The aggregation of nanoplastics (NPs) is a key issue in understanding the dynamic nature of NPs in the environment. The aggregation of NPs under various environmental conditions has not yet been ...studied. We investigated the influences of inorganic ions and natural organic matter (NOM) on polystyrene (PS) NPs aggregation in solutions. Results showed that PS NPs remained stable in wide ionic strength solutions of NaCl (1–100 mM) and CaCl2 (0.1–15 mM), and only in low ionic strength FeCl3 solutions (0.01 mM). However, obvious PS NPs aggregation was observed in FeCl3 solutions with an increase in ionic strength (0.1 and 1 mM). Moreover, NOM had a negligible effect on PS NPs aggregation in all ionic strengths of NaCl and CaCl2 solutions and in low ionic strength FeCl3 solutions (0.01 mM). However, NOM reduced PS NPs aggregation in an intermediate ionic strength FeCl3 (0.1 mM) solution and increased aggregation in a high ionic strength FeCl3 (1 mM) solution. Based on the theoretical analysis of interaction forces among PS NPs, the Derjaguin–Landau–Verwey–Overbeek force was a contributor governing PS NPs aggregation either in the absence or presence of NOM. In addition, other factors, including electrostatic heterogeneity of PS NPs surfaces, steric repulsion induced by NOM, and clusters formed via bridging effect in the presence of NOM also contributed to altered PS NPs aggregation under selected conditions. The PS NPs-NOM clusters were directly observed using a cryogenic scanning electron microscope.
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•Effects of inorganic ions and NOM on the aggregation of NPs were first studied.•High valence of ions is liable to induce NPs aggregation than low valence of ions.•Effect of NOM on NPs aggregation is dependent on specific solution conditions.•DLVO force is a contributor affecting the aggregation of NPs.•Cryo-SEM was used to directly observe the in-situ morphology of NPs in suspensions.
Microplastics have received growing attention as carriers of organic pollutants in the water environment. To better understand the contribution of hydrophobic interaction, hydrogen-bonding ...interaction, π-π interaction and electrostatic interaction on the adsorption of hydrophilic compounds on microplastics and their adsorption behavior in natural waters, polyethylene terephthalate (PET, <150 μm) was used as an adsorbent and 4-chlorophenol (MCP), 2,4-dichlorophenol (DCP) and 2,4,6-trichlorophenol (TCP) were used as adsorbates. The results of batch adsorption experiments showed that chlorophenols (CPs) reached adsorption sites of PET through film diffusion and intra-particle diffusion. pH greatly affected the adsorption capacity. Hydrophobic interaction was the main adsorption mechanism of undissociated CPs on PET. Hydrogen-bonding interaction was also an adsorption mechanism between undissociated CPs and PET, and the contribution of hydrogen-bonding interaction to adsorption decreased with the increase of chlorine content. Meanwhile, the increase of chlorine content was favorable to the hydrophobic interaction between undissociated CPs and PET. However, higher chlorine content CPs with lower pKa values tended to dissociate at neutral pH condition and resulted in stronger electrostatic repulsion with PET. The increase of solution ionic strength and fulvic acid content negatively affected the adsorption of DCP and TCP on PET, but did not show significant impacts on MCP adsorption. Similarly, the adsorption capacity obtained using Taihu lake water and Bohai seawater as matrices was much lower than that using laboratory water for both DCP and TCP, while the adsorption coefficient (Kd) of MCP remained at approximately 10.6 L/kg to 11.4 L/kg in the three different solution matrices. The Kd values exhibited using natural water matrices consistently followed the order of DCP > MCP > TCP. This study provides insights into the fate of CPs in the presence of microplastics and suggests that the potential risks posed by CPs and microplastics to aqueous ecosystems merit further investigation.
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•Chlorophenols adsorption by polyethylene terephthalate (PET) was studied.•The adsorption process by PET is controlled by film and intra-particle diffusion.•The highest adsorption capacities were observed at pH 4.•Hydrophobic interaction was the main adsorption mechanism of chlorophenols on PET.•Hydrogen-bonding interaction enhanced the adsorption of chlorophenols on PET.
