Carbon dioxide removal from triethanolamine solution using living microalgae-loofah biocomposites

Abstract

Nowadays, the climate change crisis is an urgent matter in which carbon dioxide (CO₂) is a major greenhouse gas contributing to global warming. Amine solvents are commonly used for CO₂ capture with high efficiency and absorption rates. However, solvent regeneration consumes an extensive amount of energy. One of alternative approaches is amine regeneration through microalgae. Recently, living biocomposites, intensifying traditional suspended cultivation, have been developed. With this technology, immobilizing microalgae on biocompatible materials with binder outperformed the suspended system in terms of CO₂ capture rates. In this study, living microalgae-loofah biocomposites with immobilized Scenedesmus acuminatus TISTR 8457 using 5%v/v acrylic medium were tested to remove CO₂ from CO₂-rich triethanolamine (TEA) solutions. The test using 1 M TEA at various CO₂ loading ratios (0.2, 0.4, 0.6, and 0.8 mol CO₂/mol TEA) demonstrated that the biocomposites achieved CO₂ removal rates 3 to 5 times higher than the suspended cell system over 28 days, with the highest removal observed at the 1 M with 0.4 mol CO₂/mol TEA (4.34 ± 0.20 g_CO2/g_biomass). This study triggers a new exploration of integration between biological and chemical processes that could elevate the traditional amine-based CO₂ capture capabilities. Nevertheless, pilot-scale investigations are necessary to confirm the biocomposites's efficiency.

Fig. 1

Overview of experimental procedure: (a) TEA preparation, (b) biocomposites fabrication, (c) TEA tolerance test, (d) binder toxicity test, (e) binder adhesion test, and (f) CO₂ removal test.

Fig. 2

TEA tolerance test of S. acuminatus to TEA solution at different concentrations: (a) 0.005, (b) 0.05, (c) 0.5, (d) 1, and (e) 2 M, using CO₂ loading levels of 0, 0.4, and 0.8 mol CO₂/mol TEA, respectively, over a period of 7 days. Bar chart indicates cell density. CL = CO₂ loading, uppercase letters represent the effect of the same CO₂ loading levels from day 0 to day 7, and lowercase letters represent the effect of different CO₂ loading levels on the same day. The same letters indicate that the mean values of those data sets are not statistically significantly different (p > 0.05) using Tukey’s post hoc analysis. (Mean StDev; n = 3).

Fig. 3

TEA tolerance test of S. acuminatus to TEA solution at different concentrations: (a) 0.005, (b) 0.05, (c) 0.5, (d) 1, and (e) 2 M, using CO₂ loading levels of 0, 0.4, and 0.8 mol CO₂/mol TEA, respectively, over a period of 7 days. Solid line graph indicates pH with microalgae, and the dashed line graph indicates pH without microalgae. CL = CO₂ loading.

Fig. 4

(a) Binder toxicity test of acrylic medium to S. acuminatus using specific growth rate along with (b) images of the test over 7 days, (c) binder adhesion test of cells on the biocomposites at different the binder ratios (0, 2.5, 5, 7.5, 10, 20, 40, and 60%v/v) using cumulative percentage of cell released, and (d) decision matrix for selecting the appropriate binder ratio; the same lower case letters indicate that the mean values of those data sets are not significantly different (p > 0.05) using Tukey’s post hoc analysis (Mean StDev; n = 3).

Fig. 5

SEM images present the morphology of the microalgae-loofah biocomposites before and after the binder adhesion test at binder ratios of 0% (a and b), 5% (c and d), and 60% (e and f) %v/v, respectively, at 500 magnification.

Fig. 6

CO₂ removal test using the biocomposites system (B) and the suspension system (S) from (a) TEA solution at CO₂ loading of 0.8 mol CO₂/mol TEA, with varying TEA solution concentrations (0.1, 0.25, 0.5, and 1 M, respectively) and (b) 1 M TEA solution at different CO₂ loading levels (0.2, 0.4, 0.6, and 0.8 mol CO₂/mol TEA, respectively), over a period of 28 days. Every 4 days, the TEA solutions were measured the amount of CO₂ removed and the TEA solutions were refreshed into the bottle with the same concentration and CO₂ loading. (Mean StDev; n = 3).