Desalinisation

 

Desalination, desalinisation, or desalinization refers to any of several processes that remove salt and other minerals from saline or brackish water. Desalination uses either thermal or membrane technologies. Thermal technologies include: Multiple-Effect Distillation (MED), and Multi-Stage Flash Evaporation (MSF). Membrane technologies include: Reverse Osmosis (RO), Electrodeionisation (EDI), and Electrodialysis (ED). The largest desalinisation plant in the world (due to come online in 2014) is in Saudi Arabia and uses MSF and RO technology. Historically the desalinisation market has been led by seawater plants in the Gulf States and brackish water plants in the US.

 

Pumice Filtration Media in Desalinisation

There are many types of granular filtration media that can be used in the pre-treatment of water prior to reverse osmosis (RO) and seawater reverse osmosis (SWRO) such as pumice, anthracite and sand. Traditionally anthracite was used, however in recent years the multiple benefits of using pumice filtration media have been widely reported and a surge in the number of large scale plants using this technology has taken place.

 

Pumice filtration media is used in the pre-treatment of saline or brackish water prior to desalinisation. This preliminary treatment removes the coarse particulates prior to the next stage of treatment, typically reverse osmosis (RO) using a membrane filtration process.

 

Reverse osmosis (RO) and seawater reverse osmosis (SWRO) are desalinisation processes that produce potable water by forcing the pre-treated seawater against a semi-permeable membrane, producing pure water on one side and concentrated brine on the other. The brine returns to the sea, while the potable water is stored or distributed for human consumption.

 

Desalination plant - UF membranes

 

Pumice Filtration Media has been used worldwide for many years in the pre-treatment of seawater for desalinisation for both human consumption and industrial use.

Typical filter layout

Pumice is a very versatile filtration media and can be used for pre-treatment for MF, UF, NF and RO membranes.

 

All pumice filters employ the same basic principle; a rapid gravitational filtration of raw water through a granular media. Pumice filtration media can be used in single media filtration, dual media filtration (DMF) or multi media filtration (MMF) in conjunction with sand and gravel depending on the quality of water to be treated. The versatility of pumice filtration media enables it to be used to solve difficult filtration problems. Filtration can be achieved within a rapid gravity or pressure filter, with optimum filtration performance ensured through regular backwashing via nozzles in the filter floor.

 

Advantages of using Pumice Filtration Media in Desalinisation

The advantages of using pumice filtration media over conventional granular filter media in desalinisation applications are:

 

Reduced pressure loss through the filter; the unique nature of pumice allows increased solids retention capacity, higher particulate loadings and therefore much increased filter run times without a deterioration in filtrate quality.

 

Reduced headloss; this filtration in depth avoids the build up of particulates within the top section of the filter bed reducing headloss across the filter.

 

Reduced backwash rates; pumices lightweight nature (approximately 400kg per cubic metre) means lower backwash rates are needed to fully expand the filter bed. This generates substantial savings in the operating costs of the filtration plant as backwash consumption requirements are typically 30% lower than using traditional media.

 

Increased bed expansion; the lightweight nature of pumice filtration media gives increased bed expansion over traditional media using the same backwash rate. Again this generates substantial savings in energy and water usage, which equates to a reduction in pumping requirements and enables a downsizing of the filtration plant.

 

Can be used at elevated temperatures; pumice can be used at temperatures ranging from 0-40 degrees celcius.

 

Can be used in saline or fresh water; pumice has been proven to work successfully in saline or fresh water conditions.

 

High filtrate quality; pumice filtration media is also used when extremely high quality filtrate is required and can remove suspended solids down to 10 microns.

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Typical Grades

Pumice Filtration Media No.3 0.2 – 0.5mm
Pumice Filtration Media No.5 0.8 – 1.3mm
Pumice Filtration Media No.6 1.2 – 2.4mm
Pumice Filtration Media No.8 2.0 – 3.5mm

 

All our pumice filtration media has British Standard approval (BS EN 12906-1999) and UK Drinking Water Inspectorate approval. Additionally our pumice filtration media meets all the chemical and physical testing requirements for AWWA B-100 and DIN EN 12906.


Additionally our pumice filtration media is NSF-61 approved and meets all the chemical and physical testing requirements for AWWA B-100 and DIN EN 12906.



 

Further information

For further information on pumice in desalinisation applications please feel free to contact us at: desal@desalinisation.co.uk. Or for further information on our range of pumice filtration media please follow the link: Pumice Filtration Media.

 

 

References

If you would like further information or details on where our Pumice Filtration Media has been successfully used please do not hesitate to contact us at: references@desalinisation.co.uk.

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