Enhanced activation of peroxymonosulfate by CNT-TiO2 under UV-light assistance for efficient degradation of organic pollutants

CNT-TiO₂ composite is used to activate PMS under UV-light assistance. Superior performance is due to the enhanced electron-transfer ability of CNT. SO₄•⁻, •OH and ¹O₂ play key roles in the degradation of organic pollutants. In this work, a UV-light assisted peroxymonosulfate (PMS) activation system was constructed with the composite catalyst of multi-walled carbon nanotubes (CNT) - titanium dioxide (TiO₂). Under the UV light irradiation, the photoinduced electrons generated from TiO₂ could be continuously transferred to CNT for the activation of PMS to improve the catalytic performance of organic pollutant degradation. Meanwhile, the separation of photoinduced electron-hole pairs could enhance the photocatalysis efficiency. The electron spin resonance spectroscopy (EPR) and quenching experiments confirmed the generation of sulfate radical (SO₄•⁻), hydroxyl radical (•OH) and singlet oxygen (¹O₂) in the UV/PMS/20%CNT-TiO₂ system. Almost 100% phenol degradation was observed within 20 min UV-light irradiation. The kinetic reaction rate constant of the UV/PMS/20%CNT-TiO₂ system (0.18 min⁻¹) was 23.7 times higher than that of the PMS/Co₃O₄ system (0.0076 min⁻¹). This higher catalytic performance was ascribed to the introduction of photoinduced electrons, which could enhance the activation of PMS by the transfer of electrons in the UV/PMS/CNT-TiO₂ system.     

Effects of cultivation strategies on the cultivation of Chlorella sp. HQ in photoreactors

Heterotrophic cultivation caused high level of ROS and high lipids accumulation. HMTC is the best culture strategy for improving the microalgal biomass. Chlorella sp. HQ had great nutrient removal capacity under five culture strategies. The effects of cultivation strategies (including autotrophic cultivation (AC), heterotrophic cultivation (HC), fed-batch cultivation (FC), heterotrophic+ autotrophic two-stage cultivation (HATC), and heterotrophic+ mixotrophic two-stage cultivation (HMTC)) on the growth and lipid accumulation of Chlorella sp. HQ and its total nitrogen (TN) and total phosphorus (TP) removal in secondary effluent were investigated in column photoreactors. The results showed that the TN and TP removal rates ranged between 93.72%–95.82% and 92.73%–100%, respectively, under the five different strategies. The microalgal growth potential evaluated by the maximal growth rate (R_max) was in the order of HMTC>HC>FC>AC>HATC. The values of biomass, total lipid yield, triacylglycerols (TAGs) yield, and total lipid content of the microalga cultivated in the last 5 d increased significantly, but the TAGs productivities of the five strategies were lower than those in the first 7 d. Compared with all the other cultivation strategies, the TAGs productivity and yield after 12 d of cultivation under the heterotrophic condition reached the highest values accompanying the highest level of intracellular reactive oxygen species (ROS), in which the TAGs yield reached 40.81 mg/L at the end of the cultivation period. The peaks in TAGs yield and ROS level suggested that HC was beneficial for lipids accumulation via regulating the cellular redox status and exerting ROS stress on microalgal cells. In summary, HMTC was the best cultivation strategy for improving the microalgal biomass and HC was the best strategy for microalgal TAGs accumulation to produce biodiesel.     

Recovery of Ni(II) from real electroplating wastewater using fixed-bed resin adsorption and subsequent electrodeposition

Resin adsorption and subsequent electrodeposition were used for nickel recovery. Treated wastewater can meet the Electroplating Pollutant Discharge Standard. The spent resin is completely regenerated by 3 BV of 4% HCl solution. 95.6% of nickel in concentrated eluent was recovered by electrodeposition. Effective recovery of high-value heavy metals from electroplating wastewater is of great significance, but recovering nickel ions from real electroplating wastewater as nickel sheet has not been reported. In this study, the pilot-scale fixed-bed resin adsorption was conducted to recover Ni(II) ions from real nickel plating wastewater, and then the concentrated Ni(II) ions in the regenerated solution were reduced to nickel sheet via electrodeposition. A commercial cation-exchange resin was selected and the optimal resin adsorption and regeneration conditions were investigated. The resin exhibited an adsorption capacity of 63 mg/g for Ni(II) ions, and the average amount of treated water was 84.6 bed volumes (BV) in the pilot-scale experiments. After the adsorption by two ion-exchange resin columns in series and one chelating resin column, the concentrations of Ni(II) in the treated wastewater were below 0.1 mg/L. After the regeneration of the spent resin using 3 BV of 4% (w/w) HCl solution, 1.5 BV of concentrated neutral nickel solution (>30 g/L) was obtained and used in the subsequent electrodeposition process. Using the aeration method, alkali and water required in resin activation process were greatly reduced to 2 BV and 3 BV, respectively. Under the optimal electrodeposition conditions, 95.6% of Ni(II) in desorption eluent could be recovered as the elemental nickel on the cathode. The total treatment cost for the resin adsorption and regeneration as well as the electrodeposition was calculated.     

