Assessment of the Concentration of Petroleum Hydrocarbon in Oily Wastes Residual Ash at Bodo-Ogoni Remediation Site, Nigeria

Hydrocarbon wastes generated from remediation activities contain Total Petroleum Hydrocarbon (TPH), Polyaromatic Hydrocarbon (PAH) and Heavy Metals whose respective concentrations are yet to be determined. There is limited available literature particularly in Nigeria, on whether the concentration of these wastes after treatment exceeds permissible limits. The present work aims to determine the concentration of petroleum hydrocarbon in the residual ash from the treated (incinerated) oily wastes from the Bodo-Ogoni remediation activities. Oily wastes residual ash samples were collected from six treatment sites, each divided into four replicates in a Completely Randomized Design. A total of twenty-four residual ash samples were collected and taken to National Oil Spill Detection and Response Agency (NOSDRA) Reference Laboratory, Port Harcourt for extraction. The concentration of TPH, PAH and heavy metals in untreated hydrocarbon wastes were also determined and used for the control experiment. The extracts were analyzed using AGILENT 7890A-GC and Atomic Absorption Spectrophotometer (AAS) modelled 240FS, manufactured in USA. The results show six residual pollutants; Cadmium, Lead, Zinc, Manganese, TPH and PAH below the Nigeria Department of Petroleum Resources (DPR) Intervention Level but exceeded the DPR Target Level for TPH and PAH. The descending order of concentration of PAH obtained from the treatment sites gwere; 1.24 + 2.4 mg/kg (Paschal), 4.76 + 7.48 mg/kg (ITS), 10.46 + 14.68 mg/kg (TMCH) and 16.14 + 6.36 mg/kg (Mosab). Similarly, the concentration of TPH was 320.18 + 355.13 mg/kg (TMCH), 463.25 + 205.29 mg/kg (ICREN) and 501.11 + 300.79 mg/kg (Networld) against TPH 12,000 mg/kg, PAH 23 mg/kg, Cadmium 0.15 mg/kg, Lead 0.59 mg/kg, Zinc 3.45 mg/kg and Manganese 2.8 mg/kg (untreated wastes). Two treatment sites only recorded concentration of heavy metals, while four reformed inefficiently and couldn’t detect the concentration of How to cite this paper: Gbarakoro, T. N., & Bello, A. D. (2022). Assessment of the Concentration of Petroleum Hydrocarbon in Oily Wastes Residual Ash at Bodo-Ogoni Remediation Site, Nigeria. Journal of Geoscience and Environment Protection, 10, 1-15. https://doi.org/10.4236/gep.2022.105001 Received: January 24, 2022 Accepted: May 6, 2022 Published: May 9, 2022 Copyright © 2022 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/


Introduction
Hydrocarbon is the principal component of petroleum wastes formed when crude oil's properties change as a result of changes in eternal conditions. The formation of oily wastes are commonly caused by cooling below the cloud point, evaporation of light ends, mixing with in compatible materials, and the introduction of water to form emulsions (Johnson & Affam, 2019). In the formation of oily wastes from remediation of hydrocarbon pollutants, involving thermal treatment, the process include drying, followed by pyrolysis and disintegration of organic structures into tars, gasses and char with the evolvement of volatile inorganics such as alkali metals, where reduction in levels of heavy metals is determined later on as higher temperatures are attained (Nzikhou & Stanmore, 2013).
The improper disposal of petroleum hydrocarbon wastes in the environment creates a modification in the chemical and physical properties of the surrounding soils (Robertson et al., 2007), deficiency in nutrients and stunted growth in vegetation of receiving soils as the oily wastes are fixed into soil pores (Trofimov & Rozanova, 2003), reduction in hygroscopic moisture, hydraulic conductivity, wetting power of soils and decrease in the diversity of soil microorganisms (Suleimanov et al., 2005). Several methods; thermal, mechanical, biological and chemical have been ap- Reduction in concentration of heavy metals in oily wastes has been reported to be influenced by the treatment facilities, length of exposure to high temperature of the particles (Zeuthen, 2007), and behavior of heavy metals (Nzikhou & Stanmore, 2013;Obernberger et al., 2006). Heavy metals caused by applications of some biomass materials may become concentrated after use into residual wastes (Nzikhou & Stanmore, 2013), and during combustion Pb, Zn and Cd tend to vaporize and re-condense on the surface of fine particles or ash when incinerated (Obernberger et al., 2006).
Low temperatures in treatment facilities caused increase in the concentration of Cd, Pb, in the ash, but at temperature above 1250˚C a reduction in concentration occurred (Obernberger et al., 2006). Zeuthen (2007) showed that a combination of type of furnace, length of exposure to high temperature plays key roles in the reduction of the concentration of heavy metals in hydrocarbon waste.
Accordingly, Cd, Pb are among the metals that increased in concentration in the finer aerosol particles formed in a 22 mwt grate incinerator, but thermodynamic equilibrium is attained in large particle from grate furnaces because of the length of exposure to high temperature of the particles, and under incineration conditions Cd and Pb read almost ten minutes to diffuse out of an ash particle of the size found in incinerators.
In 2008, two major oil spills from shell petroleum development company The generated wastes are taken to treatment facilities for the production of residual ash to assess the concentrations of petroleum hydrocarbon chemicals and ascertain if it exceeds permissible limits. However, there is little or no information on the chemical composition of such wastes after treatment in the Nigeria Nation, in spite of the fact that the non-reduction of the concentration of hydrocarbon wastes generated from remediation activities disposed on the soil will have a devastating impact on the functioning of the soil ecosystem and its services.
This present study was undertaken with an objective to determine the concentration of petroleum hydrocarbon in the residual ash from the treated (incinerated) oily wastes from the Bodo-Ogoni remediation activities. This present study is important as it indicates the concentration of the TPH, PAH and heavy metals contained in treated oily wastes. The efficiency of the treatment facilities in the reduction of the concentration of the hydrocarbon wastes is also exposed by the study.

