Oil removal from produced water by conjugation of flotation and photo-Fenton processes

Highly efficient lead removal from water by Nd0.90Ho0.10FeO3 nanoparticles and studying their optical and magnetic properties

Ho-doped NdFeO3 was synthesized using the citrate method. The X-ray diffraction (XRD) illustrated that Nd0.90Ho0.10FeO3 was crystalline at the nanoscale, with a crystallite size of 39.136 nm. The field emission scanning electron microscope (FESEM) illustrated the porous nature of Nd0.90Ho0.10FeO3, which increases the active sites to absorb the heavy metals on the sample surface. Energy-dispersive X-ray (EDX) data assures the prepared sample has the chemical formula Nd0.90Ho0.10FeO3. The magnetic properties of Nd0.90Ho0.10FeO3 were determined using the magnetization hysteresis loop and Faraday's method. Many magnetic parameters of the sample have been discussed, such as the coercive field, the exchange bias (Hex), and the switching field distribution (SFD). Ho-doped NdFeO3 has an antiferromagnetic (AFM) character with an effective magnetic moment of 3.903 B.M. The UV-visible light absorbance of Nd0.90Ho0.10FeO3 is due to the transfer of electrons from the oxygen 2p state to the iron 3d state. Nd0.90Ho0.10FeO3 nanoparticles have an optical direct transition with an energy gap Eg = 1.106 eV. Ho-doped NdFeO3 can adsorb many heavy metals (Co2+, Ni2+, Pb2+, Cr6+, and Cd2+) from water. The removal efficiency is high for Pb2+ ions, which equals 72.39%. The Langmuir isotherm mode is the best-fit model for adsorbing the Pb2+ ions from water.

Removal of organic pollutants in shale gas fracturing flowback and produced water: A review

Shale gas has been developed as an alternative to conventional energy worldwide, resulting in a large amount of shale gas fracturing flowback and produced water (FPW). Previous studies focus on total dissolved solids reduction using membrane desalination. However, there is a lack of efficient and stable techniques to remove organic pollutants, resulting in severe membrane fouling in downstream processes. This review focuses on the concentration and chemical composition of organic matter in shale gas FPW in China, as well as the hazards of organic pollutants. Organic removal techniques, including advanced oxidation processes, coagulation, sorption, microbial degradation, and membrane treatment are systematically reviewed. In particular, the influences of high salt on each technique are highlighted. Finally, different treatment techniques are evaluated in terms of energy consumption, cost, and organic removal efficiency. It is concluded that integrated coagulation-sorption-Fenton-membrane filtration represents a promising treatment process for FPW. This review provides valuable information for the feasible design, practical operation, and optimization of FPW treatment.

Evaluation of Fenton and modified Fenton oxidation coupled with membrane distillation for produced water treatment: Benefits, challenges, and effluent toxicity

Membrane distillation is a promising technology to desalinate hypersaline produced waters. However, the organic content can foul and wet the membrane, while some fractions may pass into the distillate and impair its quality. In this study, the applicability of the traditional Fenton process was investigated and preliminarily optimized as a pre-treatment of a synthetic hypersaline produced water for the following step of membrane distillation. The Fenton process was also compared to a modified Fenton system, whereby safe iron ligands, i.e., ethylenediamine-N,N'-disuccinate and citrate, were used to overcome practical limitations of the traditional reaction. The oxidation pre-treatments achieved up to 55% removal of the dissolved organic carbon and almost complete degradation of the low molecular weight toxic organic contaminants. The pre-treatment steps did not improve the productivity of the membrane distillation process, but they allowed for obtaining a final effluent with significantly higher quality in terms of organic content and reduced Vibrio fischeri inhibition, with half maximal effective concentration (EC₅₀) values up to 25 times those measured for the raw produced water. The addition of iron ligands during the oxidation step simplified the process, but resulted in an effluent of slightly lower quality in terms of toxicity compared to the use of traditional Fenton.

