The effect of water type on the absorption and desorption of carbon dioxide in bubble columns

Employing newly developed plastic bubble wrap technique for biofuel production from diatoms cultivated in discarded plastic waste

Algal culturing in photobioreactors for biofuel and other value-added products is a challenge globally specifically due to expensive closed or open photobioreactors associated with the high cost, problems of water loss and contamination. Among the wide varieties of microalgae, diatoms have come out as potential source for crude oil in the form of Diafuel™ (biofuel from diatoms). However, culturing diatoms at large scale hypothesized as diatom solar panels for biofuel production is still facing a need for facile and economical production of value-added products. The aim of this work was to culture diatom (microalgae) in a closed system by sealing the reactor rim tightly with very cheap priced and used plastic bubble wrap material which is generally discarded in a lodging and transportation of goods. To optimize it, different plastic wraps discarded from a plastic industry were tested first for their permeability to gases and impermeability to water loss. It was found that among different varieties of plastic bubble wraps, low density polyethylene (LDPE) bubble wrap material which was used to seal glass containers as photobioreactors allowed harvest of maximum Diafuel™ (37%), lipid (35 μgmL^-1), highest cell count (1152 × 10² cells mL^-1), maximum CO₂ absorbance (0.084) with almost no water loss and nutrient uptake for 40 days of experiments. This was due to its permeability to gases and impermeability to water. To check usability of such LDPE bubble wrap on other microalgae it was therefore tested on the red-green microalgae Haematococcus pluvialis, which showed scope to be scaled up for astaxanthin production using discarded bubble wrap packing material. This study thus would open up a new way for decreasing plastic disposal and with reuse for sustainable development and application of diatom in biofuel production which could find applications in environmental and industrial sectors.

Modeling of CO2 Capture with Water Bubble Column Reactor

The demand for carbon capture is increasing over time due to rising CO2 levels in the atmosphere. Even though fossil emission could be decreased or even eliminated, there is a need to start removing CO2 from the atmosphere. The removed CO2 could be either stored permanently to a reservoir (CCS, Carbon Capture and Storage) or utilized as a raw material in a long-lasting product (CCU, Carbon Capture and Utilization). The capture of CO2 could be done by direct air capture, or capturing CO2 from biogenic sources. Amine absorption is the state-of-the-art method to capture CO2, but it has some drawbacks: toxicity, high heat demand, and sorbent sensitivity towards impurities such as sulfur compounds and degradation in cyclic operation. Another potential solvent for CO2 could be water, which is easily available and safe to use in many applications. The problem with water is the poorer solubility of CO2, compared with amines, which leads to larger required flow rates. This study analyzed the technical feasibility of water absorption in a counterflow bubble column reactor. A dynamic, one-dimensional multiphase model was developed. The gas phase was modeled with plug flow assumption, and the liquid phase was treated as axially dispersed plug flow. CO2 capture efficiency, produced CO2 mass flow rate, and the product gas CO2 content were estimated as a function of inlet gas and liquid flow rate. In addition, the energy consumption per produced CO2-tonne was calculated. The CO2 capture efficiency was improved by increasing the liquid flow rate, while the CO2 content in product gas was decreased. For some of the studied liquid flow rates, an optimum gas flow rate was found to minimize the specific energy consumption. Further research is required to study the integration and dynamical operation of the system in a realistic operation environment.