Remediation of Polychlorinated Biphenyls (PCBs) in Contaminated Soils and Sediment: State of Knowledge and Perspectives

Polychlorinated biphenyls (PCBs) are one of the persistent organic pollutants (POPs) used worldwide between the 1930 and 1980s. Many PCBs can still be found in the environment such as in soils and sediments, even though their use has been heavily restricted. This review summarizes the most frequent remediation solutions including, phytoremediation, microbial degradation, dehalogenation by chemical reagent, and PCBs removal by activated carbon. New insights that emerged from recent studies of PCBs remediation including supercritical water oxidation, ultrasonic radiation, bimetallic systems, nanoscale zero-valent iron based reductive dehalogenation and biofilm covered activated carbon, electrokinetic remediation, and nZVI particles in combination with a second metal are overviewed. Some of these methods are still in the initial development stage thereby requiring further research attention. In addition, the advantages and disadvantages of each general treatment strategy and promising technology for PCBs remediation are discussed and compared. There is no well-developed single technology, although various possible technologies have been suggested. Therefore, the possibility of using combined technologies for PCB remediation is also here investigated. It is hoped that this present paper can provide a basic framework and a more profound prospect to select successful PCB remediation strategies or combined technologies

Biofilms at work: Bio-, phyto- and rhizoremediation approaches for soils contaminated with polychlorinated biphenyls

Organohalide contaminants such as polychlorinated biphenyls (PCBs) have been released into the environment for decades due to anthropogenic activities, but are also naturally produced in small amounts through volcanic eruptions and geochemical processes. Although toxic to humans and other organisms, the natural production of these compounds has resulted in the evolution of naturally occurring organohalide-respiring bacteria that possess the enzymes necessary to degrade PCB compounds to non-toxic products. The efficiency of PCB degradation can be improved by facilitating the formation of organohalide-respiring biofilms. During biofilm colonization on a surface or interface, bacteria are encased in an extracellular polymeric substance (EPS) or “slime,” which allows them to share nutrients and remain protected from environmental stresses. Effective bioremediation of PCBs involves facilitation of biofilm growth to promote cooperation between bacteria, which can be further enhanced by the presence of certain plant species. This review aims to give an overview of biofilm processes involved in the detoxification of PCBs including anaerobic and aerobic PCB degradation by bacteria as well as the ability of plants to stimulate microbial activity and degradation (rhizoremediation and phytoremediation)

Spatial Distribution of PCB Dechlorinating Bacteria and Activities in Contaminated Soil

Soil samples contaminated with Aroclor 1260 were analyzed for microbial PCB dechlorination potential, which is the rate-limiting step for complete PCB degradation. The average chlorines per biphenyl varied throughout the site suggesting that different rates of in situ dechlorination had occurred over time. Analysis of PCB transforming (aerobic and anaerobic) microbial communities and dechlorinating potential revealed spatial heterogeneity of both putative PCB transforming phylotypes and dechlorination activity. Some soil samples inhibited PCB dechlorination in active sediment from Baltimore Harbor indicating that metal or organic cocontaminants might cause the observed heterogeneity of in situ dechlorination. Bioaugmentation of soil samples contaminated with PCBs ranging from 4.6 to 265 ppm with a pure culture of the PCB dechlorinating bacterium Dehalobium chlorocoercia DF-1 also yielded heterologous results with significant dechlorination of weathered PCBs observed in one location. The detection of indigenous PCB dehalorespiring activity combined with the detection of putative dechlorinating bacteria and biphenyl dioxygenase genes in the soil aggregates suggests that the potential exists for complete mineralization of PCBs in soils. However, in contrast to sediments, the heterologous distribution of microorganisms, PCBs, and inhibitory cocontaminants is a significant challenge for the development of in situ microbial treatment of PCB impacted soils

Dehalorespiration with Polychlorinated Biphenyls by an Anaerobic Ultramicrobacterium▿

Anaerobic microbial dechlorination is an important step in the detoxification and elimination of polychlorinated biphenyls (PCBs), but a microorganism capable of coupling its growth to PCB dechlorination has not been isolated. Here we describe the isolation from sediment of an ultramicrobacterium, strain DF-1, which is capable of dechlorinating PCBs containing double-flanked chlorines added as single congeners or as Aroclor 1260 in contaminated soil. The isolate requires Desulfovibrio spp. in coculture or cell extract for growth on hydrogen and PCB in mineral medium. This is the first microorganism in pure culture demonstrated to grow by dehalorespiration with PCBs and the first isolate shown to dechlorinate weathered commercial mixtures of PCBs in historically contaminated sediments. The ability of this isolate to grow on PCBs in contaminated sediments represents a significant breakthrough for the development of in situ treatment strategies for this class of persistent organic pollutants

