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Using waste for propulsion ?



 
 
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  #11  
Old November 28th 16, 12:14 AM posted to sci.space.policy
William Mook[_2_]
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Default Using waste for propulsion ?

Quite right. Magic is required to convert ALL waste to methane. But there is the possiblity of methane production. What's the science of that say?

Let's look into it;

David House states in his excellent book that 1000 lbs of human waste produces about 0.6 cubic meters of biogas. Now a short ton is 2,000 pounds. A metric ton is 2,204.62 pounds and one cubic meter equals a thousand litres.

So, that's 1,323.6 litres of biogas at standard temperature and pressure (STP) for each ton of human feces processed.

Now at STP 22.4 litres of a gas equate to one molar gram for the gas. 59.08 molar grams of gas per metric ton of feces.

Now on a volume basis, biogas consists 40% carbon dioxide and 60% methane - with small quantities of materials like hydrogen sulphide - all of must be removed to get pure methane.

Methane's molecular weight is 16. Carbon dioxide's molecular weight is 44. So, methane is 60% of the volume or 35.45 moles of that gas. Times 16 grams per mole that's 567.2 GRAMS per METRIC TON of feces! 40% carbon dioxide is 23.63 moles of that gas - times 44 grams per mole that's 1,039.7 GRAMS per METRIC TONS of feces!

On average humans eliminate 128 g of fresh feces per person per day with a pH value of around 6.6. Fresh feces contains

75% water and
21% organic solids,
5% bacterial biomass
5% nitogenous matter
5% carbohydrate
3% fats
2% other
4% calcium and iron phosphates

100 persons produce 12.8 kg per day. On a 280 day trip 100 persons produce 3.58 metric tons. In an efficient anaerobic digester (which has its own mass and must be carried aboard ship) this produces 2.03 KILOGRAMS of methane gas over the entire 280 day period.

Since the anaerobic digester is likely to weigh more than 2.03 kg its inclusion in the process is a net negative.

Now;

(1) Removing the water and purifying it for reuse, saves a substantial amount of water, 2.685 metric tons! Removing 9.637 litres of water PER DAY from 12.8 kg per day - is likely to involve a device far smaller than 2.685 tons - so this is a NET GAIN.

(2) Reducing the fats, carbohydrates, biomass, to water and carbon dioxide, and then reducing water to hydrogen and oxygen, and the carbon dioxide using the hydrogen to methane then to carbon and water, produces useful products that may be recycled - and also produce a net gain.

(3) Reducing the nitrogenous matter - to hydrogen and nitrogen gas - that may be used in a closed cycle system also produces a net gain.

(4) leaving dried ash consisting of calcium and iron phosphates that may be stored for later use on Mars.

So, a one ton system that recycles water and oxygen and eliminates CO2 produces carbon black that is used to absorb odours, and make phosphate powders that may fertilise plant growth on Mars, allows us to reduce bringing along 9.6 metric tons of consumables.

So, this is what we can expect from a well-designed system.


  #12  
Old November 28th 16, 02:11 AM posted to sci.space.policy
William Mook[_2_]
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Default Using waste for propulsion ?

On Sunday, November 27, 2016 at 4:37:05 PM UTC+13, JF Mezei wrote:
On 2016-11-26 20:22, William Mook wrote:
Methane is pyrolysed using solar energy to reduce methane to carbon and hydrogen again;

CH4 + solar energy --- C + 2 H2


Is there a point in spending energy to do that when methane is the
primary fuel for the vehicle ?


Because the weight of the energy generator is modest when compared to the savings in weight of consumables used.

Please understand what you are saying. You need oxygen to burn methane. I calculated earlier tha an anaerobic digester produces 2.03 kg of methane from the waste produced by 100 people over 280 days of a mission. Each kg of methane releases 55.6 megajoules of heat energy when combined with 8.12 kg of oxygen! Used in this way the CO2 produces 8 Watts per day of heat energy. It also produces 5.58 kg of CO2 and 4.57 litres of water over the course of the mission when used this way.


