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The covalent modifications resulting from chlorine reactions with peptide-bound amino acids contribute to pathogen inactivation and disinfection byproduct (DBP) formation. Previous research suggested that histidine is the third most reactive of the seven chlorine-reactive amino acids, leading to the formation of 2-chlorohistidine, 2-oxohistidine, or low-molecular-weight byproducts such as trihalomethanes. This study demonstrates that histidine is less reactive toward formation of chlorine transformation products (transformation time scale of hours to days) than five of the seven chlorine-reactive amino acids, including tyrosine (transformation time scale of minutes). Chlorine targeted tyrosine in preference to histidine within peptides, indicating that chlorine reactions with tyrosine and other more reactive amino acids could contribute more to the structural modifications to proteins over the short time scales relevant to pathogen inactivation. Over the longer time scales relevant to disinfection byproduct formation in treatment plants or distribution systems, this study identified β-cyanoalanine as the dominant transformation product of chlorine reactions with peptide-bound histidine, with molar yields of ∼50% after 1 day. While a chlorinated histidine intermediate was observed at lower yields (maximum ∼5%), the cumulative concentration of the conventional low-molecular-weight DBPs (e.g., trihalomethanes) was ≤7%. These findings support the need to identify the high-yield initial transformation products of chlorine reactions with important precursor structures to facilitate the identification of unknown DBPs.

A novel and sustainable Pd–Sn bimetallic catalyst supported by fly ash-derived zeolite Na-X (Zeolite-XF) was developed for highly reactive and N2-selective reduction of nitrate in water. The surface characteristics of Zeolite-XF and Pd–Sn/Zeolite-XF were identified via various surface analyses, which showed formation of zeolite Na-X crystals with high purity and uniform dispersion of Pd and Sn nanoparticles on the surfaces of Pd–Sn/Zeolite-XF. Pd–Sn/Zeolite-XF showed a 43.1 × 10−3 s−1 turnover frequency (TOF) with almost 90% N2 selectivity under optimal conditions, which is 4–92 times higher than those of previously reported Pd based bimetallic catalysts. The great catalytic activity was elucidated by XPS and H2-pulse chemisorption analysis, demonstrating that Zeolite-XF enhanced metal dispersion and increased the active metallic sites of Pd and Sn nanoparticles. Furthermore, the optimized Pd–Sn/Zeolite-XF catalyst was tested for reduction of nitrate in real groundwater, which showed the complete removal with 94% N2 selectivity. The experimental results obtained from this study can provide a new insight that discarded solid waste can be converted to value-added environmental materials for synthesis of highly active catalysts, which surpass other freshly synthesized and commercially produced materials.

The present study aimed to investigate the relationship between the desorption and biodegradability of phenanthrene sorbed to biochars by employing two approaches that may change the desorption and biodegradability: the use of powdered biochars and nonionic surfactants. Biochars derived from two feedstocks (rice husk and sewage sludge; pyrolyzed at 500 °C but showing different aromaticity) were used. When the biochars were powdered to obtain particles f d e s ) increased from 0.303 to 0.431 for sewage sludge biochars. On the other hand, f d e s for rice husk biochars remained virtually unchanged (from 0.264 to 0.255). The mass fractions of the biodegraded phenanthrene ( f b i o ) increased from 0.191 to 0.306 for rice husk biochars and from 0.077 to 0.168 for sewage sludge biochars. When a nonionic surfactant was added at the sub-critical micelle concentration (CMC), f b i o increased by 4.7 times and 8.3 times for rice husk and sewage sludge biochars. For both types of biochars, f b i o was larger than f d e s when the surfactant was added. This study suggests that the addition of nonionic surfactants can be considered if the inhibition of microbial activity is of concern in soils and sediments treated by biochar.

