Showing papers in "Environmental Science & Technology in 2018"

Microplastics and Nanoplastics in Aquatic Environments: Aggregation, Deposition, and Enhanced Contaminant Transport

Abstract: Plastic litter is widely acknowledged as a global environmental threat, and poor management and disposal lead to increasing levels in the environment. Of recent concern is the degradation of plastics from macro- to micro- and even to nanosized particles smaller than 100 nm in size. At the nanoscale, plastics are difficult to detect and can be transported in air, soil, and water compartments. While the impact of plastic debris on marine and fresh waters and organisms has been studied, the loads, transformations, transport, and fate of plastics in terrestrial and subsurface environments are largely overlooked. In this Critical Review, we first present estimated loads of plastics in different environmental compartments. We also provide a critical review of the current knowledge vis-a-vis nanoplastic (NP) and microplastic (MP) aggregation, deposition, and contaminant cotransport in the environment. Important factors that affect aggregation and deposition in natural subsurface environments are identified and c...

Impacts of Microplastics on the Soil Biophysical Environment

Abstract: Soils are essential components of terrestrial ecosystems that experience strong pollution pressure. Microplastic contamination of soils is being increasingly documented, with potential consequences for soil biodiversity and function. Notwithstanding, data on effects of such contaminants on fundamental properties potentially impacting soil biota are lacking. The present study explores the potential of microplastics to disturb vital relationships between soil and water, as well as its consequences for soil structure and microbial function. During a 5-weeks garden experiment we exposed a loamy sand soil to environmentally relevant nominal concentrations (up to 2%) of four common microplastic types (polyacrylic fibers, polyamide beads, polyester fibers, and polyethylene fragments). Then, we measured bulk density, water holding capacity, hydraulic conductivity, soil aggregation, and microbial activity. Microplastics affected the bulk density, water holding capacity, and the functional relationship between the microbial activity and water stable aggregates. The effects are underestimated if idiosyncrasies of particle type and concentrations are neglected, suggesting that purely qualitative environmental microplastic data might be of limited value for the assessment of effects in soil. If extended to other soils and plastic types, the processes unravelled here suggest that microplastics are relevant long-term anthropogenic stressors and drivers of global change in terrestrial ecosystems.

Catalytic removal of aqueous contaminants on N-doped graphitic biochars: inherent roles of adsorption and nonradical mechanisms.

Abstract: Environmentally friendly and low-cost catalysts are important for the rapid mineralization of organic contaminants in powerful advanced oxidation processes (AOPs). In this study, we reported N-doped graphitic biochars (N-BCs) as low-cost and efficient catalysts for peroxydisulfate (PDS) activation and the degradation of diverse organic pollutants in water treatment, including Orange G, phenol, sulfamethoxazole, and bisphenol A. The biochars at high annealing temperatures (>700 °C) presented highly graphitic nanosheets, large specific surface areas (SSAs), and rich doped nitrogen. In particular, N-BC derived at 900 °C (N-BC900) exhibited the highest degradation rate, which was 39-fold and 6.5-fold of that on N-BC400 and pristine biochar, respectively, and the N-BC900 surpassed most popular metal or nanocarbon catalysts. Different from the radical-based oxidation in N-BC400/PDS via the persistent free radicals (PFRs), singlet oxygen and nonradical pathways (surface-confined activated persulfate–carbon compl...

Microplastics in Swiss Floodplain Soils.

Abstract: Microplastics (MPs) are small (<5 mm diameter) but have clear implications for the environment. These artificial particles are found in and pose threats to aquatic systems worldwide. MPs have terrestrial sources, but their concentrations and fates in the terrestrial environment are poorly understood. While global plastic production continues to increase, so do the environmental concentrations and impacts of MPs. In this first study of MPs in floodplain soils, we developed a method for identifying, quantifying, and measuring the sizes of most commonly produced MPs in soil by FT-IR microscopy. For small MP (<1 mm) analysis, MP were separated by density separation and oxidation of organic matter. In this study we analyzed 29 floodplains in Swiss nature reserves associated with catchments covering 53% of Switzerland. We found evidence that 90% of Swiss floodplain soils contain MPs. The highest MP concentrations were associated with the concentration of mesoplastics (5 mm − 2.5 cm diameter), indicating plastic...

