permitted to be disposed of. It is a good rule of thumb to only buy what you need, and to use it up as it is intended to be used. And, occasionally, there are EPA sponsored household hazardous waste drop-off programs. For a look at the general prohibitions see section 8-9-2 of the East Moline City Code. This applies to industry and the general public. Here's a link to those prohibitions.
7. Are all wastewater treatment plants the same?
No. There are tertiary treatment systems, various lagoon treatment systems, oxidation ditches, BNR systems are coming into vogue with nutrients phosphorous and nitrogen reduction, and other methods for wastewater treatment are used. There are differences in pretreatment screening and grit removal, aeration systems can be quite different, and anaerobic digesters can have a wide variety of design. Plus, we have not even touched on disinfection practices. The receiving stream and plant location itself can make a big difference in treatment schemes.
So there can be many different factors used in the design of wastewater treatment plants.
8. What becomes of the treated waste residuals?
In treating the waste water, we concentrate the solids through the treatment processes. This occurs in the anaerobic digesters. We have five anaerobic digesters. We use two of them as primary digesters. They are in a mix mode process. The other three are for solids separation and settling. As the solids and liquids separate, we draw off the liquid supernate. When we have removed that portion, the solids are sent to the mix tank. From there they are sent to the filtration room where we have two 2 meter Roediger belt tower presses. With the addition of polymer, we increase the solids level from 2-4% solids to 20-27% solids. This is taken for disposal to the landfill.
9. Do you have tours?
Yes. We have had many guests for tours. One of the most interesting was a group of visitors from Russia. They represented many different civil positions from several different cities. After the tour we exchanged a few small gifts. Since the Ringling Barnum and Bailey Circus was in town that week, we gave each of them a box of animal crackers, and had some bottled Pepsi to cool our parched throats. In return, we received many fine Russian chocolates with really cool wrappers. If you are interested in a tour of the facility, give us a call @ (309) 752-1580.
10. Have there been any changes since the last upgrade?
Yes. After the 1975 upgrade not much was changed until we installed the belt presses in 1997. In 1999, we changed over the boiler and replaced all the natural gas lines. Last year we upgraded the methane collection system. We are currently looking at a SCADA system for better plant monitoring and control. We have future plans to upgrade the screening areas and pumping areas. We are hoping for approval with the bar screen upgrade this coming year.
11. What regulations if any are there for wastewater disposal?
The Safe Drinking Water Act was two-fold in purpose. Besides the intent of providing a safe water to drink, it also looked at how to protect the source water(s.) The obvious place to look was the point source contributors of contamination to those waters. Wastewater treatment plants became the targets. Also in the mix was Wastewater plants had to begin to assess what they received and from who. For POTW's that received more than one million gallons a day, a Pretreatment Program was established. It came from the Federal level that industrys could be categorized by what they do and what they could contribute to the waste stream. They became known as Categorical Industries with categorical pollutant limits. It further required a look at non-categorical contributors. Based on discharge flow and potential for treatment interference. Treatment plant schemes and interference factors lead into the development of Local Limits of discharge. These limits are re-evaluated every five years. This forced permits to be written, sampling programs by both industry and POTW's to commence, and enforcement of pollutant limits and reporting requirements be undertaken.
Pollutants have a potential of impacting not only the receiving stream, but the treated residual solids can be impaired by pollutants, and get restricted disposal status. There is a huge monitoring program involved. Compliance monitoring and reporting is required in monthly, semi-annually, and annual increments. EPA spot checks all dischargers with their own sampling regularly.
So are there regulations? You bet, but prior to these , the result was having places like the Love Canal and other sites now on Superfund Cleanup lists.