If you have a byproduce that is useless, it makes sense to spend energy
to convert it to components that are of use for the ship or passengers.


Precisely. The real issue of a designer is to compare the mass of the equipment needed to the mass of consumables saved. Concentrating photovoltaics that are hyper-efficient by use of the full solar spectrum, are very light weight per unit power. Extracting water in a partial vacuum at near room temperature, is likewise very efficient. Oxidising human waste is also efficient weight wise - and very clearn and odour free. Reducing hydrocarbons to water and carbon dioxide - and taking all carbon dioxide and reducing it to methane, not for fuel use, but to reduce that to carbon black - an odour absorber - and hydrogen - a carbon dioxide absorber - and recycling the oxygen back into the cabin - that's the most efficient system people have come up with.


But if you have a by product that can be used be engines, is there a
point converting it to something else ?


Because the weight of material is low compared to the weight of the hardware to make it happen. Methane in conventional systems is produced by bacterial action taking 10 days or more, and involves a very tiny fraction of the total waste.

Methane is processed on board the ISS, but not this way.

Water is electrolysed into hydrogen and oxygen. The oxygen is breathed producing carbon dioxide The carbon dioxide is scrubbed from the air by combining with the hydrogen to make methane and water again. The methane is broken down into carbon black and hydrogen again. The carbon black is used to absorb odours. The hydrogen is used to scrub the air of carbon dioxide. This is a Sabatier reactor.

As far as feces is concerned, there are more direct and less massive and more easily controlled methods One more direct method is to extract water from wastes at low presure near room temperature. Then make hydrogen peroxide from some of the water and some oxygen and solar electricity. Then chemically react the hydrogen peroxide with the dried waste solids forming CO2 and water at near room temperature without a lot of heat. The CO2 and water are processed as described above - and made part of that process.

In the end you carry a few days supply of water and oxygen aboard, and a machine that processes all wastes into oxygen and water. The only thing you consume is food concentrates which are reconstituted using water. You end up with carbon black and phosphate powder and small quantities of nitrogen and oxygen and water - which serve to replace losses from the cabin. The carbon black is used to absorb odours and keep the air smelling fresh. The phosphates are carried to Mars and used as fertilisers there.



Now that for the station, they bag human waste, and any methane that i
produced just accumulates in those bags until Progress burns up. So this
is not part of the equation on the ISS.


That's true, but the ISS does recycle urine for its water content, and does recycle carbon dioxide for its oxygen content using solar energy. This can be extended to all wastes and the highest best use of that waste is to close the consumable loop with a machine that weighs less than the consumables saved.

7 people producing 128 grams of feces per day produce 250 kg over a 280 day period. With a conventional anaerobic digester this produces 128 grams (1/8th kg) of methane gas. Not much at all.


The question is how a 100-pax ship handles human waste on a 3-4 month
journey to Mars.


Well at 128 grams per person per day 100 persons produce 12.8 kg of feces per day. Over 120 days 1,536 kg of feces. In an efficient anaerobic digester this totals about 1 kg of methane gas. When combined with 4 kg of oxygen it produces 2.75 kg of CO2 and 2.25 litres of H2O along with 55.6 megajoules. That's about 5.3 watts per day.

As I've said multiple times already, the highest best use of this stuff is to extract water from it at low partial pressure and room temperature, and then oxidise the dried residue with hydrogen peroxide again at low temperature, and process the CO2 and H2O generated in the waste gas process stage of the air regenerator. This reduces the feces to about 16 kg of carbon black and 4 kg of phosphates over the period - recovering all the water and oxygen for use aboard ship.



The passengers never generate a significant amount of methane relative to the propellant. That's the point.


And when they build airplanes, they try to shave grams off here and
there.