Identifying the Nonradical Mechanism in the Peroxymonosulfate Activation Process: Singlet Oxygenation Versus Mediated Electron Transfer

Abstract: Select persulfate activation processes were demonstrated to initiate oxidation not reliant on sulfate radicals, although the underlying mechanism has yet to be identified. This study explored singlet oxygenation and mediated electron transfer as plausible nonradical mechanisms for organic degradation by carbon nanotube (CNT)-activated peroxymonosulfate (PMS). The degradation of furfuryl alcohol (FFA) as a singlet oxygen (1O2) indicator and the kinetic retardation of FFA oxidation in the presence of l-histidine and azide as 1O2 quenchers apparently supported a role of 1O2 in the CNT/PMS system. However, the 1O2 scavenging effect was ascribed to a rapid PMS depletion by l-histidine and azide. A comparison of CNT/PMS and photoexcited Rose Bengal (RB) excluded the possibility of singlet oxygenation during heterogeneous persulfate activation. In contrast to the case of excited RB, solvent exchange (H2O to D2O) did not enhance FFA degradation by CNT/PMS and the pH- and substrate-dependent reactivity of CNT/PMS ...

Fe(III)-Doped g-C3N4 Mediated Peroxymonosulfate Activation for Selective Degradation of Phenolic Compounds via High-Valent Iron-Oxo Species.

Abstract: Herein, we proposed a new peroxymonosulfate (PMS) activation system employing the Fe(III) doped g-C3N4 (CNF) as catalyst. Quite different from traditional sulfate radical-based advanced oxidation processes (SR-AOPs), the PMS/CNF system was capable of selectively degrading phenolic compounds (e.g., p-chlorophenol, 4-CP) in a wide pH range (3–9) via nonradical pathway. The generated singlet oxygen (1O2) in the PMS/CNF3 (3.46 wt % Fe) system played negligible role in removing 4-CP, and high-valent iron-oxo species fixated in the nitrogen pots of g-C3N4 (≡FeV═O) was proposed as the dominant reactive species by using dimethyl sulfoxide as a probe compound. The mechanism was hypothesized that PMS was first bound to the Fe(III)-N moieties to generate ≡FeV═O, which effectively reacted with 4-CP via electron transfer. GC-MS analysis indicated that 4-chlorocatechol and 1,4-benzoquinone were the major intermediates, which could be further degraded to carboxylates. The kinetic results suggested that the formation of ...

Insight into Multiple and Multilevel Structures of Biochars and Their Potential Environmental Applications: A Critical Review

Abstract: Biochar is the carbon-rich product of the pyrolysis of biomass under oxygen-limited conditions, and it has received increasing attention due to its multiple functions in the fields of climate change mitigation, sustainable agriculture, environmental control, and novel materials. To design a “smart” biochar for environmentally sustainable applications, one must understand recent advances in biochar molecular structures and explore potential applications to generalize upon structure–application relationships. In this review, multiple and multilevel structures of biochars are interpreted based on their elemental compositions, phase components, surface properties, and molecular structures. Applications such as carbon fixators, fertilizers, sorbents, and carbon-based materials are highlighted based on the biochar multilevel structures as well as their structure-application relationships. Further studies are suggested for more detailed biochar structural analysis and separation and for the combination of macros...

