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John Ogle’s Biofloc System

Early Promise, Then Problems

 

On August 9, 2011, I interviewed John Ogle, who recently retired from the University of Southern Mississippi’s Gulf Coast Research Laboratory.  In 1989, as a research associate in fisheries and shrimp aquaculture at the lab, John embarked on a two-decade long series of experiments on a very simple form of biofloc shrimp farming.  His goal: to create a shrimp farming system that would be profitable in the United States.

 

When I interviewed John in 2004, he talked about his first experience with bioflocs and described his culture system:

 

 

Edited Excerpts from the 2004 Interview

 

Shrimp News: When did you begin looking at bacterial flocs as a tool in shrimp farming?

 

John Ogle: In 1989, we were running experiments on all kinds of filtration systems, and we weren’t particularly happy with any of them.  Out of frustration, in November 1989, we stocked a raceway that had no filters with Penaeus vannamei—just to see what would happen.  We ran an airline down the middle of the raceway, and in about 30 days we had bacterial floc.  We knew what it was because it’s the same type of floc that appears in sewage treatment lagoons.  Our raceways actually produced a light floc that we called fluff.

 

That was our first experience with floc, and we have been using it as a biofilter ever since.  We even designed and built a new building to study its use as a biofilter.  In fact, we don’t use any other kind of filter.  We even use floc in our shrimp nurseries.

 

Shrimp News: In your first trials, how much aeration did you use?

 

John Ogle: We used a one-inch pipe with holes drilled in it and ran it on a little Sweetwater L-20 Blower.  Oxygen levels stayed high, from 4 to 12 parts per million, averaging around 6 ppm.  At production densities, these systems remained stable for about 12 weeks, but as the shrimp grew larger, oxygen levels dropped and growth slowed.  We lost a tank that was in production for 22 weeks and contained 25-gram shrimp.  The load was so high that the oxygen dropped and we lost them.  Some of our zero-exchange, floc-filter systems have been running for a year, and the shrimp are still perking along.  The floc is so thick you can almost scoop it out with a fish net.  What we’re trying to find out now is what levels of floc are ideal for shrimp farming, and then we plan to build a system that takes advantage of those levels.

 

 

August 9, 2011, Interview

 

Shrimp News: When I interviewed you, back in 2004, you were very optimistic about the results that you were getting from some of your first experiments with bioflocs.  Does that optimism continue today?

 

John Ogle: There may have been some inherent flaws in the floc system that we developed, but I’ll get to that in a moment.  First, I want to describe the traditional zero-exchange system so that you understand the difference between it and my system.

 

With traditional zero-exchange systems, you have a tank for your animals, another tank where you remove the solids, and a couple of supplemental tanks to remove dissolved organics and disinfect the water.  Add a big biological filter and all the pumps to keep the system running and you’ve got an expensive, complicated system that can be more difficult to manage than your shrimp.  There can be from one to five pumps on these systems, plus an air pump.  All of them can fail and cause the system to fail.

 

Shrimp News: Tell me about your biofloc system?

 

John Ogle: The system that I designed was really simple, just a tank and an airline, eliminating all the pumps and all the water treatment equipment.  Tank space is devoted to growout, not equipment.  When you put vannamei into a tank with oxygen and feed, you get flocs, and the flocs become the surface material that nitrifying bacteria grow on.  The flocs become your filter.  No external filters needed.  These systems are low cost and easy to operate, so we were really got excited about them.

 

Then, we began to run into problems—stability and variability problems.  When we started running trials, we ran one, six-cubic-meter tank at a time.  Then we got a new building, where we had twelve, fifty-cubic-meter tanks.  We ran a lot of experiments in the big tanks, but for reasons that we never discovered, only about 30% to 40%, or so, of the tanks would survive and do well.  Six or seven would always crash and die.  Nitrite levels in the tanks that were failing were always high.