Interactive effects of single,binary and trinary trace metals (lead,zinc and copper) on the physiological responses of Kandelia obovata seedlings

Environmental Geochemistry and Health - Heavy metals are considered important environmental contaminants, and their mixture toxicity on plants has complex mutual interactions. The interactive...     

Comparison of CNT-PVA membrane and commercial polymeric membranes in treatment of emulsified oily wastewater

CNT-PVA membrane was fabricated and compared with polymeric membranes. The separation performance was evaluated by homemade and cutting fluid emulsions. The three membranes show similar oil retention rates. CNT-PVA membranes have higher permeation fluxes compared with polymeric membranes. CNT-PVA membrane shows higher fouling resistance. Membrane separation is an attractive technique for removal of emulsified oily wastewater. However, polymeric membranes which dominate the current market usually suffer from severe membrane fouling. Therefore, membranes with high fouling resistance are imperative to treat emulsified oily wastewater. In this study, carbon nanotube-polyvinyl alcohol (CNT-PVA) membrane was fabricated. And its separation performance for emulsified oily wastewater was compared with two commercial polymeric membranes (PVDF membrane and PES membrane) by filtration of two homemade emulsions and one cutting fluid emulsion. The results show that these membranes have similar oil retention efficiencies for the three emulsions. Whereas, the permeation flux of CNT-PVA membrane is 1.60 to 3.09 times of PVDF membrane and 1.41 to 11.4 times of PES membrane, respectively. Moreover, after five consecutive operation circles of filtration process and back flush, CNT-PVA membrane can recover 62.3% to 72.9% of its initial pure water flux. However, the pure water flux recovery rates are only 24.1% to 35.3% for PVDF membrane and 6.0% to 26.3% for PES membrane, respectively. Therefore, CNT-PVA membrane are more resistant to oil fouling compared with the two polymeric membranes, showing superior potential in treatment of emulsified oily wastewater.     

Source attribution for mercury deposition with an updated atmospheric mercury emission inventory in the Pearl River Delta Region,China

Estimated anthropogenic Hg emission was 11.9 tons in Pearl River Delta for 2014. Quantifying contributions of emission sources helps to provide control strategies. More attentions should be paid to Hg deposition around the large point sources. Power plant, industrial source and waste incinerator were priorities for control. A coordinated regional Hg emission control was important for controlling pollution. We used CMAQ-Hg to simulate mercury pollution and identify main sources in the Pearl River Delta (PRD) with updated local emission inventory and latest regional and global emissions. The total anthropogenic mercury emissions in the PRD for 2014 were 11,939.6 kg. Power plants and industrial boilers were dominant sectors, responsible for 29.4 and 22.7%. We first compared model predictions and observations and the results showed a good performance. Then five scenarios with power plants (PP), municipal solid waste incineration (MSWI), industrial point sources (IP), natural sources (NAT), and boundary conditions (BCs) zeroed out separately were simulated and compared with the base case. BCs was responsible for over 30% of annual average mercury concentration and total deposition while NAT contributed around 15%. Among the anthropogenic sources, IP (22.9%) was dominant with a contribution over 20.0% and PP (18.9%) and MSWI (11.2%) ranked second and third. Results also showed that power plants were the most important emission sources in the central PRD, where the ultra-low emission for thermal power units need to be strengthened. In the northern and western PRD, cement and metal productions were priorities for mercury control. The fast growth of municipal solid waste incineration were also a key factor in the core areas. In addition, a coordinated regional mercury emission control was important for effectively controlling pollution. In the future, mercury emissions will decrease as control measures are strengthened, more attention should be paid to mercury deposition around the large point sources as high levels of pollution are observed.     

Carbon nanotubes-incorporated MIL-88B-Fe as highly efficient Fenton-like catalyst for degradation of organic pollutants

