International Journal of Marine Science 2015, Vol.5, No.27: 1-11
5
on the day treatment was applied (0 d).
Redox potential
in the control and treatments during
the experiment decreased until the end of the experiment
(Figure 3 B). Measurement of environment quality for
0 day was conducted 9 hours after application of
treatment. The effect of oxygen usage by microbes
during 9 hours before measurement was expressed in
the difference of redox potential value in the control
and the 3 other treatments. In the control, the redox
potential was higher than 100 mV during early stage
of experiment (0 – 16 days after treatment). Due to
technical error, no data was available by the 23
rd
day.
From 60-90 days after treatment, the ORP value was
negative until the end of the experiment ((-160) –
(-449) mV). In all bioremediation treatments, the
value at day 0, 9 hours after the application, was
already lower than the control (23 - 50 mV). From the
3
rd
day after treatment until the end, the ORP value
was declining. The lowest value was
observed in FSC
treatment (- 455 mV) at the 90
th
day.
Salinity varied but pH value was relatively stable
during the experiment (Figure 3 C and D). Salinity
outside and in the control mesocosm was lower than
in the treatments which were in the range of 27 - 34
ppt and 13 – 56 ppt, respectively. The lowest salinity
was observed on the 90
th
day after treatment when it
rained for about 6 hours before the sampling time.
Higher salinity in all treatments were detected when
fertilizer was applied on day 0 and days 16 of the
experiment. The range value on days 0 and 16 of the
treatment were 40 – 45 ppt and 39 – 46 ppt. On the
other sampling days, salinity returned to almost
normal conditions with an average range of 33.1 –
33.7 ppt in each treatment. pH value fluctuated within
a very small range during the experiment (Figure 3D).
The range and mean value of pH in the control and t
reatment was 6.5 – 7.3 and 6.25 – 6.8, respectively.
3 Discussions
The primary goal of the present study was to
investigate suitable biological remediation approaches
for anticipating oil spills in Cilacap sandy beach
(Indonesia). It has been conducted by comparing four
bioremediation strategies. This present study indicated
that biostimulation, or a combination of biostimulation-
bioaugmentation, is promising for enhancing
oil-degradation when oil spills occur on the Cilacap
coast. It was showed by the oil depletion percentage
(Figure 1) and the value of the decay rate with
biostimulation only, and with combinations of
fertilizer
and microbes, which were always higher than
the control
(Table 1), except for the biostimulation-only treatment
in the early stage.
It was interesting to note that the Cilacap coastal
environment was able to degrade crude oil naturally at
a high level of 60.31 + 3.93 % over 3 months for a
pollution level of 100 g/kg oil in the sediment (
Figure
1).
The result is high compared with other previous
studies in Indonesia, California and Hongkong
(unpublished data, Bento et al., 2005). This high
intrinsic capability
may be caused by several
factors, such a
s environmental conditions, oil
characteristics and the availability of oil-degrading
microbes in this coastal area. Environment condition
can be showed at outside mesocosm data (Table 2).
Arabian light crude oil was predominant oil used by
Cilacap oil refinery unit (IBP, 2009). Therefore, the
site exposed prior to this oil and the native microbes
might have capability to degrade the contaminant. The
presence of PAH-degrading bacteria in the sediment
in mangrove swamps in this area has been reported
(Syakti et al., 2008). However, it can be predicted that
the limits of nutrient and microbial availability will
occur when more than 100.000 mg/kg oil is spilled . It
was proved by the increase of oil depletion rate when
the addition of nutrient only and nutrient plus
microbes applied in this present study. Therefore,
bioremediation technology can be applied to make
oil-clean up faster in Cilacap coastal.
Biostimulation, by adding slow release fertilizer
Gramafix at a nominal concentration of 7.5 gr N/kg
sediment or 15g N/ kg sediment, enhanced oil
depletion. This result supports many previous works
indicated that the capability of indigenous bacteria can
be enhanced by addition of nutrients (exp. slow
release fertilizer) (Xu et al., 2003; Xu et al., 2005;
Darmayati, 2010). The fertilizer impacted on the
increase of biomass which was followed by a decrease
in DO that is consumed by bacteria and a depletion of
oil in the sediment (Figure 2 and Figure 3).
Numbers of bacterial cells in bioremediation
treatments were higher than the control during
experiment. In the present work, there was a strong
positive correlation between the
total cell number and
