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In the present study, we pyrolyzed a waste tire at various temperatures under an N 2 atmosphere and a water environment in an autoclave reactor to investigate the effect of water on tire degradation. The analysis involved a comparison of product distribution, char properties, oil composition, and the behavior of heteroatom elements (especially oxygen, nitrogen, and sulfur) under different atmospheres. Elemental analysis, functional-group identification, and chemical state analysis of sulfur were performed for chars. In addition, the chemical composition, elemental composition, and molecular weight of the produced oils were evaluated. The heavy fraction of oils, not detectable by gas chromatography-mass spectrometry (GC-MS), was analyzed through Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The findings revealed that high temperatures promoted oil cracking, resulting in the formation of light oils in both pyrolysis and hydrolysis processes. Compared to pyrolysis, hydrolysis generated a higher yield of low molecular–weight oil. Elevated hydrolysis temperatures promoted aromatization, yielding an oil with a low H/C ratio and a high double bond equivalent number. Consequently, the concentration of aromatics in the light fraction of oils generated from the hydrolysis process exceeded that in oils from the pyrolysis process. Temperature exhibited a limited impact on oil composition during the pyrolysis process. Hydrolysis promoted the release of heteroatom-containing compounds at low temperatures. During pyrolysis, nitrogen was gradually released from the solid phase, whereas nitrogen-containing compounds were released early during hydrolysis, with gas-phase nitrogen accounting for more than 50 wt% at 320 °C. A maximum D-limonene yield of 45.58% was obtained at 360 °C within 0 min of hydrolysis, with the potential conversion of D-limonene into aromatics at higher hydrolysis temperatures. These results contribute to the understanding of tire valorization via hydrolysis. [Display omitted] • Higher temperatures can promote the formation of aromatics. • Hydrolysis promote the early release of nitrogen-containing compounds. • Higher hydrolysis temperatures can promote the formation of sulfide. • Temperature has a weak effect on oil composition for pyrolysis process. • Extensive of NxOy, NxOySz, NxSy, Nx and Ox classes formed. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing for oil and gas extraction produces large volumes of wastewater, termed flowback and produced water (FPW), that are highly saline and contain a variety of organic and inorganic contaminants. In the present study, FPW samples from ten hydraulically fractured wells, across two geologic formations were collected at various timepoints. Samples were analyzed to determine spatial and temporal variation in their inorganic composition. Results indicate that FPW composition varied both between formations and within a single formation, with large compositional changes occurring over short distances. Temporally, all wells showed a time-dependent increase in inorganic elements, with total dissolved solids increasing by up to 200,000 mg/L over time, primarily due to elements associated with salinity (Cl, Na, Ca, Mg, K). Toxicological analysis of a subset of the FPW samples showed median lethal concentrations (LC 50) of FPW to the aquatic invertebrate Daphnia magna were highly variable, with the LC 50 values ranging from 1.16% to 13.7% FPW. Acute toxicity of FPW significantly correlated with salinity, indicating salinity is a primary driver of FPW toxicity, however organic components also contributed to toxicity. This study provides insight into spatiotemporal variability of FPW composition and illustrates the difficulty in predicting aquatic risk associated with FPW. [Display omitted] • Flowback and produced water exhibits considerable spatiotemporal variation. • FPW composition varies substantially both within and between geologic formations. • Substantial variation in FPW composition occurs over short physical separation. • Toxicity of FPW to Daphnia magna varies within a well over time and between wells. • Salinization of FPW is a primary driver of toxicity and target for remediation. [ABSTRACT FROM AUTHOR]

