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European Journal of Applied Sciences – Vol. 10, No. 5
Publication Date: October 25, 2022
DOI:10.14738/aivp.105.12301. Douglas, R. K., Fou, A., & Araka, P. P. (2022). Use of Rice Husk Ash for Copper, Chromium, Zinc, and Lead Bioremediation in Crude
Oil-Contaminated Soil. European Journal of Applied Sciences, 10(5). 27-33.
Services for Science and Education – United Kingdom
Use of Rice Husk Ash for Copper, Chromium, Zinc, and Lead
Bioremediation in Crude Oil-Contaminated Soil
Reward Kokah Douglas
Department of chemical engineering
Niger Delta University, Wilberforce Island, Nigeria
Ayebatin Fou
Center for Occupational Health and Safety
University of Port Harcourt, Port Harcourt, Nigeria
Peremelade Perez Araka
Department of Agriculture and Environmental Engineering
Rivers State University, Port Harcourt, Nigeria
ABSTRACT
In this study, 1kg soil sample was artificially contaminated with 250ml crude oil and
incubated for 4-day; and heavy metals-copper (Cu), chromium (Cr), zinc (Zn), and
lead (Pb) concentrations were measured by flame atomic adsorption spectrometry
(AAS) to be 11.68mg/kg, 38.96mg/kg, 59.34mg/kg, and 28.56mg/kg, respectively.
Fresh rice hush ash (RHA = 0.5kg) was prepared from rice husk (RH) and used for
the bioremediation of these metals in a 2-month laboratory experiment. The RHA
reduced the Cu, Cr, Zn, and Pb concentrations by 33%, 29%, 27%, and 25%,
respectively. Considering the quantity of RHA to the contaminated soil mass ratio
(0.5:1.0), and the short period of the experiment (i.e., 2-month), RHA amendment is
promising for the bioremediation of heavy metals polluted soils. This study
provides the first reference point on the effectiveness of RHA for the remediation of
heavy metals in polluted soils in the Niger Delta, Nigeria. Thus, we recommend field- trials and longer-term study to better assess the long-term applicability of this
option for bioremediation of polluted soils.
Keywords: Crude oil-polluted soil; heavy metal; amendment; bioremediation
INTRODUCTION
Soil pollution by heavy metals (HMs) is a significant global problem since they can cause
challenges to human health and ecosystems [1-3]. HMs are toxic, bioaccumulative, and
persistence in existing environments. Heavy metals have physiological effects on living
organisms as they are not degradable [4].
The sources of heavy metals in the environment (soil) are numerous, and basically
anthropogenic. These include oil spills incidences, vehicle emissions, metal plating/finishing
operations, disposal of industrial waste, fertilizer applications, fly ash from
incineration/combustion processes, among others [5]. Also, anthropogenic actions such as
mining, smelting, chemical production and factory emissions release large quantities of Cd and
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European Journal of Applied Sciences (EJAS) Vol. 10, Issue 5, October-2022
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Pb into the soil environment, causing significant soil pollution [6-7]. These metals can be
conveyed, via the soil-crop-food nexus, to cause threats to human well-being. Crude oil contains
Cobalt (Co), Cupper (Cu), Lead (Pb), Ion (Fe), Magnesium (Mg), Manganese (Mn), Zinc (Zn),
Cadmium (Cd), Chromium (Cr), and Nickel (Ni). Among which, Cd and Pb contamination of soil
throughout the world has become a priority environmental concern [8, 9]. Aslo, Cd and Pb have
been identified as priority pollutants by the US Environmental Protection Agency.
Crude oil spills in the Niger Delta region has undoubtedly affected the HM contents in the soils.
In the Niger Delta region of Nigeria, the heart of the oil and gas industry (OGI), anthropogenic
sources reported in [6-7] cannot be the prime source of HM pollution since these activities are
not present; rather the activities of the OGI in the region. Again, the soils in the region are
already fertile, and requires little or no fertilizer application to enhance soil fertility for plant
growth. Therefore, HM contamination due fertilizer application cannot be an attribute here. It
is also pertinent to mention that there is no soil survey study yet in the Niger Delta region
Nigeria reporting on HM concentrations in pristine soils in the region. Thus, there is research
need to evaluating HM contents in pristine soils to make comparison with contaminated soil at
laboratory-scale to checkmate the influence of crude oil spills on HM contents in soils.
