I recently got a question on why bloodworms (midge fly larvae) seem to impact the AOB population more than the standard BOD removing or heterotrophic bacterial population. Given you only see worms when you have low BOD, high oxygen - why is ammonia the first effluent quality problem following a midge infestation.
Well it all goes back to how fast bacteria reproduce. The heterotrophic (carbonaceous) or just simply BOD removing microbes in wastewater tend to grow very quickly. In making bioaugmentation products, you can have a bioreactor reach maximum population density within 24 hours with many Bacillus and Pseudomonas cultures that can double every 30 - 60 minutes depending upon substrate and environmental conditions. The fastest reproduction time is called µ(max) or maximum growth rate. For AOB, nitrifiers, growth rate is measured in hours - 7 - 8 hours in laboratory environments. In wastewater facilities you are looking at 10 - 12 hours as maximum growth rate.
Now how does this lead back to midge larvae causing more problems with effluent ammonia numbers? Simply, the midge larvae consume bacteria in the form of floc. They eat all microbes present including heterotrophic and ammonia oxidizing bacteria. Since the AOB reproduce as a slower rate, the percentage of AOB drops more than for the faster growing heterotrophic bacteria. Therefore, while we lose total MLSS (biological solids) to the larvae’s consumption, the AOB bacteria a disproportionately impacted.
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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