Description of Study Site
The study was conducted at collection site located at Bodo (N4˚36'29.7"N; E7˚15'30.2"), and characterized by low-lying mangrove vegetation and numerous tidal creeks lined with soft mud, substrates on the shorelines and abandoned fish ponds.

Research Design
The six treatment sites were each replicated four times in a Completely Randomized Design.

Sample Collection
The petroleum hydrocarbon solid wastes which comprised contaminated soil, glasses, plastics, vegetation generated during the clean-up at Bodo Creek were collected in 50 cm polythene bags. Liquid oily wastes were also collected from the collection sites in 50 liters jerry cans. Both solid and, liquid oily wastes were segregated at Bodo Patrick waterside segregation point and thereafter to the various treatment sites. At the end of treatments, residual ash-waste samples were collected from stored batches at each of the treatment activities. Untreated samples were also collected before treatment.

Extraction of TPH and PAH
Ten grams each of aliquot of untreated and treated well-mixed ash samples were placed in a solvent rinsed beaker and added anhydrous sodium sulphate until the ash particles were loosened. Twenty millitres of 50 ml dichloromethane solvent was added and shaken in a vortex mixer for 5 minutes. The samples were then placed in a sonicator for 10 minutes at 70˚C. At the end of the duration, the extract was filtered through a glass funnel containing glass wool and anhydrous sodium sulphate. Thereafter, the extract was transferred to a Teflonlined screw cap for analysis.

Extraction of Heavy Metals
One gram of ash samples and untreated samples were weighed and transferred into test tubes and 20 ml aqua regial (hydrochloric acid and nitric acid; 3:1) solution was added. The resulting mixtures were digested for about I hour at 100˚C on a hot plate. The resulting digests were allowed to cool and then filtered into a 100 ml flask and made up to mark with deionized water and analysed in an atomic absorption spectrophotometer (AAS) (AAS Raleigh WF × 320) after calibrating the equipment with different standard concentrations.
The concentration of four element Cd, Pb, Zn and Mn were determined in both untreated and treated hydrocarbon wastes. The selected metals concentrations were calculated in mg/kg being the closet benchmark in EGASPIN measurement.

Statistical Analysis
The data obtained from the extraction and analysis were subjected to statistical analysis using analysis of variance (ANOVA). This was done to determine significant differences in concentrations of TPH and PAH between the ashes collected from the treatment sites.

Results
A total of six (6) residual pollutants comprising four (4) heavy metals; cadmium, lead, Zinc and manganese and two petroleum hydrocarbons (TPH and PAH) were obtained in all the samples. All the results are expressed in from of mean ± standard deviation for four replicates per parameter. The total concentration of TPH and PAH obtained from the six sites indicate that the concentration of the residual ash was below the department of petroleum resource intervention (DPR,   Olawuyi and Zibima (2018) stated that the values of TPH and PAH stipulated by EGASPIN, the regulatory agency in Nigeria for which intervention or remediation would be conducted is extremely high as it is 5000 mg 1 kg (TPH) and 40 mg 1kg (PAH) our study agrees with this report particularly as the concentration of TPH recorded at two treatment sites; ICREN (463.25 ± 205.29 mg 1 kg); and TIMCH (320.18 ± 355.13 mg 1 kg) is high enough, yet it is below the intervention limit. This is caused by inefficiency of treatment facilities or process. The marginal or slight significant difference recorded in statistical data give credence to this study.

Discussion
The results obtained in our study implies that the treated oily wastes (ash) still contain higher levels of TPH and PAH in spite of the reduction in concentration over the untreated oily wastes.
This is because the values obtained though were below those obtained in the untreated oily wastes, they were all above the target values (50 mg/kg TPH and The increased in concentration of ash after treatment is caused by the temperature of the treatment facilities which were not more than 100˚C and could not stop the re-condensation. This probably led Zeuthen (2007) to report that, high temperatures of 1250˚C, under incineration conditions made Cd and Pb to diffuse out of ash within 10 minutes of exposure. Our study indicates the inefficiency of treatment facility pointed out.
The increase values of heavy metals recorded in our study were all above target values and this is supported by the statistical data which pointed out significant difference (P < 0.05) between heavy metal content across sites and their target values (Appendixes 1-6).

Conclusion
The concentration of TPH, PAH, and heavy metals contained in treated hydro- sults showed that the remediation activities did not reduce the concentration of heavy metals to permissible limit, indicating that the treatment facilities were not efficient, though a reduction in TPH and PAH was achieved. With reference to available literature, the high metal concentration is caused by non-application of required temperature in the treatment process and the weakness of the treatment facilities.
The study has added to knowledge that the remediation of Bodo-Ogoni hydrocarbon polluted sites is yet to achieve the reduction of metal concentration, and therefore requires a more appropriate approach.