High-concentration Pollutants Research Articles

Start-up of pilot-scale ANAMMOX reactor for low-carbon nitrogen removal from anaerobic digestion effluent of kitchen waste

The pilot-scale simultaneous denitrification and methanation (SDM)-partial nitrification (PN)-anaerobic ammonia oxidation (Anammox) system was designed to treat anaerobic digestion effluent of kitchen waste (ADE-KW). The SDM-PN was first started to avoid the inhibition of high-concentration pollutants. Subsequently, Anammox was coupled to realize autotrophic nitrogen removal. Shortcut nitrification–denitrification achieved by the SDM-PN. The NO2–-N accumulation (92 %) and NH4+-N conversion (60 %) were achieved by PN, and the removal of TN and COD from the SDM-PN was 70 % and 73 %, respectively. After coupling Anammox, the TN (95 %) was removed with a TN removal rate of 0.51 kg·m−3·d-1. Microbiological analyses showed a shift from dominance by Methanothermobacter to co-dominance by Methanothermobacter, Thermomonas, and Flavobacterium in SDM during the SDM-PN. While after coupling Anammox, Candidatus kuenenia was enriched in the Anammox zone, the SDM zone shifted back to being dominated by Methanothermobacter. Overall, this study provides new ideas for the treatment of ADE-KW.

Bi-element gradient doped B/N-TiO2-x synthesized by one-step solvothermal method enhances the photocatalysis of Cr(VI)

Studying the influence of non-uniform distribution of bi-element doping on the surface structure and photocatalytic performance of TiO2 in interface photocatalytic processes can be an interesting research topic. Taking B/N bi-element doped TiO2 as an example, this article reports an extremely simple gradient doping method of TiO2 and its enhancement mechanism for high concentration wastewater treatment. The surface enrichment and doping of B caused by electrostatic and atomic radius factors changed the charge properties of the complex during the induction of in-situ reduction of Ti4+. The defects in gap N and Ti3+ lead to the formation of intermediate states, resulting in a narrowing of the band gap of the composite to 2.58 eV. The gradient doping of two atoms endows the optimal photocatalyst with a larger specific surface area (114 m2∙g), stronger photocurrent response (0.179 mA·cm−2), suitable Ti3+/Ov double defect structure, and surface positive charge properties. These characteristics improve the effective treatment of high-concentration pollutants by the preferred B2/N-TiO2-x [e.g., 0.0059 min−1 for 0.5 g·L-1 Cr(VI)] and sustainable treatment (removal efficiency > 90 % within 5 cycles). The synthesis strategy will provide a fast, simple, and safe method for the design and synthesis of new TiO2 based catalysts in the future.

Research on Dust Migration and Dust Deposition Rules of Breathing Zone in Fully Mechanized Mining Face.

The dust in the breathing zone of the fully mechanized mining face poses a serious threat to the lives and health of the workers, and clarifying the distribution and settlement pattern of the dust in the breathing zone is an important foundation for reducing dust concentrations in the breathing zone and improving the workers' working environment. The dust concentration distribution at the mining face and the settlement results of different dust particle sizes along the breathing zone were analyzed in detail using a combination of computational fluid dynamics simulation and downhole measurements by establishing a highly simulated 3D solid model of the 2302 fully mechanized mining face at the Xinqiao coal mine. The study's findings reveal that dust from advanced support and coal-cutting processes converge within 20-60 m of the coal mining region, generating a high-concentration pollution zone at the height of the sidewalk breathing zone. The particle size of dust in the breathing zone is primarily concentrated between 1 and 40 μm, and the fully mechanized mining face is split into a rapid settling area, a medium settling area, and a slow settling area based on particle size settling speed. Eddy currents in the return airway lead to an increase in dust particles of 20-40 μm in the breathing zone area. The results of the study can provide a theoretical basis for dust management at the fully mechanized mining face for the breathing zone area.

