Simple, Cheap and Portable: A Filter-Free Desalination System | Hacker News Reader

Simple, Cheap and Portable: A Filter-Free Desalination System

spectrum.ieee.org

35 pointssohkamyung8 comments

The claim is "filter-free", but the device also uses an "electromembrane". So... how is that not a filter? Because it's electrified?

The selling point of this device is that it doesn't need filter changes in the field. Okay. So, how many liters of seawater can in process before it needs an "electromembrane" change?

It's not my field of expertise, maybe I'm just really missing something obvious. Or maybe it's hype and BS tarnishing an otherwise good advancement. Can't tell.

> So, how many liters of seawater can in process before it needs an "electromembrane" change?

It doesn't need regular changes, because it's not a filter.

That's also why it's called an "electromembrane" and not a "filter"... Because (can you you hear me in the back) it's not a filter.

If you want technical details in how the device operates, you should probably not be consulting pop sci news articles that are written from press releases... Maybe Wikipedia has an article about it, say https://en.m.wikipedia.org/wiki/Electromembrane_extraction ?

As others point out, it's not a filter since it pushes contaminates away from a particular zone on the membrane, and that zone is where they harvest the fresh water. Flush those contaminates away from the surface of the membrane with contaminated water, clear a new zone of uncontaminated water, harvest, (literally) rinse and repeat.

Nothing to wear out. I'm sure it will require cleaning of some sort (what doesn't) but it sounds like the membranes are designed to be a permanent solution with minimal maintenance. Pretty clever!

The energy consumption quoted in the article is super confusing. Do they mean it uses 9 Wh in the hour that it takes to produce 0.3 L of water? So do they mean it consumes 9 W while operating and uses 30 Wh/L of water produced? How does that compare per litre to the energy used by reverse osmosis? Seems like that would have been a useful stat to include in the article!

EDIT: I looked up, this source [1] says 2.98 kWh/m^3 for modern, commercial scale RO, so that seems to be about 3 Wh per litre? That seems a lot better?

1. https://uh.edu/uh-energy/educational-programs/tieep/content/...

Their pitch is that while this solution makes less water volume and requires more energy than existing solutions, it doesn't have consumable filters or require regular maintenance for cleaning. So you can just plug it into a solar panel, collect the water, and forget about it, versus needing to have someone trained to maintain the system and supplied with spare parts. I'm not sure I buy this because it seems like you'd still need to have pre-filters that need maintenance and/or replacement, and it seems like it would be a better use of time and money to just improve RO systems, but at least in theory it does have a value proposition.

The way it's described in the article was pretty clear that it pushes all contaminates, including solids, away from a particular zone on the membrane - and that's where the uncontaminated water is harvested from.

So no, it doesn't sound like it needs pre-filters. Obviously the fewer contaminates the easier/faster it will probably work. A simple settling tank would dramatically reduce the really big stuff and the rest sounds like it would be trivial for this tech to deal with. It's a very interesting technology!

Given that TFA says that RO is 3-4x more efficient, maybe it's 9Wh/L?

This doesn't really seem that compelling. I don't believe that in the real world a system like this can produce drinkable water without at least pre-filters that require maintenance. And unless I'm misinformed, the cost and availability of replacement RO membranes isn't what's limiting the use of RO desalination or water purification where it's needed.

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