[Trisha]

Once the facility is already built and we assume everything is mechanically going well, your goal is to keep the microbes happy. Unhappy microbes = reduced biogas production.

Common operational factors that stress out the microbes:

-Overfeeding

-Temperature swings (more common in the winter when feedstocks are fed frozen into warm digester)

-Nutrient deficiency for high fat digesters or digesters with limited feedstock variety

-Changing parameters (T, pH, feeding rate) faster than the microbes can react

-Inhibition or toxicity (there are many types of microbe inhibition)

I’ve linked an article about the Top 10 Things to Make Your Digester Biology Happy. It’s a starting point for understanding some of the biological operational factors that influence biogas production.

https://azuraassociates.com/digester-biology-top-10/

azuraassociates.com

Top 10 Things to Make Your Digester Biology Happy – AZURA

Top 10 Things to Make Your Digester Biology Happy – AZURA

[Trisha]

The concentration of H2S in the biogas will depend on the 1) feedstocks 2) pH 3) temperature. Generally, higher protein feedstocks produce more H2S. Decreasing pH and temperature pushes more H2S in the gas phase (instead of staying in the digestate). There’s a wide range of pH and temperatures that you can operate at to minimize the H2S in the biogas. But pH and temperature won’t fix a problem caused by too much protein (and therefore too much H2S). I’ll link a YouTube video explaining these dynamics.

But if you’re wanting a single H2S or other contaminant concentration that you must not cross, that will depend on the equipment manufacturer’s design for your system and the pipeline standards.

How to Manage H2S in your Digester: https://www.youtube.com/watch?v=GlpwWKjazxg&t=193s

[Trisha]

Moving from running stable to running optimally is like the experience of going from an average fit person into an athlete. Digesters are biological systems. We (and digester microbes) train to become athletes by eating a diet that sustains the effort of pushing ourselves out of our comfort zone.

For digesters, pushing to optimal performance looks like:

· Looking for the highest caloric feedstocks (e.g. fats)

· Reducing the lowest value feedstocks (e.g. slow degraders, high lignin content, etc.)

· Like in weightlifting, maximizing the organic loading rate with progressive overload

· Addressing nutritional deficiencies, if any (e.g. trace metals, balancing the diet)

Optimal performance also depends on your anatomy, which in our case is the equipment:

· Clearing up “dead zones” in the digester tank* (e.g. floating layer of plastic, crusts, settled grit, etc.)

· Heating up feedstock storage tanks to ferment and break down the feedstocks prior to the digester

· Running the digester and feedstock tank at a consistent and optimal temperature

· Thorough digester and feedstock tank mixing

In Azura’s experience, the 10-20% improvements come from progressively increasing fat content, supplementing any nutritional deficiencies, and operating the feedstock storage tank like a fermentation tank.

*I’ve linked an article about dead zones since I believe people often underestimate its impact on what optimal performance looks like for their system. Or maybe have never heard of it before.

azuraassociates.com

Is Your Digester Smaller Than You Think? – AZURA

Is Your Digester Smaller Than You Think? – AZURA