Remediation projects

INTRODUCTION

Following the rising population of the world and daily life demands supplied through

industrialization and agricultural systems, the need for preservation of ecosystems is increasingly

needed. The repeated occurrence of environmental threats such as oil spills, oil theft, pipeline

vandalism and additional reasons, it is imperative to give attention to the cleaning of the polluted

and/disrupted ecosystems. One of the most economical and stable approaches to cope with this

vital task is the use of the techniques developed through progresses in an interdisciplinary science,

bioremediation.

Bioremediation refers to the use of living microorganisms to degrade environmental pollutants or

to prevent pollution. It is also the application of various technology for removing pollutants from

the environment as well as restoring the original natural surroundings and preventing further pollution. It takes advantage of various living organisms including bacteria, fungi, algae, and

plants in order to remediate the contaminated ecosystems.

Treatment of hydrocarbon impact at concentrations beyond intervention levels in the site can be

achieved by achieved by on-site and ex-situ bioremediation. This is done by excavation of the

soil area in oil impacted sites using an excavator and a pale loader to a desired depth. It also

involve the excavation of top soil and deposited at the storage area of the project site while the

impacted soil is usually transferred serially to the biocell for treatment. Sequel to the serial transfer

of the impacted soil to the biocell, it is tilled twice daily and intermittently treated with desired

nutrient that enhances the bioremediation process. The nutrient solution comprises of a mixture

of the chemical and water at a known and pre-tested ratios respectively. The tilling of the soil

under treatment is usually done in order to homogenize and increase the surface area for

atmospheric aeration and microbial activities in a biocell. The process is complimented by

nutrient amendment while all ex-situ land farming would be done in an engineered biocell to

prevent cross-contamination. The remedial treatments is then applied and the soil characteristics

analyzed after set periods. Soil physicochemical parameters, such as moisture content, pH value,

electrical conductivity, organic-carbon and total-nitrogen contents, organic parameters such like

total petroleum hydrocarbon (TPH), Polyaromatic hydrocarbon (PAHs), and Benzene, Tuolene,

Ethylbenzene, and Xylene (BTEX) and biological parameters like total heterotrophic-bacteria

(THB) count and Petroleum Utilizing Bacteria (PUB) are analysed to comply with recommended

guidelines.

The Processes involved in Ex-situ and In-situ Remediation of Hydrocarbon Pollution in SoilMobilization

Personnel and material are mobilized to site after the payment securing the FTO for the site.

Equipment/apparatuses mobilized include an excavator, pale loader, pumping machines, TOT

tanks for mixing of treatment solution, gas tester, soil auger, sample containers etc.

Site Preparation

Site preparation is usually undertaken by the community labor support after an initial safety

tool box meeting on the hazards associated with use of hand tools. This activity involves the

clearing of bush and dead woods from the site to give room for the remediation work.

Preparation of Engineered Biocell

An engineered bio-cell is an engineered treatment facility that is designed to handle contaminated

materials without introducing secondary contamination. It offers an innovative method for

treating small quantities of soils contaminated with low to intermediate concentrations of

petroleum hydrocarbons. This is usually made in different sizes partitioned in sections (modular

approach) depending on the quantity of contaminated soil to be treated. Adding moisture and

nutrients such as nitrogen and phosphorus can enhance microbial activity. The microbial activity

degrades the petroleum-based constituents adsorbed to soil particles, thus reducing the

concentrations of these contaminants. Bio-cells use naturally occurring microbes to degrade fuels

and oils into carbon dioxide and water. Under optimum nutrient, moisture, oxygen, and

temperature conditions, native bacteria in the contaminated soil use the TPH as a food source.

Clean soil can then be returned to the original excavated site or used as fill where needed. Bio

cells are capable of treating soils contaminated with petroleum-based fuels and lubricants,

including diesel fuel, jet fuel, and lubricating and hydraulic oils. The microbes use the

contaminants as a food source and thus destroy them. By carefully controlling air flow and

moisture levels, the treatment time can be reduced.The bio-cell consists of commercial roll off- dumpsters converted into fully contained

bioremediation units. Individual units can treat contaminated soil of small quantity and several

units may be combined at one site for larger soil volumes. An impermeable high density poly

ethylene (HDPE) liner of 1.5mm to 2.5mm thickness is use to cover the entire unit after filling

the bottom with clay sand to prevent the liner from been torn in the treatment process.

A leachate collection system is installed at the bottom of the container to capture excessive

moisture in the system. Perforated pipes, installed under the contaminated soil, are connected to

a blower that facilitates the aeration of the soil. If off-gas treatment is not required, blowing air

through the soil is recommended. The container is covered with an impermeable liner to prevent

the release of contaminants and/or contaminated soil to the environment, and to protect the soil

from wind and precipitation.

