City Of Greeley

Greeley's Wastewater System

The sewer system in Greeley is clean, tight and well maintained. The entire system is cleaned ever 18 to 20 months and some sections are taken care of more often. There has been more reportable sanitary sewer overflows and were only four system backups in the year 2006. The entire system is televised with a specialized camera system to document the need for repairs. Two to three miles of sewer line are rehabilitated each year with cured-in-place pipe.

Wastewater Collection Division
A wide variety of work is performed by this division including routine cleaning of sewer lines, inspection of sewer lines, maintenance of the sewage pumping stations, rehabilitation of the system and responding to emergencies.

Wastewater Treatment Division
The staff treats wastewater to meet or exceed EPA and Colorado Department of Public Health & Environment requirements. The WPCF goal is to maintain or improve the water quality of the Cache la Poudre River. The staff also treats organics (biodegradable material) that enters the plant and converts them to biosolids that are used to improve soil composition and increase crop production for local farmers.

Industrial Pretreatment Program
The City of Greeley Industrial Pretreatment Program is a program within the Water Pollution Control Facility. The IPP is dedicated to ensuring the quality of the water discharged from the treatment plant to the Poudre River. In order to accomplish this, the IPP is required to address discharges from industrial and commercial users into the sanitary sewer system.

Sewerline Index Map

Greeley Wastewater Virtual Tour

Below is a map that outlines the plant processes, from the raw sewage entering the plant, to the treated water that is discharged into the Cache la Poudre River. You can either click on any area of the map to learn about a specific process or begin the tour below.


Tour Stop 1
Residential, Commercial, and Industrial Wastewater

An average of 8-9 million gallons of wastewater is treated every day at the WPCF. This comes from homes, businesses, and industries within Greeley. Because Greeley’s plant, like most wastewater treatment plants, is designed to treat domestic sewage only, great care must be taken to ensure that hazardous materials are not put down the drain. When hazardous or toxic materials end up at the WPCF, they can upset the delicate processes that turn the raw sewage into clean water and quality biosolids.

How can residents help protect water quality?
As a Greeley resident, you can help protect the environment by properly managing wastes in your home. Many products such as cleaners, pesticides, and paint contain hazardous ingredients, and therefore must not be dumped down the drain. Weld County has two Household Hazardous Waste Collection sites, one in Greeley at 1311 North 17th Avenue, and another in Dacono at 5990 Weld County Road 11-1/2. Weld County residents may take their household hazardous waste to the site for recycling, reuse, or proper disposal. To find out more about the program, including days and hours of operation, please call the hotline at 970-304-6415, extension 2233.

In addition to the Household Hazardous Waste Program, the County has also developed a program for small businesses. To request an information packet, call 970-304-6415, extension 2206.

Restaurants can help by taking the necessary steps to keep fat, oil, and grease out of their wastewater. This includes following good housekeeping practices in the kitchen and having a properly sized and maintained grease interceptor. Click here for restaurant information.

Businesses that produce silver-rich waste from film or x-ray processing can help by joining our Best Management Practices Program.

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Tour Stop 2
Wastewater Collection System

In order for wastewater to be treated at the wastewater treatment plant, it must travel there from all over the City via the collection system. After the wastewater leaves Greeley homes, businesses, and industries, it flows through pipes to the City's sewer lines in the streets and then on to larger trunks that take it to the wastewater treatment plant.

The wastewater collection system is built so that gravity carries the sewage from higher elevations within the system to the treatment plant. In some areas of the City, however, wastewater must be pumped up using lift stations to continue the process of gravity flow to the plant.

Obstructions in the sewer lines from items such as body wipes, paper towels, and grease can restrict the flow, and cause sewage to back up into homes and businesses. The Collection department routinely cleans all major sewer lines in the City, and uses a special camera to trace blockages back to their source.

Learn more at the Wastewater Collection website.

