# Microalgal Biomass Generation via Electroflotation: A Cost-Effective Dewaring Technology
## 7 Cost Analysis of Dewatering Approaches for Microalgal Biomass Production
\[\text{Cost B/cost A}=(\text{size B/size A}) \tag{6}\]  
where, cost A and B represent the unit operation purchase cost with capacity size A and B, and n is the corresponding equipment scaling factor in the range 10-100% of maximal capacity [100]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Type of Algal Biomass Production** & **Economic Performance** & **References** \\ \hline Open cultivation system for dilute solutions & \(\xi\) 0.5-2/kg of algae & [94] \\ \hline Closed cultivation system & \(\xi\) 0.1-0.6/kg of algae & [94] \\ \hline Single-step harvesting and dewatering using centrifugation process & AUD 12.10 & [15] \\ \hline Single-step harvesting and dewatering using sedimentation process & AUD 3.7–4.1 & [15] \\ \hline Single-step harvesting and dewatering using primary flotation USD 0.833 & AUD 1.86–2.08 & [15] \\ \hline Single-step harvesting and dewatering using secondary flotation & AUD 0.833 & [15] \\ \hline Secondary harvesting and dewatering using filtration & AUD 0.22–0.66 & [15] \\ \hline Secondary harvesting and dewatering using centrifugation & AUD 1.21 & [15] \\ \hline Dewatering in settling ponds & USD 5.8 & [97] \\ \hline Dewatering in membrane & USD 178 & [97] \\ \hline Dewatering in centrifuge & USD 478 & [97] \\ \hline Dewatering in dissolved air flotation & USD 29 & [97] \\ \hline Dewatering in filter press & USD 70 & [97] \\ \hline Dewatering in electrocoagulation & USD 157 & [97] \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Economic performances of various algal biomass production systems. In another study by [PERSON] (2013), the cost of harvesting _Chlorella_ species in a 10,000 L capacity, using distinct harvesting and dewatering methods were evaluated. It was estimated that 55 kWh/10 m\({}^{3}\) of total energy was consumed with Australian dollar (AUD 12.10) energy cost in single-step harvesting and dewatering centrifugation process. Whilst, the estimated total cost of primary harvesting and dewatering methods, such as sedimentation is $3.7-4.1, primary flotation is $1.86-2.08, and secondary flotation is $0.833. Moreover, the estimated total cost of secondary harvesting and dewatering approaches, such as filtration and centrifugation are $0.22-0.66 and $1.21, respectively [15]. It can be noted from the study that the flotation method of microalgal harvesting and dewatering to produce biomass leads to a reduction in total cost, compared to other dewatering approaches. Further, [PERSON] et al. (2016) recently evaluated the economics and process design for the algal biomass production in open pond systems via dewatering approaches, such as hollow fiber membrane, gravity settling and centrifugation, for downstream conversion to increase the solid biomass concentration up to 20 wt.%. In this study, the installation capital costs of the dewatering technology in the case of settling ponds, membrane, and centrifuges were $5.8, $178, and $478, respectively, per volume feed rate, $/(m\({}^{3}\)/day). Likewise, the installation capital cost of alternative dewatering approaches, such as DAF has been estimated as $29, whereas electrocoagulation and filter press were $157 and $70, respectively, per volume feed rate to $/(m\({}^{3}\)/day). Even though DAF method can lead to lower installation cost compared to other dewatering approaches, the high power demand and operational cost for flocculants such as chitosan, may eventually increase the total cost of the process. Thus, it has been identified that DAF and electrocoagulation can reduce the total cost of final algal biomass concentration to 20%, compared to other approaches and also eliminates the centrifugation process [97]. It is evident from these studies that flotation dewatering approach can be useful in reducing the total cost of the microalgal biomass production.