Expanding Issues in Desalination

Abstract

For this book, the term desalination is used in the broadest sense of the removal of dissolved, suspended, visible and invisible impurities in seawater, brackish water and wastewater, to make them drinkable, or pure enough for industrial applications like in the processes for the production of steam, power, pharmaceuticals and microelectronics, or simply for discharge back into the environment.From space, the earth is a blue planet, covered three quarters of surface by oceans and one quarter by land. Seawater contains 35 to 40 grams per liter of dissolved salts, too salty to drink or use. At any moment in time, about 0.04% of the water is in the process of being recycled through the atmosphere by the heat from the sun. Distilled water from clouds, condense as rain or snow, is falling mostly in the ocean. Only 2.5% of the Earth's total water is fresh water, but two-thirds of this water is locked away from man's use in ice caps and glaciers. The estimated one third (0.8%) of fresh water sink into the deep aquifers, or flows into lakes and rivers then to the sea.Water, being a most powerful solvent, leaches soluble salts and erodes rocks from the ground, and becomes increasingly saline and turbid before reaching the sea, or equilibrates as brackish water in the lakes and aquifers. Being the essential medium for microbial and aquatic life, it is filled with living and non-living biotic organic matter. Much of the complex suspended organic and inorganic matter in water are colloidal particles, smaller than 1 micron (1 nanometer) in size, hence invisible to naked eyes.Human needs drive the technology of desalination of water. The need is exacerbated by the mismatch of population densities with the natural distribution of available water on land. Like other basic technologies, the mountain of published information on this subject can hardly be captured in one book. Major desalination processes involve thermal evaporation known as Multi-Stage Flash Distillation (MSF), Multiple-Effect Distillation (MED) and Vapor Compression Distillation (VC). Since 1970s, technologies using semi-permeable membranes grew rapidly to compete with distillation to minimize energy consumption. Reverse Osmosis (RO) now is becoming favored over MSF even in oil-rich countries of the Persian/Arabian Gulf. Ion-exchange resins are used to soften or deionize water. Electrodialysis (ED) commercially introduced in the early 1960s also uses semi-permeable membranes. It finds greater application in industrial rather than municipal applications. Minor desalination processes include freezing, membrane distillation and solar humidification. XIV PrefaceFor students and workers in the field of desalination, this book provides a summary of key concepts and keywords with which detailed information may be gathered through internet search engines. Papers and reviews collected in this volume covers the spectrum of topics in desalination of water, too broad to delve into in depth. The literature citations in these papers serve to fill in gaps in the coverage of thi...

Biofouling of Polyamide Membranes: Fouling Mechanisms, Current Mitigation and Cleaning Strategies, and Future Prospects

“…Temperatures higher than 35 °C at a pH of 12 (or higher) is not recommended due to the potential for hydrolysis of the membrane fabric backing [244]. High pH cleaners typically include detergents and/or chelants to help penetrate the biofilm for more effective removal [7].…”

“…While polyamide membranes offer advantages over CA membranes in terms of rejection, operating pressure, and wider operating pH range, there are limitations to these polyamide membranes. Perhaps the most problematic issues for users of polyamide membranes is controlling deposition of foulants, in particular, microorganisms, on the membranes [6,7,8,9,10,11]. Biofouling leads to performance (flux and rejection) losses, and corresponding shorter useful membrane life [9,12].…”

Applications of Chelating Agents in the Upstream Oil and Gas Industry: A Review

“…Most of these chemicals are organic-based compounds. The chelation process is very useful in applications in the medical area, such as nutritional supplements, removal of toxic metals from the body, contrast in magnetic resonance imaging (MRI) scanning, chemical water treatment, and other engineering applications …”

“…There are two main different types of chelating agents used frequently: aminopolycarboxylic acids (APCA) and phosphonates. Nitrilotriacetic acid (NTA) was the first group of chelating agents to be synthesized from the APCA group for application in stimulation and scale removal treatments. , Ethylenediaminetetraacetic acid (EDTA) was formulated from a reaction of a monochloroacetic acid with ethylenediamine in the presence of sodium hydroxide. Diethylenetriaminepentaacetic acid (DTPA) is another type of chelating agent that has a higher stability constant. , Also, chelating agents prepared from hydroxyaminopolycarboxylic acids (HAPCAs), such as hydroxylethylethylenediaminetriacetic acid (HEDTA) and hydroxylethyliminodiacetic acid (HEIDA), are used.…”

“…The second type of chelating agents, phosphonates, has many synthesized types, such as diethylenetriaminepentamethylenephosphonic acid (DTPPH) and nitriletrimethylenephosphonic acid (NTMP). The most important phosphonate chelating agent is 1-hydroxyethane-1,1-diphosphonic acid (HEDP), because it is widely used in a broad variety of applications Figure shows the chemical structure of the phosphonate chelating agents.…”