Gravity-driven membrane (GDM) filtration has been investigated for almost 10 years. The technology is characterized not only by relatively lower transmembrane pressures which can be achieved by ...gravity (extremely low energy consumption), but also by the phenomenon of flux stabilization: A biofilm is allowed to form on the membrane and a stabilization of flux occurs which is related to biological processes within the biofilm layer on the membrane. This enables stable operation during a year or longer without any cleaning or flushing. Initially, the technology was developed mainly for household drinking water treatment, but in the meantime, the research and application has expanded to the treatment of greywater, rainwater, and wastewater as well as the pretreatment of seawater for desalination. This review covers the field from the rather fundamental research on biofilm morphology and microbial community analysis to the impact of feedwater composition, process parameters and organic removal performance. Not only household applications, but also for community-scale treatment and full-scale applications are discussed. In addition, the application potential is highlighted in comparison to conventional ultrafiltration. Finally, an overall assessment is illustrated and the research and development needs are identified.
•Flux stabilization in gravity-driven UF has first been reported in 2010.•Many papers have described this process for water and wastewater treatment.•Mechanisms of biofilm formation and fouling have been studied.•Improved removal of dissolved compounds has been reported.•Total costs can be lower than conventional UF, depending on the scale of application.
The mechanisms governing interactions among various natural organic matter (NOM) fractions and the subsequently impact on ultrafiltration process have not been systematically studied. In this work, ...bovine serum albumin (BSA), humic acid (HA), sodium alginate (SA) were applied as model NOM to explore the influence of the interactions among NOM on ultrafiltration process. Results indicated that tryptophan-like fluorescence fraction was the dominant reaction fraction of HA to react with SA and BSA. Different interactions among model NOM not only changed the interception order of fluorescence fractions by ultrafiltration from fulvic acid-like, humic-like and tryptophan-like in BSA/HA mixture to tryptophan-like, humic-like and fulvic acid-like in BSA/HA/SA/kaolin mixture, but also remarkably influence the membrane fouling behavior. In BSA/HA mixture, new-generated aggregates with molecular weight (MW) of 10 kDa could not pass though ultrafiltration membrane and mainly contributed to chemical reversible fouling. In BSA/HA/SA mixture, SA simultaneously reacted with BSA and HA to generate aggregates with larger MW which could be washed down by physical cleaning. In BSA/HA/SA/kaolin mixture, the aggregates with MW of 10 kDa and chemical reversible fouling were disappeared due to the adsorption role of kaolin. These findings could further improve our understanding regarding membrane fouling mechanisms of raw water with different components.
We present a summary of part of the phytogeographic results described in the author’s PhD thesis. In this case, we characterise and validate several syntaxa of subsaline meadows in the
nom. corr. ...alliance (class.
) in Catalonia (incl. NE Spain and SE France) and in other regions of the Western Mediterranean (N Algeria, Languedoc and Provence). In total, we study six syntaxa in geobotanical terms, based on synthetic tables and factor analyses of correspondence published previously in the thesis: one alliance (
), two associations and three subassociations (
subass.
, subass.
, subass.
;
).
The quality and quantity of natural organic matter (NOM) has been observed to evolve which poses challenges to water treatment facilities. Even though NOM may not be toxic itself, its presence in ...water has aesthetic effects, enhances biological growth in distribution networks, binds with pollutants and controls the bioavailability of trace metals. Even though NOM has heterogeneous functional groups, the predominant ones are the carboxyl and the phenolic groups, which have high affinities for metals depending on the pH. The properties of both the NOM and the trace elements influence the binding kinetics and preferences. Ca2+ prefers to bind with the carboxylic groups especially at a low pH while Zn2+ prefers the amine groups though practically, most cations bind to several functions groups. The nature of the chemical environment (neighboring ligands) the ligand finds itself equally influences its preference for a cation. The presence of NOM, cations or a complex of NOM-cations may have significant impact on the efficiency of water processes such as coagulation, adsorption, ion exchange resin and membrane filtration. In coagulation, the complexation between the coagulant salts and NOM helps to remove NOM from solution. This positive influence can further be enhanced by the addition of Ca2+. A negative influence is however, observed in lime-softening method as NOM complexes with Ca2+. A negative influence is also seen in membrane filtration where divalent cations partially neutralize the carboxyl functional groups of NOM thereby reducing the repulsion effect on NOM and increasing membrane fouling. The formation of disinfection by-products could either be increased or reduced during chlorination, the speciation of products formed is modified with generally the enhancement of haloacetic acid formation observed in presence of metal cations. This current work, presents in details the interactions of cations and NOM in the environment, the preference of cations for each functional group and the possible competition between cations for binding sites, as well as the possible impacts of the presence of cations, NOM, or their complex on water treatment processes.
