Advances in bioremediation of crude oil polluted environment
Till now, crude oil pollution is a common challenge in the Niger Delta region of Nigeria. Several studies have shown how use of biological remediation can help to detoxify and restore ecosystems damaged by crude oil spillage.
Several studies have shown that response actions include site cleanup via recovery of free phase oil, subsequent reduction of the residual petroleum hydrocarbon concentrations to an acceptable value, followed by restoration of the environment to its previous utility status. Options for the reduction of residual petroleum hydrocarbon concentrations are preferably eco-safe techniques. After a cleanup exercise, detoxification of soils polluted with residual petroleum hydrocarbon compounds is necessary.
According to researches, there are different methods by which the concentrations of these pollutants (total petroleum hydrocarbon – TPH, and polynuclear aromatic hydrocarbon – PAH) could be reduced to fall within the acceptable level. The major mechanism involves degradation processes. Degradation generally applies to the breakdown or transformation of complex materials into simpler ones.
Studies have shown that various types of degradation processes include: thermal degradation that occurs via the application of heat; mechanical degradation, which takes place by the application of mechanical force; photo degradation, which is the transformation of complex compounds by the action of sunlight; oxidation/chemical degradation that occurs by the addition of chemicals; and biodegradation, which proceeds by the action of microorganisms (yeast, fungi, or bacteria).
Several researches have shown that organic substances that can be broken down by the action of microorganisms are said to be biodegradable. The technique that enables the application of biodegradation to clean up biodegradable organic pollutants from the environment is referred to as bioremediation. An example of a class of organic compounds that can be detoxified via biodegradation is petroleum-derived hydrocarbons.
Researchers have demonstrated the efficacy of the novel, eco-safe and nanotechnology based bioremediation technique (CNB-Tech) in the remediation and restoration of petroleum impacted soils to beneficial end products.
Iheoma M. Adekunle, Nedo Osayande and Temitope T. Alawode published the study titled “Biodegradation of Petroleum-Polluted Soils Using CNB-Tech – The Nigerian Experience” in a paper, Biodegradation and Bioremediation of Polluted Systems – New Advances and Technologies.
Research method employed was a practical pilot-scale remediation using a biodegradation process referred to as CNB-Tech. Permissions to procure petroleum impacted soil material consignments from the Shell Petroleum Development Company’s remediation project site and to conduct the pilot-scale project were obtained from the appropriate authorities in the company. The spill site of about 15.6 hectares was situated between latitude 4°N and longitude 7° 7.5’E, in Eleme Local Government Area of Rivers state. This site was impacted by crude oil in 1969 as a result of damage by external device to Bomu-Bonny Trans Niger Pipeline (TNP) at Ejema and was accompanied by fire outburst. The hydrocarbon pollution was therefore up to 42 years long at the time of the study (ERMS, 2011). With the assistance of project site workers, clay soil sample bulk was collected in 2 x 200 L plastic drums, which were immediately conveyed to the pilot-scale remediation project site in Shell Industrial Area (Shell IA), Port Harcourt.
CNB-Tech biodegradation procedures were then applied to the samples. Untreated clay soil samples served as controls. Both controls and tests were replicated three times. Composite samples, collected under appropriate conditions and methods (before and after treatment) were sent to an ISO certified laboratory in the United States of America, USA (by courier) and another in Nigeria for the analyses.
As a demonstration of the beneficial utility of the end product, the CNB-Tech remediated soils were used to grow indicator crops, namely Zea mays (corn), Telfairia Occidentalis (fluted pumpkin), and Manihot esculenta (cassava) in screen house farming scheme but only the results of the second crop are reported in this presentation.
Comparative evaluation of growth performances for cassava crop grown in crude-oil-polluted soils remediated using biodegradation technique (RENA) adopted by a reputable oil company in Nigeria and the innovative CNB-Tech
In this study, soil samples from one of the rural communities in Rivers State, Nigeria, called Bomu (K-Dere) in Gokana, Ogoniland, where crude-oil-impacted farm land area was remediated using RENA technique, were collected and used for this comparative evaluation.
