Removal Efficiencies Of Polychlorinated Biphenyls Research Articles

Influence of transition metal catalysts on the decomposition product distribution of PCBs and PCDD/Fs

In this study, reliable and stable polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) generation systems were used to investigate catalyst performance. The distribution characteristics of PCBs and PCDD/Fs after reaction were evaluated under different simulated flue gas conditions using NiO- and MnO2-loaded γ-Al2O3 and ZSM-5 catalysts. The results showed that the active metal of the catalyst affected mainly the decomposition efficiency, the substrate type affected the distribution characteristics of PCBs, and both the active metal and substrate type jointly determined the fingerprint distribution characteristics of PCBs. Moreover, there was an apparent marginal effect of the active metal loading on the same catalyst and the decomposition efficiency of the pollutants. In the temperature range of 100–350 °C, temperature variation had little effect on the removal efficiency of PCBs, but the gas–solid phase distribution characteristics of the pollutants changed significantly, and large amounts of di- and tri-CBs were generated in the products at 200 °C. A small amount of water generated hydrogen via the water–gas shift reaction at medium temperature, which promoted the hydro-dechlorination reaction of the chlorinated organics. However, excess water in the substrate gas competes with the pollutants for adsorption sites and reduces the reaction activity of the catalyst.

Chemical remediationandadvanced oxidation process of polychlorinated biphenyls in contaminated soils: a review.

Polychlorinated biphenyls (PCBs) are synthetic organic compounds ubiquitously distributed worldwide due to their persistence, long-range atmospheric transport, and bioaccumulation. Owing to teratogenic properties, PCBs are a global environmental problem. Different physical, biological, and chemical techniques are utilized for the remediation of PCBs. This review paper discusses the recent development in photocatalytic and chemical techniques for the remediation of PCBs in contaminated soils. In particular, the photocatalytic degradation of PCBs combined with soil washing, Fe-based reductive dichlorination, and advanced oxidation process (Fenton advance oxidation and persulfate oxidation) is discussed and reviewed in detail. The review suggested that advanced oxidation is an efficient remediation technique with 77-99% of removal efficiency of PCBs. Persulfate oxidation is the most suitable technique which could work at normal environmental conditions (such as pH, temperature, soil organic matter (SOM), etc.). Different environmental factors such as pH, temperature, and SOM affect the Fe-based reductive dechlorination and Fenton advance oxidation techniques. The surfactants and organic solvents used in soil washing combined with photocatalytic degradation affect the degradation capability of these techniques. This review will contribute to PCBs degradation by the detailed discussion of development in chemical technique future perspective and research needs.

Optimization using the response surface methodology for adsorption of polychlorinated biphenyls (PCBs) from transformer oil by magnetic CMCD-Fe3O4@SiO2 nanoparticles

The main objective of this work was to synthesis a novel magnetic nanoparticles functionalized with β-cyclodextrin and use it to refine transformer oil contaminated with high concentration of PCBs. Carboxymethyl-β-cyclodextrin modified Fe3O4@SiO2 magnetic nanoparticles (CMCD-Fe3O4@SiO2) were fabricated by grafting onto the core-shell silica magnetic nanoparticles surface using carbodiimide. The successful synthesis of nanocomposites was characterized by FTIR, XRD, VSM, SEM, TEM, VSM, TGA and EDX analysis. Hereinafter, the application of response surface methodology (RSM) based on the central composite design (CCD) was employed for optimization of the interactive effects of the three main variables on the removal efficiency of PCBs. A quadratic model was applied as a final model to measure the adequacy and the significance of the individual and interactive effects of variables via analysis of variance. The design matrix under the optimum conditions exhibited that the maximum PCBs removal of 82% was attained to be at adsorbent dosage, contact time and temperature of 10 mg/mL, 30 min, and 50 °C, respectively. The obtained results revealed that the adsorbent dosage is known as the key operating parameter (P < 0.0001) affecting PCB removal efficiency. Thermodynamic parameters (ΔH0 > 0, ΔG0 > 0, ΔS0 > 0) were confirmed that the adsorption process was nonspontaneous and endothermic and assess physical phenomena occurring on the surface of adsorbent. The experimental results were proposed that the as-synthesized β-cyclodextrin -modified magnetic nanoparticles could be an ideal candidate for purification of PCB compounds from contaminated transformer oil owing to its simple process and rapid separation and good reusability after five times.

