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ISOLATION AND CHARACTERIZATION OF HYDROCARBON-DEGRADING MICROBES FROM BENIN RIVER AND OVIA RIVER SEDIMENTS AND THEIR APPLICATION IN OILY WASTEWATER TREATMENT.
CHAPTER ONE
INTRODUCTION
1.1 Background to the Study
This pollution of freshwater ecosystems by petroleum hydrocarbons is one of the most widespread and ecologically devastating aspects of the oil economy in Nigeria, that has long since spread to other areas, beyond the regularly reported wetland and coastal pollution of the Niger Delta, to cover inland river systems in states along the major petroleum transportation routes, refinery sites, and regions with ongoing artisanal refining operations. Two important freshwater systems in Edo State that fulfill essential functions in the community as sources of water, economic activities as artisanal fisheries, agricultural irrigation systems, and biodiversity-supporting freshwater systems include the Benin river
In the polluted freshwater systems, petroleum hydrocarbons are the main long-term sink, which in this case is river sediments, where sorptive organic and mineral particles adsorb the hydrocarbons of the water column and concentrate them in benthic habitat, where they store the hydrocarbons that lasts years to decades after the events of contamination (Obieze et al., 2021; Az Successive generations of bacteria and fungi with evolved complex enzymatic systems to metabolize aliphatic, aromatic, and polycyclic aromatic hydrocarbons as sole or co-metabolic carbon and energy sources are selected by the hydrocarbon-enriched sedimentary setting (Chikere et al., 2022; Abioye et al., 2021). These naturally occurring, silt dwelling, hydrocarbon degraders form an unexploited biological resource potentially of significant practical use: their enzymatic activity and resistance to petroleum compounds, evolved in the local ecological and geochemical environment of the rivers of the Edo State, have them as prime candidates in biotechnological systems aimed at purifying oily wastewaters produced by the local industries.
Industrial effluent in the form of the oily wastewater is a mass type of effluent emission generated by industrial and commercial activities on a large scale across the diverse range of industrial and commercial processes common in Benin City and its environs. Petroleum hydrocarbons, emulsified oils, greases, and other organic contaminants are also found in aqueous release of vehicle maintenance workshops, petroleum product retail stations, palm oil processing mills, mechanical fabrication workshops, diesel generator repairs, and food processing plants with different concentrations (Adetunji and Ogunlaja, 2021; Taiwo and Gbadebo, 20 Depending on the prevailing circumstances, where the unavailability of efficient wastewater treatment systems is seen in most small and medium industrial facilities in Benin City, these oily effluents are often released liberally into the storm drains, open channel and finally into the river systems that supply the city with drainage to continue the hydrocarbon contamination cycle recorded in the Benin and Ovia River sediment surveys (Oghenejoboh et al., The design of the economically viable biological treatment facilities to treat the oily wastewater, based on the locally sourced microbial agents that are adapted according to the hydrocarbon compositions of the local industrial effluents is therefore one of the environmental management concerns with direct impacts that could be relevant to the water quality protection in Edo State.
Biological treatment of oily wastewater with microorganisms that degrade hydrocarbons uses existing potential of diverse genera of bacteria such as Pseudomonas, Rhodococcus, Bacillus, Acinetobacter, Alcaligenes, Nocardia, and Mycobacterium, or fun The effectiveness of these degraders in effluents of wastewater management is critically dependent upon the type of hydrocarbon-based effluent of interest, physicochemical characteristics of treatment system, and presence of co-substrates and micronutrients in treatment system, in addition to genetic and physiological characteristics of the microbial strains used. The local strains of chronic-contaminated Benin and Ovia River sediments have the specific benefit of being already pre-adapted to the hydrocarbon composition, temperature, pH, ionic strength and milieu of nutrients of the local aquatic environment, with potentially better in situ performance than model laboratory strains or commercially isolated degraders cultured under temperate or industrially standardized conditions (Nwachukw
Although the theoretical and practical success of the hydrocarbon-degrading microorganisms of Benin and Ovia River sediments is promising, a systematic scientific study of Benin and Ovia River sediment microbial resource has yet to be published. Studies of microbiology in river sediments in Edo State are rare and are limited to general bacteriological screening based on fecians indicators and there are no studies that describe the nature of hydrocarbon degraders, their enzymatic profiles, or potential biotechnological uses. This knowledge gap is not only important in the view of the unknown microbial biodiversity but also in that the gap deprives the local industrial stakeholders, environmental management agencies, and designers of wastewater treatment systems of the locally calibrated microbial data on which to design and optimize the biologically based oily wastewater treatment systems that best suit the local industrial environment of the Edo State. The current research paper is instigated by the necessity to work out such gap with the help of intensive microbiological research of Benin and Ovia River sediments as suppliers of new hydrocarbons-degrading agents.
