Mehrdad Ebrahimi
Technische Hochschule Mittelhessen
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Featured researches published by Mehrdad Ebrahimi.
Open Environmental Sciences | 2007
K. Shams Ashaghi; Mehrdad Ebrahimi; Peter Czermak
Produced water is any fossil water that is brought to the surface along with crude oil or natural gas. By far, pro- duced water is the largest by-product or waste stream by volume associated with oil and gas production. The volume of produced water is dependent upon the state of maturation of the field. There is a need for new technologies for produced water treatment due to increased focus on water conservation and environmental regulation. Each time regulatory agencies initiate more stringent environmental control treatment technologies are refined to meet the updated standards. The Euro- pean standard for effluent from onshore petroleum activities requires less than 5 mg/l total hydrocarbons (HC) and less than 10 mg/l suspended solids; such low concentrations are unattainable when classical separation processes are used. To overcome the challenges posed by more stringent regulations, operators have turned to membrane filtration schemes which have the potential to minimize additional costs and disposal issues. Ceramic ultra- and nanofiltration membranes represent a relatively new class of materials available for the treatment of produced water. They can be manufactured from a variety of starting materials and can be processed in different ways to yield products with broad ranges of physical- chemical advantages and applications. While these membranes are effective in the separation of oils, emulsions and silts, they are prone to fouling by waxes and asphaltenes. The issues needing to be addressed are the prevention of membrane fouling during operation and the provision of an expedient, cost-effective and non-hazardous means of cleaning fouled membranes. Currently, there are not enough existing studies related to the treatment of oilfield produced water using ce- ramic membranes.
Advances in Biochemical Engineering \/ Biotechnology | 2013
Zoltán Kovács; Eric Benjamins; Konrad Grau; Amad Ur Rehman; Mehrdad Ebrahimi; Peter Czermak
The market for prebiotics is steadily growing. To satisfy this increasing worldwide demand, the introduction of effective bioprocessing methods and implementation strategies is required. In this chapter, we review recent developments in the manufacture of galactooligosaccharides (GOS) and fructooligosaccharides (FOS). These well-established oligosaccharides (OS) provide several health benefits and have excellent technological properties that make their use as food ingredients especially attractive. The biosyntheses of lactose-based GOS and sucrose-based FOS show similarities in terms of reaction mechanisms and product formation. Both GOS and FOS can be synthesized using whole cells or (partially) purified enzymes in immobilized or free forms. The biocatalysis results in a final product that consists of OS, unreacted disaccharides, and monosaccharides. This incomplete conversion poses a challenge to manufacturers because an enrichment of OS in this mixture adds value to the product. For removing digestible carbohydrates from OS, a variety of bioengineering techniques have been investigated, including downstream separation technologies, additional bioconversion steps applying enzymes, and selective fermentation strategies. This chapter summarizes the state-of-the-art manufacturing strategies and recent advances in bioprocessing technologies that can lead to new possibilities for manufacturing and purifying sucrose-based FOS and lactose-based GOS.
Desalination and Water Treatment | 2012
Mehrdad Ebrahimi; Zoltán Kovács; Maren Schneider; Peter Mund; Peter Bolduan; Peter Czermak
Abstract Oil and gas industries generate large amounts of wastewater as a byproduct in both onshore and offshore production operations. This wastewater is commonly referred to as “produced water” (PW). PW is very difficult to treat and its characteristics changes by well to well. Treatment of this PW could improve the economic viability of these oil and gas fields and lead to a new source of water for beneficial use. This work describes a research project that evaluated the multistage treatment process of oilfield produced water generated from tank dewatering with different ceramic membranes. The investigations focus on the characterization of permeate flux using various ceramic microfiltration (MF), ultrafiltration (UF) and nanofiltration (NF) membranes as potential techniques for efficient treatment of tank dewatering produced water (TDPW). Results for average flux rates, flux degradation, removal of organic substances (measured as TOC) and inorganic substances (measured as the electrical conductivity (...
Desalination and Water Treatment | 2015
Mehrdad Ebrahimi; Steffen Kerker; Sven Daume; Morgan Geile; Frank Ehlen; Ina Unger; Steffen Schütz; Peter Czermak
AbstractThe focus of this study was on the development and application of ceramic hollow fiber membrane (CHFM) technology for the treatment of oilfield produced water (PW) prior to disposal/discharge into the environment. PW refers to any fossil water that is brought to the surface along with crude oil or natural gas. It is a complex mixture of dispersed oil, dissolved organic compounds, suspended solids, production chemicals, heavy metals, and natural radioactive minerals. PW is difficult to handle/treat and represents the largest volume of waste associated with the oil and gas industry. It can have different potential impacts on offshore or onshore environments depending on where it is discharged. Therefore, the development of effective treatment technologies for PW is essential from both ecological and economic standpoints. The first stage of any treatment process for PW consists of a significant reduction in the level of dispersed hydrocarbons and suspended solids. In a second and often in a third sta...
