2.2. Life cycle assessment
Fig. 1 depicts the system boundary for comparison of harvesting processes, as shown within the dotted line. The functional unit and basis of comparison for the harvesting processes was 1 kg dry weight of N. oleoabundans biomass. Only the algal harvesting processes are compared, while upstream (cultivation) and downstream (processing of algae fractions into fuels and chemicals, management of residual biomass) are assumed to be equivalent among all methods. With the exception of ferric sulfate, harvesting efficiencies are roughly equivalent (95–98%), and so the input stream of algae was assumed to be constant, thus allowing for the cultivation step to remain outside of the system boundary. All water is assumed to be recirculated, with limited spent material (such as used polyethylene filters) to waste management. Unflocculated algae are assumed to be recirculated in the ferric sulfate case.