Death of Digester Version 1

Taking apart the old digester in the field So around mid-December, disaster struck. Some of the pipes on the digester froze and broke, and it was cold enough that in-field repairs, and the modifications needed to enable the system to last through the winter were deemed unreasonable. Thus, we made the decision to bring it back to Clarkson to thaw it out and recondition it. Turns out that this was quite a lot more complex that originally assumed.
Originally, we thought we could just drain the tank, hitch it up, and tow it home. Upon our arrival on site it was immediately obvious that this was not going to work. First off, the trailer tires were frozen solid into the ground. Second off, it appeared to be full of silt. Therefore, we had to take it apart on site, to get it empty enough to move it. At right shows Yotam, Dave, and I stripping equipment from the lid. We wanted to get all the heavy stuff off, so we could lift the lid and see what we were dealing with on the inside.

Remoing the lid from the old digester The farm hands, being very helpful through the whole project, brought over their front end loader with the bail lifting attachment. We hooked up the chains and lifted off the lid. Shown here is Yotam and I unhitching the chains and getting it apart and onto the ground. The lid on this is more cumbersome than heavy, with all of those pipes and things going down the center. This is why I chose to have nothing but the bare minimum of plumbing going through the lid. It is still a big job to get the lid off, but you no longer need a crane to do it.

What happens when a digester silts up What was inside of the tank when we finally climbed back up to look. All that black in the tank that you can see is in fact sand-compacted manure. Rather the consistancy of very thick mud. We tried draining it first using all available valves and pumps, but it did not work. This material is almost non-Newtonian. Go find a bunch off mud, wet it down, and mix in sand at about a 1:1 ratio, and then fill a four foot diameter tank with 5 feet of the stuff. This was why we could not roll the digester, or even get it off the jacks. It was full of several thousand pounds of wet terrible muddy sand. Of course, this happened in December, its 12 degrees, and it's getting dark. We can't leave it there, or it would freeze solid by morning.

Me, covered in manure, climbing out of the tank What's that you say? Shoveling? Yep. We ran back to the hardware store after we saw what we had to do, and got a shovel. Into the tank I went. For the next three hours I shoveled sand laden shit out of the tank, heaving each 50 pound load over my head. Let no one ever tell you that shoveling out tanks is easy: Most shovels are too long to operate functionally in a confined space, so the handle keeps banging into the side. I ruined my raincoat, a pair of shoes, a pair of pants, and a set of gloves. I am very glad I had water proof boots and gloves, however. We were debating waiting to do this the next day, but the tank had been heated as of about 3 hours before this photo was taken, and the manure was still warm and steamy. At least it was warm in the tank.

Frozen depths of the tank the next day The next day, the bottom of the tank was essentially rock. It is basically a manure-sand composite, very strong, and very hard to get out. It doesn't shatter like ice, so you cannot chip it, and it is really dense, so takes a lot of heat to melt it. Furthermore, it is sitting in the bottom of what is at this point an ice-chest, which made it even harder to thaw out.
Just beneath this photo is the 'false bottom', part of our sand-separation system, and beneath that is more frozen sand. I could not get all of this out in the field, since it required more demolition time and equipment that what we had available. Eventually, I enlisted the help of some fellow grad students in April when it warmed up to thaw it out. We ran steaming hot water over this material for hours, shoveling it as it thawed. We had nearly a weeks worth of eight hour days remove this material and the false bottom from the tank.

Shipping out in the snonw Notice in the first photo at the top of this page, we have blue skies and loveliness. When shoveling the tank out, it was a cloudless, starry night. The next day, we went back to hitch up and start driving home, and it starts snowing. Dave was driving the trailer, and I was following behind in a car full of other pieces and parts. We almost got back to Clarkson without incident, unless you count the slipping on ice with a giant crowbar and sledge hammer, the tire exploding on the roadway, or the struggle to find a place to park a sad-looking poop digester for a few days while we track down tire repair people.