Agriculture Reference
In-Depth Information
phase (45-68 °C) that might last several days to several weeks basically depending
on the nature of the C compounds in the composted materials; (iii) second me-
sophilic phase takes place when mesophilic microorganisms recolonize the sub-
strate and lasts a couple of months, and (iv) the maturation or curing phase, which
might extend to several months and actually leads the never-ending maturation of
organic matter (Insam and de Bertoldi
2007
). The length of any composting phase
depends on the type of feedstock and on the process efficiency, which is controlled
by several factors such as moisture, aeration frequency and composting technol-
ogy (Ryckeboer et al.
2003
). Microbial communities present in the compost are
the result of dynamic complex interactions between the microorganisms and their
environment during each different composting phase. Starting from the first meso-
philic phase through the whole process time, the self-selection process of compost-
ing microbial communities take place by the continuous increasing of the autoch-
thones microorganism to the detriment of the exogenous one (Hermann and Shann
1997
). Incessantly and in a very short lapse of time, compost material conditions
change and the succession of bacterial communities follow it subsequently (Yama-
moto et al.
2009
). Zymogenous microorganism present in the raw materials rapidly
decomposes soluble and easily degradable substrates, which results in production of
organic acids that are responsible for decreasing pH to acidic values during the first
days of the composting process (Beffa et al.
1996
). Fungi and yeasts take advantage
of this environmental conditions until the ammonification process increases the pH
promoting bacterial metabolism. The mean generation time is shorter for bacteria
than for fungi; it gives a great advantage to bacteria, which could better adapt to the
rapidly changing environment than fungi. As a result, bacteria are responsible for
most of the initial decomposition and, therefore, for the compost heat production
(Ryckeboer et al.
2003
). As compost temperature increases, thermophilic micro-
organisms take over and the process passes to the second phase. The temperature
in the compost pile typically increases rapidly to 55-65 °C within 24-72 h of pile
formation: it is the composting active phase. In the active 'thermophilic' phase,
temperatures are enough high to kill pathogens, devitalize weed seeds and break
down phytotoxic substances.
Temperature is the major selective factor for microbial populations among pH,
moisture and C/N ratio (Rebollido et al.
2008
). High temperature during the com-
posting active phase of is a result of the microbial activity, which in the same time
affects the composition of microbial communities (Fuchs
2010
). The presence of
very specific flora dominated by actinobacteria is important for compost hygieni-
zation through the production of microbial antibiotics. During this phase, oxygen
must be replenished through passive or forced aeration, or turning the compost pile
(Cooperband
2002
). The high temperature in this stage accelerates the breakdown
of proteins, fats, and complex carbohydrates, e.g., cellulose and hemicelluloses, but
it is important that temperature should not exceed 70 °C as at this temperature only
few species resists and thus mass microbial recolonization is retarded (Insam and
de Bertoldi
2007
). After most of the degradation has taken place the temperature
decreases and the mesophilic phase starts. Mesophilic microorganisms reemerge in
the process and take over the last stage, which is the maturation or curing stage of
compost (Garcia-Prendes
2001
).
