ETBE and MTBE are used as oxygenate gasoline additives in petrol. In groundwater, the substances are mobile and poorly degradable (especially anaerobically). Under oxygen-rich conditions MTBE and ETBE can be biodegraded via TBA into harmless end products. Various bacteria are involved in this degradation. At an industrial site in Rotterdam Arcadis is currently using a biosparge system to stimulate aerobic degradation of MTBE, ETBE and TBA.
To gain insight into whether the biosparge screen actually stimulates this biodegradation, Arcadis asked Orvion to screen contaminated groundwater that is directly and indirectly influenced by the biosparge screen for:
We used ORVIdecode analyses to provide insight into the diversity of the bacterial population in both samples. The results show that oxygen is present in the groundwater (aerobic or microaerophilic). It is unlikely that conditions in the groundwater are anaerobic, since no strictly anaerobic bacteria are predominant in the groundwater. In one sample microaerophilic bacteria are predominantly present (iron oxidising and sulphur oxidising bacteria).
In the other sample, aerobic ammonium oxidising bacteria in particular are most dominant. Furthermore, on the basis of the results of the ORVIdecode analysis it appears that the potential for degradation of MTBE, ETBE and/or TBA is present in both groundwater samples. Two specific species that are related to MTBE, ETBE and TBA degradation have been demonstrated, namely Methylibium petroleiphilum and Variovorax paradoxus.
In short, the DNA screening shows that the correct aerobic conditions are present in the soil and that there is a suitable bacterial population for degradation. The next step is to measure the activity of the biomass and to map the area affected by the biosparging. This allows the biosparge system to be optimised for the most effective remediation possible.
Paul Appeldoorn is a Civil Engineer. His ambition is to solve problems. New biotechnologies make it possible to look at soil remediation, water treatment or industrial processes with fresh eyes. But the technology only works if the problem is dissected and there is a clear financial advantage for the customer. Keep questioning until the core of the problem has been achieved and be honest about what works and what does not work.