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Environmental Sciences
Procedia Environmental Sciences 18 (2013) 694 - 702
2013 International Symposium on Environmental Science and Technology (2013 ISEST)
Bioremediation of hydrocarbon contaminated soil using
selected organic wastes
P. Agamuthu *, Y.S. Tan, S.H. Fauziah
Institute of Biological Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
Abstract
Traditionally soil remediation has been known to be among the most expensive treatments in the world. Thus, various strategies have been opted to investigate the most cost-effective solution to deal with contaminated sites. Among the highly potential approach is bioremediation since many studies have reported of its effectiveness in removing numerous pollutants from many contaminated sites. It mainly involved biostimulation where organic or inorganic components were introduced to enhance indigenous microbial growth that directly degrades the contaminants. This paper aims to identify potential organic wastes in enhancing the biodegradation of used lubricating oil in contaminated soil. To achieve the objective, sewage sludge and cow dung were selected as the organic components to be added individually into the 10% (w/w) used lubricant oil-contaminated soil. Each set up with 1.5kg of used lubricant oil-contaminated soil were added with 10% of the organic matter (sewage sludge or cow dung) and left for degradation for 98 days in plastic vessels. Periodic sampling of soil from each vessel was carried out at 14 days interval for total petroleum hydrocarbon analysis, and isolation and enumeration of bacteria. Results indicated that after 98 days of exposure to the organic matters, biodegradation of used lubricant in the soil were much higher than that of the control set-ups. Cow dung amended set-ups showed 94% biodegradation while sewage sludge amendment gave 82%, as compared to the control set-up (56%). This probably was due to the presence of additional nutrient in the organic matter amended soil which enhanced the indigenous microbes' degradation capabilities. As for the performance, the biodegradation rate of the two organic matters differed due to the differences in the nutrient content, particularly of available N and P. In addition, cow dung amended-soil was found to have improved soil physiochemical characteristics that enabled speedy adaption by the microbes to the contaminated soil. Statistical analysis indicated a significant difference at P<0.05. Based on the first order kinetics model, cow dung amended soil gave the highest biodegradation rate of 0.2086/day with used-lubricant half-life of 3.32 day. On the other hand, sewage sludge amended soil has a biodegradation rate of 0.149/day with used-lubricant half-life of 4.65 days. These biodegradation rates were significantly higher than that of the control soil (0.0915/day) and autoclaved soil (0.0309/day). As for the microbial counts, cow dung amended soil recorded (69-122) x107 CFU/g while sewage sludge amended soil recorded (63-96) x 107 CFU/g. On the other hand the control soil recorded (52-73) x107 CFU/g. Again, the presence of available nutrients required by the microbes could be the contributing factor to the high distribution of microbes in the organic matter amended soil as compared to the control soil. In conclusion, cow dung and sewage sludge can be an effective organic amendment for the biodegradation of used lubricant contaminated soil.
* Corresponding author. Tel.: +603 7967 6756; fax: +603 7967 4178. E-mail address: agamuthu@um.edu.my.
1878-0296 © 2013 The Authors. Published by Elsevier B.V.
Selection and peer-review under responsibility of Beijing Institute of Technology.
doi: 10.1016/j.proenv.2013.04.094
Both organic matters proved to enhance the multiplication of indigenous microbes thus enabling rapid biodégradation of the contaminant in the soil.
© 2013 The Authors. Published by ElsevierB.V.
Selection and peer-review under responsibility of Beijing Institute of Technology. Keywords: Biostimulation; cow-dung; used lubricant; soil pollution
1. Introduction
Environmental contaminations have always been a serious issue worldwide. It involved contamination to various media namely soil, water and air. In order to prevent destruction to the ecosystem of the contaminated sites, these media need to undergo a thorough treatment process. The remediation procedure could be as simple as introducing certain chemicals into the system, to a highly complex procedure involving several chemical and biological processes. This is normally applicable to areas involving pesticide contamination, metal and metalloid pollution, petroleum contaminations, and many more [1-6]. Between the three media, soil contaminations has been reported to be the most threatening due to the fact that contaminants have the capacity to affect the indigenous organism that dwell in the soil and destroy the food chain [1,5]. Consequently, soil remediation has been known to be among the most expensive treatments in the world. Thus, various strategies have been opted to investigate the most cost-effective solution to deal with contaminated sites.
