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Determination of Dissolved CO2 Concentration in Culture Media: Evaluation of Ph Value and Mathematical Data

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Determination of Dissolved CO2 Concentration in Culture Media: Evaluation of Ph Value and Mathematical Data processes Article Determination of Dissolved CO2 Concentration in Culture Media: Evaluation of pH Value and Mathematical Data Amir Izzuddin Adnan 1, Mei Yin Ong 1, Saifuddin Nomanbhay 1,* and Pau Loke Show 2 1 Institute of Sustainable Energy, Universiti Tenaga Nasional, Kajang 43000, Selangor, Malaysia; [email protected] (A.I.A.); [email protected] or [email protected] (M.Y.O.) 2 Department of Chemical and Environmental Engineering, Faculty of Science and Engineering, University of Nottingham Malaysia, Jalan Broga, Semenyih 43500, Selangor, Malaysia; [email protected] * Correspondence: [email protected]; Tel.: +60-3-8921-7285 Received: 23 September 2020; Accepted: 26 October 2020; Published: 29 October 2020 Abstract: Carbon dioxide is the most influential gas in greenhouse gasses and its amount in the atmosphere reached 412 µmol/mol in August 2020, which increased rapidly, by 48%, from preindustrial levels. A brand-new chemical industry, namely organic chemistry and catalysis science, must be developed with carbon dioxide (CO2) as the source of carbon. Nowadays, many techniques are available for controlling and removing carbon dioxide in different chemical processes. Since the utilization of CO2 as feedstock for a chemical commodity is of relevance today, this study will focus on how to increase CO2 solubility in culture media used for growing microbes. In this work, the CO2 solubility in a different medium was investigated. Sodium hydroxide (NaOH) and monoethanolamine (MEA) were added to the culture media (3.0 g/L dipotassium phosphate (K2HPO4), 0.2 g/L magnesium chloride (MgCl2), 0.2 g/L calcium chloride (CaCl2), and 1.0 g/L sodium chloride (NaCl)) for growing microbes in order to observe the difference in CO2 solubility. Factors of temperature and pressure were also studied. The determination of CO2 concentration in the solution was measured by gas analyzer. The result obtained from optimization revealed a maximum CO2 concentration of 19.029 mol/L in the culture media with MEA, at a pressure of 136.728 kPa, operating at 20.483 ◦C. Keywords: carbon dioxide; culture media; microorganism; optimization 1. Introduction Fossil fuels are broadly acknowledged as being the principal source of energy, and since the First Industrial Revolution the amount of carbon dioxide (CO2) in the atmosphere has risen from 280 µmol/mol to 412 µmol/mol. The resulting CO2 emissions contribute significantly to worldwide climate change [1]. Up to now, the deployment of cutting-edge low-carbon fossil-energy technologies was considered to be the ultimate solution. Preventing worldwide climate change can be achieved by taking two long-term emission objectives into account. First, CO2 emissions have had to reach their highest point, and then in the second half of the century, the goal has had to be to strive to achieve net greenhouse gas neutrality, by balancing anthropogenic emissions by the sources with the removal by sinks [2]. Hence, it is crucial to decrease such anthropogenic emissions. Second, CO2 can be captured and used as a significant feedstock to produce valuable commodities. As the world population increases, the need for energy supply rises at an exponential rate. Subsequently, to meet this demand, new and renewable energy sources are required. Along this line, treating CO2 as a feedstock to many value-added chemicals and fuels addresses both emission-control and energy supply challenges [3]. Processes 2020, 8, 1373; doi:10.3390/pr8111373 www.mdpi.com/journal/processes Processes 2020, 8, 1373 2 of 15 The concepts mentioned above are commonly used in carbon management from a climate change perspective. The term used is CO2 capture, utilization, and sequestration (CCUS). The carbon capture and storage (CCS) approach in reducing CO2 emissions is particularly common nowadays [4]. It refers to technologies that emphasize the selective removal of waste CO2 from a large point source, its compression into a liquified gas, and finally its transportation and sequestration to a storage site where it will not enter the atmosphere such as underground geologic formations, including depleted oil and gas reservoirs or oceans [5]. Meanwhile, carbon capture and utilization (CCU) technologies capture CO2 to be recycled for an additional application. It differs from CCS in that CCU does not permanently sequester the CO2 waste, but rather, treats it as a renewable carbon feedstock to complement the conventional petrochemical feedstocks for conversion into other substances or products with higher economic value [6]. However, due to the thermodynamically stable nature of CO2, utilizing it in chemical reactions is challenging. High energy input is required to breakdown carbon atoms in CO2 molecules, which is one of the reasons why CO2 is not extensively used in current chemical industries. Nevertheless, autotrophic microorganisms are well-known for their ability to