Septicity in wastewater refers to the byproducts of fermentative or anaerobic microbial processes. When redox conditions drop as microbes consume available dissolved oxygen, the organisms use alternative electron acceptors ending with the production of organic acids, hydrogen gas, and methane. In most EQ tanks, we have fermentative respiration occurring. Fermentation produces organic acids - if sulfate was present in the influent it will also result in H2S production. In an EQ tank we don't usually see much growth of methanogens which would convert organic acids into methane. While this microbial process does reduce overall ultimate BOD (BOD20) or COD, the process can create treatment challenges if the biological treatment unit. How can high organic acids upset a biological treatment unit?
- Short chain organic acids are very readily degradable. Coupled with the low redox potential of the septic water, this creates a very high oxygen demand at the biological system inlet. Low D.O. conditions favor organisms with higher surface areas - which are the low DO filaments.
- Sulfides with the organic acids can also promote the growth of filaments with sulfur metabolism - this includes Thiothrix sp., Type O21N and Beggiatoa.
- Odors - short chain volatile fatty acids, mercaptans, and sulfides formed in the EQ tank can "flash off" from the well mixed & aerated biological treatment unit causing odor complaints.
- Increase redox potential to prevent fermentative respiration & sulfate respiration
- To increase redox potentials, you can add aeration/mixing. We are not looking for a DO residual just increase redox potential to a point where fermentation does not occur.
- If aeration is not possible, you can add nitrate. Add just enough nitrate to prevent strongly negative redox conditions. Other alternative electron acceptors are available, but nitrate is a low cost, stable option.
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