Environmental disturbance caused by crude oil pollution has been reported almost all over the world either on agricultural land or marine environment. Petroleum products and their related derivatives become one of the major sources of environmental pollution. During its processing starting from extraction to storage, crude oil may be discharged into the environment resulting in pollution of the ecosystem. As the impacts to the environments are considerably extensive, from which the oil derivatives have adverse effects on the ecosystems including soils and water, the effort to search for effective technique and new materials for the removal of such substances from contaminated sites is considered to be very highly important .
Numerous efforts have been done to remove crude oil spill polluting water media, including mechanical, biological, chemical and adsorption methods. These include the use of minerals like zeolite with strong characteristics as a molecular sieve, both natural and synthetic     and various agricultural wastes with high adsorbent properties like sugarcane bagasse and rice hull , corncobs , banana peels  as well biodegradation and bioaugmentation , and also natural rubber/reduced graphene composite . Nevertheless, the use of zeolite is most widely reported in the effort to remove oil spill. The synthetic zeolite used includes those derived from fly ash, whereas the natural one is that with clinoptilolite mineral in dominance.
Due to hydrophobic characteristic of the oil in water, oil removal from sea water is somewhat different to that found in oil-polluted soil due to hydrophobic characteristic of the oil in water. When oil spill took place at ocean, then it would be more difficult to handle as the oil will drift away and spread by time. Therefore, it is very important to apply such adsorbent capable of adsorbing oil very fast in a significant volume and hold the oil for a considerably long period. Protecting marine life from pollution caused by accidental spoiled crude oil becomes an urgent issue now. Thus, quick actions should be executed to avoid further widespread impacts. One of these actions is the cleaning-up process, which requires pumping, skimming, and storing the contaminated seawater. This operation requires deep knowledge of the physical and chemical proprieties of pollutant fluid that would help in calculating the power requirements for the cleaning-up process. In term of microbial bioremediation technology, global patent data show that Pseudomonas sp., Bacillus sp., and Rhodococcus sp. are the top three active ingredients .
The use of different zeolite types to refine some pollutant oils has been widely reported as described above. However, a natural zeolite from Bayah, Banten, Indonesia, has been known as a clinoptilolite zeolite with various use including soil amendment, feeds, and water purification  as well as potential greenhouse gas sequestration on peat soils , but not yet as oil spill adsorbent. Therefore, the present study reports the potential application of this material to be used as crude oil adsorbent, especially the one that pollutes sea water.
2. Materials and Methods
2.1. Physico-Chemical Properties
A 100-mesh zeolite originating from Bayah, Banten, Indonesia was used in this experiment and subjected to selected physico-chemical analyses. Pore structure including specific surface area, pore volume, and average pore diameter was determined based on N2-sorption analyses . Chemical analyses performed including pH, cation exchange capacity (CEC), silica, aluminum, calcium, sodium, and potassium elemental analyses by using standard laboratory analyses outlined by SNI 13-3494-1994 (ICS 73.080). Chemical data analyses of the crude oil samples were provided by Indonesia Research Institute of Oil and Gas (Lemigas) Jakarta.
2.2. Mineralogical Characteristics
Mineralogical composition of zeolite powder was determined by using x-ray diffraction (XRD) analysis by running at 0˚ - 30˚ 2-theta with CuKa at the Research Institute for Mineral and Coal (Tekmira) Bandung. Identification of the mineral present was carried out by using major intensive peak characterizing the mineral .
2.3. Adsorption Capacity
Adsorption capacity analyses of the Bayah zeolite was performed by using CO2 and CH4 adsorption analyses at Chemical Engineering Department, University of Gadjah Mada, Yogyakarta, employing gas adsorption/desorption isotherm by using Quanta chrome Instruments version 11.03.
2.4. Experimental Design
Laboratory experiments were carried out by reacting various ratios of crude oil to zeolite powder with and without microbial enrichment into a 250-mL jar containing Java Sea seawater (3.7% NaCl and pH 6.7). The oil: zeolite ratio tested were 50% (P1), 100 (P2), 200 (P3) and 400 (P4)% (v/w) with constant weight of zeolite (13 g) and various oil volume (6.5 mL - 52 mL) and observed for seven days at room temperature. The observations were any change of the oil-zeolite flocculates, volume of oil adsorbed, weight of zeolite forming the flocculates, and supporting evidences from microscopic observation. Each treatment had three replicates. The microbes used for zeolite enrichment was Bacillus subtilis. which have been identified before as hydrocarbon consuming bacterium. This bacterium was lodged in Microbiology and Environmental Laboratory of Indonesian Research Institute for Biotechnology and Bioindustry (IRIBB). As a source of inoculum, B. subtilis was grown on Luria Broth (LB) medium consisting of (g/L): 0.5 g sodium chloride, 10 g tryptone, and 5 g yeast extract. The liquid culture was incubated at 30˚C in a rotating shaker at 200 rpm for 48 hours. After the incubation period, several inoculum concentrations, i.e. 5%, 7.5%, and 10% (v/w) were employed by spraying the Luria Broth medium containing fresh culture of the bacterium. Observations made were similar to those experiments without microbial inoculation.
