Evaluation of activated carbon fiber supported nanoscale zero-valent iron for chromium (VI) removal from groundwater in a permeable reactive column.

An activated carbon fiber supported nanoscale zero-valent iron (ACF-nZVI) composite for Cr(VI) removal from groundwater was synthesized according to the liquid phase reduction method. The techniques of N2 adsorption/desorption, FESEM, EDX, XRD and XPS were used to characterize the ACF-nZVI composite and the interaction between the ACF-nZVI composite and Cr(VI) ions. Batch experiments were conducted to evaluate the effects of several factors, including the amount of nZVI on activated carbon fiber (ACF), pH value, initial Cr(VI) concentration, and co-existing ions on Cr(VI) removal. The results indicate that presence of ACF can inhibit the aggregation of nanoscale zero-valent iron (nZVI) particles and increase its reactivity, and the Cr(VI) removal efficiency increases with increasing amounts of nZVI on ACF and a decrease in the initial Cr(VI) concentration. In acidic conditions, almost 100% of Cr(VI) in solution can be removed after 60 min of reaction, and the removal efficiency decreases with increasing initial pH values. The Cr(VI) removal is also dependent on the co-existing ions. Reusability experiments on ACF-nZVI demonstrate that the ACF-nZVI composite can keep a high reactivity after five successive reduction cycles. The removal mechanisms are proposed as a two-step interaction including the physical adsorption of Cr(VI) on the surface or inner layers of the ACF-nZVI composite and the subsequent reduction of Cr(VI) to Cr(III) by nZVI.

Molecular insights into microbial transformation of bioaerosol-derived dissolved organic matter discharged from wastewater treatment plant.

Wastewater treatment plants (WWTP) are important sources of aerosol-derived dissolved organic matter (ADOM) which may threaten human health via the respiratory system. In this study, aerosols were sampled from a typical WWTP to explore the chemical molecular diversity, molecular ecological network, and potential toxicities of the ADOM in the aerosols. The high fluorescence index (>1.9) and biological index (0.66-1.17) indicated the strong autogenous microbial source characteristics of the ADOM in the WWTP. DOM and microbes in the wastewater were aerosolized due to strong agitation and bubbling in the treatment processes, and contributed to 74 % and 75 %, respectively, of the ADOM and microbes in the aerosols. The ADOM was mainly composed of CHO and CHOS accounting for 35 % and 29 % of the total number of molecules, respectively, with lignin-like (69 %) as the major constituent. 49 % of the ADOM transformations were thermodynamically limited, and intragroup transformations were easier than intergroup transformations. Bacteria in the aerosols involved in ADOM transformations exhibited both cooperative and divergent behaviors and tended to transform carbohydrate-like and amino sugar/protein-like into recalcitrant lignin-like. The microbial compositions were affected by atmosphere temperature and humidity indirectly by modulating the properties of ADOM. Tannin-like, lignin-like, and unsaturated hydrocarbon-like molecules in the ADOM were primary toxicity contributors, facilitating the expression of inflammatory factors IL-ß (2.2-5.4 folds), TNF-α (3.5-7.0 folds), and IL-6 (3.5-11.2 folds), respectively.

Formation of halogenated macromolecular organics induced by Br- and I- during plasma oxidation/chlorination of DOM: Highlighting competitive mechanisms.

