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these were partly internalised for some biomass flows (e.g. used cooking oil contributed
significantly to biofuel production in the UK) they were not internalised for others (e.g.
large quantities of wood are imported from Scandinavia). Yet SKIN is not designed to
cover negative network externalities. Secondly, the team had a strong interest in policy
implementation and the effect of different policy instruments on the different process
innovations. This resulted in the conceptual idea of a network (of nodes and ties) that is
differentially influenced by the implementation of government policies. Two policy in-
struments were selected: facilitation of recyclate use (that is source-segregated organic
waste that has been recycled and ceased to be considered waste by the regulator) and
renewable energy policy.
3TheToyModl
In specifying the agent-based model we followed ideas presented in [7]. In the toy
model we considered only a limited number of actors relevant for the growth of the
bio-based economy. We implemented food processors, composters, aerobic digesters,
and biofuel refineries. In each time step, the following happens: (i) the waste suppliers,
(ii) food processors supply any existing waste contracts that they have, (iii) new waste
contracts are made. The exchange of biomass by necessity conforms to a constant mate-
rial and energy balance. Material flow analyses are the stronghold of industrial ecology
and they were integrated in the model by specifying in-flows and out-flows for each
type of bio-processor, which allowed tracking the material energetic footprint of the
biomass traded.
The maintenance of constant material and energy balance allows tracking of certain
ecological effects of network evolution, including carbon emissions. Furthermore, a
decision was made that proved to be crucial for the further development of the ABM:
agents would exchange materials according to prices. While information on current
prices for waste and primary resources was easy to obtain, prices are influenced by
factors external to the system. The prices, which translate into costs or revenues for
companies are matched by two cost components constituting the firm agent; on-going
operational costs and start-up costs, modelled as a loan repayable with interest over
time. Using this setup, the financial position of each company is updated each period
by the income generated from energy production and any gate fees receivable, less the
cost of materials, operating costs and realisation of start-up costs. This position must
remain positive, if not the company goes bankrupt and is eliminated from the model.
The rules of the agent-based model thus read:
1. The food processors produce waste.
2. Food processors supply any existing waste contracts that they have. Finances are
updated accordingly.
3. New waste contracts are made and finances updated accordingly.
4. Food processors update the price that they pay to get rid of waste: if they have
managed to get rid of all their waste, then they decrease the price they pay, if they
have waste left, then they increase the price they pay.
5. Finances of food processors are updated - they receive money for the products that
they develop and pay money to get rid of all remaining waste to landfill.
