Algae

Development of a land-based photobioreactor for marine seaweed and its integration into agricaltural operations

Co-funded by: Fachagentur Nachwachsende Rohstoffe e.V. (FNR)

Project duration: 07/2014 to 08/2017

Project management: Prof. Dr.-Ing. Eckhard Kraft

Problemstellung

„Die Mobilisierung großer Mengen fossiler Brennstoffe im Zuge der globalen Industrialisierung hat in den vergangenen Jahrzehnten zu einer Zunahme der atmosphärischen CO2-Konzentration und in Folge zu einem sich weltweit abzeichnendem Klimawandel geführt. Eine beherzte Reduktion der CO2-Emissionen ist demnach eine der wichtigsten ökologischen Prioritäten der kommenden Jahrzehnte. In diesem Zusammenhang werden große Hoffnungen auf eine Umstellung von fossilen auf regenerative Energieträger gesetzt, da letztere klimaneutral produziert und genutzt werden können. Nachdem die nachwachsenden Energierohstoffe der ersten Generation jedoch wegen erheblicher Flächennutzungskonflikte in die Kritik geraten sind, wird zurzeit intensiv nach ressourceneffizienteren Rohstoffen geforscht. Diesbezüglich erscheinen Mikro- und Makroalgen besonders vielversprechend, da sie gegenüber terrestrischen Pflanzen hochproduktiv sind und auch auf unwirtlichen bzw. zur Nahrungsmittelproduktion ungeeigneten Flächen gezüchtet werden können. Um weitere Erkenntnisse zu den Eigenschaften von Makroalgen als Energieträger zu gewinnen wird an der BU Weimar eine meerwasserunabhängige marine Makroalgenanlage zur Energieproduktion konzipiert.“

Project objective

Aiming at the development of a sustainable strategy for a resource-efficient production of renewables, a macroalgae cultivation plant is to be introduced and implemented on an agricultural biogas plant. By thriving on waste materials as nutrient and carbon supply, macroalgae reduce the overall environmental impact of the biogas plant and increase its economic potential.

Core elements of the project are:

  • the investigation of optimal system parameters for macroalgae cultivation in closed systems,
  •  the development of a seawater-independent, land-based macroalgae cultivation plant,
  • the design of a cultivation process, sustainable both in an energetic and financial perspective,
  • the implementation of a user-friendly cultivation system.

Eventually, the overall sustainability of the concept is to be assessed using balancing methods focussing on environmental and financial issues.

Project results

Starting with an investigation on the methane production potentials, lab-scale experiments using different algae to inoculum ratios demonstrated that macroalgae are not detrimental to an anaerobic process. Instead, they reached promising results lying between 139 and 518 NL CH4/kg oTR. The red algae Palmaria palmata achieved the highest methane production, even lying within the vicinity of the yields achievable with maize (518 NL compared to 570 NL CH4/kg oTR).

Based on literature data and lab-scale experiments on growth enhancing parameters, a prototypal cultivation plant has been built with a capacity of 3.6 m3. The fully automated plant is equipped with sensors continuously measuring water pressure and flow to monitor hydraulics in the recirculation system. Feedback control triggers the flue gas (e.g. carbon dioxide) supply to the reactors using the actual pH-values of the cultivation medium. Consecutive cultivation experiments with selected macroalgae species demonstrated the overall functionality of the cultivation system. However, acid-forming flue gas components made the pH-value of the cultivation medium drop to algae damaging levels within days. The flue gas supply thereby had little effect on the carbon limitation of the algae and thus cultivation experiments had to be conducted without a supplementary carbon supply. The achieved daily growth rates with Ulva spp. (1 - 7%) remained behind the expected growth rates documented in literature - suggesting that unknown factors are limiting growth. In order to increase the productivity of the cultivation plant, further research needs to focus on optimizing the nutrient and light supply.

Balancing the overall concept of cultivating macroalgae as a renewable energy source, demonstrated that it is neither sustainable in an energetic, nor in a financial way. However, considering current market prices, selling it as a product, for instance as food, would result in a plus of 32€ per kg of cultivated macroalgae.