Green roofs have become popular in urban areas as a solution to restore green space in cities and mitigate urban problems. In this study, the economic and environmental sustainability of using green roofs for rooftop agriculture (i.e., roof farms) is evaluated and compared with that of using green roofs as extensive gardens of flowers and non-edible plants with low maintenance (i.e., roof gardens) based on these two green roofs that were installed and operated for over five years in a university building in Seoul, Korea. The life cycle cost analysis results show that the total cost of the roof garden is 38.9% lower than the flat roof whereas the total cost of the roof farm is 68.3% higher than the roof garden. The environmental impacts of both the roof garden and farm were 2.4–35 times as high as those of the flat roof. The need to frequently replenish the lightweight soil over its lifetime was the main contributor to both the economic cost and environmental impacts of the roof farm, suggesting a need to develop cost-effective and environmentally benign lightweight soil materials. A survey was also conducted to investigate public preferences and perceptions of these two green roof options. Over 80% of the respondents expressed the necessity for green roofs in urban areas, and 79.3% preferred roof gardens over farms. Our results show that roof farms have several merits in urban areas, especially social benefits, but future research should focus on improving their economic and environmental sustainability.

This study investigates the effect of anionic surfactant modification on activated carbon (AC) to enhance the adsorption of ammonium ion in aqueous solution. Sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) or sodium octanoate (SO) was used for the modification. At the initial aqueous concentration of 55 mg NH4-N/L and the adsorbent dose of 50 g/L, the SDS-modified AC showed the highest ammonium removal efficiency of 82% among the modified ACs studied. The hydrophobic group of SDS was strongly attached to AC showing almost negligible desorption after the modification. At the same time, the sulfate functional group of SDS provided ion exchange sites favorable for the ammonium ion adsorption. By maximizing SDS loading to the AC, ammonium removal efficiency can further be improved (5% increase). When Na+, K+ or Ca2+ coexisted in the ammonium solution at the concentration of 55 mg/L, the inhibition effect of these cations on ammonium removal efficiency was negligible (

Following the Food Safety Modernization Act of 2011 in the U.S., guidelines for disinfection washes in food packaging facilities are under consideration to control pathogen risks. However, disinfectant exposures may need optimization because the high concentrations of chlorine disinfectant promote the formation of high levels of disinfection byproducts (DBPs). When chlorine doses up through the 200 mg/L as Cl2 range relevant to the current practice were applied to spinach and lettuce, significant DBP formation was observed, even within 5 min at 7 °C. Concentrations of volatile chlorinated DBPs in washwater were far higher than typically observed in disinfected drinking water (e.g., 350 μg/L 1,1-dichloropropanone). However, these DBPs partitioned to the aqueous phase and so represent a greater concern for the disposal or reuse of washwater than for consumer exposure via food. The volatile DBPs represent the low-yield, final products of chlorination reactions with multiple biomolecular precursors. The initi...

Rapid reduction of aqueous ClO4(-) to Cl(-) by H2 has been realized by a heterogeneous Re(hoz)2-Pd/C catalyst integrating Re(O)(hoz)2Cl complex (hoz = oxazolinyl-phenolato bidentate ligand) and Pd nanoparticles on carbon support, but ClOx(-) intermediates formed during reactions with concentrated ClO4(-) promote irreversible Re complex decomposition and catalyst deactivation. The original catalyst design mimics the microbial ClO4(-) reductase, which integrates Mo(MGD)2 complex (MGD = molybdopterin guanine dinucleotide) for oxygen atom transfer (OAT). Perchlorate-reducing microorganisms employ a separate enzyme, chlorite dismutase, to prevent accumulation of the destructive ClO2(-) intermediate. The structural intricacy of MGD ligand and the two-enzyme mechanism for microbial ClO4(-) reduction inspired us to improve catalyst stability by rationally tuning Re ligand structure and adding a ClOx(-) scavenger. Two new Re complexes, Re(O)(htz)2Cl and Re(O)(hoz)(htz)Cl (htz = thiazolinyl-phenolato bidentate ligand), significantly mitigate Re complex decomposition by slightly lowering the OAT activity when immobilized in Pd/C. Further stability enhancement is then obtained by switching the nanoparticles from Pd to Rh, which exhibits high reactivity with ClOx(-) intermediates and thus prevents their deactivating reaction with the Re complex. Compared to Re(hoz)2-Pd/C, the new Re(hoz)(htz)-Rh/C catalyst exhibits similar ClO4(-) reduction activity but superior stability, evidenced by a decrease of Re leaching from 37% to 0.25% and stability of surface Re speciation following the treatment of a concentrated "challenge" solution containing 1000 ppm of ClO4(-). This work demonstrates the pivotal roles of coordination chemistry control and tuning of individual catalyst components for achieving both high activity and stability in environmental catalyst applications.