Rebuilding high-quality near-surface ozone data based on the combination of WRF-Chem model with a machine learning method to better estimate its impact on crop yields in the Beijing-Tianjin-Hebei region from 2014 to 2019

In recent years, the problem of surface ozone pollution in China has been of great concern. According to observation data from monitoring stations, the concentration of near-surface ozone (O3) in China has gradually increased in recent years, and ozone concentration often exceeds the contaminant limit standard, especially in the Beijing-Tianjin-Hebei (BTH) region. High O3 concentration pollution will adversely affect crop growth, which can cause crop yield losses. Therefore, it is urgent to recognize the situation of ozone pollution in the BTH region and quantitatively evaluate the crop yield losses caused by ozone pollution to develop more effective pollution prevention and control policies. However, the monitoring of ozone concentration in China started relatively late compared with some developed countries, and currently, long-time series data covering the BTH region cannot be obtained, which makes it difficult to evaluate the impact of ozone on crop yield. Therefore, a new method (WRFC-XGB) was proposed in this study to establish a high-precision near-surface O3 concentration dataset covering the whole BTH region from 2014 to 2019 by integrating the Weather Research and Forecasting with Chemistry (WRF-Chem) model with the extreme gradient boosting (XGBoost) machine learning algorithm. Through verification with ground observation station data, the results of WRFC-XGB are satisfactory, and R2 can reach 0.78–0.91. Compared with other algorithms, the accuracy of the near-surface ozone concentration dataset is greatly improved, which can be used to estimate the impact of surface ozone on crop yield. Based on this dataset, the yield loss of winter wheat, rice, and maize caused by O3 pollution was estimated by using the response equation of the relative yield and ozone dose index. The results showed that the total yield losses of winter wheat, rice and maize from 2014 to 2019 were 2659.21 million tons, 49.23 million tons and 1721.56 million tons due to ozone pollution in the BTH region, respectively, and the highest relative yield loss of crops caused by O3 pollution could be 29.37% during 2014–2019, which indicated that the impact of ozone pollution on crop yield cannot be ignored, and effective measures need to be developed to control ozone pollution, prevent crop production loss, and ensure people's food security.

Migration Behavior of NH4+ and Na+ in a Bentonite-Clay Mixed Soil Column and Numerical Simulation

The landfill barriers effectively prevented the migration of high-concentration pollutants, such as NH4+ and Na+, from the landfills to the surrounding environment. However, due to the high hydraulic head inside the landfill compared to the surrounding environment, NH4+ and Na+ can migrate towards the outside of the landfill barrier with the infiltrating solution, potentially causing harm to the surrounding environment. To address this, saturated mixed soil column samples made of bentonite and Shanghai clay, with bentonite contents of 3% and 10%, were used in this study. Permeability coefficients of the column samples in solutions are obtained by using permeation tests, and using NaCl and NH4Cl solutions with concentrations of 37.4 mmol/L and 74.8 mmol/L, respectively. The concentration-depth result of the column samples after permeation tests was determined using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and Ion Chromatography (ICS-1100). Numerical simulations are used to investigate the effect of downstream solute concentration of the barriers on upstream solute concentration, dry density, and bentonite content of the barriers. The results indicate that the permeability coefficient of the soil column samples exposed to NH4Cl solution is greater than that of samples exposed to NaCl solution. This can be attributed to the stronger cation exchange of montmorillonite for NH4+, resulting in less swelling of the bentonite and more micro-pores, leading to an increase in the permeability coefficient. The concentration of Na+ is higher than that of NH4+ at the same depth of the column samples, indicating that Na+ has a higher migration rate in the column sample. This could be attributed to the relatively fast diffusion of Na+ on the surface of the bentonite and larger hydration radius of Na+. According to the simulation results, the recommended values for the bentonite clay mixed-soil barrier wall are as follows in this study: a thickness of 43 cm, a dry density of 1.5 g/cm3, and a bentonite content of 5%.

Numerical investigation on particle removal and energy consumption of supplied and recirculated ventilation for industrial workshop

In the weld back-cleaning process, many high-concentration pollutants are produced, which can lead to health problems after prolonged exposure. In this study, a novel recirculating stratified ventilation system is proposed that combines supply and recirculating ventilation. It reduces indoor particulate concentration and exhausts air volume based on the air gouging process in a casting workshop. The influences of the supplied and recirculated air velocities on the particle removal efficiency and energy consumption were investigated and compared with those of a traditional exhaust system. The computational fluid dynamics-discrete phase model coupling method was adopted. First, the feasibility of the model was verified using previously published experimental data. The concentration of the unsteady particles was then simulated with different supplied and recirculated air velocities in the ventilation system. The particles were dispersed owing to the influence of the heat-source temperature. With an increasing supplied air velocity and constant recirculated air velocity, the average particle concentration was decreased. The results show that the particle removal efficiency can be improved by approximately 100%, and 90% of the energy can be saved to achieve the same removal efficiency as a traditional ceiling exhaust system.

