[Peter]

Many digester owners select feedstocks based on two main factors: fuel value (how much methane or energy the material can produce) and economics (hauling costs, contract length, tipping fees, etc.). However, as we see it, making decisions solely on these criteria can be short-sighted.

We encourage clients to take a more holistic approach by balancing fuel value with other key characteristics such as degradability, nutritional content, contamination levels, and how each of these factors interacts with the specific design and biology of their digester system. At Azura, we’ve seen firsthand how a poor match between feedstock and system can lead to operational disruptions, reduced gas yields, and dead bugs.

To assess fuel potential, the Biomethane Potential (BMP) test is the industry standard. However, BMP tests are time-consuming and costly, which may not make sense for early-stage projects or when resources are limited.

In many cases you can accurately estimate the methane production potential of manure and agricultural residues without a lengthy and expensive BMP test, by analyzing key feedstock characteristics. Most of the characteristics are similar to forage characteristics that are analyzed for animal nutrition – such as:

• Total and volatile solids (dry matter and organic matter)
• Protein, fat, and carbohydrate composition
• Recalcitrant organic matter (e.g., cellulose, lignin, woody stems, and other hard-to-degrade components)

At Azura we apply correction factors based our experience with manure and food waste feedstocks collected across North America to account for recalcitrant materials that are unlikely to break down and produce biogas. This ensures a realistic estimate that avoids overestimation. We call this refined metric Total Digestible Energy (TDE), a fast and practical estimate of biogas production compared to long BMP tests.

Building an in house database of TDE can help predict biogas production for digesters receiving feedstocks from multiple sources. It can be a useful tool for plant operators to understand the nutritional value of what they feed their digesters, identify nutritional gaps, and closely monitor if they are efficiently converting feedstock to gas.