Evaluation of the Removal Efficiency of PCBs from Five Wastewater Treatment Plants in Jordan

The levels of persistent organic pollutants, polychlorinated biphenyls (PCBs), were investigated in influent, effluent, and sludge of five wastewater treatment plants (WWTPs) in Jordan. Concentrations of 12 dioxin-like PCBs were determined. The extraction of PCBs from wastewater samples was done by solvent extraction using dichloromethane/hexane 1:1 mixture. The concentrated extracts were sequentially subjected to multilayer silica gel, basic alumina, and florisil chromatography columns for further cleanup. Sludge samples were extracted in a Soxhlet apparatus, using petroleum ether. PCB determination has been completed using gas chromatography equipped with mass spectrometry detector. The total concentrations of PCBs in influent samples ranged from 34.65 to 228.3 ng L−1, in effluent samples from 16.1 to 123.88 ng L−1, and in the sludge samples from 51.1 to 223.85 ng kg−1. In three of the investigated wastewater treatment plants, the amount of PCBs in sludge exceeded the limit proposed by European Union legislation. The total removal efficiencies of the total PCBs were evaluated and ranged from 34.8 to 88.1% for Aqaba and Abu-Nsair WWTP, respectively. The values of incremental lifetime cancer risk due to exposure to PCBs in sludge samples were also estimated in this study, and they ranged from 2.415 × 10−7 to 1.193 × 10−6 for adults. The number of people suspected to have cancer due to the exposure to the sludge of the WWTPs in Jordan is between 4 and 20 out of ten million.

Effects of the presence of nanoscale zero-valent iron on the degradation of polychlorinated biphenyls and total organic carbon by sediment microbial fuel cell

The degradation of polychlorinated biphenyls (PCBs) and total organic carbon (TOC) by sediment microbial fuel cell (SMFC) with/without nanoscale zero-valent iron (NZVI) addition was investigated. It was found that the combined application led to the highest removal efficiencies of PCBs (37.55 ± 1.11%) and TOC (49.72 ± 1.54%) in all circumstances and produced a higher power density (108.89 mW/m2) and a corresponding lower internal resistance (264 Ω) than operation employing SMFC only. The TOC removal efficiency and the total production of electricity were linear. High-throughput sequencing of anodic microbial communities indicated that the electrode participation can increase the abundance of electrogenic bacteria (Geobacter and Pseudomonas) and the NZVI addition can reduce the oxidation reduction potential of the system and therefore enrich some bacteria (Longilinea and Desulfofustis) beneficial to the degradation of organic matter.

Remediation of PCB-contaminated soil using a combination of mechanochemical method and thermal desorption.

The combination of mechanochemical method and thermal desorption for remediating polychlorinated biphenyls (PCBs) in contaminated soil was tested in this study. The effects of grinding time and heating time on PCB removal efficiency were investigated. The contaminated soil, mixed with CaO powder at a weight ratio of 1:1, was first ground using a planetary ball mill. After 4h of grinding, the total PCB concentration and its toxic equivalence quantity (TEQ) decreased by 74.6 and 75.8%, respectively. Then, after being heated at 500°C for 60min, the residual PCBs in mechanochemical + thermal treated soil decreased to 247ng/g, resulting in a removal efficiency of 99.95%. The removal effect can be promoted by longer grinding time and heating time; however, increased energy consumption was inevitable. The combination of grinding time and heating time should be optimized in a practical remediation process.

Biodegradation of Polychlorinated Biphenyls Using a Moving‐Bed Biofilm Reactor

As persistent organic pollutants, polychlorinated biphenyls (PCBs) are rarely degraded in nature environment. Biodegradation is an effective method for the removal of PCBs from contaminated wastewater. In this study, an assessment of the performance of a combined moving‐bed biofilm reactor and a membrane filtration system (MBBR‐MF) for the treatment of PCB‐containing wastewater was performed. Simulated wastewater containing PCB77 was treated in an MBBR system. PCB removal efficiency was investigated at different sections of the combined MBBR‐MF system. The results showed that the removal efficiencies for PCB77 in the anaerobic MBBR were 73 and 84.4% in the aerobic section. The possible biodegradation products were investigated. The results of gas chromatography–mass spectrometry indicate that the PCBs were converted into small molecules that were easily mineralized under aerobic conditions. Thus, the MBBR technology could have potential for biodegradation use of PCB‐contaminated wastewater.

