Development, optimization, and economic evaluation of a novel attached growth algae cultivation system
Creators: name: Johnson, Michael
Publisher: name: No Publisher Supplied
Year: 2017

description: The focus of this work was to evaluate a novel attached cultivation system developed by AL-G Technologies Inc. through lab-scale experiments for its ability to produce algae biomass and then to utilize these learnings to model its commercial operation at large-scale. The intention of conducting this work was to determine if this unique cultivation platform had potential advantages over traditional open raceway ponds and photobioreactor systems as these traditional systems are limited in their financial viability. It was demonstrated that several algae and cyanobacteria species (Parachlorella kessleri, Tetraselmis chuii, Botryococcus braunii, Thalassiosira sp., Chaetoceros calcitrans and Oscillatoria sp.) could be cultivated on the system and that P. kessleri could achieve potential large-scale productivities exceeding 10 grams of dry biomass m-2 d-1. Through cultivation experiments, it was shown that freshwater algae species tend to grow better than marine algae and substantial salinity gradients retard growth.    rates. Contrary to the original hypothesis, it was demonstrated that attached growth on the system does not significantly alter the nutritional composition of algae in a favorable manner and that while the nutritional composition of the nutrient solution can be rapidly changed to remove a nutrient constituent (e.g., nitrogen), this does not result in as rapid of an accumulation of lipids as it does in traditional suspended growth systems. Through the cultivation experiments, it was also demonstrated that algae on the system are carbon limited and their growth rates increase with supplemental carbon provided they are continually harvested and dense biofilms do not form that limit irradiation and gas diffusion.   Through basic research experiments it was shown that our current mechanical harvesting approach is not operationally or financially scalable and thus we evaluated an irrigation-based harvesting system that was able to achieve a harvest concentration of 1.4 grams of dry biomass L-1. These findings were combined to model the financial viability of the system where it was demonstrated that the system could achieve a production cost of $7.53 to $16.17 kg-1 of algae, which would be in suspension requiring subsequent dewatering and processing. This production cost varied based on the location of the system within the United States and the production was primarily driven by temperature because it drove the cost of heating the greenhouse that contained the system, as well as by the productivity of the algae. Based on the high production cost, the system would be limited commercially to the production of a few nutritional products (e.g., astaxanthin, omega-3 fatty acids, β-carotene) and fishery feed. Therefore, future research efforts with the system should focus on the growth of marine algae species, limiting salinity gradients, and minimizing contamination. However, there are currently no substantial benefits of this system in comparison to traditional systems as it costs 3 to 8 times more to construct and up to 35 times more to operate to produce the same quantity of algae biomass per area under ideal conditions compared to traditional systems.