True, but creating and capturing methane purifying it to the standard needed for use as a propellant, recovers far less propellant than the equipment weighs. So the process adds weight. Where waste processing makes sense is recycling all the components where possible. The principal savings is in water usage. The next is recovery of oxygen and production of carbon black.. Third is the production of phosphates.

Small potatoes compared to total weight of aircraft like an A380,
but at the end of the day it does matter. 200 grams removed from a seat,
means 80kg weight saving when you have 400 seats, or the weight or an
extra passenger or 80kg of extra cargo you can carry.


Right, and the same thing applies here. The weight of a propellant line and valve to carry the grams of methane you might produce to the propellant tank is likely to weigh more than the propellant recovered, even if the balance of the system was massless.

100pax over 3-4 months will consume large amounts of food.


True, but most of that ends up in the air as CO2

That is a lot
of mass


True, but they produce primiarly water and CO2. The methane is a secondary process that's far down on the list of things produced. 3.65 kg per day of consumables - 0.128 kg per day of feces - from that MICROGRAMS PER DAY of methane. Got it?

that you have to lift and accelerate out of earth's orbit
towards mars most of which will become waste.


100 people produce 12.8 kg per day. If they spend one day on orbit before boosting into a trans-Mars trajectory they might gather milligrams of methane. This is inconsequential when compared to the METRIC TONS of methane consumed.

Not doing anything with it
means wasting that mass which you spent much fuel accelerating.


You're making a false choice. Just because its not used as propellant doesn't mean its not used. The ISS uses the Sabatier reaction to process water into hydrogen and oxygen. The oxygen is breathed. The hydrogen is used to scrub the CO2 from the air converting it into methane and water.

To this system folks have added other processes. Especially aboard nuclear subs. Methane is easily pyrolysed into hydrogen and carbon black. Water is easily electrolysed into hydrogen and oxygen. Hydrogen is used to continue scrubbing the air, oxygen is breathed, and carbon black is used to absorb odours.

The ISS also processes urine into clean water which recovers the vast majority of water consumed that is not make its way back into the atmosphere.

http://www.iflscience.com/space/amer...ssians-refuse/

https://www.nasa.gov/pdf/146558main_...%204_10_06.pdf

  #13  
Old November 28th 16, 02:29 AM posted to sci.space.policy
William Mook[_2_]
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Posts: 3,840
Default Using waste for propulsion ?

On Monday, November 28, 2016 at 2:24:42 AM UTC+13, Alain Fournier wrote:
On Nov/27/2016 at 1:17 AM, Fred J. McCall wrote :
JF Mezei wrote:


100pax over 3-4 months will consume large amounts of food. That is a lot
of mass that you have to lift and accelerate out of earth's orbit
towards mars most of which will become waste. Not doing anything with it
means wasting that mass which you spent much fuel accelerating.


I know it's hard for you, but think about it. Most of the mass of
food (and feces) is water. You're going to get the water back for
recycling on the back side of the process. That means each person
will generate 1-2 ounces of solid waste per day once the water has
been recovered (and you'll get 3-6 ounces of water out of the same
waste stream). Let's use the larger number as more 'favorable' to
your case; 100 people (not sure what 'pax' are when they're up and
dressed) will generate around 12.5 pounds of solid waste per day. That
waste is a mix of dead bacteria, indigestible food elements like
cellulose, minerals, and indigestible fats. You're not going to turn
it into methane without giving up a lot of the recovered water and
even then most of it isn't going to 'convert'. Recovering the water
is more valuable, since you can make things like breathing air out of
that stuff. So you're going to accumulate a little over half a ton of
such cruft during the course of the trip.


[You should use normal units instead of those ounces and pounds, it
would make your post easier to read for normal people, and lessen the
risk of errors from unit conversions.]

It's not one or the other. You can very well recover the methane and the
water and grow food. Plants don't need the methane from human waste to
grow. So after extracting methane, the waste isn't any less fertile than
it was before extraction.

