Too acidic. Generally if there’s a problem, it’s that the slurry is too acidic (pH below 7). If there is a lot of new, raw, green material placed in the digester or if too much material is added at once, the acid-forming bacteria have a field day. The methane bacteria are so annoyed by the high acid concentration, they simply can’t function. When this occurs, it can take a long time for the methane process to get underway naturally. Low pH is a constant risk and must be countered by plenty of carbon waste, such as leaves and straw, or wood ashes.
If a measured amount of new material—no more than one-fortieth of the total liquid volume of the tank—is added, then the new material has to be dilute enough not to upset the balance. At startup, though, there’s a lack of microorganisms and an inclination toward excessive acidity. Understanding this, we can see why some of the early literature on making methane states that the startup time can be anywhere from three weeks to three months.
I mentioned the acidity problem to a friend with whom I was working at the time. He said, “I make a lot of wine at home. Every once in awhile, I have the same problem. When I do, I add a little baking soda. It straightens out the condition right away.”
The baking soda added to my digester worked like a charm. Within three days, I had methane on the way. This is the secret for keeping your digester sweet and happy. Just add a little at a time until the pH is just right. If the pH keeps dropping, add baking soda periodically until the acid-forming bacteria are no longer producing excessive acid. Don’t be fooled if a lot of gas is produced. The baking soda itself will produce some carbon dioxide.
If the pH gets so low the digester “sours,” it is very difficult to revive and must be pumped out by a septic service and restarted. The Maitreya digester has not experienced this problem.
Too cold. You’ll need to know how hot the tank is, day to day, season to season. To eliminate the guesswork, install sensors both inside and outside the tank. Record these temperatures over a period of time. Then you will know how efficiently the tank is retaining heat, at what rate the temperature drops when no heat is added, and how much energy is needed to raise the temperature. If this is done, then a reliable calculation can be made of how much heat is needed to maintain working temperature if “free” heat is not available. Heat conservation, more than any other factor, determines whether a methane system will “fly” or not.
—Adapted from “The Methane Process” by Al Rutan (HP28)