Nitrification Efficiency in Cold Weather
Understanding the Impact of Temperature on Nitrifying Bacteria
by Deborah Lee , Aquafix Microbiologist
Removing ammonia is essential in wastewater treatment, yet nitrifying bacteria are among the most sensitive and slowest-growing microorganisms. Nitrifying bacteria are highly sensitive to cold, and as temperatures drop, nitrification rates can decrease by up to 50%, making ammonia removal more challenging in wastewater treatment. Bioaugmentation with acclimated nitrifiers (Nitrifier Pro) will help stabilize an restore nitrification in cold conditions and improve overall system performance.
Nitrifiers Vs Heterotrophs
Nitrifiers
Doubling Rate: 22-48 Hours
4-6% of total bacterial population
Heterotrophs
Doubling Rate: 20-30 Minutes
> 90% of bacterial population
Bacteria Growth in Summer Temperature
Heterotrophic organisms (floc-formers) use organic carbon for energy generation and their cells and cellular components. Autotrophic organisms, such as nitrifiers, don’t use organic carbon molecules for energy. Instead, they use the oxidation of ammonia to nitrite or nitrite to nitrate to generate energy. Autotrophic nitrifiers don’t use organic carbon for their cells, but instead use inorganic carbon (e.g. CO2 or HCO3–) similar to plants. This does not give them as much energy for growth as heterotrophs and results in a very slow growth rate (doubling time of 22hr-48hr) compared to most heterotrophs (about 20 minutes).
Nitrifier Growth in Cold Temperatures
Autotrophic nitrifiers also grow much slower than heterotrophic bacteria (0.5 day doubling time) at temperatures below 50° F (10° C). The optimal temperature for nitrification is in the range of 82°-90° F (about 28°-32° C). When the temperature decreases by 10° C, the nitrification rate generally decreases by 50%. A sudden decrease from 20° C to 10° C was found to cause a larger decrease in the nitrification rate than a gradual temperature decrease. With a sudden temperate change (cold shock), the rate of nitrification may decrease by even more than 50%.
The stable operation and high-efficiency nitrogen removal at low temperatures could be enhanced by applying bioaugmentation treatment with mixed nitrifying culture acclimated to winter temperatures. This can start the nitrifying population at a higher cell number and possibly introduce nitrifiers that are better adapted and able to grow faster in cooler temperatures. Adding just nitrifiers to replenish the missing nitrification steps can be more economical than trucking in another plant’s mixed liquor or waiting 3-4 weeks for environmental nitrifiers to come into the plant and become established. It does not take a lot of added nitrifier cells to see an increase in nitrification, provided the plant has environmental conditions that would support nitrification.
Ammonia Control Solutions
Microanalysis & Filament Origins
Our Microanalysis & Filament Origins test identifies major and minor filaments, and explains the operational implications of their origin. We review your floc structure, sludge age, and oxygen penetration so that we can offer definitive treatment and process recommendations. Results are available within 24–48 hours after samples arrive.
Nitrifier Pro
Nitrifier Pro is an ultraconcentrated blend of heterotrophic and autotrophic nitrifiers. With Nitrifier Pro, you can fully recover your plant’s ammonia removal capabilities in as little as four days.
Dynamic Duo
Dynamic Duo provides heterotrophic and autotrophic nitrifying bacteria that reduce ammonia into nitrate and nitrite. It also supplements high concentrations of autotrophic ammonia-oxidizing and nitrite-oxidizing bacteria, such as Nitrospora, Nitrosomonas, Nitrospira, and Nitrobacter, to then convert nitrate and nitrite into non-detect forms of nitrogen.
About the Author
Deborah Lee is a Senior Microbiologist at Aquafix with 12 years of experience studying nitrifying bacteria. She works with our wastewater clients to understand nitrifier populations and how to improve them.