Nanofiltration for the Treatment of Oil Sands-Produced Water

This chapter summarizes nanofiltration (NF) studies focused on the treatment of thermal in-situ steam-assisted gravity drainage (SAGD)-produced water streams in the Alberta, Canada, oil sands industry. SAGD processes use recycled produced water to generate steam, which is injected into oil-bearing formations to enhance oil recovery. NF has potential applications in the produced water recycling treatment process for water softening, dissolved organic matter removal, and partial desalination, to improve recycle rates, reduce make-up water consumption, and provide an alternative to desalination technologies (thermal evaporation and reverse osmosis). The aim of this study was to provide proof-of-concept for NF treatment of the following produced water streams in the SAGD operation: warm lime softener (WLS) inlet water, boiler feed water (BFW), and boiler blowdown (BBD) water. Commercial NF membranes enabled removal of up to 98% of the total dissolved solids (TDS), total organic carbon (TOC), and dissolved silica, which is significant compared to the removal achieved using conventional SAGD-produced water treatment processes. More than 99% removal of divalent ions was achieved using tight NF membranes, highlighting the potential of NF softening for oil sands-produced water streams. The NF process configurations studied provide feasible process arrangements suitable for integration into existing and future oil sands and other produced water treatment schemes

Drinking water coagulation with polyaluminum coagulants: Mechanisms and selection guidelines

In recent years, polyaluminum coagulants have received considerable interest as drinking water coagulants. Many types of polyaluminum coagulants are commercially available, including polyaluminum chloride (PACl), aluminum chlorohydrate, and polyaluminum sulfate (PAS). Unlike alum, these products differ in their basicity and strength, and can contain varying amounts of other substances, such as sulfate, silica, and calcium. The chemistry of polyaluminum coagulants is not well known, coagulation mechanisms have not been studied as extensively, and comprehensive guidelines on the selection and use of these different polyaluminum coagulants currently do not exist. In this research, several polyaluminum coagulants were examined for five different raw water types and three solid-liquid separation processes. Coagulants of different chemistry were evaluated: alum, PACl, PAS, and aluminum chlorohydrate. PACls of low, medium, and high basicities, with or without sulfate were examined. The solubility and Al speciation of the coagulants were investigated. As well, treatment experiments were performed with five widely different water supplies with sedimentation, dissolved air flotation (DAF) and direct filtration. The performance of the coagulants was evaluated for turbidity and NOM removal. Guidelines were developed for choosing polyaluminum coagulants and selecting doses based on water quality parameters, coagulant characteristics, and treatment process. The results of this research indicate that significant differences exist between the solubility of the PACls, PAS, aluminum chlorohydrate, and alum. Aluminum chlorohydrate had the highest solubility and the highest pH of minimum solubility, followed by the PACls, PAS, and alum. For the PACls, the pH of minimum solubility tended to increase with increasing basicity. The Al speciation data indicated that high basicity PACls contain the largest fraction of dissolved polymeric species in solution over the broadest pH range. The polymeric fraction present, or the pH range over which polymer was present, decreased as basicity was decreased. The selection of the appropriate coagulant for a given water treatment application was found to depend on the chemical characteristics of the coagulant, the characteristics of the raw water, and the treatment process used. High basicity PACls were found to be effective for all model waters under a wide variety of treatment conditions. PACls with added sulfate or silica were found to be especially effective for sedimentation applications. The presence of sulfate was detrimental for treatment by direct filtration. All of the PACls were effective for DAF treatment applications, although raw water alkalinity did have some influence on coagulant selection

Removal of Organoselenium from Aqueous Solution by Nanoscale Zerovalent Iron Supported on Granular Activated Carbon

