1 day pathogen death temperature
1 day pathogen death temperature
ambient (outdoor) air temperature at noon i ''
ambient (outdoor) air temperature at noon
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TEMPERATURE CURVES OF FROZEN HUMANURE COMPOST PILES, AT 8" AND 20" DEPTHS, AFTER SPRING THAW
The above compost piles were situated outdoors, in wooden bins, on bare soil. The compost was unturned and not manually aerated in any way. No compost starters were used. Ingredients included humanure, urine, food scraps, hay, weeds, and leaves (and some chicken manure on the 1994 compost). The compost was frozen solid through the winter, but exhibited the above temperature climb after thawing in the spring. Fresh material was added to the compost pile regularly while these temperatures were being recorded on unmoved thermometers. The hot area of the compost pile remained in the upper section of the compost as the pile continued to be built during the following summer. In the fall, the entire compost pile cooled down, finally freezing and becoming dormant until the following spring, when it regained consciousness and heated again. It is evident that the internal heat of a compost pile is relatively independent of the ambient temperatures as the heat is generated by internal microbiological activity, not outside air temperature.
deposits from the sawdust toilet, which contained raw hardwood sawdust, humanure including all urine, and toilet paper. In addition to this material, kitchen food scraps were added to the pile intermittently throughout the winter, and hay was used to cover the toilet deposits on the pile. Some weeds and leaves were added now and then.
The material was continuously collected from a family of four. Nothing special was done to the pile at any time. No unusual ingredients were added, no compost starters, no water, no animal manures other than human (although a little chicken manure was added to the pile charted on the right, which may explain the higher composting temperatures). No turning was done whatsoever. The compost piles were situated in a three-sided, open-topped wooden bin on bare soil, outdoors. The only imported materials were raw sawdust, a locally abundant resource, and hay from a neighboring farm (less than two bales were used during the entire winter).
Two thermometers were used to monitor the temperature of this compost, one having an 8" probe, the other having a 20" probe. The outside of the pile (8" depth) shown on the left graph was heated by thermophilic activity before the inside (20" depth). The outside thawed first, so it started to heat first. Soon thereafter, the inside thawed and also heated. By April 8th, the outer part of the pile had reached 500C (1220F) and the temperature remained at that level or above until April 22nd (a two-week period). The inside of the pile reached 1220F on April 16 th, over a week later than the outside, and remained there or above until April 23rd. The pile shown in the right graph was above 1220C for 25 days.
Since 1993, I have monitored my humanure compost temperatures continuously, year round. The compost typically reaches 120 degrees F. (49C), at a depth of 20", in early spring and now stays there all summer and fall. In the winter, the temperature drops, but the compost piles have not frozen since 1997. In fact, the compost ther-mophiles seem to be adapting to the cold winters of Pennsylvania and it is not uncommon for my compost to read temperatures over 100 degrees F all winter long, even when the ambient air temperature is in the single digits. The maximum temperature I have recorded is about 149 degrees F. (65C), but more typical temperatures range from 110F (44C) to 122F (50C). For some reason, the compost seems to stay around 120F most of the summer months (at a depth of 20").
According to Dr. T. Gibson, Head of the Department of Agricultural Biology at the Edinburgh and East of Scotland College of Agriculture, "All the evidence shows that a few hours at 120 degrees Fahrenheit would eliminate [pathogenic microorganisms] completely. There should be a wide margin of safety if that temperature were maintained for 24 hours." 2
Incidentally, I am writing this paragraph on February 24, 2005. I emptied four 5-gallon humanure compost buckets this morning before I started writing. The outdoor temperature was 22 degrees F. The compost temperature at 20" depth was just over 100 degrees F. I glanced at the clock before I started emptying the compost, then again after I had finished and washed my hands. Exactly fifteen minutes had elapsed. This is a weekly chore and more time consuming in the winter because a gallon jug of water has to be carried out with the compost in order to rinse the buckets (the rain barrel at the
Humanure Hacienda is drained during the winter months and no water is available there). I have never paid much attention to how time-consuming (or not) humanure composting can be, so I was surprised that it took only fifteen minutes to empty four buckets at a leisurely pace during the worst time of year.
I shouldn't be surprised, though, because we've developed an efficient system over the years — we use a four-bucket system because two buckets are easier to carry than one, and four buckets will last approximately one week for a family of four, which means only emptying compost on a weekly basis. In the winter, one gallon of water is required for rinsing purposes for every two compost buckets. That means four people will need 1/2 gallon of water each per week for toilet use, requiring about four minutes per person per week for compost emptying.
Granted, there is additional time required to acquire and stockpile cover materials — a job usually done in the summer or fall (we go through about ten bales of straw or hay each year, plus a pickup truck load of sawdust). A few minutes each week are also needed to refill cover material containers in the toilet room (in our household this is usually a job for the kids). The biggest task is wheelbarrowing the compost to the garden each spring. But then, that's the whole idea — making compost.
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