Wastewater Citizens Academy

City of Greenfield, Indiana Citizens’ Academy

 

Getting Started

 

The Greenfield Water & Sewer Utility consists of 2 Water Filtration Plants, one Wastewater Treatment Facility, Water Distribution and Sewer Collection Maintenance Crews. The Water Plant Operation Crew totals 5 men. The Wastewater operations are handled by 9 individuals.

Two clerical-coordinators handle the offices, while one Superintendent oversees both Utilities (Note that since the Citizen's Academy, a new Water Superintentant has been hired.)

Drinking water is pumped to the plants from 9 separate underground wells. A large underground aquifer supplies excellent water to the City of Greenfield. At 14 to 16 grains of hardness, it is considered fairly “hard water”. Many homes use a water softener to combat the effects of hard water.

 

The Treatment Plants located north of I-70 on North Franklin Street and East Main Street basically filter the water; add chlorine for dissinfection and phosphates to fight copper and other material build-up in the water lines.

 

 

 

 

Now What?

 

Homes, Business and Industry use this life giving water in many ways. Once used, it is time to get this finite resource cleaned-up and returned to the environment.

 

Sewage, or wastewater, is transported through the sanitary sewer system at a velocity of about two feet per second. Any slower and the solids in the wastewater would get stuck in the pipes. These sewer lines continue to flow sewage downhill, but once they approach 25 feet deep, lift stations pump the sewage back near the surface. The sewage then continues its path toward the Wastewater Treatment Plant.

 

The first treatment plant in Greenfield was built around 1932. Before this system was built, septic tanks were the only form of sewage treatment available. Eventually, this could have attributed to groundwater contamination. New sanitary sewers were often designed to also transport storm water during rain events.

These “combined sewers” caused enormous problems at the Treatment Plant, as the flow could increase 10 times the normal rates. Some of the water would also discharge sewage and storm water into open ditches, causing even more problems. The combined sewer overflows or “CSO’s became a major problem for the environment. Indianapolis and other cities will be spending billions of dollars to minimize the deleterious effects CSO’s have on our environment.

 

 

 

Greenfield Goes Another Way

 

In 1991, a Long Term Control Plan (LTCP) for CSO’s had been submitted to the Indiana Department of Environmental Management (IDEM) for approval. This plan would have kept any combined sewers in service and a 1 million gallon over-flow pond would have been constructed just outside of the Treatment Plant. The big problem with this plan, in the estimation of the new Superintendent, was that the pond designed to contain the excess storm water would fill up in about an hour. History had shown that the plant and numerous storm water ditches would continue to be inundated with pollution problems.

 

Greenfield decided to ask IDEM to scrap the LTCP and commence with a new plan to separate the storm and sanitary sewers. Included with this paper, we had enclosed several letters and documents that dealt with the new plan.

 

Greenfield was one of, if not the first city to be removed from IDEM’s “Combine Sewer Overflow Cities” list. Although most Indiana cities are on this list, we wanted off of it. Thousands of dollars per year would have been spent to study the negative environmental impact CSO’s had on our town and treatment facility. Money not spent on the CSO problems could pay for upgrades to the plant and sanitary sewers.

 

Within the last five years, just over $8.5 million was spent to upgrade the treatment plant. About $300,000 is spent every year on rehabilitating the sanitary sewer mains and laterals to homes in Greenfield. We are definitely ahead of most other cities in Indiana and possibly the nation, when it comes to sewer rehabilitation. Methods used in our sewer program include pipe bursting, “cured-in-place” pipe and “fold & form” rehabilitation. Sewer manholes, a point of entry for sewer maintenance, are often replaced or externally patched with space-age sealants to prevent clear-water from entering the sanitary system.

 

New Technologies

 

The first major plant expansion was completed in 1980, where the treatment process was converted to the “activated sludge” process. This change followed a previous upgrade in 1960, where primary clarification was followed by a trickling filter process. It was a circular tank of media with various sizes of stone and was continually sprinkled with sewage. Bacteria grew on the media and cleaned the sewage as it passes over the material. Activated sludge systems handle higher flows by introducing sewage into aerated tanks of “mixed liquor.” This chocolaty brown water contains billions of bacteria that use sewage as food.

 

Plant operators are trained to manage and manipulate the bacterial population. Settling tanks, return activated sludge, waste activated sludge, primary sludge, biosolids, filters, dissinfection systems, flow meters, laboratory testing and numerous operational changes are needed to maintain a healthy, well-operating plant.

