Membrane and Desalination Technologies

Membrane science and technology have experienced a long historical development in laboratory study before realizing their first significant industrial application in the 1960s. With nearly 50 years of rapid advancement, today, membrane-based processes enjoy numerous industrial applications and have brought great benefits to improve human life. In this chapter a general introduction is given to membrane technology in terms of the historical development, current status and future prospects. It begins with a description of the basic terms such as membrane, membrane structures, membrane classifications and membrane configurations. Membrane processes based on the different driving forces applied, the operation modes for filtration and membrane fouling are also briefly introduced. Section 2 is an overview of the historical development of membranes and membrane processes, including reverse osmosis, ultrafiltration, nanofiltration, microfiltration, gas separation, pervaporation and membrane bioreactors. Section 3 describes major applications and commercial relevance of the above-mentioned processes. In Sect. 4, future market development trends for membrane technology are indicated and critical technical challenges for further growth of the membrane industry are addressed. In addition, some promising novel applications of membrane technology are pointed out in the final section.

This chapter mainly describes the principles of membrane formation process for polymeric membranes. With a brief introduction of relevant background information such as various membranes and membrane processes, a comprehensive list of polymer materials, which are suitable for making membranes, has been given. The most common technique used to prepare polymeric membranes – phase inversion process, including thermally induced phase separation (TIPS) and diffusion induced phase separation (DIPS), is discussed in detail. The thermodynamic behavior of the casting polymer solution, the process of membrane formation, and the fabrication of hollow fiber and flat sheet membranes are involved.

The thermodynamic description of the polymer solution is based on the concepts of spinodal, binodal, vitrification boundary, gelation boundary et al. in the phase diagram. The linearized cloud point curve correlation is presented. In addition, two important parameters, the approaching ratio of the polymer solution and the approaching coagulant ratio, are discussed in association with membrane formation. For the membrane formation process, the delay time and gelation time are two macroscopic time scales, which influence the membrane morphologies simultaneously. The formation of nascent porous membranes, the vitrification of the membrane morphology and the membrane surface formation are described. The macrovoid formation is related to the viscous fingering phenomenon. In the fabrication of hollow fiber membranes, the shear flow of the polymer solution inside the spinneret and the elongation flow in the air gap strongly influence the performance of resultant membranes. Thus, the shear flow and elongation flow are discussed in great detail. The hydrodynamics of the polymer solution at the casting window in the process of preparing flat sheet membranes is also concerned.

Fouling alleviation and control in full-scale reverse osmosis (RO) processes can be seriously hindered by ineffective fouling characterization. Fouling characterization is currently done primarily by measuring the silt density index (SDI) of feed water and monitoring the average permeate flux of full-scale RO processes. However, the SDI or related fouling indices have been known not capable to catch all possible foulants to RO membranes, and the average permeate flux may fail to correctly reflect membrane fouling in full-scale RO processes under certain circumstances.

In this chapter, an advanced characterization method is introduced for membrane fouling in full-scale RO processes. An inclusive fouling potential indicator is proposed for a better characterization of the fouling strength of feed water, which is defined in a way that it can be easily determined with a small lab-scale RO membrane device and that it is readily usable to predict fouling development in the full-scale RO processes. A model based on basic membrane filtration and mass conservation principles is presented to calculate the average permeate flux in a full-scale RO process as fouling is progressing. The main intention of the advanced characterization method is to provide a reliable assessment of membrane fouling in the full-scale RO processes, so that the need for pilot tests can be significantly reduced.

The United States Environmental Protection Agency (US EPA) promulgated the Long Term 2 Enhanced Surface Water Treatment Rule, which has identified membrane filtration as a treatment technology that may be used to achieve the required level of Cryptosporidium treatment. This rule, along with the companion: Stage 2 Disinfectants and Disinfection By-products Rule, constitutes the principal US regulations for the application of the membrane technology in potable water treatment.

The primary elements of the regulatory requirements for membrane filtration including the definition of membrane filtration, as well as challenge testing, direct integrity testing, and continuous indirect integrity monitoring, are summarized in this chapter. The requirements and procedure for challenge testing, which is required to demonstrate the ability of the treatment process to remove a specific target organism, are explained in detail. The removal efficiency demonstrated during challenge testing establishes the log removal value (LRV) or removal credit that a membrane process would be eligible to receive. The core requirements of direct integrity testing and continuous indirect integrity monitoring are fully discussed. Design example and case studies are presented. Various water and wastewater physicochemical processes (such as, conventional sand filtration, direct filtration, contact filtration, slow sand filtration, cartridge filtration, diatomaceous earth filtration, dissolved air flotation, sedimentation, lime softening, coagulation, bank filtration, second stage filtration, continuous backwash upflow dual sand filtration, UV, chlorination, chloramination, ozonation, chlorine dioxide oxidation, etc.) are compared with membrane filtration for removal and/or inactivation of Cryptosporidium, Giardia, and virus.