아임계수 분해를 이용한 난분해성 물질로 오염된 토양의 정화 연구

This study examined remediation of soil contaminated with polychlorinated biphenyls (PCBs) and other persistent organic pollutants by using subcritical water. Our results showed that removal efficiency of PCBs from soil and treatment temperature were linearly proportional under subcritical conditions. The removal efficiency as increased as reacting period increased. PCBs contaminating fine particles in soil were less effectively removed than those in entire contaminated soil. Reaction of the zero-valent iron and PCBs under subcritical condition produced dechlorinated product, where most of the PCBs were oxidised while little remained as dechlorinated. Other organic pollutants, such as TPH, BTEX, TCE/PCE, and chlorpyrifos, were removed by more than 90% at 300°C. Considering removal efficiency and identification of by-products, we suggest that subcritical water treatment may be effectively applied to soils contaminated with various persistent organic pollutants.

Hydrodechlorination of polychlorinated biphenyls in contaminated soil from an e-waste recycling area, using nanoscale zerovalent iron and Pd/Fe bimetallic nanoparticles

Soil pollution by polychlorinated biphenyls (PCBs) arising from the crude disposal and recycling of electronic and electrical waste (e-waste) is a serious issue, and effective remediation technologies are urgently needed. Nanoscale zerovalent iron (nZVI) and bimetallic systems have been shown to promote successfully the destruction of halogenated organic compounds. In the present study, nZVI and Pd/Fe bimetallic nanoparticles synthesized by chemical deposition were used to remove 2,2',4,4',5,5'-hexachlorobiphenyl from deionized water, and then applied to PCBs contaminated soil collected from an e-waste recycling area. The results indicated that the hydrodechlorination of 2,2',4,4',5,5'-hexachlorobiphenyl by nZVI and Pd/Fe bimetallic nanoparticles followed pseudo-first-order kinetics and Pd loading was beneficial to the hydrodechlorination process. It was also found that the removal efficiencies of PCBs from soil achieved using Pd/Fe bimetallic nanoparticles were higher than that achieved using nZVI and that PCBs degradation might be affected by the soil properties. Finally, the potential challenges of nZVI application to in situ remediation were explored.

Effect of temperature and particle size on the thermal desorption of PCBs from contaminated soil

Thermal desorption is widely used for remediation of soil contaminated with volatiles, such as solvents and distillates. In this study, a soil contaminated with semivolatile polychlorinated biphenyls (PCBs) was sampled at an interim storage point for waste PCB transformers and heated to temperatures from 300 to 600 °C in a flow of nitrogen to investigate the effect of temperature and particle size on thermal desorption. Two size fractions were tested: coarse soil of 420-841 μm and fine soil with particles <250 μm. A PCB removal efficiency of 98.0 % was attained after 1 h of thermal treatment at 600 °C. The residual amount of PCBs in this soil decreased with rising thermal treatment temperature while the amount transferred to the gas phase increased up to 550 °C; at 600 °C, destruction of PCBs became more obvious. At low temperature, the thermally treated soil still had a similar PCB homologue distribution as raw soil, indicating thermal desorption as a main mechanism in removal. Dechlorination and decomposition increasingly occurred at high temperature, since shifts in average chlorination level were observed, from 3.34 in the raw soil to 2.75 in soil treated at 600 °C. Fine soil particles showed higher removal efficiency and destruction efficiency than coarse particles, suggesting that desorption from coarse particles is influenced by mass transfer.

Surfactants-enhanced electrokinetic transport of xanthan gum stabilized nanoPd/Fe for the remediation of PCBs contaminated soils

Polychlorinated biphenyls (PCBs) in the environment pose long-term risk to public health because of their persistence and toxicity. In this study, a novel technology called EK+nano (electrokinetic technology combined with engineered nanoparticles) was used to remediate polychlorinated biphenyls (PCBs) contaminated soil. Three different surfactants (anionic surfactant – SDBS, nonionic surfactant – Brij35 and biosurfactant – rhamnolipid) for enhancing the solubilization of soil PCBs were applied separately with xanthan gum stabilized nanoPd/Fe. The stabilized nanoPd/Fe was injected in the compartment located 3cm from the anode chamber daily in EK tests. The results indicated that the surfactants addition enhanced the solubilization capacity of PCB28 significantly but did not affect the stability of xanthan gum–nanoPd/Fe suspension. The nanoparticles were successfully transported along with the soil column by EK, and apparent increase of Fe content was found toward the cathode. Higher electroosmotic flow favored the migration of nanoparticles, but the degradation was limited without addition of surfactant. Brij35–xanthan gum stabilized nanoPd/Fe gave the highest removal efficiency of PCBs, both in batch experiments and EK tests, in which the removal rates of approximately 50% and 20% were achieved, respectively. The functions of SDBS and rhamnolipid in soil PCBs removal were not significant in all tests.