Nanoscale zerovalent iron particles (nZVI) immobilized on coconut shell-based granular activated carbon (GAC) were studied to remove organoselenium from wastewater. A chemical reduction technique that involves the application of sodium borohydride was adopted for the adsorbent preparation. The texture, morphology and chemical composition of the synthesized adsorbents were analyzed with a scanning electron microscope (SEM), nitrogen adsorption–desorption isotherms and X-ray diffraction (XRD). Batch experiment with various pHs and contact times were conducted to evaluate nZVI/GAC adsorption performance. The results showed that nZVI/GAC has a strong affinity to adsorb selenomethionine (SeMet) and selenocysteine (SeCys) from wastewaters. The maximum removal efficiency for the composite (nZVI/GAC) was 99.9% for SeCys and 78.2% for SeMet removal, which was significantly higher than that of nZVI (SeCy, 59.2%; SeMet, 10.8%). The adsorption kinetics were studied by pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models. Amongst the two, PSO seemed to have a better fit (SeCy, R2 > 0.998; SeMet, R2 > 0.999). The adsorption process was investigated using Langmuir and Freundlich isotherm models. Electrostatic attraction played a significant role in the removal of organoselenium by nZVI/GAC adsorption. Overall, the results indicated that GAC-supported nZVI can be considered a promising and efficient technology for removing organoselenium from wastewater

Removal of Organoselenium from Aqueous Solution by Nanoscale Zerovalent Iron Supported on Granular Activated Carbon

Nanoscale zerovalent iron particles (nZVI) immobilized on coconut shell-based granular activated carbon (GAC) were studied to remove organoselenium from wastewater. A chemical reduction technique that involves the application of sodium borohydride was adopted for the adsorbent preparation. The texture, morphology and chemical composition of the synthesized adsorbents were analyzed with a scanning electron microscope (SEM), nitrogen adsorption–desorption isotherms and X-ray diffraction (XRD). Batch experiment with various pHs and contact times were conducted to evaluate nZVI/GAC adsorption performance. The results showed that nZVI/GAC has a strong affinity to adsorb selenomethionine (SeMet) and selenocysteine (SeCys) from wastewaters. The maximum removal efficiency for the composite (nZVI/GAC) was 99.9% for SeCys and 78.2% for SeMet removal, which was significantly higher than that of nZVI (SeCy, 59.2%; SeMet, 10.8%). The adsorption kinetics were studied by pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models. Amongst the two, PSO seemed to have a better fit (SeCy, R2 > 0.998; SeMet, R2 > 0.999). The adsorption process was investigated using Langmuir and Freundlich isotherm models. Electrostatic attraction played a significant role in the removal of organoselenium by nZVI/GAC adsorption. Overall, the results indicated that GAC-supported nZVI can be considered a promising and efficient technology for removing organoselenium from wastewater

Colloidal Fouling of Nanofiltration Membranes: Development of a Standard Operating Procedure

Fouling of nanofiltration (NF) membranes is the most significant obstacle to the development of a sustainable and energy-efficient NF process. Colloidal fouling and performance decline in NF processes is complex due to the combination of cake formation and salt concentration polarization effects, which are influenced by the properties of the colloids and the membrane, the operating conditions of the test, and the solution chemistry. Although numerous studies have been conducted to investigate the influence of these parameters on the performance of the NF process, the importance of membrane preconditioning (e.g., compaction and equilibrating with salt water), as well as the determination of key parameters (e.g., critical flux and trans-membrane osmotic pressure) before the fouling experiment have not been reported in detail. The aim of this paper is to present a standard experimental and data analysis protocol for NF colloidal fouling experiments. The developed methodology covers preparation and characterization of water samples and colloidal particles, pre-test membrane compaction and critical flux determination, measurement of experimental data during the fouling test, and the analysis of that data to determine the relative importance of various fouling mechanisms. The standard protocol is illustrated with data from a series of flat sheet, bench-scale experiments

Study of the Aggregation Behavior of Silica and Dissolved Organic Matter in Oil Sands Produced Water Using Taguchi Experimental Design

Plant equipment fouling is one of the major problems affecting the performance of steam assisted gravity drainage (SAGD) bitumen extraction processes. The produced water that is treated and reused as boiler feedwater contains high concentration of silica and dissolved organic matter (DOM), and silica and carbon have been found to be principle components of steam generator and heat exchanger foulants. The interactions between silica and SAGD DOM were studied in this research to provide insight into possible fouling mechanisms and mitigation methods. The effects of physicochemical process parameters such as different types of organics, salts, and colloids in the silica–DOM co-precipitation are studied at different concentrations and pHs. In order to study the effects of all physicochemical process parameters at three different levels with a minimum number of experiments, Taguchi experimental design is employed. Analysis of variance is performed to evaluate the contribution of each parameter in the silica–DOM aggregation process. The study revealed that the rate of silica organic co-precipitation varies mainly with the nature of the organics. Further, at higher ionic strength and lower pH of the solution, an enhanced silica–organic aggregation is observed. Multivalent cationic salt is found to be a good coagulating agent to remove humic-like DOM fraction from SAGD produced water