If you want to recuperate the water that was lost in the fermentation,
you can burn the methane and make electricity, water and CO2. The CO2
will be taken by the plants you want to grow. Of course, if you do so,
that means you can't use Mr Mezei's idea of burning the methane as
rocket propellant. Which probably isn't worth the trouble anyway.

Even growing food on the spaceship probably isn't worth the trouble. The
trip is not long enough to do serious farming. I think that the best use
of human waste on a spaceship bringing colonists to Mars is to store it.
Land it on Mars. And then, once on Mars compost it and use it to grow
food. You will want to have lots of fertilizer handy for your colony on
Mars.


Alain Fournier


Depends entirely on the size of the ship. A 100 passenger ship, it makes sense to recycle air and water certainly, and reduce all waste to carbon and phosphates. A 10,000 person colony ship - now you get to the size where growing stuff makes sense. But even this is a function of technology. The Stanford Torus studies of the 1970s involved growing conventional crops and livestock. Today, with the ability to grow meat in a test tube, and assemble it using 3D bio-printers, it is not beyond the realm of near-term possibility that we will be able to have self sustaining systems for as few as 100 people or less.

11% conversion efficiency of sunlight to biomass - using advanced algal strains - a square meter of solar collector exposed to sunlight in space - is capable of capturing sufficient energy to produce 0.55 kg of dry matter per day. We consume 0.55 kg of dry matter per day.

Since chlorophyll uses only specific colours we can even sort through the spectrum to efficiently drive photovoltaics and use dyes to shift colour intensities, to improve efficiencies - and collect sufficient power to run a self contained system.

Conceptually Algae produces agar. Agar grows cells in culture. Cultured cells are assembled with 3D printers into food items. Waste is processed into feed for algae. A litre of contained fluid is required to produce about 5 grams per day under ideal conditions. So, each square meter of sunlight at 1 AU translates to 110 litres. Ideal intensity, at the colours required are around 310 Watts per square meter. The algae reactor is 110 kg per person. Cell cultures and other hardware add another 40 kg per person. A total of 150 kg per person. So, 272 days at 0.55 kg per day - we have break-even.

Now changing up the atmosphere getting rid of O2 - or lowering it substantially - permits lowering the amount of water - in a sort of aeroponic setup -

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC426129/

Which could vastly reduce the amount of water needed to perhaps 10 litres - insteads of 110 litres - reducing the break even flight time to less than 30 days.


  #14  
Old November 28th 16, 04:26 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default Using waste for propulsion ?

Alain Fournier wrote:

On Nov/27/2016 at 1:17 AM, Fred J. McCall wrote :
JF Mezei wrote:


100pax over 3-4 months will consume large amounts of food. That is a lot
of mass that you have to lift and accelerate out of earth's orbit
towards mars most of which will become waste. Not doing anything with it
means wasting that mass which you spent much fuel accelerating.


I know it's hard for you, but think about it. Most of the mass of
food (and feces) is water. You're going to get the water back for
recycling on the back side of the process. That means each person
will generate 1-2 ounces of solid waste per day once the water has
been recovered (and you'll get 3-6 ounces of water out of the same
waste stream). Let's use the larger number as more 'favorable' to
your case; 100 people (not sure what 'pax' are when they're up and
dressed) will generate around 12.5 pounds of solid waste per day. That
waste is a mix of dead bacteria, indigestible food elements like
cellulose, minerals, and indigestible fats. You're not going to turn
it into methane without giving up a lot of the recovered water and
even then most of it isn't going to 'convert'. Recovering the water
is more valuable, since you can make things like breathing air out of
that stuff. So you're going to accumulate a little over half a ton of
such cruft during the course of the trip.


[You should use normal units instead of those ounces and pounds, it
would make your post easier to read for normal people, and lessen the
risk of errors from unit conversions.]


