How the physical characteristics of a pile drive temperature

How the physical characteristics of a pile drive temperature

We constructed a second model to characterize the effect of water activity (Aw), pH, and % moisture (DM) on the temperature profile of stacked poultry litter piles. The details of Model 2 are given in Appendix 1. B.

The pH of the poultry litter piles increased in the first 7 to 10 days after stacking, then decreased. This may be related to the volatilization of nitrogen as ammonia in the first few days after stacking. We found that the more basic the pH of the litter material, the more heat the pile generated (see Figure 4). A 5 C difference was observed between piles with neutral to slightly acidic pH versus those with basic pH readings at any point in time. Based on this data, litter treatments that lower pH may also inhibit the heating process of stacked litter.

Water activity was also positively correlated with temperature. Our model predicts that litter piles with higher Aw activity will be 20 C hotter than those with low Aw (see Figure 5). Since water activity reflects the biologically available water for microbial metabolism this result is not unexpected. Optimal Aw for log-phase growth of coliform bacteria in manure is around 0.95 or above, while static growth will occur at Aw of 0.75 to 0.95 (Reimann, personal communication).

We conclude that the heat produced at higher pH and Aw is the by product of bacterial metabolism. Based on these findings, we hypothesize that the lower temperatures observed for pile 2 were due to lower Aw and DM. In our visual appraisal of the litter material of pile 2, we had noted that it had more rice hulls versus manure than the other piles. This probably indicates that the moisture necessary to drive the heating reaction in the pile is provided by the manure. While water activity is not an easy parameter to measure, it is somewhat related to the % moisture or DM of the litter, which is an easily measurable parameter, requiring only a scale and an oven or microwave oven. Aw was the parameter that had the greatest single influence on the temperature profile of stacked poultry litter in our model. This information could be used by a producer to increase the moisture content of litter that was too dry to heat well. Possibly, foggers could be used to add moisture to the litter before scraping and transport.