Tag Archives: treatment plants

What Happens When I Flush? A Story About Your Poop…

It isn’t magic, it is your water bill working for you…

When you wash, brush, or flush, the water leaves your home and flows mostly by gravity down pipes to one of our wastewater treatment plants.

There are over 4,600 miles of pipe used to collect the wastewater in the collection system. Utility crews clean pipelines to prevent blockages and spills. They also clear blocked pipes, maintain pumping stations, repair damaged pipes, and connect new customers. Our plant operators work 24/7 to protect public health and the environment.

What is wastewater, and where does it go?

Used water (wastewater) from inside homes and businesses flow through thousands of miles of pipes to one of five wastewater treatment plants. The used water includes detergents, food, paper, and industrial & human waste. The collection system includes pipes, manholes, and pumping stations.

But how does it all work? Below is a quick explanation:

Pumping Influent

Wastewater flows by gravity from homes and businesses to the wastewater treatment plant. It enters the plant at a low elevation, usually near a creek. The wastewater is pumped uphill to begin treatment. Gravity moves water through the treatment process.

Preliminary Treatment

Screens remove large objects such as bottles,  branches, wipes, and trash. Grit chambers remove grit, sand, sediment, and gravel.

A big part of the wastewater treatment process is to separate the solids from the liquids and the liquids from the solids…


Primary Treatment

Wastewater flows slowly through large tanks called primary clarifiers. This allows the heavier organic solids to settle down to the bottom of the tank. The settled material or primary sludge is pumped from the tank to a digester for further treatment.

Secondary (Biological) Treatment

Air bubbles are forced through the wastewater to encourage certain types of useful bacteria and microorganisms (microscopic single-cell organisms, think amoeba) to grow. These ‘bugs’ consume organic pollutants in the wastewater. They break pollutants (i.e. ammonia) into simpler forms (nitrates).

Final Clarification

The bacteria and microorganisms from the biological treatment phase are settled out of the wastewater in large tanks called final clarifiers. The bacteria/bugs are reused again in the treatment process…

Very similar to the primary clarifiers, the water moves slowly to allow the settling process to occur. Settled material or sludge that is pumped from the bottom of the clarifiers goes to digesters for further processing.


Even though the wastewater flowing from the final clarifiers appears to be clear, there may be very tiny particles remaining. The flow is passed through a bed of sand or fine mesh screens called an effluent filter. This filter removes these particles.


The processed wastewater (effluent) is disinfected with ultraviolet (UV) light to neutralize any remaining harmful microorganisms.

Cascade Returns Water to Creek

The final stage of treatment is disinfection and then the water flows over a cascade of steps to the creek. The cascade steps looks and acts like a large waterfall putting oxygen from the atmosphere back to the water. The water may have a foam look as it travels down the creek due to the oxygen.



Digesters are large tanks where the solids removed from the clarifiers are heated, mixed, and treated with biological processes to remove harmful bacteria, break down fats and oils, and overall reduce the volume of solids. 


The solids removed from the digesters still contain a large amount of water. This water is removed for treatment. The treated biosolids are collected and returned to the environment. The biosolids are nutrient-rich byproducts of wastewater treatment. Biosolids are land applied on agricultural or farmers’ fields to as soil amendments and a source of fertilizer. 

Wastewater treatment operators and our laboratory professionals test both the water and solids throughout the process.

Did you know…

  1. Our oldest plants were built in the 1920s.
  2. Part of designing for treatment plants includes ensuring space for expansion for generations.
  3. Staff can take parts of the wastewater plant offline for cleaning, repairs, and upgrades all while treating the constant flow.

Additional resources:

What does a growing city mean to wastewater treatment plants?

Why does wastewater cost more than water on my bill?

How does CLTWater respond to a wastewater overflow?

Is the odor from a wastewater plant or sewer manhole?

A Growing City Means Growing Treatment Plants

When you reflect on jobs that people are passionate about, wastewater treatment plant operators aren’t usually at the top of that list. However, the passion was palpable as I spoke with three employees at the Mallard Creek Wastewater Treatment Plant, which is currently undergoing updates and expansion due to our growing community. They have a deep understanding of the importance of the work they are doing in the community and how it contributes to the growth of the area and our current quality of life.