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Tour Stop 3
Preliminary Treatment-- Screening and Grit Removal

When the wastewater reaches the treatment plant, it first travels through coarse bar screens in the influent wet well. Large items such as plastic, sticks, and rags get caught on the coarse bar screens and must be removed manually by the operators to avoid clogging or damage of plant equipment.

The influent wastewater must then be lifted up into the plant, to an elevation where gravity can facilitate flow throughout the plant processes. Three large vertical pumps are used to lift the wastewater up into the plant.

Once in the plant, the flow rate is measured by Parshall flumes. This is important for record keeping, as well as process control purposes. 

Next, rotary bar screens remove smaller items such as toilet paper and plastic. These screenings are then transported through a screw conveyor where they are washed, dewatered, and compressed. Washing the screenings returns the organic material to the wastewater, so it can be treated in subsequent treatment processes. The screenings are then collected and transported to a garbage dumpster by the conveyor.

Grit, which consists of small materials such as sand, cinders, coffee grounds, and gravel, is then removed in circular tanks called grit chambers. The velocity of wastewater flow is slowed to about 1 foot per second. This allows the grit to settle to the floor of the chamber and the lighter organic material to flow out of the chamber with the remaining wastewater. From the bottom of the chamber, the grit moves into a center storage hopper and is pumped to a grit concentrator to separate it from its carrier liquid. 

From there, the grit is pumped to the grit classifier, which separates it from any remaining organic material. The screw conveyor then collects the grit and deposits it in the dumpster.

Screening and grit removal processes are essential to wastewater treatment because they reduce clogging of pipes, protect moving mechanical equipment and pumps from abrasion and abnormal wear, and prevent accumulation of non-degradable materials in basins and tanks.

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Tour Stop 4
Primary Treatment -- Removal of Suspended, Settleable and Floatable Materials

After screening and grit removal, the wastewater flows to three large circular tanks called primary clarifiers. Primary clarifiers remove a large amount of suspended, settleable, and floatable materials from the wastewater.

As the wastewater flows through the primary clarifiers, its velocity is reduced to approximately 1-2 feet per minute. This allows the heavier particles, called primary sludge, to settle to the bottom of the tank, and the lighter particles to float to the surface.

The primary sludge is scraped from the bottom of the clarifiers and into a sludge hopper by a circular collector. From there, the sludge pumps draw it into sludge grinders immediately upstream of the pumps. This is to grind the sludge into small enough particles that will not damage the pumps. The primary sludge is then pumped to the primary digesters for treatment into biosolids. 

The floatable material, called scum, is removed from the surface of the clarifier and into the scum trough by a large arm that rotates around the tank, across the surface of the water. It then flows from the scum trough to the scum pit, where it is mixed with scum from the secondary clarifiers. The mixed scum is then pumped to the digesters for treatment into biosolids.

After a detention time of approximately 2 hours, the remaining clarified water flows into a channel that takes it downstream for further treatment.

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Tour Stop 5
Advanced Secondary Treatment -- Aeration Basins, Activated Sludge, and Secondary Clarifiers

After screening, grit removal, and primary clarification, the wastewater then flows through the activated sludge treatment process. This is a process in which microorganisms use waste particles in the wastewater for food, and oxidize wastes to obtain energy for growth and reproduction. In doing so, the organisms convert the dissolved and suspended material into settleable solids to be removed in the next process step.

Another function of the secondary treatment process is nitrification, or the conversion of ammonia to nitrate, and denitrification, which is the removal of nitrate from the effluent wastewater. Nitrification/denitrification is important because of concerns over ammonia toxicity to aquatic organisms and the fate of nitrogen compounds in downstream groundwater drinking supplies.

After a detention time of approximately 3 hours in each aeration basin, the wastewater is then sent to the secondary clarifiers for further settling and skimming.

The material that settles out here is called activated sludge. Some of this sludge is returned to the aeration basins, giving it the name return activated sludge. The remaining sludge, called waste activated sludge, is sent to the thickening centrifuge and then to the digesters for further processing into biosolids.

