This work was supported through the Regional Algal Feedstock Testbed project, U.S. Department of Energy DE-EE0006269. We also thank Esteban Jimenez, Jessica Peebles, Francisco Acedo, Jose Cisneros, RAFT Team, Mark Mansfield, UA power plant staff, and TEP power plant staff for all their help.

1. Growth system: outdoor open raceway pond settings
<ol>
	<li>Set up the open raceway ponds close to the flue gas source (containing 8&#8211;10% CO2). Ensure water and electricity are available at the pond reactor location and that the reactor is not in the shade the majority of the day (Figure 1).</li>
	<li>Capture flue gas during the post-combustion process using a 0.95 cm fuel hose, a few meters before the flue gas enters the stack to be discharged into the atmosphere (<stro...

In this study, we demonstrate that synergistically coupling flue gas carbon capture and microalgae cultivation is possible in a hot semi-arid climate. The experimental protocol for the semi-automated raceway pond system integrates state-of-the-art technology to monitor relevant parameters in real time that correlate to algal growth when using flue gas as a carbon source. The proposed protocol is intended to reduce uncertainty in algal cultivation, which is one of the main drawbacks of raceway ponds20</s...

Global warming is one of the most important environmental issues that the world faces today1. Studies suggest that the major cause is the increase in greenhouse gas (GHG) emissions, mainly CO2, in the atmosphere due to human activities2,3,4,5,6,7. In the U.S., the largest density of CO2 emissions originates mainly from fossil fuel combustion in the energy sector, specifically electric power generation plants3,7,8,9. Thus, carbon capture and utilization (CCU) technologies have emerged as one of the major strategies to reduce GHG emissions2,7,10. These include biological systems that utilize sunlight to convert CO2 and water via photosynthesis, in the presence of nutrients, to biomass. The use of microalgae has been proposed due to the fast growth rate, high CO2 fixation ability, and high production capacity. Additionally, microalgae have broad bioenergy potential because the biomass can be converted into products of interest, such as biofuels that can replace fossil fuels7,9,10,11,12.
Microalgae can grow and achieve biological conversion in a variety of cultivation systems or reactors, including open raceway ponds and closed photobioreactors13,14,15,16,17,18,19. Researchers have studied the advantages and limitations that determine the success of the bioprocess in both cultivation systems, under either indoor or outdoor conditions5,6,16,20,21,22,23,24,25. Open raceway ponds are the most common cultivation systems for carbon capture and utilization in situations where flue gas can be distributed directly from the stack. This type of cultivation system is relatively inexpensive, is easy to scale up, has low energy costs, and has low energy requirements for mixing. Additionally, these systems can easily be co-located with the power plant to make the CCU process more efficient. However, there are some drawbacks that need to be considered, such as the limitation in CO2 gas/liquid mass transfer. Although there are limitations, open raceway ponds have been proposed as the most suitable system for outdoor microalgal biofuel production5,9,11,16,20.
In this article, we detail a method for microalgae cultivation in open raceway ponds that combines carbon capture from the flue gas of a natural gas power plant. The method consists of a semi-automated system that controls flue gas injection based on the culture pH; the system monitors and records the Chlorella sorokiniana culture status in real time using optical density, dissolved oxygen (DO), electroconductivity (EC), and air and pond temperature sensors. Algal biomass and flue gas injection data are collected by a data logger every 10 min at the Tucson Electric Power facility. Algae strain maintenance, scale up, quality control measurements, and biomass characterization (e.g., correlation between optical density, g/L, and lipid content) are performed in a laboratory setting at the University of Arizona. A previous protocol outlined a method for optimizing flue gas settings to promote microalgae growth in photobioreactors via computer simulation26. The protocol presented here is unique in that it utilizes open raceway ponds and is designed to be implemented on-site at a natural gas power plant in order to make direct use of the flue gas produced. Additionally, real time optical density measurements are part of the protocol. The system as described is optimized for a hot semiarid climate (K&#246;ppen BSh), which exhibits low precipitation, significant variability in precipitation from year to year, low relative humidity, high evaporation rates, clear skies, and intense solar radiation27.