Drinking Water Disinfection Byproducts (DBPs) and Human Health Effects: Multidisciplinary Challenges and Opportunities

Abstract: While drinking water disinfection has effectively prevented waterborne diseases, an unintended consequence is the generation of disinfection byproducts (DBPs). Epidemiological studies have consistently observed an association between consumption of chlorinated drinking water with an increased risk of bladder cancer. Out of the >600 DBPs identified, regulations focus on a few classes, such as trihalomethanes (THMs), whose concentrations were hypothesized to correlate with the DBPs driving the toxicity of disinfected waters. However, the DBPs responsible for the bladder cancer association remain unclear. Utilities are switching away from a reliance on chlorination of pristine drinking water supplies to the application of new disinfectant combinations to waters impaired by wastewater effluents and algal blooms. In light of these changes in disinfection practice, this article discusses new approaches being taken by analytical chemists, engineers, toxicologists and epidemiologists to characterize the DBP classes driving disinfected water toxicity, and suggests that DBP exposure should be measured using other DBP classes in addition to THMs.

Oxidation of Organic Compounds in Water by Unactivated Peroxymonosulfate

Abstract: Peroxymonosulfate (HSO5– and PMS) is an optional bulk oxidant in advanced oxidation processes (AOPs) for treating wastewaters. Normally, PMS is activated by the input of energy or reducing agent to generate sulfate or hydroxyl radicals or both. This study shows that PMS without explicit activation undergoes direct reaction with a variety of compounds, including antibiotics, pharmaceuticals, phenolics, and commonly used singlet-oxygen (1O2) traps and quenchers, specifically furfuryl alcohol (FFA), azide, and histidine. Reaction time frames varied from minutes to a few hours at pH 9. With the use of a test compound with intermediate reactivity (FFA), electron paramagnetic resonance (EPR) and scavenging experiments ruled out sulfate and hydroxyl radicals. Although 1O2 was detected by EPR and is produced stoichiometrically through PMS self-decomposition, 1O2 plays only a minor role due to its efficient quenching by water, as confirmed by experiments manipulating the 1O2 formation rate (addition of H2O2) or li...

Validation of a Method for Extracting Microplastics from Complex, Organic-Rich, Environmental Matrices.

Abstract: Complex and organic-rich solid substrates such as sludge and soil have been shown to be contaminated by microplastics; however, methods for extracting plastic particles have not yet been systemically tested or standardized. This study investigated four main protocols for the removal of organic material during analysis of microplastics from complex solid matrices: oxidation using H2O2, Fenton’s reagent, and alkaline digestion with NaOH and KOH. Eight common polymer types were used to assess the influence of reagent exposure on particle integrity. Organic matter removal efficiencies were established for test sludge and soil samples. Fenton’s reagent was identified as the optimum protocol. All other methods showed signs of particle degradation or resulted in an insufficient reduction in organic matter content. A further validation procedure revealed high microplastic extraction efficiencies for particles with different morphologies. This confirmed the suitability of Fenton’s reagent for use in conjunction wi...

Is Sulfate Radical Really Generated from Peroxydisulfate Activated by Iron(II) for Environmental Decontamination

Abstract: It is well documented that the traditional Fenton reagent (ie, the combination of Fe(II) and H2O2) produces hydroxyl radical (•OH) under acidic conditions, while at near-neutral pH the reactive intermediate converts to ferryl ion (Fe(IV)) that can oxidize sulfoxides to produce corresponding sulfones, markedly differing from their •OH-induced products However, it remains unclear whether Fe(IV) is generated in the Fe(II) activated peroxydisulfate (PDS) process, where sulfate radical (SO4•-) is long recognized as the dominant intermediate in literature Here we demonstrated that SO4•- oxidized methyl phenyl sulfoxide (PMSO, a model sulfoxide) to produce biphenyl compounds rather than methyl phenyl sulfone (PMSO2) Interestingly, the formation of PMSO2 was observed when PMSO was treated by the Fe(II)/PDS system over a wide pH range, and the yields of PMSO2 were quantified to be ∼100% at acidic pH 3-5 The identification of Fe(IV) in the Fe(II)/PDS system could also reasonably explain the literature results on alcohol scavenging effect and ESR spectra analysis Further, a Fe(IV)-based kinetic model was shown to accurately simulate the experimental data This work urges re-evaluation of the Fe(II)/PDS system for environmental decontamination, given that Fe(IV) would have different reactivity toward environmental contaminants compared with SO4•- and/or •OH

Electronic Structure Modulation of Graphitic Carbon Nitride by Oxygen Doping for Enhanced Catalytic Degradation of Organic Pollutants through Peroxymonosulfate Activation.

