Current Trends and Future Developments on (Bio-) Membranes

Membrane Technology for Water and Wastewater Treatment - Advances and Emerging Processes

Angelo Basile, Antonio Comite

• Publisher: Elsevier
• Year: 2020
• Print ISBN: 9780128168233
• eBook ISBN: 9780128168240
• Topic: Technology & Engineering
• Subtopic: Microbiology
• Index: Technology & Engineering

Current Trends and Future Developments in Bio-Membranes: Membrane Technology for Water and Wastewater Treatment - Advances and Emerging Processes presents recent advances and a status update on the applications of membrane processes to both urban and industrial wastewater. Specific case studies of membrane technologies are described. Membrane processes have been widely studied, but their application in the wastewater sector is increasing rapidly. The book deals with the applications to the wastewater sector (e.g. MBR, NF, RO, ED) and emerging membrane technologies (e.g. MBfR, MD, FO, MFC). Specific case studies of membrane technology application and relevant wastewaters (e.g. municipal, dairy, oily refinery, etc.) are also discussed. - Presents recent advances of wastewater treatment using membrane processes - Outlines novel and emerging membrane technologies, e.g., membrane distillation, forward osmosis and membrane biofilm reactors - Includes recent developments of more consolidated membrane processes, e.g., membrane biological reactors, nanofiltration, reverse osmosis, etc., either for water treatment or desalination - Includes interesting and instructive case studies on the application of membrane technologies to various wastewater sources, e.g., municipal, dairy, olive mill, refinery, pulp and paper

Part I

Advances in novel membrane technologies for water and wastewater

Outline

• Chapter 1 Wastewater treatment by membrane distillation
• Chapter 2 Integration of membranes into bioelectrochemical systems for enhanced treatment performance
• Chapter 3 Forward osmosis for water treatment and desalination
• Chapter 4 Photocatalytic membrane reactors for wastewater treatment
• Chapter 5 Inorganic materials for upcoming water purification membranes
• Chapter 6 Electrodialysis for wastewater treatment—Part I: Fundamentals and municipal effluents

Chapter 1

Wastewater treatment by membrane distillation

Antonio Comite, Marcello Pagliero and Camilla Costa, Department of Chemistry and Industrial Chemistry, University of Genoa, Genoa, Italy

Abstract

Membrane distillation (MD) has been around since the 1960s but only recently it has been widely studied, mainly for desalination. Its application in wastewater treatment is emerging more and more, but despite its great potential for the realization of zero-liquid-discharge systems, many advances are still needed for its acceptance by industrial operators. This chapter introduces the basic components of MD, and then, through a review of literature examples, applications of MD in the treatment of wastewater are explored. In the last part of the chapter, the integration of MD with other treatments is explored and some considerations about economics are reviewed.

Keywords

Direct contact membrane distillation; air-gap membrane distillation; vacuum membrane distillation; wastewater; fouling; hydrophobic membranes

1.1 Introduction

Water is considered a resource at risk due to pollution and the world’s increasing population. Efficient policies for effective water distribution and consumption are needed to protect this resource and to minimize wastewater generation. Therefore, to achieve water sustainability it becomes mandatory to consider wastewater as a valuable resource for generating again safe water. Technological processes such as membrane technology are key to advanced water and wastewater treatments. To effectively implement policies for water and wastewater management, membrane processes such as microfiltration (MF) and reverse osmosis (RO) have been widely applied on a commercial scale for water depuration, desalination, and wastewater treatments. Nevertheless, other emerging membrane processes are attracting greater attention and, among these, membrane distillation (MD), which, although still in the initial commercialization phase in the desalination field, is among the membrane processes expected to enable zero-liquid-discharge (ZLD) or to maximize water recycling while minimizing wastewater volumes [1].

The first MD patent was filed by Bodell in 1963 [2] back when suitable inherently hydrophobic membranes were not yet available. When hydrophobic polymer membranes appeared on the market the first studies on MD were devoted to desalination and then to food processing. While researchers have studied the application of MD to wastewater over the last two decades there are challenges that must be addressed before this technology can be applied at a commercial level for wastewater treatment. Fig. 1.1 shows the general trend of MD in scientific publications from the mid-1980s up to 2018. As can be seen, the number of papers addressing wastewater treatment is still limited.

Figure 1.1 Publication trend in the last two decades using the keywords (a) “membrane distillation,” (b) “membrane distillation desalination,” and (c) “membrane distillation wastewater” in the title search field of ScienceDirect (Elsevier).

In recent years many books and reviews have been published on the subject of MD [3–9]. At the beginning of this chapter, we give an overview of MD and later we discuss the main parameters for its application in the wastewater sector. In particular selected examples found in the literature will be reviewed.

1.2 Overview of membrane distillation

The distillation process exploits the differences in volatility to separate the components of a liquid solution. The vapor pressure of a pure liquid can be empirically estimated by using the Antoine equation:

${\mathit{log}}_{10}(p°)=A-\frac{B}{T+C}$ (1.1)

(1.1)

where p° is the vapor pressure (Pa or bar); T is the temperature (K or °C); and A, B, and C are the constants for each substance. For pure water expressing the vapor pressure in Pa and the temperature in K, the Antoine’s constants are A=23.1964, B=3816.44, and C=46.13 [10,11]. By increasing the temperature the vapor pressure increases. When nonvolatile solutes are diluted in a water solution the Raoult equation can account for the change in the vapor pressure p_f:

$p_f=x_w{p}_w^o$ (1.2)

(1.2)

where x_w is the molar fraction of water. For more concentrated solutions in which the solute–water interactions are more important x_w needs to be replaced by the water activity:

$p_f=a_w{p}_w^o={\gamma }_w{x}_w{p}_w^o$ (1.3)

(1.3)

where a_w is the water activity and γ_w is the activity coefficient for water. Therefore when a solute is present usually the vapor pressure is lower than for pure water. The evaporation takes place at the interface between the liquid and the vapor phases and thus the molar flow rate of evaporation depends on the evaporation surface area and on the water flux. When the evaporation interface is mediated by a porous membrane that is not filled by the liquid phase, but only by the vapor phase, the distillation process is deferred to as MD. Considering an aqueous feed, a hydrophobic porous membrane can create a controlled and known (from geometrical considerations) evaporation surface. Then only the vapors of the volatile components, solvent, and/or other volatile species in the feed will diffuse through the porous structure of the membrane to the other side where they can be drained out by vacuum or a sweep gas, or condensed in a liquid phase that may have direct contact with the membrane surface. Which is an isothermal process that exploits a concentrated salt solution, known as draw solution, on the condensing side of the membrane to create a vapor pressure gradient which drives the water mass transfer [4].

MD is essentially a thermally driven separation process in which a hydrophobic porous membrane in contact with a hotter liquid solution (usually an aqueous one) works as an artificial evaporation interface. By simultaneously exploiting a gradient of temperature between the feed phase and the collecting phase on the permeate side and a sufficiently high contact area...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of contributors
• Preface
• Part I: Advances in novel membrane technologies for water and wastewater
• Part II: Advances in membrane technologies for industrial applications
• Index