Date of Graduation

8-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Chemical Engineering

Advisor/Mentor

Wickramasinghe, S. Ranil

Committee Member

Qian, Xianghong

Second Committee Member

Zhang, Wen

Third Committee Member

Almodovar, Jorge

Fourth Committee Member

Haan, Teow Yeit

Keywords

Produced water; Hybrid membrane processes; Electrocoagulation

Abstract

Produced water (PW) is considered the largest industrial wastewater stream in the world. PW generated from oil and gas operations generally contains a range of contaminants including high total dissolved solids, high total suspended solids, polar and nonpolar organic compounds, and low surface tension dissolved species. Treating PW is very challenging and applying only membrane-based technologies is not sufficient due to membrane fouling, which affects their long-term performance. Hence, integrated membrane processes are required to treat PW effectively. Hybrid membrane processes, which may result from combining a conventional process with a membrane separation, could be used to address the issues of fouling (and wetting), and maximize water recovery. In this dissertation, several hybrid membrane processes are reviewed and the effects of important parameters that determine the performance of these hybrid systems are discussed. While the highly impaired PW is often deep well injected, there is a great deal of interest in treating and recovering this water for beneficial uses. However, the need to use multiple unit operations is essential if these wastewaters are to be recovered. Electrocoagulation (EC) is considered a promising pretreatment technology. In this study, the use of aluminium electrodes for electrocoagulation as a pretreatment operation was investigated. The effects of electrode arrangement, applied current, reaction time, initial pH, and inter electrode distance on the quality of the treated water have been investigated. EC results showed good removal of turbidity (95%), total suspended solids, TSS (90%), and total organic carbon, TOC (70%) by carefully choosing the reaction conditions. Sedimentation was used to separate the treated water from the sludge. The quality of the feed PW can strongly affect the performance of the EC. In addition, a combined electrocoagulation – microfiltration – membrane distillation (EC-MF-MD) process had been used to treat PW. In this work, EC was followed by MF to pretreat the wastewater prior to MD. After EC, the TOC was reduced from 120 mg L-1 to 64 mg L-1. Tangential flow MF using a 0.1 micrometer pore size polyethersulfone membrane was used to separate the particulate matter after EC and to further reduce the TOC to 44 mg L-1. MD was used to desalinate the pretreated PW resulting in a high quality treated water (reducing the total dissolved solids (TDS) concentration from 245,300 mg L-1 to 56 mg L-1). Three membranes with very different surface morphology were tested here: commercially available polyvinylidene fluoride, electrospun poly (vinylidene fluoride-co-hexafluoropropylene) nanofibers and multiwalled carbon nanotube coated polytetrafluoroethylene. The surface properties of an ideal membrane that is resistant to wetting and provides high flux is likely to depend on the TDS and properties of the PW. The integrated electrocoagulation-ultrafiltration-membrane distillation and crystallization process (EC-UF-MDC) was also used to treat PW. The focus of this work was to determine the feasibility of this integrated process for increasing water recovery. The results of this work suggest that optimizing the various unit operations in this integrated process could be used to recover PW. Dissolved organic compounds are known to foul the hydrophobic membrane used in MD. In this study, a significant reduction in membrane fouling was obtained by EC pretreatment, which can lead to a long-term durability of MD system. In addition, the use of MDC can help mitigate the scale formation. Also, treating PW will preserve surface and groundwater, which form 80% of the water utilized in hydraulic fracturing, and reduce the amount of PW directly disposed in Class II disposal wells, which further address the main cause of earthquakes. Finally, the integrated EC-MF pilot-scale system will be used to pretreat and reuse PW. The EC reactor (37.5 L) was built based on experiences gained from working with a laboratory scale (1 L). The integrated process will be evaluated at Texas Tech University (TTU). The design and construction of the EC-MF system are discussed in this work. The pilot-scale system has a capacity of treating 3600 L/day PW. The system layout is also discussed in this study. The EC-MF process was designed based on 70% feed water recovery. Turbidity, TSS, and TOC analysis will be obtained for samples collected during the 5 days operation. The goal of this work is to achieve a reduction of 95, 90, and 70% for turbidity, TSS, and TOC, respectively, which is the pretreated PW quality needed to be further treated by TTU.

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