A Review of Membranes Classifications, Configurations, Surface Modifications, Characteristics and Its Applications in Water Purification

Abstract

Today, membrane separation technologies are widely used in many areas of water and wastewater treatment. Membrane processes can be used to produce potable water from surface water, groundwater, brackish water, or seawater, or to treat industrial wastewaters before they are discharged or reused. Membrane separation systems have many advantages over traditional water or wastewater treatment processes, lower operating and maintenance costs in comparison to conventional systems consisting of coagulation, clarification, and aerobic and anaerobic treatments. • Membrane separation systems are easy to operate and the performance is more reliable. • Membrane systems give a compact and modular construction, which occupies less floor space in comparison to the conventional treatment systems. In this review, we will introduce fundamental concepts of the membrane and membrane-separation processes, such as membrane definition, membrane classification, membrane formation, module configuration, transport mechanism, system design. Four widely used membrane separation processes in water and wastewater treatment, namely, microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), will be discussed in detail. Some basic requirements for membranes are • high flux of the product, good mechanical strength for supporting the physical structure, good selectivity for the desired substances. Generally, high selectivity is related to membrane properties, such as small pores and high hydraulic resistance or low permeability.. The permeability increases with increasing density of pores, and the overall membrane resistance is directly proportional to its thickness. Therefore, a good membrane must have a narrow range of pore sizes, a high porosity, and a thin layer of material. Membranes can be either dense or porous. Separation by dense membranes relies on physicochemical interaction between the permeating components and the membrane material. Porous membranes, on the other hand, achieve separation by size exclusion, where the rejected material may be either dissolved or suspended depending on its size relative to that of the pore. Membranes can be organic (polymeric) or inorganic (ceramic or metallic), according to its composition, and their morphology is dependent on the nature of the material. There is a need for improved membranes that have higher efficiency and are more resistant to the chemical environment, especially chlorine. This article summarizes the art of membrane technology.