Within IDEA, the potential of side-stream use in algae-value chains is being investigated. In this context, several pilot scale algae growth and harvesting trials were performed during the past months. More precisely, an on-site continuous harvesting of a mixed algae culture grown on low carbon process water in an open pond was operated for 70 days to evaluate the robustness and reliability of the membrane based MAF technology. The permeate generated in the trial was subsequently used to cultivate Chloromonas in closed bioreactors. Further, Chlorella was grown in a 9000 L photobioreactor that was fed with recycled CO2. Again, the membrane based MAF technology was used to continuously dewater the Chlorella biomass and recirculate the medium. Finally, Scenedesmus is being grown on pre-treated digestate as source of nutrients at pilot scale. This newsletter provides more information on these trials, along with some other project updates.
Long-term continuous harvesting of algae biomass from an open pond that is treating N-containing low carbon process water
Previously, we communicated on mixed algae cultures grown on N-containing process water. At Yara Sluiskil (The Netherlands), two 100 m³ algae ponds are operational for reducing the nitrogen content in the process water from a demineralisation unit.
Efficient harvesting of the algae biomass from open pond systems is challenging as processing of larger amounts of low-density algae culture is required. Within IDEA, the MAF submerged membrane-based technology (VITO) was evaluated for realizing a first dewatering of such a mixed low-density algae culture. As good dewatering results were obtained in off-site MAF trials performed (up to > 200 times volume reduction), a continuous on-site harvesting trial was prepared.
End of September 2022, VITO mobilized its pilot MAF unit to Yara Sluiskil. The MAF algae harvesting unit was installed next to open pond under a shelter and was connected to the open pond. During the subsequent 70 days (till mid-December), the PLC controlled system was operated continuously (24/24 and 7/7).
The functioning was monitored remotely, and biomass was collected from the system twice a week. During the first weeks of the trial, the focus was on collecting algae biomass ( > 10 kg DM) for further use in the IDEA projects. Afterwards, the robustness & reliability of the MAF-technology received special attention. In total, more than 150 m³ of algae culture was pumped from the pond and dewatered in the MAF-unit.
In respect to the degree of dewatering, Volume Concentration Factors (VCF) up to 100 were reached. This implies that the algae were concentrated up to 100 time. About 98% of the extracted algae culture was converted into algae-free permeate that can be discharged or used for other application. In respect to maintenance needs, usually a weekly maintenance is sufficient for the MAF technology thanks to the backwashable membranes. In the current field trial, a lower frequency (once every 3 weeks) was proven to be possible as well. In conclusion, a stable and robust operation of the MAF algae harvesting technology was observed. The impact of the harvesting approach on the algae production yield in the pond is a topic that remains to be explored, but it is expected that with efficient harvesting the nitrogen removal capacity of the pond can be improved.
On January 17th, the harvesting results were presented by VITO to YARA stakeholders and were positively received. During a joint visit to the MAF pilot set-up that was operational on the pond, the functioning of the MAF-harvesting was demonstrated.
Pilot scale Chloromonas cultivation on N-containing low carbon process water
The cultivation of higher value ‘axenic’ algal species on low carbon process water is also being investigated during IDEA. Algal species that were cultivated before in IDEA (like Nannochloropsis, Porphyridium, Chloromonas, Chlorella, Scenedesmus) were evaluated for their growth potential on process water at lab scale.
In Autumn 2022, a pilot scale (1500 L & 300 L photobioreactors) growth trial with Chloromonas was performed in the Sunbuilt demonstrator (VITO/Thomas More, Belgium). Like previously realized for a Nannochloropsis growth trial, permeate from the on-site trial described above was transported to VITO for pre-treatment before starting the cultivation in the photobioreactors.
A good algal growth was observed by Thomas More but the appearance of the culture was different compared to previous pilot scale growth trials. Highly dividing cells, grouped in clusters, were observed as well as oily substances in the growth medium and oil droplets/globules inside the cells. For these reasons, harvesting was performed by VITO via centrifugation, which resulted in relatively low yields.
