Para-Chlorophenol (4-CP) Removal by a Palladium-Coated Biofilm: Coupling Catalytic Dechlorination and Microbial Mineralization via Denitrification

Rapid dechlorination and full mineralization of para-chlorophenol (4-CP), a toxic contaminant, are unfulfilled goals in water treatment. Means to achieve both goals stem from the novel concept of coupling catalysis by palladium nanoparticles (PdNPs) with biodegradation in a biofilm. Here, we demonstrate that a synergistic version of the hydrogen (H-2)-based membrane biofilm reactor (MBfR) enabled simultaneous removals of 4-CP and cocontaminating nitrate. In situ generation of PdNPs within the MBfR biofilm led to rapid 4-CP reductive dechlorination, with >90% selectivity to more bioavailable cyclohexanone. Then, the biofilm mineralized the cyclohexanone by utilizing it as a supplementary electron donor to accelerate nitrate reduction. Long-term operation of the Pd-MBfR enriched the microbial community in cyclohexanone degraders within Clostridium, Chryseobacterium, and Brachymonas. In addition, the PdNP played an important role in accelerating nitrite reduction; while NO3- reduction to NO2- was entirely accomplished by bacteria, NO2- reduction to N-2 was catalyzed by PdNPs and bacterial reductases. This study documents a promising option for efficient and complete remediation of halogenated organics and nitrate by the combined action of PdNP and bacterial catalysis.