Rethinking our approach to wet weather infrastructure

As extreme weather phenomena become more frequent and infrastructure continues to age, increasing the resilience of water and wastewater systems has emerged as prominent theme in the industry.

s extreme weather phenomena become more frequent and infrastructure continues to age, increasing the resilience of water and wastewater systems has emerged as prominent theme in the industry.

This comes as no surprise to Jim Fitzpatrick, a principal process engineer with Black & Veatch. “Across our industry, we’ve very good at taking care of water during normal, average conditions. We’ve perfected our ability to plan, design, operate and regulate that condition,” he told me during a recent interview. But extreme droughts and storms over the past decade have “really made us open our eyes and say, ‘Is what we’re doing here really the right thing to do to take care of water over that entire spectrum?’”

That’s what resiliency is all about, he said.

“To really take care of business over that entire spectrum, it requires a balancing act of our infrastructure in four major areas,” he noted. They are: source control, conveyance, storage, and treatment.

“We’ve done the first three really well as an industry for many, many years,” he said. But now people are demanding high water quality over the entire spectrum, not just at average conditions, he explained. “That’s where treatment alternatives have some play.”

For some twenty years, enhanced high-rate treatment technologies have gotten very good at taking care of wet weather flows, he noted. More recently, over the past decade, some of these technologies have evolved to also treat water during dry conditions. “We call those ‘dual use’ applications,” he said. Instead of being used only during wet weather, which is maybe 5 percent of the time, these dual-use enhanced high-rate treatment technologies can be used across the entire water spectrum. “Now we can get a lot better use of our investments if we’re using them all the time,” he said.

How common are these dual-use systems? Not very, at least not yet. “If you look across the United States, there are probably 30 to 50 examples of enhanced high-rate treatment [systems],” said Fitzpatrick, “and there are about a dozen of them being dual-used.”

These dual-use systems generally target one of two objectives under dry weather conditions: to polish effluent for higher use (such as reuse or nutrient removal); or as a primary treatment step. “That’s really beneficial if you want to divert some of that influent organic carbon and use it to make energy,” he explained. By capturing more energy before turning on blowers and other energy-intensive equipment at the biological step, a 25-percent energy savings can be realized. “And for digesting,” he added, “we can increase biogas production by about 25 percent.”

These technologies present an interesting value proposition to those utilities striving to increase their resiliency. “You get a lot more bang for your buck with that investment,” said Fitzpatrick. With their versatility, dual-use enhanced high rate treatment technologies, while perhaps not yet mainstream, may inspire us to rethink our approach to wet weather infrastructure.

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