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