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4 questions a wastewater utility should ask before expanding

September 19, 2023

By Sara Arabi

Wastewater facilities are essential as communities grow. A smart, strategic approach to expansion is critical.

The last few years have driven major migration and reshaped towns and cities across North America. From 2021 to 2022, US counties with populations under 1 million gained residents. But major metros like Los Angeles and New York lost population. In Canada, a record number of people moved out of the Greater Toronto area from 2020 to 2021. And smaller towns like Carleton Place, Ontario, and Cowansville, Quebec, grew as much as 4 percent.

When communities boom, utilities are pinched. Development strains wastewater treatment plants (WWTP) and makes treatment more complex. These plants may not be ready for the population influx or the influent flows and loads that come with them.

Sometimes a city or town needs to increase (or even double) capacity without having the physical space to expand. 

The Fish Creek Wastewater Treatment Plant in Calgary, Alberta.

The challenges of delivering reliable, equitable, and cost-effective access to clean water can be daunting. With aging infrastructure and constrained budgets, utilities have to support a growing population. At the same time, they need to protect the environment and establish long-term climate resilience.

So, what does this mean for your wastewater utility? We’ve seen success using a smart, strategic approach. And here are four questions to ask as you take on a WWTP expansion.

1. What needs to be done?

When an existing WWTP hits critical capacity limits and it becomes clear that the infrastructure is too small, it’s time for a long-term expansion. Thankfully, there are guidelines for this in most places. In Colorado, for example, the Department of Health requires towns to make expansion plans when their facilities reach 80 percent capacity. At 95 percent, construction must begin.

But expansion doesn’t always mean building something bigger. And reaching capacity could indicate a few things.

Asking yourself these types of questions can help: Where is your wastewater treatment facility hitting a bottleneck? Do you need to build more digesters to process solids, or is there a greater need to adjust liquids processing? Have you assessed the condition of your assets?

We can’t tackle everything at once, so figure out what needs to be done first and build out a phased approach. It can also be helpful to explore alternative options. For example, a new trend in the industry is intensification, or doing “more with less, in less.” This is when a WWTP adjusts to meet requirements without a major physical expansion.

Exploring intensification was key for the City of Calgary’s Fish Creek WWTP. The solution allowed the WWTP to meet tougher effluent standards while staying within the existing infrastructure and compact footprint. This required us to carefully assess and model various processes including:

  • Aerobic granular sludge (AGS)
  • Integrated fixed activated sludge
  • Membrane bioreactor
  • Enhanced nutrient removal stage processes
  • Biological aerated filter

During our analysis for the Fish Creek project, we saw the potential to use some of those technologies to repurpose existing secondary clarifiers. This means reduced lifecycle costs at the plant.

The island of Oahu also faces geographic limitations. For the City of Honolulu’s Sand Island WWTP expansion, we realized intensification was the only true option. Sand Island is the largest WWTP on Oahu, and our two-phased approach helped the plant upgrade existing facilities to improve its treatment capacity. Now the facility meets new, stricter regulations in an efficient manner.

When an existing WWTP hits critical capacity limits and it becomes clear that the infrastructure is too small, it’s time for a long-term expansion.

2. How will you plan for future growth?

One of the hardest parts of expansion for a wastewater utility is the unknown growth in a future population. The impact of climate change on water accessibility is another crucial factor. That’s why a well-thought-out master and facility plan is essential for expansion.

When we lead a master planning process, we conduct an analysis of flows and loads for the existing WWTP. We also assess the plant’s overall condition and equipment. Where is it in its lifecycle?

A master plan determines the best technologies for addressing expansion requirements and future environmental compliance demands. A master plan is usually for a 20-year timeframe. It outlines a schedule of regulatory milestones, design targets, and capacity stages.

As time goes by, we revisit our clients’ master plans. Regulations, report requirements, or other factors may change over time, and we want to make sure improvements are still relevant.

An inside look at the Bonnybrook Wastewater Treatment Plant expansion in Calgary, Alberta.