Study on Retrofitting of Small-scale Water Supply Facility using aeration and Closed-circuit Reverse Osmosis

Objectives : A water treatment system, combining aeration and reverse osmosis (RO) processes, was introduced to improve water supply facilities in a small village where additional water treatment was required due to high concentrations of natural radioactive substances, nitrate nitrogen, and fluoride. In this study, CCRO(Closed-circuit reverse osmosis) was first introduced for commercial use in Korea. With this system, we evaluated its water treatment efficiency and effectiveness of blending the aerated water and RO permeate for improved waterworks in rural areas.Methods : The removal rate of major pollutants and other ionic substances was evaluated by analyzing the water quality of raw water and unit processes. In addition, the operational efficiency of a small-scale water supply facility was verified and optimized by evaluating a change in operational characteristics depending on the blending ratio of the treated waters by aeration and CCRO processes.Results and Discussion : Up to 86% of the radon contained in raw water was removed by the aeration process within 2 hours, and 98.9% of uranium, 85.5% of nitrate nitrogen, and 82.8% of fluoride were removed by the RO process. In the case of other ionic substances, more than 80% was removed on average by the RO process. The higher blending ratio of RO permeate up to 75% resulted in the better quality of the final treated water. However, since requiring the high flux and pressure (at 1.8 m<sup>3</sup>/hr and 7.6 bar, respectively), CCRO operation resulted in a relatively high specific power consumption at 0.27 kWh/m<sup>3</sup>.Conclusion : In this study, we found that the major contaminants (natural radioactive substances, nitrate nitrogen, and fluoride) were effectively removed by the water treatment system wherein the aeration and CCRO processes were combined. In particular, it was confirmed for the first time in Korea that the stable operation and water treatment efficiency of the CCRO process was satisfactory for commercial purposes. It could produce high-quality tap water through the blending of waters treated by aeration and CCRO, expecting that meeting drinking-water quality standards would be attainable even when raw water contains high-concentration pollutants.

Synergistic Effect of Atmospheric Boundary Layer and Regional Transport on Aggravating Air Pollution in the Twain-Hu Basin: A Case Study

The impact of structural variations in the atmospheric boundary layer (ABL) during the regional transport of air pollutants on its local pollution changes deserves attention. Based on multi-source ABL detection and numerical simulation of air pollutants over the Twain-Hu Basin (THB) during 4–6 January 2019, the mechanism of the rapid growth of atmospheric pollutant concentrations in Xianning by the synergistic effect of regional transport and ABL evolution is explored, and the main conclusions are obtained as follows. The vertically stratified atmosphere is noticeable at nighttime, and the heavy humidity of near-surface fog within the stable boundary layer (SBL) promoted the generation and cumulative growth of secondary PM2.5 components during the pollution formation stage. The horizontal transport characteristics of atmospheric pollutant concentration peak were observed in the residual layer (RL) of 500–600 m. At the pollution maintenance stage, the convective boundary layer (CBL) developed during the daytime, and northerly wind transported high-concentration pollutants from the north to the THB. Under the combined action of horizontal transport and turbulent mixing, the high-concentration atmospheric pollutants in the mixing layer (ML) from the ground to the 500 m height were mixed uniformly and maintained accumulation growth. The next day, the strong vertical turbulent mixing caused the downward transport of high-concentration pollutants in the RL during nighttime due to the development of the CBL again, resulting in a doubling of near-surface pollutant concentration in a short time. With the development of ABL turbulence, local pollution dissipated rapidly without the continuous input of pollutants from external regions. This study emphasizes the importance of multi-scale processes impact on pollution variation, that is, regional transport of atmospheric pollutants at the CBL development stage for the rapid growth of PM2.5 concentration in the ML.

