Salt-loving Microorganisms Can Help Cleanup Salty Produced Water
EPSCoR Update - May 2021
The oil and gas (O&G) industry produces large volumes of salty wastewater or produced water (PW) during the extraction, transportation, and storage of crude oil. PW is a complex mixture of organic and inorganic compounds and often contains a high-level of salt, reaching > 30% salinity. Depending on the age of the oil well, some estimates indicate that roughly 9 barrels of PW are generated per barrel of oil; this amounts to roughly 21 billion barrels of PW per year in the USA alone, representing a significant quantity of a useful resource for water-stressed regions in USA and the world if treated cost-effectively.
As water resources are dwindling, water-users such as industry, agriculture, and households are competing more and more for access to clean water. Added to these stresses, freshwater use by the O&G industry is expected to further intensify competition and conflicts between water users and unconventional O&G operations.
O&G production is critical to the economies of many countries and states, including Oklahoma. However, the vast amounts of PW handling represent one of the more significant environmental challenges to the oil industry, not only from an environmental point of view, but also from a technical and cost view. The most economical option for disposal of this large volume of wastewater has been deep-well injection. While this form of disposal has been viable historically, increased earthquake events and environmental damage have occurred in recent years due to increased injection of PW. Hence, there is a need for cost-effective cleanup technology to allow PW to be used for beneficial purposes.
Dr. Babu Fathepure, Professor of Microbiology and Molecular Genetics at Oklahoma State University (OSU) collaborated with Drs. Mark Krzmarzick (OSU), Robert Murdoch (Battelle Memorial Institute-Ohio), and Frank Loeffler (University of Tennessee-Knoxville) as well as William Marsh and Brenden Heise (students at OSU) to explore an integrated microbes-and-membrane approach to clean up toxic saline PW for beneficial uses. The research team aims to study different membrane systems for cost-effective desalination of bioremediated PW.
“We have been investigating the hydrocarbon degradation ability of salt-loving (halophiles) microorganisms from various petroleum-impacted high-salinity environments.” Fathepure said. “We have enriched and isolated several pure cultures of bacteria that degrade aliphatic, aromatic, and other organics typically found in PW at high salinity ranging from 3- 30% NaCl,” Fathepure added.
The team analyzed the genomics and metagenomics of hydrocarbon-degrading cultures to gain greater insight into their ecology, physiology, and mechanism of hydrocarbon degradation under high-salinity conditions. “The uniqueness of our approach lies in the application of these specialized halophilic microbes to remove toxic organics in PW, as no other microorganisms can survive extreme salinities,” Fathepure said.
The clean bioremediated saline PW, assuming that it meets environmental standards, can be re-used in the O&G industry or for other beneficial uses where salinity is not an issue. Alternatively, it can be desalinated using a membrane system for irrigation and other uses.
The team have evaluated the ability of a microbial culture enriched from a briny oil-field soil sample from Kuwait to degrade hydrocarbons in PW obtained from the Wilcox formation, Payne County, OK and the Mississippian formation, Grant County, OK and have set up laboratory-scale bioreactors with PW and inoculated with the Kuwait culture.
“Our results showed complete degradation of benzene, toluene, ethylbenzene, and xylenes (BTEX) in PW from Payne County in 9 days (Figure 1), suggesting the culture’s potential to remediate the PW. On the other hand, degradation of the same compounds in PW from Grant County did not occur even after 4 weeks of incubation by the same bacterial culture (Figure 2)”, Fathepure said. “We do not know the exact reason for this inhibition, but our analysis of the PW showed very high levels of total dissolved solids (TDS), NaCl, and heavy metals in this PW compared to PW from Payne County,” Fathepure added.
The team further investigated the effect of dilution of the toxic PW on BTEX degradation by the culture. The team mixed the toxic PW (Grant County) with raw wastewater (WW) from Stillwater municipal wastewater treatment plant at various proportions. “Surprisingly, our results showed a complete degradation of BTEX within 5 days. These results are very encouraging because bioremediation of extremely toxic PW can still be accomplished simply by mixing with municipal wastewaters or other wastewaters and we have shown that our strategy can clean up two different wastewaters,” Fathepure said. However, initial screening is needed to determine the toxicity of PW. In fact, a similar strategy is already in use in Brazil, where PW is mixed with municipal wastewater to clean up toxic PW biologically.
Figure 1. Biodegradation of BTEX in PW from Payne County by Kuwait culture. The Kuwait culture can completely degrade BTEX compounds in 9 days. No degradation of BTEX (only benzene results shown) occurred in uninoculated bioreactors, suggesting that the Kuwait culture is responsible for the observed degradation of BTEX compounds.
Figure 2 A. Biodegradation of BTEX in PW from Grant County. B. Biodegradation of BTEX in PW mixed with wastewater (50% PW + 50% WW). These results show that no degradation of BTEX occurred in PW from Grant County even after 4 weeks of incubation. However, complete degradation of BTEX occurred with just 5 days when the PW was mixed with municipal wastewater, suggesting mixing with other wastewater can reduce toxicity of PW.
The research group have also isolated a pure culture of a halophilic bacterium that degrades both aromatic and aliphatic hydrocarbons in the presence of salt ranging from 5 – 24% NaCl from the Payne County PW. “This organism has been designated as Modicisalibacter sp. strain Wilcox and is a close relative of Modicisalibacter tunisiensis isolated from an oil-field water in Tunisia and we have sequenced strain Wilcox’ genome,” Fathepure said. Genome analysis predicted the presence of several genes for the degradation of a variety of aliphatic and aromatic hydrocarbons as well as genes that confer resistance to a variety of heavy metals. This work has been recently published in Scientific reports journal. Please refer to Scientific Reports. 2021. 11(1):6943.
This work was supported in part by the National Science Foundation under Grant No. OIA-1946093 through OK NSF EPSCoR.