An additional set of growth trials and analyses is being elaborated to examine whether the observed physiochemical properties of the algae biomass are a result of stresses induced by the used process water, or by other parameters.
Chlorella cultivation on recycled CO2 in 9000 L photobioreactor & continuous harvesting with medium re-use
Heirbaut LV is an agricultural company (dairy cattle) in Temse (Belgium) that envisions circular farming. The manure produced by cows is converted in a digestor into biogas (CO2/methane mixture) and digestate rich in nutrients (like nitrogen and phosphorus). Heirbaut did install photobioreactors to grow microalgae on recycled CO2 and is also exploring the potential of the digestate as nutrient source.
In autumn 2022, as part of the IDEA project, a Chlorella culture was grown on recycled CO2 in a 9000 L photobioreactor. The CO2 originated from the off gas after burning of pre-treated biogas. The nice weather in September/October stimulated the Chlorella growth well, although growth rates and culture densities were lower compared to summer cultivations. A MAF-filtration unit was installed by VITO next to the photobioreactor for continuous harvesting of the algae.
The algae-free MAF permeate was recycled via immediate re-injection into the photobioreactor system. For 4 weeks, 5-8 % of the reactor volume was dewatered daily with an average medium recycling of 97 %. Technically the growth and MAF-harvesting systems were operating synchronised. Twice a week, the MAF-concentrated Chlorella biomass was further dewatered by VITO using centrifugation. A new pilot scale growth trial is being prepared for harvesting Chlorella in a similar way in Spring 2023. At that time of the season, higher growth rates and higher harvesting percentages are expected to be possible.
On November 29th, Heirbaut LV organized an open day, allowing the general public to visit the farm, including the algae cultivation part. About 100 people with different background took the opportunity to see the algae growth and MAF harvesting infrastructure, and to taste Chlorella containing food like waffles, ice-cream, chocolate and cheese. Watch the video here.
Larger scale digestate pre-treatment & growth of Scenedesmus on digestate at pilot scale
Within IDEA, the potential to re-use nutrients present in digestate (after digestion of plants and/or manure) for algae cultivation is being evaluated. During the past months, this research was leveled to pilot scale. To this end, Swansea University (UK) pretreated 100 L of digestate that was provided by Heirbaut LV. The pretreatment was realized by settling of solids and the subsequent MF membrane filtration of the liquid phase, using membrane cartridge with a pore size of 0.2 µm at a pressure of 1.5 bars. A pilot Scenedesmus growth trial with the digestate as nutrient source is currently ongoing at Swansea University in photobioreactors installed in a greenhouse with 2,600L total capacity.
Despite the winter conditions, algae growth is ongoing, be it slowly, due limited light access and low temperature.
A Chloromonas growth trial on digestate is being prepared by Heirbaut LV.
Short updates
What happens with the algae biomass that is harvested during the different pilot trials? Each of the algae growth trials described above aims at producing at least 3 kg of algae biomass (on dry matter basis) for further processing in the project. More specifically, after harvesting, the wet biomass is subjected to a cell disruption step and is subsequently freeze-dried for storage.
Part of the biomass is also being defatted to generate an algae oil and a partially defatted algae meal. The algae biomass (fractions) are currently being analyzed for composition and safety aspects. Next, the algae biomass samples will be used in application trials to evaluate their potential as ingredients for cosmetics, feed, food and agro applications.
IDEA+ event: The IDEA capitalization project will conclude in 2023 with an event. This event will be organized on September 28th 2023 as a physical meeting hosted by VITO in Mol (Belgium). More details on the programme are to follow and will be available on the IDEA website. All stakeholders involved in algae values chains are welcome to attend the event and to share experiences!
Recently published IDEA scientific publications:
Hayes, M., L. Mora & S. Lucakova. 2022. Identification of Bioactive Peptides from Nannochloropsis oculata Using a Combination of Enzymatic Treatment, in Silico Analysis and Chemical Synthesis. Biomolecules12,1806. https://doi.org/10.3390/biom12121806