Effect of bubble cutting on spray characteristics and dust control performance in the effervescent atomization

Effervescent atomization performance depends on the bubble size inside the mixing chamber, consequently influencing the spray dust control performance. This paper proposes an optimization of atomization quality and dust control performance by incorporating a bubble cutter in the atomizer mixing chamber. The effects of the bubble cutter aperture on spray characteristics and flow characteristics were experimentally investigated under different operating conditions. Experimental results showed that Sauter means diameter (SMD) decreases with increasing injection pressure and gas-liquid mass flow ratio (GLR). Furthermore, SMD initially increased and then decreased by reducing the aperture of the bubble cutter from 500 µm to 80 µm. In particular, high injection pressure (Pi =0.6 MPa) and low gas-liquid mass flow ratio (GLR=0.09) strengthened the effects of the bubble cutter aperture on SMD. Moreover, bubble cutter causes a contiguous concentrated droplet size distribution, but it has little effect on droplet velocity. Ultimately, the optimal bubble cutter aperture on the efficiency of respirable dust control efficiencies was theoretically calculated. The dust control efficiency is a maximum at the bubble cutter with an aperture of 230 µm for the effervescent atomizer in this paper. Spray dust control efficiency reaches 93.15 %, which effectively solves the problem of high dust concentration pollution in the mechanized working environment.

Groundwater Pollution Model and Diffusion Law in Ordovician Limestone Aquifer Owe to Abandoned Red Mud Tailing Pit

Red mud is a strong alkaline solid waste pollutant produced in the process of aluminum smelting, which causes great pollution to the regional groundwater environment due to its high content of fluorine and aluminum and high concentration of strong alkali. In this study, fluoride ion was selected as the model contaminant, and a numerical model of the groundwater flow field and solute transport was developed using GMS software to simulate and analyze the migration patterns of fluoride contaminants caused by the red mud pit for the fractured karst geohydrological conditions. The results demonstrated that the groundwater model and flow pattern were mainly controlled by atmospheric precipitation recharge, given flow boundary conditions and leakage of rivers and drains. When the concentration of fluorine pollutants in the red mud yard was 60.0 mg/L, the maximum migration distance of F− in the groundwater of the ordovician limestone aquifer was 473, 1160, 1595 and 1750 m after 1, 5, 10 and 15 years of bottom leakage, and the additional transport distances were 687, 435 and 155 m every 5 years, respectively. The range of F− pollution plume was 0.37 km2, 1.15 km2, 1.95 km2 and 2.14 km2, respectively and the range of newly added pollution plume was 0.78 km2, 0.80 km2 and 0.19 km2, respectively, every five years. Both indicated that with the extension of time, the migration and diffusion rate of pollutants slow down, and the diffusion volume increased first and then decreased. The F− pollution plume spread from the red mud pit to the northeast, which was consistent with the flow of groundwater. The high-concentration pollution plume was mainly distributed in the Ordovician limestone fractured aquifer in the northeast. This study revealed the migration law of red mud pollutants, and provided a scientific decision-making basis for the prevention and control of red mud groundwater pollution in the future.

Groundwater Risk Assessment of a Rock Cave Type Landfill with Nontraditional Solid Waste

Rock cave landfill has the characteristics of superior geological conditions and strong risk controllability. In this study, taking the first rock cave type nontraditional solid waste landfill in a uranium mine in China as an example, combined with the hydrogeological conditions and engineering characteristics of the mining area, the solute transport model of underground water in a rock cave type nontraditional solid waste landfill was constructed, and the characteristic pollutants were identified, and the pollution migration law of total chromium in the impervious barrier with damaged holes was simulated and characterized. The results show that the leakage of pollutants will affect the groundwater environment when the impervious barrier of the landfill is damaged. The pollution plume exceeding the standard is mainly concentrated in the groundwater aquifer within the landfill area, which is less likely to spread to the off-site environment. The vertical high concentration pollution plume is primarily distributed in the landfill layer. According to the characteristics of rock cave landfills, it is suggested that hazardous solid waste should be separated from surrounding rock. The research results can provide technical guidance for groundwater environment prediction and prevention measures for the same type of project.

