Pee Engine

[longbyte1]

I'm sure you could flush your toilet with urine rather than tap water.

[Tommygun]

Last time I checked human waste generally wasn't conductive.

Are there scientist that do empirical studies on thing like this?

Anyways I'd go with a nuclear pee steam engine.

[Duxwing]

Anyways I'd go with a nuclear pee steam engine.

If you're going nuclear, then you might as well go all the way. Start with a large photovoltaic system, capacitor bank, and pulsed laser array. Purify the urine into water, first by filtration and next by reverse osmosis, and hydroxide the water into hydrogen and oxygen. Separate and dry the hydrogen and pump it into a vacuum with strong magnetic fields. Cast a mighty arc through the hydrogen, heating it until the molecular bonds break, electrons fly away, and bare protons smash and fuse into helium nuclei, heating the vacuum chamber and thereby the surrounding water, which therefore becomes steam that drives a turbine that turns a dynamo that produces current to power this whole contraption at greater scale!

-Duxwing

[Pds314]

Slight problem here. Much like the whole "convert your car to run on water" scheme, you have to put a lot of energy into it. There are only a hand full of ways to store that much energy in something lighter than 2H2+O2. Namely, Li+F, Be+O, H+F, a hypothetical graphene flywheel, or a nuclear reactor or something even more terrifying and radioactive. RTGs are a possibility, but expect extremely show conversion rates. The same is true of solar panels

So unless you use one of those, you are pretty much screwed because you'd be better off replacing your giant batteries with rocket fuel of equal mass in the first place. If you've found an efficient way to extract energy from the chemical ones, you're probably better off making a rocket with them instead, especially BeO, with about 570 maximum theoretical ISP. The problem is pumping 1600 K liquid Be around the same rocket as 90 K liquid O2. At least it would be hypergolic...

And if you have a graphene flywheel, you can probably use it for a very powerful thermal rocket based around a heating element. If you have a reactor, that IS the heating element.

Long story short: conservation of energy says that in order to make a kg of urine into rocket fuel, you need the energy from a kg of rocket fuel. If you have that, then why not just use the rocket fuel as rocket fuel?

[Goddess Bhavani]

Front end of a cow. Cows ferment their food in their stomachs, not their guts, and that's where the methane is produced - and it gets belched out. (If, for some reason, they can't belsh then they are in very serious difficulty and a veterinarian needs to puncture the affected stomach-lobe. They have a 4-part stomach.) The bacteria in their guts don't have a lot to work on, so a lot less fermenting goes on. Instead, that's the point where the animal absorbs the nutrients released by fermentation in their stomachs. As a result, they fart a lot less than they belch.

Darn, the things you learn from KSP forums

Okay, how does one connect the front end of the cow to the methane intake, while still feeding the cow from the same end?

[RainDreamer]

Darn, the things you learn from KSP forums

Okay, how does one connect the front end of the cow to the methane intake, while still feeding the cow from the same end?

You can always make a cyborg cow, hook it up to machines with a pipe directly plug to its stomach to extract methane.

Now that I think about it, this is probably why aliens has been collecting our cows way back then.

[softweir]

Put a herd of cows into a large, airtight storage space and filter the methane from the air.

There was a cow-related explosion in Germany: http://www.bbc.co.uk/news/world-europe-25922514