On Energy Balance and Production Costs in Tubular and Flat Panel Photobioreactors

Reducing mixing in both flat panel and tubular photobioreactors can result in a positive net energy balance with state-of-the-art technology and Dutch weather conditions. In the tubular photobioreactor, the net energy balance becomes positive at velocities < 0.3 ms-1, at which point the biomass production cost is 3.2 €/kg dry weight. In flat panel reactors, this point is at an air supply rate < 0.25 vol vol-1 min-1, at which the biomass production cost is 2.39 €/kg dry weight. To achieve these values in flat panel reactors, cheap low pressure blowers must be used, which limits the panel height to a maximum of 0.5 m, and in tubular reactors the tubes must be hydraulically smooth. For tubular reactors, it is important to prevent the formation of wall growth in order to keep the tubes hydraulically smooth. This paper shows how current production costs and energy requirement could be decreased.Reducing mixing in both flat panel and tubular photobioreactors can result in a positive net energy balance with state-of-the-art technology and Dutch weather conditions. In the tubular photobioreactor, the net energy balance becomes positive at velocities < 0.3 ms-1, at which point the biomass production cost is 3.2 €/kg dry weight. In flat panel reactors, this point is at an air supply rate < 0.25 vol vol-1 min-1, at which the biomass production cost is 2.39 €/kg dry weight. To achieve these values in flat panel reactors, cheap low pressure blowers must be used, which limits the panel height to a maximum of 0.5 m, and in tubular reactors the tubes must be hydraulically smooth. For tubular reactors, it is important to prevent the formation of wall growth in order to keep the tubes hydraulically smooth. This paper shows how current production costs and energy requirement could be decreased

Effects of shear stress on the microalgae Chaetoceros muelleri

The effect of shear stress on the viability of Chaetoceros muelleri was studied using a combination of a rheometer and dedicated shearing devices. Different levels of shear stress were applied by varying the shear rates and the medium viscosities. It was possible to quantify the effect of shear stress over a wide range, whilst preserving laminar flow conditions through the use of a thickening agent. The threshold value at which the viability of algae was negatively influenced was between 1 and 1.3 Pa. Beyond the threshold value the viability decreased suddenly to values between 52 and 66%. The effect of shear stress was almost time independent compared to normal microalgae cultivation times. The main shear stress effect was obtained within 1 min, with a secondary effect of up to 8 min

Neochloris oleoabundans oil production in an outdoor tubular photobioreactor at pilot scale

Oil production was tested with Neochloris oleoabundans in a 6 m3, horizontal soft sleeve tubular reactor from 22 October to 7 November in Matalascañas, southern Spain. Biomass productivity during the nitrogen replete phase was 7.4 g dw m−2 day−1. Maximum lipid content in the biomass was 39% and average lipid productivity during the nitrogen depletion phase was 2.0 g m−2 day−1. Nitrogen depletion of the cultures was carried out in order to enhance fatty acid formation, using the inverse nitrogen quota in the biomass to predict the fatty acid content. TFA concentration at harvest was 14%DW, compared to a value of 17%, predicted by the inverse nitrogen quota. The overall feasibility of the horizontal tubular technology for microalgal oil production, including mixing energy expenditure, was evaluated

Development of industrial scale microalgae production

The work concerns large scale production of microalgae in photobioreactors and involves both technical-economic studies, productivity modeling and validation in industrial scale. Chapter 2 is an economical comparison of the 3 major microalgal production technologies: open raceway ponds, tubular photobioreactors and flat panel photobioreactors. The assessment of the operational performance of the three technologies was based on published productivity results from experimental photobioreactor and pilot plant studies. Effects of scale, site and various optimization options were included in a sensitivity analysis. Reducing auxiliar energy requirements for mixing with the two photobioreactor technologies was identified as a major challenge in the development of photobioreactor production of microalgal biomass, particularly for biofuel application. A standard hydraulic examination of auxiliary energy use with tubular- and flat panel photobioreactors was carried out in Chapter 3, resulting in general design recommendations. In chapter 4, a model of microalgal growth as a function of irradiance and temperature was developed in the laboratory and extended with an irradiation model for a specific flat panel reactor. The model was used to optimize the design of the flat panel photobioreactor and was validated in a study of a full-scale installation of the photobioreactor. Chapter 5 and 6 describes the design and development of operating techniques for a tubular photobioreactor for production of microalgal oil, based on recommendations in chapters 2 and 3. A laboratory protocol to compare the suitability for oil production in microalgal strains was developed and a laboratory method to determine the minimum biomass concentration in an outdoor tubular photobioreactor. On the basis of that, two strains, Neochloris oleoabundans and Chlorococcum littorale were selected for further work. A method, the inverse nitrogen quota, was developed to predict and steer microalgal oil production, in terms of total fatty acid content, based on assimilated nitrogen and biomass yield. The method is strains-specific and was completed for the two selected strains. A pilot plant with a 6 m3 tubular photobioreactor was designed and constructed in southern Spain and growth and oil production with the two selected microalgal strains  was  tested. The general discussion includes a resume of the achievements in chapters 2-6 and an analysis of the current stage of development and a future outlook of the microalgal R & D field.   It is noticed that well managed outdoor production trials may match laboratory results in terms of photosynthetic efficiency, but a gap remains between experimental and routine practice. Also, the cost of photobioreactor manufacturing should be reduced. Recent proliferation of the microalgal production sector and public-private development partnerships hold promise that the future may bring cost-competitive microalgal commodity products

Developing microalgal oil production for an outdoor photobioreactor

In this paper the preparations are described to develop a production of oil rich microalgal biomass under south European conditions. Ten microalgal species were compared in shake flasks in an incubator for potential for oil production. Potential oil production capacity was assayed as maximum total fatty acid (TFA) concentration and volumetric TFA productivity. TFA concentration ranged from 5 to 40% DW while TFA productivity rate ranged from 0 to 204 mg TFA L−1 day−1. To control the oil enrichment process in the outdoor microalgal batch culture, a quadratic equation was proposed, predicting the TFA concentration based on biomass inverse nitrogen quota. A concentrated substrate was developed to add to sea water, made from natural sea-salt and tap water.</p

Developing microalgal oil production for an outdoor photobioreactor

In this paper the preparations are described to develop a production of oil rich microalgal biomass under south European conditions. Ten microalgal species were compared in shake flasks in an incubator for potential for oil production. Potential oil production capacity was assayed as maximum total fatty acid (TFA) concentration and volumetric TFA productivity. TFA concentration ranged from 5 to 40% DW while TFA productivity rate ranged from 0 to 204 mg TFA L−1 day−1. To control the oil enrichment process in the outdoor microalgal batch culture, a quadratic equation was proposed, predicting the TFA concentration based on biomass inverse nitrogen quota. A concentrated substrate was developed to add to sea water, made from natural sea-salt and tap water