Valency distributions and geochemical fractions of arsenic and antimony in non-ferrous smelting soils with varying particle sizes

Arsenic and antimony are common toxic metalloids found in associated minerals. These metalloids generally cause high-concentration pollution in non-ferrous metal smelting soils; however, few studies have investigated the pollution characteristics of these two metalloids at non-ferrous smelting sites using varying soil particle sizes. In this study, the valency distributions and geochemical fractions were investigated with varying soil particle sizes (≤ 0.05, 0.05–0.25, 0.25–1, and 1–2 mm). Soils were mainly concentrated in ≤ 0.05 and 0.05–0.25 mm with mass percentages of 32.97% and 29.02%, respectively. The highest total As and Sb concentrations in ≤ 0.05 mm were found to be 20,350 and 3655 mg/kg, respectively. In addition, As(Ⅲ), As(Ⅴ), Sb(Ⅲ), and Sb(Ⅴ) concentrations in this soil particle size were found to be 224, 19,813, 1036, and 24 mg/kg, respectively. The geochemical fractions of As and Sb in varying soil particle sizes were mainly residual, accounting for 50% and 90% in the ≤ 0.05 mm. Soil may bind ≤ 0.25 mm due to the disparity found in the geochemical compositions and valency distributions of arsenic and antimony. X-ray diffraction and scanning electron microscopy/energy dispersive system analysis confirmed that arsenolite accumulated in particle sizes of ≤ 0.05 and 0.05–0.25 mm. The results of this study may provide a scientific reference for risk assessment and restoration strategies for non-ferrous metal smelting soils.

Coupling morphology control and surface I grafting for boosting the photocatalytic activity of Bi2O2[BO2(OH)] nanosheets

Photocatalytic performance of semiconductors is currently limited by low solar light utilization, rapid charge recombination and limited reactive sites. Reducing the thickness of layered photocatalysts can shorten the charge transport distance to inhibit their recombination and provide more reactive sites. Surface ionic grafting can broaden the light absorption range and promote the separation efficiency of carriers. In this work, the surface iodine ion modified Bi2O2[BO2(OH)] nanosheets are synthesized by combining the surfactant-assisted hydrothermal method and room-temperature KI solution treatment route. These nanosheets show increased photoabsorption in visible region, enlarged specific surface area and promoted charge separation. Compared with the pristine Bi2O2[BO2(OH)], the surface I- modified Bi2O2[BO2(OH)] nanosheets exhibit substantially strengthened photocatalytic performance for degradation of BPA, which increases beyond 25 times. The total organic carbon content (TOC) test reveals that the mineralization process of BPA. Electron spin resonance (ESR) measurements disclose the radicals that play dominant role in the photocatalytic process and confirm their increased yield over I- modified Bi2O2[BO2(OH)] nanosheets. In addition, BiOB-S-I2 also shows universality for degradation of a variety of high-concentration pollutants, including rhodamine B, methyl orange, methylene blue, phenol, 2,4-dichlorophenol and tetracycline hydrochloride. This study may provide a combined strategy for exploring high-performance photocatalysts via microstructure control and surface ionic decoration.

The dominant microbial metabolic pathway of the petroleum hydrocarbons in the soil of shale gas field: Carbon fixation instead of CO2 emissions

In shale gas mining areas, indigenous microorganisms degrade organic pollutants such as petroleum hydrocarbons into carbon dioxide (CO2) and water (H2O) through aerobic metabolism. A large quantity of CO2 emissions will exacerbate the “Greenhouse effect”. Based on the clean sieved soil and oil-based drilling fluid in the shale gas mining area, this experiment set three concentration gradients (3523 ± 159 mg/kg, 8715 ± 820 mg/kg and 22,031 ± 1533 mg/kg) to treat the soil, and each group was disposed for the same amount of time (63 days). By analyzing the dynamic changes of microbial diversity and the abundance of key functional genes for carbon fixation, the impact of petroleum hydrocarbons on carbon fixation potential was discovered, and the natural attenuation law of petroleum hydrocarbons in contaminated soil was explored. It provided the scientific research basis of ecology for the carbon cycle, carbon allocation, and carbon fixation in microbial remediation of petroleum hydrocarbon contaminated soil. The results obtained indicated the following: i) The removal rate of petroleum hydrocarbons under high-concentration pollution (45.33 ± 3.90%) was significantly lower than low and medium-concentration pollution. The TPH concentration removal rate of each group was the largest in the early stage of culture (1-5d), and there was no significant correlation between the TPH content and the community composition (R2 = 0.0736, P > 0.05). ii) Composition and function of Carbon Fixation associated microbiota were assessed by 16S rRNA sequencing and PICRUSt (phylogenetic investigation of communities by reconstruction of unobserved states) analysis. The main carbon fixation pathway in this study is the reductive citric acid cycle, because there was no shortage of enzymes that can affect subsequent reactions.

