Many of you know that about 6 years ago we installed a methane digester, and through a process of heat and mixing convert manure to methane gas which is pumped as a gas through big generators in order to produce electricity. With these generators and this system we often can produce between 500-700 KWH 24 hours a day 365 days a year.
The actual process in the digester is pretty simple but somewhat difficult to explain with out knowledge of the inside of the structure. If you stay tuned over the next couple weeks we will actually go inside the empty digester for a full explanation of the process. In a nutshell, the generators create heat which we use to heat the manure to 100 degree’s, then bacteria that love manure grow and a byproduct of their growth is methane. We use this methane to power the generators and we also pump this gas back into the digester to stir the manure in order to prevent the solids from settling.
Well, over the last 6 years the mixing mechanism began to deteriorate for a variety of reasons. Last year we noticed some problems. The digester was still operating and producing electricity, but we recognized that we were getting some significant solids built up in the structure. These solids were limiting our throughput, and our ability to keep the manure 100 degrees. Below 100 degrees the bacteria are unable to effectively produce methane and the entire process stops.
The above picture is a basic photo of structure. It is 200ft long by 75ft wide by 16 feet deep, and holds about 1.6 million gallons of manure. We knew this was a big project. With the consultation of the company that installed the digester we contacted a firm called Veolia Environmental Services to manage the cleanout.
In preparation for the event, we began pumping whatever liquid we could on Thursday June 6, and pumped for 3 days, until we were left with mainly solids. Then Sunday afternoon June 9, Veolia arrived and set up their blowers, and other gas removal devices. Monday morning the methane gas was clear, but we also realized we had some work to do to get ready for Veolia to enter the pit.
In order to get the excavator into a convenient location we needed to take the sheet metal off of the nearby barn and cut down a 4 foot concrete wall, and more water had seeped out of the manure and we needed to pump for another 20 minutes or so before we could lower the first skid steer into the hole.
In the above picture you see 2 excavators. One is preparing to lift the first Skid Loader and lower it into the pit, the other is sitting just inside the barn where we removed the wall (left of picture). You will also notice yellow oxygen tanks in the foreground and a man in a white Tyvek coveralls. The individuals from Veolia wore these suits and strapped an oxygen tank to each Skid Loader to supply their gas mask while they were in the digester pit. The gasses they were concerned about were Ammonia, Hydrogen Sulfide (H2S), and Methane.
We had successfully evacuated all the methane out of the digester by Monday morning, , but the Ammonia and H2S would stay in the system until most of the solid manure was removed. The individuals all carried gas meters, and if for some reason the Methane levels spiked, they would evacuate immediately, due to the explosion risk. The Ammonia, and H2S while still important were less of a concern as long as they were using oxygen.
While the entire project has been stressful, Monday was by far the most intense. Above is a photo of us lowering the first Skid loader into what is called the skidsteer pit. Of course, in our digester the skidsteer pit is actually 9 inches too short and barely wide enough to fit a skidsteer and as you can see we were forced to lower it nose first. This took about 4 attempts to make it fit into the hole.
Stay tuned for more exciting news as we detail this event which we hope will soon be part of Bridgewater Dairy’s history!