The increasing use of strategies incorporating nanoscale zero valent iron (nZVI) for soil and groundwater in situ remediation is raising some concerns regarding the potential adverse effects nZVI ...could have on indigenous microbial communities and ecosystem functioning. This review provides an overview of the current literature pertaining to the impacts of nZVI applications on microbial communities. Toxicity studies suggest that cell membrane disruption and oxidative stress through the generation of Fe2+ and reactive oxygen species by nZVI are the main mechanisms contributing to nZVI cytotoxicity. In addition, nZVI has been shown to substantially alter the taxonomic and functional composition of indigenous microbial communities. However, because the physico-chemical conditions encountered in situ highly modulate nZVI toxicity, a better understanding of the environmental factors affecting nZVI toxicity and transport in the environment is of primary importance in evaluating the ecological consequences that could result from a more extensive use of nZVI.
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•nZVI toxicity towards microbes is highly modulated by environmental conditions.•Cell membrane disruption and oxidative stress contribute to nZVI toxicity.•Microbes have developed adaptative responses to nZVI toxicity.•nZVI disturbs microbial community taxonomic and functional composition.
An advanced oxidation process of combining cobalt and peracetic acid (Co/PAA) was developed to degrade sulfamethoxazole (SMX) in this study. The formed acetylperoxy radical (CH3CO3 •) through the ...activation of PAA by Co (Co2+) was the dominant radical responsible for SMX degradation, and acetoxyl radical (CH3CO2 •) might also have played a role. The efficient redox cycle of Co3+/Co2+ allows good removal efficiency of SMX even at quite low dosage of Co (<1 μM). The presence of H2O2 in the Co/PAA process has a negative effect on the degradation of SMX due to the competition for reactive radicals. The SMX degradation in the Co/PAA process is pH dependent, and the optimum reaction pH is near-neutral. Humic acid and HCO3 – can inhibit SMX degradation in the Co/PAA process, while the presence of Cl– plays a little role in the degradation of SMX in this system. Although transformation products of SMX in the Co/PAA system show higher acute toxicity, the low Co dose and SMX concentration in aquatic solution can efficiently weaken the acute toxicity. After reaction in the Co/PAA process, numerous carbon sources that could be provided for bacteria and algae growth can be produced, suggesting that the proposed Co/PAA process has good potential when combined with the biotreatment processes.
Chemical oxidation using peracetic acid (PAA) can be enhanced by activation with the formation of reactive species such as organic radicals (R–O•) and HO•. Thermal activation is an alternative way ...for PAA activation, which was first applied to degrade micropollutants in this study. PAA is easily decomposed by heat via both radical and nonradical pathways. Our experimental results suggest that a series of reactive species including R–O•, HO•, and 1O2 can be produced through the thermal decomposition of PAA. Sulfamethoxazole (SMX), a typical sulfa drug, can be effectively removed by the thermoactivated PAA process under conditions of neutral pH. R–O• including CH3C(O)O• and CH3C(O)OO• has been shown to play a primary role in the degradation of SMX followed by direct PAA oxidation in the thermoactivated PAA process. Both higher temperature (60 °C) and higher PAA dose benefit SMX degradation, while coexisting H2O2 inhibits SMX degradation in the thermoactivated PAA process. With a variation of solution pH, conditions near a neutral value show the best performance of this process in SMX degradation. Based on the identified intermediates, transformation of SMX was proposed to undergo oxidation of the amine group and oxidative coupling reactions. This study definitively illustrates the PAA decomposition pathways at high temperature in aquatic solution and addresses the possibility of the thermoactivated PAA process for contaminant destruction, demonstrating this process to be a feasible advanced oxidation process.
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•Ultrafine magnetic carbonaceous sorbents are successfully prepared by ball milling.•Biochar/Fe3O4 exhibits fast and high sorption for carbamazepine and tetracycline.•Ultrafine ...biochar/Fe3O4 and AC/Fe3O4 can be separated magnetically.•Ball milling is effective for degradation of adsorbed CBZ/TC on the adsorbents.•Addition of quartz sand improves the mechanochemical degradation of CBZ.
