Researchers cultivated a mixed culture of salt-tolerant cyanobacteria in a rotating algae biofilm reactor (RABR) using wastewater from oil and gas extraction. The RABR was found to have an optimal rotation rate of 2.0 revolutions per minute, requiring 0.4 Watts of power and 0.33 megajoules of energy per gram of biomass cultivated. Hydrothermal liquefaction of the biomass produced an average of 34.9% biocrude, conserving approximately 50% of the energy content of the original biomass.

1. ACADEMIA Letters
Waste to value: algae-based biofuel utilizing oil and gas
extraction wastewater
Ronald Sims, Utah State University
Benjamin Peterson, Utah State University
Abstract
A mixed culture of naturally occurring salt-tolerant filamentous cyanobacteria was cultivated
on wastewater from the oil and gas extraction industry with a rotating algae biofilm reactor
(RABR) for transformation to biocrude. A RABR rotates a microalgae growth platform to
alternatively expose attached microalgae to sunlight and to wastewater. Rate of rotation of
the RABR was related to biomass yield and power and energy required to cultivate biomass,
with an optimum rotation rate of 2.0 revolutions per minute (rpm), power requirement of 0.4
W/gm and energy requirement of 0.33 MJ/gm. Rate of rotation was the only statistically
significant factor affecting RABR performance. Microalgae was transformed into biocrude
through hydrothermal liquefaction (HTL), with a yield of 35%. Approximately 50% of the
energy content of the biomass was conserved as biocrude.
Introduction
Produced water defined by the U.S. EPA (2020) as reported in 40 CFR Part 435 is the water
(brine) brought up from the hydrocarbon-bearing strata during the extraction of oil and gas.
Approximately 14 billion barrels of the water are produced annually [Reynolds, 2003; Veil,
et al. 2004). On average seven barrels of produced water are generated for every one barrel
of crude oil generated [Arthur et al. 2005], and the number of hydraulically fractured wells
Academia Letters, December 2021
Corresponding Author: Ronald Sims, ron.sims@usu.edu
Citation: Sims, R., Peterson, B. (2021). Waste to value: algae-based biofuel utilizing oil and gas extraction
wastewater. Academia Letters, Article 4460. https://doi.org/10.20935/AL4460.
1
©2021 by the authors — Open Access — Distributed under CC BY 4.0

2. increased from 36,000 in 2010 to over 300,000 in 2015 (EPA 2020). Currently the industry
does not treat the water and instead reinjects it back into the land from which it was drawn,
so there is a risk of drinking water contamination (Lyman, et al. 2013), and there is limited
data regarding treatability of produced waters and a need for additional research (EPA, 2020).
The problem is that current disposal and treatment methods are expensive. Disposal costs can
range from $0.30 a barrel to $105 a barrel depending on site location [EPA 2020, Arthur et
al, 2005, Pruder et al. 2006)]. This high cost is due to the lack of cost-effective methods of
wastewater treatment. The high costs of disposal along with the large amount of produced
water to dispose is what provided the basis for the development of a microalgae cultivation
system that integrated produce water treatment with bioproduct production in this project.
Wood, et al. (2015) demonstrated the first successful cultivation of cyanobacteria biomass
on produced water with production of the high-value product phycocyanin using a rotating
algae biofilm reactor (RABR). Christensen and Sims (2012) used a RABR to evaluate the en-
ergy required to produce microalgae cultivated on municipal wastewater which indicated that
a suspended treatment system required more energy than the RABR system (1.4 W/m2 com-
pared to 1.7 W/m2 ). Biocrude was produced from municipal and dairy wastewater cultivated
microalgae using the RABR technology (Barlow, et al. 2016).
The RABR is a biofilm technology that rotates a substratum for microalgae cultivation
into colored and turbid wastewater to uptake microalgae nutrients nitrogen and phosphorus
and then into the atmosphere to receive energy as sunlight and carbon dioxide (Wood et al.
2015).
In the research reported here, produced water was used as a medium to evaluate power
and energy requirements for cyanobacteria microalgae cultivation in RABRs, the effect of
operation in terms of revolutions per minute, and the energy conserved in the transformation
of microalgae biomass to biofuel as biocrude.
Materials and Methods
Produced water. Produced water was taken from the Uintah Basin, Eastern Utah and char-
acterized by Chemtech-Ford Analytical Laboratories, Sandy, Utah (chemtechford.com). Nu-
trients were present with total nitrogen and total phosphorus concentrations of 78 mg/L and
16 mg/L, respectively (N:P molar ratio of 11). Dissolved solids concentration was typical for
produced water at 65,500 mg/L.
Microalgae biomass. Two strains of filamentous cyanobcateria capable of growth on pro-
duced water were combined into one mixed culture for inoculation of the RABRs. One strain
was isolated from the Wastewater Lagoon System for the City of Logan, Utah and the other
Academia Letters, December 2021
Corresponding Author: Ronald Sims, ron.sims@usu.edu
Citation: Sims, R., Peterson, B. (2021). Waste to value: algae-based biofuel utilizing oil and gas extraction
wastewater. Academia Letters, Article 4460. https://doi.org/10.20935/AL4460.
2
©2021 by the authors — Open Access — Distributed under CC BY 4.0