CNTs were incorporated into MIL-88B-Fe to get a new Fenton-like catalyst (C@M). Fe(II) was introduced in C@M to get a fast initiation of Fenton-like reaction. Fe(II) content in C@M was related with oxygen-containing functional groups on CNTs. C@M shows efficient catalytic degradation of pollutants over a wide pH range. Iron-based metal organic frameworks have been verified to be efficient heterogeneous Fenton catalysts due to their open pore channels and highly uniform distribution of metallic centers. In these catalysts, however, the iron element is mainly in the form of Fe(III), which results in a process required to reduce Fe(III) to Fe(II) to initiate Fenton reaction. To address this problem, carbon nanotubes (CNTs) with electron-rich oxygen-functional groups on the surface were incorporated into the metal organic frameworks (MIL-88B-Fe) to improve Fe(II) content for an enhanced Fenton-like performance. The prepared CNT@MIL-88B-Fe (C@M) showed much stronger catalytic ability toward H₂O₂ than MIL-88B-Fe. The pseudo-first-order kinetic constant for phenol degradation by C@M (0.32 min^–1) was about 7 times that of MIL-88B-Fe, and even higher than or comparable to the values of reported heterogeneous Fenton-like catalysts. Moreover, the Fenton-like system could effectively degrade various kinds of refractory organic pollutants and exhibited excellent catalytic activity over a wide pH range (4–9). XPS analysis confirmed that Fe(II) content of the catalyst gradually increased with CNT loadings. Electron spin resonance analysis showed that the signal intensity (•OH) of C@M was much higher than MIL-88B-Fe, which was consistent with the degradation efficiency of pollutants. Furthermore, the Fe(II) content of the catalyst gradually increased along with the oxygen-functional group content of CNTs. The result demonstrated that oxygen-containing functional groups of CNTs have a significant impact on the enhanced catalytic performance of C@M. This study provides a new insight to enhance Fenton reaction by using nanocarbon materials.     

Degradation of extracellular genomic,plasmid DNA and specific antibiotic resistance genes by chlorination

Extracellular DNA structure damaged by chlorination was characterized. Integrity of extracellular ARG genetic information after chlorination was determined. Typical chlorine doses will likely effectively diminish extracellular DNA and ARGs. Plasmid DNA/ARGs were less readily broken down than genomic DNA. The Bioanalyzer methodology effectively documented damage incurred to DNA. There is a need to improve understanding of the effect of chlorine disinfection on antibiotic resistance genes (ARGs) in order to advance relevant drinking water, wastewater, and reuse treatments. However, few studies have explicitly assessed the physical effects on the DNA. Here we examined the effects of free chlorine (1–20 mg Cl₂/L) on extracellular genomic, plasmid DNA and select ARGs. Chlorination was found to decrease the fluorometric signal of extracellular genomic and plasmid DNA (ranging from 0.005 to 0.05 mg/mL) by 70%, relative to a no-chlorine control. Resulting DNA was further subject to a fragment analysis using a Bioanalyzer, indicating that chlorination resulted in fragmentation. Moreover, chlorine also effectively deactivated both chromosomal- and plasmid-borne ARGs, mecA and tetA, respectively. For concentrations >2 mg Cl₂//L × 30 min, chlorine efficiently reduced the qPCR signal when the initial concentration of ARGs was 10⁵ copies/mL or less. Notably, genomic DNA and mecA gene signals were more readily reduced by chlorine than the plasmid-borne tetA gene (by ~2 fold). Based on the results of qPCR with short (~200 bps) and long amplicons (~1200 bps), chlorination could destroy the integrity of ARGs, which likely reduces the possibility of natural transformation. Overall, our findings strongly illustrate that chlorination could be an effective method for inactivating extracellular chromosomal- and plasmid-borne DNA and ARGs.     

An asymmetric analysis of the impacts of energy use on carbon dioxide emissions in the G7 countries

Environmental Science and Pollution Research - The foremost theme of the paper is to explore the asymmetric/symmetric impact of energy consumption on the carbon dioxide emission of G7 countries...     

Spatial distribution characteristics of soil organic carbon in subtropical forests of mountain Lushan,China

The study on the spatial distribution of forest soil organic carbon (SOC) is of great significance for accurate assessment of carbon storage in forest ecosystems. In the present study, by taking eight kinds of forest soils of Mountain Lushan in the subtropical area as the research object, we studied the spatial distribution characteristics of SOC in this mountainous area. The results showed that the SOC content and SOC density (SOCD) of main forest types in the Mountain Lushan were lower than the national and the world average. The soil layer of Lushan forest was thinner, and the SOC and active SOC (ASOC) contents of different forest types and SOCDs are the highest in the surface soil. SOCD of the topsoil accounts for 32.64–54.03% of the total SOCD in the whole soil profile. Surface litter is an important source of SOC, and the different vegetation types are the important reason for the different spatial distribution of SOC in this area. Soil SOC contents in the high-altitude forest (bamboo forest, deciduous broadleaf forest, Pinus taiwanensis forest, evergreen-deciduous forest, and coniferous-broadleaved mixed forest) were higher than those in the low-altitude forest (evergreen broadleaf forest, shrub, and Pinus massoniana forest). However, the difference in SOC content exhibited at the altitude gradient is significantly lower than that in SOC in the soil profile. This indicates that both soil depth and elevation are the important factors that affected SOC distribution. However, the influence of soil depth on spatial distribution of SOC may be more complex than that of altitude. Vegetation types and soil properties are the main reasons for the large differences of reduction rate in the contents of SOC and ASOC.