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

Summary

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.

Abstract

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.

Introduction

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 activities^2,3,4,5,6,7. In the U.S., the largest density of CO₂ emissions originates mainly from fossil fuel combustion in the energy sector, specifically electric power generation plants^3<....

Protocol

1. Growth system: outdoor open raceway pond settings

1. Set up the open raceway ponds close to the flue gas source (containing 8–10% 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).
2. 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 (Figure 2).
3. Remove water from the flue gas using a 20 L water trap and a condenser (coil length ~12 m) between the s....

Results

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.......

Discussion

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

Materials

List of materials used in this article

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