Advances in the molecular microbial ecology capacities used in the study allow the use of amplicon sequencing, screening of functional gene degeneres to degradation pathway genes (alkB, nah, catA, bphA, todC), and metagenomics to identify both cultivative and uncultivable data sets of the hydrocarbon-degrading community. Such molecular tools coupled with classical isolation and enrichment strategies and biotechnological performance analysis in laboratory wastewater treatment systems will permit the fundamental characterization of hydrocarbon-degrading communities in sediments and the identification and assessment of high-performance strains to treat the applied oily wastewater.
1.2 Statement of the Problem
There are documented threats to aquatic biodiversity, riparian community health, and ecological integrity of these important water resources of the Edo State petroleum hydrocarbon contamination of the Benin and Ovia Rivers. Meanwhile, the oily wastewater produced by the large and diverse manufacturing and service industrial sector of Benin City still goes unfinishedly treated even though the economically viable variants of biological treatment technologies have not been optimized to suit local characteristics of effluent and microbial ecology. The hydrocarbon-degrading microbial communities resident in the sediments of these polluted rivers constitute natural biological resource of direct application to the current contamination issue and the problem of oily wastewater treatment, however the resource is completely uncharacterized and not implemented. This is where the current research comes in to fill this scientific and technological gap with the conduct of the first systematic isolation, molecular characterization and practical assessment of hydrocarbon-degrading microorganisms in Benin and Ovia River sediments in the application of their oily wastewater treatment.
1.3 Justification for the Study
The scientific rationale of the proposed study lies in the twin virtue of increasing the understanding of the ecology of microbial degradation of hydrocarbons in tropical Nigerian river sediments -a region virtually novel to the published literature -and of producing a characterized library of local adapted hydrocarbon-degrading cultures with proven capacity to degrade local produced oily wastewater. Its practical basis is the actual and increasing demand of biologically treating oily wastewater inexpensively by small and medium industries in Benin City that cannot obtain and/or afford any other physicochemical treatment installations. Environmentally, the creation of such locally tested solutions can potentially lead to a reduction in the hydrocarbon load on the Benin and Ovia River systems, which can go along with the larger objectives of the Edo State Environmental Sanitation Law, and the national effluent discharge standards of the National Environmental Standards and Regulations Enforcement Agency (NESREA) (Adetunji and Ogunlaja, 2021; Tai
1.4 Aim and Objectives of the Study
The aim of this study is to isolate and characterize hydrocarbon-degrading microorganisms from the sediments of Benin River and Ovia River, Edo State, and to evaluate their efficacy in the biological treatment of oily wastewater.
The specific objectives are to:
- Assess the physicochemical properties and hydrocarbon contamination profiles of sediment samples collected from selected sites along the Benin River and Ovia River.
- Isolate and enumerate hydrocarbon-utilizing bacteria and fungi from river sediment samples using selective enrichment and spread plate techniques.
- Characterize isolated hydrocarbon degraders using morphological, biochemical, and molecular (16S rRNA for bacteria; ITS for fungi) methods and screen for hydrocarbon degradation pathway genes.
- Evaluate the hydrocarbon degradation efficiency of selected isolates and consortia in batch culture experiments using representative petroleum hydrocarbon substrates and authentic oily wastewater samples.
