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

Abstract 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.