Dechlorination of polychlorinated biphenyl congeners by anaerobic microorganisms from river sediment

Efficient biostimulation of microbial dechlorination of polychlorinated biphenyls by acetate and lactate under nitrate reducing conditions: Insights into dechlorination pathways and functional genes

Microbial-catalyzed reductive dechlorination of polychlorinated biphenyls (PCBs) is largely affected by the indigenous sediment geochemical properties. In this study, the effects of nitrate on PCB dechlorination and microbial community structures were first investigated in Taihu Lake sediment microcosms. And biostimulation study was attempted supplementing acetate/lactate. PCB dechlorination was apparently inhibited under nitrate-reducing conditions. Lower PCB dechlorination rate and less PCB dechlorination extent were observed in nitrate amended sediment microcosms (T-N) than those in non-nitrate amended microcosms (T-1) during 66 weeks of incubation. The total PCB mass reduction in T-N was 17.6% lower than that in T-1. The flanked-para dechlorination was completely inhibited, while the ortho-flanked meta dechlorination was only partially inhibited in T-N. The 7.5 mM of acetate/lactate supplementation recovered PCB dechlorination by resuming ortho-flanked meta dechlorination. Repeated additions of lactate showed more effective biostimulation than acetate. Phylum Chloroflexi, containing most known PCB dechlorinators, was found to play a vital role on stability of the network structures. In T-N, putative dechlorinating Chloroflexi, Dehalococcoides and RDase genes rdh12, pcbA4, pcbA5 all declined. With acetate/lactate supplementation, Dehalococcoides grew by 1-2 orders of magnitude and rdh12, pcbA4, pcbA5 increased by 1-3 orders of magnitude. At Week 66, parent PCBs declined by 86.4% and 80.9% respectively in T-N-LA and T-N-AC compared to 69.9% in T-N. These findings provide insights into acetate/lactate biostimulation as a cost-effective approach for treating PCB contaminated sediments undergoing nitrate inhibition.

Effect of polyhydroxyalkanoates on the microbial reductive dechlorination of polychlorinated biphenyls and competing anaerobic respirations in a marine microbial culture

The effect of polyhydroxyalkanoates (PHAs) with different composition on the reductive dechlorination activity of a polychlorinated biphenyls (PCBs) dechlorinating marine microbial community and on the activity of sulfate-reducing (SRB) and methanogenic bacteria (MB), were investigated in marine sediment microcosms and compared with the main monomer, 3-hydroxybutyric acid (3HB). Despite PHAs were fermented more slowly than 3HB, all electron donors stimulated constantly sulfate-reduction, methanogenesis and, only transiently, PCB reductive dechlorination. No relevant differences were observed with different compositions of PHAs. According to electron balances, the majority of the supplied electrons (50 %) were consumed by SRB and to less extent by MB (9-31 %), while a small percentage (0.01 %) was delivered to OHRB. In the studied conditions PHAs were confirmed as potential slow‑hydrogen releasing compounds in marine environment but their fermentation rate was sufficiently high to mainly stimulate the competitors of organohalide respring bacteria for electron donors.

Reactivity of Pd/Fe bimetallic nanotubes in dechlorination of coplanar polychlorinated biphenyls

A new class of bimetallic materials based on palladium-decorated iron nanotubes is described that demonstrates high reactivity in dechlorination reactions. This high dechlorination efficiency was attributed to the high surface area to volume ratio of the hollow nanotubes structure. Herein, we evaluated the effect of different conditions, such as the nanotube size, and the palladium loading on the efficiency of the dechlorination of PCB 77, a model coplanar polychlorinated biphenyl (PCB), by the Pd/Fe bimetallic nanotubes system. The efficiency of the dechlorination was lowered by decreasing the tube diameter from 200 to 100 nm. In addition, the interior surface as well as the exterior surface of the as-synthesized Pd/Fe bimetallic nanotubes was found to contribute to the high efficiency of the dechlorination of PCB 77. The dechlorination of PCB 77 by Pd/Fe bimetallic nanotubes demonstrated small activation energy indicating diffusion controlled reaction. The as-prepared Pd/Fe bimetallic nanotubes showed extended lifetime activity when used in multiple dechlorination cycles.

Bacterial degradation of aromatic compounds

Aromatic compounds are among the most prevalent and persistent pollutants in the environment. Petroleum-contaminated soil and sediment commonly contain a mixture of polycyclic aromatic hydrocarbons (PAHs) and heterocyclic aromatics. Aromatics derived from industrial activities often have functional groups such as alkyls, halogens and nitro groups. Biodegradation is a major mechanism of removal of organic pollutants from a contaminated site. This review focuses on bacterial degradation pathways of selected aromatic compounds. Catabolic pathways of naphthalene, fluorene, phenanthrene, fluoranthene, pyrene, and benzo[a]pyrene are described in detail. Bacterial catabolism of the heterocycles dibenzofuran, carbazole, dibenzothiophene, and dibenzodioxin is discussed. Bacterial catabolism of alkylated PAHs is summarized, followed by a brief discussion of proteomics and metabolomics as powerful tools for elucidation of biodegradation mechanisms.