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Backwash Recovery

Water is a precious resource. It is the center of the universe for aquarium life support systems.

Sometimes it can be surprising how much time is spent avoiding the topic of water in zoos & aquariums. We learn all about the adaptive processes of deep sea invertebrates, the fascinating science of electroreceptivity in elasmobranchs, and sequential hermaphroditism in certain species of fishes and gastropods.

Yet, the linchpin that is water: chemistry, quality, and conservation, is often left out.

Look, I get it. Water isn't sexy. When there is the open mouth grimace of a sand tiger shark swimming past an acrylic window, you don't really want a nagging little voice on your shoulder screeching on about how water's hydrogen bonding and polarity influence some of its most unique qualities. But it is important.

Aquatic life support is such a fascinating field for that reason: it's all about that one piece. Water. AND WE ARE STILL LEARNING. Learning about how to move it more efficiently, test it more accurately, and conserve it most wisely.

Conserving, thus becomes the topic of this piece. We tackle the un-sexy here at AEI. Just look at our team (kidding).

This blog was actually inspired by Al (aka the boss), who emailed me pretty much out of nowhere.

"I think we should do an article on the backwash recovery system we did for the Smithsonian," he said.

(Cue me, internally, random but okay...)

But then he continued, "There are so many places that could utilize that type of system."

And the more I thought about it, the more it makes sense. Why aren't we promoting water conservation techniques? Especially ones that are currently running, that have proven to be effective? Call it a case study, or shameless self-promotion (see figure 1) on our end (we built it), but it works. And maybe it could work for you, too.

Backwashing refers to the process of pushing water literally backwards through a system's filter media. Typically, spent backwash water is either discharged with/out treatment to a sanitary sewer system or is treated and recycled.

Whether you are discharging with or without treatment (can you even discharge without treatment anymore?) you are losing water. That water will need to be replaced or you will quickly find yourself with fish that are left high and dry. What do you do? Consistently fill a system with tens of thousands of gallons of water ($$$)?

That is where the concept of backwash recovery comes in, taking what would be discharged, and treating it for reuse in the system. AEI designed and built such a system for pools along the "American Trail" exhibits at Smithsonian National Zoo.

There are 4 pools being controlled by one fully automated LSS:

  • One sea lion exhibit pool (300,000 gal)

  • Two sea lion holding pools (10,000 gal each)

  • One seal exhibit pool (125,000 gal)

  • Two seal holding pools (10,000 gal each)

  • Total: 465,000 gallons.

We partnered with Andy Aiken & Lewis Howie for a complete design/build of the backwash recovery system. The reason for this add on to the existing Seal and Sea Lion LSS was multilayered. Obviously it was to save on water usage, and reclaim some of the saltwater loss. Prior to the BWR system, they were running the sand filters on a 24 hour/7 day a week cycle.

The Installation:

Breaking It Down

  1. The ozone system was treating all 4 pools with 2- O3 generators and could not regulate ORP properly for any given pool. We provided 2 new O3 generators and re-piped the O3 supply lines to have a 1-to-1 ratio with the pools, therefore allowing the operators to control ORP based on the reading in each individual pool.

  2. Seal and Sea Lion fecal clean up was a monumental task due to the water waste when vacuuming the pools, and it would clog the recovery basin. We installed a new suction line which feeds directly to the drum filter of the newly installed BWR system, removing the larger particles before being diverted to the BWR basin. This has a few benefits, but most importantly it allowed the Smithsonian to control the coliform bacteria count which was plaguing the exhibit pools.

  3. Additionally we install mixing fans in the recovery basin to keep all fecal material suspended so it could be filtered out by the skimmer & drum filter during the normal BW cycle.

The result of this extension of the backwash system? An over 85 percent reduction in water consumption (compared to standard design models).

I'd call that a win for water conservation.


Figure 1:

Shameless self-promotion.

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