An architect’s rendering of the new influent pump station and equalization tank.

If growth in the area was allowed to outpace the development of the sewer infrastructure, it would cause a very messy problem for the city. Development can only occur where there is the infrastructure to support it. As the University area continues to grow quickly, the infrastructure must be built and updated to meet the increase in demand. Recent studies have shown that for every one million dollars Charlotte Water invests into its utilities and infrastructure, it leads to 17.7 million dollars in economic output. Investment in our infrastructure allows the kind of growth that protects our quality of life.

As such, the Mallard Creek Wastewater Treatment Plant has several updates and additions planned over the next eight years. The original facility was built in 1979 and has been expanded over time. The original buildings are still in operation, but some of the equipment and buildings need to be replaced. By updating the facility, the plant will grow and have increased capacity and efficiency. The current facility handles 12 million gallons per day, however, when all the updates are completed, the plant will be able to handle 16 million gallons per day!

One concern of an expanding wastewater treatment plant for many is the odor. One goal for the updates is to increase odor control so that the plant isn’t a nuisance. As many would imagine, before touring this wastewater treatment plant, I had mentally prepared for a strong odor throughout the facility. However, I was pleasantly surprised that the odor was mostly contained to the part of the facility where the wastewater entered untreated. Throughout the rest of the facility, I wouldn’t have known that I was standing so close to millions of gallons of wastewater.

This is where sewage is strained of larger pieces of garbage before entering the rest of the plant. This equipment is being replaced. It will be covered to help with odor control.
This is the pump house, built in 1979 with various changes made over the years. This building will also be replaced with new pumps and a new building to accommodate the new pumps.

These ad hoc additions over the years left the facility with a mismatch of equipment of assorted sizes and capacities. For example, right now there is an assortment of pumps that have been added over the years of all different sizes. This makes redundancy difficult. Redundancy is the ability of the other pumps to handle the extra flow when one pump is down for maintenance. By replacing the pumps with six new pumps that are all equal in size and capacity, the strain on individual pumps is lessened, and their capacity to handle maintenance issues is increased.

This is the day tank that assists the plant in managing capacity during times of fluctuating flows.

Another portion of this project is the equalization tanks that are being added. One that handles five million gallons and another that can hold 15 million gallons. Throughout the day and night, the flow of sewage coming into the plant varies; the equalization tanks hold flow during the higher flow times to even the flow into the plant. This reduces the strain on the equipment and makes testing more accurate. The smaller tank handles day-to-day variations while the larger tank handles large storms and flooding. These tanks also allow the plant to temporarily shut down sections of the plant for updates and maintenance.

The location of the new equalization tank. Charlotte Water and its contractors will be digging 65 feet under the ground to place the influent pump station which will be adjacent to the equalization tank.

Many systems and buildings within the plant will be touched by at least one phase of the project. There are four phases, with phase one being launched by the end of 2022. Most of the work of phase one will begin in 2023 with plans to be completed by the end of 2026. 

It is easy to ignore or not even consider how much work goes into keeping our city clean and sanitary for the more than one million people (and counting!) who live here. As we continue to grow, we are grateful for the City employees who plan for and accommodate the continued growth of our city. There is a lot of work that goes into planning and sustaining the foundation that keeps Charlotte running.

Water Treatment Plants are Award Winning, Again!

Congratulations to staff from Vest, Franklin and Lee Dukes Water Treatment Plants for receiving the North Carolina Area Wide Optimization Program Certificate for 2017.  The AWOP certificate was created in 2000 through a joint program between the EPA and states to help drinking water systems meet successively more stringent regulations and achieve higher levels of drinking water quality.

Vest Water Treatment Plant – 10 Years; Pictured left from right John Huber, Mark Hahn from NCDENR, Steve Clift, Gabe Sasser, and Angela Lee

Franklin Water Treatment Plant – 9 Years; Pictured from left to right: John Huber, Mark Hahn from NCDENR, Terry Crowe, Gabe Sasser, and Angela Lee

Lee Dukes Water Treatment Plant – 13 Years; Pictured From Left to Right: John Huber, Mark Hahn from NCDENR, Dave Banick, Gabe Sasser and Angela Lee