Comparison of continuous and day time only mixing on Tetraselmis suecica (Chlorophyta) in outdoor raceway ponds

Abstract

The mixing of microalgae bioreactors is important as it circulates cells in and out of the light zone and reduces boundary layers, benefiting photosynthesis and nutrient uptake. However, mixing is also a major economical factor, impacting on power consumption and operating costs, and it remains a barrier for those locations where no electrical supply is available. Combining solar panels with algae ponds can help to alleviate the power cost burden, but if solar panels are the sole source of generated electricity for a regional raceway pond system, the paddle wheels will only operate during day time. This study investigated the growth of halophilic green alga Tetraselmis suecica, in outdoor paddle wheel-driven open ponds under three different mixing regimes. The first experimental condition was a continuously mixed regime, while in the second and third conditions, the paddle wheels were stopped overnight and restarted 1 h after sunrise or 1 h before sunrise, respectively. Growth rate, biomass productivity and cell weight showed no statistically significant difference during the period when the culture was growing under optimal environmental conditions. Chlorophyll fluorescence measurements of photosystem II maximum quantum yield in the light (F v ′/F m ′) over a 24-h period found no significant differences between cultures, further suggesting that under favourable conditions ceasing mixing overnight may have no undesirable impact on Tetraselmis health or productivity. These findings imply a potential 37 % power saving and a 33 % reduction in energy-associated costs. During a heat stress event, Tetraselmis was negatively impacted in all ponds to the same degree; however, the continuously mixed pond recovered faster than ponds that were not mixed overnight.

CULTIVATION OF Chlorella vulgaris IN MEDIUM SUPPLEMENTED WITH DESALINATION CONCENTRATE GROWN IN A PILOT-SCALE OPEN RACEWAY

“…The cultures grown in BBM control showed a biomass concentration of around 275 mg L -1 , while for BBM + DC the result was 220 mg L -1 . Actually, the outdoor cultivation of C. vulgaris resulted in an average biomass concentration of 250 mg L -1 and the data reported herein for the biomass concentration of the outdoor culture are comparable with results obtained by Cuello et al (2015), which ranged from 263 to 403 mg L -1 using Tetraselmis suecica (Chlorophyta) in open raceway ponds.…”

Cost-Effective and Efficient Production of Carbohydrates from an Alkalihalophilic Leptolyngbya sp. in a Photobioreactor with Periodical Mixing

“…To solve this problem, floating PBRs aimed at using free wave energy and hydraulic power as the mixing energy were developed, but their production was unstable since the wave energy is intermittent, causing a high level of dissolved oxygen accumulation and low biomass productivity . Recently, ceasing nighttime aeration and mixing have been proposed to reduce the mixing cost, − but these studies did not evaluate the impact of intermittent mixing on the cultures in daytime, and it is not sure whether this mixing mode can support good growth of microalgae.…”

How do microalgae perceive light in a high-rate pond? Towards more realistic Lagrangian experiments

“…The benefit of mixing has been extensively discussed in the literature to: (i) prevent cell sedimentation, (ii) ensure nutrient homogeneity, and (iii) facilitate CO 2 transfer, while removing excess oxygen to limit photorespiration and oxidative stress [ 7 ]. Moreover, stirring also directly impacts light reception at the cell scale in a mixed turbid environment [ 8 ].…”