The boundary for each system includes a flue gas pre-treatment phase which is com­mon for all three cultivation options. The flue gas pre-treatment phase involves the pumping requirement to blend CO2 with compressed air. The majority of emissions are Scope 2 electricity emissions, as shown in Fig. 14. The primary source of electricity in the chosen location is brown coal, and this is regarded as a high-emission intensive generator, thus the high emission factor of 1.22 CO2-e/kWh is used (NGER, 2008).

As seen in Fig. 14, Scope 2 emissions for the HTR and ELR (primarily due to electricity consumption by the airlifts) are significantly higher than the Scope 2 emissions for the RP (due to the low electricity consumption by the paddle wheel). The Scope 2 emissions for the HTR and ELR are 186,691.52 tonnes CO2-e/year and 166,916.41 tonnes CO2-e/year, respectively; whilst for the RP the emissions are only 10,564.07 tonnes CO2-e/year. Scope 1 emissions are due to the capturing efficiencies that exist in the cultivation system. For the HTR and ELP, the efficiency of absorption was set at 95% whilst for the RP the capturing efficiency was 90% [6]. Considering both emissions, it is clear that the RP is the best process option as it captures the highest amount of CO2-e (71,213.70 tonnes CO2-e/year). Note that in considering Scope 2 emissions, the audit considers emission produced in the gen­eration of electricity—an emission from another independent facility. Thus RP is the most “truly” environmentally friendly option, as it considers all possible GHG emissions due to the process. However, under the CPRS requirements, only Scope 1 emissions are considered. If the CPRS requirements are considered then the HTR and ELR capture the largest amount of CO — gases: 87,157.89 tonnes CO — — e/year. Thus if the algae cultivation process was part of an emission-intensive industry, the HTR and ELR would be the best option. However, it is important to consider eco­nomic factors such as the cost of electricity usage by the HTR and ELR systems.