Semester

Summer

Date of Graduation

2022

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Lian-Shin Lin

Committee Co-Chair

Harry O. Finklea

Committee Member

Fernando Lima

Committee Member

Leslie Hopkinson

Committee Member

Emily Garner

Abstract

Freshwater use for power generation represents the second-largest water use globally. In the United States, freshwater withdrawals for thermoelectric power accounted for 38% of the total freshwater withdrawals for all uses in 2010. Cooling systems are the most water-intensive part of the thermoelectric generation process. For instance, one 300 MW power generator required about 20,000 m3/h circulating cooling water. The cooling operation discharges a large volume of wastewater in the form of blowdown water (10-20% of the consumed water) that requires treatment for reuse or surface discharge. Produced water (PW), the fluid which returns to the surface from hydraulic fracturing during oil and gas production, is one of the largest waste streams in the petroleum industry. More than 70 billion barrels of PW were generated globally in 2009, and 21 billion barrels were produced in the US. It was estimated that approximately 1 million gallons per gas well on average was generated in the Marcellus Shale region. In such a region where blowdown and produced waters are often in close proximity, opportunities exist to develop innovative approaches for water recovery and the generation of useful products from co-managing both waters.

This research aims at developing a co-treatment process to manage BD water and PW jointly for water recovery and generation of useful products. The treatment process consists of mixing, softening, activated carbon filtration, and reverse osmosis (RO) followed by thermal desalination. It is designed to take advantage of the complimentary chemistry of two waters to create chemical and energy synergisms that reduce the chemical and energy footprints of the treatment process. First, sulfate and carbonate from BD water could form chemical precipitation with scale-forming cations in the PW (e.g., Ca, Ba, Sr), which can be achieved by mixing both waters. Second, the high salt content of PW can increase the TDS concentration of the feed stream to the RO, which in turn generates RO reject with a higher TDS concentration that can be more economically concentrated to 10-lb brine by the thermal desalination. Additional opportunities also exist for using the RO reject or the concentrated brine in electrolysis to generate useful products (e.g., NaOH and Cl2) that can be used for softening and other beneficial uses. The research objectives include 1) development of a co-treatment process and evaluate its feasibility of targeted contaminants removal, treatment footprint reduction, and useful products generation, 2) development of a brine electrolysis system to generate sodium hydroxide and chlorine from the concentrate stream of the co-treatment process, and 3) techno-economic analysis of the co-treatment approach and process optimization.

Two treatment scenarios: BD/PW co-treatment and BD water treatment were conducted to evaluate the feasibility and efficiency of the co-treatment compared to the treatment of a single waste stream. Experiments in both scenarios were conducted in batch and continuous operation modes. In all the BD/PW co-treatment experiments, mixing the two streams at a BD: PW volumetric ratio of 10:1 without any chemical addition resulted in >90% Ba removal. In both treatment scenarios, the softening treatment using alkaline chemicals resulted in >99% removal of divalent metals (Ca2+ and Mg2+, Ba2+, and Sr2+), and >90% TOC removal was achieved by activated carbon filtration. RO treatment of the softened mixture resulted in 97-99% TDS rejection and 40-95% water recovery in different experiments.

Brine electrolysis using a two-compartment electrochemical cell reliably generated sodium hydroxide (NaOH, pH >12, faradic efficiency 93%) and free chlorine (faradic efficiency 32%) from NaCl solutions. The generated sodium hydroxide was applied alone or combined with sodium carbonate for softening of three produced water samples

Finally, in the last chapter, the techno-economic analysis was conducted in two different ways: 1) economic comparison between two different scenarios on a lab scale using the experimental and 2) techno-economic analysis of the BD/PW co-treatment on a real-world scale using experimental data and data from published works. In addition, a sensitivity analysis was performed on all major costs and revenues to indicate the parameters which have the greatest effect on the economy of the treatment plant.

Experimental data along with similarly published works confirmed the feasibility of BD/PW co-treatment. Economics analysis also showed that in terms of chemical consumption, the co-treatment process has a unit chemical cost two times less than the sum of the unit chemical cost of BD water and PW treated separately. In terms of energy consumption for 10-lb brine production, considering that 1) RO has significantly lower energy consumption than thermal desalination, and 2) PW alone cannot be fed into RO due to high TDS, the RO treatment of BD/PW can generate concentrate stream for downstream thermal desalination and 10-lb brine production, more economically than BD alone.

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