Biofilm formation vs. PCB adsorption on granular activated carbon in PCB-contaminated aquatic sediment

Abstract

Purpose: Granular activated carbon (GAC) that is both an efficient PCB adsorbent and a good growth support for microorganisms is considered suitable for in-situ remediation of PCB-contaminated aquatic sediments. Here the potential competition between biofilm formation and PCB (Aroclor 1260) adsorption on GAC in a PCB-contaminated aquatic sediment is investigated. Materials and methods: GACs, both coated and uncoated with biofilm or PCBs, were incubated with sediment. Each was monitored for biofilm development and PCB adsorption by a) cryo-scanning electron microscopy, b) real-time quantitative PCR analysis of the 16S rRNA, c) T-RFLP (Terminal Restriction Fragment Length Polymorphism), and d) chemical analysis, respectively. Results and discussion: Biofilm formation on the GAC by the sediment's bacteria was rapid and occurred in three stages: initial adherence of discrete bacteria; an increase in biomass associated with a shift in bacterial diversity; and exopolymeric matrix production. The density and biodiversity of the multispecies biofilm depended on the biofilm's age. The addition of Aroclor 1260 to the sediment resulted in a decrease of the biofilm biomass, whereas Aroclor 1260 previously adsorbed on the GAC prior to contact with the sediment did not affect the biofilm biomass or its formation dynamics. Similarly, a biofilm previously developed on the GAC did not significantly decrease PCB adsorption, although contact of the GAC with the sediment did hamper adsorption of the higher chlorinated PCB congeners. Conclusions: A mature multispecies bacterial biofilm developed in one month on GAC in contact with aquatic sediment does not hamper PCB adsorption, and PCB adsorption does not affect biofilm formation. Those findings are important for the application of remediation strategies.