Ball milling was used to prepare two ultrafine magnetic biochar/Fe3O4 and activated carbon (AC)/Fe3O4 hybrid materials targeted for use in pharmaceutical removal by adsorption and mechanochemical degradation of pharmaceutical compounds. Both hybrid adsorbents prepared after 2h milling exhibited high removal of carbamazepine (CBZ), and were easily separated magnetically. These adsorbents exhibited fast adsorption of CBZ and tetracycline (TC) in the initial 1h. The biochar/Fe3O4 had a maximum adsorption capacity of 62.7mg/g for CBZ and 94.2mg/g for TC, while values obtained for AC/Fe3O4 were 135.1mg/g for CBZ and 45.3mg/g for TC respectively when data were fitted using the Langmuir expression. Solution pH values slightly affected the sorption of TC on the adsorbents, while CBZ sorption was almost pH-independent. The spent adsorbents with adsorbed CBZ and TC were milled to degrade the adsorbed pollutants. The adsorbed TC itself was over 97% degraded after 3h of milling, while about half of adsorbed CBZ were remained. The addition of quartz sand was found to improve the mechanochemical degradation of CBZ on biochar/Fe3O4, and its degradation percent was up to 98.4% at the dose of 0.3g quarts sand/g adsorbent. This research provided an easy method to prepare ultrafine magnetic adsorbents for the effective removal of typical pharmaceuticals from water or wastewater and degrade them using ball milling.
2-methylisoborneol (2-MIB) and geosmin are two odor-causing compounds that are difficult to remove and the cause of many consumer complaints. In this study, we assessed the degradation of 2-MIB and ...geosmin using a UV/persulfate process for the first time. The results showed that both 2-MIB and geosmin could be degraded effectively using this process. The process was modeled based on steady-state assumption with respect to the odor-causing compounds and either hydroxyl or sulfate radicals. The second order rate constants for 2-MIB and geosmin reacting with the sulfate radical (SO4−) were estimated to be (4.2 ± 0.6) × 108 M−1s−1 and (7.6 ± 0.6) × 108 M−1s−1 respectively at a pH of 7.0. The contributions of the hydroxyl radical (OH) to 2-MIB and geosmin degradation were 3.5 times and 2.0 times higher, respectively, than the contribution from SO4− in Milli-Q water with 2 mM phosphate buffer at pH 7.0. The pseudo-first-order rate constants (kos) of both 2-MIB and geosmin increased with increasing dosages of persulfate. Although pH did not affect the degradation of 2-MIB and geosmin directly, different scavenging effects of hydrogen phosphate and dihydrogen phosphate resulted in higher values of kos for both 2-MIB and geosmin in acidic condition. Bicarbonate and natural organic matter (NOM) inhibited the degradation of both 2-MIB and geosmin dramatically through consuming OH and SO4− and were likely to be the main radical scavengers in natural waters when using UV/persulfate process to control 2-MIB and geosmin.
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•Degradation of 2-MIB and geosmin by UV/persulfate was evaluated for the first time.•A model was set up to study the kinetics in UV/persulfate process for the first time.•Impacts of different conditions including pHs and dosages of persulfate were discussed.•Different scavengers including NOM and bicarbonate ions were discussed.
To achieve greater separation performance and antifouling properties in a thin-film composite (TFC) nanofiltration membrane, cellulose nanocrystals (CNCs) were incorporated into the polyamide layer ...of a TFC membrane for the first time. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the successful formation of the CNC-polyamide composite layer. Surface characterization results revealed differences in the morphologies of the CNC-TFC membranes compared with a control membrane (CNC-TFC-0). Streaming potential measurements and molecular weight cutoff (MWCO) characterizations showed that the CNC-TFC membranes exhibited a greater negative surface charge and a smaller MWCO as the CNC content increased. The CNC-TFC membranes showed enhanced hydrophilicity and increased permeability. With the incorporation of only 0.020 wt % CNCs, the permeability of the CNC-TFC membrane increased by 60.0% over that of the polyamide TFC without CNC. Rejection of Na2SO4 and MgSO4 by the CNC-TFC membranes was similar to that observed for the CNC-TFC-0 membrane, at values of approximately 98.7% and 98.8%, respectively, indicating that divalent salt rejection was not sacrificed. The monovalent ion rejection tended to increase as the CNC content increased. In addition, the CNC-TFC membranes exhibited enhanced antifouling properties due to their increased hydrophilicity and more negatively charged surfaces.
Uptake, transport and toxicity of engineered nanomaterials (ENMs) into plant cells are complex processes that are currently still not well understood. Parts of this problem are the multifaceted plant ...anatomy, and analytical challenges to visualize and quantify ENMs in plants. We critically reviewed the currently known ENM uptake, translocation, and accumulation processes in plants. A vast number of studies showed uptake, clogging, or translocation in the apoplast of plants, most notably of nanoparticles with diameters much larger than the commonly assumed size exclusion limit of the cell walls of ∼5-20 nm. Plants that tended to translocate less ENMs were those with low transpiration, drought-tolerance, tough cell wall architecture, and tall growth. In the absence of toxicity, accumulation was often linearly proportional to exposure concentration. Further important factors strongly affecting ENM internalization are the cell wall composition, mucilage, symbiotic microorganisms (mycorrhiza), the absence of a cuticle (submerged plants) and stomata aperture. Mostly unexplored are the roles of root hairs, leaf repellency, pit membrane porosity, xylem segmentation, wounding, lateral roots, nodes, the Casparian band, hydathodes, lenticels and trichomes. The next steps towards a realistic risk assessment of nanoparticles in plants are to measure ENM uptake rates, the size exclusion limit of the apoplast and to unravel plant physiological features favoring uptake.