[I am using normal units; they're just not YOUR normal units. My post
was from an American to an American, so 'normal' people don't have any
problems reading it. You know, it's only you SI snobs who whinge
about this sort of thing. To use YOUR preferred units, I would have
had to convert everything for you. Then the guy I'm talking to would
have to convert it back so it was in units he's used to using. I've
been using both US and metric units interchangeably for over 40 years.
If you can't deal, then don't. But don't expect me to make special
efforts just for you.]


It's not one or the other. You can very well recover the methane and the
water and grow food. Plants don't need the methane from human waste to
grow. So after extracting methane, the waste isn't any less fertile than
it was before extraction.


What 'methane' is there to recover? To get methane from ****e, you
have to process the ****e, removing carbohydrates. That makes it less
fertile because you've removed all the carbon and hydrogen. You can't
'recover' the water because you need it as part of processing the
****e.


If you want to recuperate the water that was lost in the fermentation,
you can burn the methane and make electricity, water and CO2. The CO2
will be taken by the plants you want to grow. Of course, if you do so,
that means you can't use Mr Mezei's idea of burning the methane as
rocket propellant. Which probably isn't worth the trouble anyway.


Indeed. How much power, equipment, space, and effort are you going to
expend to try to make half a tonne of ****e 'useful'.


Even growing food on the spaceship probably isn't worth the trouble. The
trip is not long enough to do serious farming. I think that the best use
of human waste on a spaceship bringing colonists to Mars is to store it.
Land it on Mars. And then, once on Mars compost it and use it to grow
food. You will want to have lots of fertilizer handy for your colony on
Mars.


I don't think so, either. Probably makes more sense to just start
dumping it in a crater someplace.


--
"We come into the world and take our chances.
Fate is just the weight of circumstances.
That's the way that Lady Luck dances.
Roll the bones...."
-- "Roll The Bones", Rush
  #15  
Old November 28th 16, 04:53 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default Using waste for propulsion ?

JF Mezei wrote:

On 2016-11-27 01:17, Fred J. McCall wrote:

cellulose, minerals, and indigestible fats. You're not going to turn
it into methane without giving up a lot of the recovered water and


Ok, that is a fair point. I had not considered that aspect.


So now, the question becomes whether the ISS program would start to
develop and test systems that can process solid human waste (they
already have one for urine) to recover as much as possible from it.


That's a long, long way down the road, if ever. First they need to do
a lot of work here on Earth.


"turning it into food/veggies" is basically composting the waste. And
guess what, composting requires O2 and generates methane.


Guess what? I don't think that's what they're talking about.



Not much it can be used for, which is why they throw it away on ISS.


They throw it away on ISS because they don't have any system to process
it ...


Because there's nothing useful it can be 'processed' into.


... and with only 3 to 6 occupants who get monthly deliveries by
Progress/Dragon/Cygnus (and formerly Shuttle, HTC and ATV).


Irrelevant. Do you seriously think processing ****e will
substantially reduce resupply requirements? It won't, which is why
they just toss it.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #16  
Old November 28th 16, 05:05 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default Using waste for propulsion ?

There appears to be something wrong with your numbers. With an input
of 3.58 metric tons of waste you eliminate 9.6 metric tons of
supplies. So if instead of loading supplies initially you just loaded
****, they could fly forever, gaining 6 tonnes of supplies with each
recycling. Conservation of mass and all that...

Your trip time is also 100 days longer than the longest anyone is
talking about. NASA Reference Architectures assume 180 day transits.
Musk assumes 90-120 days.

William Mook wrote:

Quite right. Magic is required to convert ALL waste to methane. But there is the possiblity of methane production. What's the science of that say?

Let's look into it;

David House states in his excellent book that 1000 lbs of human waste produces about 0.6 cubic meters of biogas. Now a short ton is 2,000 pounds. A metric ton is 2,204.62 pounds and one cubic meter equals a thousand litres.

So, that's 1,323.6 litres of biogas at standard temperature and pressure (STP) for each ton of human feces processed.

Now at STP 22.4 litres of a gas equate to one molar gram for the gas. 59.08 molar grams of gas per metric ton of feces.

