Agriculture Reference
In-Depth Information
3.3.3.1
Convective Aeration
Due to self-heating, along with the porous nature of a compost pile, air tends to
rise from the core of a compost pile and become filtered by cooler matter near
the top surface, then be released to the environment (Hubbe et al.
2010
; Zambra
et al.
2011
). Fresh air tends to be drawn in through the sides of the pile, complet-
ing the convective cycle. Lignocellulosic materials, which are often referred to as
the “bulking agents” of composting, play an essential role in maintaining suitable
porosity (Luz Cayuela et al.
2012
). Zambra et al.
2011
were able to model the
turbulent flows of air associated with such convection. However, in view of the
widespread use of passive convection, especially in household composting efforts,
there is a need for more study in this area.
3.3.3.2
Forced Aeration
The use of pressurized air, usually injected at the base of a compost pile, has be-
come a common practice, especially in large-scale composting operations. Several
recent studies have considered the optimization of such systems (Yanez et al.
2010
;
Arslan et al.
2011
; Fontenelle et al.
2011
; Lashermes et al.
2012
; Wang et al.
2012b
).
Arslan et al. (
2011
) reported finding an optimum level of aeration. Studies consid-
ered in an earlier review article (Hubbe et al.
2010
) have indicated that aeration
rate can be used as a practical control tool to more reliably achieve optimal thermal
conditions during composting.
3.3.3.3
Anaerobic Processing
Though anaerobic processing does not fall within the usual definition of compost-
ing, various recent researches have revealed some common features. For instance,
even though composting is supposed to entail aerobic conditions, oxygen levels
often become depressed within a compost pile (Zambra et al.
2012
) and localized
anaerobic zones can result (Luz Cayuela et al.
2012
). One of the key differences
between the two kinds of processes is that whereas a well-managed composting
process can be carried out in the open air, anaerobic processes need to be covered in
order to collect foul-smelling, toxic, and sometimes flammable gases (Monlau et al.
2013
). However, if a system has been set up to collect and utilize the gases, then a
positive net impact on the environment can be expected from anaerobic digestion of
organic wastes (Hermann et al.
2011
; Chairattanamanokorn et al.
2012
). Gases such
as hydrogen and methane produced by anaerobic digestion of organic wastes have
the potential to be used in place of fossil fuels (Chairattanamanokorn et al.
2012
).
Hermann et al. (
2011
) regarded anaerobic digestion as preferable to composting in
certain cases, since it allows for the recovering of bio-based fuels, while also pro-
viding a residue of solids that are suitable for use as soil conditioners.
