By: Valerie Anne Edwards, President, Alken-Murray Corp.
Edited by DeAna Vitela, Director, AquaBio Environmental Technologies, Inc.

There are aeration system marketing companies that promise you that all you have to do to fix odor in your lagoon is to purchase a large expensive aeration system, because aerobic bacteria do not create nasty odors. So, you harness your resources for a capital expenditure, figuring that you will recoup from the good relations your odor control plan will promote in your community. You install the system and you pull the switch. The motors rumble, the surface bubbles and gunk starts to rise from the bottom and…and…the stench is overpowering, much worse than it was before. You turn in horror to the aeration company installer, who tells you not to worry, just give it some time. Well, you have just spent a ton of money, so you agree to let it run for awhile, but it does not improve.

Why? When you have a lagoon with little or no aeration, and allow untreated runoff and waterfowl feces also untreated, to enter into it, it stratifies, with only the top layer receiving any air. The oxygen demand of the waste quickly robs the lower layers of any oxygen they contained at startup, so obligate anaerobes (bacteria that cannot function WITH air) are encouraged to proliferate, while the obligate aerobes (bacteria that cannot function WITHOUT air) rise to the surface or die off. The level of organic matter in the lagoon is much greater than the natural initial bacterial population in the lagoon can handle, so the cycle of breakdown is slowed while the proportion of strains changes and the new population struggles to catch up to the tremendous volume of waste.

Let’s be honest here, you don’t find 1,000 assorted waterfowl naturally congregating together in a small area in nature. If such a population assembled in nature, it would quickly denude the land of nutrients and would die of starvation. So a natural urban lagoon was not designed to handle the volume of waste from urban runoff, and large populations of waterfowl and must work hard to adapt to it. Until the hydrogen sulfide volume, produced by obligate anaerobe Desulfovibrio desulfuricans, becomes so incredible over a period of time, maybe two to five years, that a large growth of bacteria is encouraged to develop from the small amounts of these strains of slow growing, generally obligatory anaerobic strains, some arriving from the animal intestines, you will develop a relatively stinky, relatively stable lagoon, depending on the landscaping and prevailing winds.

When you add aeration, you kill off the predominant obligate anaerobic bacteria (like the aeration man said it would), leaving only a tiny population of bacteria capable of aerobic respiration (which the aeration man didn’t count on). Digestion halts, the lagoon contents are stirred up, volatilizing the gases, so it smells much worse.

Does this mean that AquaBio or Alken-Murray opposes aeration? The answer is “Absolutely not”.

If you apply the correct species of facultative anaerobes (bacteria that can function either with or without air), in sufficient quantity to seed the lake and gradually introduce higher levels of aeration, you can competitively exclude the undesirable strains, while you encourage a faster, less odorous, and more complete digestion of waste. Although aeration for a large lagoon is expensive to install and to run, if you have already installed the system, AquaBio can make it work for you.