Oil field-produced water treatment: characterization, photochemical systems, and combined processes

Produced water, a mixture of inorganic and organic components, comprises the largest effluent stream from oil and gas activities. The removal of contaminants from this wastewater is receiving special attention of the researchers since most of them are persistent and difficult to remove with simple techniques. Several technologies from conventional to advanced oxidation processes have been employed to treat produced water. However, the achievement of greater efficiency may be conditioned to a combination of different wastewater treatment techniques. Hereupon, the present paper discusses three important aspects regarding produced water treatment: analytical methods used for characterization, relevant aspects regarding photochemical systems used for advanced oxidation processes, and combined techniques for treating oil field wastewaters. Analytical methods employed for the quantification of the main species contained in produced water are presented for a proper characterization. Photochemical aspects of the reaction systems such as operating conditions, types of irradiation sources, and technical details of reactors are also addressed. Finally, research papers concerning combined treatment techniques are discussed focusing on the essential contributions. Thus, this manuscript aims to assist in the development of novel techniques and the improvement of produced water treatment to obtain a high-quality treated effluent and reduce environmental impacts.

Current Challenges and Advancements on the Management of Water Retreatment in Different Production Operations of Shale Reservoirs

Nowadays, water savings on industrial plants have become a significant concern for various plants and sections. It is vitally essential to propose applicable and efficient techniques to retreat produced water from onshore and offshore production units. This paper aimed to implement the PFF (Photo Fenton Flotation) method to optimize the water treatment procedure, as it is a two-stage separation technique. The measurements were recorded for the HF (hydraulic fracturing) and CEOR (chemically enhanced oil recovery) methods separately to compare the results appropriately. To assure the efficiency of this method, we first recorded the measurements for five sequential days. As a result, the total volume of 2372.5 MM m3/year of water can be saved in the HF process during the PFF treatment procedure, and only 20% of this required fresh water should be provided from other resources. On the other hand, the total volume of 7482.5 MM m3/year of water can be saved in CEOR processes during the PFF treatment procedure, and only 38% of this required fresh water should be provided from other resources. Therefore, the total water volume of 9855 MM m3 can be saved each year, indicating the efficiency of this method in supplying and saving the water volume during the production operations from oilfield units.

Protocol for Preparing Synthetic Solutions Mimicking Produced Water from Oil and Gas Operations

Produced water (PW) is the water associated with hydrocarbons during the extraction of oil and gas (O&G) from either conventional or unconventional resources. Existing efforts to enhance PW management systems include the development of novel membrane materials for oil-water separation. In attempting to evaluate these emerging physical separation technologies, researchers develop various formulations of test solutions aiming to represent actual PW. However, there is no clear scientific guideline published in the literature about how such a recipe should be prepared. This article develops a protocol for preparing synthetic solutions representing the characteristics and behavior of actual PW and enabling the performance comparisons of different oil-water separation membranes at the bench scale level. In this study, two different brine recipes were prepared based on salts present in actual PW, crude oil was used as the hydrocarbon source, and a surfactant was added to disperse the oil into the aqueous phase. The recipe is accessible to the wider scientific community and was proven to be reproduceable, homogenous, stable, and comparable to actual PW field samples through analytical monitoring measurements and bench scale evaluations.

Fouling mitigation in produced water treatment by conjugation of advanced oxidation process and microfiltration

This work explored the use of ozonation and photoperoxidation before the microfiltration process to reduce fouling. Produced water was synthesized with salt, viscosifier, and surfactant. The additives influence on membrane fouling was evaluated. Photoperoxidation process led to an overall better performance than ozonation in terms of oil removal and fouling reduction. The maximum oil removal efficiency was 86%, obtained for emulsions with salt after 2 h of treatment (COD: H₂O₂ ratio 1:1, UV dose of 965 J/m²). The inclusion of chemical additives impaired the oxidative power of hydroxyl radicals leading to a moderate oil removal; however, they were still able to reduce membrane fouling, mainly in oil/water emulsions with viscosifier. Higher salt concentration promoted fouling resistance and also benefited the permeate quality. Cross-flow microfiltration process integrated with photoperoxidation was able to improve the permeate flux from 84 to 182 L/m².h after 3 h of exposure to UV radiation, resulting in a permeate with less than 10 mg/L of oil content. Graphical abstract.

