Synergistic effect of adsorption and photocatalytic degradation of oilfield-produced water by electrospun photocatalytic fibers of Polystyrene/Nanorod-Graphitic carbon nitride.

Graphitic carbon nitride with nanorod structure (Nr-GCN) was synthesized using melamine as a precursor without any other reagents by hydrothermal pretreatment method. XRD, FTIR, SEM, N2 adsorption-desorption from BET, UV-Vis DRS spectroscopy, and photoluminescence were used to characterize the prepared samples. Also, the photoelectrochemical behavior of nanoparticles was studied by photocurrent transient response and cyclic voltammetry analysis. Polystyrene (PS) fibrous mat was fabricated by electrospinning technique and used as a support for the stabilization of the nanoparticles. The performance of the synthesized nanoparticles and photocatalytic fibers (PS/Nr-GCN) was evaluated in oilfield-produced water treatment under visible light irradiation. During this process, oil contaminants were adsorbed by hydrophobic polystyrene fibers and simultaneously degraded by Nr-GCN. The removal efficiency of chemical oxygen demand (COD) has been obtained 96.6% and 98.4% by Nr-GCN and PS/Nr-GCN, respectively, at the optimum conditions of pH 4, photocatalyst dosage 0.5 g/L, COD initial concentration 550 mg/L, and illumination time 150 min. The gas chromatography-mass spectroscopy analysis results showed 99.3% removal of total petroleum hydrocarbons using photocatalytic fibers of PS/Nr-GCN. The results demonstrated that the GCN has outstanding features like controllable morphology, visible-light-driven, and showing high potential in oily wastewater remediation. Moreover, the synergistic effect of adsorption and photocatalytic degradation is an effective technique in oilfield-produced water treatment.

Saline wastewater treatment by bioelectrochemical process (BEC) based on Al-electrocoagulation and halophilic bacteria: optimization using ANN with new approach.

ABSTRACTIn the present study, a bioelectrochemical reactor (BEC) was utilized to treat two types of real saline produced water (PW). BEC was designed based on the combination of electrocoagulation (EC) process with halophilic microorganisms, and it was assessed in terms of biodegradation of hydrocarbons. The effects of various operating parameters including the current density, electrical contact time (On/Off), hydraulic retention time (HRT), and total dissolved solids (TDS) at different levels on the chemical oxygen demand (COD) removal efficiency, settleability, and performance of isolated halophilic microorganisms were examined. Additionally, a novel neural network (ANN) approach modelling using adaptive factors was used to predict and optimize the effects and interactions between operating parameters during BEC process by predicting complicated mechanisms and variations associated with microorganisms. In addition, a new algorithm was developed for the sensitivity analysis to achieve the optimum operating conditions and obtain maximum efficiency in COD removal, sludge volume index (SVI), mixed liquor suspended solids (MLSS), and specific electrical energy consumption (SEEC), simultaneously. BEC was found to be significantly more effective at removing most hydrocarbons, particularly pristine and phytane. In addition, the results showed a significant improvement in settling ability of the biological flocs with average SVI of 91.5 mL/g and a size of 178.25 µm using BEC. Based on estimated operating costs and energy consumption, BEC was more cost-effective and efficient than other bioelectrochemical systems.

Synthesis, characterization, and application of α-Fe2 O3 @TiO2 @SO3 H photo-Fenton catalyst for photocatalytic degradation of biologically pre-treated wood industry wastewater.

The efficiency of removing chemical oxygen demand (COD) and turbidity from wood wastewater was investigated using a sequencing batch reactor (SBR) and the photo-Fenton process. A total of 94.78% of COD reduction and 99.9% of turbidity removal were observed under optimum conditions of SBR, which consisted of an organic loading rate (OLR) of 0.453 kg COD m-3  day-1 , mixed liquor suspended solids (MLSS) of 4564 mg L-1 , and cycle time of 48 h. A magnetic α-Fe2 O3 @TiO2 @SO3 H nanocatalyst was prepared as a heterogeneous Fenton reagent. The Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), and elemental mapping (MAP) analyses were performed to determine the structure and morphology of synthesized photocatalyst. The response surface methodology (RSM) was used to optimize the process based on a central composite design (CCD). The maximum photocatalytic degradation of 87.54% and COD reduction of 83.35% were achieved at a dosage of 0.6 g L-1 of catalyst, 30 mg L-1 of H2 O2 , and pH of 3.5 for 45 min. The results indicated that a combination of the SBR process and α-Fe2 O3 @TiO2 @SO3 H could be used as an effective method for the treatment of wood wastewater. PRACTITIONER POINTS: A combination of the SBR and photo-Fenton process was introduced as an impressive method for wood industry wastewater treatment. The efficiencies of COD, BOD5 , NO3 -N, PO4 -P, and color removal were obtained according to the standard limits in Iran. To our knowledge, this study is the first report of the use of synthesized α-Fe2 O3 @TiO2 @SO3 H photocatalyst for the wood industry wastewater treatment.