In this study, ultraviolet based advanced oxidation processes (UV-AOPs) including UV/persulfate (UV/PS), UV/chlorine, and UV/H2O2 were employed to alleviate ultrafiltration membrane fouling during ...the treatment of algae-laden water. The results show that UV/PS pretreatment exhibited the best performance on fouling control, followed by the UV/H2O2 pretreatment. The fouling mitigation performance improved with the increase of oxidant dose. However, UV/chlorine pretreatment aggravated membrane fouling, and the irreversible fouling resistance increased by five times compared with that of raw water. The dissolved organic carbon (DOC) in the algae-laden solution was reduced after UV/PS pretreatment, while either UV/chlorine or UV/H2O2 pretreatment had little influence on the DOC of feed water. UV/PS and UV/H2O2 pretreatments were effective in the degradation of fluorescent compounds, thus reducing the deposition of organic matter on the membrane surface. Additionally, the decreased concentration of hydrophobic organics, algal cells, and debris in feed water after UV/PS pretreatment was also contributed to the fouling alleviation. The aggravated irreversible fouling after UV/chlorine pretreatment was probably ascribed to the increased accumulation of hydrophobic fractions in the membrane pores. Modeling result indicates that membrane fouling during the filtration of raw algae-laden water was dominated by intermediate blocking and cake filtration mechanisms. Both UV/PS and UV/H2O2 pretreatments transformed the combined fouling mechanism into standard blocking, while UV/chlorine pretreatment aggravated the pore blocking in the initial filtration period.
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•UV/PS pretreatment effectively mitigated fouling caused by algae-laden water.•UV/H2O2 pretreatment reduced fouling at high H2O2 dose.•UV/chlorine pretreatment significantly aggravated irreversible fouling.•Intrinsic mechanisms of membrane fouling after UV-AOPs pretreatment were proposed.
•Modeled phage heteroaggregation using modified-Smoluchowski aggregation theory.•Adapted batch assays from nanoparticle studies to characterize phage attachment.•Phage removal can be altered by ...manipulating velocity gradient.
The validity and usefulness of implementing bacteriophages into water treatment systems as agents of targeted bacterial inactivation is yet to be determined. While some concerns are still more purely biological in nature other concerns are still chiefly rooted in design feasibility. This work investigated bacteriophage heteroaggregation, a process whereby phages attach to non-host background particles, to explore different design options for water quality engineers, especially tuning mixing velocity. This was done by adapting batch/mixing assays, originally developed to study inert particle heteroaggregation, to characterize bacteriophage and kaolinite heteroaggregation using modified Smoluchowski parameters under different ionic strength conditions. This work found that regardless of the ionic strength or the tested phage to kaolinite ratios heteroaggregation occurred rapidly and was likely driven by extended DLVO forces. A model of bacteriophage-kaolinite heteroaggregation was generated and showed promising correspondence with observed laboratory data. This model, along with other findings, suggests that should bacteriophages be utilized as agents of host inactivation they ought to be used following particle separation processes to reduce the likelihood of phage scavenging through attachment to particulate matter rather than the targeted bacteria.
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Predicting nanoparticle fate in aquatic environments requires mimicking of ecosystem complexity to observe the geochemical processes affecting their behaviour. Here, 12 nm Au nanoparticles were added ...weekly to large-scale freshwater wetland mesocosms. After six months, ~70% of Au was associated with the macrophyte Egeria densa, where, despite the thermodynamic stability of Au
in water, the pristine Au
nanoparticles were fully oxidized and complexed to cyanide, hydroxyls or thiol ligands. Extracted biofilms growing on E. densa leaves were shown to dissolve Au nanoparticles within days. The Au biodissolution rate was highest for the biofilm with the lowest prevalence of metal-resistant taxa but the highest ability to release cyanide, known to promote Au
oxidation and complexation. Macrophytes and the associated microbiome thus form a biologically active system that can be a major sink for nanoparticle accumulation and transformations. Nanoparticle biotransformation in these compartments should not be ignored, even for nanoparticles commonly considered to be stable in the environment.
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