Results and discussion
3.1. Initial chemical compositions of EFB and decanter cake slurry
The results of the initial chemical composition of EFB and
decanter cake are shown in Table 2. The content of nitrogen,phosphorus, magnesium, calcium, silica and moisture of the decanter
cake slurry are much greater than those of the EFB. On the other
hand, the contents of organic matter and organic carbon content of
the EFB are higher than those of the decanter cake slurry. The calculated
C/N ratio for EFB and decanter cake slurry was 63.67 and
21.72, respectively. This indicates that none of them could be directly
used as source of nitrogen to plant since their C/N ratio is
not less than 20.3.2. Temperature distributions of compost materials with time
Analysis of Variance for the temperature of the compost with respect
to time (day) was carried out. The temperature was measured
at depth of 0.5 m, 1.0 m and 1.5 m. The treatments, the time and
their interactions were found to be highly significant (P < 0.0001)
at the respective measured depths and the overall average distribution
of the depths. Duncan’s Multiple Range Test was performed to
compare the means of the temperature of the compost material
mixed with decanter cake slurry and the temperature of the compost
without decanter cake slurry at depths of 0.5 m, 1.0 m and
1.5 m(Table 3). At all the depths they were found to be significantly
different at 5% significance level. The mean temperature of the compost
mixed with decanter cake slurry at all the measured depths
was higher than the mean temperature of the compost without
decanter by 4.2–5.1 C. Higher mean temperatures indicate that
the microbes in the compost material with decanter cake slurry
are more active in the decomposition process than the microbes
in the compost material without the decanter cake slurry. The temperature
trends with days of the compost materials at all measured
depths are significantly different with the treatment. The colour of
the composting materials changed from brown to blackish brown
and the high temperature of the compost materials could be obviously
felt as the decomposition progressed. This phenomenon initially
occurred at random spots on the composting materials but
became uniform with time and after several turning operations
on the compost. The presence of black soldier fly larvae on the surface
of the composting material was visible during the initial days
of the decomposition process before the beginning of the first turning
operation on the composting materials. This is normal for any
moist, nitrogen-rich compost and also an indication of healthy compost
material. The population of the larvae however decreased with
time after several turning operation.
The changes in the measured mean temperature for the three
composting materials subjected to three different treatments are
shown in Fig. 1. The control shows the least trend in temperature
due to lack of aeration and consequent minimal microbial activities
as seen in the graph. The mean temperature distributions of the EFB
with decanter cake slurry and turning are slightly higher than that
of the EFB without decanter cake slurry throughout the duration of
the decomposition period as indicated in Fig. 1. This may be due to