Hope all goes well.

  Earlier this evening  NBC nightly news had a piece about a dairy farmer/cheese factory in Minnesota sp?  doing that.

 They had a 6,000 dollar electric bill every month and a HUGE waste problem.

They built a digester that was as tall as a grain silo and looked to be at least 5 times as big around.

They fed it with cattle waste then fed the methane to several large generators.   They are producing enough electricity to offset all of there use. And supplying 60 other homes around them with all the power they need. Also the affluent left over feeds there pastures.

 The article should be online at NBC's website.

 Fry's system mainly consisted of a large anaerobic digester, 2 converted diesel engines for electric generation, a good storage design and some scrubber systems.

 Journey to forever has one of his publications available on the web: http://journeytoforever.org/biofuel_library/MethaneDigesters/MDToC.html

 A must read for anyone wishing to get into this.. the University of Colorado also did extensive research into the subject at one time.

 It really depends on the scale of production your friend wishes to get into, and what raw materials he has to use.

 For a digester to properly convert any waste materials the temperature should be held between 80 and 100 F this is usually done by burning off part of the methane produced to heat a water loop. Stirring of the slurry also increases production.

 Safety is a VERY important factor in this, as a mixture of between 4% and 25% methane to air is explosive. You must insure there is no available oxygen content in your storage and piping systems, and these systems are considered an explosion hazard.

 Usually these systems aren't economically viable unless you run a large farm,and have the waste to deal with. I doubt very seriously you would be legal building a system within a metropolitan area.

 Also methane gas has a much less energy potential than any of the other common heating gases.  

For small setups, though, the general consensus is that you need a large amount of excrement, and perhaps some greenery thrown in as well, to produce a usable amount of gas.  You also need to make sure the amount of solids is high in relation to the amount of liquids.  The output of a typical toilet, for instance, contains much more water than could be productively digested.  Maintaining one seems like a full time job.

I've been thinking about putting together something like this as a small septic system for a while now, using a sealed plastic 55 gallon drum.  Since your post, I've given it some more thought. The design I have in mind would basically separate the liquids and solids under pressure with some type of filter.  The solids would be digested.  The liquids would be bled off by a trap valve into a grey water disposal pit.  It would probably also include some sort of relief valve.  I don't see any reason the entire thing couldn't be made of plastic.

Hopefully it would produce enough gas to maintain a small pilot light.  The drum could be insulated or buried fairly easily.