utilize light to fix atmospheric CO2 during the process of photosynthesis. These microorganisms can capture energy in the light cycle and store it for converting adenosine diphosphate (ADP) and nicotinamide adenine dinucleotide phosphate (NADP) into adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) respectively. They then utilize these energy molecules during a dark cycle for transforming CO2 into valuable organic compounds [7]. Research has been done recently on altering the molecules of autotrophic cyanobacteria and algae through metabolic engineering to take advantage of their abilities to treat CO2 [8]. Microorganisms require macronutrients, micronutrients, and vitamins to grow [9]. Based on these requirements, a culture broth is required as a growth medium in a closed system, such as a bioreactor, for the production of biomass or organic compounds [10]. Therefore, increasing the CO2 solubility in a culture broth is an important step toward CO2 utilization by microorganisms. Al-Anezi et al. studied the effect of temperature, salinity, and pressure on CO2 solubility in different aqueous solutions [11]. The relationship between these parameters on CO2 solubility was presented. Where gas solubility reduced between the temperatures of 25 ◦C and 60 ◦C, the effect was less evident at a higher temperature. Meanwhile, higher pressure (one to two bars) resulted in higher gas solubility. Additionally, the study stated that gas solubility decreased as salt increased in the solution. Yincheng et al. compared the CO2 removal efficiency of sodium hydroxide (NaOH) and aqueous ammonia [12]. The study involved the capture of CO2 in a spray column, and a fine spray of ammonia and NaOH was used. The key finding of the study was the value of mole ratios of NaOH and ammonia to CO2 suitable for the spray column, which is 4.43 and 9.68 respectively. Additionally, Martins da Rosa et al. researched the CO2 fixation of Chlorella using monoethanolamine (MEA) [13]. Through this research, it was found that the CO2 intake was higher for the growth of algae using a certain mass concentration of MEA; 50 mg/L and 100 mg/L for this particular strain of algae. However, the treatment of CO2 decreased if the MEA concentration used was very low or very high. Thus, the concentration of MEA used was dependent on the microorganism used. The present paper will investigate various features that determine the concentration of CO2 dissolved in a culture solution. First, to determine the maximum CO2 concentration in the NaOH aqueous solution as a comparison, a steady rate of CO2 was supplied for a certain time. NaOH was chosen because the CO2 absorption capacity of NaOH solution is high, with a mass ratio of capture, w(NaOH/CO2) equal to 0.9 [14]. Second, MEA and culture media were used as the absorbent to determine the capability of both solutions in capturing CO2. Next, different kinds of culture media solutions were prepared; with the addition of either NaOH or MEA, and the absorption was carried out under the same conditions as the previous run in a batch reactor. From the experimental results, the absorption behavior is presented according to pH and time. Then optimization was run by software to determine the optimized condition for CO2 absorption. Processes 2020, 8, 1373 3 of 15 2. Materials and Methods Processes 2020, 8, x 3 of 16 2.1. Carbon Dioxide (CO ) Delivery System 2. Materials and Methods2 A batch-typed glass (borosilicate) cylindrical reactor (Bio Gene®, Australia) with a built-in motor, 2.1. Carbon Dioxide (CO2) Delivery System the total volume capacity of 5 L (D = 140 mm; h = 325 mm), equipped with a pressure gauge, (RS Components,A batch-typed Johor glass Bahru, (borosilicate Johor, Malaysia),) cylindrical reactor pH (BOQU (Bio Gene®,® Shanghai,, Australia) with China) a built-in and motor, temperature probe (DPSTARthe total volume Manufacturing capacity of Sdn.5 L (D Bhd., = 140 Kualamm; h = Lumpur, 325 mm), Malaysia)equipped with was a employedpressure gauge, for the(RS carbon Components, Johor Bahru, Johor, Malaysia), pH (BOQU®, Shanghai, China) and temperature probe dioxide(DPSTAR (CO2) absorption Manufacturing as Sdn. shown Bhd., in Kuala Figure Lumpur,1. The Malaysia) reactor was was employed connected for the to carbon a pressurized dioxide gas mixture(CO tank2) absorption (Gaslink Industrialas shown inGases Figure Sdn.1. The Bhd., reactor Puchong, was connected Selangor, to a pressurized Malaysia) gas through mixture atank flowmeter (HERO TECH(Gaslink® ,Industrial Puchong, Gases Selangor, Sdn. Bhd., Malaysia) Puchong, with Selangor, a valve Malaysia) for controlling through the a flowflowmeter rate of(HERO the mixture. ® The compositionsTECH , Puchong, of the Selangor, gas mixture Malaysia) were with 90% a COvalve2 andfor controlling 10% Nitrogen the flow (N rate2). Forof the providing mixture. The a vacuum space insidecompositions the reactor, of the gas a vacuum mixture were pump 90% (vacuubrand CO2 and 10% Nitrogen®, Wertheim (N2). For am providing Main, Baden-Württemberg,a vacuum space inside the reactor, a vacuum pump (vacuubrand®, Wertheim am Main, Baden-Württemberg, Germany) was mounted with a valve.
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