Recently, an increasing number of pharmaceutical compounds has become fluorinated. Owing to their pharmacological efficacy, the use of these fluorinated pharmaceuticals continues to grow, and they constitute 20% of the drugs on the current market. However, only a few studies have investigated the fate and transformation of these emerging contaminants in natural and engineered aquatic environments. In the present study, the H2-based reductive transformation of three fluorinated pharmaceutical compounds (levofloxacin, sitagliptin, and fluoxetine) were investigated using alumina-supported monometallic and bimetallic catalysts of the Pt-group noble metals (i.e., Ru, Rh, Pd, and Pt) under ambient temperature and pressure conditions. Degradation of all three compounds was observed with catalytic reactivity ranging from 4.0 × 10−3 to 2.14 × 102 L/(min·gcat), in which fluoxetine generally showed the highest reactivity, followed by sitagliptin and levofloxacin. The fluorination yields and transformation products were characterized for each fluorinated compound and three different degradation mechanisms were elucidated: 1) hydrodefluorination of C-F bond to C H bond, 2) hydrogenation of aromatic ring, and 3) reductive cleavage of C O bond from phenyl ether. Toxicity assessment using Aliivibrio fischeri showed there were no significant changes in toxicity over levofloxacin and sitagliptin degradation, suggesting the formation of no highly toxic by-products during catalytic reduction. For fluoxetine, an increased toxicity was observed during its degradation while ECOSAR-predicted toxicity values of all identified intermediates were lower than that of fluoxetine, suggesting the formation of unidentified secondary by-products that contribute to the overall toxicity. The study showed that catalytic reduction is a promising remediation process for treating and defluorinating the fluorinated pharmaceutical compounds.

Particle size of biochar may strongly affect the kinetics of hydrophobic organic compound (HOC) sorption. However, challenges exist in characterizing the effect of biochar particle size on the sorption kinetics because of the wide size range of biochar. The present study suggests a novel method to determine a representative value that can be used to show the dependence of HOC sorption kinetics to biochar particle size on the basis of an intra-particle diffusion model. Biochars derived from three different feedstocks are ground and sieved to obtain three daughter products each having different size distributions. Phenanthrene sorption kinetics to the biochars are well described by the intra-particle diffusion model with significantly greater sorption rates observed for finer grained biochars. The time to reach 95% of equilibrium for phenanthrene sorption to biochar is reduced from 4.6-17.9days for the original biochars to

Ion exchange (IX) is the most common approach to treating nitrate-contaminated drinking water sources, but the cost of salt to make regeneration brine, as well as the cost and environmental burden of waste brine disposal, are major disadvantages. A hybrid ion exchange-catalyst treatment system, in which waste brine is catalytically treated for reuse, shows promise for reducing costs and environmental burdens of the conventional IX system. An IX model with separate treatment and regeneration cycles was developed, and ion selectivity coefficients for each cycle were separately calibrated by fitting experimental data. Of note, selectivity coefficients for the regeneration cycle required fitting the second treatment cycle after incomplete resin regeneration. The calibrated and validated model was used to simulate many cycles of treatment and regeneration using the hybrid system. Simulated waste brines and a real brine obtained from a California utility were also evaluated for catalytic nitrate treatment in a packed-bed, flow-through column with 0.5 wt%Pd-0.05 wt%In/activated carbon support (PdIn/AC). Consistent nitrate removal and no apparent catalyst deactivation were observed over 23 d (synthetic brine) and 45 d (real waste brine) of continuous-flow treatment. Ion exchange and catalyst results were used to evaluate treatment of 1 billion gallons of nitrate-contaminated source water at a 0.5 MGD water treatment plant. Switching from a conventional IX system with a two bed volume regeneration to a hybrid system with the same regeneration length and sequencing batch catalytic reactor treatment would save 76% in salt cost. The results suggest the hybrid system has the potential to address the disadvantages of a conventional IX treatment systems.