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Summer time collection system and wastewater treatment plant odors. Is hydrogen sulfide the only thing you should monitor?

7/30/2018

 
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With oxygen being less soluble in warmer water and higher temperatures triggering microbial growth, summer months can bring an explosion in biological activity in both collection systems and wastewater treatment plants. While microbial growth is good for reducing pollutants, it also has unwanted side effects including:
  • Corrosion from hydrogen sulfide and acids
  • Nuisance odors from volatile organic acids and hydrogen sulfide
  • Potential worker exposure to hydrogen sulfide
  • Organic acids and sulfides can trigger filamentous bulking in some activated sludge units
Anaerobic conditions (low redox potentials) trigger biological growth that creates the problem compounds. We often think of anaerobic conditions as any Dissolved Oxygen (DO) below zero. However, there is a number of electron acceptors (oxygen alternatives) that will not result in hydrogen sulfide or other odor causing microbial byproducts. Potential alternative electron acceptors include:
  • Hydrogen peroxide 
  • Nitrate
  • Ferric iron
What we know as problem anaerobic activity occurs when microbes use sulfate as an electron acceptor releasing sulfides into solution. At the same time as sulfate is used as an electron acceptor, other bacteria begin fermentative respiration producing volatile organic acids. While volatile fatty acids are great in anaerobic digesters as methanogen food, in open wastewater plants and collection systems organic acids can cause odor complaints. 

The different electron acceptors and different "levels" of anaerobic conditions are why I always ask for pH and redox information when doing odor control projects. As pH increases, sulfides and volatile organic acids remain more soluble and stay in the water column. This is why some odor control methods include adding caustic or other base solutions. ORP or Redox Potential gives us information on what electron acceptor is being used by microbes. At a pH of 7, when we are above -150 mV ORP - you will be using non-sulfate electron acceptors and odors will be minimal. Control strategies with ORP include adding peroxide, nitrate, or other electron accepting alternative.

With all the options, I like to pick a solution that best fits the system and problem. Do a system survey to see where problem originate and then think of various options. I have written on system using lift-station aeration systems (blowers), pure oxygen injection with nano-bubbles, nitrate solutions, and even targeted hydrogen peroxide additions. All have merits and ways to improve their effectiveness. The key is to not pick a solution until you do the survey.

garbage disposal leaking link
11/26/2018 10:37:21 pm

I like to pick a solution that best fits the system and problem. Do a system survey to see where problem originate and then think of various options.


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    Author

    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.

    View my profile on LinkedIn

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