1.1. Soil bioremediation
Remediation refers to the removal, destruction, or transformation of contaminants to less harmful substances. To treat contaminated sites, physicochemical and biological remediation can be conducted. Among the highly potential approach is bioremediation since many studies have reported of its effectiveness in removing numerous pollutants from many contaminated sites [3,4,6]. Generally, bioremediation technologies can be classified as in situ or ex situ. In situ bioremediation involves treating the contaminated material at the site while ex situ involves the removal of the contaminated material to be treated elsewhere [7]. Different techniques are employed depending on the degree of saturation and aeration of an area. In situ techniques are defined as those that are applied to soil and groundwater at the site with minimal disturbance. Ex situ techniques are those that are applied to soil and groundwater at the site which has been removed from the site via excavation for soil or pumping for water [8]. It mainly involved biostimulation where organic or inorganic components were introduced to enhance indigenous microbial growth that directly degrades the contaminants.
1.2. Biostimulation
Biostimulation is the addition of substrates, vitamins, oxygen and other compounds that stimulate microorganism activity so that they can degrade the petroleum hydrocarbons faster. Stimulation of microorganisms by the addition of nutrients brought large quantities of carbon sources which tend to result in a rapid depletion of the available pools of major inorganic nutrients such as N and P [9]. An example of this is the addition of fertilizer to an oily wastewater. This works by supplying nutrients that are limiting the growth of the bacteria for the oil contaminated wastewater such as nitrogen and phosphorous. With this addition, the organisms can rapidly degrade the oil utilizing it as the carbon source and the fertilizer as the nitrogen and phosphorous source [10].
Combinations of inorganic nutrients often are more effective than single nutrients where a low level of macronutrients and a high level of micronutrients were required to stimulate the activities of indigenous microbes [11,12]. The greatest stimulation was recorded with a solution consisting of 75% sulphur, 3% nitrogen and 11% phosphorus. Activated sludge has been suggested to be a useful source of nitrogen for PAH biodegradation in soils as well as a range of natural materials such as peat, compost and manure[13,14].
1.3. Organic waste utilization
Inadequate mineral nutrient, especially nitrogen, and phosphorus, often limits the growth of hydrocarbon utilizing bacteria in water and soil. Addition of nitrogen and phosphorus to an oil polluted soil has been shown to accelerate the biodegradation of the petroleum in soil [15]. It was reported that 18.7% and 31.2% higher crude oil biodegradation in soil amended with chicken droppings and fertilizer, respectively, compared to un-amended control soil after 10 weeks while degradation of crude oil in soil amended with melon shells as source of nutrients was 30% higher than those of un-amended polluted soil after 28 days [15,16].
Addition of a carbon source as a nutrient in contaminated soil is known to enhance the rate of pollutant degradation by stimulating the growth of microorganisms responsible for biodegradation of the pollutant. It has been suggested that the addition of carbon in the form of pyruvate stimulates the microbial growth and enhances the rate of PAH degradation [17]. Mushroom compost and spent mushroom compost (SMC) are also applied in treating organo-pollutant contaminated sites [18]. Addition of SMC results in enhanced PAH-degrading efficiency (82%) as compared to the removal by sorption on immobilized SMC (46%). It is observed that the addition of SMC to the contaminated medium reduced the toxicity, added enzymes, microorganisms, and nutrients for the microorganisms involved in degradation of PAHs [19]. Therefore, utilization of organic waste in the bioremediation of soil seems a highly potential area. This will reduce the amount of organic waste sent to landfill, thus reduce the emission of landfill gases and also provide a cheap source of organic additive for the remediation purpose. Nevertheless, extensive research is crucial in order to identify suitable organic wastes to be utilized in the soil bioremediation. Therefore, this paper aims to identify potential organic wastes in enhancing the biodegradation of used lubricating oil in contaminated soil.
2. Materials and Methods
2.1. Organic waste collection
To achieve the objective, sewage sludge and cow dung were selected as the organic components to be added individually into the 10% (w/w) used lubricant oil-contaminated soil. Used lubricating oil was collected from Perodua Service Centre in Petaling Jaya, Selangor while sewage sludge (SS) was collected from a sewage treatment facility namely, Indah Water Konsortium (IWK) in Kuala Lumpur. Cow Dung (CD) was collected from Feedlot Farm, HS NADA Pvt Ltd. in Kuang, Selangor. The physicochemical properties of soil and organic wastes were determined and recorded.