The major remediation technique adopted by one of Nigeria’s leading international oil companies (the Shell Petroleum Development Company, Port Harcourt, Nigeria) for crude-oil-impacted soil, at the time of study, is referred to as RENA (Remediation by Enhanced Natural Attenuation). Permission to conduct the investigation was obtained from the designated authority of the oil company. Sample collection was supervised by (i) two representative staff of the oil company, (ii) a community relations officer (CRO) and (iii) some representatives of the community youth forum. Due to low literacy level, oral interviews were conducted on the community representatives to elicit information on factors such as (i) type of actions taken during the RENA remediation project, (ii) common utility of the land area prior to spill and (iii) experiences of farmers utilizing the remediated land area. Information was also obtained from the staff of the oil company on the mode of RENA remediation works carried out at the study site.
Information from literature review showed that most researchers focused on two major factors: (i) isolation of potential hydrocarbon degrading microbial strains and biostimulation via nutrient augmentation. For instance, isolated about 15 hydrocarbon-degrading bacterial and fungal species from three bitumen deposits believed to be of relevance in biodegradation of petroleum (kerosene and diesel) contaminated systems in Nigeria. Carried out an experiment involving biostimulation with agricultural fertilizers to evaluate the biodegradation of hydrocarbon compounds found in a crude-oil-polluted agricultural soil at different levels of soil water.
Petroleum pollution of an agricultural soil was simulated on the field by pouring crude oil on the cells from perforated cans. Biostimulation options were (i) introduction of mineral fertilizers and (ii) periodic application of different amounts of water. Results showed an increase in the total heterotrophic bacterial (THB) counts and a corresponding reduction in soil organic carbon and total hydrocarbon content (THC) at the end of the six-week remediation period. The implication is that by manipulating soil water content and nutrient levels (via inorganic fertiliser application), microbial population and activity were stimulated, suggesting that the level of water in the soil is a major factor that affects biodegradation rate. The use of isolated microbial strains to biodegrade petroleum hydrocarbon has not been successfully applied at the field scale for the remediation and restoration of crude-oil-polluted soils. Most of these works are still at the laboratory scale.
In practice, oil companies in Nigeria contract out bioremediation projects to certified vendors who then apply approved technologies under the supervision of the particular oil company and National Regulatory Agencies. The most commonly practiced bioremediation is land farming, a process believed to utilise indigenous microorganisms to biodegrade petroleum hydrocarbon pollutants under specified conditions.
This is a type of biodegradation by enhanced natural attenuation, which goes by different names for different companies such as RENA for the Shell Petroleum Development Company, Nigeria. Limitations of in situ biodegradation via land farming where environmental controls are not put in place are highlighted.
The issues highlighted clearly show that in situ biodegradation via land farming without the necessary environmental control measures, as often practiced, do not achieve legislative compliance and do not meet best management practices locally or internationally and constitute risk to the environment and public health.
According to the study, most remediation/biodegradation guidelines for detoxification of petroleum hydrocarbons are developed mainly for TPH or total mineral oil concentration but the spill of crude oil into the soil could cause varying degrees of toxicity, phytotoxicity, mutagenicity and carcinogenicity actions. Ecotoxicity bioassays should therefore be incorporated as supplementary tools for monitoring treatment effects. In a situation where, for instance, the end-use of the land is farming, using reduction of petroleum hydrocarbon concentrations as the only or major index for closeout of remediation projects without recourse to other ecological and socio-environmental factors poses some threats to the environment in terms of soil quality, food security, food safety and means of livelihood for the populace. These in turn could stimulate poverty; endanger public health and impact negatively on national security.
The researchers concluded: “CNB-Tech is an innovative, time-effective, cost-effective and eco-friendly remediation technique developed for the detoxification and restoration of crude-oil-impacted environmental matrices polluted with petroleum hydrocarbons, incorporating biodegradation process. This study revealed that it compares and has the potential to excel over some existing biodegradation procedures employed by many oil industries, especially in developing countries. Presently, a mini field-scale project sponsored by National Tertiary Education Trust Fund (TETFUND) is ongoing, focusing on optimization of the CNB-Tech in readiness for field-scale applications for industrial operations and safety assessments of different crops grown in the treated soils.”
Another study on the effect of nutrients on bioremediation of crude oil-polluted water was published in American Journal of Environmental Science and Engineering.
The researchers from the Department of Chemical Engineering, Federal University of Petroleum Resources, Effurun, Delta State, noted: “Crude oil pollution has been a common challenge in the Niger Delta region of Nigeria. The use of biological remediation has helped to detoxify and restore the ecosystems damaged by crude oil spillage. Nutrient addition has been proven to be an effective strategy to enhance oil biodegradation, as they could utilise crude oil as the source of carbon and energy and give a reasonably high biodegradation rate.
