New Mexico Geological Society Annual Spring Meeting — Abstracts

The rapid industrialization over the past century has led to a significant increase in the emission of flue gases, particularly carbon dioxide (CO₂), into the atmosphere. As a result, atmospheric CO₂ levels have now slightly surpassed 410 ppm, a concentration that continues to rise alarmingly due to ongoing anthropogenic activities. These elevated levels of CO₂ are a primary driver of global warming and climate change, which in turn contribute to the loss of biodiversity, destruction of natural habitats, and substantial economic losses on a global scale.

In response to these environmental challenges, there has been a growing research interest in CO₂ capture and sequestration techniques aimed at reducing and ultimately eliminating excess CO₂ from the atmosphere. Among the various methods under investigation are adsorption, absorption, cryogenic separation, and carbon sequestration through pre- and post-combustion processes. One particularly promising approach among these methods is the utilization of CO₂ by algae. Algae have the ability to capture carbon from CO₂ and convert it into valuable products, such as biofuels and protein capsules, offering both environmental and economic benefits. This process not only helps in mitigating CO₂ emissions but also contributes to the production of renewable energy.

To enhance CO₂ utilization in algal systems, an innovative mass transfer device to improve dissolution of gaseous CO₂ evaluated in this study. This CO₂ saturator consists of a vertical tube of varying area of cross section through which the algal broth is circulated from the algal pond while gaseous CO₂ is injected at the top of the tube. The principle behind this saturator is to maximize the hold-up and the residence time of the CO₂ bubbles, within the saturator to maximize CO₂ dissolution. This innovation has the potential to significantly improve the efficiency of CO₂ capture in algae cultivation systems over the current method of direct injection into the algal pond. Field experiments were conducted to evaluate the performance of this CO₂ saturator in both winter and summer trials at Wastewater Treatment Plant, Las Cruces. These trials were carried out in four 1000L raceway ponds with microalgae species, Scenedesmus obliquus using reclaimed water from the treatment plant. The performance of the saturator was compared with that of a conventional gas diffuser.

The performance of the innovative saturator and the conventional diffuser was assessed based on several key metrics, including carbon utilization efficiency (CUE), mass transfer coefficient(k_La), and CO2 retaining efficiency. For the summer trial, the saturator demonstrated an average CUE of 74%, outperforming the diffuser, which achieved a CUE of 52%. The mass transfer coefficient for the saturator was also notably higher, averaging 9.35 hour^-1 compared to 2.46 hour^-1 for the diffuser, indicating enhanced CO₂ dissolution capability. Additionally, the saturator’s average transfer efficiency during the summer trial was 94%, whereas the diffuser reached only 83%. In the winter trial, although both systems exhibited lower overall efficiencies due to colder temperatures, the saturator maintained a higher average CUE of 86.5% and transfer efficiency of 97%, compared to the diffuser’s 57% CUE and 87% transfer efficiency. This comparative analysis highlights the saturator’s superior performance in both seasonal trials, particularly in CO₂ transfer and utilization, making it a more efficient system for CO₂ dissolution and algae growth enhancement.

Keywords: flue gas, saturator, utilization, residence time, reclaimed water, carbon utilization efficiency