Title:
Increasing Economic Efficiency of Cultivating Microalgae by Recycling Process Water
Author(s):
Neubauer, M., Bauer, L., Lanschützer, E., Cayir, P., Sonnleitner, A., Meixner, K., Fritz, I., Drosg, B.
Document(s):
Paper
Abstract:
Microalgae cultivation is a water-intensive process where a lot of medium (nutrient supply) is used as process water, in order to give the organisms an appropriate habitat. Thus, water recycling in microalgae cultivation is desirable, not only to reduce the water demand but also energy and other input demands. To achieve these goals, medium recovery by recycling the maximum amount of process water is suggested. In addition, a large quantity of unmetabolized nutrients are lost if nutrient medium is disposed after harvest. Therefore, two strains of interest were observed and optimization experiments were performed. Arthrospira platensis is well known from literature. However, there is only few data available regarding process water recirculation. The main reason for cultivating A. platensis is the high amount of proteins and phycocyanin. Nannochloropsis limnetica gets more and more attention due to high amount of lipids in its biomass. While focusing on these aims, various experiments evaluating growth conditions and biomass of the microalgae were conducted. Based on those results, reduction potential and costs were calculated. The cultivation experiments of A. platensis showed highest growth and protein content at higher illumination intensities (10500 lux). The results were similar for N. limnetica. Regarding temperature, A. platensis showed highest growth and c- phycocyanin content at 25°C and 35°C. Whereas N. limnetica grew best at 25°C, with highest accumulations of lipids at 15°C. For both strains, A. platensis and N. limnetica recirculation experiment demonstrated that within multiple cultivation cycles OD values did not significantly drop, but rather rose in later cultivation cycles. This shows that process water does not have a negative effect on growth. As to biomass composition, a rather stable protein and c-phycocyanin contend was seen throughout all recirculations in A. platensis cultures. Lipid contends of N. limnetica cultures decreased slightly over multiple recycling steps. However, a minimum of 20% lipids in its biomass is still respectable. By comparing mass balances of A. platensis and N. limnetica, the main differences between those are nutrient and CO2 consumption as well as biomass production. By recycling medium, costs for fresh water consumption and wastewater production were reduced by about 80 %. Costs for nutrient consumption can be reduced for A. platensis by 35 % and N. limnetica by 14 %. However, costs for pressurized air, CO2 and direct energy demands are not affected by the recirculation. In the chosen scenario it can be assumed that a recirculation management can lead to a reduction of running costs by 1.6 - 7.8 % of the end product. The same is true for overall energy demand. Concluding, it can be said that basic knowledge about cultivation conditions and their effects on growth and biomass composition were achieved. Furthermore, it was shown that recycling of process water doesn’t inhibit growth. Also, biomass compositions didn’t change over multiple recycling steps. Those results were achieved for A. platensis at temperatures around 30°C, for N. limnetica around 15°C. For common glass house cultivation in central Europe, this observation suggests a combination of the two strains, cultivating A. platensis in summer and N. limnetica in winter. Shading and heating could be reduced while enough light is provided. However, there is still a lot of potential for optimizing cultivation, harvest and addition of nutrients especially at larger scale.
Keywords:
microalgae, energy demand, N. limnetica, A. platensis, recirculation
Topic:
Industry Track
Subtopic:
Advances in Large Scale Gasification
Event:
29th European Biomass Conference and Exhibition
Session:
IAV.7.10
Pages:
1404 - 1408
ISBN:
978-88-89407-21-9
Paper DOI:
10.5071/29thEUBCE2021-IAV.7.10
Price:
FREE
