North Little Rock Wastewater’s (NLRW) primary purpose is to treat wastewater and release clean water back into the environment, but our responsibilities also extend to disposing of byproducts from water reclamation processes, including biosolids.
What Are Biosolids?
The wastewater that enters our water reclamation facilities (WRFs) contains impurities including microorganisms and solids. NLRW uses two different processes to reclaim wastewater: mechanical treatment (Faulkner Lake and Maumelle WRF) and lagoon treatment (White Oak and Five Mile Creek WRFs).
Mechanical water reclamation begins by straining out large objects such as rags, then continues in primary clarification tanks, where large particles settle out. The particles removed from the bottom of these tanks are sludge. The water is piped from primary clarifiers to aeration basins, where a colony of bacteria is meticulously fostered to digest the remaining organic pollutants. This water is taken to secondary clarifiers, the last place for solids to settle out before the water flows through disinfection chambers and into the environment. The solids removed from the bottom of secondary clarifiers are also sludge. Some of the sludge is pumped back into the aeration basins to boost the bacterial colony and the rest is pumped into lagoons for storage. The stored sludge is further digested by bacteria over time. Upon removal from the lagoons, we call this sludge biosolids.
Lagoon-based water reclamation also begins with straining. Then the water flows into a lagoon equipped with aerators. There, solids settle out and bacteria break down organic compounds. The solids that settle out are called biosolids. The water flows through disinfection chambers and into the environment.
How Are Biosolids Disposed of?
There are three primary options for biosolids disposal: landfilling, incineration, and land-application. Landfilling is both costly and burdens the area’s solid waste disposal system. Incineration releases substances into the air. Land application, with proper precautions in place, increases soil health and water retention, provides nutrients for plants, and allows nature to finish the process of waste reclamation in a safe and efficient manner.
According to the Environmental Protection Agency (EPA), in 2022, 56 percent of biosolids in the United States were land applied, 16 percent were incinerated, 27 percent were landfilled, and 1 percent were disposed of via other means.
For the sake of cost, community wellbeing, and environmental improvement, NLRW land applies biosolids.
What Are the Risks of Land Applying Biosolids?
Due to safety regulations and best practices, land applying biosolids poses minimal risks to humans and the environment.
Biosolids for land application must meet EPA standards for bacteria and contaminant concentrations. Additionally, the receiving land must pass a thorough evaluation prior to receiving biosolids. Even once approved, biosolids may only be applied in appropriate weather conditions, and the soil is closely monitored for contaminants and nutrient levels, especially nitrogen. When the soil reaches the maximum allowable level of any contaminant, application at that site immediately and permanently ceases.
Per- and Polyfluoroalkyl Substances (PFAS)
As research on per- and polyfluoroalkyl substances (PFAS) has developed, concerns about exposure to these “forever chemicals” has grown. PFAS have been identified in biosolids in various concentrations around the country. The EPA is conducting research into the source, prevalence, and potential health effects of PFAS in biosolids, as well as the best way to address PFAS contamination. Regulations and best practices may change as our knowledge develops, but currently the EPA, U.S. Department of Agriculture, and U.S. Food and Drug Administration all allow land application of biosolids.
The Future of Biosolids Disposal at NLRW
NLRW intends to build a biosolids processing facility in the next several years. With technologies ever-changing and regulations regarding PFAS being finalized, plans for the facility are in the early conception phase. Regardless of the specific details, the goal is to improve our ability to dispose of biosolids in the way that most benefits our community, our customers, and our environment.