<table border="0" cellpadding="0" cellspacing="0" style="width:1767px;" width="1766">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Adjustable speed motor (paddle wheel system)</td>
			<td style="width:204px;">Leeson</td>
			<td style="width:161px;">174307</td>
			<td style="width:1116px;">Lesson 174307.00, type: SCR Voltage; Amps:10</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Aluminum weight boats</td>
			<td style="width:204px;">Fisher Scientific</td>
			<td style="width:161px;">08-732-102</td>
			<td>Fisherbrand Aluminum Weighing Dishes</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ammonium Iron (III) (NH&#8324;)&#8325;[Fe(C&#8326;H&#8324;O&#8327;)&#8322;]</td>
			<td>Fisher Scientific</td>
			<td>1185 - 57 - 5</td>
			<td>Medium preparation. Ammonium iron(III) citrate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Ammonium Phosphate</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td>7722-76-1</td>
			<td>This chemical is used for the optimized medium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Ampicillin sodium salt</td>
			<td style="width:204px;">Sigma Aldrich</td>
			<td>A9518-5G</td>
			<td>This chemical is used for avoiding algae contamination</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Autoclave</td>
			<td>Amerex Instrument Inc</td>
			<td></td>
			<td>Hirayama HA300MII</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bacto agar</td>
			<td style="width:204px;">Fisher Scientific</td>
			<td>BP1423500</td>
			<td>Fisher BioReagents Granulated Agar</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Bleach</td>
			<td style="width:204px;">Clorox</td>
			<td style="width:161px;"></td>
			<td>Germicidal Bleach, concentrated clorox</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Boric Acid (H3BO3)</td>
			<td style="width:204px;">Fisher Scientific</td>
			<td>10043-35-3</td>
			<td>Trace Elelements: Boric acid</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:285px;">Calcium chloride dihydrate (CaCl2*2H2O)</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td>10035-04-8</td>
			<td>Medium preparation. Calcium chloride dihydrate</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:285px;">Carboys (20 L)</td>
			<td style="width:204px;">Nalgene - Thermo Fisher Scientific</td>
			<td>2250-0050PK</td>
			<td>Polypropylene Carboy w/Handles</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Centrifuge</td>
			<td style="width:204px;">Beckman Coulter, Inc</td>
			<td style="width:161px;"></td>
			<td>J2-21</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Chloroform</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td>67-66-3</td>
			<td>This chemical is used for lipid extraction</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Citraplex 20% Iron</td>
			<td style="width:204px;">Loveland Products</td>
			<td>SDS No. 1000595582 -17-LPI</td>
			<td>https://www.fbn.com/direct/product/Citraplex-20-Iron#product_info</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:285px;">Cobalt (II) nitrate hexahydrate (Co(NO3)2*6H2O)</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td style="width:161px;">10026-22-9</td>
			<td>Trace Elements: Cobalt (II) nitrate hexahydrate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Compressor</td>
			<td style="width:204px;">Makita</td>
			<td>MAC700</td>
			<td>This equipment is used for the injection CO2 system</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Control Valve</td>
			<td style="width:204px;">Sierra Instruments</td>
			<td style="width:161px;">SmartTrak 100</td>
			<td>This item needs to be customized for your application. In our case, it was used a 5% CO2 and 95% air mixture.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:285px;">Copper (II) Sulfate Pentahydrate (CuSO4*5H2O)</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td style="width:161px;">7758-99-8</td>
			<td>Trace Elements: Copper (II) Sulfate Pentahydrate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Data Logger: Campbell unit CR3000</td>
			<td style="width:204px;">Scientific Campbell</td>
			<td style="width:161px;">CR3000</td>
			<td>This equipment is used for controlling all the system, motoring and recording data</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Dissolvde Oxygen Solution</td>
			<td style="width:204px;">Campbell Scientific</td>
			<td style="width:161px;">14055</td>
			<td>Dissolved oxygen electrolyte solution DO6002 - Lot No. 211085</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;width:285px;">Dissolved Oxygen probe</td>
			<td style="width:204px;">Sensorex</td>
			<td>&#65279;</td>
			<td>DO6400/T Dissolved Oxygen Sensor with Digital Communication</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Electroconductivity calibration solution</td>
			<td style="width:204px;">Ricca Chemical Company</td>
			<td style="width:161px;">2245 - 32 ( R2245000-1A )</td>
