Development of alga-based photovoltaic devices: Electron transport from photosynthesis via the cell wall to electrodes

Project Information

EnergUP

Grant agreement ID: 892632

DOI

10.3030/892632

Project closed

EC signature date 2 March 2020

Start date 1 September 2020

End date 30 July 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 139 850,88

EU contribution

€ 139 850,88

Coordinated by

HUN-REN SZEGEDI BIOLOGIAI KUTATOKOZPONT
Hungary

Periodic Reporting for period 1 - EnergUP (Development of alga-based photovoltaic devices: Electron transport from photosynthesis via the cell wall to electrodes)

Reporting period: 2020-09-01 to 2022-08-31

Summary of the context and overall objectives of the project

Renewable energy sources are of high interest due to the shortage of the fossil energy sources and the present energy crisis. One possible way to obtain green energy is the use of photosynthetic organisms to directly produce electricity in various bio-photovoltaic devices (BPVs) or also called bio-photo electrochemical cells (BPECs).
Alga-based current production could be advantageous for several reasons, such as 1) being an environmental friendly way of sunlight energy conversion, and 2) the potential to decrease the energy consumption of alga biomass production by including self-sustainable bioreactors in the production system. The fact that these photosynthetic algae capture CO2 while produce O2, is a further positive aspect.
Although BPVs provide a promising alternative for producing energy, the efficiency of the available systems is inadequite for industrial use. The aim of the EnergUP project was to improve the alga-based, light-dependent current production by targeting various elements of the process.
Objectives of this Marie Skłodowska Curie Action (MSCA) have been to (1) enhance the electron flow from alga cells towards the electrodes of the BPVs by modofying internal electron transport processes, to (2) investigate the possible barrier effect of the wall surrounding the cells, and to (3) establish an alga cell immobilization method for a more efficient current production.
Overall, the rate of current production was sustantially increased by certain specific electron transport mutations in the green algae cells. On the other hand, it turned out that the presence of the cell wall has minor or no effect on the the current production. However, wild-type cells of various origin can have huge variation in the current producing capacity, most probably due to differences in their cellular metabolism. In the frame of the present project, various alga species have been screened using two newly developed bio-photovoltaic setups and strains with high current production capacity were identified.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We developed two novel bio-photovoltaic devices in the frame of this project.
(1) We designed a small-volume BPV device to carry out measurements on up to eight samples simultaneously. This setup enables varying the light intensity and to test its effect on current production. This device requires a small culture volume and it is designed to carry out short term measurements (up to one hour). The major application of this bio-photovoltaic setup is to screen algae strains and test the effects of various treatments for the identification of potential target points for increasing the rate of current production.
Using the small-volume BPV, we tested the effects of several treatments and conditions, including dark pre-treatments and light treatments at various intensities on the efficacy of current production. In parallel, various physiological parameters were also measured to obtain information on culture fitness before and after applying the current production protocol. These measurements helped us to pinpoint which conditions are best suited for producing high current and maintaining cell viability.
The above mentioned BPV device was applied to study various mutant strains affected in photosynthetic electron transport. Our data revealed that the redox state of the photosynthetic electron transport, namely the plastoquinone (PQ) pool has vital role in the current production by green algae. With specific mutations increasing the reduction level of the PQ-pool, we could increase 5 to 10 fold the maximal current production of the cells. Maximum current production was obtained at moderately high light intensities (in the range of 500 µmol photons m-2s-1, which is less than the maximum intensity of sunlight).
In addition, we investigated alga strains with eliminated or modified cell wall, but found no clear connection to the current production capacity. Thus, we concluded that the cell wall is not a limiting factor for the electron transfer feeding current production and current production cannot be enhanced by modifying it.
(2) We constructed a large-volume BPV device for liquid cell cultures for long-term measurements. This experimental setup enables measuring the light induced current production for several days and it does not require specific pretreatment of the cell culture, such as harvesting or concentrating. The obtained currents are outstanding, i.e. several times higher than reported so far, and this experimental system does not require expensive or toxic materials. This large-volume PBV device allows testing the previously preselected (using small-scale BPV device) strains in a larger volume, and less stressful conditions. It also provides a great opportunity for testing the effect of immobilisation on the current producing capacity of the cells.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Research of algae-based energy production is of high interest and matches one of the most important aims of Horizon Europe. The EnergUP Marie Skłodowska Curie Action (MSCA) project enabled the establishment of a new line of research on BPVs in the host institute; after the closing of the EnergUP project, the research will be continued by a postdoctoral fellow, Dr. Nia Petrova, who has obtained a three-year individual fellowship on this topic. In addition, thanks to the close connection with the University of Szeged, several university students had the opportunity to learn about this technique and participate in the construction and testing of the BPV devices. Two students were involved in research, one students has already defended his BSc thesis and another BSc thesis is in progress. The principles of the technique and the operation of the device have been also demonstrated to the broader audience at events, such as the European Researchers’ Nights and Fascination of Plant Day. These events provide a unique opportunity to promote the utilization of green energy and the scientific way of thinking in the society. Thus the obtained results advance not only the research field, but also enhance the awareness of society regarding algae-based BPVs.
During the project, we aimed at optimizing the measuring conditions not only for obtaining maximal current production of the alga cells but also to maintain their viability. During the construction of the devices and setting up the measuring protocols we were searching for low cost and low toxicity materials to ensure the sustainability in future industrial scale applications.

Close view of the small-volume BPV device. It can monitor up to eight samples simultaneously, illumi

Our specialised BPV device consists of a potentiostate controlled by a computer, a thermoregulated s

Photograph of the large-volume BPV device containing immobilised algae cells. The device allows test

For the experiments the cells were grown in liquid cultures

Our laboratory have acces to a broad range of algae species and various mutant strains possessing sp