One of our frequent contributors, David Russell, suggested I reach out to the Chemical Processing audience for ideas on addressing the algal bloom at the Lincoln Memorial Reflecting Pool.

Russell, founder of Global Environmental Operations Inc., is a registered professional engineer in multiple states. He specializes in hazardous waste management and pollution control across six continents. Add to that the fact that he grew up watching his father build large commercial pools in the Chicago area, and he knows a few things about pools and maintenance. Commercial pools are state health-regulated, requiring full water filtration four times daily (every six hours) and chlorine levels maintained between 0.5 to 3 mg/L, with a maximum of 5 mg/L, he noted.

Sunlight and warm temperatures are the enemy of chlorine, he also pointed out.

"I've seen a sunny day take a chlorine level in a pool from 0.5 mg/L to less than 0.1 mg/L in a matter of a few hours," he said in a LinkedIn post.

Here are the particulars he put together (the link is from Wikipedia for more background): The National Mall's Reflecting Pool is massive. It’s about 2,030 feet long, 167 feet wide and holds about 6.75 million gallons of water. Filtering it four times daily like commercial pools would require pumping about 18,750 gallons per minute through a filter house of up to 10,000 square feet — enough water to supply a city of 45,000.

Dave has posted his full solution to his blog.

Now, let's start offering up our own solutions. Send me your ideas ([email protected]), and I will keep a running list here. You can choose to be anonymous, but please give me some generic credentials so we know you're one of us!

Reader Solutions

Regarding the reflecting pool, make sure they do not use "biocides" as that will open up a whole avenue of issues, permits, toxicity, exposure to people and animals, etc.

When we work with ponds, lakes, lagoons, etc., we use natural bacteria to remove the organics and nutrients so that algae cannot grow, instead of using toxic chemicals. Mixing and aeration, though, are critical, as bacteria are not just magic.

Dave is correct. Any large body of water will get contamination and organics in it from leaves, debris, dust, birds, humans, etc.

Organics will allow bacteria and algae to grow. Once algae starts to grow, it becomes a runaway train, as algae can fix nitrogen from sunlight and then start to grow even faster.

Quite a few things were wrong with the solutions used in trying to solve the reflecting pool problems.

Many paints have nitrogen in them. They can check the Safety Data Sheet (SDS), but if the paint had nitrogen as part of the composition, and sunlight breaks down the paint and releases the organics — which most paints have in them, as well as nitrogen — they immediately create a source for the algae to start to grow quickly.

Adding ozone or peroxide to kill algae was another terrible solution, as this would break down the paint even faster. Also, if you "kill" algae, they only die and re-release the nutrients (C, N and P), and then more algae will grow, so it's not a good long-term solution.

While bacteria can break down organics and nitrogen, without mixing and a filtering solution to remove the bacteria that grow, you will just wind up with solids in the pond, eventual odors and more issues.

We used a stain on our concrete flooring at our facility instead of paint — not only a better solution, but cheaper, easier to use and more durable.

For concrete pool decks and ponds, concrete stain is generally superior to paint. Stains penetrate the concrete pores, creating a breathable, fade-resistant and non-peeling finish. Paint sits on the surface as a film and is prone to bubbling, chipping and delamination when exposed to constant moisture. (Google)

Many ponds also put in solar fountains so they are "green" and require less electricity to run, as well as providing the air mixing that is usually required, and they are aesthetically pleasing in a pond.

It looks like they will need a number of solutions to fix this mess at the reflecting pools, as there is now more than one issue present.

Tracy Finnegan
President, Environmental Leverage, Inc.
www.EnvironmentalLeverage.com

I hope you don’t mind if I take this opportunity to address the peeling paint while the rest of you figure out how to combat the algal bloom.  One does not need a PhD in organic chemistry or to have worked in the paint and coatings industry for 50 years, but rather could use just a little common sense to understand that water/water vapor seeping through a substrate will do so with enough force to delaminate a surface coating that has been designed to seal the substrate against water incursion.  Think blistered, cracked and peeling house paint.  So, how to fix the reflecting pool?  Blast off all surface paint and sealing coats down to bare concrete.  Stain but don’t seal the concrete to the desired color. This approach will allow water to percolate unimpeded through the concrete. 

Norman L. Polston 

Cover the pool with a glass-clad polycarbonate panel and use projectors under to project images from a calm lake or ocean.

R. Balaji, Ph.D.