Application of Cordia trichotoma sawdust as an effective biosorbent for removal of crystal violet from aqueous solution in batch system and fixed-bed column

In this work, for the first time, Cordia trichotoma sawdust, a residue derived from noble wood processing, was applied as an alternative biosorbent for the removal of crystal violet by discontinuous and continuous biosorption processes. The optimum conditions for biosorption of crystal violet were 7.5 pH and a biosorbent dosage of 0.8 g L^-1. The biosorption kinetics showed that the equilibrium was reached at 120 min, achieving a maximum biosorption capacity of 107 mg g^-1 for initial dye concentration of 200 mg L^-1. The Elovich model was the proper model for representing the biosorption kinetics. The isotherm assays showed that the rise of temperature causes an increase in the biosorption capacity of the crystal violet, with a maximum biosorption capacity of 129.77 mg g^-1 at 328 K. The Langmuir model was the most proper model for describing the behavior. The sign of ΔG⁰ indicates that the process was spontaneous and favorable, whereas the ΔH⁰ indicates an endothermic process. The treatment of the colored simulated effluent composed by dyes and salts resulted in 80% of color removal. The application of biosorbent in the fixed-bed system achieved a breakthrough time of 505 min, resulting in 83.35% of color removal. The Thomas and Yoon-Nelson models were able to describe the fixed-bed biosorption behavior. This collection of experimental evidence shows that the Cordia trichotoma sawdust can be applied for the removal of crystal violet and a mixture of other dyes that contain them.

Colloid chemistry and experimental techniques for understanding fundamental behaviour of produced water in oil and gas production

Due to increasing volumes of produced water and environmental concerns related to its discharge, water treatment has become a major challenge during the production of crude oil and natural gas. With continuously stricter regulations for discharging produced water to sea, the operators are obliged to look for ways to improve the treatment processes or re-use the water in a beneficial way, for example as a pressure support during oil recovery (produced water re-injection). To improve the knowledge of the underlying phenomena governing separation processes, detailed information of the composition and interfacial properties of produced water is undoubtedly useful and could provide valuable input for better understanding and improving separation models. This review article summarizes knowledge gained about produced water composition and the most common treatment technologies, which are later used to describe the fundamental phenomena occurring during separation. These colloidal interactions, such as coalescence of oil droplets, bubble-droplet attachment or partitioning of components between oil and water, are of crucial importance for the performance of various technologies and are sometimes overlooked in physical considerations of produced water treatment. The last part of the review deals with the experimental methodologies that are available to study these phenomena, provide data for models and support development of more efficient separation processes.

Feasible analysis of reusing flowback produced water in the operational performances of oil reservoirs

Water reuse is considered one of the most efficient and optimum ways in petroleum industries to address the water scarcity problem. The effluents which are made by the petroleum operations are supposed to be one of the hazardous materials when they are discharged to the environment. The objective of this study is to measure the volume of the required water for the operational performances of the studied oil field. To do this, the necessary water and the volume of provided treated water for the waterflooding, tertiary flooding, and hydraulic fracturing procedures are appropriately measured and by the utilization of photo-Fenton/flotation are administered to remove the oil droplets. According to the observational measurements, it is clarified that hydraulic fracturing has supplied approximately 93% of its required water by the treatment of flowback water and it virtually eliminated the necessity of fresh water from local or domestic water resources. Moreover, the total freshwater that has been saved in this oil field is investigated about 80% of the total required water for their performances. Consequently, the lower need of fresh water from local resources would reduce the unnecessary expenses to provide this volume of water and would save fresh water for about 2750 inhabitants for 1 year to overcome the issue of water scarcity in the world.