			<td>Conductivity Standard, 5000 uS/cm at 25C (2620 ppm TDS as NaCl)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Electroconductivity probe sensor</td>
			<td style="width:204px;">Hanna Instruments</td>
			<td>HI3003/D</td>
			<td>Flow-thru Conductivity Probe - NTC Sensor, DIN Connector, 3m Cable</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:285px;">Ethylenediaminetetraacetic acid disodium salt dihydrate (Na2EDTA*2H2O)</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td>6381-92-6</td>
			<td>Medium Preparation: Ethylenediaminetetraacetic acid disodium salt dihydrate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Filters</td>
			<td style="width:204px;">Fisher Scientific</td>
			<td>09-874-48</td>
			<td>Whatman Binder-Free Glass Microfiber Filters</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Flasks</td>
			<td style="width:204px;">Fisher scientific</td>
			<td>09-552-40</td>
			<td>Pyrex Fernbach Flasks</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Furnace</td>
			<td style="width:204px;">Hogentogler</td>
			<td style="width:161px;">Model: F6020C-80</td>
			<td>Thermo Sicentific Thermolyne F6020C - 80 Muffle Furnace</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Glass dessicator</td>
			<td style="width:204px;">VWR International LLC</td>
			<td style="width:161px;">75871-430</td>
			<td>Type 150, 140 mm of diameter</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Glass funnel</td>
			<td style="width:204px;">Fisher Scientific</td>
			<td style="width:161px;">FB6005865</td>
			<td>Fisherbrand Reusable Glass Long-Stem Funnels</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Laminar flow hood</td>
			<td>Fisher Hamilton Safeair</td>
			<td></td>
			<td>Fisher Hamilton Stainless Safeair hume hood</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:285px;">Magnesium sulfate heptahydrate (MgSO4*7H2O)</td>
			<td>Fisher Scientific</td>
			<td>10034 - 99 - 8</td>
			<td>Medium Preparation: Magnesium sulfate heptahydrate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Methanol</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td>67-56-1</td>
			<td>Lipid extraction solvent</td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:285px;">Micro bubble Diffuser</td>
			<td style="width:204px;">Pentair Aquatic Eco-Systems</td>
			<td>1PMBD075</td>
			<td>This equipment is used for the injection CO2 system</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Microalgae: Chlorella Sorokiniana</td>
			<td style="width:204px;">NAABB</td>
			<td style="width:161px;">DOE 1412</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Microoscope</td>
			<td></td>
			<td></td>
			<td>Carl Zeiss 4291097</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Microwave assistant extraction</td>
			<td style="width:204px;">MARS, CEM Corportation</td>
			<td style="width:161px;"></td>
			<td>CEM Mars 5 Xtraction 230/60 Microwave Accelerated Reaction System. Model: 907601</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">MnCl2*4H2O</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td>13446-34-9</td>
			<td>Manganese(II) chloride tetrahydrate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Mortars</td>
			<td style="width:204px;">Fisher Scientific</td>
			<td>FB961B</td>
			<td>Fisherbrand porcelein mortars</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Nitrogen evaporator</td>
			<td style="width:204px;">Organomation</td>
			<td style="width:161px;"></td>
			<td>N-EVAP 112 Nitrogen Evaporatpr (OA-SYS Heating System)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Oven</td>
			<td style="width:204px;">VWR International LLC</td>
			<td style="width:161px;">89511-410</td>
			<td>Forced Air Oven</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Paddle Wheel</td>
			<td style="width:204px;"></td>
			<td style="width:161px;"></td>
			<td>8-blade horizontal axis propeller. This usually comes as part of the paddlewheel reactor.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Paddle wheel motor</td>
			<td>Leeson</td>
			<td>M1135042.00</td>
			<td>Leeson, Model: CM34025Nz10C; 1/4 HP; Volts 90; FR 34; 62 RPM.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Pestles</td>
			<td style="width:204px;">Fisher Scientific</td>
			<td>FB961M</td>
			<td>Fisherbrand porcelein pestles</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">pH and EC Transmitter</td>
			<td style="width:204px;">Hanna Instruments</td>
			<td>HI98143</td>
			<td>Hanna Instruments HI98143-04 pH and EC Transmitter with Galvanic isolated 0-4V.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">pH calibration solutions</td>
			<td style="width:204px;">Fisher Scientific</td>
			<td style="width:161px;">13-643-003</td>
			<td>Thermo Scientific Orion pH Buffer Bottles</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">pH probe sensor</td>