Electrochemical oxidation (EO) can effectively remove recalcitrant organic contaminants from produced water (PW) but the formation of toxic oxidation byproducts (OBPs) is an unintended consequence. This study has rigorously investigated the OBPs formation during the EO treatment of a simulated PW containing phenol - a common organic contaminant existing in PW, as a model contaminant. In the absence of ammonia, free chlorine was generated from Cl- oxidation to serve as the main oxidant for phenol oxidation. During the EO process, 2,4,6-trichlorophenol and 2,6-dichlorobenzoquinone were identified as the critical intermediates that led to the formation of carbonaceous OBPs (C-OBPs). Some C-OBPs like chloroform (TCM), chloral hydrate (CH), and trichloroacetic acid (TCAA) reached their peak concentrations of 15 – 180 μM that were then reduced to 1 – 115 μM via volatilization and/or electrochemical reduction. When ammonia was present, nitrogenous OBPs (N-OBPs) were formed with the peak levels of 1 – 10 μM at the chlorination breakpoint (when ammonia was completely removed) that were subsequently reduced below 1 uM via volatilization and/or hydrolysis. It was observed that ammonia significantly decreased the formation of both C-OBPs and chlorate due to the consumption of free chlorine. A higher current density accelerated OBPs formation rates with different effects on volatile and non-volatile OBPs. The results of this study will enhance our understanding of OBPs formation precursors and mechanisms during electrochemical process and help develop strategies for proper control of OBPs to achieve safer electrochemical wastewater treatment. [Display omitted] • Oxidation byproducts are formed during electrochemical treatment of produced water. • Trichlorophenol and dichlorobenzoquinone serve as intermediates for C-OBPs formation. • N-OBPs are formed in ammonia-containing produced water due to chloramine production. • Ammonia reduces C-OBPs and chlorate production by consuming free chlorine. • Higher salinity and current density accelerate OBPs formation rates. [ABSTRACT FROM AUTHOR]

• Gulf war spilled oil was significantly affected by vaporization, due to the high surface temperatures in the desert. • Comparison with data from other oceanic oil spills showed that less significant degradation occurred in Gulf war soil samples. • Chemical compositions differ between contaminated soils at different depths from the surface. In this study, molecular-level chemical compositions of soils contaminated by oil spilled during the Gulf War were studied. Two soil samples, respectively collected at 0.1 m and between 0.5 and 1 m below the surface from an oil spill site, were extracted with organic solvents and water. The extracts were analyzed via ultrahigh resolution FT-ICR and two-dimensional gas chromatography/high resolution mass spectrometry. The data showed that the spilled oil was significantly affected by vaporization due to high surface temperatures in the desert. The data obtained with (+) atmospheric pressure photo ionization (APPI) and (-) electrospray ionization (ESI) coupled with ultrahigh resolution–mass spectrometry (UHR-MS) indicated that the degradation of aromatic compounds and increase in oxygen-containing classes occurred in the following order: surface soil > below surface soil > crude oil. The oxygenated compounds were confirmed by principal component analysis. The score and loading plots of O x and SO x showed that they were the major contributors to differentiate the samples. However, a comparison with previously reported oceanic oil spills showed that less significant degradation occurred even after almost 30 years. Our data can provide an information basis for designing a strategy for clean-up and restoration efforts of Gulf War oil spills. [ABSTRACT FROM AUTHOR]

Accidental releases of highly saline produced water (PW) to land can impact soil quality. The release of associated salts can clog soil pores, disperse soil clays, and inhibit plants and other soil biota. This study explores a novel remediation technique using ferrocyanide to enhance the evaporative flux of soil porewater to transport dissolved salts to the soil surface, where crystallization then occurs. The addition of ferrocyanide modifies crystal growth that enhances salt transport, allowing salt efflorescence on the soil surface and physical removal. Release sites were simulated through beaker sand column experiments using two PWs collected from the Permian Basin. PW composition altered efflorescence, with up to ten times as much ferrocyanide required in PWs than comparable concentrations of pure NaCl solutions. The addition of EDTA reduced dissolved cation competition for the ferrocyanide ion, improving PW salt recovery at the soil surface. The speciation model, PHREEQC, was used to predict the onset of salt precipitation as a function of evaporative water loss and model the effect of aqueous ferrocyanide and EDTA speciation on efflorescence. The results highlight the utility of predictive modeling for optimizing additive dosages for a given release of PW. [Display omitted] • Evaporative flux remediation of soil is enhanced with crystallization modifiers. • Prussian yellow reduces salt crystallization in sands polluted with produced waters. • Single salt solutions oversimplify the behavior of real produced waters. • For some produced waters, remediation is enhanced with EDTA complexing agent. • PHREEQC is an effective tool for predicting crystallization during evaporation. [ABSTRACT FROM AUTHOR]

