Dependency of Microalgal Production on Biomass and the Relationship to Yield and Bioreactor Scale-up for Biofuels: a Statistical Analysis of 60+ Years of Algal Bioreactor Data

Abstract

Since the 1950s, research has been undertaken to promote algal oil as a sustainable alternative to fossil fuels. This paper statistically analyzed 317 studies of algal bioreactors to determine the interdependence of biological and physical factors affecting oil yield. Algal growth rates in bioreactors often (71 %) exceeded maximal growth rates cited in the literature, and biomass was generally higher than maximum values cited for laboratory cultures. Growth rate decreased with increasing biomass, and biomass, not growth, dominated production rate, which was higher in closed than in open bioreactors. Except for Chlorella cultured in horizontal tubular reactors, there were no statistical differences in algal production when grown in different types of reactors. Production decreased with increasing bioreactor volume, but increased with surface to volume ratio of the bioreactor. In contrast, estimated oil yields increased with bioreactor volume. Four groups of bioreactors were identified based on their oil yields and biomass production: (1) higher yields with lower production were limited to open systems with volumes ≥10 4 L; (2) higher yields with higher production were almost exclusively closed bioreactors from 10 2 to 10 3 L; (3) lower yields with higher production were closed systems from 3 to 99 L; and (4) lower yields with lower production were a mix of open and closed systems with diverse volumes. Based on these groups, it is suggested that intermediate volume bioreactors with higher surface to volume ratios could give higher yields and production rates and would avoid the environmental and scale-up problems inherent in large bioreactors currently being used commercially to culture microalgae.

Nannochloropsis gaditana grown outdoors in annular photobioreactors: Operation strategies

“…Nonetheless, biomass productivity values were low compared to other works [5,28,43,44], representing only 16-30% of the maximum productivity found in the above-mentioned studies. This may be a result of several factors that influence productivity and are related with the design of the PBR's; the bottleneck effect [45]; inefficient mixing [46]; temperature; and or irradiation levels [15]. In fact, differences in the irradiation levels could also contribute to explain the higher biomass productivity found in the second experimental set.…”

Contribution of Anaerobic Digestion Coupled with Algal System towards Zero Waste

“…What really makes the use of algae a thriving technology is that these microorganisms have the potential to efficiently remove nutrients from wastewater and provide high-value biomass energy with low cost. Enclosed bioreactors and open ponds are the two predominant methods for microalgal cultivation (Figure 2) [53]. Interestingly, closed photoreactors provide sterility and allow for much greater control over culture parameters such as light intensity, CO 2 , nutrient levels and temperature, and thus higher biomass productivities can be reached [11].…”

Bio-production of gaseous alkenes: ethylene, isoprene, isobutene

“…A variety of organisms have been used for bio-production of gaseous alkenes [ 74 – 76 ], but many display issues due to inefficient pathways or when scaling up to industrial levels. One organism is not ideal for producing the many petrochemicals needed from varying feedstocks, but there are a suite of characteristics that should be intrinsic to any organism under consideration for use as a cell factory.…”