Preparation and application of α-Fe2O3@TiO2@SO3H for photocatalytic degradation and COD reduction of woodchips industry wastewater.

In this study, we investigated the efficiency of photocatalytic degradation and chemical oxygen demand (COD) reduction from woodchips industry wastewater using α-Fe2O3@TiO2@SO3H. A magnetic α-Fe2O3@TiO2@SO3H was prepared as a heterogeneous photo-Fenton catalyst. The Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), and elemental mapping (MAP) analyses were performed to determine the structure and morphology of synthesized photocatalysts. The response surface methodology (RSM) was used to optimize the photo-Fenton process based on a Box-Behnken design (BBD). The parameters such as catalyst dosage, H2O2 dosage, pH, and contact time on photocatalytic degradation and the reduction of COD were studied. The maximum photocatalytic degradation of 93.75% and COD reduction of 86.54% were achieved at a dosage of the catalyst of 1 g L-1, H2O2 dosage of 40 mg L-1, and a pH of 3.5 at 45 min. The kinetics of the photo-Fenton process was studied for the woodchips wastewater treatment under optimum conditions. The pseudo-second-order kinetic model for photocatalytic degradation and COD reduction was obtained. The results indicated that a α-Fe2O3@TiO2@SO3H could be used as an effective heterogeneous photocatalyst for the treatment of woodchips industry wastewater. Preparation and application of α-Fe2O3@TiO2@SO3H for photocatalytic degradation and COD reduction of woodchips industry wastewater.

Treatment of wood industry wastewater by combined coagulation-flocculation-decantation and fenton process.

In the present research, the efficiency of turbidity and chemical oxygen demand (COD) reduction from the wood industry wastewater (WIW) by the use of a combined coagulation-flocculation-decantation (CFD) - Fenton process was studied. Firstly, the performance of three coagulants such as ferric chloride (FeCl3 ), aluminum sulphate (alum), and polyaluminum chloride (PACl) was evaluated. The polyacrylamide (PAM) was used as a flocculant. The results showed that the polyaluminum chloride had a high removal efficiency. The COD reduction of 84.1% and turbidity removal of 82.0% of were obtained in coagulation-flocculation-decantation (CFD). Secondly, Fenton process was optimized, by the use of a response surface methodology (RSM), with application of a central composite design (CCD). The maximum turbidity and COD removal obtained by this process were 94.1% and 72.5% respectively, under optimal conditions ([Fe2+ ] = 250 mg/L, [H2 O2 ] = 500 mg/L, pH 3.5, time 60 min). The kinetics of COD and turbidity removal were determined by the model of first order. In conclusion, the combination of coagulation-flocculation-decantation (CFD) - Fenton process presented as a remarkable method for wood wastewater treatment. PRACTITIONER POINTS: A combination of coagulation-flocculation-decantation and Fenton process was introduced for the wood industry wastewater treatment. A designed experimental approach for treatment of wood industry wastewater using a Fenton process was studied. The yields of COD, BOD5 , N-NO3 , P-PO4 , and dye removal were obtained according to the standard limits in Iran.

Removal of TCOD and phosphate from slaughterhouse wastewater using Fenton as a post-treatment of an UASB reactor.