Abstract: Oxygen-doped graphitic carbon nitride (O-CN) was fabricated via a facile thermal polymerization method using urea and oxalic acid dihydrate as the graphitic carbon nitride precursor and oxygen source, respectively. Experimental and theoretical results revealed that oxygen doping preferentially occurred on the two-coordinated nitrogen positions, which create the formation of low and high electron density areas resulting in the electronic structure modulation of O-CN. As a result, the resultant O-CN exhibits enhanced catalytic activity and excellent long-term stability for peroxymonosulfate (PMS) activation toward the degradation of organic pollutants. The O-CN with modulated electronic structure enables PMS oxidation over the electron-deficient C atoms for the generation of singlet oxygen (1O2) and PMS reduction around the electron-rich O dopants for the formation of hydroxyl radical (•OH) and sulfate radical (SO4•-), in which 1O2 is the major reactive oxygen species, contributing to the selective reactivity of the O-CN/PMS system. Our findings not only propose a novel PMS activation mechanism in terms of simultaneous PMS oxidation and reduction for the production of nonradical and radical species but also provide a valuable insight for the development of efficient metal-free catalysts through nonmetal doping toward the persulfate-based environmental cleanup.

Oxidation Processes in Water Treatment: Are We on Track?

Abstract: Chemical oxidants have been applied in water treatment for more than a century, first as disinfectants and later to abate inorganic and organic contaminants. The challenge of oxidative abatement of organic micropollutants is the formation of transformation products with unknown (eco)toxicological consequences. Four aspects need to be considered for oxidative micropollutant abatement: (i) Reaction kinetics, controlling the efficiency of the process, (ii) mechanisms of transformation product formation, (iii) extent of formation of disinfection byproducts from the matrix, (iv) oxidation induced biological effects, resulting from transformation products and/or disinfection byproducts. It is impossible to test all the thousands of organic micropollutants in the urban water cycle experimentally to assess potential adverse outcomes of an oxidation. Rather, we need multidisciplinary and automated knowledge-based systems, which couple predictions of kinetics, transformation and disinfection byproducts and their to...

Metal Organic Framework with Coordinatively Unsaturated Sites as Efficient Fenton-like Catalyst for Enhanced Degradation of Sulfamethazine.

Abstract: A novel Fenton-like catalyst, metal organic framework MIL-100(Fe) with FeII/FeIII mixed-valence coordinatively unsaturated iron center (CUS-MIL-100(Fe)), was synthesized, characterized, and used for the degradation of sulfamethazine (SMT). The catalytic performance of CUS-MIL-100(Fe) was investigated on the basis of various parameters, including initial pH, H2O2 concentration, catalyst dosage, and initial SMT concentration. The results showed that CUS-MIL-100(Fe) could effectively degrade SMT, with almost 100% removal efficiency within 180 min (52.4% mineralization efficiency), under the reaction conditions of pH 4.0, 20 mg L–1 SMT, 6 mM H2O2, and 0.5 g L–1 catalyst. Moreover, CUS-MIL-100(Fe) displayed a higher catalytic activity than that of MIL-100(Fe) for SMT degradation. Combined with the physical–chemical characterization, the enhanced catalytic activity can be ascribed to the incorporation of FeII and FeIII CUSs (coordinatively unsaturated metal sites), the large specific surface area, as well as th...

