Renewable Energy & Sustainability News

Keeping a Healthy Anaerobic Digester Diet

What Does a Healthy Anaerobic Digester Diet Consist of?

Digesters love organic waste – like foods, manure and biosolids. But the compositions and methane potentials of these different waste streams are important factors to consider when feeding a digester. Here are a few facts we live by to ensure a healthy anaerobic digester diet at our waste-to-energy facilities.

Our digesters take in about 70% food waste.

Food waste is a great feedstock for our digesters because of its high biodegradability. Residual food waste typically has the highest methane potential compared to other anaerobic digester (AD) feedstock. The higher the methane potential, the more renewable energy created!

Lipid-rich foods, like used oil or ice cream, and easily-degradable carbohydrates are highly attractive for AD due to their high methane yields.

Although there are many great benefits to utilizing food waste as an AD feedstock, there can be some hurdles. The mono-digestion of food waste often times leads to digester instability, which is why co-digestion is common practice.

Biosolids make up around 25% of our digester feedstock. Animal manure makes up about 5%.

When biosolids and manures are added to the feedstock there is a dilution of any toxic substances, an enhancement of nutrients, and a beneficial effect on microorganisms.

Manures and biosolids have great buffering capacity. This means they provide alkalinity, or act as a neutralizer, if any food waste negatively impacts the digester’s pH. Most food waste, like fruits and vegetables, have an acidic pH value that can harm the AD process.

Biosolids also add a large quantity of microorganisms that are beneficial to the growth of the different microbes involved in the AD process.

The processing of biosolids and manures, along with food waste, is essential for optimal digester health. Because AD is a promising and sustainable technology for converting organic waste into energy, it’s important that we continue to improve digestion efficiencies and processing performance at our facilities.

Cari Oberfield