“The effect of biostimulants on the bioremediation of crude oil-polluted water was investigated in this study. Four samples, each having crude oil to water ratio of 1:4 was used. Three sets of samples were each inoculated with microbial load 1x 106cfu/ml of Aspergillus niger, and Pseudomonas aeruginosa as microbial consortium.
“All the samples, including the controls, were closely observed for a period of seven weeks at one-week interval for the physiochemical parameters such as pH, Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), Total Hydrocarbon Content (THC), turbidity, and total microbial count. Of all these parameters, only BOD, DO, turbidity, and THC were seen to decrease generally with time of remediation for all the samples. Maximum reductions in value of 94.04 per cent, 97.45 per cent, and 99.09 per cent were achieved for turbidity, BOD, and THC respectively at the microbial consortium load of 1x 10 6cfu/ml.”
Also, another study published in International Journal of Sciences demonstrated bioremediation of crude oil contaminated soil using cow dung.
Crude oil contaminated soils were obtained from an oil pit in Burutu L.G.A. of Delta State and the Cow dung was collected from Garki slaughterhouse along Benin-Sapele-Warri road Delta, Nigeria. The samples were sundried for a period of one week and kept in the laboratory. 500g of crude oil contaminated soil was weighed into four different containers labeled A, B, C and D. The soil was amended with the application of cow dung at various weights of 100g, 150g and 200g/kg respectively leaving sample D without amendment which served as the control for a period of 10 weeks. The microbiological and physiological analysis of crude oil contaminated soil amended with cow dung was investigated using standard cultural techniques. The Total Heterotrophic Bacterial count for the samples A, B, C and D treatment options increased. The Total Hydrocarbon Utilizing Bacterial Count for the A, B, C, and D treatment options increased respectively and sample D control increased slightly. The Nitrate concentration increased from (0.04mg/kg to 0.11mg /kg). Phosphate concentration also increased from (1.72mg/kg to 5.72mg/kg). Percentage losses of total hydrocarbon for the three treatment options A, B and C at the end of 10 weeks were 29.3 per cent, 44.13 per cent and 68 per cent respectively. From the results obtained it can be concluded that cow dung has demonstrated high potential in enhancing bioremediation of crude oil contaminated soil.
Another study on bioremediation of a crude-oil polluted agricultural-soil at Port Harcourt, Rivers State, concluded: “This study showed that an increase in fertilizers, along with tilling for aeration, could decrease the level of carbon by increasing the population of hydrocarbon utilizing bacteria. However, too much fertilizer (nitrogen, phosphorus and potassium) could hinder microbial activity due to high concentrations of ammonia gas. Therefore, the right amount of fertiliser must be used to achieve the best remediation control for hydrocarbon in agricultural soils.”
Another study on an insight into the current oil spills and on-site bioremediation approaches to contaminated sites in Nigeria published in the journal Environmental Science and Pollution Research, noted that remediation by enhanced natural attenuation (RENA) is a feasible technique for restoring petroleum hydrocarbon-contaminated sites, but it might be ineffective when limited to tiling, windrows, and fertilizer applications due to the presence of non-biodegradable residues and contaminants beyond the aeration depth.
According to the study, “however, bioremediation techniques ranging from non-supplemented in-situ and fertilizer supplemented in-situ to mixed in-situ and ex-situ bio-cells supplemented RENA are feasible approaches for spill sites. However, challenging limitations with regard to RENA application failures in the region include delayed responses to spill emergency, large amounts of un-recovered spilled oil, and un-implemented legislative guidelines for spill cleanup. Nevertheless, the temperature, moisture, nutrient, oxygen, and pH of the soil are essential parameters to be considered when implementing a land farming remediation approach.”
Researchers have also used bioremediation on soils contaminated with Nigerian petroleum products using composted municipal wastes.
The study published in the journal Environmental Health and Toxicology assessed the efficiency of ready-to-use, source-separated, composted municipal organic wastes of Nigerian origin on degradation of soil TPHs in soils polluted with petroleum products (crude oil, diesel, and spent engine oil) in screen house experiments.