Now on a volume basis, biogas consists 40% carbon dioxide and 60% methane - with small quantities of materials like hydrogen sulphide - all of must be removed to get pure methane.

Methane's molecular weight is 16. Carbon dioxide's molecular weight is 44. So, methane is 60% of the volume or 35.45 moles of that gas. Times 16 grams per mole that's 567.2 GRAMS per METRIC TON of feces! 40% carbon dioxide is 23.63 moles of that gas - times 44 grams per mole that's 1,039.7 GRAMS per METRIC TONS of feces!

On average humans eliminate 128 g of fresh feces per person per day with a pH value of around 6.6. Fresh feces contains

75% water and
21% organic solids,
5% bacterial biomass
5% nitogenous matter
5% carbohydrate
3% fats
2% other
4% calcium and iron phosphates

100 persons produce 12.8 kg per day. On a 280 day trip 100 persons produce 3.58 metric tons. In an efficient anaerobic digester (which has its own mass and must be carried aboard ship) this produces 2.03 KILOGRAMS of methane gas over the entire 280 day period.

Since the anaerobic digester is likely to weigh more than 2.03 kg its inclusion in the process is a net negative.

Now;

(1) Removing the water and purifying it for reuse, saves a substantial amount of water, 2.685 metric tons! Removing 9.637 litres of water PER DAY from 12.8 kg per day - is likely to involve a device far smaller than 2.685 tons - so this is a NET GAIN.

(2) Reducing the fats, carbohydrates, biomass, to water and carbon dioxide, and then reducing water to hydrogen and oxygen, and the carbon dioxide using the hydrogen to methane then to carbon and water, produces useful products that may be recycled - and also produce a net gain.

(3) Reducing the nitrogenous matter - to hydrogen and nitrogen gas - that may be used in a closed cycle system also produces a net gain.

(4) leaving dried ash consisting of calcium and iron phosphates that may be stored for later use on Mars.

So, a one ton system that recycles water and oxygen and eliminates CO2 produces carbon black that is used to absorb odours, and make phosphate powders that may fertilise plant growth on Mars, allows us to reduce bringing along 9.6 metric tons of consumables.

So, this is what we can expect from a well-designed system.


  #17  
Old November 28th 16, 05:19 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default Using waste for propulsion ?

JF Mezei wrote:

On 2016-11-27 18:14, William Mook wrote:

Since the anaerobic digester is likely to weigh more than 2.03 kg its inclusion in the process is a net negative.


Fair enough. But since there will have to be some sort of sceptic tank
somewhere, the weight of that digester is mostly already there on the
ship. Unless the toilets vent to space.


You don't need a 'sceptic tank', or even a septic tank. You need
sanitary holding tanks, which are much smaller. You need a
desiccators to recover the water, which is much smaller. And you need
a closet to store the waste in. The 'digester' is additional
equipment.


And if you wish to extract the water from the waste, then you also need
some sort of a tank and whatever hardware to extract the water from it.

So what if the same hardware gets water and methane from waste?


So what if there's magic pixie dust?


also you mentioned anaerobic digester. Aren't aerobic ones far more
efficient ?


Do you really want the entire ship to smell like ****e?


As a side question: of the ECLSS systems tested on the station, are all
of them scaleable to support 100 pax? Would this be done by growing
them or just installing many system of current sise ?


I'd expect a different system.


(pax is standard abbrev for "passenger" for those who don't know).


Standard for whom? It can mean lots of different things. Just type
'passengers' and stop trying to sound smarter than you are.

PAX could mean Passengers, Personnel, Paired Box Gene, Paxon
(Network), Patuxent River Naval Air Station (Maryland), Private
Automatic Exchange, Penny-Arcade Exposition (video game convention),
Portable Archive Exchange, Per Annum Exclusive, Potassium Amyl
Xanthate, Programming, Administration and Execution System (US Army),
Poly Aluminium Chloride, Picatinny Arsenal Explosive, Profiling Agent
for Exchange, Passenger Assistance Required (VRE), Per Annum Exchange,
or Professional Autocrossers. There are probably others.

