RNG Digester Technology

RNG or Renewable Natural Gas is the new buzzword in Michigan agriculture. The process of treating manure in an anaerobic digester takes advantage of naturally occurring bacteria and harnessing their ability to make methane in a controlled environment. It is an idea that has been around for many years and it works very well. RNG from manure captures the gas produced by the decomposition of manure, cleans it, and puts it into the natural gas pipelines.

In nature, as bacteria break down the manure, they release methane, carbon dioxide, and other gasses. These bacteria are found in the guts of all animals (including humans). Personally, I have found that mine really like beans. In an anaerobic environment (no oxygen) and at the right temperature, the bacteria who specialize in methane production out-compete the other bacteria. The digester is a large tank that provides an environment for these bacteria to thrive, the bacteria eat the manure and produce more gas which can be collected.

Methane is a colorless and odorless gas made up of carbon and hydrogen. The natural gas used to heat our homes and cook dinner is composed mainly of methane. Natural gas deposits that we mine for energy are the result of a whole bunch of organic matter that was buried many years ago. The big idea with RNG is that instead of drilling for more gas, we capture the gas that is already being made in manure pits. Since the gas is produced by bacteria eating manure from animals that were fed crops, and since the manure nutrients are recycled onto crop fields, this is a renewable source of energy. An additional benefit of methane capture is that since methane is a greenhouse gas with 310 times more warming potential than Carbon Dioxide, by using a digester to treat the manure it keeps that gas from escaping into the atmosphere.

The recent interest in Manure RNG is being driven by some large natural gas buyers who are paying a premium for renewable energy. Many researchers are concerned about the contributions of fossil fuels to global climate change. For that reason, many states have passed legislation that require power companies to include renewable energy in their portfolio. That number of states is growing, and the states are some of the largest energy consumers in the country (California for one). As a result, renewable energy from wind, solar, and other sources is becoming more financially competitive compared to traditional fossil fuels because the long term costs of the traditional fossil fuels had not been accounted for. Those costs are finally becoming apparent in climbing global temperatures, shifting weather patterns, and rising sea levels.

Is a digester and RNG right for your farm? As with all things, there is an economy of scale to be considered. The digester is a complicated structure that requires a significant investment to design and build. The equipment to collect and clean the gas produced is also expensive and technically complex to operate. The final step is to be able to get the gas into the pipeline, which is not as easy as just pumping it backwards into the farm’s existing gas line (if the farm even has one). These projects typically take into account a farm’s location, their size, and if the infrastructure necessary is already available.

In Michigan, the other hurdle is that there is an upper limit on the size of a farm due to some permitting restraints. If a farm goes above that size limit, the type of permit that is required is more complicated, is more costly, and the farm is treated under some of the same rules as a landfill or a wastewater treatment plant. As a result, some farms are looking into the potential for building community digesters where multiple farms bring their manure to a central location for treatment and bring home the treated manure to spread on their land like usual.

Currently there are several on-farm digester applications in front of the state for permit applications. CJD Farm Consulting, Inc. is excited to be a part of these new ventures and we expect to see many more digester projects in the state to take advantage of the energy from the waste products. If you have questions or want to discuss your options, give us a call sometime at 616-608-5022.