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tireplaces 'n bunnies
26 jun 1997
"brendan a. niemira"  writes:

>i've always been opposed to the use of human feces...

that may be a cultural prejudice :-) kids seem to learn this early. ("put that
down!") i recall some horrified west philadelphia free-school parents who were
told by their young children about a fascinating classroom science experiment
they were doing, watching various vegetables, slices of bread, etc, decay,
as molds and maggots took over. the teacher came close to being fired...

i got an angry reaction ("disgusting!") from our sustainable living center
youth hostel manager when i showed her an inexpensive medical potty chair
and suggested it might serve as a $2k "composting toilet" if the 1 or 2 
people infrequently occupying our solar cabin were to pretend to be animals,
and "sheet compost" (no pun intended) the bucket contents somewhere in the
6 square miles of surrounding woods. nonono. "composting toilets" are more
expensive and complicated machines :-)

>there are a lot of nasty parasites that can build up when you eat food from
>plants fertilized with it, even if it comes solely from healthy people. 

how about just spreading the compost on the lawn, or mulching around trees,
vs. fertilizing a food crop. house heating and sewage treatment are reasonable
goals, even if the compost is discarded. composting can be a lot more than
just piling up leaves. some deliberate engineering cited by rodale includes:

1) the indore process (india, 1920-30), layered heaps or trenches, a labor-
intensive "adaptation and systematization of practices observed in china
and india for centuries," with a digestion period of about 90 days,

2) a modification by jackson and wad, adding half-digested sewage sludge to
reduce the digestion period to about 15 days, 

3) the beccari process (italy), which used an insulated cell of approximately
20 yd^3, requiring about 40 days,

4) the verdier process, used in the french city of cannes, which added
leachate recirculation, reducing retention time to 20 days,

5) the dutch vam process (1932) for disposal of city refuse ("24 hours after
sprinkling the refuse with bacteria-rich water, the temperature has risen to
140 or 158 degrees"),

6) the frazer process (chicago) maybe the first attempt to use forced air,
which allegedly achieved "complete stabilization in 20-28 days," and

7) the earp-thomas process (new jersey), used in several cities, eg paris,
seoul, and reading, pa, in which "a vertical cylinder divided into sections
or floors forms a continuous flow digester with internal rotating booms," and
ground waste mixed with seed bacteria enters the top section, and works its
way down, floor by floor, heating as it descends, until "after 24-48 hours,
it has reached the bottom layer and the composting process is considered
by the inventors to be complete."

surely some of this engineering can be rediscovered, if we start caring about
it again. solar house heating development got stuck when we discovered cheap
oil and gas. maybe composting development got stuck when we discovered nitrogen
fertilizers, and more machines meant less manure, and people found out they
could always transport and dump solid waste "somewhere else."

suppose a well-designed "composting fireplace" could remove 50% of the energy 
from some sort of compost in a week, vs 3 months, at a rate of heat production
of something like 5kbtu/168hours-lb = 30 btu/hr-lb, so a 10k btu/hr compost
heater required 333 lb of compost at 30lb/ft^3 (50% h2o), ie 11 ft^3, eg a
3 foot cube or a 4' high by 3' diameter cylinder, refilled once a week in
a house needing 200k btu/day of heat, including hot water...

>i've talked with some of our extension people about this and they're not
>very keen on the idea, either,

perhaps they have the same cultural bias :-) i wonder if they've read the
1992 nraes-54 "on-farm composting handbook," or rodale's 1971 "complete book
of composting" ("...our oldest existing reference to the use of manure in
agriculture is to be found on a set of clay tablets of the akkadian empire,
which flourished in the mesopotamian valley a thousand years before moses
was born.") the book includes a section on compost poetry, with contributions
from robert herrick, john dryden and walt whitman ("behold this compost!
behold it well!/perhaps every mite has once form'd part of a sick person...")

>since although temperatures in a compost pile get high, there's been no good
>demonstration that they get high enough to kill the wee beasties.

pick your pathogen (rodale, page 669):

                      no growth beyond   death within    at

  salmonella typhosa  46 c               30 min          55-60c 
  salmonella spp                         60              55 
  shigella spp                           60              55
  escherichia coli    "most die within one hour at 55c, and
                       within 15 to 20 minutes at 60c"
  endamoeba hisolytica cysts     "thermal death point is 68c"
  taenia saginata                         5              71
  trichinella spiralis larvae    "thermal death point 62-72c"
  necator americanus             "death within minutes at 45c"
  brucella abortus or suis                3              61
  micrococcus pyogenes var. aureus       10              50
  streptococcus pyogenes                 10              54
  mycobacterium tuberculosis var hominus 20              66
  corynebacterium diptheriae             45              55
  aids                                                    ?
  polio                                                   ?
  mad cow disease                                      >100

the nreaes book says "the strictest regulations relate to sewage sludge
composting. to destroy pathogens in sewage sludge, current federal regulations
require temperatures to be held at 131f [55c] or higher for three consecutive
days in the coldest section of an aerated compost pile or composting vessel.
in windrows, uniform temperatures are difficult to achieve. therefore the
regulations for windrow composting dictate fifteen consecutive days at 131f."

it should be easy to estimate and assure a minimum temperature in an insulated
vessel, with very few temperature probes, if compost conductivity ranges from
2 to 4 cal/(hr-cm2-degreesc/cm), without deliberate aeration.

>i suppose that if this compost were going to be used to heat the house 
>directly, or to fertilize the lettuce and carrots for the 100 bunnies used
>to heat the house, it might be ok, but that's probably not how most people
>would use their compost.

normally active 39.22 btu/h standard 5.41 lab wabbits emitting 19.31 btu/h
of latent heat might live on top of the compost and eat lettuce and carrots
that grow out of it, in a interesting glazed vivarium. this composter might
need a warning notice. ("danger: sexual situations.")

>to the best of my knowledge, though, human urine seems to be a great
>addition, being essentially pathogen free and a source of extra nitrogen
>and water, which most compost piles can use.

especially leaves. reported first order decay coefficients for maple leaves
are 0.015 kg/kg-day and for oak leaves 0.009 kg/kg-day. they need moisture,
oxygen and nitrogen to speed up this process. maybe duckweed harvested from
a shallow reflecting pond, and the occasional carp.

the garpster  writes:

>recently nick mentioned a use for old tires would be to make compost rings
>out of them. i am interested in this idea as one i can put across here in
>mexico, but is there no chemical migration from the tires to the compost?

that's what i'd like to know, having recently received all these pcb storage
regulations, along with pa der residual waste transportation daily operational
record forms wm-348 (6/92), "to be kept in the cab of each waste transportation
vehicle, as required by 25 pa code section 299.219(a)," along with instructions
for marking my 1975 ford pickup truck "residual waste--code 510," according to
pa section 285.218(iii), if it's "a vehicle or conveyance that is ordinarily
or primarily used for the transportation of solid waste."
 
what happens to the toxic contents of tires (if any) when they are added to
asphalt to make roads? or when sections of tires without steel are ground up
to make "gravel" for playgrounds? 

>and wouldn't compost accumulate in the tires rather than water, obviating
>the need to puncture 'em, cut 'em or turn 'em inside out.

i would hope the compost hiding inside the tires in a warm pile with some
sort of roof would stay dry, and just sit there and act as insulation.

>wow, that last one sounds like one helluva challenge!

turning tires inside out sounds like work. it might be easier to burn holes
in the sidewalls with an acetylene torch in one hand and a garden hose in
the other, on a windy day. 

nick


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