Enhanced removal of 2,4-dichlorophenol by coupling of Pd nanoparticles with biofilm

The persistence of chlorinated phenols in the environment is a major concern due to their persistence and toxicity, yet advanced remediation methods are actually limited. For instance, reductive dechlorination of chlorophenols utilizing palladium nanoparticles (PdNPs) supported on hydrogen-transfer membranes is not fully efficient. Here we tested the simultaneous microbial-driven and Pd-catalyzed reduction of 2,4-dichlorophenol (2,4-DCP) for removal rate, selectivity of reduction products, and optimal reaction conditions. For that we compared three hydrogen-based membrane reactors: a ‘Pd-biofilm reactor’ with Pd nanoparticles and a biofilm, with two controls: a ‘biofilm reactor’ with biofilm alone, and a ‘Pd-film reactor’ with Pd nanoparticles alone. Results show that the Pd-biofilm reactor removed 89.3% of total phenols, versus 15.7% for the biofilm reactor and 19.5% for the Pd-film reactor. The strong adsorption capacity of Pd-biofilm enhanced dechlorination. This elevated local chlorophenols concentration led to a 2–4 times higher reduction rate within Pd-biofilm compared to abiotic Pd-film. The presence of nitrate enhances phenol removal over Pd-biofilm but inhibited 2,4-DCP dechlorination. Similarly, high concentrations of nitrite, above 250 μM, inhibited 2,4-DCP reduction, predominantly in microbial processes rather than in catalytic reduction. Increasing hydrogen pressure facilitated the reduction of both 2,4-DCP and nitrate by Pd-biofilm, with an optimal pH of 7.0 for Pd-biofilm. The Pd-biofilm reactor decreased total phenols from 5–10 mg L-1 to the recommended threshold of 0.1 mg L-1 in 55 days, thus appearing as an efficient technique to clean chlorophenol-contaminated waters.