2.2. Microcosm set-up
Approximately 1.5kg of soil (sieved with 2mm mesh size) was placed in plastic vessels labeled A, B, C and D. The soil was then polluted with 10% (w/w) used lubricating oil (150g) and left undisturbed for two days. After two days, 10% of each organic waste namely CD and SS were individually supplemented into each oil polluted soil labeled C, and D respectively and mixed thoroughly. Vessel B served as control
with only soil and used lubricating oil. Also, an additional control (comprising of autoclaved soil and 0.5% (w/w) NaN3) in vessel A was set up to observe the degradation of lubricating oil in the soil due to non-biological factors. The moisture content was adjusted to 60% by the addition of water, and the content was tilled for aeration three times a week throughout the experimental period. The plastic vessels were incubated at room temperature (30 ± 2C) in triplicates.
2.3. Determination of total petroleum hydrocarbon
Anhydrous sodium sulphate (Na2SO4) was added to soil samples to absorb soil moisture. Hydrocarbon content of the soil samples was determined by suspending 10g of soil sample in 20ml of toluene (AnaLar grade) in a 250ml flask. After shaking for 60 minutes on an orbital shaker (model N-Biotek-101M), at 200 RPM, the liquid phase of the extract was measured at 420nm using DR/4000 Spectrophotometer. The total petroleum hydrocarbon (TPH) in soil was estimated using the standard curve derived from fresh used engine oil diluted with toluene. TPH data was fitted to first-order kinetics model [20] with,
y = ae-kt
Y = the residual hydrocarbon content in soil (g kg-1), A = the initial hydrocarbon content in soil (g kg-1), k = the biodegradation rate constant (d-1), and t = time (d).
The model estimated the biodegradation rate and half-life of hydrocarbons in soil relative to treatments applied. Half-life was then calculated using the model of Yeung et al. [20] as
Half life = ln(2)/k
This model was based on the assumption that the degradation rate of hydrocarbons positively correlated with the hydrocarbon pool size in soil.
2.4. Enumeration and Identification of soil bacteria
Soil samples from each oil polluted soil were taken every 14 days for the enumeration of total Aerobic Heterotrophic Bacteria (AHB). Samples were diluted and 0.1ml were plated on nutrient agar medium (Oxoid) for isolation of AHB with the addition of 50^g/ml nystatin to suppress the growth of fungi. Plates were incubated at 300C for 24 hours before the colonies were counted.
Hydrocarbon utilizing bacteria (HUB) in the soil samples were enumerated using oil agar (OA) [21] (1.8g K2HPO4, 4.0g NH4Q, 0.2g MgSO4-7H2O, 1.2g KH2PO4, 0.01g FeSO4-7^O, 0.1g NaCl, 20g agar, 1 ml used engine oil in 1000ml distilled water). The oil agar plates were incubated at 30C for 5 days before the colonies were counted. The bacterial colonies were randomly picked, and pure culture was obtained by repeated sub-culturing on nutrient agar (Oxoid). The bacterial isolates were characterized using microscopic techniques (Gram staining) and biochemical tests.
3. Results and Discussions
3.1. Results of the physicochemical analysis
The physicochemical properties of the soil and organic waste used for the bioremediation trials are detailed in Table 1.
Table 1. Physicochemical Properties of Soil and Organic Wastes Used for Bioremediation.
Parameter Soil Sewage Sludge (SS) Cow Dung (CD)
pH 5.75 7.69 7.00
Nitrogen (%) 0.15 0.34 0.54
Phosphorus (mg/kg) 8.02 308.10 622.34
Potassium (mg/kg) 69.30 94.60 77.80
Organic C (%) 4.33 6.92 8.97
Moisture (%) 2.20 35.00 16.20
C : N 29: 1 20 : 1 16:1
The initial soil pH value used for the bioremediation was relatively acidic in nature (5.75). Soil pH is important because most microbial species can survive only within a certain pH range. Furthermore, soil pH can affect availability of nutrients.
