Aerobic digestion

[ar81]

I have found the proper info on anaerobic digestion.
Biogas is produced.

This is the equation I found
C6H12O6 = 3CO2 + 3CH4

This is the content of biogas
Methane, CH4 50-75
Carbon dioxide, CO2 25-50
Nitrogen, N2 0-10
Hydrogen, H2 0-1
Hydrogen sulfide, H2S 0-3 (where the heck did surfur came out from? why isn't it in the equation?)
Oxygen, O2 0-2

Methane can be used to produce electricity and I already have the equation.
CO2 can be absorbed using several reactions, including Sabater reaction
Nitrogen can be stored.
Hydrogen can be used for Sabater reaction
O2 is used for breathing

Hydrogen sulfide (highly toxic, I do not like the idea of having it onboard a spacecraft) can be used for
-Production of thioorganic compounds (methanethiol, ethanethiol, and thioglycolic acid)
-Alkali metal sulfides (used for degradation of biopolymers)
-In analytical chemistry (qualitative inorganic analysis of metal ions)
-A precursor to metal sulfides
-Miscellaneous applications (purification of metal ores by flotation, modification of behavior of metallic catalysts used a refinery, etc)

However, for aerobic digestion I am unable to find any leads. Only this is what I have.

Organic waste + O2 = Compost + ???

And I do not have proportions.
I am unable to find any information on aerobic digestion.
Any help?

 

[dougkeenan]

Do you want to account for the heat produced in composting as well?

 

[ar81]

Do you want to account for the heat produced in composting as well?

May be, may be not. I am dealing with mass, not really energy.
Energy could be useful for "cultural" purposes here, or perhaps for future development.

 

[dougkeenan]

OK. Just don't put the heaps next to anything that catches fire!

 

[ar81]

Aerobic digestion is useful to turn solid waste into compost.
For human waste high temperatures are required to get rid of biohazards, so if it produces heat that's fine.
The problem is that I do not have proportions for the equation and making a wild guesstimate is not what I would like. I would like approximates, not not just wild guess.

 

[stjimmy225]

aerobic digestion is respiration,
C6H12O6 + 6 02= 6CO2 + 6H20
there is very little glucose left in human waste it mostly consists of long chain undigestable sugars such as cellulose and other waste products which the body cannot utilise. However bacteria etc are more than capable of breaking down these into a good food source and releasing the nitrogen into a form usable by plants. for instance cellulose which is a major constituent of solid waste can be broken down to release sugars, this is important in things like the digestive tract of cows and other ruminants, in making compost it is not the sugars you are trying to release it is the nitrates and other trace elements that are most important as it is these which will sustain plants.

 

[ar81]

What is the proportion of celulose vs glucose?
C6H12O6 + Celulose + 6 02= 6CO2 + 6H20 + Celulose
I would be working with mass proportions, so I would need to know what is the approximate percentage of celullose in solid waste.

According to wikipedia...
Celullose is (C6H10O5)n
Cellulose is the structural component of the primary cell wall of green plants.
About 33 percent of all plant matter is cellulose (cotton is 90 percent and that of wood is 50 percent).
Since the diet of the crew is based on vegetables, I guess a good estimate could be 70% of glucose.

It seems that cellulose chains are broken by bacteria... any equation for that?
Or should I estimate that 100% of cellulose becomes compost for plants without having any byproducts?

------------------------

Not related directly with the issue, but I found this interesting link
http://www.fao.org/docrep/003/w4988e/W4988E06.htm

 

[stjimmy225]

cellulose is digested by bacteria by removing the branches on the molecule and then removing 3 carbon molecules at a time to feed into the respiratory chains.however i stress that degredation of human waste is not to release sugars, it is to release nitrates and other elements, this is so that any plants can grow well as plants make their own sugars by photosynthesis.

 

[ar81]

Do we have a formula for that?
I have tried to find a formula for Cellulolysis, but I failed...

 

[stjimmy225]

cellulose is a massive molecule and varies in size immensely between parts of cells let alone whole organisms so it is very difficult to quantify it, cellulose is basically long chains of glucose stuck together though so the basic respiration equations should hold true enough.I'm not entirely sure what you require though, if you took an average of cellulose's molecular weight it would be around 10,000kD which is around 60 mlecules of glucose per unit of cellulose

 

[ar81]

For stechiometric calculations, cold it be correct to think that

1 molecule of cellulose = 60 molecules of glucose

I understand that cellulose chains are broken by bacteria.
What is the resulting product? Does it break chains to produce any sugar like glucose or fructose or other? If that's the case, then you would have full respiration.

Also, I understand that human solid waste treatment at high temperatures produce fertilizer. fertilizer has nitrogen and potasium, so respiration equation is not enough to explain the composting process.

 

[stjimmy225]

i just dug out my text book and found that cellulose can be comprised of 1000's of glucose molecules linked together so im sorry for the confusion there, the breaking down of cellulose gives full respiration (ie carbon dioxide and water release). respiration by bacteria breaks down all the sugars and organic molecules.
the release of phosphates and nitrogen comes from the breaking down of these large molecules such as proteins that contain these elements, fertilizer is not a sugar source, it is a source of these crucial elements as they are usually locked up, for instance iron is common in solid waste due to the bodies disposal of damaged hemoglobin molecules from red blood cells.

 

[ar81]

Ok, so if we apply respiration to solid waste you should end up having CO2 and H2O and the amount of solid byproduct should be a small pile of minerals that forms the compost. How much should that pile of minerals account for of the initial waste mass? 10%? 5%?

 

[stjimmy225]

i'd say thats a good figure, if you have any other problems trying to sort out biological steps etc just give me a shout and i'll gladly give you a hand

 

[ar81]

So it looks like in a simplistic model you have

From a plant point of view
Plants -> Dead plants - > H2O + CO2 + Minerals -> Plant

From a human point of view
Food + H2O -> Solid waste + Liquid waste -> H2O + CO2 + Minerals -> Food + H2O

O2 -> CO2 -> O2

However, for organic waste you have anaerobic digestion that will produce biogas that is used for the boiler to heat water, to produce electricity to light the greenhouse and to heat the bioreactor to kill bacteria.

 

[Notebook]

Someone has solved your problem:-

http://news.bbc.co.uk/1/hi/england/devon/7517116.stm

Downside is you need a large herd of zero-g tolerant Freisans, or a very large supply of pasties!

N.

 

[ar81]

Great news!! What people think that is just "being ecological to save touchy feeling plants and animals" could prove to be space technology to be used inside spacecraft.

I found this on aerobic digestion
http://acta.chem-soc.si/49/49-4-931.pdf