3. Results and Discussion
3.1. Properties of Zeolite and Crude Oil
Based on XRD analysis the Bayah zeolite consists of clinoptilolite (75%) with other minerals such as mordenite and quarts present as accessory minerals (Figure 1). Most application of this mineral in Indonesia was reported focused on agricultural sector especially in soil amendment and fertilizer industries . Based on these characteristics, the opinion that such mineral has a great potential as adsorbent of greenhouse gas sequestration at peat land area especially for oil palm cultivation . Employing this evidence and supported also by previous studies reported by others     , this particular mineral originated from Bayah was considered to be potential as oil spill adsorbent.
(a) (a) (b)
Figure 1. X-Ray Diffractogram (a) and Scanning Electron Microscopes (b) of Bayah zeolite indicating the dominant mineral of clinoptilolite.
Table 1. Physico-chemical characteristics of the Bayah zeolite.
Table 2. Chemical data of crude oil used in the experiment.
3.2. Effect of Zeolite-Oil Ratio on Crude Oil Removal
Figure 2 shows the hydrophobicity nature of crude oil staying at the surface of sea water containing 3.7% NaCl and pH of 6.7. The addition of zeolite powder to the crude oil promoted flocculation resulting in the formation of zeolite-oil mixture and sedimented instantly (Figure 3). The flocculate remained stable during seven days of incubation.
Table 3 shows the effect of selected ratios of oil-zeolite on the capability of the mineral in adsorbing the oil. It is indicative statistically that 1:1 ratio of oil to the mineral provided the highest percentage of oil adsorbed by zeolite (86.28%) compared to the other treatment with a lower value, i.e. 48.47% (P1), 47.30% (P3), and 24.11% (P4). In contrast, almost all zeolite added was flocculated and sedimented in zeolite-oil mixture (95.99% - 98.56%) leaving a smaller quantity in dispersed form (1.44% - 4.01%).
Figure 4 shows the relationship between oil-zeolite ratios and the ability of the mineral to adsorb the oil. Based on the equation, the optimum oil-zeolite ratio is reached at 94.1%. This means that a ton of 100-mesh zeolite could adsorb 0.94 cubic meters spoiled oil. However, the economic value of this technique should take into accounts the price of the mineral and the value of environmental impact created by the spoiled oil.
3.3. Effects of Microbially Enriched Zeolite on Crude Oil Removal
The effect of B. subtilis addition at different concentration on zeolite significantly correlated with the oil volume adsorbed by the mineral (Figure 5). Based on the equation, it is indicative that the bacterium identified as hydrocarbon consuming isolate reached its maximum effect at 2.07% (v/w) concentration with 88.35% (v/w) oil adsorbed. As reported by , B. subtilis was among the top three most common microbe patented for microbial bioremediation of oil contaminated seawater. The reason is that this bacterium has been recognized to be able of consuming hydrocarbon substance as source of energy. Improving the capacity of oil adsorption by bacterial addition is suspected related to the increase of surface area of the mineral upon microbial enrichment. Our data (not shown here) indicated that specific surface area of zeolite and zeolite + B. subtilis were 23.41 and 34.85 m2/g, respectively, with a smaller pore diameter size (10.32 nm) of the later compared to the former (12.98 nm) and improved pore volume by 23.3% (0.073 vs 0.090 cm3/g). However, this interesting phenomenon needs further study to determine the role of bacterium in improving zeolite characteristics as oil adsorbent.
Table 3. The effect of selected ratios of oil-zeolite on the capability of the mineral in adsorbing the oil.
1)Figures followed by the letter(s) in the same column are not significantly different according to Duncan’s Multiple Range Test at P < 5%.
Figure 2. Strong hydrophobicity of crude oil to sea water. Dark color on the surface is crude oil spills.
Figure 3. Instant flocculation of crude oil by zeolite observed after seven days of incubation.
Figure 4. Relationships between oil-zeolite ratios and relative amount of oil adsorbed.
Figure 5. Effect of bacterial inoculum (B. subtilis) addition on the spilled-oil adsorbed.
Bayah clinoptilolitic zeolite has been shown to have highly potential characteristics as a sorbent for spoiled oil in seawater. Addition of a 100-mesh powder at 1:2 (w/v) ratio could adsorb the oil up to more than 86%. The addition of zeolite to oil spills in seawater promoted a stable flocculation. Oil adsorbing capacity improved by the addition of a bacterial inoculum B. subtilis. As this study was carried out at laboratory conditions, further study is required to confirm the results especially under field condition.
The authors wish to thank to PT Minerindo Trifa Buana and the Indonesia Research Institute of Oil and Gas (Lemigas), Jakarta for their valuable supports and provision of experiment materials.
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