By Amanda Peele, Project Analyst, UNC Environmental Finance Center
Where does water go when it spirals down the drain? Whether from a home, a local brewery, or the car wash down the street, it likely ends up in a public wastewater system. Public wastewater systems protect human health and the environment by removing contaminants from wastewater and releasing treated water back into local waterways.
However, not all wastewater is the same. Wastewater from peoples’ homes is often easier to treat than the wastewater generated by businesses and industries. Navigating the treatment of high-strength wastewater can be a daunting—and expensive—task. However, even small utilities can manage high-strength wastewater with the right tools and strategies.
What is high-strength wastewater?
Wastewater may contain many kinds of contaminants. “High-strength” wastewater contains higher contaminant concentrations than is typically found in “normal” wastewater from residential users. Wastewater “strength” is determined by the concentration of contaminants in wastewater. Table 1 details a few contaminants that utilities track to gauge the strength of the wastewater entering their systems, including biological oxygen demand (BOD), total suspended solids (TSS), and fats, oils, and grease (FOG).
| Contaminant | Definition | Common Sources |
| Biochemical Oxygen Demand (BOD) | A measure of how much oxygen will be used by aerobic bacteria in wastewater to convert organic material. High BOD indicates a loss of oxygen available to the ecosystem and life within it. | High BOD is especially common in discharges from users such as food processing industries, including breweries and dairies. |
| Total Suspended Solids (TSS) | Undissolved organic material, including sediment, silt, plant, and animal matter. High concentrations can make waterways septic, killing flora and fauna in the receiving environment. | Users that discharge wastewater with high levels of TSS include those that produce a lot of food waste, such as restaurants and food processing industries, and human waste, such as nursing homes and hospitals. |
| Fats, Oils, and Greases (FOGs) | Fats and oils tipped down household drains. Trade waste oils from garages and manufacturing. Anaerobic bacteria decompose fats and oils, using up oxygen and releasing toxic gases that have the potential to harm organisms. | These are often a byproduct of cooking, so they are especially common in discharge from food service establishments. Other sources include car washes and automobile repair shops. |
How does high-strength wastewater affect wastewater systems?
High-strength wastewater may result in increased overall costs, additional treatment steps, and potential compliance issues. For example, to process high BOD wastewater, the system must run aeration processes more frequently, increasing the electricity bill and general operational costs. Pushing the system to keep up also accelerates wear and tear on infrastructure, leading to higher capital costs.
Additionally, wastewater utilities are held to certain treatment standards to comply with their National Pollutant Discharge Elimination System (NPDES) permits. High-strength wastewater can challenge utility treatment capacity, potentially resulting in “pass-through” when partially treated waste spills into local waterways. These events often lead to fines for the utility.
Under-treated discharges may also occur when blockages due to the buildup of FOG in wastewater systems cause sanitary sewer overflows (SSOs), releasing untreated sewage into the environment. SSOs could also trigger NPDES permit violations and fines. Likewise, high volumes of TSS can clog sewer lines and damage vital system infrastructure.
Smaller Systems, Bigger Challenges
Utilities derive most of their revenues from user rates and fees, so they must design their rates to recover service costs. High-strength wastewater drives up costs for utilities of all sizes; however, small systems typically have limited customer bases and customer data, making it difficult to quantify these costs of service provision. Small systems likely face lower contaminant load capacities that are especially challenged by high-strength wastewater and increase the potential for fines. With slim margins and customer affordability concerns, small systems must consider how to process and charge for high-strength wastewater treatment.
Small systems can use several tools and strategies to minimize and manage the impact of high-strength wastewater on their systems. Formal cost-of-service studies tailor rate and fee structures based on the cost of providing service to different customer classes, but they may be expensive.
If a cost-of-service study is outside the current budget, an initial financial self-assessment provides an alternative. If this assessment shows that utility expenses outweigh revenues, the utility may need to consider raising rates and/or revisiting their rate structure(s). This change could be as simple as creating customer classes and associated rate structures that differentiate resident users from high-strength-generating users. Other methods include:
- Creating a high-strength waste surcharge.
Many states allow utilities to recover the additional costs of treating high-strength wastewater by establishing surcharges for commercial and industrial users based on the concentration of contaminants in their wastewater. There is no universally accepted standard for what constitutes “strong” wastewater. However, the US Environmental Protection Agency (EPA) recommends establishing a “surcharge ceiling” to ensure the utility doesn’t exceed contaminant loading capacities.
Many municipalities with existing high-strength surcharges share their parameters publicly, which small systems might use as a benchmark to get started. A cost-of-service study to determine typical contaminant amounts produced by certain industries in their service area may help establish “high-strength” wastewater parameters. Importantly, surcharges can be costly to enforce, depending on how the utility plans to monitor and sample high-strength wastewater dischargers. Systems can recapture monitoring costs by including them in high-strength surcharges.
- Implementing a pretreatment program.
Pretreatment refers to activities carried out by commercial and industrial users to reduce or eliminate contaminants in their wastewater before discharging. Pretreatment programs benefit wastewater systems by shifting some of the burden of treating high-strength wastewater to the users themselves. Though monitoring and enforcement costs can be significant, they may be offset by savings in operational and long-term capital costs. The EPA’s National Pretreatment Program delegates authority to local governments to develop and enforce pretreatment standards for any user that discharges waste with reasonable potential to interfere with the normal operation of its public wastewater system.
- Divert high-strength waste.
Rather than recovering costs, utilities can avoid them in the first place. Utilities can divert high-strength wastewater before treatment and find alternatives for disposal. An example would be hauling waste to the plant, placing it in a drying bed, and later disposing it in a landfill.
Systems may find other uses for high-strength waste that can improve their operations. Wastewater treatment often involves removing total nitrogen from wastewater through biological denitrification, a process requiring a steady carbon source that many utilities struggle to come by, which may limit treatment capacity. In some cases, high-strength users produce excess carbon, and utilities may contract with these users to support treatment capacity and reduce any high-strength fees that would accrue to the user.
Conclusion
Treatment of high-strength wastewater—and how to manage it financially—will look different in each community, primarily due to variations in infrastructure, local regulations, and available resources. Tailoring wastewater management strategies to the specific needs and characteristics of a community is crucial for ensuring efficiency and sustainability. The Environmental Finance Center Network offers several tools and resources to guide utilities through examining their financial health, from initial assessments to rate considerations, as they begin addressing high-strength wastewater challenges in their system.
Need technical assistance? The Environmental Finance Center Network is here to help!
The Environmental Finance Center Network offers free one-on-one technical, managerial, and financial assistance for small water and wastewater systems. To read more about technical assistance or to express interest in our support, fill out our interest form: https://efcnetwork.org/get-help/.