Produced Water Quality: The Effects of Different Separation Methods for Water and Chemical Floods

Gravity settling represents the main oil-water separation mechanism. Many separation plants rely only on gravity settling with the aid of demulsifiers (direct or reverse breakers) and other chemicals such as water clarifiers if they are required. Yet, other complementary separation methods exist including filtration, flotation, and centrifugation. In terms of results and more specifically with respect to the separated produced-water, the main threshold on its quality is the dispersed oil content. Even with zero discharge and reinjection into hydrocarbon formations, the presence of residual oil in the aqueous phase represents a concern. High oil content results into formation damage and losses in injectivity which necessitates formation stimulations and hence additional operational expenses. In this work, we investigated the effects of different separation techniques on separated water quality. In addition, we studied the impact of enhanced oil recovery (EOR) chemicals on the different separation techniques in terms of efficiency and water quality. Based on the results, we identified potential improvements to the existing separation process. We used synthetic well-characterized emulsions. The emulsions were prepared at the forecast water: oil ratio using dead crude oil and synthetic representative brines with or without the EOR chemicals. To clearly delineate and distinguish the effectiveness of different separation methods, we exacerbated the conditions by preparing very tight emulsions compared with what is observed on site. With that, we investigated three separation techniques: gravity settling, centrifugation, and filtration. First, we used Jar Tests to study gravity settling, then a benchtop centrifuge at two speeds to evaluate centrifugation potential. Finally, for filtration, we tested two options: membrane and deep-bed filtrations. Concerning the water quality, we performed solvent extraction followed by UV analyses to measure the residual oil content as well as light transmission measurements in order to compare the efficiency of different separation methods. The results of analyses suggest that gravity settling was not efficient in removing oil droplets from water. No separation occurred after 20 minutes in every tested condition. However, note that investigated conditions were severe, tighter emulsions are more difficult to separate compared to those currently observed in the actual separation plant. On the other hand, centrifugation significantly improved light transmission through the separated water. Accordingly, we can conclude that the water quality was largely improved by centrifugation even in the presence of EOR chemicals. In terms of filtration, very good water quality was obtained after membrane filtration. However, significant fouling was observed. In the presence of EOR chemicals, filtration lost its effectiveness due to the low interfacial tension with surfactants and water quality became poor. With deep-bed filtration, produced water quality remained good and fouling was no longer observed. However, the benefits from media filtration were annihilated by the presence of EOR chemicals. Based on these results and at least for our case study, we conclude that centrifugation and deep-bed filtration techniques can significantly improve quality of the separated and eventually reinjected water. In terms of the effects of EOR chemicals, the performance of centrifugation is reduced while filtrations are largely impaired by the presence of EOR chemicals. Thereby, integration of any of the two methods in the separation plant will lead to more efficient produced-water reinjection, eliminating formation damage and frequent stimulations. Yet, it is important to note that economics should be further assessed.

Produced Water Quality: the Effects of Different Separation Methods

Gravity settling represents the main oil-water separation mechanism. Many separation plants rely only on gravity settling with the aid of demulsifiers (direct or reverse breakers) and others chemicals such as water clarifiers if they are required. Yet, other complementary separation methods exist including filtration, flotation, and centrifugation. In terms of results and more specifically with respect to the separated produced-water, the main threshold on its quality is the dispersed oil content. Even with zero discharge and reinjection into hydrocarbon formations, the presence of residual oil in the aqueous phase represents a concern. High oil content results into formation damage and losses in injectivity which necessitates formation stimulations and hence additional operational expenses. In this work, we investigated the effects of different separation techniques on separated water quality. Based on the results, we identified potential improvements to the existing separation process. We used synthetic well-characterized emulsions. The emulsions were prepared at the forecast water:oil ratio using dead crude oil and synthetic representative brine. To clearly delineate and distinguish the effectiveness of different separation methods, we exacerbated the conditions by preparing very tight emulsions compared with what is observed on site. With that, we investigated three separation techniques: gravity settling, centrifugation, and filtration. First, we used jar tests to study gravity settling, then a benchtop centrifuge at two speeds to evaluate centrifugation potential. Finally, for filtration, we tested two options: membrane and deep-bed filtrations. Concerning the water quality, we performed solvent extraction followed by UV analyses to measure the residual oil content as well as light transmission measurements in order to compare the efficiency of different separation methods. The results of analyses suggest that gravity settling was not efficient in removing oil droplets from water. No separation occurred after 20 minutes in every tested condition. However, note that investigated conditions were severe, tighter emulsions are more difficult to separate compared to those currently observed in the actual separation plant. On the other hand, centrifugation significantly improved light transmission through the separated water. Accordingly, we can conclude that the water quality was largely improved by centrifugation. In terms of filtration, very good water quality was obtained after membrane filtration. However, significant fouling was observed. With deep-bed filtration, produced water quality remained good and fouling was no longer observed. On the basis of those results, we conclude that for our case study, centrifugation and deep-bed filtration techniques can significantly improve quality of the separated and eventually reinjected water. Thereby, integration of any of the two methods in the separation plant will lead to more efficient produced-water reinjection, eliminating formation damage and frequent stimulations. Yet, it is important to note that economics should be further assessed.