Quality Criteria for the Analysis of Microplastic in Biota Samples: A Critical Review

Abstract: Data on ingestion of microplastics by marine biota are quintessential for monitoring and risk assessment of microplastics in the environment. Current studies, however, portray a wide spread in results on the occurrence of microplastic ingestion, highlighting a lack of comparability of results, which might be attributed to a lack of standardization of methods. We critically review and evaluate recent microplastic ingestion studies in aquatic biota, propose a quality assessment method for such studies, and apply the assessment method to the reviewed studies. The quality assessment method uses ten criteria: sampling method and strategy, sample size, sample processing and storage, laboratory preparation, clean air conditions, negative controls, positive controls, target component, sample (pre)treatment, and polymer identification. The results of this quality assessment show a dire need for stricter quality assurance in microplastic ingestion studies. On average, studies score 8.0 out of 20 points for "completeness of information" and 0 for "reliability". Alongside the assessment method, a standardized protocol for detecting microplastic in biota samples incorporating these criteria is provided.

Worldwide Distribution of Novel Perfluoroether Carboxylic and Sulfonic Acids in Surface Water

Abstract: Driven by increasingly stringent restrictions on long-chain per- and polyfluoroalkyl substances (PFASs), novel fluorinated compounds have emerged on the market. Here we report on the occurrences of several perfluoroalkyl ether carboxylic and sulfonic acids (PFECAs and PFESAs), including hexafluoropropylene oxide dimer and trimer acids (HFPO-DA and HFPO-TA), ammonium 4,8-dioxa-3H-perfluorononanoate (ADONA), chlorinated polyfluorinated ether sulfonic acid (6:2 Cl-PFESA), and its hydrogen-substituted analogue (6:2 H-PFESA) in surface waters from China (n = 106), the United States (n = 12), the United Kingdom (n = 6), Sweden (n = 10), Germany (n = 14), The Netherlands (n = 6), and Korea (n = 6). Results showed that HFPO-DA, HFPO-TA, and 6:2 Cl-PFESA (median = 0.95, 0.21, and 0.31 ng/L, respectively) were frequently detected in all countries, indicating ubiquitous dispersal and distribution in global surface waters. The presence of 6:2 H-PFESA was widely detected in China (detection rate > 95%) but not in any ...

Potable Water Reuse through Advanced Membrane Technology.

Abstract: Recycling water from municipal wastewater offers a reliable and sustainable solution to cities and regions facing shortage of water supply. Places including California and Singapore have developed advanced water reuse programs as an integral part of their water management strategy. Membrane technology, particularly reverse osmosis, has been playing a key role in producing high quality recycled water. This feature paper highlights the current status and future perspectives of advanced membrane processes to meet potable water reuse. Recent advances in membrane materials and process configurations are presented and opportunities and challenges are identified in the context of water reuse.

Hyperthermophilic Composting Accelerates the Removal of Antibiotic Resistance Genes and Mobile Genetic Elements in Sewage Sludge

Abstract: Composting is an efficient way to convert organic waste into fertilizers. However, waste materials often contain large amounts of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) that can reduce the efficacy of antibiotic treatments when transmitted to humans. Because conventional composting often fails to remove these compounds, we evaluated if hyperthermophilic composting with elevated temperature is more efficient at removing ARGs and MGEs and explored the underlying mechanisms of ARG removal of the two composting methods. We found that hyperthermophilic composting removed ARGs and MGEs more efficiently than conventional composting (89% and 49%, respectively). Furthermore, the half-lives of ARGs and MGEs were lower in hyperthermophilic compositing compared to conventional composting (67% and 58%, respectively). More-efficient removal of ARGs and MGEs was associated with a higher reduction in bacterial abundance and diversity of potential ARG hosts. Partial least-squares path modeling suggested that reduction of MGEs played a key role in ARG removal in hyperthermophilic composting, while ARG reduction was mainly driven by changes in bacterial community composition under conventional composting. Together these results suggest that hyperthermophilic composting can significantly enhance the removal of ARGs and MGEs and that the mechanisms of ARG and MGE removal can depend on composting temperature.

