Agriculture Reference
In-Depth Information
study showed that the evolution of moisture content, oxygen levels, as well as tem-
peratures within a compost pile are strongly dependent on both time and location.
Surely, one might conclude, if the temperature at the core of a compost pile can be
considered to be at an ideal level, then the temperature at the outside of such a pile,
especially near to the base of the pile, could be regarded as being in a substandard
condition. Support for such a hypothesis can be found in the widespread practice
of periodically “turning” compost piles (Wang et al.
2011
; Zhao et al.
2011a
; Luz
Cayuela et al.
2012
). The outer layers of a compost pile provide some insulation,
allowing the pile to heat up internally as a consequence of metabolic activity.
3.3.2
Research Strategies Related to Energy Flows during
Composting
Progress has been reported recently with respect to experimental systems and theo-
retical models, both having the aim of better understanding the dynamics of thermal
interactions during composting.
3.3.2.1
Experimental Systems
On the experimental side, one of the most notable advances has entailed the design of
small-scale reactors that can faithfully replicate the thermal effects that are routinely
observed in a full-scale compost pile (Lashermes et al.
2012
). This was achieved by
use of a set of matching reactors (smaller than 10 L), the wall temperatures of which
could be precisely controlled. During the initial six days of composting the wall
temperatures were controlled to be within the range of 1-2 °C below the measured
core temperature of each mini-batch. In this way, “self-heating” within each batch
was allowed to proceed despite the fact that the composted mass was insufficient
to provide self-insulation against excessive cooling. Then, during later phases of
composting, the temperature was programmed to mimic the prevailing temperatures
measured for full-scale operations. The cited authors reported high reproducibil-
ity when carrying out side-by-side replications. By contrast, inadequate heating is
sometimes observed when composting is carried out in insufficiently large batches
in the absence of temperature control (Paradelo et al.
2013
). As has been shown by
Hermann et al. (
2011
), attempts to biodegrade materials under near-ambient tem-
perature conditions can be expected to yield substandard results in terms of such
outcomes as the rates of chemical changes, the killing of pathogens, and the ability
to degrade certain materials such as poly-lactic acid (PLA).
Research undertaken at full-scale composting facilities offers another highly prom-
ising and practical approach. For example, the following recent studies were carried
out at industrial-scale facilities (Hachicha et al.
2012
; He et al.
2013
; Karadag et al.
2013
). An advantage of such systems is that they are inherently realistic and commer-
cially relevant. A disadvantage is that the experimental conditions are seldom allowed
to deviate from within a comfort zone prescribed by those in charge of the operation.
