Abstract

The ability of acclimatized mixed culture from sewage waste sludge was tested to biodegrade (PAHs): naphthalene and phenanthrene each with a concentration of 300 mg/L. Sewage sludge was selected as an inexpensive source of mixed culture of microorganisms, usually available in large quantities in wastewater treatment plants. Two types of reactors were employed in the investigation: shake flask and roller bioreactors. Complete biodegradation of naphthalene and phenanthrene was achieved in the shake flask bioreactor after 13 and 14 days of treatment, respectively. The corresponding durations in the roller bioreactor were 11 and 12 days. The obtained results show that the said culture is capable of consuming PAHs as energy and carbon source and have a promising application in bioremediation of PAH contaminated environments. The biodegradation of naphthalene was enhanced when using the roller bioreactor compared to its biodegradation in the shake flask bioreactor. The microorganisms’ specific growth rate was raised from 0.014 to 0.022 h^-1 due to the enhanced mixing in the roller bioreactor. No enhancement was observed for phenanthrene biodegradation when using the roller bioreactor: the microorganisms’ specific growth rate was equal to 0.016 h^-1 for the shake flask bioreactor compared to 0.012 h^-1 for the roller bioreactor. Logistic models were employed for the description of the microorganisms’ growth and the PAHs degradation in both shake flask and roller bioreactor. Additionally, second order inhibition model was used to describe the possible inhibitions. The results obtained from the models well-matched the biodegradation experimental data with R² of more than 97%.

Keywords: Naphthalene; Phenanthrene; PAHs; Roller bioreactor; Shake flask reactor