Treatment of produced water originated from oil and gas production wells: a pilot study and cost analysis

Produced water originated from oil and gas production wells was treated by a pilot-scale system including pre-treatment (chemical precipitation), pre-filtration, and post-filtration units. Pre-filtration unit consisted of sand filter, granulated activated carbon (GAC) filter, and ultrafiltration (UF) membrane. Post-filtration unit included reverse osmosis (RO) membrane unit. In this study, two different RO membranes including sea water (SW) and brackish water (BW) membranes were comparatively evaluated in terms of treatment and filtration performance. Besides, a cost analysis was conducted for a real scale RO membrane unit by using the data obtained from the pilot plant study. Average fluxes of 12.7 and 9.4 L/m² h were obtained by SW and BW membrane units, respectively. Higher COD and conductivity removal efficiencies were obtained by SW membrane in comparison to BW membrane. Total cost of 0.88 €/m³ was estimated for a RO plant treating produced water with a flowrate capacity of 300 m³/d.

Ozonation of offshore produced water: kinetic study and fuzzy inference system modeling

Ozonation has been recently proposed as a treatment option to remove toxic and recalcitrant organics from offshore produced water (OPW). In this study, experimental and modeling approaches were used to investigate the removal of polycyclic aromatic hydrocarbons (PAHs) from OPW by ozonation. It was found that ozonation can effectively remove PAHs by following the pseudo first-order kinetic model, which could cover both direct and indirect ozonation pathways. The decay rate constants of most PAHs were as low as 0.01-0.16 min^-1, possibly due to the interference caused by OPW matrix. The effects of ozone dose, bubble size, pH, and temperature on five representative PAHs were investigated along with their possible interactions. Based on the experimental results, a novel multi-output adaptive network-based fuzzy inference system (MO-ANFIS) was developed to model the removal of four individual PAHs and total PAHs. The overall RMSE and R between measured and modeled removal rates were 6.60% and 0.98, respectively, indicating a good model fit. This study demonstrated the effectiveness of ozonation in OPW treatment and the potential applicability of MO-ANFIS for process modeling and control.

Parameters Affecting Adsorption and Photocatalytic Degradation Behavior of Gentian Violet under UV Irradiation with Several Kinds of TiO2 as a Photocatalyst

The photocatalytic decolorization of Gentian violet (GV) from an aqueous solution was studied by focusing on comparison of the photoactivity of different type of TiO2 catalyst. The process was carried out under a variety of conditions. The efficiency of P25-Degussa and PC50-Millennium photocatalysts were compared. The effect of different parameters such as pH, initial dye concentration, catalyst loading and the presence of some anions on both adsorption in the absence of light and the degradation under UV irradiation have been studied. 365 nm UV-A lamp was employed as irradiation source. The kinetic study showed that no correlation was observed between the adsorption capacity of the catalyst and its photoactivity, despite of this the effect of various parameters on adsorption and photocatalytic kinetic behavior was practically similar on various catalysts. The photocatalytic degradation of GV followed first-order reaction kinetics and the higher adsorption and photocatalytic degradation were obtained at the alkaline medium (pH = 10 for P25 and pH = 8 for PC50). However, the reaction at the acidic medium was gradually delayed due to the effect of charge repulsion. The presence of some anions (Cl−, SO42−, NO3−) in the medium at higher concentration was found to reduce the adsorption and to inhibit the degradation.

Iron-based adsorbent prepared from Litchi peel biomass via pyrolysis process for the removal of pharmaceutical pollutant from synthetic aqueous solution

A porous iron-based adsorbent obtained from litchi peel via pyrolysis process was prepared in this work, in order to evaluate its adsorptive potential for the removal of a pharmaceutical dye (amaranth) from aqueous solution. The material was characterized by X-ray diffraction, nitrogen adsorption-desorption isotherms, and scanning electron microscopy. Several isotherm and kinetic models were tested aiming to represent the amaranth dye adsorption. The prepared sample presented magnetic property, and a mesoporous texture constituted of graphite and three iron-based phases. The adsorption kinetics of amaranth on the adsorbent followed the pseudo-second-order model, whereas the equilibrium data were in good agreement with the BET isotherm, being represented by a sigmoid-shaped adsorption isotherm. The maximum adsorption capacity for the amaranth dye was found to be 44.87 mg g^-1, demonstrating that the material prepared in this work showed to be a promising adsorbent for the removal of amaranth from aqueous solution.