- Optimize key process parameters (pH, temperature, nitrogen and phosphorus supplementation, inoculum density) for maximum hydrocarbon degradation efficiency and propose a bioaugmentation protocol for application in oily wastewater treatment.
1.5 Research Hypotheses
H₀₁: Sediments from contaminated sites in the Benin and Ovia Rivers do not harbour significantly greater densities of hydrocarbon-degrading microorganisms than sediments from reference uncontaminated sites.
H₀₂: Hydrocarbon-degrading isolates from Benin and Ovia River sediments do not achieve significantly greater degradation of petroleum hydrocarbons in oily wastewater compared to uninoculated controls.
H₀₃: Microbial consortia assembled from multiple hydrocarbon-degrading isolates do not demonstrate significantly enhanced degradation efficiency relative to individual pure culture isolates.
1.6 Scope of the Study
The study will be restricted to sediment samples collected from selected sites along the Benin River and Ovia River, with site selection based on documented contamination history and proximity to pollution point sources. The oily wastewaters used for treatment experiments will be obtained from vehicle maintenance workshops and petroleum product filling stations in Benin City. Hydrocarbon degradation performance will be assessed by measurement of total petroleum hydrocarbon reduction and selected individual hydrocarbon fractions using gas chromatography. Molecular characterization will employ 16S rRNA gene sequencing for bacteria and ITS region sequencing for fungi, supplemented by functional gene PCR screening. The study will not extend to pilot-scale or field-scale treatment system construction.
1.7 Significance of the Study
This study will produce the first documented microbial resource library of hydrocarbon-degrading bacteria and fungi indigenous to Benin and Ovia River sediments, constituting a novel contribution to the knowledge of microbial biodiversity and hydrocarbon ecology in Edo State. The characterization of functional degradation genes in these isolates will enrich the global database of petroleum hydrocarbon catabolic gene diversity from tropical riverine environments. The applied component of the study will provide, for the first time, an empirically validated biological treatment protocol for oily wastewater using locally sourced microbial agents, offering a practical, cost-accessible, and ecologically appropriate technological solution to one of Benin City’s most prevalent industrial pollution challenges. The findings will be directly transferable to environmental practitioners, regulatory agencies, and small industrial operators seeking affordable compliance solutions for oily effluent discharge management.
1.8 Definition of Terms
Hydrocarbon-Degrading Microorganisms: Bacteria and fungi capable of utilizing petroleum hydrocarbons as sole or supplementary sources of carbon and energy through enzymatic oxidation pathways, including alkane hydroxylases, ring-hydroxylating dioxygenases, and aromatic ring-cleaving enzymes.
River Sediment: The accumulated particulate material deposited at the bottom of a river channel, composed of mineral particles, organic matter, and living organisms, and serving as a major sink and reservoir for hydrophobic organic pollutants including petroleum hydrocarbons.
Oily Wastewater: Aqueous effluent containing petroleum-derived or biological oils, greases, and their emulsions, generated by vehicle maintenance, petroleum retail, food processing, and other industrial activities, characterized by elevated oil and grease content, biological oxygen demand, and chemical oxygen demand.
Bioaugmentation: The deliberate introduction of exogenous microorganisms with specific metabolic capabilities into a contaminated environment or treatment system to enhance the rate or extent of pollutant degradation.
Functional Degradation Genes: Genes encoding enzymes directly involved in hydrocarbon catabolism, used as molecular markers for hydrocarbon-degrading capacity; examples include alkB (alkane monooxygenase), nah (naphthalene dioxygenase), catA (catechol 1,2-dioxygenase), and bphA (biphenyl dioxygenase).
Enrichment Culture: A microbiological technique in which growth conditions, particularly the carbon source, are specifically designed to select for and amplify the growth of organisms with targeted metabolic capabilities from a complex environmental sample.
Benin River: A major freshwater river in Edo State originating from the confluence of several tributaries in the northern part of the state, flowing southward into the Forcados River of the Niger Delta, serving as a critical water supply and aquatic biodiversity corridor for communities in its catchment.
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