The Open Food Science Journal | 2007
Larisa Engel; Philipp Schneider; Mehrdad Ebrahimi; Peter Czermak
A method for immobilization of β-galactosidase from Kluyveromyces lactis on an adsorptive membrane for the continuous synthesis of galacto-oligosaccharides from lactose was carried out. The immobilization was performed at 4, 10, 15 and 40°C. Two strongly basic anion exchange membranes with tradename Mustang TM Q and Sartobind TM Q were investigated. In static experiments, the highest enzyme activity was measured on Mustang TM Q membranes at the immobi- lization temperature of 10°C. The synthesis of GOS was performed in a Continuous Membrane-Chromatography- Reactor-System (CMCRS) at 40°C and pH 7.0 using 20 wt% initial lactose concentration. The investigated membranes proved to be a good support for the continuous process at high convective flow rates in the enzyme reactor system. Up to 82% lactose conversion with 24% GOS yield was achieved at different fluxes. The corresponding reactor productivity for the production of GOS from lactose in the CMCRS was 98.7 grams GOS per hour and cubic centimeter membrane vol- ume, which significantly exceeds previously reported results.
Desalination and Water Treatment | 2013
Mehrdad Ebrahimi; Oliver Schmitz; Steffen Kerker; F. Liebermann; Peter Czermak
Abstract The purpose of this research paper is to assess the effects of the process parameters—membrane rotational speed (1,200, 1,500 and 1,800 rpm), volume concentration factor (VCF) and feed characteristics—in terms of oil and total organic carbon (TOC) separation capability, permeability and permeate quality. For this, a series of membrane filtration experiments were carried out systematically using rotating ceramic filter discs in a fed-batch operating mode. The variation of membrane rotational speed was found to minimize the membrane fouling in a significant amount. High oil (>99%) and TOC rejection (>98%) was achieved with both microfiltration (MF) and ultrafiltration (UF) membranes, independent of the rotational speed and the feed concentration The experimental results are presented for the dynamic cross-flow MF (0.2-μm pores) and UF (7-nm pores) of oilfield produced water as well as oily model solutions (OMS).
International Journal of Artificial Organs | 2005
Peter Czermak; Mehrdad Ebrahimi; Gerardo Catapano
Poor water properties, use of concentrated bicarbonate, and biofilm growth in pipes and storage tanks often cause dialysis water and dialysate contamination with bacteria and endotoxins. High-flux dialysis with bicarbonate may favor endotoxin transfer from the dialysate into the blood exposing patients to serious short-and long-term side effects. Ultrafiltration across hydrophobic synthetic membranes effectively removes endotoxins from dialysis water by combined filtration and adsorption. However, repeated sterilization worsens the membrane separation properties,and limits their use. Ceramic membranes are generally more resistant to harsh operating conditions than polymeric membranes, and may represent an alternative for endotoxin removal. Previously, we proved that the ceramic membranes commercially available at that time were not retentive enough to ensure production of endotoxin-free dialysis water. In this paper, we investigated the endotoxin removal capacity of new generation commercial ceramic membranes with nominal molecular weight cut-off down to 1,000. In dead-end filtration, all investigated membranes produced water meeting, the European standards, or close to,when challenged with low endotoxin concentrations, but only one membrane type succeeded at high endotoxin concentrations. In cross-flow filtration, none produced water meeting the European standard. Moreover, sterilization and rinsing procedures altered the separation properties of two out of three membrane types.
Membranes (Basel) | 2015
Mehrdad Ebrahimi; Nadine Busse; Steffen Kerker; Oliver Schmitz; Markus Hilpert; Peter Czermak
Pulp and paper waste water is one of the major sources of industrial water pollution. This study tested the suitability of ceramic tubular membrane technology as an alternative to conventional waste water treatment in the pulp and paper industry. In this context, in series batch and semi-batch membrane processes comprising microfiltration, ultrafiltration and nanofiltration, ceramic membranes were developed to reduce the chemical oxygen demand (COD) and remove residual lignin from the effluent flow during sulfite pulp production. A comparison of the ceramic membranes in terms of separation efficiency and performance revealed that the two-stage process configuration with microfiltration followed by ultrafiltration was most suitable for the efficient treatment of the alkaline bleaching effluent tested herein, reducing the COD concentration and residual lignin levels by more than 35% and 70%, respectively.
Membranes | 2016
Daniel Humpert; Mehrdad Ebrahimi; Peter Czermak
Utilization of renewable resources is becoming increasingly important, and only sustainable processes that convert such resources into useful products can achieve environmentally beneficial economic growth. Wastewater from the pulp and paper industry is an unutilized resource offering the potential to recover valuable products such as lignin, pigments, and water [1]. The recovery of lignin is particularly important because it has many applications, and membrane technology has been investigated as the basis of innovative recovery solutions. The concentration of lignin can be increased from 62 to 285 g∙L−1 using membranes and the recovered lignin is extremely pure. Membrane technology is also scalable and adaptable to different waste liquors from the pulp and paper industry.
Separation Science and Technology | 2015
Rong Fan; Mehrdad Ebrahimi; Hendrich Quitmann; Peter Czermak
In lactic acid fermentation broth systems, membrane fouling is characterized as the crucial factor in limiting ceramic membrane life-time and efficiency. This study aimed to find the limiting factor of this process and seek an effective solution. By quantitative analysis using resistance-in-series model, the cake layer resistance is demonstrated to be the dominant factor in a steady state. A cake compressibility index was measured as high as 2.09. Within the low transmembrane pressure range, the cake resistance was manipulated through crossflow velocity regulation to achieve a better membrane performance. A new correlation between flux and cell density was also introduced.