1.7.1 Cultivation Economics

The economic model, as shown in Fig. 9, identified the raceway pond as the cheap­est production system ($2.77/kg) followed by the HTR ($9.91/kg). The ELR was the most expensive option ($12.98). The greater complexity of the reactor-style systems was found to require a much greater level of FCI, $2.7 billion for the HTR system and $3.6 billion for the ELR system compared with only $0.73 billion for the raceway ponds. This FCI was represented in annual cost terms as the deprecia­tion of the cultivation system, expressed in Fig. 9, by the black equipment cost por­tion of the graph. Figure 9 shows these higher equipment costs are the major contributors to the greater overall production cost. Furthermore, the magnitude of FCI required to build the reactor-style systems makes investment in these alterna­tives unlikely, at least on such a vast scale.

The running cost of each cultivation system is represented by the grey segment in Fig. 9 and is examined in greater detail in Fig. 10, which divides the costs into specific components. Notably, the major contributors to the annual running costs shown in Fig. 10 were found to vary greatly between the raceway pond and the reactor-style systems. Major contributors to the annual running costs of the raceway

Raceway Pond HTR ELR

E Electricity H Culture Medium H Wastewater Treatment

□ Maintenance DD Other Expenses

Fig. 10 Breakdown of annual running costs for different cultivation systems pond were found to be the culture medium and the wastewater treatment, while in the reactor-style systems’ electricity consumption and maintenance costs were the great­est contributors to running costs. The larger volume of fluid processed in the raceway pond system, due to its lower volumetric productivity, led to greater culture medium and wastewater treatment costs. In contrast, the larger maintenance costs of the HTR and ELR systems resulted from the greater complexity of the system operation.

The considerably larger electricity consumption of the reactor-style systems could be attributed to the use of an airlift pump to mix the culture, which used significantly larger amounts of energy to operate than the simple paddle wheel used

H Capital Costs □ Electricity Costs □ Flocculant Cost

Fig. 11 Biomass dewatering costs for raceway pond (RP) in the raceway pond system. Despite the lower production costs of the raceway pond system, it is necessary to account for the risk of additional costs resulting from con­tamination of the algal culture. This risk is a significant drawback in the use of raceway ponds for cultivation compared to the use of reactor-style systems. Contamination results from a lack of control and exposure to the external environ­ment, and can lead to lower growth rates of biomass unsuitable for downstream.