A thorough understanding of produced water (PW) quality is critical to advance the knowledge and tools for effective PW management, treatment, risk assessment, and feasibility for beneficial reuse outside the oil and gas industry. This study provides the first step to better understand PW quality to develop beneficial reuse programs that are protective of human health and the environment. In total, 46 PW samples from unconventional operations in the Permian Basin and ten surface water samples from the Pecos River in New Mexico were collected for quantitative target analyses of more than 300 constituents. Water quality analyses of Pecos River samples could provide context and baseline information for the potential discharge and reuse of treated PW in this area. Temporal PW and river water quality changes were monitored for eight months in 2020. PW samples had total dissolved solids (TDS) concentrations ranging from 100,800–201,500 mg/L. Various mineral salts, metals, oil and grease, volatile and semi-volatile organic compounds, radionuclides, ammonia, hydraulic fracturing additives, and per- and polyfluoroalkyl substances were detected at different concentrations. Chemical characterization of organic compounds found in Pecos River water showed no evidence of PW origin. Isometric log-ratio Na-Cl-Br analysis showed the salinity in the Pecos River samples appeared to be linked to an increase in natural shallow brine inputs. This study outlines baseline analytical information to advance PW research by describing PW and surrounding surface water quality in the Permian Basin that will assist in determining management strategies, treatment methods, potential beneficial reuse applications, and potential environmental impacts specific to intended beneficial use of treated PW. [Display omitted] • Comprehensive analyses of produced water (PW) quality in the Permian Basin. • Temporal characterization of PW and river water quality in the Permian Basin. • Quantitatively analyzed > 300 analytes for organics, inorganics, and radionuclides. • Provide baseline analytical information to advance PW research for potential reuse. • Filled knowledge gap regarding PW quality to support science-based decision making. [ABSTRACT FROM AUTHOR]

Treatment and reuse of produced water (PW), the largest wastewater stream generated during oil and gas production, provides a promising option to address the increasing clean water demands. High-performance treatment technologies are needed to efficiently remove the organic and inorganic contaminants in PW for fit-for-purpose applications. Photocatalytic membrane reactor (PMR) is an emerging green technology for removal of organic pollutants, photoreduction of heavy metals, photo-inactivation of bacteria, and resource recovery. This study critically reviewed the mechanisms of photocatalysis and membrane processes in PMR, factors affecting PMR performance, rational design, and evaluation metrics for PW treatment. Specifically, PW characteristics, photocatalysts properties, membranes applied, and operating conditions are of utmost importance for rational design and reliable operation of PMR. PW pretreatment to remove oil and grease, colloidal and suspended solids is necessary to reduce membrane fouling and ensure optimal PMR performance. The metrics to evaluate PMR performance were developed including light utilization, exergetic efficiency, water recovery, product water improvement, lifetime of the photocatalyst, and costs. This review also presented the research gaps and outlook for future research. [Display omitted] • Photocatalysis reduces membrane fouling in photocatalytic membrane reactor (PMR). • Affecting factors, rational design and evaluation metrics of PMR are proposed. • PMR degrades organic and inorganic contaminants in produced water. • Recovery of valuable minerals from produced water using PMR is of interest. [ABSTRACT FROM AUTHOR]

Effective extraction of useful resources from high-salinity textile wastewater is a critical pathway for sustainable wastewater management. In this study, an integrated loose nanofiltration-electrodialysis process was explored for simultaneous recovery of dyes, NaCl and pure water from high-salinity textile wastewater, thus closing the material loop and minimizing waste emission. Specifically, a loose nanofiltration membrane (molecular weight cutoff of ~800 Da) was proposed to fractionate the dye and NaCl in the high-salinity textile wastewater. Through a nanofiltration-diafiltration unit, including a pre-concentration stage and a constant-volume diafiltration stage, the dye could be recovered from the high-salinity textile wastewater, being enriched at a factor of ~9.0, i.e., from 2.01 to 17.9 g·L−1 with 98.4% purity. Assisted with the subsequent implementation of electrodialysis, the NaCl concentrate and pure water were effectively reclaimed from the salt-containing permeate coming from the loose nanofiltration-diafiltration. Simultaneously, the produced pure water was further recycled to the nanofiltration-diafiltration unit. This study shows the potential of the integration of loose nanofiltation-diafiltration with electrodialysis for sufficient resource extraction from high-salinity textile wastewater. [Display omitted] • Integration of loose nanofiltration (NF) with electrodialysis is proposed for textile wastewater treatment. • Loose NF-diafiltration enriches the dye from 2.01 to 17.9 g·L−1 with a purity of 98.4%. • 99.94% of salt is removed by loose NF-diafiltration with 7 diavolumes. • Subsequent electrodialysis effectively recovers water and salt from NF-diafiltration permeate. • No significant fouling of ion exchange membranes is observed in electrodialysis performance. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: This work describes a batch single-stage electrochemical process to remove quantitatively the ammonium ion from produced waters from petroleum exploration of the Campos’ Basin, seeking to fulfil the directories of the National Brazilian Environmental Council. The anode was made out of titanium covered by a layer of RuO2 +TiO2 oxides (Dimensionally Stable Anode), whereas the cathode was made out of pure titanium. Anodic and cathodic compartments were separated by a membrane. The applied current varied from 0.3 to 1.5A. As the current increased NH4 + removal was faster and pH was rapidly decreased to 3. The pH of the anodic compartment increased to ∼10. When the current was 0.92A chlorine evolution was observed after 40min or only 15min when that current was 1.50A. In this voltage a deposit containing alkali-earth metal hydroxides/sulphates was formed on the membrane surface of the cathode side, thus suggesting a diffusion process from the anodic to the cathodic compartment. The maximum current applied to the cell must not exceed ∼0.70A in order to avoid chlorine evolution. Ammonia removal was over 99.9wt% at 0.68A in about 75min. [Copyright &y& Elsevier]

