water purification

Similar to an individual recently I have been trying to purify water for a wastewater recovery septic system, 3 options I was considering was:

1) RO - maybe the cheapest , and the way to go, water doesnt need to be 100% clean, just enough so that we can still get a clean toilet flush, it was suggested that i may go through filters quick.

2) a Electrolytic cell powering a Galvanic cell, now i realize that the reaction will take more energy to split than to recombine using water only but my solution to that problem lies in the fuel hidden in the waste water in the form of ammonia and nitrates which takes less energy to split, then i can pipe the h2 and recombine it in the other cell as pure water. with a bit of energy surplus. Does this make sense to anyone else? few problems anyway though , I would prolly need huge cells that cost huge $$. but just wanted to hear how yall felt about this.

3)
The specific heat capacity of water is 4,200 Joules per kilogram per degree Celsius (J/kg°C).
this leads me to the distillation process which requires huge amounts of energy, = 336000kj to heat 1kg from 20deg to 100deg. PLUS I read somewhere else that it takes almost that same amount of energy to go from 100deg liquid to 101deg gas...?
So going shopping i see lots of distillers like this:
Considering that the kettle holds 1kg, id need 672000kj to evaporate it all.

But I often wonder what if i move the condenser like this so that the steam inside transfers heat to the water that needs it, thus recycling almost all the energy. but I have seen no setups like this which leads me to believe there is a flaw to my plan. Can anyone see it?

Dr_Doggy said:

Similar to an individual recently I have been trying to purify water for a wastewater recovery septic system, 3 options I was considering was:

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Just a dumb idea but one if I was in your place I'd have to try.

Why not save your "gray water"? https://www.watereducation.org/aquapedia/gray-water And use it to flush the toilet. Doing it helps your septic tank too, grey water is an extra burden in the septic tank. So by making a drain from say your clothes washer to a tank, like a 55 gallon plastic drum and fitting a pump to the drum to your toilet, the grey water gets a second use as the flush source. And no filtering or distilling needed.

Dr_Doggy said:

3)
The specific heat capacity of water is 4,200 Joules per kilogram per degree Celsius (J/kg°C).
this leads me to the distillation process which requires huge amounts of energy, = 336000kj to heat 1kg from 20deg to 100deg. PLUS I read somewhere else that it takes almost that same amount of

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It is only 336kJ or 0.093 kWh

We have an aerobic septic system, where every day once a day there are aerobic sprinklers that put the 'gray water' onto the yard.
The only real maintenance or energy going into the system is an aerator. The purpose of the aerator is to supply oxygen for the bacteria to break down the waste properly. There is also a chlorine tank (about 3 feet long and as big around as a coffee can) . The purpose of the chlorine tank is to pass the 'gray water' through it before it goes on to the yard. This chlorine tank only needs to be refilled once every 6 months to a year.

In your situation you could capture some of the 'gray water' that would be going out into the yard and recycle it into your toilet tanks.

Dr_Doggy said:

But I often wonder what if i move the condenser like this so that the steam inside transfers heat to the water that needs it, thus recycling almost all the energy. but I have seen no setups like this which leads me to believe there is a flaw to my plan.

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I know nothing about septic systems, but with reference to recovering heat from distillation, the ISS WRS does just that.

In this schematic its done in the box with the green dots running horizontally labelled 'regenerative heat exchanger':

The same document has the sentence: "The process is very energy efficient as the heat of vaporization required for boiling of the pretreated urine at reduced pressure is provided by the condensed product water."

Of course, they have the advantage of being able to reduce the pressure of the water -- thus reducing the energy required to make it boil -- for free; whereas you'd need to run a vacuum pump to do that on earth.

I doubt it would work for that still setup in your pic -- which going by the hooch jar ready to collect the output, is for distilling liquor -- because changing the thermodynamics of the thIng and you could screw up the clean separation of the methanol/ethanol. (Or maybe it would enhance it. Dunno.)

If I'm really bored later, I might try running a simulation to see how much energy you could save; but I haven't done a heat flow sim for years, so I've probably forgotten a lot.

I believe that there is a flaw to your plan, sorry. The water coming out will be at 100°C.

Dr_Doggy said:

But I often wonder what if i move the condenser like this so that the steam inside transfers heat to the water that needs it, thus recycling almost all the energy. but I have seen no setups like this which leads me to believe there is a flaw to my plan. Can anyone see it?

View attachment 133637

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I would suggest you have a look at a "counter-flow heat exchange", which should extract almost all of the energy, and the water outflow temperature will be very near the inflow temperature. As I understand it, a counter-flow exchange is basically the continuous (i.e. "infinite"-stage) version of a multi-stage exchange system.

dougy83 said:

I believe that there is a flaw to your plan, sorry. The water coming out will be at 100°C.

