## 2 Materials and Methods
### Growth Assessment  
Samples (50 mL) were taken on a daily basis and microscopic observation was performed in order to monitor contaminations, which were never above 2% of cell counts.  
Optical density (OD) and dry weight (DW) were measured to follow microalgal growth. OD was performed at 540 nm using a spectrophotometer (4251/50, Zuzi, Spain). DW was determined using a 0.7 \(\upmu\)m glass fiber filter (VWR, Portugal) in a moisture analyzer (MA 50.R, RADWAG, Poland). In order to neutralize the salt weight, the culture was washed with an equivalent volume of ammonium formate solution at 35 g L\({}^{-1}\).  
Figure 3: Structural details of the pilot raceways installed in Allmicroalgae facilities. (**a**) Three baffles in the circular endings of the ponds were installed in both standard and modified raceways. Single eight-flat-bladed paddlewheel was installed right after one of the semicircular ends of one of the channels; (**b**) standard raceway paddlewheel with 0.870 m width and (**c**) modified raceway with 0.475 m.  
Areal biomass productivity, \(P\) (g L\({}^{-1}\) d\({}^{-1}\)), was determined by Equation (1):  
\[P\big{(}gm^{2}d^{-1}\big{)}=\frac{(X_{2}-X_{1})V}{(t_{2}-t_{1})A} \tag{1}\]  
where \(X_{2}\) (g L\({}^{-1}\)) and \(X_{1}\) (g L\({}^{-1}\)) represented the DW times \(t_{1}\) (s) and \(t_{2}\) (s), respectively, \(V\) (m\({}^{3}\)) was the raceway volume and \(A\) (m\({}^{2}\)) the ground area occupied by the bioreactor.  
Specific growth rate, \(\mu\) (d\({}^{-1}\)), was expressed as a ratio between the difference final and initial logarithmic biomass concentrations (\(X_{2}\) and \(X_{1}\), respectively) and the associated time range (\(t_{2}\) and \(t_{1}\), respectively), as seen in Equation (2).  
\[u=\frac{ln(X_{2})-ln(X_{1})}{t_{2}-t_{1}} \tag{2}\]  
Global productivity and growth rate refer to the whole assay (13 days). Maximum productivity and growth rate were calculated based on the highest values obtained daily.  
The lipid production/energy consumption ratio (\(L\)/\(kW\)) was calculated through the following equation:  
\[L/kW\ =\ \frac{P\ \times\ L\ \times\ A\times 13}{p} \tag{3}\]  
where \(L\) (%) was the lipid content, 13 days the total extension of the assay, and \(p\) the power consumption.  
The photosynthetic efficiency (PE) was determined by equation 4, as previously described by Quelhas et al. (2019) Quelhas et al. (2019).  
\[PE=\frac{(X_{2}-X_{1})\times V\times HHV}{\sum_{t1}^{t2}rad\times A\times t} \tag{4}\]  
where rad (kW m\({}^{-2}\)) was the radiation that reaches the reactor, \(t\) (s) was the time between solar radiation measurement and HHV was the higher heating value, calculated based on elemental (CHN) analysis by Equation (5), as described by Callejon-Ferre et al. (2019):  
\[HHV\big{(}kJg^{-1}\big{)}=-3.393+0.507C-0.341H+0.067N \tag{5}\]  
A spectrophotometric analysis (Genessys 10S UV-VIS spectrophotometer (Thermo Scientific, Massachusetts, USA)) was used to measure the nitrate concentration of the medium. Samples were centrifuged for 10 min at 2000 g (MiniStar Silverline, VWR, Portugal). The OD of the sample was calculated from the difference at 220 nm and twice the value at 275 nm and compared with a calibration curve with sodium nitrate (Stein