Environmental risks and challenges associated with neonicotinoid insecticides

Abstract: Neonicotinoid use has increased rapidly in recent years, with a global shift toward insecticide applications as seed coatings rather than aerial spraying. While the use of seed coatings can lessen the amount of overspray and drift, the near universal and prophylactic use of neonicotinoid seed coatings on major agricultural crops has led to widespread detections in the environment (pollen, soil, water, honey). Pollinators and aquatic insects appear to be especially susceptible to the effects of neonicotinoids with current research suggesting that chronic sublethal effects are more prevalent than acute toxicity. Meanwhile, evidence of clear and consistent yield benefits from the use of neonicotinoids remains elusive for most crops. Future decisions on neonicotinoid use will benefit from weighing crop yield benefits versus environmental impacts to nontarget organisms and considering whether there are more environmentally benign alternatives.

Enhancement of H2O2 Decomposition by the Co-catalytic Effect of WS2 on the Fenton Reaction for the Synchronous Reduction of Cr(VI) and Remediation of Phenol

Abstract: The greatest problem in the Fe(II)/H2O2 Fenton reaction is the low production of ·OH owing to the inefficient Fe(III)/Fe(II) cycle and the low decomposition efficiency of H2O2 (<30%). Herein, we report a new discovery regarding the significant co-catalytic effect of WS2 on the decomposition of H2O2 in a photoassisted Fe(II)/H2O2 Fenton system. With the help of WS2 co-catalytic effect, the H2O2 decomposition efficiency can be increased from 22.9% to 60.1%, such that minimal concentrations of H2O2 (0.4 mmol/L) and Fe2+ (0.14 mmol/L) are necessary for the standard Fenton reaction. Interestingly, the co-catalytic Fenton strategy can be applied to the simultaneous oxidation of phenol (10 mg/L) and reduction of Cr(VI) (40 mg/L), and the corresponding degradation and reduction rates can reach up to 80.9% and 90.9%, respectively, which are much higher than the conventional Fenton reaction (52.0% and 31.0%). We found that the expose reductive W4+ active sites on the surface of WS2 can greatly accelerate the rate-l...

Biodegradation of Polyethylene and Plastic Mixtures in Mealworms (Larvae of Tenebrio molitor) and Effects on the Gut Microbiome.

Abstract: Recent studies have demonstrated the ability for polystyrene (PS) degradation within the gut of mealworms (Tenebrio molitor). To determine whether plastics may be broadly susceptible to biodegradation within mealworms, we evaluated the fate of polyethylene (PE) and mixtures (PE + PS). We find that PE biodegrades at comparable rates to PS. Mass balances indicate conversion of up 49.0 ± 1.4% of the ingested PE into a putative gas fraction (CO2). The molecular weights (Mn) of egested polymer residues decreased by 40.1 ± 8.5% in PE-fed mealworms and by 12.8 ± 3.1% in PS-fed mealworms. NMR and FTIR analyses revealed chemical modifications consistent with degradation and partial oxidation of the polymer. Mixtures likewise degraded. Our results are consistent with a nonspecific degradation mechanism. Analysis of the gut microbiome by next-generation sequencing revealed two OTUs (Citrobacter sp. and Kosakonia sp.) strongly associated with both PE and PS as well as OTUs unique to each plastic. Our results suggest ...

Tannic Acid/Fe3+ Nanoscaffold for Interfacial Polymerization: Toward Enhanced Nanofiltration Performance

Abstract: Conventional thin-film composite (TFC) membranes suffer from the trade-off relationship between permeability and selectivity, known as the “upper bound”. In this work, we report a high performance thin-film composite membrane prepared on a tannic acid (TA)-Fe nanoscaffold (TFCn) to overcome such upper bound. Specifically, a TA-Fe nanoscaffold was first coated onto a polysulfone substrate, followed by performing an interfacial polymerization reaction between trimesoyl chloride (TMC) and piperazine (PIP). The TA-Fe nanoscaffold enhanced the uptake of amine monomers and provided a platform for their controlled release. The smaller surface pore size of the TA-Fe coated substrate further eliminated the intrusion of polyamide into the substrate pores. The resulting membrane TFCn showed a water permeability of 19.6 ± 0.5 L m2– h–1 bar–1, which was an order of magnitude higher than that of control TFC membrane (2.2 ± 0.3 L m–2 h–1 bar–1). The formation of a more order polyamide rejection layer also significantly ...

