[Digestion] Food-waste anaerobic digester at University of Colorado

[adkarve]

This refers to the fertilizer effect of compost. Composting reduces the bulk
of organic waste to be handled, so that it can be easily transported from
the cities to agricultural lands. But because the agronomists look at
compost as a substitute for chemical fertilizers, the quantities recommended
for application per unit area are very high. For instance, if a crop is to
be supplied with about 100 kg N per ha, and if the compost has about 0.2 to
0.5 percent N, one would require almost 20 to 50 tonnes of compost per ha.
The transport cost of such huge quantities of compost from the cities to the
farms is often higher than the cost of chemical fertilizers. This situation
discourages farmers from using in their fields compost made in urban
centres. When a farmer grows any crop in his field, only about 30 to 40% of
the total biomass represent the economically important component of the
crop. The rest of the material can go back into the field as organic
amendment. It is not enough to provide the full complement of NPK required
by next crop, but it acts as food for the soil micro-organisms. They
decompose the soil minerals and make some of the mineral elements available
to the crop plants. Some micro-organisms also fix atmospheric nitrogen. We
therefore advocate the application of relatively small quantities of
non-composted biomass to the soil. The quantity to be applied is about 25 kg
dry matter per ha, once every 2 to 3 months. No chemical fertilizers are
applied to such fields at all. Farmers generally get the same level of yield
under this practice as under application of the full recommended dose of
chemical fertilizers. Even if they get a lower yield than with chemical
fertilizers, their profit per unit area is higher than using chemical
fertilizers. We also found that crops grown under this practice generally do
not suffer from pest attack. We are not yet sure about the reason for lower
pest intensity, but a plausible explanation is, that when the
micro-organisms decompose soil minerals, the silicate ions that are freed
from the minerals, are taken up by the plants. These ions get deposited in
the cell walls of plants in the form of silica. This makes these plants
harder to chew, which in turn discourages insects from attacking them.
 Because of the reluctance of farmers to carry compost from the cities to
their farms, the practice of making compost from city waste is no longer
used by city administrations as a method of waste disposal. In view of the
present energy crunch, and in view of the fact that the cities themselves
are guzzlers of energy, producing methane from food waste (from households
and restaurants, from vegetable and fruit markets and from slaughterhouses)
appears to be the best alternative.
Yours
A.D.Karve

----- Original Message -----
From: Art Krenzel <phoenix98604 at msn.com>
To: Jason Woods <jdwoods21 at hotmail.com>; <digestion at listserv.repp.org>
Sent: Wednesday, October 24, 2007 11:41 PM
Subject: Re: [Digestion] Food-waste anaerobic digester at University of
Colorado


> Jason,
>
> It all depends upon what your definition of viable means.
>
> If you want to recover energy, anaerobic digestion is a great choice for a
> small scale demonstration.
>
> If you want to do waste disposal, composting is a good option.  There is
> little or no chance to collect energy from composting.
>
> Small scale energy production does not have all the big numbers associated
> with it that a production facility might but if you include the
educational
> aspect and energy from small scale waste design concept, such a sized
system
> is viable.  At 1500 tons (70% moisture) collected over 9 months would be a
> nice little green education project for the University to undertake.
Making
> a small system work has a great deal of challenges, especially in Boulder,
> CO which has a REAL winter.
>
> Art Krenzel, P.E.
> PHOENIX TECHNOLOGIES
> 10505 NE 285th Street
> Battle Ground, WA 98604
> 360-666-1883  voice
> phoenix98604 at msn.com