humanure

burn · Post by **burn** » Wed Jan 21, 2004 7:28 pm

Hello,
I presently have a bucket and sawdust system producing about one 16 liter bucket every three days/ three cubic meters compost per year. I'm considering a methane digester and it seems that it might be advantageous to use a flush toilet for that purpose. I took out the flush toilet to put in the bucket system and it would be easy to replace. I would appreciate your thoughts on that. Used the calculator on your website(great site btw) and reached a figure of 150 gallons. What do you reccomend as a pump? how often and what quantity should be pumped in? I would add sawdust for the c/n ratio. Before I saw your design,

I thought of building a plug type horizontal digester out of welded plastic barrels, maby three or four in a row.Any thoughts/recommendations on that idea?
I like your toilet design, seems a lot friendlier than toting buckets every three days.

Post by **Bob** » Sun Jan 25, 2004 4:47 pm

Hi burn,

I'm curious about your goals. Are you primarily interested in reducing maintenance and hassle of hauling buckets of humanure? Or are you hoping to generate enough biogas heat to be useful?

I don't know the details of your calculator run, but I tried plugging in 5 people flushing a .5 liter flush toilet (e.g. Sealand Marine) 4 times a day, then adding about 7 lbs of sawdust and 7.5 lbs of additional water per day to come up with a reasonable slurry concentration (6.2%) and C/N ratio (24). This would work in a 150 gal digester, producing about $0.40 worth of gas per day, if the propane it offset cost $1.50 / gallon.

Now I don't know what you pay for fuel gas, but if it is anything close to $1.50 / gallon, the annual value of biogas generated will be about $150. Not a whole lot of value for quite a bit of cost and work (and sawdust).

But if your primary goal is to quit hauling buckets of humanure out every three days, I'd try adding a lot less sawdust (e.g. 2 lbs/day) and water (none) and going with a 80 gallon digester. This system would be about 1/2 the size and cost, but accomodate more people (up to 8 ) flushing the same toilet 4 times/day. The value of the gas would be about $75/year, but it would be a lot less work and cost.

Anyway, I'm just thinking out loud here. Don't know near enough about your particular circumstances or goals to say more. Regarding a suitable pump, I've had good luck with diaphragm pumps, both manual and electric, but I haven't tried pushing that much sawdust through them, so can't say how well they'd work with that.

burn · Post by **burn** » Mon Jan 26, 2004 2:45 am

Thank you for your thoughts. When I saw your 3-barrel composting toilet design I thought hmmm, it would be nice not ot have to haul buckets all the time. Then I came across the digester design I thought it would be good to produce gas with this material but it seems, from what you are saying that it wouldn't be worth my while for such a small amount of gas.

So... I'm thinking the three barrel system. Are you using that yet and how is it working out?
Thanks, Burn

Post by **Bob** » Tue Jan 27, 2004 12:22 pm

No, I'm not using it yet. I have some space constraints I need to work out. (To replace the existing digester with this system will require relocating and/or modifying a bunch of other stuff -- a big job that I'm finding easy to put off.)