Biodegration of petroleum hydrocarbon and its functional groups by selected protozoan species.
Kachieng’a, Leonard Owino
Kachieng’a, Leonard Owino
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Abstract
Over the past century, major pollution of water sources has occurred as a result of deliberate operational discharges or accidental spills, largely due to anthropogenic activities. This, therefore, necessitates the exploration of short- to long-term measures to reverse the catastrophic situation facing freshwater sources. The overall aim of this study was to investigate the role of selected protozoan species in the biodegradation of hydrocarbon chains of petroleum oil by-products and its specific functional groups. To achieve the main goal of the study, two aquatic environments were used: petroleum-contaminated water aquifer and municipal wastewater. The study was conducted in three phases and addressed three specific objectives.
During the study period, the ciliate protozoan species were isolated from South African petroleum-contaminated water aquifer located in Gezina as well as from Daspoort wastewater treatment plant using conventional methods. In the former contaminated aquatic environment, four ciliates were isolated and they included: Paramecium, Epistylis, Opercularia and Vorticella. In the later wastewater treatment aquatic environment, three ciliate protozoa comprising Aspidisca, Trachelophyllum and Peranema were isolated.
In the first phase, the main focus was on the investigation of the biodegradation of petroleum hydrocarbons in wastewater by a consortium of selected protozoan species (Paramecium sp., Vorticella sp., Epistylis sp. and Opercularia sp.). Three series of experimental studies were considered for a period of 20 d: (i) the biodegradation capability of the isolates; (ii) the synergistic effect of isolates; and (iii) the toxicity effect of the hydrocarbons. The biodegradation capacity of the individual protozoa was approximately 50% and that of a consortium of the four protozoa was >65% after the first 14 d. Their biodegradation rates increased to >75% and to >90% for individual isolates and for the consortium after 20 d of the study, respectively. In terms of the synergistic effect of the isolates, the majority of the protozoan isolates were observed to have a positive interaction with synergy indices of > 0.5 from the onset of the study up to the 16th day, and thereafter the synergy indices of < 0.5 representing less or no interaction was noted during the study. During the first two days, hydrocarbon toxicity [calculated as percentage of inhibition (%E)] was found to have little or no effect on the individual isolates or on the consortium of isolates (<10%). Thereafter, toxicity progressively increased from <10% to <40% up to the 16th day of the study period. Higher toxicity levels were detected between the 18th and 20th day with the percentage of inhibition reaching >40%. The overall outcomes of this part of the study highlight the potential application of a consortium of the selected ciliates (Paramecium sp., Vorticella sp., Epistylis sp. and Opercularia sp.) in the biodegradation of petroleum hydrocarbons in various freshwater sources, due to their greater capacity to survive in a harsh environment.
The second phase addressed the second objective, which assessed the capability of the selected individual protozoan isolates Aspidisca sp., Trachelophyllum sp. and Peranema sp as well as a consortium of these isolates in the hydrocarbon biodegradation. The study demonstrated that the individual isolates were able to biodegrade an average of 72% of the petroleum hydrocarbon and their consortium was found to have the capability to biodegrade ≥ 80% of the hydrocarbons aliphatic groups such as short-chain alkanes, alcohol/ester compounds and partially aromatic hydrocarbons.
Finally, the third phase addressed the objective three, which focused on kinetics of petroleum oil biodegradation by a consortium of protozoan isolates (Aspidisca sp., Trachelophyllum sp. and Peranema sp.) through processes such as natural attenuation, nutrient supplementation and biostimulation. The study showed an increase in the percentage removal of petroleum oil at lower petroleum concentrations and a gradual decrease in the percentage removal as the initial concentrations of the petroleum oil increased: 39%, 27%, 22%, 12%, 10% for various petroleum oil concentrations of 50, 100, 150, 200, 250 mg/L, respectively. This trend was also observed in glucose-supplemented culture media where the reduction was at 45% and 78% for petroleum concentrations of 250 mg/L and 50 mg/L, respectively. The biodegradation of petroleum oil was also achieved between 33 and 90% for 50 mg/L and 250 mg/L respectively when Tween® 80 surfactant was supplemented in the media. In terms of their degradation rate constants, the natural attenuation process revealed that for the petroleum oil concentration of 50, 100, 150, 200 and 250 mg/L, their kinetic rate constants ranged in the order of ≥0 to ≤0.50, ≥0 to ≤0.35, ≥0 to ≤0.25, ≥0 to ≤0.14 and ≥0 to ≤0.11 during the study. For glucose as a nutrient supplement, the degradation rate constant (k) increased from 0 day-1 to 0.8 day-1 when exposed to the lowest oil concentration of 50 mg/L, and decreased from 0 day-1 to 0.25 day-1 when exposed to the highest petroleum oil concentration of 250 mg/L. On the study regarding the kinetic half-life, overall enhancement of the degradation rate was achieved when adding the Tween® 80 surfactant compared to the first two biodegradation processes. The longest half-life was achieved after 217 d during the natural attenuation process for samples with an oil concentration of 250 mg/L and this was reduced to 85 d using the glucose-supplemented process. There was a further decrease to 45 d when Tween® 80 surfactant was added during the biostimulation process. The highest efficiency of ≥20% of Tween® 80 was also observed between 6 and 18 d and thereafter it decreased slightly to ≤20%.
In conclusion, this study suggests the use of a consortium of protozoan species for the biodegradation of various hydrocarbon components, which are toxic to end-users, unlike the use of individual protozoan isolates, which lack the diverse biodegradation capacity or capability required for the biodegradation of petroleum oil spill in water or environment.
Description
Submitted in partial fulfilment of the requirements for the degree, Doctor of Philosophy in Science in the Department of Environmental, Water and Earth Sciences
Faculty of Science at the Tshwane University of Technology.
Date
2018-04-01
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Tshwane University of Technology
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Keywords
Protozoan, Biodegradation, Petroleum oil, Alkanes, Wastewater