Hydraulic fracturing creates large volumes of flowback and produced water (FPW). The waste is a complex mixture of organic and inorganic constituents. Although the acute toxicity of FPW to freshwater organisms has been studied, few have attempted to discern the interaction between organic and inorganic constituents within this matrix and its role in toxicity. In the present study, bioaccumulation assays (7-d uptake and 7-d elimination period) with FPW (1% dilution) were conducted with the freshwater oligochaete, Lumbriculus variegatus , to evaluate the toxicokinetics of inorganic elements. To evaluate the interacting role of organics, bioaccumulation of elements in unmodified FPW was compared to activated carbon treated FPW (AC-modified). Differences in uptake and elimination rates as well as elimination steady state concentrations between unmodified and AC-modified treatments indicated that the organics play an important role in the uptake and depuration of inorganic elements in FPW. These differences in toxicokinetics between treatments aligned with observed growth rates in the worms which were higher in the AC-modified treatment. Whether growth differences resulted from increased accumulation and changes in toxicokinetic rates of inorganics or caused by direct toxicity from the organic fraction of FPW itself is still unknown and requires further research. [Display omitted] • Activated carbon reduced organic concentrations in FPW by nearly 70%. • Organics affected the uptake and elimination of inorganics in FPW. • Organics directly or indirectly affected the toxicity of FPW. • Strontium mimics calcium accumulation in Lumbriculus variegatus. [ABSTRACT FROM AUTHOR]

Produced water is a major waste problem in oil production yet it also represents a potential water source if treated properly, especially in arid regions. In this study, we investigate the anaerobic treatability of an oil-produced water with extremely high chemical oxygen demand (COD) and total dissolved organic carbon (TOC) from Wyoming's Greater Green River Basin using anaerobic microcosms inoculated with a microbial consortium derived from a brewery wastewater treatment facility. The results demonstrate that for this water and an appropriate microbial inoculation, high-COD/TOC can be effectively removed with concomitant energy recovery as a form of methane. 93% and 89% of the COD and TOC were removed with a final high methane yield of 33.9 mmol/g carbon (848 μmol/g carbon/day). Chemical analyses showed that the ethylacetate-extractable compounds were much more amenable to biodegradation than the CH 2 Cl 2 extractable compounds. Furthermore, compounds that were added during drilling and completion remained in the water and contributed significantly to the COD and anaerobic degradability. This study demonstrates that produced waters are amenable to anaerobic biological treatment and also that thorough chemical analyses are necessary to fully understand the potential for treatment. ga1 • Oil-produced water with extremely high COD and TOC can be effectively treated anaerobically. • 93% COD and 89% TOC removal was achieved with microbes from a brewery wastewater facility. • A final high methane yield of 33.9 mmol/g carbon (848 μmol/g carbon/day) was achieved. • High COD concentration may be due to glycerol added during well drilling/completion. [ABSTRACT FROM AUTHOR]

