Agriculture Reference
In-Depth Information
3.5.5
Composting and Sustainability in Life Cycle Assessment
Life cycle assessment can be defined as an attempt to numerically account for the
various contributing impacts of a certain process or product on the environment. Typ-
ically the goal is to quantify impacts all the way from the acquisition of raw materials
(“cradle”) up to the point of final disposal (“grave”). Questions can be raised such
as, “What else could have been done, instead of the proposed process or product, and
what would be the net effect on the environment?” Criteria can include the amounts
of greenhouse gases produced, the amounts of fossil fuel used, or the amounts of
carbon converted into a form that is likely to remain stable for many decades.
Important recent work relative to the life cycle assessment of composting
has been reported by Hermann et al. (
2011
). These authors set out to compare
conventional composting (which the authors call “industrial composting”), versus
biodegradation at ambient temperature (which was misleadingly called “home com-
posting”), anaerobic digestion, and incineration. Based on data from the literature,
the four processes were compared relative to the decomposition and processing of
seven commonly composted materials. When emphasis was placed on minimiza-
tion of carbon dioxide (with allowance made for the displacement of fossil fuel by
produced biofuel), anaerobic digestion was judged to be the most eco-friendly tech-
nology in cases where it could be applied. Surprisingly, composting under ambient
temperature conditions was judged to produce less CO
2
than conventional compost-
ing, for which temperatures are allowed to rise during the process. Incineration was
also judged to be more eco-friendly than composting, when the main attention is
paid to just CO
2
and energy. Although these findings may help to curb an overzeal-
ous view of composting, two points need to be considered: First, none of the alter-
native systems considered in the study—with the possible exception of composting
under ambient temperatures—was able to provide an amendment for rich topsoil.
And second, the study seems to have neglected problems due to very slow biodeg-
radation and an increased likelihood of anaerobic conditions if the temperature of
composting is not allowed to rise enough to stimulate convection of air, as well as
proliferation of the most effective microbial communities.
3.5.6
Composting and Sustainability in Greenhouse Gas
Emissions
Arguably, one of the most important aspects of the addition of lignocellulosic mate-
rials during composting of organic waste materials consists of the minimization of
greenhouse gas emissions (Yang et al.
2011
). In general, generation of gases such as
methane, hydrogen, and volatile organic compounds can be minimized by establish-
ing an initial C:N ratio greater than about 25, or preferably above 60 (Hubbe et al.
2010
). Application of sludge and/or inadequately matured compost to soil is to be
avoided, since anaerobic conditions in the soil can lead to uncontrolled production
of biogases (Huang et al.
2010
; Bonoli and Dall-Ara
2012
).
