Indonesia, an agricultural and tropical country, has abundant natural
resources that can be used as a source of bioenergy raw materials in the form of
biomass, which can be exploited to deal with the scarcity of fossil energy in the
future. One of the raw materials is cow manure. Beside as a source of pollution, this
manure can be used as the raw material for biogas.
In the research of dilution ratio optimization in laboratorial scale gas
production, we use modified 20 l jerry can biodigester, then it is applied on the field
in semi-pilot scale by using biodigester fix dome 9m
3
. Experiment method in
laboratorial and field scales are used. The treatment is by adding dilution and
agitation, while the observed variable is the gas production. For laboratorial scale
data analysis, descriptive and multivariate statistics are used., whereas for field scale
analysis, descriptive statistic is used.
The results obtained showed that the breaking down efficiency of the material
in the substrates (VS, TS, COD), the ratio of 1:3 are respectively 81.28%, 80.63%,
and 80.63%. With 1:1 dilution the breaking down efficiency of VS, TS, COD are
respectively 79.69%, 78.36%, and 77.20%. With 1:5 dilution, the ratio of breaking
down efficiency of VS, TS, COD are respectively 50.28%, 50.64%, and 49.77%, and
with 1:7 dilution the breaking down efficiency of VS, TS, COD are respectively
50.46%, 50.54%, and 49.72%. The highest biogas production at a ratio of 1:3 dilution
is 1.11 per day, and the fastest biogas production ratio 1:1 is the average production
of 1.03 l per day. The lowest gas production with dilution ratio of 1:5 and 1:7 are
respectively 0.43 l per day and 0.37 l per day. Henceforth it is recommended for
semi-pilot scale with a dilution ratio of 1:3, and 1:1 . Agitation affects significantly to
the breaking down efficiency of the dissolved materials and the production of
biogas. The breaking down efficiency with dilution ratio 1:3 is higher than ratio
1:1. Measurement result of COD, TS, VS for the ratio 1:3 are respectively 78.45%,
82.56%, and 82.75%. For breaking down with ratio 1:1, the efficiency of COD, TS,
VS are respectively 51.64%, 65.22%, and 57.67%. The average production is 18
m
3
/day for the dilution ratio 1:3 with agitation, and 6.62 m
3
/day without agitation,
while 1:1 dilution is 6.16 m
3
/day. The conclusion is that the ratio of dilution affects
the breaking down efficiency of the dissolved materials in each of the parameter
measured, as well as on biogas. Agitation can increase the efficiency of dissolved
materials in the substrate and increase biogas production of semi-pilot scale.
Key words : biodigester, biogas, dilution ratio, agitation, organic reduction efficiency