• Degradation kinetics showed strong matrix effects of OPW on PAH oxidation. • Iodide as the leading oxidant consumer altered the degradation trend of aromatics. • Ozone showed the dominant effect on PAHs removal. • UV-LED and TNA inhibited the generation of brominated by-products. • Aromatics contributed to higher acute toxicity than brominated by-products. Offshore produced water (OPW) containing hazardous substances such as polycyclic aromatic hydrocarbons (PAHs) needs to be treated prior to discharge. This study integrated a photocatalytic ozonation system with TiO 2 nanotube arrays (TNA) and UV-light-emitted diode (UV-LED) irradiation and applied to treat OPW. Experimental and modeling efforts were made to evaluate the degradation efficiencies of PAHs, examine the behaviors of the OPW composition (e.g., phenols, iodide, and bromide), and investigate the oxidation intermediates and the associated toxicity and biodegradability. The results indicated that ozone significantly enhanced the oxidation rates and removed the PAHs within 30 min, while the TNA showed strong photocatalytic capability. In the early stage, iodide was a strong ozone competitor, accelerating phenol degradation but inhibiting PAH oxidation, whereas UV-LED fortified the effect. The degradation of aromatics was altered by iodide and bromide at different stages. The contributions of four toxicants to the acute toxicity of OPW were quantified and ranked (PAHs > bromoform > phenols > dibromopentane). The EC 50 value increased from 3 % to 57 %, and the biodegradability was doubled with less footprint in 28-day biodegradation tests. Overall, it is recommended to sequentially oxidize the matrix of OPW by ozonation and PAHs by the UV-LED/TNA/ozone system. [ABSTRACT FROM AUTHOR]

Halophilic consortia strengthen the system against salinity up to a threshold level. Using biocarriers provides an environment with greater resistance to toxicity. Walnut shell captures oil compounds that need more retention time for biodegrdation. Sludge in MBBR has lower volume index and greater particle size distribution. Bacteria and yeast are both involved in the biodegradation of oil in a consortium. 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. [ABSTRACT FROM AUTHOR]

• Ion aggregation phenomenon was found under the polarity reversal electric field. • Soil water-holding capacity would increase with the ion content. • The ion aggregation process significantly impact the bacteria growth. • Transport of bacteria under electric field was affected by water-holding capacity. • The biodegradation promotion effect was weak when ion content extremely high or low. This study investigated changes in soil ion content and soil water-holding capacity during electro-bioremediation (EK-Bio) of petroleum contaminated saline soil (ion content of 3.92 g/kg). The results indicated that the soil ions surrounded the electrodes with increasing time, thus changing the soil water-holding capacity. According to the Van Genuchten model fitting results, the soil residual water content (θr) increased with the soil ion content, which represented a capacity decrease of the soil water supply. At the end of the EK-Bio experiment, the θr values in the soil near (site A) and far from (site B) the electrodes were 19.1 % and 12.1 %, where the soil ion content was 7.92 g/kg and 0.55 g/kg, respectively. The ion aggregation process significantly impacted the growth of soil microbial. The bacteria numbers decreased when the soil ion content was high (7.41 g/kg, site A) and low (0.84 g/kg, site B) after 70 days of treatment. The applied electric field significantly enhanced the bioremediation efficiency. However, the biodegradation promotion effect was the weakest at site A. The synergistic effect between the applied electric field and degrading bacteria was delayed. [ABSTRACT FROM AUTHOR]

• Identical bands were observed in the fingerprint region of different infrared spectra. • Chemical shifts of XPS spectra of N1s, O1s and Al2p after adsorption were explained. • DFT calculations were carried out to illustrate the coordination adsorption. One of the main challenges in cleaning crude oil-contaminated soil is the unknown adsorption mechanism between residual oil and soil. Herein, infrared spectrometer (IR) is used to detect the existence of dibutylphthalate (DBP) and pelargonamide on montmorillonite (MMT) surface. In addition, after the adsorption of DBP and pelargonamide on MMT, the bands in fingerprint region of the two IR spectra are almost identical, indicating coordination bonds were formed on the surface of MMT. X-ray photoelectron spectroscopy (XPS) is employed to detect the chemical environment of N, O and Al. The reverse migration of Al2p spectrum and forward migration of N1s and O1s spectra indicate the coordination adsorption of carbonyl and amine groups on MMT surface. Then, density functional theory (DFT) calculations are applied to make a further explanation of the bonding mechanisms of DBP and pelargonamide onto MMT surfaces. The result shows that there are two types of aluminum on the surface of MMT acting as Lewis acid sites in coordination adsorption, namely Al3+/Si4+ isomorphic substitutions and Al3+ adsorbed on MMT by means of electrostatic adsorption. Meanwhile, the oxygenium on the surface of MMT acts as Brønsted bases in hydrogen bonding adsorption. [ABSTRACT FROM AUTHOR]

