Groundwater remediation using an enricher reactor-permeable reactive biobarrier for periodically absent contaminants

A tailored permeable reactive bio-barrier for in situ groundwater remediation: removal of 3-chlorophenol as a case study

The present study explored bacterial aerobic biodegradation of reduced carbon-contaminants (RCC) in a pilot system mimicking remediation of a saturated aquifer in a permeable reactive biobarrier (PRBB). Bioaugmentation was performed with a pure culture of Pseudomonas putida macro-encapsulated in a cellulose-acetate porous envelope and integrated transversely to the flow trajectory of the fluid in the biobarrier and compared with controls without capsules. The macro-encapsulation technique applied allowed the incorporation of a built-in nutrient core for the slow release of macronutrients, i.e. N, P, instead of exogenous nutrients supply. 3-Chlorophenol (3CP) at a concentration range of 350-500 mg/L was chosen as an RCC model compound. The findings indicate efficient 3CP biodegradation during the PRBB operation with a similar degree of transformation (76 ± 2% and 72 ± 2%) and mineralization (55 ± 4% vs. 49 ± 3%) for exogenous and built-in nutrients supply, respectively. The extent of dechlorination in both cases (54 ± 10% vs. 40 ± 2%, respectively) followed mineralization rather than transformation, suggesting that Cl^- release took place in late transformation stages. Negligible decontamination was observed in the control system without bioaugmentation. Concluding, tailored PRBB with macro-capsules incorporating a built-in nutrient core to support bacterial growth presents a significant environmental advantage controlling excess nutrients release required in bioremediation of oligotrophic systems.

Enricher reactor--permeable reactive biobarrier approach for removing a mixture of contaminants with substrate interactions

A laboratory-scale enricher reactor (ER) - permeable reactive biobarrier (PRBB) system was studied to address performance loss of a PRBB due to substrate interactions among a mixture of benzene, toluene, ethylbenzene, and xylene (BTEX) in groundwater, when the mixture reappeared after a 10-day absence period. Toluene and BTEX as an inducer in ER were compared to investigate toluene as a potential single inducer in ER. PRBBs without ER augmentation experienced performance losses ranging from 11% to 35% for PRBBs initially inoculated with toluene degraders and 22% to 33% for PRBBs initially inoculated with BTEX degraders. Bacterial communities changed substantially in these PRBBs after the absence period, which could contribute to the performance losses. PRBBs augmented with toluene degraders overcame the inhibition interaction between benzene and toluene, and showed a superior removal performance for toluene degradation suggesting that toluene can be used as a single inducer in an ER.