3. strain from Great Salt Lake, Utah.
RABR construction and operation. Polystryene was used to make rotating algae biofilm
reactors (RABRs) with each RABR containing 23 disks (19 cm diameter by 2 cm thickness)
rotated through produced water with 60% of disk surface above the water level and 40% below
in a channel that contained 175 L. RABRs were located in a greenhouse to prevent precipi-
tation and windblown dust from entering the produced water. Microalgae was harvested by
mechanical scraping. Voltage meters were used to monitor power consumption required for
the cultivation of the biomass.
Environmental parameters. Average values for temperature and pH were 20.5 °C and 8.3,
respectively. Average photosynthetically active radiation (PAR) inside the greenhouse was
112.4 umoles/m2/sec.
Statistical analysis. A test of 1.0 and 2.0 rpm was used to determine which factors were
significant (p-value less than 0.05) regarding biomass yield using the statistical program SAS.
Factors evaluated included: (1) combination of east facing vs. west facing and disk position;
(2) combination of rpm and disk position; (3) combination of rpm and side harvested; and (4)
individual factors of side and rpm. Following this analysis, additional values of 0.5, 2.0, and
5.0 rpm were evaluated for biomass yield and power requirements.
Hydrothermal Liquefaction (HTL). Harvested biomass was converted into biocrude using
a 500-ml HTL pressure reactor with pressure at 14.5-16.2 Mpa. After drying the solid phase
was resuspended in dichloromethane, centrifuged, decanted, and filtered twice more to ensure
biocrude recovery.
Results and Discussion
Results of SAS analysis indicated that rpm (speed) had a significant relationship with biomass
yield (p-value = <0.0001) while other factors were not significant at p-value of 0.05. Further
testing at 0.5, 2.0, and 5.0 rpm was conducted to measure yields and power requirements.
Power requirement for biomass harvesting by mechanical scraping after 30 days was consid-
ered insignificant and was not included.
Yield of biomass is a critical parameter in assessing biomass production for biofuels pro-
duction. Results are shown in Table 1. A rotation rate of 2.0 rpm demonstrated the highest
yield per unit of power input calculated as both watts (W) at 7.4 gm-dw/W and megajoules
(MJ) at 3.0 gm-dw/MJ. At 0.5 rpm, the lower yield per unit power input may be related to
lower mass transfer rates of nutrients from produced water to biofilm due to a thicker water
layer at the biofilm-water boundary layer causing resistance to mass transfer. At 5.0 rpm, the
lower yield per unit power input may be due to increased sloughing of biofilm from the RABR
Academia Letters, December 2021
Corresponding Author: Ronald Sims, ron.sims@usu.edu
Citation: Sims, R., Peterson, B. (2021). Waste to value: algae-based biofuel utilizing oil and gas extraction
wastewater. Academia Letters, Article 4460. https://doi.org/10.20935/AL4460.
3
©2021 by the authors — Open Access — Distributed under CC BY 4.0

