Abstract:
Crude oil exploration and exploitation has significantly impacted the Niger Delta,
Nigeria wetlands and its ecosystems. Studies suggest that acidification is
ongoing with several acid forming and acid tolerant microbes identified in the
Niger Delta wetlands. The efficient remediation of the crude oil contaminants in
the acidified wetlands is the only alternative left to the Niger Delta for effective
ecological restoration of the environment. In this research, different combinations
of bioremediation strategies were investigated to enhance the remediation of
simulated crude oil contaminated acidic wetlands similar to the Nigeria Niger
Delta wetlands contamination conditions. A series of mesocosm experiments
subjected to wetland condition and a combination of treatments were evaluated
as follows: for biostimulation experiment, Food waste anaerobic digestate
(FWAD), and Tween 80 surfactant were individually added to the mesocosms at
10%, 20% and 30% w/w respectively with soil in the mesocosm experiments. For
bioaugmentation experiments, mesocosms were enriched with Pseudomonas
aeruginosa, Bacillus subtilis, or microbes indigenous to the crude oil spiked soil.
Sequel to the results of these experiments, an optimised combination of FWAD
(30% w/w) plus Tween 80 (30% w/w), Tween 80 (30% w/w) plus indigenous
microbes, and digestate (30% w/w) plus Tween 80 (30% w/w) plus indigenous
microbes were investigated. For each set of the experiments, pristine soil,
acidified soil, and crude oil spiked acidified soil were maintained as controls. Total
petroleum hydrocarbon (TPH) contents, soil basal respiration, and soil microbial
communities’ dynamics were measured over 112 days of the experiments. For
the biostimulation experiment, the FWAD and Tween 80 each at 30% (w/w)
resulted in the highest petroleum hydrocarbons degradation (> 87% removal in
49 days). Augmentation with indigenous microbes enhanced the extent of
degradation of the petroleum hydrocarbons (up to 80% in 49 days). For the
optimised combined strategies, digestate (30% w/w) plus Tween 80 (30% w/w)
plus indigenous microbes resulted in degradation of the hydrocarbons by > 98%.
The correlation between basal respiration, microbial community and
hydrocarbons showed that the more the biogenic CO₂ produced by the relevant
microbial community, the faster the rate of the hydrocarbons degradation. Gram
positive bacteria were the dominant microbial group in the FWAD, Tween 80
surfactant, indigenous microbes, and combined digestate (30% w/w) plus Tween
80 (30% w/w) plus indigenous microbe mesocosms. This research has
demonstrated that acidified wetlands contaminated by petroleum hydrocarbons
can be effectively remediated using low carbon biomaterials and indigenous
microbial consortia. This conclusion was further confirmed by the more than 90%
maize germination and undetectable bioavailable hydrocarbons recorded at the
end of the experiment in these mesocosms. Potential exists for further studies in
low carbon remediation of weathered hydrocarbons contaminants in various
types of wetlands and sediments using FWAD, Tween 80 surfactant, and
indigenous microbes.