Effects of porous activated carbon on TiO2 photo‐activity for high concentration 2,4‐DCP degradation as environmental remediation

To efficiently address environmental pollution, we synthesized AC‐coupled TiO2 nano‐photo‐catalysts and applied it to the degradation of high concentration 2,4‐dichlorophenols (2,4‐DCP). Herein, we have successfully coupled activated carbon (AC) to TiO2 by a sol gel method. The as‐prepared optimized‐amount TO/10AC nano‐composites delivered unprecedented photo‐catalytic activity as compared to the pristine TO nano‐particles and degraded 100% 2,4‐DCP in 2 h. According to the fluorescence spectrum, temperature‐programed desorption curve, and O2 electrochemical reduction curve related to the generated OH amounts, it is inferred that the photo‐catalytic activity is ascribed to the coupled AC for accepting electrons, promoting O2 adsorption and promoting reactant adsorption. More importantly, no obvious deactivation was observed even after running at least five cycles; this excellent stability makes them auspicious photo‐catalyst for the degradation of high concentration pollutants in practical applications. Besides, the scavenger experiments confirmed that super oxide radicals were the main active species that involve during the photo‐catalytic degradation of 2,4‐DCP. This work delivers a viable approach to develop the photo‐catalysis by coupling a proper amount of AC with the TO for the remediation of high concentration environmental pollutants.

Improving the performance of biotrickling filter microbial fuel cells in treating exhaust gas by adjusting the oxygen content of the anode tank

A biotrickling filter (BTF) was combined with a microbial fuel cell (MFC) to remove ethyl acetate from exhaust gas while generating electricity in the process. The results indicated that the use of carbide porous ceramic rings (CPCR) as auxiliary anodes produced more biomass and exhibited a high average removal efficiency (98%), making it a superior microorganism growth carrier compared with carbon coke. When CPCR was used as the cathode in the BTF-MFC, the maximum power density (PD) was 5.64–14.8% of that achieved when carbon cloth was used as the cathode, revealing that CPCR is not a suitable cathode. The maximum elimination capacity (EC) and output voltage of the two-stage BTF-MFC (tBTF-MFC) were only 69.4% and 68.4% of those of the single-stage BTF-MFC (sBTF-MFC), presumably because of voltage reversal. Although the output voltage and EC in the tBTF-MFC were less than those in the sBTF-MFC, the follow-up field application involves stacking multiple small MFCs to remove high-concentration pollutants and generate a high power output. Additionally, continuously adding sodium sulfite decreased the average dissolved oxygen; generated an averaged closed-circuit voltage of 477 mV; and produced a maximum PD of 71.7 mW/m3. These findings demonstrated that the aforementioned method can effectively improve the problem of oxygen and MFC anodes competing for electrons, thus delivering a method that enhances MFC performance through controlling the amount of oxygen in practical applications.

Fructose-regulated ZnO single-crystal nanosheets with oxygen vacancies for photodegradation of high concentration pollutants and photocatalytic hydrogen evolution

ZnO-based photocatalysts have been widely applied to photocatalytic reactions. However, the pure phase ZnO is rarely used in degradation of refractory pollutants and photocatalytic hydrogen evolution due to its poor photo-redox ability. In this study, we develop a novel surface atom regulation strategy using fructose molecules containing hydroxyl groups to improve photo-oxidation ability of ZnO. Interestingly, the fructose-regulated ZnO nanosheets with oxygen vacancies exhibit more positive surface valence band maximum than that of pristine ZnO. The photogenerated holes with strong oxidation capacity can be formed on the fructose-regulated ZnO nanosheets. The fructose-regulated ZnO nanosheets can rapidly degrade high concentration of phenol and other organic pollutants, which is difficultly achieved by the pristine ZnO nanosheets. In addition, photocatalytic H2 production activity is also found on our pure phase ZnO. This work provides a new design strategy for modifying the surface structure of photocatalysts to improve photocatalytic performance.

