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Abstract Polychlorinated biphenyls (PCBs) cause serious impacts on the environment and organisms, due to their hypertoxicity, thermal stability and persistence. This study investigated the effects of temperature, reaction time and total flow rate on the low-temperature catalytic decomposition of Aroclor 1254. A modified iron-exchange method was adopted because it allows higher metal loading rates than the traditional impregnation method. We used this method to prepare three active carbon supported Fe/Ni bimetallic catalysts with different Fe/Ni molar ratios. The results indicated that the Fe/Ni bimetallic catalysts showed great potential in Aroclor 1254 decomposition. Among Fe/Ni molar ratios, Fe/Ni-1/3-C demonstrated the strongest performance with a decomposition efficiency greater than 90% even at the relatively low temperature of 200 °C. Thermodynamic analysis confirmed that the dechlorination of Aroclor 1254 over Fe/Ni-1/3-C obtained the minimum activation energy of 8.0 kJ/mol. Aroclor 1254 was decomposed rapidly over Fe/Ni-1/3-C, with a total decomposition efficiency of 83.4% at 10 min and 93.8% at 30 min. The kinetics analysis indicated a stepwise dechlorination of Aroclor 1254 over Fe/Ni-1/3-C. In addition, the total flow rate indicated a negative effect on the decomposition of Aroclor 1254 due to the decreased retention time. Graphical abstract Unlabelled Image Highlights • Aroclor 1254 can be decomposed efficiently over AC-based Ni-Fe bimetallic catalyst. • Decomposition efficiency of Aroclor 1254 was over 93% at low temperature of 250 °C. • Fe/Ni-1/3-C was the most potential for Aroclor 1254 degradation at 200–250 °C. • The flow rate of carrier gas showed less effect on Aroclor 1254 degradation. • Aroclor 1254 was dechlorinated stepwise over Fe/Ni-1/1-C by kinetics analysis. [ABSTRACT FROM AUTHOR]

Abstract Bimetallic catalysts supported on activated carbon (AC) with high metal loadings were prepared by an ion-exchange method. AC-supported Ni-Cu, Ni-Zn and Ni-Pd bimetallic catalysts were used to decompose Aroclor 1254, which is one of the most commonly used commercial mix of polychlorinated biphenyls. Characterization by scanning electron microscopy and energy-dispersive X-ray analysis showed that the metals were uniformly distributed on the surfaces and inside the catalysts. The efficiencies of Aroclor 1254 decomposition were measured at different reaction temperatures and times. With increasing temperature, the catalytic activities increased and the activation energies of the reactions decreased, resulting in higher decomposition efficiencies. At 300 °C in a nitrogen atmosphere, Aroclor 1254 decomposition efficiencies of 99.3%, 99.4% and 99.5% were achieved for reactions with Ni-Cu/C, Ni-Zn/C and Ni-Pd/C, respectively. The kinetics and pathway of the decomposition reaction were discussed, and we concluded that the reactivity of the chlorine atoms located on the benzene rings followed the order para-position > meta-position > ortho-position. The PCBs were dechlorinated stepwise to form the final biphenyl product. The design concept and synthetic strategy developed in this study are of great significance in the disposal of chlorinated organic compounds, for use with the existing adsorption technology of AC. Graphical abstract Unlabelled Image Highlights • AC-supported bimetallic catalysts were prepared using an ion-exchange method. • Below 300 °C, Ni-Cu/C decomposed Aroclor 1254 more efficiently than Ni-Zn/C or Ni-Pd/C. • Up to 300 °C, all the catalysts can decompose Aroclor 1254 with an efficiency >99%. • PCBs are dechlorinated stepwise to form the final biphenyl product. [ABSTRACT FROM AUTHOR]