These plans can also play a role in setting or meeting specific goals or targets. This is the case for the City of Calgary’s Bonnybrook Wastewater Treatment Plant Expansion Program. We completed a master plan to help with the integration of existing and future cogeneration facilities. With steady population growth and evolving regulatory requirements, we expect ongoing expansion of Bonnybrook. The master plan is projected to save the city $7.5 million while reducing carbon dioxide emissions by 94 percent.

A completed master plan will become the roadmap for your wastewater treatment facility as the surrounding area grows and changes; it will lay the groundwork for future upgrades. Once the master plan is complete, your project is ready to move into the design phase.

3. Who are you serving?

Next, it’s important to look at your service area and customer base. Growth is good for local economies and development, but it puts a strain on the facilities supporting commercial and residential customers. Utilities should consider both types of customers in an expansion.

To serve customers better, some municipalities on the East Coast of the US are looking into regionalization. Shared pooling with local utilities is a practical approach that lowers expenses and risks from expansion.

So, what does that look like? Instead of expansion of solids processing at each individual WWTP, facilities are coming together to build one large incinerator for sludge. A biosolids facility that serve more than one WWTP for sludge processing help facilities meet more stringent biosolid regulations.

One example is the Washington Suburban Sanitary Commission’s (WSSC) Piscataway Water Resource Recovery Facility BioEnergy Project in Prince George’s County, Maryland. We’ve designed this project to take solids from five WSSC facilities and treat them using thermal hydrolysis process, followed by anaerobic digestion to enhance biosolids processes. It will result in a higher bioenergy yield. A significant nitrogen load in the process also will be treated using a deammonification process. The result will be a facility that sees massive cost savings and much less energy, chemical, and hauling costs.

The win-win extends to both utilities and customers. It fosters harmony within municipalities, and it reduces the operational cost and carbon footprint.

Remember to communicate with your customers, too. It’s important they know what’s going on, why, and how it affects them in terms of money and convenience. Make sure you have a good public outreach plan in place as you begin this work. 

Commissioning recently began on the Piscataway Water Resource Recovery Facility BioEnergy Project in Maryland.

4. What are your unique challenges?

Keep in mind that every town, city, and wastewater utility have unique traits. They also have specific obstacles and limits. Those include funding, public sentiment, geographic footprint, or time. And don’t forget that permitting applications and regulatory processes vary by location.

Within the WWTP there may be other limitations, which can be addressed in the master plan. For example, consider intensification, as we noted earlier. With that approach, you can either build new tankage or using existing tankage and convert it to a newer technology.

Sometimes a utility needs to build a bigger system altogether, but the size of the site is limited. This is another situation where membrane bioreactor (MBR), AGS, or other intensified processes can help—using existing tankage or a smaller tank to achieve high effluent quality and increase capacity. Or maybe your clarifier is limiting your capacity. If that’s the case, it may be helpful to use MBR, which provides excellent solids-liquid separation in a smaller footprint.

Labor is another key factor. According to US Bureau of Labor Statistics, 8.2 percent of water plant operators will need to be replaced annually in the next decade. Advanced automation and control strategies will play an important role in future the operations. It’s essential to factor in these aspects and the addition of advanced technologies and processes that could pose a challenge during WWTP upgrades.

Time constraints can also pose challenges, especially for cities that are growing quickly. If you need to get more treatment capacity online as soon as possible, it may affect the type of construction project you’re able to take on.

Are you ready?

There are other concerns before taking on a WWTP expansion project. Among them are funding, operations, and delivery methods.

But if expansion looks likely for your wastewater facility, answer these four key questions first. This information will put you on a successful path to planning a wastewater facility expansion or upgrade that will meet the needs of your city for years to come.

  • Sara Arabi

    Sara is a wastewater engineer and practice leader in biological wastewater treatment—leading design, optimization, and troubleshooting of biological nutrient removal plants, membrane-based treatment processes, and industrial wastewater applications.

    Contact Sara
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