Environmental Engineering Reference
In-Depth Information
biomass arrangements, giving an added value to residues in a rational way.
The resulting methane can be directly used or can be upgraded to a higher
quality gas suitable as vehicular fuel or for injection to the gas grid.
Alternatively, it can be converted into electricity and heat in a combined
heat and power (CHP) unit, or to heat or steam solely (IEA 2001, IEA 2005,
Lindeboom et al. 2011). In this way, AD allows for closing energy, water
and nutrient cycles at different scales, thereby resembling the 'no-waste
policy' intrinsic to nature.
7.2
The role of anaerobic digestion in biomass chains
Anaerobic digestion as a technology has been around for a long time. Small-
scale decentralized technologies such as the Chinese dome digester and the
Indian floating dome are centuries old. In the industrialized world, AD has
been majorly employed to treat wastewater and wet residues. Major
technological applications of AD have been the treatment of sewage-derived
sludges and, since the 1980s, the treatment of industrial wastewater (van
Lier 2008; van Lier and Lubberding 2002). Other applications of the
technology are the stabilization of (semi) solid wastes and slurries, crop
residues and municipal solid waste (Mata-Alvarez et al. 2000).
The possible energy contribution from crops and manure for producing
biogas was recognized in the 1980s. However, economically, electricity from
other sources was still cheaper and this kept the concept from penetrating
the market (Baier and Delavy 2005; DeBruyn and Don 2004). Recently, the
potential of AD has been rediscovered as having a central role in delivering
higher outputs from finite biomass resources, its final use being mainly
energy applications. In the chemical industry, methane also plays a role,
being a raw material for the manufacturing of methanol (CH 3 OH),
formaldehyde (CH 2 O), nitromethane (CH 3 NO 2 ), chloroform (CH 3 Cl),
carbon tetrachloride (CCl 4 ) and some freons. Furthermore, a cheap and
efficient way of turning methane into liquid chemicals and fuels could free
the chemical industry from its dependence on fossil fuels; this path is,
however, still under development (e.g. Lindeboom et al. 2012).
Over recent years, and as the result of specific governmental incentives,
the construction of bioreactors for biogas production having energy crops as
(co) substrate has become a reality in countries like Germany, Austria and
Sweden. In Germany, for example, it is estimated that in 1997 only 450 AD
plants were functioning, while more than 6000 were producing biogas in
2010 (IEA 2011). There are more than 25 000 working biogas plants in
China and it is estimated that more than 30 million biogas plants are
working around the world (van Lier et al. 2011).
Conditions of residue availability, environmental nuisances associated
with them, the demands from the climate change agenda and the world
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