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Distillation of sea water for small islands

Does anybody have any comparisons (economic and technical) for distillation facilities on small islands? What would be the best option for 3000 to 5000 people?

The original question comes from Pikacha McLean from Bellona in the Solomon Islands

Any suggestions welcome.

From: mcleen Pikacha Sent: 30 October 2015 13:16 To: Reception Subject: Need assistance in building our water distillation system.

Thanks very much Neil. Yes we are an atoll island of more than 3000 -5000 people. Probably a small or medium distillation system will do where we do not need high maintance and easy to operate and maintain. I also like the idea of farming as well since dry season in this atoll makes it hard for locals to engage in local crops. Please suggest what is best for us. Kind regards, Mcleen

From: mcleen Pikacha Sent: 30 October 2015 13:16 To: Reception Subject: Need assistance in building our water distillation system.

Dear sir/madam,

My name is Mcleen Pikacha and I'm from a small Polynesian island called Bellona in the Solomon Islands, South Pacific. My people are currently suffering from a long drought caused by El Nino for more than some 5 months now. My island do not have water ponds, rivers, streams or wells. My people rely heavily on rain water collected in their tanks and from coconut trees. We are desperately looking for immediate help and have managed to send some tonnes of mineral waters to the island to keep them for the next few weeks or so. Though we are dealing with the immediate needs I'm looking for help to help my island people in the long term. What came into my mine as a solution is a distillation system to make use of the abundant sea water around our Island. I searched through the internet for possible help and I came across your organisation. Please if you can able to help my people let me know. We are desperate and suffering as a result of what I believe is the beginning of global warming. Please, we need help and I believe to hear from your organisation. Kind regards, Mr. Mcleen

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3 Answers

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While solar stills and Seawater Greenhouse are very interesting technologies, adoption to date is many orders of magnitude lower than the main desalination technologies of Reverse Osmosis (RO), Multi Stage Flash (MSF) and Multiple Effect Distilation (MED). MSF & MED are thermal processes & tend to only be feasible when combined with a power plant that produces steam to drive the desalination process. As such I would suggest that RO should probably be your first port of call.

RO only requires electrical energy, seawater, a small amount of chemicals and a means of disposal of the brine (most likely a well ecologically designed long sea outfall). So you can power it with any form of renewable energy available (and of course also with non-renewable sources if required). By all means compare RO with solar stills (which require a huge footprint) and Seawater Greenhouse (which is generally intended more for production of high value plants rather than potable water), but I would be surprised if RO didn't come out as the economic & technical winner in a feasibility study.

There are many different vendors of RO systems of all sizes - the 'Desalination Report 2.doc' is incorrect in this sense, you can get hand powered RO systems small enough to supply water for one person only, and the other end of the scale is unlimited, as they are modular. You should easily be able to find a number of vendors to give a competitive quote that covers your needs. You may want to start looking at vendors with a presence in your nearest larger neighbour.

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Interesting might be these innovative systems that use a special membrane distillation system (not to be confused with reverse osmosis or membrane 'filtration' systems):

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Interesting certainly, I love the idea of almost direct use of solar energy to distill the water. Somehow one would instinctively assume that it has to be more efficient than decoupled systems.

However, given the economies of scale of RO membrane production, I imagine it will be a long time before solar membrane distillation becomes competitive with decoupled PV-RO desalination where photo voltaics provide the energy for the RO process. When I say competitive I mean in terms of capex & opex including a factor for footprint land cost.

Martin Currie _ Aqueum gravatar imageMartin Currie _ Aqueum ( 2016-01-16 10:32:31 -0600 )edit

True, but these Membrane distillation systems also seem operate with much less requirements regarding maintenance, oversight and consumables like anti-scalant and cleaning solutions against bio-fouling etc. In an remote area with a lack of qualified staff, this can quickly outweight the cost advantages of RO systems due to costly down times and bringing in material & maintenance staff from far away.

Krischan Makowka gravatar imageKrischan Makowka ( 2016-01-18 02:38:02 -0600 )edit

Dear Mr Mclean,

There are a number of options in what can be done regarding water distillation and the most appropriate one will depend on the scale of operation.

A general overview can be seen in the attached document. For example it describes solar stills that can produce clean water and also a variant on this concept called the Seawater Greenhouse which additionally has an area where crops can be grown in a cooler more humid area under cover while still being able to collect clean condensed water for drinking.

And you are very welcome to come back to me with further questions on any aspect of distillation that you are interested in and we can try to provide further information.

Desalination Report 2.doc

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2015-11-04 03:06:21 -0600
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Jan 15 '16