A pilot was designed to study the removal efficiencies of total chemical oxygen demand (TCOD) and phosphate by a combined biological and chemical method. Two stages of Up-flow anaerobic sludge blanket (UASB) reactor and advanced oxidation processes was operated in batch mode. The UASB reactor was operated with hydraulic retention time of 26 h. UASB removal efficiency of TCOD and phosphate were 62.2 and 36.5%, respectively. Fenton process was used as a post-treatment so as to remove organic matter and nutrients. At this stage, the removal efficiencies of TCOD and phosphate were investigated considering the effect of parameters such as pH, hydrogen peroxide and Fe (II) dose based on Taguchi experimental design. Accordingly, under optimum conditions, pH = 3, 1000 mg/l of H2O2 and 400 mg/l of Fe (II) the removal efficiencies of TCOD and phosphate reached 95.41 and 85.29%, respectively. The combined method removed TCOD and phosphate up to 98.6 and 90.5%, respectively.

Application of isolated halophilic microorganisms suspended and immobilized on walnut shell as biocarrier for treatment of oilfield produced water.

Salinity expressed as total dissolved solids (TDS), is the most challenging parameter in bioremediation of produced water which may inhibit the microbial activities and cause sedimentation problems. The present study explores the feasibility of using walnut shell as an inexpensive and accessible adsorbent-carrier for the immobilization of isolated halophilic microorganisms for treatment of synthetic oilfield produced water. The moving bed biofilm reactor (MBBR) was examined with influent chemical oxygen demand (COD) concentrations from 900 to 3600 mg L-1, TDS concentrations from 35,000-200,000 mg L-1, and cycle times from 24 to 72 h. Comparison of the MBBR with the conventional sequencing batch reactor (SBR) indicated that both systems operated at lower influent COD and TDS concentrations satisfactorily; but at higher TDSs (above 150,000 mg L-1) the MBBR was more resistant to the shocks of toxicity (salinity) and organic load relative to the SBR. Also, the effluent turbidity was lower and the free sludge settling property was more favorable in the MBBR with average sludge volume index (SVI) of 38.8 mL g-1 compared to the SBR with SVI of 98.09 mL g-1. Microbial identification confirmed the presence of eight dominant halophilic species which were hydrocarbon degraders and/or denitrifiers.

Biological treatment of slaughterhouse wastewater: kinetic modeling and prediction of effluent.

In this study three modeling approaches consisting Modified Stover-Kincannon, multilayer perceptron neural network (MLPANN) and B-Spline quasi interpolation were applied in order to predict effluent of up-flow anaerobic sludge blanket (UASB) reactor and also to find the reaction kinetics. At first run, the average total chemical oxygen demand (TCOD) removal efficiency was 48.3% with hydraulic retention time (HRT) of 26 h and 63.8% with HRT of 37 h, at OLR of 0.77-1.66 kg TCOD/m3 d. At the second run, UASB reactor operated with OLR of 1.94-3.1 kg TCOD/m3 d and achieved the average TCOD removal efficiency of 64.74 and 72.48% with HRT of 26 and 37 h, respectively. The Modified Stover-Kincannon performed well in terms of kinetic determination with a high value of regression coefficient over 0.98. The B-Spline quasi interpolation and MLPANN indicated a great fit for effluent prediction with average R of 0.9984 and 0.9986, and MSE of 157.6050 and 129.7796, respectively; however, they gave no information about reactions occurred in the system.

Preparation and application of α-Fe2O3@MIL-101(Cr)@TiO2 based on metal-organic framework for photocatalytic degradation of paraquat.

In this study, a new magnetic α-Fe2O3@MIL-101(Cr)@TiO2 photocatalyst was successfully synthesized. The material synthesized had been fully characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, vibrating sample magnetometry, transmission electron microscopy, and Brunauer-Emmett-Teller isotherm methods. The X-ray diffraction analysis corroborates that nanoparticles are polycrystalline with rhombohedral and tetragonal crystal structures for Fe2O3 and TiO2, respectively. In addition, the photocatalytic degradation of the herbicide paraquat in the presence of α-Fe2O3@MIL-101(Cr)@TiO2 under ultraviolet (UV) irradiation was studied. The effect of experimental parameters such as the initial concentration of catalyst, the pH, and the initial paraquat was investigated. The optimal conditions were achieved for concentration of catalyst 0.2 g L-1, pH 7, and concentration of paraquat 20 mg L-1. The photocatalytic degradation efficiency was 88.39% after 15 min with α-Fe2O3@MIL-101(Cr)@TiO2 under UV irradiation. The pseudo-second-order kinetic model for photocatalytic degradation of paraquat was obtained. The catalysts could be recovered and reused without any loss of efficiency for five times in the consequent reactions. To the best of our knowledge, this is the first report on the photocatalytic degradation of paraquat using new α-Fe2O3@MIL-101(Cr)@TiO2 photocatalyst under UV irradiation condition.