 

I think the shrimp were growing faster and producing waste products faster than the bacteria in the flocs could multiply to process them.  When the shrimp began excreting waste products into the tank, ammonia levels in the tank increased and ammonia-reducing bacteria sprang to life and reduced them in a week, or so.  As the ammonia decreased, nitrites increased, but, in my opinion, the nitrite-reducing bacteria could not reproduce quickly enough to keep up with the increasing nitrite levels, which quickly rose to toxic levels, killing the shrimp and crashing the tank.  The shrimp were growing faster than the bacteria.  In our trials, sixty to seventy percent of our tanks crashed because of high nitrite levels.  Thirty to forty percent of the time the nitrite-reducing bacteria kicked in, the nitrites came down, and the shrimp grew and prospered.

 

We had other problems.  One, we could not precondition the water.  With a traditional biofilter, you can get it up and running before you stock your animals, but you can’t do that with a biofloc filter.  We tried inoculating tanks with existing flocs, but that did not work very well because shrimp seem to be essential to the production of the floc.  We tried starting tanks without shrimp by just adding shrimp feed, but no flocs developed.  There seems to be a synergistic relationship between the shrimp and floc production.  Maybe the shrimp just helped keep all the debris that would have normally settled on the pond bottom suspended in the water column.

 

Shrimp News: Why were some tanks successful and other not?

 

John Ogle: We were never able to explain why most of the tanks failed.  We still think of ourselves as shrimp farmers, but with these biofloc systems we’re basically growing bacteria in a single-cell-protein reactor, and the shrimp are just kind of along for the ride.  Scientists grow bacteria in bioreactors that are held under rigorous temperature, pH and nutrients controls.  They can keep one species of bacteria under control and produce and harvest it.  A shrimp tank is a long throw from a bioreactor.  Light levels and temperatures are constantly changing in shrimp tanks, and we aren’t dealing with one species of bacteria like they are with bioreactors, we’re dealing with an untold number of bacteria species that we know very little about.

 

In addition, protozoans, worms, nematodes and rotifers live in the flocs.  You’ve got this huge mix of critters, and it just may not be possible to control all their life cycles at one time.  You’re trying to manage a complex ecosystem.  If your conditions were constant, maybe it would be possible to control it, but your conditions are changing all the time.  Temperatures are going up and down all the time.  Light and pH levels change constantly.  The ecology of the flocs is changing.  And that’s your filter.  And then your shrimp are growing, and their increasing amounts of wastes are constantly changing everything.

 

Not only do the right bacterial species have to get established in the tank, but they also have to be able to increase their populations in concert with the increased nitrogen load from the shrimp.  All of this seems to work within the traditional biofilter, so someone has suggested that nitrite-reducing bacteria might prefer the solid substrate of a biofilter to the floating substrate in a biofloc.  Maybe that’s why our system did not work.  We were trying to control something that we didn’t completely understand.  We really knew very little about the bacteria populations in our tanks.  Even if we knew what was going on in one tank at a particular point in time, everything would begin changing the next moment and continue changing the next day, the next week and the next month.  That’s in a single tank.  After we got our new building, we were working with twelve tanks.  Trying to get all those tanks on the same page was impossible.  Something different was almost always going on in every tank.

 

Because of biosecurity regulations at our facility, we had to sterilized all our experimental tanks and water with bleach, so we were basically starting with zero-bacteria tanks.  When we put shrimp and feed into those tanks, we were probably “seeded” the tanks with a different bacterial population every time.

 

Shrimp News: What do you think of the biofloc systems that use lots of aeration and an additional source of carbon—frequently sugar—to stimulate bacterial activity?

 

John Ogle: The problem with those systems is that you’re adding sugar, which is relatively cheap, but in some cases—pound for pound—you can be adding almost as much sugar as feed.  And that gets expensive.  Once the shrimp start growing, the oxygen consumption goes way up.  In some cases, you have to use huge amounts of pure oxygen.  That’s very, very expensive.  In addition, the disposal of all the floc material becomes a problem.  How do you get rid of all the floc?  We’re producing huge amounts of single-cell protein, and then we throw it all away.  We actually have to pay someone to get rid of it.  Maintaining and balancing these systems with sugar, feed and shrimp gets very expensive and that’s why they are not delivering on their original promise.  They’re more stable than the floc system I was working on, but now I think it’s time to re-visit the traditional closed system, the clearwater system.

 

Information: John Ogle (email: jtogle@cableone.net).

 

Source: John Ogle.  Interview by Bob Rosenberry, Shrimp News International, August 9, 2011.

 

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