Produced Water Quality: Uncovering the Effects of Centrifugation for Water and Chemical Floods Using a Dispersion Analyzer

A second stage of gravity settling with the addition of demulsifiers or clarifiers is commonly used in processing plants to further treat the separated produced water. In previous work, we demonstrated gravity settling lower efficiency in removing oil carryover from produced water compared to other processing techniques. Both centrifugation and filtration were found to significantly improve the separated water quality. In this work, we focus on centrifugation and further evaluate its efficiency in improving the quality of separated water for both water and chemical floods, specifically surfactant/polymer (SP) flooding. Samples were firstly prepared to imitate the separation plant projected feed and operations. Synthetic representative brines were prepared and used with dead crude oil to prepare the oil/water emulsions. Emulsion separation was conducted at different temperatures, as well as different concentrations of SP, and the demulsifier. The kinetics and efficiency of separation were thoroughly studied over two stages of separation: primary gravity settling and secondary centrifugation. We performed gravitational separation using bottle tests in order to firstly obtain the separated produced water for use in secondary water treatment studies and to secondly further investigate gravity settling kinetics and efficiency. Water quality, in terms of oil content, was then assessed through solvent extraction and UV analyses. Samples of the produced water separated by the primary gravity settling were then exposed to secondary centrifugation. Centrifugation was performed at different rotational speeds using a dispersion analyzer. Light transmission evolution in space and time was used to study kinetics, efficiency and mechanisms of secondary centrifugation. The results reconfirmed that a single-stage gravity settling is not sufficient to reduce oil carryover to acceptable levels for disposal and re-injection into oilfields. Secondary centrifugation yielded clear and significant improvement in water quality even in the presence of EOR chemicals. With centrifugation, the separation efficiency was a function of the rotational speed. Higher rotational speeds resulted in higher creaming velocities and faster separation. In addition, creaming velocities indicated that higher temperatures yield favorable effects on oil droplets migration and separation rates. This is possibly due to the lower density and larger bouncy at higher temperatures. Based on these results, we conclude that secondary centrifugation is very efficient and effective in improving the quality of separated water. In terms of the effects of investigated EOR formulations, SP addition caused minor but manageable reduction in separated water quality at a level that would not harm conventional disposal practices.

Crystal Growth on Cenospheres from High-Calcium Fly Ash

This work presents a study of cenosphere separation from lignite high-calcium (~24 wt.%) fly ash by centrifugal method; this is the first report for Mae Moh, Thailand, fly ash with this high calcium content using this technique. The effect of centrifugal parameters on cenosphere yield and properties were investigated. Those properties include physical properties, morphology, chemical composition, and mineral phases. The recovery yields are in the range of 0.34–0.64%, approximately one third of the yield obtained from the general gravity settling method. Density, particle size, and morphology of the collected cenospheres appeared to be independent of sequence of the applied speeds and times. Interrelation of chemical composition and mineral phases was established, with the focus on calcium carbonate formation on cenosphere surface and crystallite size study. The study has revealed the preferential formation of calcite–(104) peak is observed–by cenospheres, with stable growth behavior of crystallite sizes obtained from all the centrifugal conditions. The result was compared to that obtained from the sink-float method for a better insight. The influence and limitation of the centrifugal method, the varied parameters, and the relevant reaction pathways on crystal growth process in terms of important dissolving species (i.e., Ca2+ and CO32−) behavior in the ash suspension were discussed.

A New Activated Sludge Model with Membrane Separation–Implications for Sewage and Textile Effluent

A new model for the activated sludge process with membrane separation is presented, based on the effective filtration size. A new size threshold is imposed by the membrane module. The model structure requires a modified fractionation of the chemical oxygen demand and includes chemical oxygen demand fractions entrapped in the reactor or in the flocs as model components. This way, it offers an accurate mechanistic interpretation of microbial mechanisms taking place in membrane activated sludge systems. Denim processing wastewater was selected for model implementation, which emphasized the significance of entrapped fractions of soluble hydrolysable and soluble inert chemical oxygen demand responsible for better effluent quality, while underlining the shortcomings of existing activated sludge models prescribed for systems with conventional gravity settling. The model also introduced particle size distribution analysis as a new experimental instrument complementing respirometric assessments, for an accurate description of chemical oxygen demand fractions with different biodegradation characteristics in related model evaluations.

