Remove That Debris

WWETT seminar focuses on effect of sand and grit accumulation in wastewater treatment systems.
Remove That Debris

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This year's slate of education seminars at the Water & Wastewater Equipment, Treatment & Transport Show (WWETT) wrapped up Wednesday morning.

One session, led by Denver Stutler, CEO of Florida-based Polston Applied Technologies, addressed the waste of wastewater treatment. Not the biological waste, however, which is meant to be part of the treatment process. Stutler focused on material that finds its way into a plant and remains there (i.e. sand and grit), and eventually cuts into treatment capacity and affects the biological process.

“If you don’t appreciate the problem of sand in a wastewater treatment plant, put a grain of sand in your contact lens,” says Stutler. “It’s not supposed to be there. It creates problems.”

If the image of a red, watering eye caused by a single grain of sand didn’t put the issue into perspective for the session’s attendees, perhaps some of Stutler’s real-world examples did the trick.

“Because of the restored capacity, it put on hold indefinitely about an $8 million expansion project,” says Stutler, referring to a plant in Sebring, Florida, in which his company helped remove almost 200 cubic yards of accumulated sand.

This was all accomplished without taking the plant offline. Polston Applied Technologies aims to serve plants without redundancies that can’t be shut down, Stutler says.

But whether a plant can afford to drain a settling tank or must stay online during cleaning, it's important to remember the accumulation of sand can't be ignored, says Stutler. Aging underground infrastructure is causing more sand and grit to infiltrate treatment plant processes, and grit removal is not entirely able to prevent the material from accumulating in tanks.

“They all have good separators, and they’re actively keeping them clean,” he says of plants that encounter problems. “Keep in mind it’s an accumulation over a decade or more.

“What happens is you end up with high energy costs. Blowers and diffusers are working harder to lift the sand and keep it suspended, and then you see your levels not where they’re supposed to be.

“Aeration basins are typically where we see a lot of buildup. In many cases the bubble diffusers are running 24 hours a day in order to keep sand suspended so they don’t limit their oxygen. If your amount of oxygen is reduced, your detention time is reduced, and ultimately you’re not in compliance. The important parts are not just the treatment improvements but also the energy and capital savings.”

At another Florida-area plant, Stutler says 750 cubic yards of capacity was added after removing debris accumulation, and the cost of removal was far less than the cost of adding that much capacity through an expansion.

“Between the capital savings and the energy savings, in less than 15 months, they recovered the cost for the removal of the sand,” Stutler says. “They’ll do it again in the next seven to 10 years.”


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