Application of microwave-irradiated manganese dioxide in the removal of polychlorinated biphenyls from soil contaminated by capacitor oil

The removal of polychlorinated biphenyls (PCBs) from soil contaminated with capacitor oil, using microwave (MW)-irradiated manganese dioxide (MnO2), was examined under different conditions. The effects of different types of MnO2 added as oxidant, as well as the initial amount of water, MnO2, and sulphuric acid solution, were also investigated. The removal efficiencies for dichlorobiphenyls, trichlorobiphenyls, tetrachlorobiphenyls, pentachlorobiphenyls, hexachlorobiphenyls, heptachlorobiphenyls, and octachlorobiphenyls were approximately 95.9%, 82.5%, 52.0%, 71.6%, 62.5%, 28.6%, and 16.1%, respectively, by 800 W MW irradiation for 45 min with the assistance of 0.1 g δ-MnO2 and 0.2 mL water in 1.0 g severely PCB-contaminated soil (∑PCB=1560.82 mg/kg); meanwhile, the concentrations of Mn2+ ions detected were from 10.6±1.9 mg/kg at 0 min to 108.2±7.8 mg/kg after 45 min MW irradiation, indicating that MnO2 acted as not only a MW absorber but also an oxidizer. Removal efficiencies of PCBs from contaminated soil increased with increasing the amounts of water and MnO2 added. The type of MnO2 also affected the removal of PCBs, following an order of . The addition of low concentration of sulphuric acid (such as 1.0 mol/L) solution was favourable for the removal of low chloro-substituted PCBs, but the addition of more than 1.0 mol/L sulphuric acid reduced the removal of all PCBs. The pronounced removal of PCBs from contaminated soil in a short treatment time indicates that MW irradiation with the assistance of MnO2 is an efficient and promising technology for the remediation of PCB-contaminated soil.

PCBs 함유 변압기 절연유의 화학적처리

Practical disposal of transformer insulation oil laden with PCBs (polychlorinated biphenyls) by a chemical treatment has been studied in field work. The transformer insulation oil containing PCBs was treated by the required amounts of PEG (polyethylene glycol) and KOH, along with different reaction conditions such as temperatures and times. The reaction of PEG with PCBs under basic condition produces arylpolyglycols, the products of nucleophilic aromatic substitution. Removal efficiencies of PCBs in insulation oil before and after chemical treatment were examined. The removal efficiency of PCBs was very low at lower temperatures of 25 and <TEX>$50^{\circ}C$</TEX>. Under the reaction condition of PEG 600/KOH/<TEX>$100^{\circ}C$</TEX>/2hr, removal efficiency of PCBs was approximately 70%, showing completely removal of PCBs containing 7~9 chlorines on biphenyl frame which appear later than PCB IUPAC Number 183 (2,2',3,4,4',5',6-heptaCB) in retention time of GC/ECD. However, when increasing the reaction temperature and time to <TEX>$150^{\circ}C$</TEX> and 4 hours, removal efficiency of PCBs reached 99.99% without any formation of PCDDS/PCDFs during the process. Such reaction conditions were verified by several official analytical institutions. In studying the reaction of PEG with PCBs, it confirmed that the process of chemical treatment led to less chlorinated PCBs through a stepwise process with the successive elimination of chlorines.

Numerical simulations of the combustor for waste insulating oil containing polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are classified as persistent organic compounds and used in many industries because they are incombustible, heat resistant and electrical insulators. Owing to their strong toxicity and bioaccumulative nature, their transboundary movements are controlled by the Basel Convention and their levels are monitored by United Nations Environment Programme (UNEP). One of the most general methods for treating PCBs-containing waste is high-temperature decomposition; the removal efficiency of PCBs is 99.999% at over 1200°C for a retention time longer than 2 s. However, relatively low temperatures or low oxygen levels can produce highly toxic substances such as dioxins and dibenzofurans. Therefore, the reactor for the decomposition of PCBs should be very carefully designed. In this study, numerical simulations have been carried out to design a reactor for waste insulating oil containing PCBs. The flow patterns and temperature distributions of the gas in the reactor are examined. The path lines of the fluid particles are analyzed from the numerical results and the detention time of the PCBs-containing oil in the reactor is calculated. On the basis of this result, we try to scale up from a pilot plant to a commercial plant.

