CULTURE TESTING FOR A DUAL-BIOFILM REACTIVE BARRIER FOR TREATMENT OF CHLORINATED BENZENES IN WETLAND GROUNDWATER AND SEDIMENT

Two cultures — anaerobic dechlorinating culture WBC-2 and a native aerobic culture (15B)— are being tested for use in a dual-biofilm reactive barrier for treatment of chlorinated benzenes in wetland groundwater and sediment at a Delaware Superfund site. The permeable barrier will use granular activated carbon (GAC) as a sorbent to modulate the high concentrations of tri-, di-, and mono-chlorobenzene in discharging groundwater and as a delivery and growth matrix for the cultures to allow simultaneous biodegradation under different redox regimes. Growth of the cultures on GAC significantly altered their microbial community composition compared to cultures grown without GAC, as shown by 16S rRNA Illumina iTag sequencing. For WBC-2-seeded GAC, the relative abundances of two major groups that contain dechlorinating bacteria were altered: Dehalococcoides significantly increased while Chloroflexi (Anaerolineae) significantly decreased. The 15B aerobic culture is dominated by the Betaproteobacteria group Burkholderiales, which contains known chlorobenzene degraders and nearly doubled in abundance when cultured on GAC. The Alphaproteobacteria groups Caulobacter and Rhizobiales showed an approximately 50% decrease in abundance when grown on GAC. However, no complete loss of major Bacteria groups was observed in either culture after seeding on GAC. Pseudomodales were a significant population in the 15B-seeded GAC community, and two Pseudomonas species were isolated from the 15B culture when grown on a mixture of chlorobenzenes. The Pseudomonas isolates are closely related to organisms known to degrade chlorobenzenes. Anaerobic and aerobic microcosms with the WBC-2 and 15B cultures, respectively, seeded on GAC and mixed with sand (6% GAC by dry weight) removed about 85% of amended 1,2- and 1,4-dichlorobenzene in 24 hours. Comparison of GAC-seeded microcosms to controls without the biofilms over 11 days indicated that removal occurred by biodegradation in addition to sorption. Microcosm and column experiments with both cultures seeded on GAC are underway. This study will determine the feasibility of using the two cultures to enhance both the anaerobic and aerobic biodegradation processes that can naturally co-occur in wetlands and other areas of groundwater-surface water interaction.