Produced water is the largest byproduct of oil and gas production. Due to the complexity of produced water, especially dissolved petroleum hydrocarbons and high salinity, efficient water treatment technologies are required prior to beneficial use of such waste streams. Photocatalysis has been demonstrated to be effective at degrading recalcitrant organic contaminants, however, there is limited understanding about its application to treating produced water that has a complex and highly variable water composition. Therefore, the determination of the appropriate photocatalysis technique and the operating parameters are critical to achieve the maximum removal of recalcitrant compounds at the lowest cost. The objective of this review is to examine the feasibility of photocatalysis-involved treatment for the removal of contaminants in produced water. Recent studies revealed that photocatalysis was effective at decomposing recalcitrant organic compounds but not for mineralization. The factors affecting decontamination and strategies to improve photocatalysis efficiency are discussed. Further, recent developments and future research prospects on photocatalysis-derived systems for produced water treatment are addressed. Photocatalysis is proposed to be combined with other treatment processes, such as biological treatments, to partially reduce total organic carbon, break down macromolecular organic compounds, increase biodegradability, and reduce the toxicity of produced water.

Produced water is the largest waste stream associated with oil and gas production. It has a complex matrix composed of native constituents from geologic formation, chemical additives from fracturing fluids, and ubiquitous bacteria. Characterization of produced water is critical to monitor field operation, control processes, evaluate appropriate management practices and treatment effectiveness, and assess potential risks to public health and environment during the use of treated water. There is a limited understanding of produced water composition due to the inherent complexity and lack of reliable and standardized analytical methods. A comprehensive description of current analytical techniques for produced water characterization, including both standard and research methods, is discussed in this review. Multi-tiered analytical procedures are proposed, including field sampling; sample preservation; pretreatment techniques; basic water quality measurements; organic, inorganic, and radioactive materials analysis; and biological characterization. The challenges, knowledge gaps, and research needs for developing advanced analytical methods for produced water characterization, including target and nontarget analyses of unknown chemicals, are discussed.

This study investigated the effects of an electromagnetic field (EMF) on control of membrane fouling and scaling during desalination of brackish groundwater using a pilot reverse osmosis (RO) skid. The groundwater was primarily CaSO₄ type with a total dissolved solids concentration of 5850 mg/L and hardness of 2500 mg/L as CaCO₃. Two EMF devices were installed in the pipeline before a cartridge filter and in the RO feed inlet to induce an electric signal of ±150 kHz to the groundwater. The effects of EMF on membrane scaling were evaluated under accelerated conditions, i.e., without pH adjustment and addition of antiscalant. Two-phase experiments were conducted: Phase 1 (376 h) with the EMF devices turned on after 150 h baseline operation; and Phase 2 (753 h) with the EMF devices turned on from the beginning of testing. The EMF significantly reduced membrane scaling and improved RO performance by 38.3% and 14.3% in terms of normalized water permeability decline rate after 150 h and 370 h operation, respectively. Membrane autopsy results indicated that the fouling layer formed under the influence of EMF was loose with a low density and was easily removed by hydraulic flushing.

Selective removal of arsenic from aqueous solutions with high salinity is required for safe disposal of the concentrate and protection of the environment. The use of drinking water treatment solids (DWTS) to remove arsenic from reverse osmosis (RO) concentrate was studied by batch sorption experiments. The impacts of solution chemistry, contact time, sorbent dosage, and arsenic concentration on sorption were investigated, and arsenic sorption kinetics and isotherms were modeled. The results indicated that DWTS were effective in removing arsenic from RO concentrate. The arsenic sorption process followed a pseudo-second-order kinetic model. Multilayer adsorption was simulated by Freundlich equation. The maximum sorption capacities were calculated to be 170 mg arsenic per gram of DWTS. Arsenic sorption was enhanced by surface precipitation onto the DWTS due to the high amount of calcium in the RO concentrate and the formation of ternary complexes between arsenic and natural organic matter (NOM) bound by the polyvalent cations in DWTS. The interactions between arsenic and NOM in the solid phase and aqueous phase exhibited two-sided effects on arsenic sorption onto DWTS. NOM in aqueous solution hindered the arsenic sorption onto DWTS, while the high organic matter content in solid DWTS phase enhanced arsenic sorption.

Background: Al-doped ZnO (AZO) films were successfully deposited on the glass substrates at temperature 400 °C; by aerosol-assisted chemical vapour deposition method. Zinc acetate dihydrate, aluminum nitrate nonahydrate, methanol were used as a starting material and solvent, respectively. The influences of carrier gas (N2) flow rate on the structural, optical and electrical properties of grown AZO films were full investigated. The research results indicated that the growth orientation between polar and nonpolar faces in ZnO crystal exhibited obvious difference with increasing carrier gas flow rate. Additionally, carrier gas transport also had a great effect on crystal quality, surface structure and electrical properties of the sample. The uniform AZO film with the resistivity value of 6.7×10-3 Ω·cm and optical transmittance of 80% in the visible range was obtained at a suitable carrier gas flow rate of 30 L/h. Methods: AZO films were deposited on glass substrates in air at temperature 400 °C; by the cold-wall AACVD technique. 0.1 M (mol/L) starting solution was prepared from zinc acetate [Zn(CH3COO)2·2H2O] and aluminum nitrate [Al(NO3)3·9H2O] dissolved in methanol, with a constant Al/Zn atomic ratio of 4 at.%. The reagents used in the experiments were analytical grade and utilized without further purification. The glass substrates were previously cleaned by appropriate solvents (detergent, water, methanol or acetone) and dried in air. Then they were placed into a cold-wall reaction chamber, where two clean parallel plates, 8 mm apart, were heated using a graphite block controlled by a thermostat monitored by a Pt–Rh thermocouple. The precursor solution of 35 ml was nebulized by an ultrasonic humidifier with a wave frequency of 1.7 MHz to form an aerosol mist within a glass bottle. The aerosol mist was transported by an inert gas (N2) to reaction chamber, where it evaporated and then the films deposited on the glass substrate. Carrier gas flow rate ranged from 20 L/h to 40 L/h. The substrates and films were allowed to cool to room temperature in situ and were stored in air. The film uniformity on the substrate at each end of carrier gas flow was different from the central area. Residual part of 70 mm was used for testing after cutting out 40 mm from two ends of the sample, respectively. Results: These researches mostly focused on the doping element, solvent, raw materials, concentrate, and temperature, etcetera. Carrier gas (N2) transport is also an important experimental parameter. The present work, therefore, reveals the mechanism of preferred growth orientation for faces was discussed by Fujihara theory and Boundary layer model in CVD system. In addition, the relationship between carrier gas transport and structure, optical and electrical characteristics of the AZO films were also discussed systematacially in the cold-wall AACVD system. Conclusion: In summary, the mass transport process of inert gas (N2) acted as a carrier in AACVD system has obvious effects on preferred growth orientation, crystal quality, surface structure and electrical properties of deposited films. The AZO films with different growth orientation can be obtained by only adjusting carrier gas flow rate. It has a great significance for preparing ZnO films application to different field. Based on boundary layer model, the appropriate carrier gas flow rate is beneficial to achieve high deposition rate and uniform coating film with excellent electrical properties together with light trapping structure. In this work, we fabricate the AZO film with (110) preferred growth orientation on the soda-lime glass substrates at a suitable carrier gas flow rate of 30 L/h. Meanwhile, deposited films have the resistivity value of 6.7×10-3 Ω·cm and optical transmittance of 80% in the visible range. It is a low cost and simple art, we believe the AACVD technique can potentially be used to fabricate a wider range of zinc oxide films with controlled growth orientation and morphology.