3.2. Biodegradation of used lubricating oil
The biodegradation of used lubricating oil in soil throughout the period of study, for 98 days are shown in Fig. 1. The results showed high biodegradation of used lubricating oil at the end of 98 days with soil amended with organic wastes compared to the control soil treatment. At the end of 98 days, used lubricating oil contaminated soil amended with CD showed the highest percentage of oil biodegradation with 94%, followed by soil amended with SS which is 82% compared to the un-amended control soil that showed 66% of biodegradation of oil at the end of 98 days. Used lubricating oil contaminated soil amended with organic wastes have greater oil biodegradability compared to un-amended control soil in this study.
The main difference of oil biodegradation between the soil amended with organic wastes and un-amended soil treatment occurred during the 14-28 days, where biostimulation resulted in significant increase of oil biodegradation. The addition of nutrients stimulates the degradative capabilities of the indigenous microorganisms thus allowing the microorganisms to break down the organic pollutants at a faster rate [22].
In this study, the lubricating oil contaminated soil amended with CD recorded the highest oil biodegradation of 94% compared to SS which was 82%. The reason for the results obtained might be due to differences in the nutrient contents, particularly N and P in these two organic wastes in stimulating the indigenous microorganisms. Addition of N and P to an oil polluted soil has been shown to accelerate the biodegradation of the petroleum in soil [15]. CD with the highest concentration of N and P (Table 1) explained its highest enhanced biodegradation of used lubricating oil in the soil compared to SS. N and P are known as most important nutrients needed by hydrocarbon utilizing bacteria to carry out effective and efficient biodegradative activities of xenobiotics in the soil environment. Similar results were observed in hydrocarbon contaminated soils amended with poultry and pig manure compost [17, 23].
There was 25% oil biodegradation in autoclaved soil. This biodegradation might be due to non biological factors such as, evaporation or photo-degradation. The addition of sodium azide to the autoclaved soil has completely sterilized and poisoned the microorganism left in the soil and thus it was
having low biodegradability compared to all other treatments.
14 day 28 day 42 day 56 day 70 day 84 day 98 day
Time (Days)
•Autoclaved Soil M Control Soil 6 Sewage Sludge : : Cow Dung
Fig. 1. Percentage biodegradation of petroleum hydrocarbon in soil contaminated with used lubricating oil and amended with organic wastes.
Statistical analysis showed a significant difference at P<0.05 between the amended soil and the unamended polluted soil in all the treatments, thus proving the positive contribution of organic wastes to the biodegradation of used lubricating oil in the soil. The highest net percentage oil loss was observed at 84 days in soil amended with CD which was 28.9% whereas, the highest net percentage oil loss recorded in SS amended soil at 98 days was 19.8%. From the results, contaminated soil amended with CD recorded the highest net percentage oil loss compared to SS. The effectiveness of each amendment was determined by calculating the net percentage loss of used lubricating oil in the contaminated soil as shown in Table 2.
Table 2. Net Percentage Loss of Total Petroleum Hydrocarbon in Soil contaminated with used lubricating oil and amended with organic wastes.
Time (Days)
Treatment 14 28 42 56 70 84 98
A 22.94 24.95 22.28 28.43 27.77 28.86 27.81
B 10.54 15.17 16.35 17.58 17.38 17.40 19.84
• A = Soil + Oil + CD,
• B = Soil + Oil + SS
Net % loss = % loss in TPH of oil polluted soil amended with organic wastes - % loss in TPH of unamended polluted soil.
3.3. Biodegradation rate constant and half-life of used oil
First order kinetics model [20] was used to determine the rate of biodegradation of used lubricating oil in the various treatments. Table 3 shows the biodegradation rate constant (k) and half life (t1/2) for the soil
contaminated with used lubricating oil amended with organic wastes within the 98 days of study. Data for the sampling periods were combined before this model could be used. Oil contaminated soil amended with CD showed the highest biodegradation rate of 0.2086/ day and half life of 3.32 days, whereas, the biodegradation rates and half life of soil amended with SS are 0.149/ day and half life of 4.65 days.
High biodegradation rate recorded in oil contaminated soil amended with CD might be due its high N and P contents and its buffering effects on the microbial flora in the oil contaminated soil compared to SS. The half life (time it will take for half of the hydrocarbon to degrade) is a function of biodegradation rate constant, hence the oil contaminated soil amended with CD recorded the least time (half life) of 3.32 days compared to SS which with half-life of 4.65 days. The results are further supported by other finding which reported that petroleum hydrocarbon contaminated soil amended with organic wastes have a highest degradation constant with the least half life [17, 23].
