# Microalgal Biomass Generation via Electroflotation: A Cost-Effective Dewaring Technology
## 5 Electroflotation-Facilitated Dewatering for Microalgal Biomass Generation
### Factors Affecting the Performance of Electroflotation-Based Microalgal Dewatering Process
#### 5.2.3 Electrolyte and/or Microalgal Broth Conditions  
The electrolyte and/or microalgal broth conditions may entail salinity or conductivity, pH, and initial concentration of the microalgae. For a given current density, a more conductive system generally implies shorter electrolysis time, thus lesser energy consumption in order to achieve similar microalgae dewatering performance. These were proven by [PERSON] et al. (2011), after conducting laboratory-scale batch experiments with freshwater (_Chlorella vulgaris_) and marine (_Phaeodactylum tricornutum_) microalgae. The experimental conditions were the same in both cases (anode = Al; cathode = IrO\({}_{2}\)/TiO\({}_{2}\); inter-electrode distance = 4.4 cm; pH 4) (Table 6) [73]. For a shorter electrolysis time of 20 min with 10 repetitions, the lesser energy consumption was required to reach comparable dewatering efficiency of 85% using marine macroalgae (conductivity = 43 mS/cm); and freshwater system was 30 min at 88% dewatering efficiency (conductivity of 0.8 mS/cm) [73]. Similarly, by supplementing the growth medium of certain microalgae species like _Scenedesmus obliquus_ with seawater (10%), extremely high dewatering performance, greater than 95%, (control sample < 60%) was observed. The adscititious sea salts induced self-destabilization of microalgal cells, which caused autofloculation and led to faster dewatering time [17]. However, at high current densities, the potential problem of hypochlorite formation (NaCIO; bleach) can occur, especially in systems with high NaCl concentrations as shown by [PERSON] et al. (2011) [73] and [PERSON] et al. (2010) [87].  
The pH of the microalgal broth can influence the electroflotation performance via alteration of the sizes of the generated bubbles [67] and/or the quantity of the evolved gases [76]. The pH is also known to affect the speciation of metal hydroxides, especially of Al, in solution [72; 88], which may induce coagulation and result in more efficient dewatering of the microalgal broth. For instance, decrease of initial solution pH led to enhancement in dewatering efficiency of the electroflotation system [73]. [PERSON] et al. (2010) also reported that at low to neutral initial solution pH (4-7), cell density of algae was effectively removed [87]. The performance, however, worsened with an initial pH increase (7-10). A contradictory result was reported by [PERSON] et al. (2012), who by employing a continuous process, rather found that microalgae removal efficiency, increased at a higher pH of 8 within the first 5 min of operation [79]. Afterwards, it reverted to the observations as demonstrated by the previous authors. They opened that at lower pH, floc formation intensified, leading to heavier flocs, which may have been too heavy for the microbubbles to float. Thus, instead of floating, more algal flocs rather sank and were recirculated to the cultivation tank reducing cell recovery.  
The initial concentrations of the microalgae broth can affect the frequency of inter bubble-microalgae contacts, which is also key to high performance of an electroflotation system. For a transition from batch system to the continuous alternative, [PERSON] et al. (2002) identified that the ratio of the current density (A/dm\({}^{3}\)) and microalgal loading (mg/m\({}^{3}\)h) was a useful operating and scale-up parameter to achieve high microalgae removal efficiency with minimal anode dissolution. This ratio was eventually identified as the charge dose was found to be 250 coulombs, that are required to remove a unit mass of chlorophyll a [78]. Additionally, [PERSON] et al. (2012) successfully designed a continuous system that linked the microalgaecultivation and electroflotation harvesting processes in which residual broth, post-microalgal harvesting, was recirculated and reused for microalgae cultivation [80]. This system allowed for a continuous and efficient concentration of microalgae cells as well as drove down costs.