Biodegradable Plastic Blends Create New Possibilities for End-of-Life Management of Plastics but They Are Not a Panacea for Plastic Pollution

Abstract: Plastic waste pollution is a global environmental problem which could be addressed by biodegradable plastics The latter are blended together to achieve commercially functional properties, but the environmental fate of these blends is unknown We have tested neat polymers, polylactic acid (PLA), polyhydroxybutyrate, polyhydroxyoctanoate, poly(butylene succinate), thermoplastic starch, polycaprolactone (PCL), and blends thereof for biodegradation across seven managed and unmanaged environments PLA is one of the world’s best-selling biodegradable plastics, but it is not home compostable We show here that PLA when blended with PCL becomes home compostable We also demonstrate that the majority of the tested bioplastics and their blends degrade by thermophilic anaerobic digestion with high biogas output, but degradation times are 3–6 times longer than the retention times in commercial plants While some polymers and their blends showed good biodegradation in soil and water, the majority of polymers and thei

Porous Electrospun Fibers Embedding TiO2 for Adsorption and Photocatalytic Degradation of Water Pollutants.

Abstract: Using a bipolymer system consisting of polyvinylpyrrolidone (PVP) and poly(vinylidene fluoride) (PVDF), P25-TiO2 was immobilized into thin film mats of porous electrospun fibers. Pores were introduced by dissolving sacrificial PVP to increase surface area and enhance access to TiO2. The highest photocatalytic activity was achieved using a PVDF:PVP weight ratio of 2:1. Methylene blue (MB) was used to visualize contaminant removal, assess the sorption capacity (5.93 ± 0.23 mg/g) and demonstrate stable removal kinetics (kMB > 0.045 min–1) under UVA irradiation (3.64 × 10–9 einstein/cm2/s) over 10 cycles. Treatment was also accomplished via sequential MB sorption in the dark and subsequent photocatalytic degradation under UVA irradiation, to illustrate that these processes could be uncoupled to overcome limited light penetration. The photocatalytic mat degraded bisphenol A and 17α-ethynylestradiol in secondary wastewater effluent (17 mg TOC/L), and (relative to TiO2 slurry) immobilization of TiO2 in the mat m...

Methane Production and Conductive Materials: A Critical Review

Abstract: Conductive materials (CM) have been extensively reported to enhance methane production in anaerobic digestion processes. The occurrence of direct interspecies electron transfer (DIET) in microbial communities, as an alternative or complementary to indirect electron transfer (via hydrogen or formate), is the main explanation given to justify the improvement of methane production. Not disregarding that DIET can be promoted in the presence of certain CM, it surely does not explain all the reported observations. In fact, in methanogenic environments DIET was only unequivocally demonstrated in cocultures of Geobacter metallireducens with Methanosaeta harundinacea or Methanosarcina barkeri and frequently Geobacter sp. are not detected in improved methane production driven systems. Furthermore, conductive carbon nanotubes were shown to accelerate the activity of methanogens growing in pure cultures, where DIET is not expected to occur, and hydrogenotrophic activity is ubiquitous in full-scale anaerobic digesters...

Role of Marine Snows in Microplastic Fate and Bioavailability.

Abstract: Microplastics contaminate global oceans and are accumulating in sediments at levels thought sufficient to leave a permanent layer in the fossil record. Despite this, the processes that vertically transport buoyant polymers from surface waters to the benthos are poorly understood. Here we demonstrate that laboratory generated marine snows can transport microplastics of different shapes, sizes, and polymers away from the water surface and enhance their bioavailability to benthic organisms. Sinking rates of all tested microplastics increased when incorporated into snows, with large changes observed for the buoyant polymer polyethylene with an increase in sinking rate of 818 m day–1 and for denser polyamide fragments of 916 m day–1. Incorporation into snows increased microplastic bioavailability for mussels, where uptake increased from zero to 340 microplastics individual–1 for free microplastics to up to 1.6 × 105 microplastics individual–1 when incorporated into snows. We therefore propose that marine snow ...

