Water Desalination and Its Techniques

Transcription

1 SECOND TECHNICAL SEMINAR AT PS3 JORHAT Water Desalination and Its Techniques Presented By: Partha Proteem Roy PS4 Sekoni

2 Overview of Presentation Introduction Definition Purpose of Desalination Different Techniques of Water Desalination Future Technologies Conclusion

3 Introduction

4 Need of Fresh Water Economic expansion Agriculture and food Public health Quality of life

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6 Water Distribution

7 Sources of Fresh Water Frozen Water: Fresh water source in form of ice bergs and glaciers. Surface water: The water in a river, lake or fresh water wetland. Surface water is naturally replenished by precipitation and naturally lost through discharge to the oceans, evaporation, evapotranspiration and sub-surface seepage. Under River Flow : The hyporheic zone often forms a dynamic interface between surface water and true ground-water receiving water from the ground water when aquifers are fully charged and contributing water to ground-water when ground waters are depleted. This is especially significant in karst areas where pot-holes and underground rivers are common.

8 Sources of Fresh Water Ground water: It is located in the pore space of soil and rocks. It is also water that is flowing within aquifers below the water table Rainwater harvesting: It is the accumulation and deposition of rainwater for reuse before it reaches the aquifer Desalination: Different ways to harness fresh water from saline water to cater growing need of water due to scarcity of fresh water.

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11 Distribution of Precipitation

12 Definition

13 Water Desalination Any of several processes that remove some amount of salt and other minerals from saline water. More generally, desalination may also refer to the removal of salts and minerals

14 Purpose of Desalination

15 Why Desalination? 75% of the Earth s surface is covered by water 97 % of that water is oceans Only 1% is available for drinking 80 countries suffered from water scarcity by the mid-1990s 1.5 billion people lack ready access to drinking water

16 TDS Total Dissolved Solids: It is a measure of the combined content of all inorganic and organic substances contained in a liquid in molecular, ionized or micro-granular (colloidal sol) suspended form. Level of TDS (milligrams per litre) Rating <300 Excellent Good Fair Poor >1200 Unacceptable

17 Relative proportions of dissolved salts in seawater. Dr. Ola Abdelwahab 17

18 Elemental composition of seawater Only six elements comprise about 99% of sea salts: chlorine (Cl - ), sodium (Na + ), sulfate (SO 4-2 ), magnesium (Mg +2 ), calcium (Ca +2 ), and potassium (K + ). The relative abundance (large quantity) of the major salts in seawater are constant regardless of the ocean. Only the amount of water in the mixture varies because of differences between ocean basins because of regional differences in freshwater loss (evaporation) and gain (runoff and precipitation). The chlorine ion makes up 55% of the salt in seawater. Typically, seawater has a salinity of 35 parts per thousand. Dr. Ola Abdelwahab 18

19 Harmful Effects of drinking impure water Vegetable Impurities: Peaty water, in the absence of a better supply, may be used without much harm, but if the amount of solid matter is great it may even produce diarrhoea. Under this head we must include water containing germs, for although they generally get into the water from the excretions of animals, yet, as we know, they are vegetable in nature. Here we shall meet with the most dangerous kinds of water, causing many fatal epidemics. Mineral Impurities: A moderate degree of hardness is not harmful, but if the hardness is great dyspepsia and constipation may result. Goitre seems to be due to the presence of magnesium limestone in the drinking water. Iron salts cause dyspepsia, constipation, and headache. Lead salts are especially dangerous, causing colic, paralysis, kidney disease, and sometimes death. These symptoms may occur when the amount of lead does not exceed one-tenth grain per gallon. Arsenic is dangerous and can cause cancer. Sodium causes cardiac disease. Fluoride causes crippling skeletal flourosis.

20 Natural Desalination: Water Cycle! Major Stages 1. Evaporation 2. Condensation 3. Precipitation 4. Collection

21 Different Techniques of Water Desalination

22 Membrane Technologies Chemical Approaches Thermal Technologies

23 Membrane Technologies Pressure Driven Microfiltration Ultra filtration Nano filtration Hyper filtration Electrical Driven Electro-Dialysis Electro-Dialysis Reversal

24 Membrane Process Applied Pressure psi (kpa) Minimum Particle Size Removed Application (Type, Avg Removal Efficiency %) Micro-filtration 4-70 (30-500) µm - Particle/turbidity removal (>99%) - Bacteria/protozoa removal (>99.99 %) Ultra-filtration 4-70 (30-500) μm - Particle/turbidity removal (>99 %) - Bacteria/protozoa removal (> %) - TOC removal (<20%) - Virus removal/(partial credit only) Nano-filtration ( ) daltons - Turbidity removal (>99%) - Color removal (>98%) - TOC removal (DBP control) (>95%) - Hardness removal (softening) (>90%) - Synthetic organic contaminant (SOC) removal (500 daltons and up) (0-100%) - Sulfate removal (>97%) - Virus removal (>95%) Hyper-Filtration ( ) daltons - Salinity removal (desalination) (>99%) - Color and DOC removal (>97%) - Radionuclide removal (not including radon) (>97%) - Nitrate removal (85 to 95%) - Pesticide/SOC removal (0 to 100%) - Virus removal (>95%) - As, Cd, Cr, Pb, F removal (40 to >98%)

25 Reverse Osmosis

26 Electrical Driven Electro dialysis: It utilizes electromotive force applied to electrodes adjacent to both sides of a membrane to separate dissolved minerals in water.

27 Electro Dialysis Reversal Electrodialysis reversal (EDR) is a similar process, except that the cation and anion reverse to routinely alternate current flow.

28 Challenges for Membrane Technologies Pressure Driven: Fouling and Scaling of membrane Electric Driven: Limitation of TDS. Cost is proportional to TDS (ideal for 4000 mg/l).

29 Chemical Approaches

30 Ion Exchange Technologies It can best be described as the interchange of ions between a solid phase and a liquid phase surrounding the solid, chemical resins (solid phase) are designed to exchange their ions with liquid phase (feedwater) ions, which purify the water. It can be used in combination with reverse osmosis.

31 Thermal Technologies

32 Solar Distillation

33 Multistage Flash

34 Multi Effect Distillation

35 Thermal Vapour Compression

36 Mechanical Vapour Compression

37 Absorption Vapour Compression Pressure differences occur between two tanks as a fluid mixture is transferred between them. This drives the heat exchange for evaporation and condensation of saltwater to form potable water

38 Future Technologies Electrodeionization (EDI) Membrane Distillation (MD) Freeze Separation (FS) Capacitive Deionization (CD) Rapid Spray Evaporation (RSE) Freezing with Hydrates (FH) Vacuum Distillation (VD)

39 Conclusion

40 Thank You