Dissolved Organic Matter in Steam Assisted Gravity Drainage Boiler Blow-Down Water

Steam assisted gravity drainage (SAGD) boiler blow-down (BBD) water contains high concentrations of dissolved organic matter (DOM) and total dissolved solids (TDS). A detailed understanding of the BBD chemistry, particularly the DOM composition, is important for better management and recycle of this water. In this study, we fractionated the dissolved organic matter in the BBD using DAX-8, Dowex, and Duolite resins into hydrophobic and hydrophilic fractions of acid, base, and neutral compounds. Additionally, the DOM was fractionated on the basis of size by filtering the BBD through a series of membranes with progressively tighter molecular weight cutoffs of 10, 3, and 0.5 kDa. Fluorescence excitation–emission matrix spectroscopy (EEMs), specific UV absorbance (SUVA), and FTIR were used to characterize the water samples and the different fractions. The ion exchange fractionation revealed that the DOM contained a high percentage of hydrophobic acids (39%) and hydrophilic neutrals (28.5%). The different ion exchange fractions had distinct fluorescence excitation–emission signatures. The permeate samples from the membrane fractionation, on the other hand, did not reveal any significant difference in the fluorescence EEM spectra, indicating that the hydrophilic and hydrophobic constituents of the DOM could not be separated on the basis of pore size by these membranes. The SAGD boiler blow-down water was found to be significantly concentrated in DOM compared to oil sands mining process affected water

Targeted Removal of Dissolved Organic Matter in Boiler-Blowdown Wastewater: Integrated Membrane Filtration for Produced Water Reuse

The efficacy of coagulation and membrane filtration was studied for the treatment of boiler-blowdown (BBD) wastewater to enable reuse and minimize the overall water consumption in steam-assisted-gravity-drainage (SAGD), thermally enhanced, oil recovery operations. Direct nanofiltration of chemically unadjusted BBD at its original pH was the optimal treatment option with respect to the flux stability and the removal of dissolved organic material and salinity, which if not removed would result in the fouling and failure of downstream process equipment. The naturally high solute hydrophilicity allowed for prolonged operation with an elevated flux of 60 L m⁻² h⁻¹ (LMH) and recovery up to 85% while maintaining solute removal as high as 80% and 45% for dissolved organic carbon and total dissolved solids, respectively. Comparatively, neither precoagulation nor preacidification improved the rejection of dissolved organic material or salinity and consistently resulted in increased membrane surface fouling and flux decline. The proposed filtration treatment solution would result inasmuch as a 4-fold reduction in the volume of makeup water required and BBD wastewater disposed compared to a conventional SAGD facility

Characterization of Boiler Blowdown Water from Steam-Assisted Gravity Drainage and Silica–Organic Coprecipitation during Acidification and Ultrafiltration

In thermally enhanced oil recovery operations, particularly in steam-assisted gravity drainage (SAGD), boiler blowdown (BBD) containing high concentrations of dissolved organic matter (DOM), dissolved silica, and total dissolved solids (TDS) is generated. To develop efficient tools for managing this blowdown, a detailed understanding of its chemistry is required. In this study, BBD was evaporated to yield ∼66% condensate and ∼33% concentrate blowdown (CBD). Detailed characterization of the BBD and CBD water was conducted. The effect of acidification was also studied. The acidification coprecipitates the silica and DOM, with over 90% of the silica and over 40% of the DOM precipitating at pH 4. Ultrafiltration treatment was also examined, and a major fraction of the silica and DOM in the CBD was found to foul a 100 kDa ultrafiltration membrane in the pH range of 7.5 to 9. The analysis revealed that the dominant fouling mechanism was cake filtration, indicating the formation of a silica–DOM precipitate layer on the membrane surface. These studies can provide insight regarding management options for SAGD disposal water