Environmental Engineering Reference
In-Depth Information
C
POLYMER
→ CO
2
+ CH
4
+ H
2
O + C
RESIDUE
+ C
BIOMASS
(3.2)
Aerobic bacteria have an oxygen-based metabolism from their cellular respiration
process and they use oxygen to oxidise substrates in order to obtain energy.
Oxygen is used by the organism in this aerobic biodegradation reaction (
Equation 3.1
),
which breaks down the polymer into small molecules and carbon dioxide. Four key
biological and chemical stages occur in anaerobic digestion (
Figure 3.4
). It starts irst
with the hydrolysis step where the chains of polymeric materials are broken down
into smaller constituent parts/monomers and the smaller molecules are dissolved in
the solution. The second step is acidogenesis, where the remaining components are
broken down by the acidogenic bacteria (fermentative). The third stage is acetogenesis,
where the simple molecules produced from the acidogenesis are further digested by
the acetogens to produce carbon dioxide, hydrogen and large amounts of acetic acid.
The fourth stage of this process is methanogenesis where all the intermediate products
are utilised and converted into methane, carbon dioxide and water. Biodegradation
of aromatic compounds is found to occur under anaerobic conditions. DO in the
seawater is signiicantly inluenced by biological and physical processes including:
fresh water inlux, photosynthesis, water mass transport and respiration [33].
POLYMER
Depolymerisation
Oligomers,
Dimers,
Monomers
Aerobic
Anaerobic
Microbial
Biomass, CO
2
,
H
2
O
Microbial
Biomass, CH
4
,
H
2
S, CO
2
, H
2
O
Figure 3.4
The two methods of aerobic and anaerobic biodegradation