Substantial number of techniques for HM immobilization in contaminated soils are currently in
use, including microbial remediation [10-11], chemical washing [12], physical technologies
[13], phytoremediation [14-15], and chemical immobilization [16-17]. These techniques have
been reported to have differrent remediation effectiveness and drawbacks, and different cost
implications. To date, different novel materials have been recommended for the remediation of
HM in soils, including phosphates-containing materials, Silicon-rich minerals, biochar
materials, and so on [18-20].
Biochar is an organic carbon-rich solid product produced as a result of pyrolysis of organic
matter (e.g., agricultural waste, biomass) under an oxygen-limited environment [21]. The
application of biochars for for HMs remediation have been reported in the literature [21-22].
Some researchers have modified biochar for HM in soils [23-24]. A recent study used β- mercaptoethanol to prepare thiolmodified biochar and use the product to remediate Cd and Pb
contaminated soils [25].
Globally, huge quantities of agricultural wastes have been generated at increasingly accelerated
rates, posing potentially high dangers to the environment. Consequently, in this research, we
assess a simple and cost-effective approach, using fresh rice husk to produce rice husk ash
(RHA) by sieving; and use it to remediate Cu, Cr, Zn, and Pb in crude oil-contaminated soil.
MATERIALS AND METHODS
Fresh rice husk collection and preparation of rice husk ash
Rice husk (RH) used in this study was collected from a local rice mill at Otuokpoti Community
in Ogbia Local Government Area of Bayelsa State, Nigeria. Prior to sieving, the RH was air-dried
at room temperature (21oC) in the laboratory. The RH was sieved with a 50 μm mesh sieve to
obtain rice husk ash, RHA (Figure 1).
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Douglas, R. K., Fou, A., & Araka, P. P. (2022). Use of Rice Husk Ash for Copper, Chromium, Zinc, and Lead Bioremediation in Crude Oil-Contaminated
Soil. European Journal of Applied Sciences, 10(5). 27-33.
URL: http://dx.doi.org/10.14738/aivp.105.12301
Figure 1: Rice husk ash (RHA) prepared from fresh rice husk
Soil sampling and treatment
4 kg bulk sub-surface soil sample (0-20cm) was collected with a shovel on 2 April 2021 from
the Niger Delta University Research Farm, Bayelsa State, Nigeria. Sample was taken with Ziploc
bag to the laboratory. Plant parts and pebbles were removed, and stored in a freezer at 4oC to
preserve field-moist condition. Prior to treatment of the soils, 3 kg bulk soil was measured out
of the 4kg bulk soil and divided equally into three equal portions- A, B and C (1 kg each).
Samples (A and B) were spiked with 250 ml of Nigerian crude oil. The contaminated soil
samples were properly mixed to enhance even distribution of contaminants in the samples.
Mixing was done daily for 4-days. Sample A was then treated with 0.5kg RHA,while B (without
treatment), and C (pristine soil) were all sent to Integrated Scientific and Engineering Solutions
Laboratory, Port Harcourt, Rivers State, Nigeria for heavy metal analysis.
Heavy metal analysis
Prior to HM analysis, both treated (soil + crude oil + RHA); crude oil-contaminated soil; and
pristine soil samples were air-dried and crushed with a mechanical device and pass through a
20-mesh sieve. 1 g soil sample (each) was weighed out to a 100 ml Erlenmeyer flask and added
25ml of 1N NH4OAc, pH 7.0. Each sample was placed in a shaker for 15 minutes. The solution
was filtered through Whattman filter paper NO 42 and analysed by flame atomic adsorption
spectrometry (AAS). Using the routine procedure, HMs (Cu, Cr, Zn, and Pb) concentrations were
calculated using the equation below:
Metal concentation = [metal standard conc × sample absorbance]/[standard absorbance]
(1)
RESULTS AND DISCUSSION
HM concentrations in soils
HM concentrations in both pristine and crude oil-contaminated soils were evaluated using AAS.
The HM concentrations of the pristine soil in this study are presented and compared with HM
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European Journal of Applied Sciences (EJAS) Vol. 10, Issue 5, October-2022
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background values reported by [26] in Table 1. No much difference was observed. However,
the difference could be attributed to different land use of the sampling sites.
Table 1: Heavy metal concentrations (mg/kg) in pristine soil of the current compared with
background concentrations previously reported [26].
