3.1. Composting process
3.1.1. Temperature profiles
The temperature of the composting mixture rose soon after
beginning the experiment and reached 69 ± 4 C within 2 to 4 days,
corresponding to an average increase rate of 12 C day1 (Fig. 2).
This corresponded to natural self-heating of the organic mixture
since the temperature of the external jacket of the reactor was
maintained 1–2 C below the temperature measured in the middle
of the composting mixture. Comparable increases of temperature
rise have been reported for similar sludge-based mixtures in larger
composting devices (de Guardia et al., 2008) and on full-scale
plants (Jouraiphy et al., 2005). However, the initial mixtures largely
influence the temperature increase via their nutrient balance and
their content in easily biodegradable organic fractions (Haug