Bioremediation Potential of Algae (Chlorella vulgaris) in Crude Oil Contaminated Sediment
Authors: Ugboma C. J. , Nrior R. R. , Igbudu M. E. 
Published: May 2023

Aim: To evaluate the bioremediation potential of algae (Chlorella vulgaris) in crude oil contaminated sediment.

Study Design: The study employs three (3) experimental designs using flat rubber, statistical analysis of the data and interpretation makes up the study design.

Place and Duration of Study: New Calabar River, Choba, Obio Akpor Local Government Area, Rivers State, Nigeria, was used for this study. New Calabar River lies between longitude 6°53.13E and latitude 4°53.52N in Choba. Bioremediation monitoring process lasted for 56 days; analyses were carried out at 14 days’ interval.

Methodology: Three (3) experimental set up were employed using a using flat rubber basin, each set up contained 2500g of sediment and was contaminated with 250ml of Crude Oil except Control 1 uncontaminated sediment (Us). The set up was augmented with the Chlorella vulgaris (CHL) except the control 1 and 2 (Us and Cs). Sediment profile like Temperature, pH, Nitrogen, Phosphorus, Potassium, electrical conductivity, moisture content, total organic carbon, soil organic matter and total hydrocarbon content (THC) before contamination was determined using standard analytical methods while parameters like Temperature, pH, Nitrogen, Phosphorus, Potassium and Total Hydrocarbon Contents (THC) were monitored throughout the experimental period. Microalgae and Hydrocarbon utilizing algae (HUA) were monitored throughout the experimental period using standard microbiological methods. Percentage Bioremediation was estimated from amount of THC reduction from day 1 (initial) of monitoring. Statistical analysis was carried out for microbiological and physicochemical parameters when treated using Statistical ANOVA to ascertain significant difference of mean values between various treatments.

Results: Results revealed the amount of hydrocarbon removed and % bioremediation efficiency after 56 days of monitoring with different treatment on the set up is given in a decreasing order as follows: (initial contamination value of 10525mg/kg) Cs+Chl (7700mg/kg; 73.15%) > control (Cs) contaminated without amendment of organisms (6345mg/kg 60.28%) >  and Us uncontaminated sediment 1969.96 mg/kg. The total hydrocarbon content (THC) of the treated setup decreased from (10525mg/kg initial contamination value) at the start of bioremediation to Cs+Chl (7700mg/kg: 73.15%) at the end of bioremediation. The highest count of microalgae (log10cfu/g) for each set up during the monitoring were as follows; day 0 Us (7.65) day14 Cs (7.63) day28 Us (7.70) day42 Cs+Chl (7.60) day56 Cs (7.30). It was observed that peak count was on day28 (7.70) and a decline was on day56 (7.30). The highest Hydrocarbon Utilizing Algae (Log10cfu/g) count for each set up during the monitoring were as follows; day 0 Cs+Chl (5.23) day 14 Cs+Chl (5.30) day28 Cs (5.23) day42 Cs+Chl (4.77) > day56 Cs (5.07). Decline was observed on day 42 and peak count was on day 14.

Conclusion: Results from the study revealed that Chlorella vulgaris is capable of degrading hydrocarbon components. There was a faster utilization of hydrocarbon by set up with Chlorella vulgaris than control.  Though incomplete removal of crude oil was observed in THC concentration value. This suggests that an improvement in the process is required. Such improvement could include biostimulation of the polluted sample or some chemical pretreatment of the sample. From the study, bioremediation can be said to be a viable and effective response to sediment contamination with crude oil.