photo by: Josie Heimsoth/Journal-World

Sewage sludge at the Wakarusa Wastewater Treatment Plant before it is thickened for land use is pictured on Friday, February 14, 2025.

In these bubbling basins, you’ll find some of the hardest workers in Lawrence’s water treatment system — microorganisms that tirelessly process millions of gallons of solid waste into nutrient-rich sludge.

The sludge, or biosolids, is a byproduct of human waste that’s filtered out during the water treatment process, and it will eventually go on nearby farmland to enrich the soil there. Lawrence produces a lot of it — more than 23 million gallons in 2023, or enough to fill 35 Olympic-size pools.

Processing, storing and distributing biosolids poses logistical challenges for a system as large as Lawrence’s, and the city recently launched a study on ways to improve the process and make it more sustainable. But many people don’t think much about this side of the water treatment process that’s often literally hidden below the surface.

Here’s a rundown of what biosolids are, the journey they take through the water treatment system, and what the city’s plans are for studying them.

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The reality of waste products is that they have to be put somewhere, and because of Kansas’ ample farmland and regulatory environment, biosolids commonly end up on farm fields.

Kansas has no state-level regulations for applying biosolids to farmland, so the only rules that apply are the nationwide regulations set by the Environmental Protection Agency. According to the National Biosolids Data Project, 28,728 dry metric tons of biosolids produced in Kansas were used for agricultural land in 2018.

For farmers, biosolids can serve several purposes related to soil fertility and structure. They make the soil less compact and allow water and plant roots to move through it more easily. Additionally, when biosolids decompose, they release nutrients like nitrogen and phosphorus along with organic matter.

But before biosolids can be applied to farmland, they have to undergo a specific treatment process that transforms the sludge into a usable resource. And it’s here that the city’s infrastructure comes in.

photo by: Shawn Valverde/Special to the Journal-World

The Wakarusa Wastewater Treatment Plant

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The City of Lawrence has one of the largest wastewater systems in the state. It operates the Kansas River Wastewater Treatment Plant, which opened in 1956, as well as another facility that opened in 2018, the Wakarusa Wastewater Treatment Plant. Both are managed by the City of Lawrence’s Municipal Services and Operations department, and they receive around 8 million gallons of stormwater and sewer water every day, said Jay Lovett, municipal services and operations manager for treatment at the City of Lawrence.

To produce the biosolids, they have to go through a multi-step process of separating out and processing waste. The Kansas River plant produced 19.4 million gallons of biosolids in 2023, and the Wakarusa plant produced 3.7 million gallons.

Lovett said both of the treatment plants are known as biological facilities, where microorganisms are used to treat the water passing through. But before it can get there, the water has to go through what’s called the pretreatment process, which involves removing large debris, grit and other coarse materials that could damage the plant’s equipment. Anything that can’t be eaten by the microorganisms has to leave, Lovett said.

The water then moves into the primary clarifiers, which are circular tanks with cone-shaped bottoms. In the tanks, the heavier solids in the water naturally sink to the bottom. These solids that settle out are called primary sludge, and they are sent for further processing.

Up next, the water will go through secondary treatment. Aeration basins are used to encourage the breakdown of remaining biological matter by using “air blowers” to create bubbles. Gradually, bacteria consume the organic waste, growing and reproducing, and forming the secondary sludge, also called activated sludge. This sludge is made up of the bacteria and other microorganisms that have broken down the waste.

The wastewater will then go through a secondary clarifier, where it undergoes the final removal of solids and other biological matter. Ultraviolet bulbs sterilize the bacteria, making them harmless to people and preventing them from reproducing but not killing them.

The biosolids are then stored until conditions are appropriate for applying them to the land — oftentimes, they are applied to city-owned fields surrounding the treatment plants.

photo by: Josie Heimsoth/Journal-World

Aeration basins at the Wakarusa Wastewater Treatment Plant.

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Recognizing the importance of sustainable and efficient waste management practices, an initiative has moved forward to assess and enhance the city’s biosolids management program. The City Commission authorized a $269,964 agreement with Black and Veatch in October to conduct an assessment of the current conditions of the program.

The analysis will focus not just on the residual biosolids, but on lime residuals. Lime is used to adjust the pH of wastewater, remove phosphorus as well as control the environment needed for the growth of pathogens in biosolids and more.

Omar Maali, senior project engineer with the City of Lawrence, told the Journal-World that by analyzing both residuals, the city aims to develop innovative, cost-effective and sustainable solutions for their management, covering the entire life cycle from production to disposal or beneficial reuse.

Currently, there are several key challenges in managing the sludge produced at the city’s treatment plants. Weather conditions frequently disrupt the application of biosolids, which leads to delays and inefficiencies in the management process, Maali said. The available soil in certain areas also has an excess of nutrients, which makes it challenging to apply biosolids at optimal rates without causing environmental harm.

In addition, biosolids must be applied at specific times when the ground is prepared and crops aren’t planted or being harvested. Farmers’ tight schedules or pre-planned activities, like fertilizing or planting, may not align with the availability of biosolids, resulting in missed application opportunities.

The consultant will also analyze emerging technologies that aim to reduce the volume and mass of residuals and improve sustainability, including reducing contaminants such as so-called “forever chemicals” and microplastics. A final report with findings and recommendations is anticipated to be complete towards the end of 2025.

photo by: Josie Heimsoth/Journal-World

The Wakarusa Wastewater Treatment Plant pictured February 14, 2025.