Water Purification
Purification of water mainly depends on the purpose of use. The process generally implemented depends to the nature of impurities, whether this water will be used for domestic purposes (for drinking or washing) or to be used in any industrial chemical processes or in any pharmaceutical companies.
Generally, Water impurities can be divided into three categories as listed below:
a - Solid impurities that include suspended solids
b - Dissolved impurities
c - Bacterial impurities
All the processes of purification designed mostly include these three objectives, let us discuss each in detail:
1- Solid or suspended impurities are generally dust particles, silt, fibers, and debris. These things make the water look dirty. All of these things can be easily removed through the simple process of filtration. The quality of filtration also depends on the purpose where this water is most likely to be used; if it is for drinking purposes, it can go through 5 micron filter at the least; one micron or even less being used in bottled water.
In desalination systems apart from RO fine filtration, it is required to remove debris, sand, silt and some dead marine life if sea water being used as feed water. When seawater is used as feed for the desalination plant, the very first thing is the screening system. Seawater direct flow or by pumps passing through screens removing weeds and other marine waste settled in settling tanks where all heavy particles, sand, dust and etc. are settled down and water taken from the upper level drawn by pumps to feed the desalination system for further process. Whereas in RO system fine filtration up 5 microns is required to protect membrane pores from blocking. So there are several stages being designed for the filtration for RO feed, that is the bag filters, fine filters and then finally, the 5 micron cartridge filters. This is a suitable for feed to enter into membrane system. Further to confirm there is a test called Silt Density Index (SDI), this test is to check the feed quality and to check if the filtration system is working efficiently or not, thus, giving clear indication to change or clean the bag filter, fine filters or replace cartridge filters to get better results again.
In desalination processes like RO, MSF or other systems, usually before the filtration, some chemicals are also added like acid in order to adjust the pH level as required for disinfection, anti-scaling, and anti-corrosion, along some time for coagulation as some other chemicals are being used for safety and efficiency of the systems.
There are several processes to remove or reduce the dissolved impurities. For general use like drinking, cooking, washing. Desalination is commonly required by either process which seems to be more economical and convenient whilst utilizing the local sources and maintain it’s environmentally safe standard. These processes can be listed as:
- Thermal processes
- Multi-Stage Flash Distillation
- Multi-Effect Distillation
- Vapor Compression
- Solar Distillation
- RO Membrane process
- Electrodialysis
Introduction
Desalination is simply a process to remove salts from seawater, well water or any underground water which may not be good in taste due to excessive salts. Generally, well water or brackish water has salts from 1000 to 11000 ppm TDS while seawater contains 35000 ppm TDS or more, in which the major constituent is sodium chloride.
Generally any desalination system thermal or membrane process, consist of 3 parts; one is the pre-treatment system, second is the main desalination system and the third being the post-treatment system which is just to adjust the quality as per the requirement for either drinking or any other industrial usage.
Several thermal processes being used like Multi-Stage Flash Distillation (MSF), Multi-Effect Distillation (MED or ME), and the Vapor Compression (VC) processes. These processes are mostly used for seawater. Note that the MSF system is the most widely used process in the world.
Membrane systems include Reverse Osmosis (RO) and Electrodialysis (ED), where RO can be used for brackish water and seawater, whilst ED can be used for brackish water only.
In the distillation process, the product water TDS is around 20 ppm TDS while in membrane process it can be designed to achieve 100 to 500 ppm TDS. For drinking water, the quality must be adjusted to achieve quality as according to the World Health Organization (WHO) standards.
The selection of a process is based on several parameters, such as site conditions, local circumstances, energy availability and etc. The “best” desalination system for a particular application will be the system that reliably produces water of the expected quality and quantity at a reasonable cost.
In the desalination system, the water quality produced and the thermal energy required (per unit steam, required per unit of water produced) can be expressed in terms of 2500 kJ or electrically (kWh/m3)
Generally, Water impurities can be divided into three categories as listed below:
a - Solid impurities that include suspended solids
b - Dissolved impurities
c - Bacterial impurities
All the processes of purification designed mostly include these three objectives, let us discuss each in detail:
1- Solid or suspended impurities are generally dust particles, silt, fibers, and debris. These things make the water look dirty. All of these things can be easily removed through the simple process of filtration. The quality of filtration also depends on the purpose where this water is most likely to be used; if it is for drinking purposes, it can go through 5 micron filter at the least; one micron or even less being used in bottled water.
In desalination systems apart from RO fine filtration, it is required to remove debris, sand, silt and some dead marine life if sea water being used as feed water. When seawater is used as feed for the desalination plant, the very first thing is the screening system. Seawater direct flow or by pumps passing through screens removing weeds and other marine waste settled in settling tanks where all heavy particles, sand, dust and etc. are settled down and water taken from the upper level drawn by pumps to feed the desalination system for further process. Whereas in RO system fine filtration up 5 microns is required to protect membrane pores from blocking. So there are several stages being designed for the filtration for RO feed, that is the bag filters, fine filters and then finally, the 5 micron cartridge filters. This is a suitable for feed to enter into membrane system. Further to confirm there is a test called Silt Density Index (SDI), this test is to check the feed quality and to check if the filtration system is working efficiently or not, thus, giving clear indication to change or clean the bag filter, fine filters or replace cartridge filters to get better results again.
In desalination processes like RO, MSF or other systems, usually before the filtration, some chemicals are also added like acid in order to adjust the pH level as required for disinfection, anti-scaling, and anti-corrosion, along some time for coagulation as some other chemicals are being used for safety and efficiency of the systems.
There are several processes to remove or reduce the dissolved impurities. For general use like drinking, cooking, washing. Desalination is commonly required by either process which seems to be more economical and convenient whilst utilizing the local sources and maintain it’s environmentally safe standard. These processes can be listed as:
- Thermal processes
- Multi-Stage Flash Distillation
- Multi-Effect Distillation
- Vapor Compression
- Solar Distillation
- RO Membrane process
- Electrodialysis
Introduction
Desalination is simply a process to remove salts from seawater, well water or any underground water which may not be good in taste due to excessive salts. Generally, well water or brackish water has salts from 1000 to 11000 ppm TDS while seawater contains 35000 ppm TDS or more, in which the major constituent is sodium chloride.
Generally any desalination system thermal or membrane process, consist of 3 parts; one is the pre-treatment system, second is the main desalination system and the third being the post-treatment system which is just to adjust the quality as per the requirement for either drinking or any other industrial usage.
Several thermal processes being used like Multi-Stage Flash Distillation (MSF), Multi-Effect Distillation (MED or ME), and the Vapor Compression (VC) processes. These processes are mostly used for seawater. Note that the MSF system is the most widely used process in the world.
Membrane systems include Reverse Osmosis (RO) and Electrodialysis (ED), where RO can be used for brackish water and seawater, whilst ED can be used for brackish water only.
In the distillation process, the product water TDS is around 20 ppm TDS while in membrane process it can be designed to achieve 100 to 500 ppm TDS. For drinking water, the quality must be adjusted to achieve quality as according to the World Health Organization (WHO) standards.
The selection of a process is based on several parameters, such as site conditions, local circumstances, energy availability and etc. The “best” desalination system for a particular application will be the system that reliably produces water of the expected quality and quantity at a reasonable cost.
In the desalination system, the water quality produced and the thermal energy required (per unit steam, required per unit of water produced) can be expressed in terms of 2500 kJ or electrically (kWh/m3)
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