• Blog
  • Wastewater Testing
  • Bioaugmentation Applications
  • Useful Information
  • About Us
BIOLOGICAL WASTE TREATMENT EXPERT
Contact Us

Septicity conditions - what biological & environments create "septic wastewater"

12/4/2016

 
Experienced operators see gray/black water with high H2S odors, they confidently say the water is "septic". But what is "septic" water and what upstream biochemical conditions form the odorous, high oxygen demand water. 

First septic water usually gets its dark gray color from reduced sulfides (S=) binding with iron to form iron sulfide. The binding into iron sulfide is a good thing and is often used to control H2S gas in collection systems. For quick reading, I'll give the characteristics of "septic water":

Septic Water Characteristics
  • If original water had sulfate - there will be H2S, FeS, and S= (depends on pH, and if ironi is present)Mer
  • Soluble organic acids (acetic, propionic, butyric) - odorous products of anaerobic microbial activity
  • Mercaptans - strong odor compounds formed when you have reduced sulfides and organics
  • High organic acids - increase the amount of soluble BOD5 and promote filamentous bacteria growth (from initial oxygen depression at the influent & some grow very well on organic acids)
  • Reduced sulfur species have a chemical oxygen demand that also lowers dissolved oxygen in the influent area
  • Sulfides can thios can be very toxic to ammonia oxidizing bacteria (nitrifiers) in low concentrations

Biochemistry of Septicity
  • Low ORP (redox) potentials in collection system occur as dissolved oxygen is depleted by bacteria growing on wastewater organics.
  • If nitrate is present - usually the bacteria will move to using nitrate as an alternative oxyen source. This does not create septic water as both sulfides and organic acids do not accumulate.
  • Once ORP drops sufficiently, microbial forms that can use oxygen from sulfate are favored and start to produce sulfides. Other microbes, without the ability to use sulfate, continue to grow slowly under fermentative respiration - which produces the organic acids. While organic acid production is vital in anaerobic digesters, in collection systems it can be an odor issue.
​
How to Control Septicity in Collection Systems
  • Control redox or ORP - add aeration, peroxides, or nitrate. Objective is to increase ORP above the value where sulfides or organic acids accumulate. Remember, inject redox control agents at points upstream of where you notice the problem.
  • Increase lift-station pumping frequency - don't let water sit in non-aerated areas.
  • Add aeration/mixing to equalization upstream of the treatment plant - we are not looking for a D.O. residual, we just want to keep ORP up.
Frederik Wynants
7/26/2019 12:36:28 am

Another very interesting article !

Erik Rumbaugh
7/26/2019 06:02:11 am

Thank you for the feedback. I always find new topics based on people's questions or observations. So if you find something interesting or have a question, send me an email or comment.


Comments are closed.

    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

    RSS Feed

    Click to set custom HTML

    Archives

    December 2022
    November 2022
    October 2022
    September 2022
    August 2022
    June 2022
    May 2022
    March 2022
    February 2022
    January 2022
    November 2021
    October 2021
    September 2021
    August 2021
    June 2021
    April 2021
    March 2021
    February 2021
    December 2020
    November 2020
    October 2020
    September 2020
    August 2020
    July 2020
    June 2020
    May 2020
    April 2020
    March 2020
    February 2020
    January 2020
    December 2019
    November 2019
    October 2019
    September 2019
    August 2019
    July 2019
    June 2019
    May 2019
    April 2019
    March 2019
    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    July 2018
    June 2018
    May 2018
    April 2018
    March 2018
    February 2018
    January 2018
    December 2017
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    May 2017
    April 2017
    March 2017
    February 2017
    January 2017
    December 2016
    November 2016
    October 2016
    September 2016
    August 2016
    July 2016
    June 2016
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    December 2015
    November 2015
    October 2015
    September 2015
    August 2015
    July 2015
    June 2015
    May 2015
    April 2015
    March 2015
    February 2015
    January 2015
    December 2014
    November 2014
    October 2014
    September 2014
    August 2014
    July 2014
    June 2014
    May 2014
    April 2014
    March 2014
    February 2014

Proudly powered by Weebly
Photos used under Creative Commons from Picturepest, marcoverch, perzonseowebbyra, Picturepest, Picturepest, dsearls, dungodung, Massachusetts Office of Travel & Tourism, aqua.mech, vastateparksstaff, hile, Aaron Volkening, amishsteve, Neil DeMaster, mklwong88, KOMUnews, Picturepest, kaibara87