Adsorptive Micellar Flocculation as an Efficient Method for Processing Soil Extracts Containing Both Surfactant and Polychlorinated Biphenyls: Practical Demonstration

The main purpose of the paper is to share the results and experience from processing soil extracts containing a high concentration of both anionic surfactant and polychlorinated biphenyls (PCBs) by use of method the called adsorptive micellar flocculation. The method is similar to coagulation, but the mechanism is more complicated. The flocculants examined in the laboratory section involved ferric chloride, aluminium chloride, ferric sulfate, and aluminum sulfate. It was observed that ferric chloride provides the best PCB removal efficiency from the extract. Subsequently, two extracts obtained from the pilot-scale demonstration of the PCBs leaching from the soils by the surfactant solution were processed by this method. The volume of the extracts processed was several hundred liters. The method proved it can remove PCBs from all extracts with a very high efficiency (greater than 99.99%). The residual PCB concentrations in solution were less than 1 microg/L.

PCB and AOX removal in mesophilic and thermophilic sewage sludge digestion

In this study, a comparison of the biodegradation of adsorbed organic halogen compounds (AOX) and polychlorinated biphenyls (PCB) in thermophilic and mesophilic anaerobic digestion (seeded with waste activated sludge) at different hydraulic retention times (HRT 18, 22 and 26 days in the mesophilic digester and 8, 12, 18, 22 and 26 days in the thermophilic digester) was performed. Results obtained in this work showed an enhancement of both PCB and AOX biodegradation under thermophilic conditions. The total PCB removal efficiency was in the range of 59.4–83.5% under thermophilic conditions and 33.0–58.0% under mesophilic conditions. HRT played an important role in the digester performance since high working HRTs implied more reduction of the total PCB amount in the sludge. The total PCB content in the treated sludge under thermophilic conditions lied below the cut-off limit proposed in the 3rd draft of Directive presented to the European Commission [CEC, Working Document on Sludge (3rd Draft), Commission of the European Communities Directorate-General Environment, ENV.E.3/LM, Brussels, 27 April 2000]. Besides, a bioaccumulation of lightly chlorinated PCBs was detected in the mesophilic digester, which is in concordance with the theory that the PCBs are anaerobically biodegraded by means of a reductive dechlorination mechanism. On the other hand, the AOX removal efficiency was in the range of 40.4–50.3% for thermophilic conditions and 30.2–43.2% for mesophilic conditions. The AOX content in the treated sludge of both thermophilic and mesophilic digesters did not exceed the cut-off limit proposed in the 3rd draft [CEC, Working Document on Sludge (3rd Draft), Commission of the European Communities Directorate-General Environment, ENV.E.3/LM, Brussels, 27 April 2000]. Moreover, high HRTs promoted an improvement of the AOX removal capacity of the anaerobic digestion.

Bio-anaerobic treatability study for PCBs-contaminated oil

This study investigated the bio-treatability of PCB contaminated oil for the development of design and operational parameters for the bioreactor. Input of external carbon and nutrient source in the aqueous phase was found to be required for the treatment of polychlorinated biphenyls (PCBs)-contaminated oil. Addition of surfactant was investigated for the emulsification of oil to reduce interference of contact with microorganisms and PCBs. The ratio of surfactant to oil was empirically optimized to 1 : 1. The higher PCB removal efficiency was obtained at 30 days of hydraulic retention time (HRT) in the semi-batch reactor study without cell recycle. The removal efficiency measured in mixed liquor was maintained at over 85% on average at 32 +/- 2 degrees C and 30% at 22 +/- 2 degrees C. More than 0.2 g/l/d of the organic loading rate was suggested to be maintained for various PCB loading rates (0.02-0.6 mg-PCB/l/d). For high biomass retaining and easy collection of treated oil, an Anaerobic Sequencing Batch Reactor (ASBR) was investigated. The removal of Aroclor was observed as more than 50% in the oil phase with 3 days reaction time and about 40% in overall phases, i.e. oil, liquid, biomass phases at 22 +/- 2 degrees C. US EPA verification results on the process performance are included in this presentation.

The behaviour of polychlorinated biphenyls in the primary sedimentation process of sewage treatment: A pilot plant study

The behaviour of polychlorinated biphenyls (PCB) in the primary sedimentation stage of sewage treatment has been studied using a pilot scale primary sedimentation plant. The plant was operated at different hydraulic loadings, selected to cover the range expected during normal operation of a sewage treatment works. Concentrations of PCB in raw sewage were found to be in the low ng l −1 range and in the high ng l −1 range in primary sludges. A relationship between raw sewage PCB concentrations and variations in the raw sewage flow to the full-scale sewage treatment works was evident. Removal efficiencies of PCB were found to be highest at dry weather flow and lowest at three times dry weather flow, their removals being comparable to those of suspended solids. Mass balances of PCB and suspended solids in the treatment process have been calculated and the possible sources of error considered. Comparisons of the results have been made with those of previous studies. The implications of the presence of PCB in waste waters and sewage sludges for water re-use and sewage sludge disposal are discussed.