Spontaneous Combustion Tendency in Bagasse Stockpiles: Biotic and Abiotic Responses Relation

Microbial activity in stockpiled bagasse was investigated using: (1) acidity levels within the stockpile and (2) detected amounts of flammable volatile organic compounds (VOCs) above the stockpile, as potential factors to identify their impacts on spontaneous combustion. Temperature, moisture content, microbial activity (estimated by the number of spores obtained from plate counting), pH value, amount of acetic acid at different depths (0.5, 1.0, 1.5, 2.0 and 2.5 m from the stockpile surface) and the flammable VOCs above the stockpile surface after different storage periods (100, 150, 200 and 250 days from the first stockpiled day) were investigated. The temperature and moisture content of the stockpile were in the ranges 50–65 °C and 50–65%, respectively. A decrease in the pH value (pH 4 to 3) after longer storage periods was observed, which was related to the decreases in mesophile spores (1 order of magnitude) and thermophiles spores (1 order of magnitude) within the stockpile. Increases were observed in the temperature (5–10 °C), in the production of acid (3.6% m/m on dried bagasse) and of flammable VOCs, such as ethanol in the range 118–130 µg per cubic meter of air and others above the stockpile. Acid production increased the flammable VOCs, the temperature and the moisture content, suggesting that these parameters have the potential to be used for monitoring the stockpile characteristics. The acidity level is particularly useful since it is easy to measure.