			<td style="width:204px;">Hanna Instruments</td>
			<td>HI1006-2005</td>
			<td>Hanna Instruments HI1006-2005 Teflon pH Electrode with matching pin 5m.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Pippete tips</td>
			<td>Fisher Scientific</td>
			<td>1111-2821</td>
			<td>1000 ul TipOne graduated blue tip in racks</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Pippetter</td>
			<td>Fisher Scientific</td>
			<td>13-690-032</td>
			<td>Eppendorf Reserch plus Variable Adjustable Volume Pipettes: Single-channel</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Plastic cuvettes</td>
			<td style="width:204px;">Fisher scientific</td>
			<td>14377017</td>
			<td>BrandTech BRAND Plastic Cuvettes</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Plates</td>
			<td style="width:204px;">Fisher scientific</td>
			<td style="width:161px;">08-757-100D</td>
			<td>Corning Falcon Bacteriological Petri Dishes with Lid</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Potash</td>
			<td></td>
			<td></td>
			<td>This chemical is used for the optimazed medium preparation. It was bought in a fertilizer local company</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Potassium phosphate dibasic (K2HPO4)</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td>7758 -11 - 4</td>
			<td>Medium Preparation: Potassium phosphate dibasic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Pyrex reusable Media Storage Bottles</td>
			<td style="width:204px;">Fisher scientific</td>
			<td>06-414-2A</td>
			<td>1 L and 2 L bottels - PYREX GL45 Screw Caps with Plug Seals</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Raceway Pond</td>
			<td></td>
			<td></td>
			<td>Similar equipment can be bought at https://microbioengineering.com/products</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Real Time Optical Density Sensor</td>
			<td>University of Arizona</td>
			<td></td>
			<td>This equipment was design and build by a member of the group</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">RS232 Cable</td>
			<td style="width:204px;">Sabrent</td>
			<td style="width:161px;"></td>
			<td>Sabrent USB 2.0 to Serial (9-Pin) DB-9 RS-232 Converter Cable, Prolific Chipset, Hexnuts, [Windows 10/8.1/8/7/VISTA/XP, Mac OS X 10.6 and Above] 2.5 Feet (CB-DB9P)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Shaker Table</td>
			<td></td>
			<td></td>
			<td>Algae agitation 150 rpm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Sodium Carbonate (Na2CO3)</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td style="width:161px;">497-19-8</td>
			<td>Sodium carbonate</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:285px;">Sodium molybdate dihydrate (Na2MoO4*2H2O)</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td style="width:161px;">10102-40-6</td>
			<td>Medium Preparation: Sodium molybdate dihydrate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Sodium nitrate (NaNO3)</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td>7631-99-4</td>
			<td>Medium Preparation: Sodium nitrate</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:285px;">Spectophotometer</td>
			<td style="width:204px;">Fisher Scientific Company</td>
			<td style="width:161px;">14-385-400</td>
			<td>Thermo Fisher Scientific - 10S UV-Vis GENESTYS Spectrophotometer cylindrical Longpath cell holder; internal reference dectector, Xenon flash lamp; dual silicon photodiode; 240V, 50 to 60Hz selected automatically.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Test tubes</td>
			<td style="width:204px;">Fisher Scientific</td>
			<td style="width:161px;">14-961-27</td>
			<td>Fisherbrand Disposable Borosilicate Glass Tubes with Plain End (10 ml)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Thermocouples type K</td>
			<td style="width:204px;">Omega</td>
			<td>KMQXL-125G-6</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Urea</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td style="width:161px;">2067-80-3</td>
			<td>Urea</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Vacuum filtration system</td>
			<td style="width:204px;">Fisher Scientific</td>
			<td style="width:161px;">XX1514700</td>
			<td>MilliporeSigma Glass Vacuum Filter Holder, 47 mm. The system includes: Ground glass flask attachment, coarse-frit glass filter support, and flask</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Vacuum pump</td>
			<td style="width:204px;">Grainger</td>
			<td style="width:161px;"></td>
			<td>Marathon Electric AC Motor Thermally protected G588DX - MOD 5KH36KNA510X. HP 1/4. RPM 1725/1425</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:285px;">Zinc sulfate heptahydrate (ZnSO4*7H2O)</td>
			<td style="width:204px;">Sigma-Aldrich</td>
			<td style="width:161px;">7446-20-0</td>
			<td>Zinc sulfate heptahydrate</td>
		</tr>
	</tbody>
</table>

