Producing algae in the Qatari desert: from strain to process

The Arabian Peninsula, due to its climate, availability of non-arable land, seawater, and carbon dioxide, is one of the best global locations for commercial cultivation of algae and cyanobacteria. This work focused on the screening of multiple locally isolated strains for their capability to thrive under industrially relevant conditions of elevated temperatures (up to 40 ˚C) and carbon dioxide levels (up to 30%). Two strains, Leptolyngbya sp. and Picochlorum sp., grew well at temperatures of up to 40 ˚C, and also showed a tolerance towards elevated CO2 concentrations. Both microalgae isolated, T. subcordiformis and Picochlorum sp., presented significant amounts of lipids, including high-value omega-3 fatty acids EPA and DHA. On the other hand, both cyanobacteria, Leptolyngbya sp. and Chroococcidiopsis sp., presented levels of phycobiliproteins. The isolates, all very diverse in response and products, showed promising characteristics, making them valuable strains for further investigation towards commercial applications and CO2 capture.One of the identified cyanobacteria was further investigated for its potential to produce phycocyanin, a nutraceutical with high commercial value, under desert climate conditions. Under elevated temperatures and light intensities, of up to 40 ˚C and 1800 µmol photons·m-2·s-1, Leptolyngbya sp. biomass productivity was up to 45% higher as compared A. platensis, the commercially most commonly produced strain for phycocyanin. High temperatures were found to improve both the biomass productivity and phycocyanin content, with maxima of 1.09±0.03 gX·L-1·d-1 and 72.12±3.52 mgPC·gX-1, respectively. Furthermore, various cell disruption methods and buffers were tested for the efficient extraction of high-purity phycocyanin. The best results were found through bead-beating in phosphate buffer, which showed the highest combined phycocyanin yield (169.9±3.6 mgPC·gX) and purity (7.37±0.16). The extract purities obtained for Leptolyngbya sp. are considerably higher than other reported phycocyanin purities. This, together with the strains capability to maintain relatively high biomass productivities compared to A. platensis, even under such high light intensities, make it a feasible candidate for high-value phycocyanin production in desert environments.The indoor to outdoor transition of the strain was also studied to further asses its potential as a commercially interesting strain for production in Qatar, with specific focus on the effect of high light intensities on the occurrence of photooxidation. Indoor, the strain was capable of growing at light intensities up to 5600 µmol photons·m-2·s-1, even at inoculation densities of as low as 0.1 g·L-1 (10%). Levels of chlorophyll and phycocyanin showed a significant decrease within the first 24 h, indicating some level of photooxidation, however, both were able to recover. Outdoor cultivation of the strain however showed a different response as compared to indoor experiments; within days of inoculation a loss of chlorophyll, phycocyanin, and culture turbidity was observed, irrespective of inoculum volume, suggesting that the strain had difficulties adapting to the outdoor environment. The culture did, however, recover, and clear morphological differences were observed, such as an increase in trichome length, as well as coiling of multiple trichomes to tightly packed strands. It was hypothesized that the morphological changes were induced by UV-radiation as an adaptation mechanism through increased self-shading. UV radiation however is generally not simulated under laboratory environments, causing a mismatch between indoor optimizations and outdoor realizations.Following the successful outdoor scale-up, a techno-economic analysis was applied to determine the biomass production costs for various cultivation systems and facility sizes. Different cultivation systems, production locations and facility scales were assessed in terms of their effect on biomass production costs. Flat panel and raceway pond cultivation systems had the lowest projected biomass production costs, at 3.0 and 2.9 €·kg-1, respectively, at 100 ha scale. Biomass production costs in tubular systems, both horizontal and vertically stacked, were up to 1.5 times more expensive. Locational differences in production costs throughout the region were minimal. In scaling up from 1 ha to 100 ha production facility, the largest reductions in production costs were made within the first 10 ha (67%), with further scale-up resulting in a mere 13% additional cost-savings. Finally, a sensitivity analysis indicated which improvements would have the largest impact on the overall costs of the process, as a recommendation for future research and development. Increased photosynthetic efficiencies and temperature optima had the largest impact on projected costs, which is why efforts to source local thermo- and photo- tolerant strains, such as Leptolyngbya sp., could be the key to unlock the potential of the region for algae commercialization.