Environmental Engineering Reference
In-Depth Information
related to the added value of AD to biofuel chains in Colombia. Finally,
generalized conclusions are given and future trends outlined.
7.3
A framework for approaching the role of anaerobic
digestion within biomass chains
Resource cascading - defined as the sequential exploitation of the full
potential of a resource on its path towards equilibrium - is a strategy to
improve efficiency of materials use (Fraanje 1997; Sirkin and Ten Houten
1994). AD is a technology that can play an important role in increasing the
sustainability of biomass cascades by transforming different organic flows
into useful products, contributing to the closing of material cycles. Whereas,
as noted earlier, the flexibility of the technology can be regarded as its main
positive attribute, it is also its main challenge when its contribution towards
sustainability is to be assessed, given that biogas systems can take many
forms and the differences among possible systems make them complex to
study (Borjesson and Berglund 2006, 2007).
7.3.1 Typology of anaerobic digestion biomass cascades
Biomass systems can have many forms, the biomass follows different routes
during its production and utilization time, and the feasibility of a
multifunctional biomass system is defined by the main application of
biomass (Dornburg 2004).
The role of AD can be approached either from a multifunctional
perspective, a protagonist perspective or a contributive perspective. In the
multifunctional perspective, the role of AD is that of being part of a biomass
system comprising many chains and envisaged towards the maximization of
its environmental, social and economic outcomes transforming and reusing
most by-products following a circular metabolism approach. In the
protagonist case, restrictions are not imposed by existing transformative
production processes but, in this case, AD is the main process in the chain,
like in the case of energy crop cultivation for energy production. In the
contributive perspective, AD is incorporated within existing cascades, its
added value being defined as a function of the complementary features it can
establish with existing processes. These processes will influence both the
quantity and quality of the by-products and the possibilities for reuse of the
energy and digestate after the AD process. In this sense, the configuration of
the other applications producing and transforming the original biomass
imposes restrictions that limit the sustainability outcome of the entire system
and the specific contribution of AD to the chain (Fig. 7.2).
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