Enhanced Practical Photosynthetic CO2 Mitigation

摘要

This final report highlights significant achievements in the Enhanced Practical Photosynthetic CO{sub 2} Mitigation Project during the period from 10/1/2001 through 01/02/2006. As indicated in the list of accomplishments below, our efforts during this project were focused on the selection of candidate organisms and growth surfaces and initiating long-term tests in the bench-scale and pilot-scale bioreactor test systems. Specific results and accomplishments for the program include: (1) CRF-2 test system: (a) Sampling test results have shown that the initial mass of algae loaded into the Carbon Recycling Facility Version 2 (CRF-2) system can be estimated with about 3% uncertainty using a statistical sampling procedure. (b) The pressure shim header pipe insert design was shown to have better flow for harvesting than the drilled-hole design. (c) The CRF-2 test system has undergone major improvements to produce the high flow rates needed for harvesting (as determined by previous experiments). The main changes to the system are new stainless steel header/frame units, with increased flow capacity and a modified pipe-end-sealing method to improve flow uniformity, and installation and plumbing for a new high flow harvesting pump. Qualitative system tests showed that the harvesting system performed wonderfully, cleaning the growth surfaces within a matter of seconds. (d) Qualitative tests have shown that organisms can be repopulated on a harvested section of a bioreactor screen, demonstrating that continuous bioreactor operation is feasible, with continuous cycles of harvesting and repopulating screens. (e) Final preparations are underway for quantitative, long-term tests in the CRF-2 with weekly harvesting. (2) Pilot-scale test system: (a) The construction of the pilot-scale bioreactor was completed, including the solar collector and light distribution system. Over the course of the project, the solar collector used in the light delivery system showed some degradation, but performed well overall. (b) Testing confirmed that algae can be grown in a sustainable fashion in the pilot bioreactor, even with intermittent availability of sunlight. (c) The pilot-scale tests indicated that algal growth rate followed photon delivery during productivity testing. (3) Organisms and Growth Surfaces: (a) The aeration of growth media with 5% CO{sub 2} in air stimulates cyanobacterial growth 10-20 times over that with air alone. It is possible that the rate of the stimulation of cyanobacterial growth in the CRF will be higher because cyanobacteria will be grown as a biofilm. We plan to increase the concentration to 15% CO{sub 2} in air. (b) Tests have shown a doubling time of the cyanobacterial culture of about 7.5 hours with illumination of about 170 {micro}mol m{sup -2} sec{sup -1}. All lower levels of illumination led to a decrease in the cyanobacterial growth rate. (c) Macroscopical and microscopical observations suggest that the culture of this isolate undergoes significant morphological changes after 60-70 hours of incubation in the batch culture mode. First of all, the culture begins to clump. This clumping could lead to the decrease of effective illumination of culture and may reflect a medium alkalinization. (d) Organization of our collection of the thermophilic cyanobacteria isolated from Yellowstone National Park has resulted in 13 unialgal cultures of thermophilic cyanobacteria. (e) A new species (even probably a new genus) of cyanobacteria, 5.2 s. c. 1, isolated from LaDuke Spring in Great Yellowstone Basin, demonstrates an elevated resistance to some compounds of iron. This might be very important for our project, because plant gases may have elevated amount of iron. Our study of the effect of different concentration of FeCl{sub 3}* 6H{sub 2}O on the growth of the 5.2 s.c.1 isolate showed that iron additions stimulated rather then inhibited the growth of the isolate. Because of this we would recommend this isolate for further experiments. (f) The shape of the Chlorogloeopsis siderophila cells (cyanobacteria) was found to be affected by environmental pH, which may be useful in culture quality control. Besides, the further investigation of this phenomenon suggested that the rate of cell adhesion to a glass surface decreases upon medium alkalinization. Thus, harvesting effectiveness may be improved by increasing medium pH up to 9 before harvesting of cyanobacteria from a substratum. (g) A study of the effects of Omnisil on the growth of 2.1 (III) Mastigocladus laminosum, 8.2.1 Synechococcus s.c.10, Chlorogloeopsis sp. and 3.3.2 Synechococcus s.c.1. found that only Chlorogloeopsis was able to grow in batch culture in the presence of Omnisil.