Using a concentrated Nitrosomonas culture for rapid determination of wastewater toxicity

I often get questions regarding the potential impact of new waste stream on the biological treatment unit. After looking at reference materials on the compounds, we often do direct toxicity testing. The first test looks for inhibition of heterotrophic microbes. I prefer to use PolyTox test kits here. A quick 20-minute test that requires only a BOD bottle, stir plate, and BOD probe/meter; the PolyTox test used a known standardized biomass with the data being reduced oxygen uptake due to immediate inhibition.

Often the concern is the potential impact on ammonia oxidizing bacteria (AOB), which are much more sensitive and slower growing than heterotrophic microbes. Many compounds are highly toxic to ammonia oxidizing cultures including:

• Heavy metals (Cu, Co, Pb, etc.)
  
• Cyanides/Cyanates
  
• Phenols
  
• Mercaptans
  
• Thiourea
  
• Aniline
  
• Certain Halogenated Compounds
  

 
In order to determine the potential impact on ammonia removal, we can do a simulation using a concentrated Nitrosomonas culture. There are three basic toxicity screening tests we can do using a syringe of Nitrosomonas cell paste.

1. Dilute new stream to see immediate untreated toxicity to culture
2. Simulate treatment with existing heterotrophic cultures in a shake flask simulation. Then test with the Nitrosomonas procedure.
3. Test the whole effluent toxicity using Nitrosomonas as a proxy for acute toxicity higher life forms such as ceriodaphia dubia. This requires correlating AOB inhibition to acute and chronic toxicity testing by running samples during the same period.

The test requires the use of flasks, aquarium air stones, tris buffer (ensures proper pH), and an ammonia ion selective probe (or other ammonia test). The process includes setting up dilutions of the sample and a control with buffered DI water and ammonium chloride. To all flasks, we add a 10 ml cell concentrate of AOB to ensure the sample is not biomass limited with respect to AOB. After taking initial ammonia readings, the flasks are aerated and maintained at 30oC temperature if a water bath is available. Otherwise, we perform the test at ambient lab temperature. Take ammonia readings every 30 minutes and plot the test flasks versus the control. Once ammonia drops below 5 mg/L, end testing.