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10.
Optimization of the role of tubular plastic biodigesters in
integrated farming system
Authors:
San Thy, T R Preston, Khieu Borin, Pheng Buntha and Try Vanvuth,
2005.
Livestock
Research for Rural Development.
Volume 17, Article # 132. Retrieved November 8, 2005.
http://www.cipav.org.co/lrrd/lrrd17/12/sant17132.htm
Summary: The experiment was carried out at the CelAgrid experimental farm, in
Kandal province for a period of 150 days, from April 6 to August
11, 2004. The trial comprised five treatments, consisting of
different proportions of pig and cattle manure; 100% of pig
manure and 0% of cow manure, 75% of pig manure and 25% of cow
manure, 50% of pig manure and 50% of cow manure, 25% of pig
manure and 75% of cow manure and 0% of pig manure and 100% of
cow manure. The experimental design was a Latin Square
arrangement of five periods, 30 days each. The first 20 days of
each period were for adaptation to the treatment followed by 10
days of measurement. The hydraulic retention time was fixed at
20 days. Five plug-flow biodigesters were installed using
tubular polyethylene film (internal diameter 0.64m; 2m length).
They were installed in an area with the same microclimate
condition. Total biodigester volume was 640 litres, of which 80%
corresponded to the liquid volume equal to 510 litres. Pig
manure was bought from a nearby village, and stored in an
enclosed plastic bag for two days prior to use. Cattle manure
was collected each morning from animals at CelAgrid, in which
the basal diet was untreated rice straw and ensiled cassava
foliage. The loading rate was fixed at 3.27 kg manure DM per
cubic metre of biodigester liquid volume. The actual amounts
were determined according to the experimental treatment and the
DM content of the manures. Water was added to give a solids
content (DM) of 6.54% for every treatment. Thus the total daily
charge to the biodigester was 25.5 litres of suspended manure
and water. Samples of fresh pig and cattle manure and the
corresponding effluents were taken daily on days 1 to10 of the
measurement period immediately before (manure) and after
(effluent) charging the biodigester. They were stored in a
refrigerator at -20C until required for analysis. At this point
the samples were thawed, bulked over the 10 day measurement
period and analyzed for nitrogen and ammonia using a Foss-Tecator
Kjeldahl apparatus and for organic matter by asking the samples
in a furnace oven (AOAC 1990). DM content was determined by
microwave radiation (Undersander et al 1993).Gas production was
measured daily by collecting the gas in inverted plastic bags
suspended in oil drums filled with water (San Thy et al 2003).
Abstract:
When the proportion of pig manure was increased the rate of
gas production increased by more than 50% when replacing 100%
cattle manure by pig manure. The proportion of ammonia-N in
total N increased as the manure was mixed with water (influent)
and after being fermented in the biodigester (effluent), with
higher values when the manure was from pigs rather than cattle.
It is concluded that manure from pigs produced more gas that
manure from cattle and effluent of biodigester laoded cow manure
had lower fertilizer value. It is suggested that it may be more
appropriate to recycle cattle manure through earthworms rather
than using it as substrate in biodigesters.
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