Environmental Engineering Reference
In-Depth Information
dewatered pig manure was analysed by Rafique et al. (2010). High
concentrations of lime (5%) showed maximum enhancement of gas yield
at 70
C. An increase of 78% biogas and 60% methane was observed.
8
4.4
Conclusion and future trends
A wide range of technologies are available for the pre-treatment of biogas
substrates, based on a variety of principles. When substrate composition
and pre-treatment technology are appropriately matched, the bioavailability
of the substrate increases. This can lead to an improved performance of
biogas reactors in terms of gas yield and degradation rate during anaerobic
digestion. The energy balance and costs must be considered. The energy
demand of pre-treatment depends on the technology used. In most cases,
pre-treatment methods with a low energy demand give smaller benefits to
the rate of degradation and corresponding biogas yield as compared with
pre-treatments with high energy input, but this is not always the case.
Higher gas yields result from the degradation of lignocellulose complexes
and increase in availability of recalcitrant substances. Many pre-treatment
technologies do not increase the biogas yield, but increase the degradation
rate. The energy demand of pre-treatment technology is important for a
number of reasons, including sustainability criteria as required by the EU
Renewable Energy Directive. A negative energy balance can also lead to an
uneconomical process. As high investment costs are needed in many cases, a
corresponding significant increase in gas yield is necessary to make the
process financially feasible.
Many principles of pre-treatment technology were and are developed for
other purposes, such as ethanol production from lignocellulosic feedstocks.
The influence of pre-treatment technologies on anaerobic digestion has been
investigated in recent years and there is still a huge demand for optimisation
of these technologies for the biogas industry. Ongoing research is especially
important to bring some technologies to a financially feasible level. The
investment costs for pre-treatment of recalcitrant substrates are high at the
moment due to high expenditure in process engineering. However, if these
costs are decreased to an affordable level, new substrates will be made
available for biogas production. In closing, it should be mentioned that pre-
treating all substrates with one technology is not realistic and pre-treatment
may not be financially viable or improve the energy balance for substrates
with high degradation rates.
4.5 References
Amon T, Amon B, Kryvoruchko V, Zollitsch W, Mayer K and Gruber L (2007)
'Biogas production from maize and dairy cattle manure - Influence of biomass
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