A Comparison of Nannochloropsis salina Growth Performance in Two Outdoor Pond Designs: Conventional Raceways versus the ARID Pond with Superior Temperature Management

Table 1

ARID pond and conventional raceway characteristics.

	Conventional Raceways	ARID Pond
Volume	780 L (each)	7500 L
Surface area	3 m^2	50 m^2
Surface area: volume ratio	1 : 260	1 : 150
Culture depth	25.4 cm	Basin 1: up to 15 cm; Basin 2: 20 cm; Canal (day): 60 cm; Canal (night): 150 cm
Mixing	Paddle wheel rotating at 6 rpm	Gravity driven flow from top basin to canal. Aeration at night
Current velocity	0.25 m s^−1	0.003 m s^−1
Reynolds number*	26906	407
Evaporation	Corrected daily before sampling	Corrected every 2-3 days to maintain salinity at 35 ppt
Temperature management	Covered at dusk, uncovered in morning.	Storage of culture in canal at night, circulated in basins during the day

*Assumed rectangular open-channel flow, with the characteristic length defined as the cross-sectional area divided by its wetted perimeter. For the conventional raceways, the cross-section height was taken as the culture depth (0.25 m) and its width as 0.53 m. For the ARID pond, the average culture depth (0.175 m) in the shallow basins was taken for the cross-sectional area height and 5 m for the channel width, estimated with kinematic viscosity of saltwater at 35 ppt and 15°C, 1.205e-6 m² s⁻¹.