Activation of Persulfate by Nanosized Zero-Valent Iron (NZVI): Mechanisms and Transformation Products of NZVI.

Abstract: The mechanisms involved in the activation of persulfate by nanosized zero-valent iron (NZVI) were elucidated and the NZVI transformation products identified. Two distinct reaction stages, in terms of the kinetics and radical formation mechanism, were found when phenol was oxidized by the persulfate/NZVI system. In the initial stage, lasting 10 min, Fe0(s) was consumed rapidly and sulfate radicals were produced through activation by aqueous Fe2+. The second stage was governed by Fe catalyzed activation in the presence of aqueous Fe3+ and iron (oxyhydr)oxides in the NZVI shells. The second stage was 3 orders of magnitude slower than the initial stage. An electron balance showed that the sulfate radical yield per mole of persulfate was more than two times higher in the persulfate/NZVI system than in the persulfate/Fe2+ system. Radicals were believed to be produced more efficiently in the persulfate/NZVI system because aqueous Fe2+ was supplied slowly, preventing sulfate radicals being scavenged by excess aqu...

Microplastic Abundance and Composition in Western Lake Superior As Determined via Microscopy, Pyr-GC/MS, and FTIR.

Abstract: While plastic pollution in marine and freshwater systems is an active area of research, there is not yet an in-depth understanding of the distributions, chemical compositions, and fates of plastics in aquatic environments. In this study, the magnitude, distribution, and common polymers of microplastic pollution in surface waters in western Lake Superior are determined. Analytical methodology, including estimates of ambient contamination during sample collection and processing, are described and employed. Microscopy, pyrolysis-gas chromatography/mass spectrometry (Pyr-GC/MS), and Fourier transform infrared spectroscopy (FTIR) were used to quantify and identify microplastic particles. In surface waters, fibers were the most frequently observed morphology, and, based upon PyGC/MS analysis, polyvinyl chloride was the most frequently observed polymer, followed by polypropylene and polyethylene. The most common polymer identified by FTIR was polyethylene. Despite the low human population in Lake Superior’s wat...

Urban Mining of E-Waste is Becoming More Cost-Effective Than Virgin Mining

Abstract: Stocks of virgin-mined materials utilized in linear economic flows continue to present enormous challenges. E-waste is one of the fastest growing waste streams, and threatens to grow into a global problem of unmanageable proportions. An effective form of management of resource recycling and environmental improvement is available, in the form of extraction and purification of precious metals taken from waste streams, in a process known as urban mining. In this work, we demonstrate utilizing real cost data from e-waste processors in China that ingots of pure copper and gold could be recovered from e-waste streams at costs that are comparable to those encountered in virgin mining of ores. Our results are confined to the cases of copper and gold extracted and processed from e-waste streams made up of recycled TV sets, but these results indicate a trend and potential if applied across a broader range of e-waste sources and metals extracted. If these results can be extended to other metals and countries, they p...

Microplastic Effect Thresholds for Freshwater Benthic Macroinvertebrates.

Abstract: Now that microplastics have been detected in lakes, rivers, and estuaries all over the globe, evaluating their effects on biota has become an urgent research priority. This is the first study that aims at determining the effect thresholds for a battery of six freshwater benthic macroinvertebrates with different species traits, using a wide range of microplastic concentrations. Standardized 28 days single species bioassays were performed under environmentally relevant exposure conditions using polystyrene microplastics (20–500 μm) mixed with sediment at concentrations ranging from 0 to 40% sediment dry weight (dw). Microplastics caused no effects on the survival of Gammarus pulex, Hyalella azteca, Asellus aquaticus, Sphaerium corneum, and Tubifex spp. and no effects were found on the reproduction of Lumbriculus variegatus. No significant differences in growth were found for H. azteca, A. aquaticus, S. corneum, L. variegatus, and Tubifex spp. However, G. pulex showed a significant reduction in growth (EC10 ...