"Any colony on the Moon or Mars will have to deal with various sorts
of organic waste somehow. Composting it into soil is probably the best
solution."

Methane digesters would be better, especially if you're energy-
constrained. You could even burn the methane for low-level
illumination, not just space heating and cooking.

The heat input requirements for biogas reactors are a bit high,
perhaps, but this is a good use of solar heat and low-level process
heat; and production need not be continuous if you have a way to store
methane in some quantity. So you could wait for the sun -- even if,
on the Moon, that's a long wait and a lot of storage. The smaller
dead-end lava tubes have potential for large-scale gas storage.

You might increase the effective energy yield from the methane store
by sinking its heat into the surface geology and the sky during cold
periods, to chill it for higher compression, then exploiting the
greater temperature differential from daytime solar heat to drive
Stirling cycle generators. Chilling it is a good idea just from the
point of view of reducing storage requirements, though.

Achieving the needed gas mixtures for anaerobic bacteria wouldn't be
difficult in environments where there's only trace O2 to begin with.

But wouldn't you still want to compost stuff to fertilize your crops?
I don't think so. Biogas reactors can yield good fertilizer, sooner
than a compost heap. The whole process is not much different from
composting, actually, more of an acceleration of composting than a
diversion from it, with a very useful byproduct in the form of
methane.

Extraterrestrial colonization would have to develop to a fairly high
scale and high comfort level before these sorts of economies of
resource recycling would matter so little that people would resort to
composting. I think colonists would sell their own table scraps,
houseplant clippings and sewage to bioreactor operators as soon as a
colony had any kind of market economy at all. Not only would they get
a good price, they might *need* to get a good price -- in order to
afford to buy methane for heating, cooking and lighting. Walls and
ceilings of living spaces might be significantly taken up by greenery,
not just for aesthetics, to relieve stark living conditions, to grow
greens for salads, and to earn credits for CO2-O2 recycling, but also
to generate clippings for sale to methane & fertilizer producers. It
would be different on the Moon, running mostly on a two-week cycle
(expansion in the "morning", consolidation around "twilight") rather
than continuously and more stably, as on Mars. But many of the same
technologies and lifestyle adaptations would apply to Mars.

-michael turner

On Jun 19, 9:49 pm, Robert Heller wrote:
At Thu, 17 Jun 2010 23:15:06 EDT Alain Fournier w
rote:

Someone last year grew some plant in a Moon regolith imitation. It isn'
t
the most fertile soil but you can grow stuff in it. You then compost th
e
plants that grew in the regolith to have a fertile ground for farming.
So at first fertile soil would be in limited supply, but with time you
can make as much as you want.

Organic waste = soil. This is pretty much where 'fertile' soil on the
earth came from originally. Yes, it takes time. Any colony on the M
oon
or Mars will have to deal with various sorts of organic waste somehow.
Composting it into soil is probably the best solution.

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