(best examples and good practices) on household organic waste ...

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solution are fermented (e.g., sugars fermented to alcohols), while certain
complex molecules are biologically hydrolyzed to their simpler components
(cellulose to sugar, fats to acetic acid). The overflow, rich in such intermediate
metabolites, then enters the UASB bioreactor. Then, they are transferred to a
settling tank. Supernatant is pumped to the physical separation/preparation
element as needed for makeup water, or to an aerobic tank for polishing if
necessary.
Water may be stored or used immediately as in irrigation. The solids are
dewatered for use as stabilized organic soil amendment. Some of the biogas is
used to fire boilers to maintain UASB digestion at its optimum temperature of
~35◦C. Otherwise, depending on site-specific circumstances; the gas fuels an
electrical generator via a storage tank. Waste heat from the generator
contributes to the maintenance of digestion temperature.=
12.5. The Rapid City, South Dakota plant in USA
Composting of yard trimmings in Rapid City began in 1993. In (1994) no
l<strong>and</strong>filling of yard trimmings was allowed. "A waste composition study done in
1993 showed that yard waste was 10 to 15 percent of the total MSW generated,"
In The city three dropoff sites were built, <strong>and</strong> 20 cubic yard rolloff containers at
each for collection were placed. Curbside collection is available to these
receiving city service (about 16,500 households); citizens must place yard
trimmings in kraft paper bags, which are collected the same day as garbage <strong>and</strong>
recyclables (during the season when yard trimmings are primarily generated).
Yard trimmings also can be brought to the l<strong>and</strong>fill at no charge. About half of
the annual tonnage received (about 13,000 tons in 2002) comes from the
dropoff sites; the remainder arrives either through the curbside program or
self-hauling to the l<strong>and</strong>fill.
Leaves, grass, tree limbs brush, <strong>and</strong> some manures are also accepted. All
materials are ground in a Peterson Pacific 5400 horizontal grinder before being
placed into windrows. A Scarab turner mixes <strong>and</strong> aerates the piles once a week
initially. The composting process varies <strong>and</strong> depends on the weather,
composting material, temperature, etc.. Finished compost is screened to either
three-eighth or three-quarter inches, depending on the end use. The threeeighth
inch compost is sold for $30/ton; three-quarter inch sells for $25/ton,
<strong>and</strong> the three-eighth inch rejects, mostly wood chips, sell for $10/ton. "The
production of the facilities is approximately 4000 tons per year.