Like I said, if you mean 'passengers', just type 'passengers'.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #18  
Old November 29th 16, 01:29 AM posted to sci.space.policy
Alain Fournier[_3_]
external usenet poster
 
Posts: 548
Default Using waste for propulsion ?

On Nov/27/2016 at 10:26 PM, Fred J. McCall wrote :
Alain Fournier wrote:

On Nov/27/2016 at 1:17 AM, Fred J. McCall wrote :
JF Mezei wrote:


100pax over 3-4 months will consume large amounts of food. That is a lot
of mass that you have to lift and accelerate out of earth's orbit
towards mars most of which will become waste. Not doing anything with it
means wasting that mass which you spent much fuel accelerating.


I know it's hard for you, but think about it. Most of the mass of
food (and feces) is water. You're going to get the water back for
recycling on the back side of the process. That means each person
will generate 1-2 ounces of solid waste per day once the water has
been recovered (and you'll get 3-6 ounces of water out of the same
waste stream). Let's use the larger number as more 'favorable' to
your case; 100 people (not sure what 'pax' are when they're up and
dressed) will generate around 12.5 pounds of solid waste per day. That
waste is a mix of dead bacteria, indigestible food elements like
cellulose, minerals, and indigestible fats. You're not going to turn
it into methane without giving up a lot of the recovered water and
even then most of it isn't going to 'convert'. Recovering the water
is more valuable, since you can make things like breathing air out of
that stuff. So you're going to accumulate a little over half a ton of
such cruft during the course of the trip.


It's not one or the other. You can very well recover the methane and the
water and grow food. Plants don't need the methane from human waste to
grow. So after extracting methane, the waste isn't any less fertile than
it was before extraction.


What 'methane' is there to recover? To get methane from ****e, you
have to process the ****e, removing carbohydrates. That makes it less
fertile because you've removed all the carbon and hydrogen.


Plants don't need carbon in soil, removing carbohydrates is not a
problem. Plants get their carbon from CO2 in the air.

You can't
'recover' the water because you need it as part of processing the
****e.


To recover the water see what I wrote just after:

If you want to recuperate the water that was lost in the fermentation,
you can burn the methane and make electricity, water and CO2. The CO2
will be taken by the plants you want to grow. Of course, if you do so,
that means you can't use Mr Mezei's idea of burning the methane as
rocket propellant. Which probably isn't worth the trouble anyway.


Indeed. How much power, equipment, space, and effort are you going to
expend to try to make half a tonne of ****e 'useful'.


Even growing food on the spaceship probably isn't worth the trouble. The
trip is not long enough to do serious farming. I think that the best use
of human waste on a spaceship bringing colonists to Mars is to store it.
Land it on Mars. And then, once on Mars compost it and use it to grow
food. You will want to have lots of fertilizer handy for your colony on
Mars.


I don't think so, either. Probably makes more sense to just start
dumping it in a crater someplace.


That is not what farmers do with their manure here on Earth. Earth soil
is typically more fertile than Martian soil and will not need less
fertilizer.


Alain Fournier

  #19  
Old November 29th 16, 03:53 AM posted to sci.space.policy
Fred J. McCall[_3_]
external usenet poster
 
Posts: 10,018
Default Using waste for propulsion ?

Alain Fournier wrote:

On Nov/27/2016 at 10:26 PM, Fred J. McCall wrote :
Alain Fournier wrote:

On Nov/27/2016 at 1:17 AM, Fred J. McCall wrote :
JF Mezei wrote:


100pax over 3-4 months will consume large amounts of food. That is a lot
of mass that you have to lift and accelerate out of earth's orbit
towards mars most of which will become waste. Not doing anything with it
means wasting that mass which you spent much fuel accelerating.