Membrane bioreactor (MBR) is a biochemical engineering process involving the use of both (a) a suspended growth bioreactor for biochemical reactions (such as fermentation, bio-oxidation, nitrification, and denitrification) and (b) a membrane separator for subsequent solids–liquid separation. In a chemical engineering fermentation process, the solids may be yeasts and the liquid may be an alcohol. In an environmental engineering process, the solids may be activated sludge and the liquid may be the biologically treated water or wastewater. Practically speaking, the membrane separator replaces clarifier, such as sedimentation or dissolved air flotation (DAF) in a conventional suspended growth biological process system. The membrane module can be either submerged in a suspended growth biological bioreactor, or situated outside the bioreactor. This chapter introduces historical development, engineering applications, various MBR process systems, design considerations, and practical environmental engineering applications, such as treatment of dairy industry wastes, landfill leachate, coffee industry wastes, cosmetics industry wastes, municipal waste, and potable water.

Membrane separation processes are based on the ability of semipermeable membranes of the appropriate physical and chemical nature to discriminate between molecules primarily on the basis of size and to a certain extent, on shape and chemical composition. A membrane’s role is to act as a selective barrier, enriching certain components in a feed-stream, and depleting the others. One of the chief attractions of membrane technology is the low energy requirement compared to other food processing technologies. Since membrane processes are nonthermal and do not involve a change of phases, they are energy-efficient and do not change the nature of the foods during their process operation. This chapter presents the membrane process theory and case histories of various production applications in the food industry. Operational problems and recommended engineering solutions for membrane process optimization are presented and discussed.

Due to the limited new water resources, the focus of water industry has shifted more towards reclamation, reuse and recycling of raw water/wastewater and seawater desalination. Rising treatment costs and spatial limits also pose a greater pressure on the development of alternative technologies. Compared with traditional water and wastewater treatment technologies, membrane separation has been increasingly received much more considerable interests due to wide applicability, reliable performance, low operating and maintenance costs of membrane systems. The membrane fouling is still a principal obstacle in application of this technology.

This chapter first briefly introduces basic concepts for membrane separation including membrane definition, membrane types, membrane formation and characterization, module configuration, mass transport mechanism in membranes. Key factors such as process design, economic assessment in membrane systems are also covered. Moreover, it describes fouling formation and the strategies to control membrane fouling. Several detailed case studies will be cited to explain membrane separation technology.

The purpose of this chapter is to provide the basic information on the use of membrane filtration and application of the technology in the design of potable water facilities. The main issues involved in the planning and design of membrane systems are covered: pilot testing; the considerations that influence system design and operation including operational unit processes, system design considerations, and residuals treatment and disposal; and the initial start-up phase which must be completed prior to placing the system into service and actual water production. The initial start-up phase is a critical step in the successful installation of a full-scale membrane filtration system and thus is an essential consideration in the facility planning and design process. This phase includes such tasks as initial system flushing and disinfection, system diagnostic checks, membrane module installation, integrity testing new equipment, and operator training, all of which must be completed prior to placing the system into service.

The search for potable water for quenching global thirst remains a pressing concern throughout many regions of the world. The demand for new and sustainable sources and the associated technologies for producing fresh water are intrinsically linked to the solving of potable water availability and hitherto, innovative and energy efficient desalination methods seems to be the practical solutions. Quenching global thirst by adsorption desalination is a practical and inexpensive method of desalinating the saline and brackish water to produce fresh water for agriculture irrigation, industrial, and building applications. This chapter provides a general overview of the adsorption fundamentals in terms of adsorption isotherms, kinetics, and heat of adsorption. It is then being more focused on the principles of thermally driven adsorption desalination methods. The recent developments of adsorption desalination plants and the effect of operating conditions on the system performance in terms of specific daily water production and performance ratio are presented. Design of a large commercial adsorption desalination plant is also discussed herein.

