Environmental Engineering Reference
In-Depth Information
7.5
External conditions influencing the design of an AD facility.
7.5 can effectively result in net gains in useful energy carriers (e.g. methane),
to the specific biomass chain under study.
Given that boundary conditions influence the specific technological
configuration of the AD unit as well as the potential to reuse the AD
products, the overall contribution of ADwithin a cascade will result from fine
tuning of the AD process to the specific demands coming from the context
(Fig. 7.5). Boundary conditions of relevance are climate, transport distances
of source biomass, environmental regulations and socio-economic restric-
tions. Main input material characteristics of relevance are the total solids
(TS) and their organic component as defined by the volatile solids (VS) and/
or chemical oxygen demand (COD), biodegradability properties in extent
and rate as given by the biochemical methane potential (BMP) and hydrolysis
rate (k
h
), respectively, pH and nutrient content. Obviously, the available
amount per unit time or flow, Q, largely determines the specific design. On the
other hand, the products of the AD process need to be adapted to the
receptive environment according to the demands for energy and digestate.
Energy can be demanded in the form of raw biogas (e.g. for cooking
purposes) or in the form of upgraded methane gas for vehicle use or gas grid
injection. Furthermore, energy in methane can also be delivered in the form
of heat and/or electricity. Finally, decisions regarding digestate post-
treatment need to be adapted to the possibilities in the surrounding context
for closing material cycles in terms of carbon, nutrients and water.
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