Research On The Impact Factors And Effects Of Inorganic Carbon Fixation By Mixed Microalgae

Global warming is one of the most severe challenges to mankind in the21st century, andcarbon emission reduction has become a research focus to environmental researchers.Microalgae carbon sequestration is a newly developed carbon fixation technology which canfix gaseous CO₂as well as HCO₃^-in water, thus carbon emission reduction can be achieved bythis technology. In this paper, freshwater mixed microalgae which is easy to cultivate andadaptable to environment was collected and cultivated to fix both gaseous CO₂and HCO₃^-inwater. Affecting factors of microalgae carbon fixation were analyzed, fixing capacities werecalculated, and a microalgae photobioreactor was built and run continuously to examine theHCO₃^-continuous fixation effect, which laid the foundation for the practical application ofmicroalgae HCO₃^-fixation technology.Microalgae enrichment culture experiment was conducted firstly. Experiment resultsshowed that the activity of the microalgae separated from the lake rock attachments was thehighest of several samples, and the Aquatic VI culture medium was the most effective culturemedium for freshwater mixed microalgae cultivation. CO₂microalgae fixation experimentswere conducted under summer room temperature （25℃³0℃） condition, and the optimumoperating conditions were determined as: light intensity15000lux; inlet CO₂concentration10%; initial pH9.0; microalgae concentration1100mg/L. Under optimum conditions, theCO₂fixation capacity was0.08g/（L·h）, and the relationship between CO₂fixation andmicroalgae growth were: for fixation of every1.0g CO₂microalgae can grow0.22g, or forevery1.0g growth of microalgae4.52g CO₂can be fixed.A constant light incubator-shaking table experiment system was set up, and the impactfactor experiments of microalgae fixing HCO₃^-in water were conducted in the system. Theoptimum operating conditions were determined as: temperature30℃; light/dark ratio12:12;light interval12h; light intensity6800lux; initial HCO₃^-concentration1200mg/L¹600mg/L; microalgae concentration1100mg/L; N concentration60.0mg/L; P concentration6.0mg/L.HCO₃^-continuous fixation experiment was conducted in a microalgae photobioreactor.Experiment results showed that HCO₃^-removal rate reached and stabilized at around60%during the continuous running. NH₄⁺-N was also found could be removed by microalgae, the removal rate reached above80%during the continuous running. Effluent COD was foundwould be increased after caobon fixation by microalgae, but the increase was not notable andthe water quality would not be affected seriously. Calculation results showed that the HCO₃^-fixation capacity was0.015g/（L·h）, and the relationship between HCO₃^-fixation andmicroalgae growth were: for fixation of every1.0g HCO₃^-microalgae can grow0.41g, or forevery1.0g growth of microalgae2.42g HCO₃^-can be fixed.