Sol-Gel-Encapsulated Biofilms on Biochar Effectively Degrade PCBs and Extend Biodegradation Activity under Environmentally Relevant Conditions.

Attaching aerobic, PCB-degrading cells to carbon-based sorbent materials prior to sediment application is a feasible approach for bioaugmenting contaminated sediments to improve remediation strategies. Furthermore, encapsulation of attached cells with a novel, tailored sol-gel material can protect biofilms from unfavorable environmental conditions that interfere with biofilm stability and create stress that threatens long-term biofilm viability. We systematically evaluated biodegradation and sorption of three PCB congeners (PCBs 4, 18, and 52), quantified biphenyl dioxygenase gene (bphA) abundance and expression, and characterized sol-gel and biofilm integrity of sol-gel-coated PCB-degrading biofilms on black carbon over 45 days under environmentally relevant conditions. Sol-gel coatings did not significantly inhibit PCB sorption to the black carbon, and sol-gel-coated biofilms achieved 72-92% PCB removal within 45 days, comparable to uncoated biofilms (>91%). Although PCB biodegradation rates in uncoated biofilms were >5-fold higher than sol-gel-coated biofilms, sol-gel-coated biofilms maintained >2-fold higher bphA expression levels than uncoated biofilms after 45 days of treatment. Lower temperature (10 °C) decreased PCB biodegradation extent regardless of sol-gel coating but significantly increased (10-fold higher) bphA expression levels in sol-gel-coated biofilms. Salinity (20 g/L) negatively impacted bphA expression levels (>13-fold lower after 45 days) for all treatments. Our novel sol-gel design demonstrates dual benefits: to sorb PCBs from the environment to biofilms and provide carbon sources for PCB cometabolism, thereby protecting and supporting biofilms for potential extended activity in future field applications.