Understanding the effects of halogens on the production of macromolecular disinfection byproducts (DBPs) is critical for drinking water safety. The effects of Br- and I- on the chemical diversity of dissolved organic matter (DOM) during plasma preoxidation and the subsequent formation of macromolecular halogenated DBPs after chlorination were deciphered. Plasma preoxidation changed DOM diversity from aromatic component-oriented to lignin and tannin component-oriented, resulting in 62.0% and 21.2% decreases in N-DBPs (CkHnOmNzClx formulas) and C-DBPs (CkHnOmClx formulas) after chlorination, respectively. Br- could induce the formation of organobromine compounds (OBrCs) during plasma oxidation; however, the intensities of OBrCs decreased by 56.3% (CHO formulas) and 75.2% (CHON formulas) after further chlorination. OBrCs still accounted for 79.8% of the total organohalogen compounds (OXCs, X=Cl or Br) due to the higher substitutability of bromine. I-promoted OIC production in the DOM preoxidation process, and OICs acted as intermediates to form OClCs during chlorination. When Br-and I-coexisted, Br- promoted OIC production in the DOM preoxidation process; therefore, more OBrCs and OClCs were generated due to intermediates of OICs in subsequent chlorination. Connections between OXCs and their precursors were established using network computation. The precursors of OClCs were located in the aromatic structure region (0.2 < H/C ≤ 0.7; O/C ≤ 0.67); those of OBrCs and OICs were located in the lignin (0.7 < H/C ≤ 1.5; 0.1 < O/C < 0.67) and tannin (0.6 ≤ H/C ≤ 1.5, 0.67 < O/C < 1.0) regions with relatively greater H/C and O/C ratios, respectively.

P, N, and C-related functional genes in SBR system promoted antibiotics resistance gene transmission under polystyrene microplastics stress.

Wastewater treatment plants (WWTPs) are important sinks of microplastics (MPs) and antibiotics resistance genes (ARGs). Information regarding connections between functional modules of WWTPs and spread of ARGs under MPs stress is still lacking. In this study, correlations between P-, N-, and C-related functional genes and ARGs in a sequencing batch reactor (SBR) system were evaluated under polystyrene (PS) MPs stress. Total P and chemical oxygen demand (COD) in effluent showed no significant changes under 0.5-50 mg L-1 PS MPs stress within 32 cycle treatment periods of SBR, while 0.5 mg L-1 PS MPs affected the N cycling process. PS MPs (0.5-50 mg L-1) promoted the richness and diversity of microbial community in SBR, and the denitrification process was exuberant. PS MPs with a low dosage (0.5-5 mg L-1) enhanced secretion of extracellular polymeric substances and promoted expression levels of functional genes related to C fixation, C degradation, P cycling, and N cycling. Simultaneously, aac(3)-II, blaTEM-1, and tetW increased by 27.13%, 38.36%, and 9.57% under low dosages of PS MPs stress; more importantly, the total absolute abundance of intI1 nearly doubled. 78.4% of these P-, N-, and C-related functional genes were positively correlated with intI1, thus favoring transmission of ARGs. This study firstly disclosed the underlying correlations between functional modules of WWTPs and spread of ARGs under MPs stress.

Magnetic Fe3O4 assembled on nZVI supported on activated carbon fiber for Cr(VI) and Cu(II) removal from aqueous solution through a permeable reactive column.

Magnetic Fe3O4 assembled on nanoscale zero-valent iron (nZVI) supported on an activated carbon fiber (ACF) to form nanoscale magnetic composites (nZVI-Fe3O4/ACF) for removing Cr(VI) and Cu(II) from aqueous solution through a permeable reactive column was synthesized via an in situ reduction method. The nZVI-Fe3O4/ACF composites and the interaction between nZVI-Fe3O4/ACF and both Cr and Cu ions were characterized by field emission scanning electron microscopy (FESEM) with EDX, TEM, XRD, and XPS. Batch experiments were used to analyze the effects of main factors on Cr(VI) removal and investigate the simultaneous removal of Cr(VI) and Cu(II) through a permeable reactive column. The results indicated that the ACF and Fe3O4 can inhibit the agglomeration and enhance the dispersibility of nZVI, and Fe3O4 and nZVI displayed good synergetic effects. The removal efficiency of Cr(VI) improved with the increase amount of Fe3O4 in the nZVI-Fe3O4/ACF composites. With low initial concentration of Cr(VI) and acidic conditions, ~ 90% of 20.0 mg·L-1 Cr(VI) in the solution was removed after 60 min. The removal of Cr(VI) was also affected by coexisting ions. The removal efficiency of 10.0 mg·L-1 Cu(II) was ~ 100% after 45 min of reaction, and the presence of Cu(II) can accelerate the reduction of Cr(VI). The simultaneous removal mechanisms of Cr(VI) and Cu(II) by the nZVI-Fe3O4/ACF composites also were proposed.