Commercial chlorinated paraffins (CPs) are a source of CPs in the environment, and clarification of the different CP groups present in commercial products is important for source characterization. Resolving CP congener groups is hindered by the complex CP compositions of commercial products. We used comprehensive two-dimensional gas chromatography coupled with electron capture negative ionization high-resolution time-of-flight mass spectrometry to profile 57 C 8 − C 17 CP congener groups in 18 CP-42, CP-52, and CP-70 commercial products. Very short-chain CPs (vSCCPs), including C 8 Cl 5 – 8 and C 9 Cl 5 – 9 CPs, and other chlorinated aromatic compounds were identified in the commercial products. The mass fractions of total vSCCPs, short-chain CPs (SCCPs) and medium-chain CPs (MCCPs) in the commercial products ranged from 0.02% to 3.61%, 0.75% to 51.4%, and 0.39% to 69.1%, respectively. Two-dimensional hierarchical cluster analysis with a heat map plot highlighted variations in the C 8 − C 17 CP congener group patterns among different commercial CP formulations. The principal component analysis results indicated that commercial CPs products might be important contributors to vSCCPs, SCCPs, and MCCPs in various environmental matrices. This study provides comprehensive and well-resolved compositional data for CPs in commercial products, which will be helpful for CP source characterization. Unlabelled Image • Mass fractions and profiles of 57 C 8 − C 17 CPs were resolved by GC × GC–ECNI-HRTOFMS. • vSCCPs including C 8 Cl 5 – 8 and C 9 Cl 5 – 9 CPs were identified in commercial products. • C 8 − C 17 CP congener group abundances varied among different CP-52 products. • Source association of C 8 − C 17 CPs were found between CP-52 and environment samples. [ABSTRACT FROM AUTHOR]

In this study, the reforming of toluene, as a surrogate for tar, was investigated in plasma-alone (PA) and plasma-catalytic (PC) systems. The effects of feed gas oxygen content (O 2 /(O 2 + N 2) = 0, 3, 12, 21, or 30 vol%) and the discharge power (30, 75, or 90 W) on toluene conversion, the selectivity of syngas (H 2 + CO), and undesirable liquid by-products were evaluated using the PA system. A maximum toluene conversion of 87.9% and a minimum selectivity of undesirable liquid by-products of 0.53% for ethylbenzene, and 1.24% for benzene, were obtained when the discharge power was 90 W and the oxygen content in the carrier gas was 3 vol%. However, a maximum gas selectivity of 48.4% for H 2 and 19.4% for CO was attained when the discharge power was 75 W and the oxygen content was 3 vol% and 12 vol%, respectively. The effect of the steam/carbon molar ratio (S/C) on toluene reforming was investigated using the PC system with Ni/ZSM-5 catalyst under a discharge power of 75 W. The addition of steam to the feed gas significantly enhanced the conversion of toluene to syngas. A maximum toluene conversion of 88.5% was reached with a minimum selectivity of liquid by-products (1.9% for ethylbenzene and 5.2% for benzene) when S/C was 2. However, the highest selectivity of syngas (69.8% for H 2 and 21.2% for CO) was achieved when S/C was 2.5. The catalyst employed in the plasma reforming of toluene exhibited excellent anti-carbon deposition performance. A possible reaction mechanism and pathway of toluene destruction was proposed based on analysis of both gaseous and liquid products. Unlabelled Image • Higher discharge power promotes toluene conversion and reduce by-products formation. • Appropriate oxygen content in the carrier gas is essential for toluene reforming. • Steam produce oxidizing • OH in plasma and facilitate toluene reforming to syngas. • Ni/ZSM-5 catalyst exhibit superior anti-carbon deposition performance in tar removal. • A possible reaction mechanism of toluene cracking in DBD plasma is proposed. [ABSTRACT FROM AUTHOR]

Extracellular polymeric substances (EPS) play an important role in reducing moisture content and removing heavy metals from municipal sludge. In this study, cetyl trimethyl ammonium bromide (CTAB) and primary alcohol ethoxylate (AEO 9) were used to prepare complex surfactants. Municipal sludge was treated with mixed surfactants and hydrothermal treatment (HTT) to test the sludge dewatering and heavy metal adsorption performance of EPS treated with varying proportions and contents of surfactants. The results showed that EPS with different proportions had different adsorption capacities for major heavy metals in sludge was 20.48%–29.82%. The adsorption capacity of EPS on heavy metals is significantly positively correlated with protein content (R 2 = 0.9266, P =.00). There is no significant correlation between polysaccharides (R 2 = 0.0092, P =.00) and nucleic acids (R 2 = 0.0638, P =.00) and heavy metal adsorption capacity. Combined treatment of 10% CTAB, 15% AEO 9 , and HTT produced the minimal bound water content in treated sludge, zeta potential increased by 49.2 mV and sludge specific resistance is only 0.66% of the raw sludge. Unlabelled Image • The relationship between heavy metal distribution and sludge dewatering was studied; • Changes in biopolymer composition will affect sludge dewatering performance; • Protein content is positively correlated with heavy metal adsorption. [ABSTRACT FROM AUTHOR]