I know it's hard for you, but think about it. Most of the mass of
food (and feces) is water. You're going to get the water back for
recycling on the back side of the process. That means each person
will generate 1-2 ounces of solid waste per day once the water has
been recovered (and you'll get 3-6 ounces of water out of the same
waste stream). Let's use the larger number as more 'favorable' to
your case; 100 people (not sure what 'pax' are when they're up and
dressed) will generate around 12.5 pounds of solid waste per day. That
waste is a mix of dead bacteria, indigestible food elements like
cellulose, minerals, and indigestible fats. You're not going to turn
it into methane without giving up a lot of the recovered water and
even then most of it isn't going to 'convert'. Recovering the water
is more valuable, since you can make things like breathing air out of
that stuff. So you're going to accumulate a little over half a ton of
such cruft during the course of the trip.


It's not one or the other. You can very well recover the methane and the
water and grow food. Plants don't need the methane from human waste to
grow. So after extracting methane, the waste isn't any less fertile than
it was before extraction.


What 'methane' is there to recover? To get methane from ****e, you
have to process the ****e, removing carbohydrates. That makes it less
fertile because you've removed all the carbon and hydrogen.


Plants don't need carbon in soil, removing carbohydrates is not a
problem. Plants get their carbon from CO2 in the air.


Try growing plants in soil with no carbon in it and see how that works
for you (it mostly will work very poorly, if at all).


You can't
'recover' the water because you need it as part of processing the
****e.


To recover the water see what I wrote just after:


So why make the methane in the first place if you can only burn it in
a condensing chamber? I did read what you wrote, but it made no
sense.




If you want to recuperate the water that was lost in the fermentation,
you can burn the methane and make electricity, water and CO2. The CO2
will be taken by the plants you want to grow. Of course, if you do so,
that means you can't use Mr Mezei's idea of burning the methane as
rocket propellant. Which probably isn't worth the trouble anyway.


Indeed. How much power, equipment, space, and effort are you going to
expend to try to make half a tonne of ****e 'useful'.


Even growing food on the spaceship probably isn't worth the trouble. The
trip is not long enough to do serious farming. I think that the best use
of human waste on a spaceship bringing colonists to Mars is to store it.
Land it on Mars. And then, once on Mars compost it and use it to grow
food. You will want to have lots of fertilizer handy for your colony on
Mars.


I don't think so, either. Probably makes more sense to just start
dumping it in a crater someplace.


That is not what farmers do with their manure here on Earth. Earth soil
is typically more fertile than Martian soil and will not need less
fertilizer.


I thought it was obvious what happened next, but apparently not. Once
you collect enough **** to be useful (it will take a lot more than one
trip) you can process it with in situ resources. Doing it half a
tonne at a time would just be stupid.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #20  
Old November 29th 16, 06:01 AM posted to sci.space.policy
Fred J. McCall[_3_]
external usenet poster
 
Posts: 10,018
Default Using waste for propulsion ?

JF Mezei wrote:

On 2016-11-28 21:53, Fred J. McCall wrote:

Try growing plants in soil with no carbon in it and see how that works
for you (it mostly will work very poorly, if at all).


ever heard of hydroponics ?


Ever heard of pulling your head out of your ass?


I thought it was obvious what happened next, but apparently not. Once
you collect enough **** to be useful (it will take a lot more than one
trip) you can process it with in situ resources. Doing it half a
tonne at a time would just be stupid.


When you push a ship to its limits, every percent counts. And a space
vehicle carrying 100 humans for months is way past what humans have done
so far.

And when you push limits, you need to look at every means to
reuse/recycle waste as you can find.


Do you have a point?


Simple question:

if you were top heat the **** to 100°C and collect gases coming off.
What sort or process is involved in separating water vapours from
methane and other stuff? Is is simple task of cooling it just enough to
condensate water vapours and keep the rest in gas form ?


Ever heard of 'distillation'?


--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson
 




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