A two-stage solar photobioreactor for cultivation of microalgae based on solar concentrators

Abstract

A novel two-stage experimental photobioreactor (PBR) with a total volume of 450 L and based uniquely on solar concentrators-linear Fresnel lenses-has been constructed and tested. Daily courses of irradiance, and also its distribution inside cultivation tubes, were studied in two unit types. The supra-high irradiance units in the 'roof' achieved a maximum summer value above 6 mmol photon m −2 s −1 , while irradiance in the vertical-facade units was lower than 'ambient'. In model cultivations, cultures of the cyanobacterium Arthrospira platensis were cultivated at much higher solar irradiances than those usually recorded outdoors in summer, indicating that this organism is resilient to high-irradiance (photoinhibition). Starting from a biomass density of 0.5 g L −1 at optimum temperature, the cultures grew exponentially. A two-stage cultivation process of the green microalga Haematococcus pluvialis was investigated with respect to correlations between photochemical activities and astaxanthin production. The culture was first grown in low-irradiance units, and then exposed to supra-high irradiance when the rate of astaxanthin production was 30-50% higher than in the culture exposed to 'ambient' irradiance. Within 4 days, the astaxanthin content reached 3% of dry weight, whereas under ambient irradiance the astaxanthin content was 25% lower.

Placing microalgae on the biofuels priority list: a review of the technological challenges

“…Flat plate PBRs may be partitioned into a series of internal channels (alveoli) to provide structural rigidity and to enable efficient flow of the culture medium. More novel methods of PBR illumination include solar collection devices such as light guides and Fresnel lenses (Zijffers et al 2008;Masojidek et al 2009) and energy-efficient, monochromatic light-emitting diodes (Gordon & Polle 2007;Wang et al 2007). Currently, the relatively high construction and operating costs and complexity of operation of closed PBRs limit the number of large-scale commercial systems operating globally to high-value production runs.…”

Influencing of Amino Acid Composition of Green Freshwater Algae and Cyanobacterium by Methods of Cultivation

“…The micro-algal species C. kessleri, S. quadricauda, and S. platensis were autotrophically cultivated in a solar PBR described in the study [18]. BG11 culture medium [19] was used for the cultivation of micro-algae.…”

Monitoring of Microalgal Processes

“…Monitoring light intensity inside a PBR is usually only performed for research purposes or to construct light penetration models [43,58,[60][61][62][63]. An example for [44] with a light penetration model based on the Lambert-Beer law with an experimentally determined extinction coefficient and PAR measured outside the PBR [48].…”

“…In the aforementioned example [44], the compounded effect of light absorption and scattering on light extinction in a microalgal suspension is accounted for by experimentally determining the extinction coefficient for the algal culture samples taken from the PBR at various biomass concentrations (4-40 g DW L −1 ), which is then expressed by a function including the thickness of the algal culture layer above the "measured" point and the current cell concentration in the culture. PFD is usually measured for the PAR range by a flat cosine (2π) [58,61,62,[64][65][66][67][68][69] or a fiber-optic spherical (4π) [61,62,70] quantum sensor, by a PAR dosimeter [71] or pyranometer [69]. Measurements with a spherical sensor (4π spatial angle; an example: US-SQS/L by Walz GmbH) measure radiation coming from all directions weighted equally and are suitable in situations where the amount of scattered light is very high, as in microalgal suspensions when evaluating exposure of an individual cell to light.…”