The flexibility of a treatment system refers to its ability to manage a varying tonnage and composition of waste as well as its potential availability i.e. availability of the system to process waste.
Tonnages may vary because of a range of upstream situations e.g. recycling activity, demographic changes and/or seasonal effects. Facility capacities should take into account the possible maximum tonnages that may need to be processed and flexibility in the tonnage throughput may be an important issue for the Authority. In this case, options that allow flexibility in managing a varying tonnage of waste should be awarded higher scores than those that do not.
All thermal treatment systems will be constrained by the Calorific Value (CV) of the incoming waste. Authorities should be aware of the impact of upstream recycling process on the CV of the residual waste as well as the uncertainty of future changes in waste composition that will impact such processes. A typical thermal system designed for treating as received waste will be able to manage waste within a CV range of 7 to 12 MJ/Kg. Currently residual waste (after recycling) will have a CV of about 10 MJ/kg.
Where the residual waste is subject to biological and thermal treatment the incoming waste composition and the nature of the pre-processing technology will have an impact on the relative tonnages of the organic and fuel fractions.
The divisibility of the facility capacity also needs to be considered. A modular technology may not provide the same degree of choice regarding capacity as a technology that can be built for any specified capacity. However, the ability to add on an additional module after the initial construction may be considered an advantage. Where a technology can be economically divided into two or more modules the modules may be located at different sites. If so, such a technology may score higher on flexibility although deliverability may be lower - due to the need to secure more sites and more planning consents.