The effect of compost: soil ratios and combined effect of compost-phytoremediation technique were also studied. TPH was determined spectrophotometrically, after extraction with 1:1 acetone-dichloromethane mixture at 425 nm. Soil pH, electrical conductivity, and phytotoxicity to seed germination and growth of maize (Zea mays) served as risk assessments on soil quality and evidence of recovery for the oil-impacted soil.
Results showed that the treatments increased soil pH and electrical conductivity but reduced TPH. Reductions in TPH by compost technology ranged from 40 per cent to 75.87 per cent. Toxicity to seed germination reduced from 100 per cent to 16.12 per cent. Positive correlations were obtained for plant agronomical parameters and growth period, for all treatments, with coefficients in the range of .905 to .996, p < .05. This study revealed that ready-to-use composted waste has the potential for bioremediation of soils polluted with petroleum and petroleum products. This study is a contribution to the data bank of relatively simple bioremediation methods, suitable for workers in the developing countries, where there is no easy access to high-technology facilities. However, further development of this technique to achieve zero residual TPH is recommended. Scientists at the Department of Biochemistry, College of Medicine, University of Lagos and Health Safety and Environment Department, Shell Petroleum Development Corporation, Port Harcourt, indicate that remediation enhanced natural attenuation technique could be employed to remediate a farm settlement contaminated by crude oil. They concluded: “In conclusion, indigenous soil microorganisms and other weathering mechanisms to a concentration that no longer can decrease degrade petroleum hydrocarbons. The microbial enhanced reductions of contaminants to a very low contaminant level are limited by the availability of hydrocarbons and inorganic nutrients such as nitrate and phosphates to the microorganisms.” Another study published in Research Journal of Applied Sciences employed RENA to remediate oil-contaminated site in the Gokana local government area of Rivers State of Nigeria between January and September 2006. Mineral salt medium to which crude oil had been added was used as a sole source of carbon and energy to isolate hydrocarbon utilisers from soil samples collected from different plots of the contaminated site. Two fungi Articulosprium inflata and Zoopage mitospora as well as five bacterial genera; Lactobacillus, Arthrobacter, Bacillus, Pseudomonas and Micrococcus were isolated and identified. This study also indicated that the counts of Total Heterotrophic Bacteria (THB) varied over a period of 18 weeks. The microbial and physicochemical properties of the soil samples varied with the different plots and at different periods of remediation.” Another study examined the impacts of selected leguminous tree species and kaolinite pre-amendment on oil-contaminated soil for bioremediation in the oil-bearing region of Nigeria. [ad] The study investigated the impacts of selected Leguminous Tree Species (LTS) and kaolinite pre-amendment on oil-contaminated soil. It covered assessment of different levels of contamination (0, 25, 50, 75 and 100 ml in 4000 g soil; which represents the degree of light crude oil spillage concentration as 0.0, 0.63, 1.25, 1.88 and 2.5 %v/w) on the growth performance of Albizia adianthifolia, Albizia odoratissima, Bauhinia monandra, Delonix regia, Peltophorum pterocarpum and Tetrapleura tetraptera LTS investigated. Percentage germination, seedling height, seedling girth, number of leaves and number of nodules decreased as the concentrations of crude oil in soil samples increased. LTS affected soil physicochemical properties. Soil acidity decreased; soil organic matter, carbon content and exchangeable ions increased. Nitrogen (N), Phosphorus (P) and Potassium (K) were altered in the LTS planted soil as compared to controls, but there were no significant differences. There were increased microbial counts in the crude oil-contaminated soil planted with LTS as compared with non-LTS planted soils. Hydrocarbon removal was significantly higher in LTS planted soil than in non-planted soil. D. regia planted soils had most hydrocarbon removal and had significantly more growth in terms of plant height, girth and leaf production in the field. Kaolinite (10 and 20 g samples) applications were suitable and effective sorbent agents for oil-contamination at the different oil concentrations. The sorption potential of kaolinite increased with the increase in kaolinite to 20 g. The potential re-usability of kaolinite after the initial use for oil sorption was analysed and 10 g of burnt kaolinite sorbed 43.62 per cent, while 20 g sorbed 58.90 per cent. The rate of oil sorption by fresh kaolinite was significantly higher than burnt kaolinite. Results show the considerable potential of phytoremediation protocols with LTS and kaolinite as combined remediating agents for oil spill remediation in the humid tropics. [ad]