4. compared with sloughing at 2.0 rpm. Based on the results of this testing, the highest yield per
unit of power input occurred at 2.0 rpm.
Conversely, power required to produce one unit (1 gm) of algae is the reciprocal of the
values presented in Table 1. For 2.0 rpm, power requirements for 1 gm of microalgae-based
biomass are 0.14 W/gm-dw and 0.33 MJ/gm-dw. These values indicate a reduction in power
requirements of 21% and 27% W and 36% and 45% MJ compared with rotation rates of 0.5
and 5.0 rpm, respectively. Clearly, rotation rate has an influence on both biomass yield and
power requirements regarding biofilm biomass cultivation, but not a linear relationship.
Results for hydrothermal liquefaction (HTL) showed an average biocrude yield of 34.9%.
With values of energy content of biocrude at 40 MJ/Kg and of microalgae at 28 MJ/Kg, and
using 35% recovery of biocrude in the testing conducted in this study, 1 Kg microalgae pro-
duces 0.35 Kg biocrude and is equivalent to 14 MJ biocrude energy as follows: 0.35 Kg
biocrude/Kg algae x 40 MJ/Kg biocrude = 14 MJ/Kg algae. Approximately 50% of the en-
ergy in the microalgae was converted into biocrude energy.
Conclusions
A mixed culture of naturally occurring salt-tolerant filamentous cyanobacteria was success-
fully cultivated on wastewater from the oil and gas extraction industry (produced water) from
the Uintah Basin in Eastern Utah with a rotating algae biofilm reactor (RABR).
Rate of rotation of the RABR was related to microalgae biomass yield and the amount
of power and energy required to cultivate the biomass, with an optimum rotation rate of 2.0
rpm compared with 0.5 and 5 rpm, and with a power requirement of 0.4 W/gm and energy
requirement of 0.33 MJ/gm. Rate of rotation was also the only statistically significant factor
among those evaluated that included (1) combination of side of disk (east facing vs. west
facing) and disk position; (2) combination of rpm and disk position; (3) combination of rpm
and side (east facing vs. west facing); and (4) individual factor of side and rpm.
Academia Letters, December 2021
Corresponding Author: Ronald Sims, ron.sims@usu.edu
Citation: Sims, R., Peterson, B. (2021). Waste to value: algae-based biofuel utilizing oil and gas extraction
wastewater. Academia Letters, Article 4460. https://doi.org/10.20935/AL4460.
4
©2021 by the authors — Open Access — Distributed under CC BY 4.0

5. Hydrothermal liquefaction (HTL) transformed RABR microalgae biomass into biocrude,
with a yield of 0.35 gm biocrude per gm microalgae. Approximately 50% of the energy
content of the biomass was conserved as biocrude.
Funding and facilities support
This research was supported by the Huntsman Environmental Research Center (HERC), Sus-
tainable Waste to Bioproducts Engineering Center (SWBEC), and State of Utah Science Tech-
nology and Research (USTAR) Initiative.
Conflict of interest
The authors declare there are no conflicts of interest.
Academia Letters, December 2021
Corresponding Author: Ronald Sims, ron.sims@usu.edu
Citation: Sims, R., Peterson, B. (2021). Waste to value: algae-based biofuel utilizing oil and gas extraction
wastewater. Academia Letters, Article 4460. https://doi.org/10.20935/AL4460.
5
©2021 by the authors — Open Access — Distributed under CC BY 4.0

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Academia Letters, December 2021
Corresponding Author: Ronald Sims, ron.sims@usu.edu
Citation: Sims, R., Peterson, B. (2021). Waste to value: algae-based biofuel utilizing oil and gas extraction
wastewater. Academia Letters, Article 4460. https://doi.org/10.20935/AL4460.
6
©2021 by the authors — Open Access — Distributed under CC BY 4.0