By 1945 my Grandpa had started milking about 500 milk cows. Nowadays, plus all our young stock we have about a thousand cattle. The dairy biogas plant processes the manure from those, plus food waste which we are paid a tipping fee for.
Traditional Slurry Lagoons Produce an Alarmingly High Methane Output and are a very Damaging Climate Damaging Emission
Previously the manure which comes off the cows simply went to a lagoon, and is while it was sitting there it went through the biogas (anaerobic digestion process), before being pumped out onto the fields. In the old lagoon (as on all farms which don’t have a biogas plant) the naturally occurring bacteria converted that to methane gas. Now that’s very harmful for the amount of global warming that produces, because methane is a greenhouse gas that’s 25 times as powerful as carbon dioxide.
Make no mistake, methane releases from slurry lagoons and from these dairies is a big contributor to greenhouse gas. We looked at installing an anaerobic digestion plant as an opportunity to be able to stay in the dairy industry in this area, and be sustainable both from an environmental standpoint and an economic standpoint.
The Simple Idea Behind All Biogas Plants
The idea of the on-farm biogas plant is that we take the natural bacteria that was going to occur anyways in the lagoon, and we put it into an engineered system. This engineered system is the digester here. It’s a little over a million gallons of capacity. We put about 50,000 gallons of new manure/ food waste in per day.
Once the material goes into the digester we heat it up. Once it is hot enough, it flows through the system for the 20 days. In that time the bacteria produce methane gas, which bubbles to the top and then comes out of the digester. It flows through a pipe into the generator building and we run it through the gas-engine, with the result that it produces electricity.
Electricity is sent to the power company, out via the grid. Any power we need to use we buy back.
Why Doing this is Far Less Environmentally (Greenhouse Gas Emissions) Damaging
By doing this we still make methane, but instead of the methane being released into the air we collect it. We put it through an engine. The result is that get energy out of it. The process is simply one of of getting energy from the manure and food waste, while converting the more complex compounds found in organic matter, to carbon dioxide.
There is no denying that which is still a greenhouse gas but it’s a greenhouse gases 25 times less powerful in producing climate change.
What Comes Out of the Digester
What comes out of the biogas digester, is a combination of a liquid and a fibre.
Solid digestate is what we call that fibre, and it comes out the back end of the digester tanks as a slurry. We separate the solid, from the liquid. The mixture of dirty water and fibrous matter that comes out of the digester is piped over to a separator. From there the solids go off one side, and the liquid goes into the other. The liquid digestate is good to be applied to the fields at a later time.
The digestate fibre works very well as a bedding for the cows.
The How Biogas Plant Economics Work
When building a farm anaerobic digestion plant, the capital cost is always an issue with the digester. You have to pay back that capital, and the only way you pay it back is from the revenues.
We get revenue from the power.
We get revenue from the sale of carbon credits for destroying the methane.
We get a benefit from using the fiber as a bedding material instead of buying bedding.
But, one of the biggest big things that made it possible for us here in Washington, is bringing in the food waste. With the addition of food waste, and having that extra revenue from the tipping fees and also the extra power that the high calorific values of this type of waste provides it becomes economically viable. It is that extra revenue produced by the food waste which enables us to have a higher KW output, which is so useful. And, the same is true for the other digesters that are here in Washington.
In a nutshell it’s economics, and with the food waste it’s a win-win for everyone.
There’s really no reason not to install a biogas plant, with the exception of looking at the economics to ensure it can be done profitably. Every farm, and every milk producer is different, so they each need to look at their situation.
Conclusion to the US Vanderhaak Dairy Biogas Plant Case Study
Often people say digesters are just not economically viable. I say yes, and no.
Yes, in the sense that for the right farms they are viable, but not for others. That’s why we haven’t built a whole lot of biogas plants yet, across the country (United States). But, the answer is also, no. It is no, usually, but is also possible to be a yes, because people have been entrepreneurial and found niche ways to make their biogas plants economical.
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