coupling carbon capture from a power plant with semi-automated open raceway ponds for microalgae cultivation

In the United States, 35% of the total carbon dioxide (CO2) emissions come from the electrical power industry, of which 30% represent natural gas electricity generation. Microalgae can biofix CO2 10 to 15 times faster than plants and convert algal biomass to products of interest, such as biofuels. Thus, this study presents a protocol that demonstrates the potential synergies of microalgae cultivation with a natural gas power plant situated in the southwestern United States in a hot semi-arid climate. State-of-the-art technologies are used to enhance carbon capture and utilization via the green algal species Chlorella sorokiniana, which can be further processed into biofuel. We describe a protocol involving a semi-automated open raceway pond and discuss the results of its performance when it was tested at the Tucson Electric Power plant, in Tucson, Arizona. Flue gas was used as the main carbon source to control pH, and Chlorella sorokiniana was cultivated. An optimized medium was used to grow the algae. The amount of CO2 added to the system as a function of time was closely monitored. Additionally, other physicochemical factors affecting algal growth rate, biomass productivity, and carbon fixation were monitored, including optical density, dissolved oxygen (DO), electroconductivity (EC), and air and pond temperatures. The results indicate that a microalgae yield of up to 0.385 g/L ash-free dry weight is attainable, with a lipid content of 24%. Leveraging synergistic opportunities between CO2 emitters and algal farmers can provide the resources required to increase carbon capture while supporting the sustainable production of algal biofuels and bioproducts.

