Salt Water Sewage Systems

[The Peon]

So I was sitting on the toilet and thinking about life, and my mind wandered to areas where fresh water is a luxury and how we here in the west literally take a dump into it. Why do we use fresh water to flush our toilets and use in our sewer systems? Why not use salt water from the ocean? How expensive could it be to pump it in from the ocean instead of using water treatment plants and recycle fresh water through tons of filtration systems? I know this would not be practical for many areas in the center of larger continents... but many many massive cities lie along or near the coast.

 

With modern plastic polymers surely we could use materials resistant to salt water corrosion (maybe they already exist in desalination plants?). A large micron filter could handle the larger sand particles and debris. This would alleviate a massive problem looming with fresh water, and in addition would stop the dogs from drinking out of the toilet.

 

Am I missing something here?

Edited December 18, 2012 by The Peon

[Moontanman]

Yup, the salt is what you are missing. once you "use" the water what do you do with it? If you are going to pump it back into the ocean you will have to filter it just like they do freshwater sewage...

[The Peon]

Why would it need to be filtered if it was pumped into the oceans? Don't trillions of animals do it daily?

[tomgwyther]

You can have a 'grey water' system installed. Whereby waste water from the bath/shower, is used to fill the toilet cistern.

It's easier than pumping sea water miles inland.

[Moontanman]

Why would it need to be filtered if it was pumped into the oceans? Don't trillions of animals do it daily?

 

 

"Trillions" of animals do it in freshwater rivers and lakes too but we still have to filter and process it before we pump it back in. Near shore habitats in many areas are already so polluted from run off water that swimming has to be suspended and shell fishing had to stop. Near shore marine habitats are the source of much of our seafood and easily polluted.

 

Another problem that would be a deal breaker as well is the larvae of various fouling organisms that would soon fill up the pipes unless you filtered the sea water very finely and even then a few would almost certainly get through, pipes full of sponges and sea squirts would be a problem. Intake pipes in the ocean foul even quicker as well. So such water would have to be filtered before it was used. Chlorinating sea water is of course possible but that adds yet another layer of expense that would make it no better than freshwater.

[The Peon]

Hmmm if the expenses were more or less equal for both systems, wouldn't it be more favorable to use salt water in lieu of the limited amount of fresh water on the planet? I am not only thinking about cost, but also about being more green. I mean, fresh water is limited and in many areas of the world some people don't even have steady access to clean fresh water, and here we are in the west taking dumps into it LOL!!

 

 

 

 

 

You can have a 'grey water' system installed. Whereby waste water from the bath/shower, is used to fill the toilet cistern.

It's easier than pumping sea water miles inland.

 

 

 

I was not aware of those.. why aren't they standard? I will have to look into that.. Thanks!

Edited December 19, 2012 by The Peon

[John Cuthber]

To a rough approximation fresh water is solar powered.

Rain falls on the high ground and flows down hill. we use some of it in passing and then let it continue on its way.

To use salt water would require us to pump it up hill first so we would need to spend a lot of energy doing that.

Also, if we added a lot of salt water to the system we couldn't let it run into the rivers as we do with fresh water because it would upset the local environment (and also because people living further down stream wouldn't want brackish water)

 

Then there's the cost of providing the infrastructure.

it might be just about possible for coastal cities but that's all.

On the other hand, mankind does have a lot of coastal cities.

[Externet]

Hi peon.

I find your post very interesting, for black waters only.

As stated, the main problem is the sedimentation and organism growth in the seawater intake and distribution pipes for household seawater distribution, which would be needed in parallel with existing potable water.

A parallel salty sewer would also be needed because the 'purified' salty sewage ends in rivers that may be the source of potable water later, and salt content is very undesirable in fresh water bodies.

 

The treatment of sea- black water (toilet) may not be much of a problem, as passing electric currents in the sewage plant would kill 99% + of undesirable microorganisms in it, and could be treated by some technique.

Grey waters (kitchen, bath, laundry) would become a much less volume to treat, or can be used for garden irrigation and farming with just some filtering.

[The Peon]

Thanks for sharing all your thoughts, I have learned a lot from this thread!

[zapatos]

The salt water system could be a closed loop. You would only need to pump the salt water into the system once, plus whatever it takes to top it off once in a while. Once the waste water has been cleaned up, instead of dumping it back into the ocean or rivers, you keep it in the system for reuse.

 

This would of course require duplicate infrastructure so cost/benefits would have to be weighed.

[John Cuthber]

The salt water system could be a closed loop. You would only need to pump the salt water into the system once, plus whatever it takes to top it off once in a while. Once the waste water has been cleaned up, instead of dumping it back into the ocean or rivers, you keep it in the system for reuse.

 

This would of course require duplicate infrastructure so cost/benefits would have to be weighed.

Why not do that with fresh water?

 

 

 

The treatment of sea- black water (toilet) may not be much of a problem, as passing electric currents in the sewage plant would kill 99% + of undesirable microorganisms in it, and could be treated by some technique.

Grey waters (kitchen, bath, laundry) would become a much less volume to treat, or can be used for garden irrigation and farming with just some filtering.

You have remarkable faith in these techniques: what are they?

[zapatos]

Why not do that with fresh water?

 

 

They actually do that now in California. One of the biggest issues seems to be the rather poor choice of names, which is "toilet-to-tap".

http://www.pbs.org/newshour/extra/features/us/jan-june08/water_2-11.html

 

I understand that they have been taking sewage water, treating to levels stringent enough for drinking water, then pumping it back into the groundwater. It is clean enough to drink but difficult to get over the idea that it is recycled. Seems that now they may be skipping the groundwater step.

[John Cuthber]

 

 

They actually do that now in California. One of the biggest issues seems to be the rather poor choice of names, which is "toilet-to-tap".

http://www.pbs.org/newshour/extra/features/us/jan-june08/water_2-11.html

 

I understand that they have been taking sewage water, treating to levels stringent enough for drinking water, then pumping it back into the groundwater. It is clean enough to drink but difficult to get over the idea that it is recycled. Seems that now they may be skipping the groundwater step.

Where did they think water came from? It's all recycled, and it always has been.

[Mouffa]

Seawater is actually extensively used in some pacific islands (Marshall, Nauru, Kiribati). The water is reticulated to HH and the raw sewage is discharged into the open ocean, after the reef. Advantage is that it saves precious freshwater in places where the only source of water comes from rain.

Saltwater pump are expensive tho and the system needs quite a bit of maintenance. It is obviously a concern for the environment, although if the system is well designed (the sewage is diverted away from the reef and within offshore currents), risk of coastal/reef pollution are limited (but not avoided).

Hope this help.

[EdEarl]

Nature is our guide. She provides microbes and plants that use nutrients in our waste as sustenance for their growth. In turn we depend on sustenance from other plants and animals. Most animals poop and pee on the ground and everything is recycled efficiently. We live in cities and need systems to prevent disease, but it is still best to process waste locally and with best efficiency and simplicity as possible.