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•Existing competition of cations for binding sites of natural organic matter.•Preferences of cations for carboxylic and phenolic biding sites depend on pH.•Complexation of natural organic matter modify its morphology and optical properties.•Positive and negative impacts of complexation of natural organic matter.
Microplastic (MP) pollution is a raising global concern in recent years due to its wide distribution. Additionally, most of the MPs have undergone extensive weathering in the environment, and ...weathered MPs may exhibit different physicochemical properties from pristine ones. The review reveals the change in physicochemical properties (e.g. size, color, crystallinity, mechanical property and oxygen-containing groups) and the release of additives and MP-derived intermediates (i.e. oligomers and oxygenated compounds) during weathering processes. Weathering further affects the sorption behavior of MPs for environmental pollutants because of the changed crystallinity, specific surface area and oxygen functional groups. The interaction mechanisms of pristine and weathered MPs with pollutants are summarized, and how weathering processes affect sorption behavior is critically revealed. Because of the changed size, color and surface charges, weathered MPs might be ingested by aquatic organisms in different ways from the pristine ones. The detailed effects of weathering on the ingestion of MPs are discussed, and the potential toxicity of leachates from weathering processes is evaluated. In addition, the environmental components (e.g. natural organic matter and salinity) and biofilm correlated to the sorption behavior of MPs are reviewed. As for the knowledge gap, further studies should focus on the long-term weathering of MPs and the relationships between weathering properties and sorption capacities toward pollutants. The potential risks of weathered MPs and leachates on organisms should be explored.
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•Weathering significantly changes the physicochemical properties of microplastics.•Surface area, oxygen groups and crystallinity critically affect sorption of pollutants.•Effects of weathering on the risks of microplastics and leachates are revealed.•NOM, salinity and biofilms involved in the environmental behavior are reviewed.
Concerns about possible environmental implications of nano- and micro-plastics are continuously raising. Hence, comprehensive understanding of their behaviour, bioaccumulation and toxicity potential ...is required. Nevertheless, systematic studies on their fate and possible effects in freshwaters, as well as the influence of particle-specific and environmental factors on their behaviour and impacts are still missing. The aims of the present study are thus two-fold: (i) to examine the role of the surface charge on nanoplastic stability and acute effects to freshwater zooplankton; (ii) to decipher the influence of the refractory natural organic matter (NOM) on the nanoplastic fate and effects. Amidine and carboxyl-stabilized polystyrene (PS) spheres of 200 nm diameter characterized by opposite primary surface charges and neutral buoyancy were selected as model nanoplastics. The results demonstrated that the surface functionalization of the polystyrene nanoplastics controls their aggregation behaviour. Alginate or Suwannee River humic acid (SRHA) modified significantly the surface charge of positively-charged amidine PS nanoplastic and the aggregation state, while had no significant influence on the negatively-charged carboxyl PS nanoplastic. Both amidine and carboxyl PS nanoplastics were ingested by the zooplankton and concentrated mainly in the gut of water flea Daphnia magna and larvae Thamnocephalus platyurus, and the stomach of rotifer Brachionus calyciflorus. Amidine PS nanoplastic was more toxic than carboxyl one. The toxicity decreased in the order D. magna (48 h -immobilization) > B. calyciflorus (24 h - lethality) > T. platyurus (24 h - lethality). Alginate or SRHA reduced significantly the toxicity of both amidine and carboxyl PS nanoplastics to the studied zooplankton representatives. The implications of this laboratory study findings to natural environment were discussed.