Polychlorinated Biphenyls (PCBs) in Dissolved and Particulate Phases of Urban Stormwater before and after Bioretention Treatment

The presence of dissolved polychlorinated biphenyls (PCBs) and PCBs associated with particle influent and effluent samples from a bioretention stormwater control measure was studied. The Kaplan–Meier survival procedure was used to sum PCB congeners for concentrations below detection limits. For influent samples, concentrations of dissolved PCBs ranged from 66 ± 17 to 752 ± 23 ng/L, and the concentration decreased by 66–93% in the effluent after bioretention treatment to 20.8 ± 5.1 to 53.0 ± 10.0 ng/L. The concentrations of total PCBs in the particulate phase of the influent ranged from 176 to 649 ng/g (median of 316 ng/g). The particle-based PCB concentration decreased by 99.6% in one event due to bioretention treatment. The overall PCB load reduction via bioretention treatment is estimated at 82–85%. 3,3′-Dichlorobiphenyl (PCB 11) was detected in all stormwater influent samples and constituted 3–20% of the total dissolved PCB concentration. Particulate concentrations of PCBs ranged from only 3 to 15% of the total PCB mass in stormwater samples, showing that dissolved PCBs are important and must be considered in stormwater loads. Bioretention systems are effective infrastructure facilities for the reduction of PCB loads, although additional treatment may be needed to address dissolved PCBs

Assessment of PCB Contamination, the Potential for in Situ Microbial Dechlorination and Natural Attenuation in an Urban Watershed at the East Coast of the United States

Sediment contamination is a major environmental issue in many urban watersheds and coastal areas due to the potential toxic effects of contaminants on biota and human health. Characterizing and delineating areas of sediment contamination and toxicity are important goals of coastal resource management in terms of ecological and economical perspectives. Core and surficial sediment samples were collected from an industrialized urban watershed at the East Coast of the United Stated and analyzed to evaluate the PCB contamination profile and toxicity resulting from dioxin-like PCBs as well as reductive dechlorination potential of indigenous PCB halorespiring bacteria through dechlorination activity assays. To support the experimental results an anaerobic dechlorination model was applied to identify microbial dechlorination pathways. The total PCB concentration in core samples ranged from 3.9 to 225.6 ng/g·dry weight (dw) decreasing with depth compared to 353.2 to 1213.7 ng/g·dw in surficial samples. The results of this study indicated an increase in PCB contamination over the last century as the industrial activity intensified. The toxicity resulting from dioxin-like PCBs was reduced up to 94% in core samples via 21 pathways resulting from the dechlorination model. Dechlorination rates in surficial sediment were between 1.8 and 13.2 · 10−3 mol% PCB116/day, while lower rates occurred in the core sediment samples. Dechlorination was achieved mainly through meta followed by para dechlorination. However, the rarer ortho dechlorination was also observed. Detection of indigenous PCB dechlorinating bacteria in the sediments and reduction of toxicity indicated potential for natural attenuation when point and nonpoint source PCBs in the urban watershed are controlled and PCB loading reduced

Electricity generation from wastewater using a floating air cathode microbial fuel cell

Recovering energy from wastewater is an important frontier of environmental engineering and science. Of the many proposed strategies, microbial fuel cells (MFCs) provide a direct path to electricity generation. Here, we report MFCs equipped with floating carbon-cloth air cathodes modified with manganese oxide (MnOx) or Platinum nanoparticle oxygen reduction catalysts. The performances of these MFCs were compared using domestic wastewater in a configuration suitable for electricity generation from primary settling tanks. The open-circuit voltages of the Mn-MFCs decreased gradually over time while those of the Pt-MFCs remained stable indicating that Mn leaching from the electrodes was occurring. Over 90% of the MnOx catalyst was solubilized from the cathode surface within the first two weeks of operation. Initially, the Pt-MFCs did not generate as high of a current density as MnOx but after 55 days, Pt-MFCs had a higher average maximum power density during polarization than Mn-MFCs: 65.4 ± 4.6 and 48.4 ± 10.16 mW/m2 (based on anode geometric surface area), respectively. These results show the importance of evaluating promising alternative MFC cathode catalyst like MnOx in actual wastewater since it is difficult to predict how new catalysts designed to decrease cost yet increase the efficiency of the reduction of oxygen will respond in real-world wastewater applications. Keywords: Microbial fuel cell, Biofilm, Wastewater, Energy recovery, Catalys