Efficiency evaluation of the membrane/AOPs for paper mill wastewater treatment.

The treatment of pulp and paper mill wastewater by combining an ultrafiltration (UF) membrane and advanced oxidation processes (AOPs) was investigated at a bench scale. In the present study, the effects of impressive parameters on membrane fouling such as CaCl2 (mg/L), pH, and temperature (°C) were studied using response surface methodology (RSM). According to the results yielded, at the temperature of 45°C, pH of 10 and CaCl2 concentration of 400 mg/L, the fouling reached its minimum (32%). Therefore, scanning electron microscopy (SEM) analyses showed that the average thickness of cake layer on the UF surface decreased from approximately 75.37 µm to 11.38 µm by optimizing the operating conditions. The results showed the UF permeate quality is not sufficient. Thus, AOPs applied for permeate. In this way, the performance of sulfate and hydroxyl radicals, generated by the activation of oxidants, such as persulfate ([Formula: see text]) and H2O2, by Fe(II) for removal efficiencies was examined. Accordingly, under the optimum conditions of Filtration/Fenton ([H2O2] = 15 mM, [Fe(II)] = 6 mM, pH = 3), the removal efficiency of chemical oxygen demand (COD), UV254, and UV280 was 95.02%, 86.74%, and 87.08%, respectively. This is while, in the optimum conditions of Filtration/[Formula: see text]/Fe(II) ([[Formula: see text]] = 7 mM, [Fe(II)] = 2 mM and pH = 6), the removal efficiency of COD, UV254, and UV280 reached 94.96%, 92.04%, and 90.16%, respectively. This is indicative of the fact that the process of Filtration/[Formula: see text]/Fe(II), with a lower oxidant and catalyst concentration and pH close to the neutral range is more efficient than that of Filtration/Fenton.

Application of membrane-coupled sequencing batch reactor for oilfield produced water recycle and beneficial re-use.

Oil and gas field wastewater or produced water is a significant waste stream in the oil and gas industries. In this study, the performance of a membrane sequencing batch reactor (MSBR) and membrane sequencing batch reactor/reverse osmosis (MSBR/RO) process treating produced wastewater were investigated and compared. The MSBR was operated in different hydraulic residence time (HRT) of 8, 20 and 44 h. Operation results showed that for a HRT of 20 h, the combined process effluent chemical oxygen demand (COD), total organic carbon (TOC) and oil and grease (O&G) removal efficiencies were 90.9%, 92% and 91.5%, respectively. The MSBR effluent concentration levels met the required standard for oil well re-injection. The RO treatment reduced the salt and organic contents to acceptable levels for irrigation and different industrial re-use. Foulant biopsy demonstrated that the fouling on the membrane surface was mainly due to inorganic (salts) and organic (microorganisms and their products, hydrocarbon constituents) matters.

Review of technologies for oil and gas produced water treatment.

Produced water is the largest waste stream generated in oil and gas industries. It is a mixture of different organic and inorganic compounds. Due to the increasing volume of waste all over the world in the current decade, the outcome and effect of discharging produced water on the environment has lately become a significant issue of environmental concern. Produced water is conventionally treated through different physical, chemical, and biological methods. In offshore platforms because of space constraints, compact physical and chemical systems are used. However, current technologies cannot remove small-suspended oil particles and dissolved elements. Besides, many chemical treatments, whose initial and/or running cost are high and produce hazardous sludge. In onshore facilities, biological pretreatment of oily wastewater can be a cost-effective and environmental friendly method. As high salt concentration and variations of influent characteristics have direct influence on the turbidity of the effluent, it is appropriate to incorporate a physical treatment, e.g., membrane to refine the final effluent. For these reasons, major research efforts in the future could focus on the optimization of current technologies and use of combined physico-chemical and/or biological treatment of produced water in order to comply with reuse and discharge limits.