Table 3. Biodegradation rate and half life of hydrocarbon in oil polluted soil amended with 10% organic wastes.
Treatment Biodegradation constant, k/ day Half life (t1/2) (days)
Autoclaved Soil + Oil 0.0309 22.45
Control Soil + Oil 0.0915 7.57
Soil + Oil + CD 0.2086 3.32
Soil + Oil + SS 0.1490 4.65
3.4 Microbial count
The counts of aerobic heterotrophic bacteria (AHB) in soil contaminated with used lubricating oil and amended with CD ranged between 69.0x 107 CFU/g and 122.0x 107 CFU/g while that of contaminated soil amended with SS ranged from 63.0x107 CFU/g to 96.0x107 CFU/g (Fig. 2). The un-amended control soil had the count of AHB ranging between 52.0x107 CFU/g and 73.0x107CFU/g.
Higher AHB counts in oil contaminated soil amended with CD might be due to the presence and bioavailability of more N and P into the soil that contributed to the stimulation of the microbial flora in the soil. The presence of the macro- and microelements in the CD served as a nutrient source for the growth and maintenance of microbial community [17].
14 28 42 56 70 84 98
Time (Days)
B Contra! Soil U Sewage Siudge U Cow Dung
Fig. 2. Counts of aerobic heterotrophic bacterial (AHB) population in soil contaminated with used lubricating oil amended with organic wastes.
The count of hydrocarbon utilizing bacteria (HUB) was also higher in oil contaminated soil amended with organic wastes (Fig. 3). HUB count in CD amended soil ranged from 56.0x106 CFU/g to 119.0x106 CFU/g while those amended with SS ranged from 48.0x 106 CFU/g to 99x 106 CFU/g. However, the HUB count in un-amended control soil ranged from 40.0x 106 CFU/g to 71.0x 106 CFU/g, it was relatively lower compared to organic wastes amended soil. However, in the soil treatment with autoclaved soil poisoned with sodium azide, the count of AHB and HUB was nil throughout the experimental period.
Fig. 3. Counts of hydrocarbon utilizing bacteria (HUB) population in soil contaminated with used lubricating oil amended with organic wastes.
The higher counts of AHB and HUB recorded in all the organic wastes amended soil compared to the un-mended polluted soil might be due to the result of the presence of appreciable quantities of nitrogen and phosphorus in the organic wastes, especially high nitrogen content, which is a necessary nutrient for bacterial biodegradative activities [17, 23]. The results are in agreement with the finding of Abioye et al. [17], recorded higher counts of AHB and HUB in used lubricating oil contaminated soil amended with brewery spent grain, banana skin and spent mushroom compost.
The higher microbial population counts (Fig. 2 and Fig. 3) in used lubricating oil contaminated soil amended with organic is accompanied by significant oil biodegradation (Fig. 1), indicating that the indigenous soil microbes utilized a portion of the C supplied by the diesel fuel as a potential nutrient source.
The higher counts in AHB and HUB might also due to the fact that these organic wastes were able to neutralize the toxic effects of the oil on the microbial population by rapid improvement of the soil physicochemical properties [1,10]. The organic wastes might help in improving the soil aeration and thus providing sufficient oxygen required by the microbial community which consequently favored the growth of indigenous bacteria in the soil.
4. Conclusions
In conclusion, bioremediation can be a viable and effective response to soil contamination with petroleum hydrocarbons. Biodegradation of used lubricating oil was positively enhanced by the amendment of organic wastes namely CD and SS.
Hydrocarbon utilizing bacteria (HUB) counts were 10% higher in all organic wastes amended soil, compared to un-amended control soil throughout the period of study. Percentage of biodegradation of used lubricating oil in the soil recorded 28% (CD) and 16% (SS) higher biodegradation compared to control soil without organic waste amendments.
Kinetic model of biodegradation rate showed the highest biodegradation rate of 0.2086/ day and least half life of 3.32 days in oil contaminated soil amended with cow dung. The study demonstrated the potential of CD in enhancing the growth of indigenous microorganisms in the soil which in turn increase the biodegradation rate of used lubricating oil in soil. Both organic matters proved to enhance the multiplication of indigenous microbes thus enabling rapid biodegradation of the contaminants in the soil.
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