 

 

Our Latest Upgrade

 

In 2004, an $8.5 million plant expansion was completed with the help of Commonwealth Engineers, Reynolds Construction and City employees. This upgrade covered many aspects of the plant.Each was designed to extend and improve our treatment abilities for the next 20 years. A few of these upgrades were to increase sewage pumping capacity, improve debris screening and grit collection, expand primary clarifiers, aeration capabilities, final clarifying capacities, change valve operation abilities, convert from Class “B” to Class “A” Biosolids handling and change from chlorine gas dissinfection to ultra-violet “UV” light dissinfection. All of this combined, will make us an award winning plant, far into the future.

 

 

 

 

 

Let’s Take A Walk – Pay Attention

 

As sewage flows into the plant headworks at about 2 feet per second, it moves through a circular screen that automatically removes the paper and plastics found in sanitary sewage. This new unit is working very well and is known as a Roto-Mat bar screen. The ¼ inch spaced bars keep most of the large debris from getting into our pumps and other processes.

 

Another unwanted material in sewage is grit. Grit is composed of sand, gravel, pieces of clay tile or concrete and other heavy materials. If not removed from the waste stream, this grit would cause severe damage to our pumps and other systems. No, we don’t get 100% of this material out, but our “Pista-Grit” system works much better than our old gravity channel with a chain and scraper removal system. The headworks building also houses a combination of screw conveyors that push the grit and screenings to an outdoor dumpster for disposal.

 

Following screenings and grit removal, the sewage enters a large wet well. Three 50H.P. double shafter raw sewage pumps were replaced by four – 75H.P. dry-pit submersible pumps. They are available to push the sewage to our primary clarifier tanks. Also, located adjacent to the pumps are four variable frequency drive (VFD) units and three 150H.P. centrifugal blowers. These replaced three rotary lobe blowers that were much louder and less efficient. The blowers pump air into our four aeration tanks.

 

The two west primaries were recently upgraded with new HDPE (High Density Poly-Ethylene) drive gears and drive chains. The two eastern primary clarifiers were added in the 2004 plant expansion. In these tanks, sewage is slowed from two feet/second to a 6 hour detention time. Here the heavy particles in sewage sink to the bottom of the fourteen feet deep tanks and light or greasy materials float.

 

A chain & scraper system push the light material to skimmer pipes, while the heavy “primary sludge” is pulled into an underwater hopper. One of four diaphragm pumps run on timers and pump the primary sludge to our aerated holding tank. This partially cleaned-up sewage is now sent to one of four aeration tanks as food for the micro-organisms.

 

 

 

 

 

 

 

 

 

 

It Gets Worse Before It Gets Better

 

The four aeration tanks look like bubbling chocolate milk. You may recall the new centrifugal blowers located in the headworks building. The fine-bubble diffusers on the floor of the 14ft. deep tank keep the bacteria’s need for oxygen fulfilled, keep the solids from settling and keep the bacteria mixed around with the food supply. These tanks are set up in an extended air configuration so the water molecules can meander through the tanks series within 3 to 8 hours. The sewage goes from about 100 milligrams per liter in solids to over 2,000 mg/L. At the end of these tanks the bacteria have grown, eaten, multiplied and hopefully become heavy and tired as they flow to the final clarifier tanks.

 

After leaving the dissinfection process, a short trip to the creek is where nature takes over. The clarifiers allow the bacteria to settle to the bottom in this six-hour process. The settled solids can be recycled to the aeration tanks as “Return Activated Sludge” or removed from the system as a “Waste Activated Sludge.” The plant operators use visual judgment as well as laboratory testing to make this decision. The waste sludge is sent to our aerated sludge holding tank to control bacterial populations. During the 2004 plant upgrade, three existing rectangular clarifiers were modified. For more than 20 years, a floating siphon was pulled by cables to travel from one end of the tank to the other. The siphon system pulled settled sludge from the bottom of the tank and sent it back to the aeration tanks. These clarifiers could handle about 3.2 million gallons per day. Higher flows with rain events caused poor operations, as the aeration tank water was pushed into one end and forced out the other; it had little time to settle.

 

The redesigned tanks make a more efficient circular roll down the entire length of the tank. A chain and scraper system collect the sludge for redistribution. A new circular clarifier was installed. This tank alone can handle about 3 million gallons per day. A single scraper pushes floating materials and settled sludges to an appropriate point in the tank.