In this chapter, advanced membrane technology for the reclamation of municipal wastewater has been introduced. The design of various membrane processes for this application is briefed. The investigations on the most common membrane (integrated) processes are emphasized, including (a) UF for the tertiary treatment of municipal wastewater; (b) MF-RO for the reclamation of the secondary domestic effluent; (c) Total organic carbon (TOC) removal in the reclamation of municipal wastewater by reverse osmosis (RO); (d) New option of MBR-RO for the reclamation of municipal wastewater; (e) the reclamation of a mixed sewage effluent using UF-RO. The recent R&D is highlighted.

Membrane filtration is considered as a simplified drinking water treatment process, which can remove organic impurities, as well as metal ions and other ions. Nowadays, membrane processes are increasingly employed for removal of bacteria and other microorganisms, particulate material and natural organic matter, which can impart color, tastes, and odors to the water and react with disinfectants to form disinfection by-products (DBPs). Recently, there have been several advanced technologies derived from the combination of biotechnology and filtration with application for potable water treatment. This chapter describes these techniques which includes biofiltration, membrane bioreactor, ion-exchange membrane bioreactor, and biological activated carbon adsorption-filtration. Several case studies in applying biofiltration for DBP control in bench- and pilot-scale are also demonstrated.

Freshwater is one of the scarce resources in the world. In many countries, due to freshwater shortages, searching for freshwater resources has become extremely important and desalination is known to be an essential available solution for this. In this chapter, the thermal distillation of multistage flash distillation, multieffect distillation and vapor compression and electrodialysis processes for seawater desalination are presented. The working mechanisms, important issues in design, and the recent advances of the thermal distillation and electrodialysis processes for desalination are addressed. Reverse osmosis technology is also briefly presented. A comparison of these desalination processes is given. Other important issues, such as pre- and posttreatment process, energy consumption, and environmental aspects, are discussed.

Desalination allows the use of non-conventional water sources such as seawater for the production of potable water. Reverse osmosis (RO), one of the technologies for desalination, is becoming popular in the water industry. In this chapter, theory of RO process, plant configurations, and practical considerations related to the plant operation are addressed. Factors such as high permeate flux, high solute rejection, and mechanical and chemical stability govern the production of membranes for RO. Cellulose acetate membrane is popular due to the chlorine and fouling resistance. When it comes to rejection, thin film membranes are advantageous. Membranes are usually arranged in modules. Concentration polarization and compaction are two major limiting factors in the RO technology. Feed water must be pretreated using conventional and/or membrane filtration technologies in order to minimize membrane fouling. Reduction in permeate, pressure drop over the system, and decrease in rejection are the indications for the requirement of cleaning and regeneration of membranes. Chemical and/or physical methods can be used for the cleaning and regeneration of membranes. A case study and the recent developments are discussed in order to enhance the understanding of the process.

Point-of-use (POU) system is the treatment process aimed to treat only water intended for direct consumption (drinking and cooking), typically at a single tap or limited number of taps. Point-of-entry (POE) treatment devices are typically installed to treat all water entering a single home, business, school, or facility. Reverse osmosis (RO) is recognized by the industry as one of the top POU and POE treatment technologies. This chapter describes the advantages and limitations in using RO for POU and POE applications. Types and configurations of reverse osmosis, and installation, operation and maintenance, and testing of RO are also included.

Oily wastewater treatment can be classified into two categories; primary and secondary treatment systems. The primary treatment is employed to separate floatable oils from water and emulsified oil. Secondary treatment system is aimed to treat or break emulsified oil and, then, remove oil from water. This chapter mainly describes use of classical membrane technologies, which are ultrafiltration, microfiltration, nanofiltration, and reverse osmosis, for oil–water separation. Advances in membrane technology such as membrane modification, development of inorganic membrane, and improvement of hydrophilicity of membrane for oil water separation are also discussed as well.

Ultrafiltration is a pressure-driven membrane technique whose applications are wide ranging: protein fractionation to wastewater treatment. The performance of ultrafiltration is limited by concentration polarization and subsequent fouling. Gas sparging i.e. introduction of gas bubbles along with the feed has been shown to be effective in reducing concentration polarization and thus controlling fouling. This chapter reviews the recent developments in gas-sparged ultrafiltration. The review focuses on the basics of ultrafiltration and two-phase flow hydrodynamics, the use of gas bubbles for enhancing permeate flux and its applications in bioseparation and wastewater treatment. Some practical issues and future challenges are also discussed.