Figure 1: Schematic of bio-cell

Placement of Sand bags around the Engineered Biocell

Following the construction of the engineered biocell, in order to further prepare it for an efficient

and optimum usage, sand bags are placed around it at a distance of 2m each. Laterite (sharp sand)

is also spread on the floor of the biocell to a level of 0.5m to prevent direct contact of the biocell

floor with equipment that could lead to possible wear and tearing of the polythene liner and to

prevent secondary contamination of the impacted soil. The biocell which is measured to a known

size, bordered on all sides with a 1.5m high bond walls, average stacked sand bags walls and

properly lined bottom and sides with standard

High Density Polyethylene (HDPE) of 2mm thickness with a sump fixed at the tail end is used

for the treatment of the impacted soil.

Excavation and Earthwork

The excavation of impacted soil is done in trenches and transportation of these materials to

the engineered biocell iscarried out with an excavator, and a pale loader to the desired depth.

However, the top soil which are not impacted are excavated and deposited at the storage area of

the project site while the impacted soil is transferred serially to the biocell for treatment.

Treatment of Impacted Soil Materials

Sequel to the serial transfer of the impacted soil to the biocell, the contaminated soil is tilled twice

daily using excavator and intermittently and treated with nutrientsolution comprising of a mixture

of the chemical and water at known ratios respectively. The chemical is sucked using a manual

pump in conjunction with a hose and transferred to the TOT tank before mixing with a clean

water. Clean water is also used in order to avoid further contamination or reduction in the efficacy

of the chemical. The efficacy of the treatment is aided by application of water a day after the

application of the treatment mixture for further contact of the applied solution with the underlying

layers of impacted soil in the biocell.

Gas Testing

Sequel to the excavation of the impacted areas of the project site which could expose the

environment to various gases associated with the remediation activities, gas testing is usually

done at an interval of two days on a weekly basis using Gas Tester.

Evaluation of the Contamination Status of the Treated Soil in the Biocell

Following consistent application of the treatment mixture and agitation of the impacted soil under

treatment, the contamination status of the treated soil was ascertained by random sampling of the

soil for laboratory anlysis.

Laboratory Analysis of Soil SamplesThe laboratory analysis of samples of organic pollutants are done in line with regulatory

authorities such as The United States Environmental protection Agency (USEPA), World Health

organization (WHO), Department of Petroleum resources (DPR) and Federal Ministry of

Environment (FEPA) etc. For samples containing total petroleum hydrocarbon (TPH),

10.00±0.00g of homogenized sample is quantitatively transferred into 100ml beaker and

thoroughly mixed with anhydrous sodium sulphate to absorb moisture. 10ml Dichlomethane is

added to the sample inside the beaker. Thereafter, the samples is sonicated for 30monutes at a

constant speed in an ambient temperature. The supernatant is filtered after complete extraction

into an extraction vial. The extract obtained is further concentrated to 1mlprior to GC-FID

analysis using USEPA 8015C (USEPA, 2007). Calculation of final result is obtained by relating

the absorbance to the standard calibaration curve plotted. This is obtained in the result copy

released by the laboratory. The result obtained is used to compare with the level of contamination

given by regulatory authorities to ascertain the contamination status of the treated soil.

9 Recovery and Containment of live Crude

At 10m depth, live crude was evident and has to be recovered and contained adequately. Booms

and skimmers were used to contain the live crude to prevent crossed contamination. This was

followed by the use of a local wooden Canoe on Pit base water to access the various sections of

the pit base. Personnel were therefore properly kitted with required PPE. Plastic containers were

used in fetching floating live crude for containment in a 1000 litres TOT tank.A total of 3500

litres were recovered and contained in a designated (quarantined), labeled and restricted section

of the office area.

NOTE: A 2mm thick Liners were used to blind the surface area of the designated or quarantined

area for storage of recovered crude oil.

Application of Nutrient Mixture and Water to Contaminated Soil

The nutrient mixture can be applied mechanically using a pressure pump and manually using a 2

inches hose pipe connected to a manual pump and powered with a generator. This could be

accompanied with an intermittent application of water in each of the cycles of treatment until the

level of contamination is reduced to its barest minimum.

Manual Pump

Serial Transfer of Impacted Soil into the Biocell

Tilling/Agitation of Impacted Soil for Aeration in the Biocell

Excavation of Impacted Soil Characterized by Dark Colour

Excavation of Impacted Soil in a Crude Oil Spilled Site

Raw Crude at 9m depth of the Impacted Area

Raw Crude at 9m depth of the Impacted Area

Excavation of Crude Oil Impacted Site

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