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•Surface functionalization and charge control nanosphere stability.•Amidine PS nanospheres are more toxic than carboxyl one.•Alginate and humic acid formed eco-corona on amidine PS nanospheres.•Eco-corona modulated the surface charge and reduced toxicity to zooplankton.
Natural organic matter affects the surface charge of model nanoplastics and decreases their toxicity to zooplankton in a way dependent on the nanoplastic primary functionalization.
Iron (hydr)oxides and humic acid (HA) are important active components in soils and usually coexist in the environment. The effects of HA on the adsorption and subsequent immobilization of phosphate ...on iron (hydr)oxide surface are of great importance in studies of soil fertility and eutrophication. In this study, two types of goethite with different particle sizes were prepared to investigate the phosphate adsorption behaviors and complexation mechanisms in the absence or presence of HA by combining multiple characterization and modeling studies. The adsorption capacity of micro- (M-Goe) and nano-sized goethite (N-Goe) for phosphate was 2.02 and 2.04 μmol/m2, which decreased by ∼25% and ∼45% in the presence of 100 and 200 mg/L HA, respectively. Moreover, an increase in equilibrium phosphate concentration significantly decreased the adsorption amount of goethite for HA. Charge distribution-multisite surface complexation (CD-MUSIC) and natural organic matter-charge distribution (NOM-CD) modeling identified five phosphate complexes and their corresponding affinity constants (logKP). Among these phosphate complexes, FeOPO2OH, (FeO)2PO2, and (FeO)2POOH species were predominant complexes on the surface of both M-Goe and N-Goe across a wide range of pH and initial phosphate concentrations. The presence of HA had little effect on the coordination mode and logKP of phosphate on goethite surface. These results and the obtained model parameters shed new lights on the interfacial reactivity of phosphate at the goethite-water interface in the presence of HA, and may facilitate further prediction of the environmental fate of phosphate in soils and sediments.
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•Competition of HA impedes phosphate adsorption and promotes phosphate availability.•The complete parameters of CD-MUSIC and NOM-CD model were proposed.•Five phosphate complexes and their corresponding logKP were identified.•FeOPO2OH, (FeO)2PO2 and (FeO)2POOH are predominant species on goethite surfaces.•HA has little effect on the coordination mode and logKP of phosphate on goethite.
The development of 5G system provides a unique opportunity to implement a unified wireless transmission platform that can simultaneous deliver unicast, multicast and broadcast services using the same ...spectrum and the same infrastructure. This can be achieved by developing a more capable point-to-multipoint transmission (PTM) system component, also called 5G Multimedia Broadcast Multicast Services (5G-MBMS). A properly designed 5G-MBMS could achieve the convergence of terrestrial mobile broadband and TV broadcasting systems.By inherently allowing dynamic spectrum allocation among different types of services, this converged system could offer significant higher spectrum utilization. In this paper, the power-based non-orthogonal multiplexing (P-NOM) technology is proposed in addition to the existing orthogonal time-division-multiplexing (TDM) scheme. Significant capacity gains could be achieved by using P-NOM in a 5G-MBMS system for delivering different types of broadcast services, and for delivering mixed unicast and broadcast services. The capacity benefits of a 5G-MBMS with P-NOM is demonstrated by both theoretical analysis and computer simulations. A key finding is that using a two-layer P-NOM can essentially deliver a broadcast service on top of a unicast network, each achieving nearly full capacity. Next, a complexity analysis will reveal that implementing P-NOM in a 5G-MBMS system does not require significant additional complexity at consumer devices. Finally, it will be shown that, different from the non-orthogonal-multiple-access (NOMA) technologies, using P-NOM in 5G-MBMS system requires little or no change to the existing radio resource allocation mechanisms in LTE and 5G, when one power layer is used for broadcast services delivery.
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