• Immobilized P. aeruginosa NY3 removed oil and SS in real PW with high removal capacity. • The function of the used biofilms of P. aeruginosa NY3 could be recovered. • Recovered biofilms of P. aeruginosa NY3 possess higher oil removal ability than the original ones. Produced water (PW) in oilfield, as the largest waste streams in the oil and gas production, has posed a huge threat to the ecosystem. In this work, an environmentally friendly and recyclable biofilms have been developed for treating PW. We discovered that the cells of P. aeruginosa NY3 could be easily immobilized on the surface of polyurethane foam (PUF). Removal efficiency of oil and suspended solids (SS) by immobilized P. aeruginosa NY3 was keeping above 80% and 76% both in a laboratory scale and a pilot scale under suitable pH. Low pH and high value of SS had negative effect on the degradation of oil and SS by P. aeruginosa NY3. Recovery test showed that, the activity of biofilms P. aeruginosa NY3 after running in a pilot scale could be recovered in 5 days. Removal ability of oil in the real PW by the recovered biofilms of P. aeruginosa NY3 was even higher than that of the freshly prepared biofilms. These results indicated that, with a simple pH adjustment, immobilized P. aeruginosa NY3 could be recycled for removing oil and SS in the raw PW resulted from oil production. [ABSTRACT FROM AUTHOR]

• Electrocoagulation (EC) can remove silica from oil sands in situ produced water. • Fe0-EC is better than Al0-EC since the former can also remove sulfide. • In Fe0-EC, silica removal was attributed to adsorption on FeS precipitates. • Fe0-EC consumes less energy than evaporative treatment. • Fe0-EC is a promising technology for the treatment of in situ produced water. Effective removal of silica and sulfide from oil sands thermal in-situ produced water can reduce corrosion and scaling of steam generators, enhancing water recycling and reuse in the industry. The removal of these two solutes as well as calcium and magnesium (i.e., the solutes that can also cause scaling) from synthetic and authentic produced waters by electrocoagulation (EC) was investigated in this study. In Fe0-EC, the precipitation of FeS minerals resulted in a rapid removal of sulfide and adsorption of silica onto FeS. In Al0-EC, silica was removed via adsorption onto aluminum hydroxides, but sulfide was poorly removed. In both EC systems, Ca2+ and Mg2+ were removed from the organic-free synthetic produced water but not from the authentic water, likely due to the influence of organic species. Contaminant removals in Fe0-EC were controlled by charge density (q, C/L) but not current density (i, mA/cm2). Overall, this research suggests that EC can be a promising technology for the treatment of thermal in-situ produced water. Fe0-EC appears to be a better choice than Al0-EC considering that Fe0-EC was more effective at removing sulfide, and that Fe0 anodes are usually less expensive. [ABSTRACT FROM AUTHOR]

• Sequential biowashing-biopile processes were developed for oil-contaminated soil. • Biowashing involved the indigenous soil bacteria that were grown on hemoglobin. • The enrichment culture grown on hemoglobin showed an increased surface activity. • The processes removed 86% TPH in 20 d from the Kuwaiti oil-contaminated soil. • Aged crude oil-contaminated soil can be treated in a timely and efficient manner. The application of biological processes for remediation of the aged crude oil-contaminated soil of Kuwait can be an inefficient way, thus, this study developed 20 d-sequential biowashing and biopile processes where the biowashing step uses an enrichment culture of the indigenous soil bacterial community and the biopile step includes hemoglobin-catalyzed oxidation (HCO). The residual total petroleum hydrocarbons (TPH) concentrations and CO 2 generation were measured to determine the removal efficiency, and the bacterial community changes were studied to investigate the effect of the sequential processes on the soil indigenous bacterial community. The enrichment culture grown on hemoglobin showed an increased surface activity, and this promoted desorption and emulsification of crude oil from the soil sample in the biowashing step resulting in 75% TPH removal. Potential surfactant-producing bacterial species were observed in the soil sample after biowashing. The HCO in the beginning of the biopile step removed 21% of the residual TPH, and further TPH removal was observed with a longer biopile period. Overall, the sequential biowashing and biopile processes removed 86% TPH. The results show that the developed sequential biowashing and biopile processes can be used to efficiently remediate the aged crude oil-contaminated soil of Kuwait. [ABSTRACT FROM AUTHOR]