Heavy metal
(mg/kg)
Current study [26]
Cr 1.8 2
Zn 21.2 23
Pb 9.4 11
Cu 3.6 4
Table 2: Heavy metal concentrations (mg/kg) in crude oil-contaminated soils of the current
compared with previous studies on heavy metal analysis
[27]
Heavy metal (mg/kg) Site 1 Site 2 Site 3 A [28] [29] [30] [30]
Cr 63.27 35 55.6 38.96 28.75 17.78 20 240
Zn 40.1 17.6 56.93 59.34 29.3 38.13 NA NA
Pb 17.25 12 41.29 28.56 25.02 7.44 200 625
Cu 11.11 5 12.39 11.68 11.21 7.78 0.3 100
A = current study: concentations of heavy metals in artificially crude oil-contaminated soil;
[28]: mean concentrations of heavy metals in soils impacted with crude oil in the Niger Delta,
Nigeria; [29]: mean concentrations of heavy metals in soils collected from an oil field in the
Niger Delta, Nigeria; [27]: mean concentrations of heavy metals in soils collected from crude
oil-contaminated sites in the Niger Delta region of Nigeria; and [30]: Department of Petroleum
Resources recommended target and intervention values for remediation of contaminated land
in Nigeria. NA = not available.
HM concentrations in crude oil-contaminated sites are presented in Table 2. Results of [27, 28,
29] reported heavy metal concentrations in genuinely crude oil-contaminated soils while those
of the current study are laboratory-engineered soil samples. The difference in HM
concentrations in the field samples may be due to the extent of oil spill or the different landuse
that might have influenced the background concentrations. The significant differences in the
HM concentrations of the current study (i.e., Table 1: pristine soil; and Table 2 artificially crude
oil-contaminated soil) may be ascribed to the quantity of crude oil (250ml) used for spiking the
soil (1kg). The concentrations of Cr and Cu in the current study exceeded the target values
recommended by [30] on remediation of contaminated land sites. Thus, there is need for the
assessment of the numerous crude oil-released sites in the Niger Delta region, where crude oil
spill incidents are recorded almost daily. This will help benchmark the environmental quality
in terms of HM pollution in the region. However, these values were less than the intervention
values recommended [30]. The concentrations of Pb in the current is far below the target and
intervention values by [30].
Impacts of amendment on soil HMs
Fresh rice husk (RH) amendment on crude oil-contaminated soil enhanced the biodegradation
of HMs in soil. The biodegradation potential of FRH was calculated using the formula:
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Douglas, R. K., Fou, A., & Araka, P. P. (2022). Use of Rice Husk Ash for Copper, Chromium, Zinc, and Lead Bioremediation in Crude Oil-Contaminated
Soil. European Journal of Applied Sciences, 10(5). 27-33.
URL: http://dx.doi.org/10.14738/aivp.105.12301
[(HMTbr) - (HMTar)/(HMTbr)] ×100% (2)
Where HMTbr = heavy metal concentration before remediation (t = 4 day incubation); HMTar =
heavy metal concentration after remediation (t = 2 month period).
FRH amendment enhaced the biodegradation of Cu, Cr, Zn, and Pb. The results of each metal is
computed and presented in Table 3. The effectiveness (%) of the amendment on the metals are
as follows: Cu > Cr > Zn > Pb. The concentrations of Cr and Cu after 2-month remediation still
exceeded the target values. This requires post remediation checks; and may be the quantity of
amendment be increased to enhance higher remediation efficiency [31].
Table 3: Results of HMs concentrations before remediation, after remediation, and percent
biodegradation
Heavy metal
(mg/kg)
HMTbr HMTar (t = 2month) % Biodegradation
Cr 38.96 27.84 29%
Zn 59.34 43.31 27%
Pb 28.56 21.52 25%
Cu 11.68 7.81 33%
CONCLUSION
This study aimed at assessing the biodegradation efficiency of fresh rice husk ash (RHA) for Cu,
Cr, Zn, and Pb in crude oil-contaminated soil at laboratory-scale. 0.5kg RHA to 1kg
contaminated soil mass (0.5:1.0) in a 2-month experiment reduced the concentrations of Cu, Cr,
Zn, and Pb by 33%, 29%, 27%, and 25%, respectively. Results show that fresh RHA for HMs in
contaminated soils is a promising approach. In Nigeria, at present, this research provides the
first baseline achievement guide on the application of fresh RHA for the bioremediation of soils
contaminated with HMs. Future study should consider longer-term study and field trials to
assess its applicability on bioremediation of HMs contaminated soils.
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Soil. European Journal of Applied Sciences, 10(5). 27-33.
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