Prior experimental results from our lab indicate that microalgae cultivation using a semi-automated open raceway pond can be coupled with carbon capture processes. To better understand the synergy between these two processes (Figure 2), we developed a protocol and tailored it for cultivating the green algal species Chlorella sorokiniana under outdoor conditions in a hot semiarid climate. Natural gas flue gas was obtained from an industrial power generation station. This protocol use...

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Coupling Carbon Capture from a Power Plant with Semi-automated Open Raceway Ponds for Microalgae Cultivation

A protocol is described to utilize the carbon dioxide in natural gas power plant flue gas to cultivate microalgae in open raceway ponds. Flue gas injection is controlled with a pH sensor, and microalgae growth is monitored with real time measurements of optical density.

In the United States, 35% of the total carbon dioxide (CO2) emissions come from the electrical power industry, of which 30% represent natural gas ...

This semi-automatic raceway cultivation system controlled by a pH sensor can directly capture flue gas from power plans for microalgae cultivation and can monitor microalgae growth with real-time measurements. The reactor system allows the direct capture and usage of carbon from industrial flue gas to grow microalgae in on-site semi-automated open pond raceway systems. The system can be used to cultivate alternative algae species and to capture carbon from any power plant.To set up an open raceway pond, attach a 0.95 centimeter fuel hose to capture the flue gas during the post-combustion process, a few meters before the flue gas enters the stack to be discharged into the atmosphere. Place a 20 liter water trap and an approximately 12 meter condenser between the stack and the compressor to remove water from the flue gas. To monitor algal growth, connect a real-time optical density sensor that measures the absorbance at 650 and 750 nanometers, a dissolved oxygen sensor, air and pond thermocouples, a pH sensor, and an electroconductivity sensor to a data logger.To set up a pH control system, connect a compressor and control valve system to the data logger program to manage the flue gas injection and use a tube to direct the flue gas from the control valve through a stone diffuser to the bottom of the raceway pond, then set the system to inject flue gas when the pH value was greater than 8.05 and to stop the flue gas injection when the pH is less than eight. To set up an algal culture system, set the culture room to 25 degrees Celsius in a 12-hour light, 12-hour dark cycle, and use deionized water salts and macro and micronutrients to prepare BG-11 culture medium. Use a sterile loop to select a single algal colony from the culture plate and inoculate the algae in a 50 milliliter tube containing sterile growth medium in a clean biosafety cabinet.Grow the small liquid culture on a shaker table at 120 revolutions per minute for one week. At the end of the incubation, transfer the entire volume of algal culture into 500 milliliters of liquid culture in a one liter flask and close the flask with a rubber stopper fitted with stainless steel tubing to provide aeration. Filter the air with 0.20 micron air sterilization filters and allow the culture to grow for another one to two weeks using a spectrophotometer to monitor the cell density daily.At the end of the culture period, add 500 milliliters of the liquid algal culture to eight liters of non-sterile culture medium in a 10 liter carboy and inject a mixture of 5%carbon dioxide and 95%air into the carboy. Monitor the stock plate and liquid cultures under a light microscope at the 10 and 40X magnifications once a week to ensure growth of the strain of interest. To inoculate an outdoor open raceway pond with algae, first, thoroughly clean the reactor overnight with 30%bleach.Rinse the reactor the next morning until all of the bleach has been removed and calibrate all of the sensors according to their corresponding calibration procedures. Fill the raceway pond up to 80%with water to dilute the concentrated medium and inoculate the pond with the 10 liter carboy of algae culture. Bring the pond to its final volume, then partially shade the raceway pond with wooden pallets for about three days as an adaptation strategy to avoid photo inhibition to allow the microalgae to acclimate to the culture system.To perform a batch growth experiment, inspect and record any day-to-day variations including water evaporation, paddle wheel motor and sensor functionality, or anything else out of the ordinary. Drain and inspect the compressor and water trap daily to allow the removal of any excess water and to minimize flue gas corrosion. Configure the data logger to scan each sensor measurement every 10 seconds and to store the average sensor and air and reactor temperature data every 10 minutes.Make sure that the water level remains constant at the reactor's final volume to avoid affecting the optical density measurement. After replenishing the water in the reactor, collect an algal biomass sample using a 250 milliliter bottle. Measure the optical density in the spectrophotometer.Check the quality of the algae culture three times a week by light microscopy. When a culture is close to reaching stationary phase, harvest 75%of the total algae culture volume and use two to five liters of the culture suspension to perform biomass productivity analysis in the laboratory, then process and convert the rest of the algae into the desired algal products. Here, a comparison between the sensor and laboratory measurements can be observed.Both breeding show similar trends with the data increasing as a function of time. Optical density values increase during the day, but decrease at night during respiration, indicating a change in biomass productivity, thus the integration of a real-time optical density sensor makes it possible to make effective management decisions about the overall algal production system. In this analysis, flue gas was injected from approximately 8:00 a.m.to 6:00 p.m. but was not injected between 6:00 p.m. and 8:00 a.m.This day/night cycle reflects the daylight sunlight exposure and the lack of light during the night, and consequently, the activation of photosynthesis or photorespiration respectively. As illustrated in this figure, as the algal grow rate increases, more flue gas is required, confirming that the on/off flue gas pulse injection system is effective at facilitating carbon capture and utilization through microalgae cultivation. Other physical chemical parameters can also be used to establish a correlation between the parameters and algal growth and productivity.It is important to make sure that the pH system is properly set up and that all of the sensors are calibrated before inoculating the raceway ponds with microalgae. Other methods that can be performed with the raceway pond while producing microalgae biomass include lipid, carbohydrate, or pigment extraction, ash-free dry weight measurements, and PCR quality monitoring.

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4.8K Views.  University of Arizona. This semi-automatic raceway cultivation system controlled by a pH sensor can directly capture flue gas from power plans for microalgae cultivation and can monitor microalgae growth with real-time measurements. The reactor system allows the direct capture and usage of carbon from industrial flue gas to grow microalgae in on-site semi-automated open pond raceway systems. The system can be used to cultivate alternative algae species and to capture carbon from any power plant.To set up an ...