The influence of geological structure on the characteristics of groundwater pollution in the downstream of tailing pond

A large number of high-concentration pollutants in the tailings pond polluted the local groundwater. The contaminated groundwater moves to the Yellow River (YR) 12 kilometers south of the pond through natural flow and diffusion. However, how close the contaminated groundwater to the YR was difficult to determine by visual inspection. Therefore, the groundwater quality was analyzed through borehole sampling, and the results show that the Nemero index of groundwater pollutants presents a puzzling V-shaped distribution from the tailing pond to the YR. Soil permeability analysis shows that the concentration of groundwater pollutants in the vicinity of the Yellow River had risen again, which was caused by the blockage of the clay layer in the alluvial plain of the Yellow River. The results demonstrate that the pollutants leaked from the tailings pond have reached the bank of the Yellow River. This pollution has already threatened the water quality of the Yellow River; corresponding measures should be taken to ensure the ecological safety of the Yellow River. It provides a scientific basis for solving similar environmental problems in future.

Characteristics of indoor and personal exposure to particulate organic compounds emitted from domestic solid fuel combustion in rural areas of northwest China

Household solid fuel combustion for heating in winter is a substantial source of air pollution in rural areas of northwest China. The present study investigated the concentration characteristics and health risks of particulate matter (PM) and its organic compounds, including polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs (OPAHs), and phthalate esters (PAEs). Indoor air and housewives' personal exposure (PE) samples were collected in Guanzhong Basin, among rural households relying on various solid fuels for heating in winter. Indoor PM primarily comprised fine PM (PM2.5, 76%), and its organic compounds were identified in particular abundance in households that used coal as the only domestic fuel (Group C, 96% in PM2.5). The mean concentration of PE to PM2.5 was 307 ± 120 μg·m−3, which was 2.4-times higher than the indoor concentration (130 ± 103 μg·m−3) because of the housewives' short-term exposure to high-concentration pollution emitted by solid fuel combustion. Organic compounds exhibited the same pattern, with PE samples having a 44% higher concentration than indoor samples. The correlation of PM2.5-bound organics between indoor and PE samples in Group C (R2 = 0.9) was higher than that in the group using coal and biomass (Group M, R2 = 0.6), indicating the stronger correlation of single-fuel heating method. The PE/indoor ratio of high molecular weight (HMW) PAHs in Group C (2.5) was higher than that of the other organic compounds (1.3) because HMW PAHs emitted through coal combustion had a larger effect on PE. This further led to higher incremental lifetime cancer risks (ICLRs) via inhalation pathway among housewives in Group C (2.4- and 1.2-times higher risk for PAHs and PAEs, respectively) than among those in Group M. However, inhalational ILCR values of Group M were still 2.1–340-times higher than the international safety standard (10−6). Therefore, the upgradation of domestic fuels and heating ways is urgently needed in rural area of northwest China to reduce indoor air pollution and health risks.

Efficient UV-light photocatalytic activity of TiO2@Phosphogypsum composite synthesized by sol–gel method

There is no doubt that novel and efficient photocatalyst with excellent properties based on TiO2 are highly desirable for practical applications to degrade high-concentration pollutants. Until now TiO2 nanoparticles have been successfully coupled with phosphogypsum prepared via a simple sol–gel method after calcination at different temperatures. The efficiency of the photocatalytic activity of composite can be explained by the difference of calcination temperatures in the structure of TiO2. Structures, morphologies, and surface areas were examined in all samples using specific characterization methods. In this process, the anatase and rutile structure of TiO2 nanoparticles were determined. The results obtained showed that the forms of the composite are spherical, although some nanoparticles are agglomerated. Surface area analyses showed that higher surface areas were obtained when the composite calcinated at 450 °C. We can attribute this to the small size of the particles. This study demonstrates that the synthesized composite display excellent photo-activity for degrading nitrate from aqueous solution up to 93.5% after 180 min of UV light irradiation time. Hence, we demonstrate a simple and efficient method to valorize phosphogypsum and to prepare a promising composite photocatalyst for reduction of nitrate in water and wastewater treatment process.