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How to create fresh water from salt water through filters using gravity

Image credit: Michael Liu

Michael Liu Sep 09, 2021
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Water Desalinisation using Gravity
This idea encompasses the ultimate optimization and the most energy efficient way of expanding and using Reverse Osmosis Seawater Desalinisation by using large drilled holes (augers) next to the sea joined by large drilled holes (augers) at the sea bed (see diagram) utilising gravity.
The diagram conveys a rough outline of how water desalinisation could be possible by using gravity as its power source with the use of existing membrane based reverse osmosis filter fibres currently being used in desalinisation plants.
If you look at the diagram you will see a simple but possible desalination plant scenario by the seaside which consists of -
  1. A 100 metres plus hole/auger - this is where the filtered salt water (which has now been filtered into fresh water) is drained into and eventually pumped out from.
2 & 3. Drilled holes forming catchment pipelines from the sea bed to the 100 metres plus hole/auger. At this stage they have slide in filters at each end so filtration can take place at either end; this is especially handy for continuous filtration when it comes time to change a filter at either end. The amount of holes from the sea bed to the main hole/auger is limitless.
  1. A pump at the top of the main hole/auger simply pumps out water to a set of above ground/or underground freshwater pipelines.
Numerous variations can be developed here as everything depends on creating enough water pressure to push the salt water through the filters.
  1. The angle of the salt water catchment pipe lines
  2. The depth of the sea bed filter at the top of the salt water catchment pipelines
  3. The depth of the main hole/auger
Sea bottom dredging may need to be done to create more favourable conditions.
Various cages can be built to stop sea matter (such as seaweed) blocking the top of the sea bed pipelines.
Copyright Michael Liu March 10th 2006
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General comments

Samuel Bello
Samuel Bello3 years ago
This is an interesting idea, but the principles of physics may not allow such a system to be any more efficient than existing solutions. Basically, this type of desalination uses pressure from an artificial source to make the water get filtered through a semi-permeable membrane. Instead of an artificial source, the proposed source uses the pressure that is felt as one goes lower into the water body. This pressure is a result of gravity like you stated but the work done by gravity, in this case, is equal to the work done by the pump in raising the water back to the ground level (according to the law of conservation of energy). This is why the effort that that seems to be saved by using gravity instead of an artificial source to generate the pressure is canceled out (after all, the pump moves water by generating pressure from an artificial source). The only case where this would be a practical solution is if the water is used at the height that the filtered water is dispensed and not pumped back up before it is used. (For example, it can be used efficiently in submarines)

So long as the water will be used on land, it is better to use already existing reverse osmosis desalination models that are smaller and more mobile.

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Michael Liu3 years ago
Samuel Bello Hi Samuel. Thanks for spending your time to take a look at this and give me your constructive words on this. Next time you have a bath or fill a sink with water and you pull the plug out, you will notice that the pressure in and around the sink hole is much higher than the water pressure at the bottom of the vessel when the plug is in. This is where the magic lies. cheers mike.
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Samuel Bello
Samuel Bello3 years ago
Michael Liu, I understand that the pressure increases with depth. What I am saying is that pressure generated by such a gravity-dependent system is not, in practice, a better solution. It only results in a larger and non movable compartment being used to generate the pressure. The novelty of the idea is that gravity is used to generate the required pressure. The main question here is that, is your proposed solution in any way better than already existing solutions?

All the physics principles I quoted and analyzed in my earlier comment imply that it is not better than current solutions and the proposed solution can not be developed up to the extent where it can compete with current solutions.

If you have some reasons to believe the proposed solution is better, please give a detailed explanation after going over the underlying physics principles.
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Samuel Bello
Samuel Bello3 years ago
Michael Liu By the way, the example you mentioned about the pressure being higher near the sinkhole is not accurate. The pressure is, as a matter of fact, lesser at the sinkhole that is why the fluid flows towards it. Fluids generally flow from regions of high pressure to regions of low pressure. The reason it feels like there is more pressure around that area is that; placing your hand there tries to oppose this natural movement of fluids to lower pressure regions. So what you perceive is not pressure but the momentum of the moving water. Humans cannot sense such small differences in pressure.
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Michael Liu3 years ago
Samuel Bello Hi Samuel. Thanks again for taking the time out to think about and send a response. I'm new to this site and I just had a flick through some of your ideas mate and you are an awesome ideas machine!! You keep it up mate as you will be as famous as Elon Musk one day (if you are already not). In regards to your comment on the pressure point near the sinkhole you are absolutely correct so i will try and explain it a little better. Where there is a break or weakness point where pressure can release, this is the sink hole (or the sink hole in the sea in this case), so the force of pressure will push water through. I will now try to respond to your previous message directly. cheers mike
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