Appraisal of Super-Fast Membrane Bioreactors by MASM—A New Activated Sludge Model for Membrane Filtration

The structure of existing activated models is inherently deficient in reflecting the major role of the membrane filtration. The study developed a novel model, MASM, for the membrane activated process. The effective filtration size imposed by the membrane module, entrapping larger particles, was adopted as the basis of the proposed model. The model defines a modified form of COD fractionation that accounts for the captured COD fractions as additional model components and utilizes related mass-balance relationships. It was implemented to test the fate of soluble hydrolyzable COD and the system performance of super-fast membrane activated sludge based on real data for the characterization and process kinetics of domestic sewage and denim processing effluents. Model evaluation was carried out for parallel systems with gravity settling and membrane filtration operated at a sludge age range of 0.5–2.0 d. Results reflected significantly better performance by the super-fast membrane activated sludge system for both wastewaters, underlining that it was crucially important to account for the captured COD fractions to provide an accurate evaluation of system behavior and effluent quality. This should also be identified as the major shortcoming of the ASM models for evaluating and predicting the system performance of activated sludge configurations with membrane separation.

Cell isolation and Organoid Culture from Mouse Liver and Small Intestine

Background: Organoid culture enables disease modeling and drug screening in vitro. Organoids are from organs (e.g., brain, small intestine, kidney, lung, and liver). To facilitate the establishment of liver and small-intestinal organoids, we developed a protocol for collecting cholangiocytes and crypts and culturing organoids.Methods: Cholangiocytes were collected from intrahepatic bile ducts, gallbladder, and crypts from the small intestine using gravity settling and multi-step centrifugation methods, and embedded in Matrigel to grow into three-dimensional spheroids in suitable culture medium. Passaging, cryopreservation, and thawing were performed to assess organoid cell stability. RNA and DNA extraction, as well as immunostaining procedure were optimized. For preclinical modeling, the growth rate of cholangiocyte organoids (cho-orgs) was harmonized.Results: Large amount of Cholangiocytes and small intestine crypts were collected. Cholangiocytes developed into cyst-like structures after 3–4 days in Matrigel. After culture for 1–2 weeks, small-intestinal organoids developed buds and formed a mature structure. Cho-orgs from intrahepatic bile ducts grew more slowly but were longer lasting, expressed the cholangiocyte markers Krt19 and Krt7, and recapitulated the in vivo tissue organization.Conclusions: The protocol takes 2–4 weeks to establish a stable organoid growth system. Organoids could be stably passaged, cryopreserved, and recovered. The organoids retained tissue characteristics, including marker expression.

An Assessement of the Air Quality in Apple Warehouses : New Record of Aspergillus Europaeus, Aspergillus Pulverulentus, Penicillium Allii and Penicllium Sumatraense as Decay Agents

Airborne fungi are one of the major components of aeromycobiota known to produce several fungal diseases in fruits. Their presence in indoor environment of warehouses may limit the storage period of apples. Qualitative and quantitative analysis of airborne fungal spores were conducted using gravity settling techniques to detect fungal airspora present in the atmosphere of two apple warehouses in Tunisia. In this study, 375 fungal isolates were obtained and purified. Phylogenetic analysis of Calmodulin, beta-tubulin and ITS regions coupled with phenotypic characterization helped to identify fifteen fungal species. Penicillium exhibited the highest diversity with ten species detected (Penicillium expansum, Penicillium allii, Penicillium polonicum, Penicillium solitum, Penicillium chrysogenum, Penicillium steckii, Penicillium viridicatum, Penicillium sumatraense, Penicillium italicum and Penicillium citrinum), followed by four species of Aspergillus genus (Aspergillus niger, Aspergillus pulverulentus, Aspergillus flavus and Aspergillus europaeus) and Alternaria alternata. In vivo experiments confirmed the pathogenicity of thirteen species at room temperature and under cold-storage conditions. Among them, A. europaeus, A. pulverulentus, P. allii and P. Sumatraense were described for the first time as pathogenic on apples. The present study identified the major airborne fungi associated with postharvest rot in apple storage facilities in Tunisia and may help in efficient control of post-harvest and storage fruit diseases.