The major processes investigated as dewatering alternatives in this study include single-stage dewatering using centrifugation, chamber filtration, vacuum filtration, suction filtration and a dual-stage process using flocculation followed by centrifuga­tion. In comparing the dewatering of different cultivation options, the raceway pond was approximately 15 times more expensive to dewater using a single-stage process than the reactor-style systems. This is primarily due to a combination of the significantly larger volume of the raceway pond and its much lower concentration of biomass, which requires the dewatering equipment to run for a greater length of time to process comparable amounts of dry biomass, leading to exorbitant energy costs. The costs of dewatering biomass from the raceway pond cultivation system using the four options investigated can be seen in Fig. 11. The capital costs neces­sary in the dewatering stage were found to be very low, whereas the contribution of running costs was found to be significantly larger. Of the alternatives shown in Fig. 11, the chamber and suction filtration options were found to be significantly cheaper than the single and dual-stage centrifuge systems, chiefly due to their lower electricity consumption.

However, the large consumption of electricity demanded by single-stage centrifugal recovery has other major environmental and economic impacts, which makes the dual-stage dewatering process the preferred option. As previously noted, the costs in dewatering biomass from the reactor-style cultivation systems were considerably less than the cost in dewatering raceway pond culture. In Fig. 12 filtration again appeared to be the cheapest dewatering option; however, there were a number of aforementioned hidden costs associated with fouling which were not included in the model. Significantly, as shown by the dot shaded bar in Fig. 12, the higher capital costs relative to running costs made dual-stage dewatering uncom­petitive at this smaller reactor volume and higher concentration of algae. Thus, due to its greater reliability and cost effectiveness, a single-stage centrifugal dewatering process would be the optimal production selection in the dewatering of reactor-style cultivation systems.