 

Water leaving these final clarifiers can go straight to dissinfection, but it usually heads to the Administration Building first. In this building, six large filter cells remove any particles left in the water. The Advanced Waste Treatment filters or AWT filters polish the wastewater to a point that it resembles drinking water. New electrical valves installed in the filter pipe gallery have saved numerous repair and maintenance problems. These filters supply “Non-Potable” water to several systems around the plant. Operators use it nearly exclusively to maintain the plant.

 

 

 

 

 

One Last Step Before Mother Nature

 

Thirty minute detention tanks allow chlorine gas to be introduced to the water for dissinfection. Since chlorine and chloramines are harmful to aquatic life, sulfur dioxide gas is introduced near the discharge end of the tank. Again, sulfur dioxide removes dissolved oxygen, “D.O.”, from the water. To counteract this issue, the water was aerated before it was discharged to the creek. Water leaving the AWT filters and the final clarifiers heads to the receiving stream, Brandywine Creek. Another change occurred in the last process in the 2004 upgrade.

The upgrade stopped the need to use these dangerous gases. Operators and our neighbors ran a risk of being harmed by a gas leak. Ultra-Violet light rays or a “U.V. System was installed. These bulbs are more efficient in killing disease causing bacteria such as E-coli. These dissinfecting bulbs, just like chlorine or ozone, are required by IDEM from April 1^st to October 31^st of each year. The State considers every creek, stream, river or lake in Indiana to be safe for “Full Body Contact” during this season. Therefore, treatment plants must adhere to rigorous limits to meet state requirements.

 

 

 

 

It’s There When We Need It!

 

As stated earlier, our average flow to the plant is about 3 million gallons per day in dry weather. During wet weather, or when the groundwater table is high, our flows can go over 15 MGD. A

biological system that may or may not be needed to treat this much sewage is not cost effective or practical.

 

To handle this erratic excess flow, an “Acti-Flo” system was installed. This process uses chemical-physical properties that can be turned off or on when needed. When our flows start to creep up during a rain event, the Acti-Flo system keeps about 6 MGD going to the normal biological process and up to 12 MGD can be treated by the Acti-Flo system.

The chemicals, alum and polymer, are added to the sewage in tanks with large mixers. Micro sand is introduced, and when allowed to settle, the unpleasant attributes in sewage use these chemicals to adhere them to the sand particles. Clear water leaves the system and the dirty sand is cleaned and re-introduced to the mixing tanks. Sludges from the sand are sent back to the headworks for recycling. We consider this system as our saving grace to an old sewer system that needs continued attention. Sources of clear water must be removed from the sanitary sewers.

 

 

 

 

 

The Bi-Product

 

The single most important and operator involved change in the 2004 project, was the change from Class “B” Sludge to Class “A” Biosolids. Engineers were requested on several occasions to reconfirm construction costs, operational costs and 20-year budget considerations. Class “A” Biosolids always came out a cost savings.

 

A new storage barn, two material silos, a new filter press building and a biosolids cake and material mixing system had to be constructed. In short, sludge from the aerated holding tank is dewatered in two 2-meter belt filter presses. The 2% solids sludge is converted to a cake that is about 20% solids.

 

This material is conveyed to another room where it is mixed in a pug-mill with an alkaline fly ash. The mixed product appears “pelletized” when it is conveyed by a conveyer belt, outside to a reaction bin. Here the material piles up until the operators check and record the pile temperature that should be about 52º C or 125.6º F. Three days later, the material pH must be 12.0 or higher.

 

The pH and temperature combine to make our biosolids a Class “A” material. Once tested; it is ready for use by citizens, farmers and gardeners. This Class “A” material is considered safe by IDEM and the EPA. With few restrictions, it can be used by just about anyone, anywhere.

 

 

 

 

 

 

Conclusion

Since the management of the City’s sewer system was united with that of the treatment plant, great strides have been taken to put Greenfield on top of most cities in the entire nation. In 2002, the Indiana Water Environment Federation named us the Best Small Facility in Indiana. The rehabilitation projects and homeowner lateral replacement programs are listed in the Federal Library for Private Lateral Replacements. We confidently proclaim that no one does more for their customers than our utility. All of which help reduce costs at the treatment plant and keep our customer costs down.

 

Feel free to call our office or stop in for a tour. Let us show you how we operate our facilities. We are always striving to be the best. Check us out !

 

Sincerely,

Greenfield Wastewater Utility