ABSTRACT
Bioremediation has been proven to be the most effective method of cleaning up oil contaminated soils through the application of nutrients and microorganism to contaminated soils. Hence, this research was aimed at investigating the effects of particle sizes on bioremediation of crude oil polluted sandy soils. Six different soil samples were sieved using the B.S sieve sizes. The sieve sizes were classified into X and Y such that X is fine to coarse sand while Y is very fine to coarse sand according to U.S Bureau and PRA (Public Roads Administration) soil classification system. The soil samples were polluted with escravous sweet crude oil at a uniform rate of concentration under aerobic condition. Treatment commenced after four days using nutrients and microorganism. Soil samples were examined for physiochemical and microbial characteristics for a period of 42days. The parameters examined were: moisture content, particle size distribution, total hydrocarbon content, soil pH, available nitrogen, available phosphorus, total heterotrophic bacteria and fungi count. The analysis of the soil characteristics throughout the remediation period showed that total heterotrophic bacteria and fungi counts increased in all the soil samples. THBC was highest in sample G for both fine to coarse sand(X) and very fine to coarse sand (Y ) with values of
250cfux105/g and 298 cfux105/g at least values of Cu and D50 respectively. There was a decrease in nitrogen, phosphorus, organic carbon content, moisture content, pH and total hydrocarbon content. The result of the study revealed that, the rate of hydrocarbon loss was higher in samples with less Cu and D50 values compared to samples of higher values, an indication that particle size distribution parameters could be one of the factors affecting bioremediation. The correlation coefficient(r) of THC versus Cu for fine to coarse sand(X) is
0.867 while for very fine to coarse sand is 0.923.
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
In Nigeria, particularly in the Niger Delta regions; the soils found are mostly sandy soils in shades of different colours of white, brown, grey and red. Sands are cohessionless aggregate of rounded, subangular or angular fragments of more or less unaltered rock or mineral particles of size from 0.075 -4.75mm (Murthy,2009). The sand separates recognized are: very coarse, coarse medium, fine and very fine determined from the particle size distribution curve. The coefficient of uniformity which is an index value showing the average slope of grain size distribution in a soil depends on the gradation or distribution curve of the soil sample. According to Arora (2008), the larger the numerical value of coefficient of uniformity, the more the range of particles. Sand particles because of their size have a direct impact on the porosity of the soil.
The high incidence and frequency of crude oil spill have been of great concern to Environmental Engineers in Nigeria. This has given rise to intensive research to find ways and means of generating information and data required to assist in bioremediation strategies of crude oil spills.
Before any remediation strategy can be done successfully, a lot of information would be required to aid the process (Bidemi, 2011). This information is meant to assist in the detection of and response to oil spill incidence.
Bioremediation is a means of cleaning up contaminated environments by exploiting the diverse metabolic abilities of microorganisms to convert contaminants to harmless products by mineralization, generation of carbon (IV) oxide and water, or by conversion into microbial
biomass (Baggott, 1993; Mentzer and Ebere, 1996). In Nigeria, no information is yet available regarding the commercial production of fungi or microbial inocula for use in bioremediation of oil polluted environments.
The effectiveness of bioremediation is dependent upon physical and chemical condition as well as correct analysis of the parent microbial population and environmental condition (Nedwell, 1999). It has been found that oil is degraded efficiently by oil oxidizing microorganism under laboratory and field condition (Grondeva et al., 1993). To enhance the natural cleaning action, special fertilizer which contains nutrients of nitrogen, phosphorus and potassium (NPK 15:15:15 fertilizer) is applied to the polluted site. Bioaugmentation process of bioremediation may not be effective for use in oil spill cleanup situation because the addition of non native organisms will often cause competition with the existing beneficial microorganisms (Zhu, etal., 2001).
Some of the naturally occurring microbes capable of degrading petroleum hydrocarbon are Pseudomonas, achrombacter, arthrobacter, bacillus, flavobacter, nocardia, vibrio, connybacterium, alcaligeu (all are bacteria organism).Yeast and fungi organisms are Aspergilium, candida, cladspotum, penicillum, rhodomia, trichodermia (Zhu, et al., 2001).