At this point, the treated water appears very clean, but may still contain harmful contaminants such as bacteria and viruses. It must then be sent to the ultraviolet disinfection building.

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Tour Stop 6
Ultraviolet Disinfection

Before the treated water can be released into the Cache la Poudre, it must be disinfected to prevent harmful contaminants such as bacteria and viruses from contaminating the river. The City of Greeley accomplishes this through the use of ultraviolet disinfection.

UV disinfection is a physical process that uses ultraviolet radiation (the spectrum of light between visible light and x-rays) to penetrate the cell walls of microorganisms. The optimal germicidal wavelength is 254 nm. Cell DNA and RNA are destroyed by the absorbed radiation, which prevents replication and destroys the viability of the organisms.

The final effluent can now be discharged into the Cache la Poudre River.

To get real-time flow data on the river, click the following link. You will need to scroll down to CACHE LA POUDRE AT GREELEY WASTEWATER PLANT Colorado Streamflow Data Retrieval.

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Tour Stop 7
Sludge Thickening and Digestion-- Turning Waste Into Beneficial Biosolids

Biosolids are a byproduct of specially treated and stabilized domestic wastewater. They are made up of nutrient-rich organic material, and when added to the soil, help produce a higher crop yield.

Biosolids are produced from three main sources within the wastewater treatment process: primary settleable solids collected from the bottom of the primary clarifiers, primary and secondary scum and other floating materials removed from the top of the primary and secondary clarifiers, and waste activated sludge. 

Waste activated sludge is the excess mass of microorganisms produced during the secondary stage of the treatment process. This mass is sent to a thickening centrifuge, where most of the water content is removed.

The primary settleable solids, scum, and thickened waste activated sludge are all piped to primary digesters for processing into biosolids. Primary digesters contain anaerobic bacteria that use these sources for food. This digestion process, which takes about 20 to 30 days, reduces the mass by about sixty percent, while killing disease-causing organisms such as bacteria and viruses and reducing odors. 

The resulting biosolids are dewatered in the dewatering centrifuge, resulting in a thick “cake” product that is generally the consistency of potting soil. The biosolids are now ready to be applied to local farmland.

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Tour Stop 8

The U.S. Environmental Protection Agency issued Federal regulations in 1993 for the beneficial use of biosolids to protect public health and the environment. Biosolids must meet or exceed EPA standards for trace element and pathogens concentrations. These standards are based upon more than 20 years of extensive university research, and have a large margin of safety. The City of Greeley fully complies with all State and Federal biosolids regulations.

Biosolids are beneficial in many ways:

Plants: Biosolids increase the number and size of air spaces in the soil and enhance its ability to hold together. This provides a better balance of water and air in the soil for plant growth. Biosolids contain essential plant nutrients, such as nitrogen, phosphorus, and potassium, as well as plant micronutrients such as zinc and copper .

Soil: The organic matter in biosolids improves the “tilth” or physical condition of the soil. It increases moisture retention and prevents soil compaction. Good soil tilth means that soils are easy to dig in, easy for seedlings to emerge from, and easy for plant roots to move through.

Earthworms and Soil Organisms: Organic matter in the biosolids provides food for these organisms, which in turn keep soil healthy.

One of the objectives of the City of Greeley Industrial Pretreatment Program (IPP) is to prevent the introduction of pollutants into the wastewater treatment plant that could pass through the plant untreated into the biosolids.

In order to accomplish this, the IPP must permit and regulate industrial users and waste haulers, which includes site inspections and wastewater sampling. The IPP provides education and guidance to commercial businesses on the safe use and/or disposal of wastes such as silver and mercury.

The laboratory and operations staff at the City of Greeley Water Pollution Control Facility regularly analyzes the biosolids to ensure that they comply with all State and Federal Biosolids Regulations. Some of the analyses are conducted at outside laboratories.

Waterways: Biosolids help reduce runoff and soil erosion, due to the improved structure of the soil.

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