I would suggest you have a look at a "counter-flow heat exchange", which should extract almost all of the energy, and the water outflow temperature will be very near the inflow temperature. As I understand it, a counter-flow exchange is basically the continuous (i.e. "infinite"-stage) version of a multi-stage exchange system.

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I was going to suggest the same thing but didn't know what it was called. I built one using polystyrene tiles and aluminium foil to do air exchange in an incubator and it worked very well.

Mike.

dougy83 said:

I believe that there is a flaw to your plan, sorry. The water coming out will be at 100°C.

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Not if you're making tea?

If you are distilling the water, you can recycle most of the energy of evaporation if you reduce the pressure of the steam to slightly below atmospheric pressure with a vacuum pump.

The feed water will then be boiling at slightly less than 100 °C. Converting water to steam is where most of the energy is needed. The steam is drawn through the vacuum pump, and as the pressure rises to atmospheric pressure, the steam will condense at 100 °C, so slightly hotter than the temperature that the feedwater will be boiling at, so a heat exchanger can recover the energy of evaporation back into the feed water.

The condensate can pre-heat the cold feed water up to near its boiling point with a contraflow heat exchanger.

There are losses, so external heat is needed as well, and power is needed to run the vacuum pump, but the overall power use is far less than is used simply boiling the water.

I think of it as a heat pump to pump the heat from the clean steam back to the boiling feed water, but a heat pump that uses the steam as the working fluid.

Water purification systems like this are used quite a lot. It's called Mechanical Vapor Recompression if you want to search for more details.

However, I think that reverse osmosis uses less energy.

Pommie said:

I was going to suggest the same thing but didn't know what it was called. I built one using polystyrene tiles and aluminium foil to do air exchange in an incubator and it worked very well.

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That a really simple way to do it!

Nigel Goodwin said:

Not if you're making tea?

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That seemed fair on first read, but distillation of a septic tank is going to carry over aromatic volatiles which may detract from the tea-drinking experience. Butt maybe that's your cup of tea.

Grr ... passwords , i'll just make work acct.

SO.
My apologies, looking back at it im not sure why I thought having an internal condenser would make things better... but i could still rig it to use externally, as long as the water coming out is same temp going in that still counts for efficency, right? , I wonder if there is anything else i can do to boost that efficency.

Im happy to hear mention of nasa and septic systems. I have been following those processes closely. it seems they started from fuel cells to microbe fuel cells and most recently have been focusing on algae. Another process i am looking at closely.

There of a couple of YT vids that have ppl somehow cleaning waste to drinkwater but they dont elaborate on how they are doing it.

Unfoutunately weaping beds are out of the question for me since i am on a small urban lot. As well as grey water, however i will be colecting rain water.
although I do have a few 1KL tanks at my disposal.

Just to elaborate a bit we have some rabbits and i have designed a closed loop flushing system to wash out the urine and a filter to remove the solids. Right now it uses about 40Gal per day(and i hope to step up to more). And this is the water that needs to be cleaned, just so it can cycle again and pick up more urine so 100% clean isnt required either. Another idea from YT was from the maple syrup ppl who are using ro filters to concentrate the syrup 50% of the way, but still boiling off the rest. but are saying its alot cheaper than pure boiling.

thats a plan B, but Plan A is:

I am interested to hear about the aerobic septic system, I have tried one of my own imitating the workings of a aquirium moving bed bio filter. but I am having problems getting it to cycle up. Moreover Im trying to reproduce a Anthroponics system using rabbit instead of human as a source.

AND I beleive that the plant system isnt working cos of the no bacteria problem. So I am wondering the details about the aerobic and anerobic digesters. and the ideal condidtions for bacteria, I realise that temp is a factor, which should be no problem for me since it has been 30deg all summer.
My other concern is ph & ppm where the waste is a high ph of 9-10, and ppm concentration is around 2.6k but I have tried diluteing and dropping ph with no avail. In fact the water gets darker not clearer! BUT What else could it be?

DrDoggy2 said:

Unfoutunately weaping beds are out of the question for me since i am on a small urban lot. As well as grey water,

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Don't quite understand that statement, what do you have for waste water now?

city sewer, and city laws say you need x ammount of sqft for weeping beds.
And my goal is to get the urine of of the water, or vice versa.

so i think i want to try a distillation process inside a rocket stove, which translates to about 2 cuft of wood per day or 300Kbtu(90$/day electricty), without any heat recovery. but i would like to add in a CountereFlow heat exchanger, im thinking of using 1/2" copper pipe on the inner tube and 3/4 on the outter tube, but I am having troubles establishing how long the pipes need to be? any ideas?