Analysis of biodegradation rate of crude oil contaminated soil using fertilizer or cow dung showed that fertilizer was a better nutrient source for biostimulation than cow dung (Obahiagbon and Audu 2000). Numerous laboratory studies on nutrient enhancement of oil degradation by natural occurring microorganism have concluded that, this technique is promising for use in stimulating oil degradation (Amanchukwu etal., 1989, Pitchard and Coastal 1991, Oliver etal, 1978). Excessive application of the fertilizer can lead to accumulation of nutrients in the soil. The uncertainty about the toxicity of various fertilizer formulations and microbial products inhibit broader use of bioremediation on marine
shorelines (Hoff, 1993). Field application of nutrients is influenced by temperature, water runoff, substrate and other environmental parameters that are neither fully understood nor easily quantified (Atlas, 1995).
The 1990 Gulf of Mexico spills clearly showed that bioremediation could not be measured in minutes or hours but over a period of days and weeks (Hoff, etal., 1993). The Puerto Rico spill of 1994 clearly showed that at warmer temperatures, bioremediation generally takes 6 weeks while at cooler temperature it spans to several months. This simply implies that bioremediation is not a fast process but a slow process. It has been found that addition of certain nutrients and microorganisms to crude oil contaminated soils fastens the rate of hydrocarbon loss a process called bioremediation. Obahiagbon and Audu( 2000) in their various researches have carried out extensive study of biodegradation rate of crude oil contaminated soil using fertilizer or cow dung and observed that, fertilizer was a better nutrient source for biostimulation than cow dung. Ayotamuno and Kogbara(2006) in their study found out that, crude oil contamination of agricultural soils limits the availability of oxygen in the soil layers and hence impedes the biodegradation process but they failed to investigate on the particle sizes of the soil layers to detect the porosity and voids.
Other notable researchers have also carried out studies on the physiochemical and microbial characteristic of various soils, but not much has been done on the effects of particle size on bioremediation. With this as the study background, the physical properties, chemical and microbial characteristics of the soil samples were used in the assessment of the rate of Hydrocarbon loss at the end of remediation.
1.2 STATEMENT OF PROBLEM
There are very few information about the soil particle size properties on bioremediation. Therefore, this research is aimed at investigating on the effects of particle size distribution parameters like; effective size diameter (d10), coefficient of uniformity (Cu) and average grain size (d50) as well as chemical and microbial properties of different sandy soils and their effects on bioremediation
1.3 SIGNIFICANCE OF STUDY
Since bioremediation process of cleaning up oil spills has proven to be an effective method but a slow process, this study is considered very important as it provides information and data about the particle sizes of sandy soils (Cu and D50) on bioremediation. Through intensive laboratory analysis, data generated will be used as reference tool for further research on bioremediation, academic guide to students, Engineers, contractors and consultants who wish to embark on a similar project.
Statistical Method using regression analysis was used at the end of the research to show the linear relationship and correlation coefficient of the parameters with time in days.
1.4 OBJECTIVE OF STUDY
The objectives of the study is summarised thus:
Compare the effects of particle size distribution parameters (Cu and D50) on bioremediation, characterise the soil and crude oil samples used for the experiment.
To determine the soil Physiochemical and microbial characteristics and their effects on bioremediation.
Make comparison and discuss bioremediation results of soil samples with past related projects.
1.5 SCOPE OF STUDY
1) Review of past literature on similar project
2) Sample collection and locations
3) Contamination of different sandy soil samples with crude oil at a uniform concentration of
4% each.
4) Laboratory analysis on Physical, Chemical and Microbial properties of the Soil samples.
5) Combined practice of bioaugmentation and biostimulation process of remediation respectively.
6) Weekly soil sampling for laboratory analysis (0-7) days for a period of 42days.
7) Presentation and comparison of results with past related projects.
1.6 LIMITATION
Due to the different locations where the samples were got from, large quantity of disturbed sandy soil samples required for the experimental work, were transported to the Civil Engineering Laboratory of the University of Nigeria, Nsukka, this was tedious and expensive. The non availability of required equipment, reagent and apparatus for the chemical and microbial analysis of the soil resorted to; conducting the test in a Standard Laboratory (Search Gate Laboratory Lagos, Soil Science and Microbiology Department UNN) which was capital intensive and tedious. Preserving and transporting the samples particularly during weekly sampling for 42days was tedious.
This material content is developed to serve as a GUIDE for students to conduct academic research
EFFECTS OF PARTICLE SIZES ON BIOREMEDIATION OF CRUDE OIL POLLUTED SANDY SOILS
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