Ammonia Control Strategies

Too much ammonia? Here’s what you can do today!

Image shows an anaerobic digester. Text reads NH3 gas in headspace can be a source of odor and reduce RNG quality, NH3 soluble gas in digestate - a source of digestate ammonia emissions and can cause biological inhibition, NH4+ ammonium in digestate is a nutrient source for soil and least harmful form of ammonia

If lab testing indicates that your digestate might contain too much ammonia, what can you do?

  1. NH3 gas levels can be quickly reduced by cooling, adding acidic feedstocks, reducing HRT to reduce protein conversion. 
  2. For improved stability, digesters can be operated at lower temperatures and mid-range pH levels.

Temperature and pH determine ammonia’s dominant form in a digester. Higher temperature and higher pH shift the equilibrium towards the problematic gaseous NH3 form.

The graph below plots the percent of dissolved “total” ammonia (NH3aq + NH4+) in digestate that is in the inhibitory NH3 form at different pHs and temperatures. The rest of the “total ammonia” is in the least harmful, ionized (NH4+), form. The equilibrium is more sensitive to pH.

The fraction of inhibitory NH3 can increase more than 10X over a small change in pH and temperature!

Contact Azura for more detailed solutions to your ammonia challenges.

This article first appeared in the 2024 BiogasWorld Showcase report. To view the full report visit the BiogasWorld website.

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