Study for lightweight finger vein recognition based on a small sample.

To address several common problems of finger vein recognition, a lightweight finger vein recognition algorithm by means of a small sample has been proposed in this study. First of all, a Gabor filter is applied to deal with the images for the purpose of that these processed images can simulate a kind of situation of finger vein at low temperature, such that the generalization ability of the algorithm model can be improved as well. By cutting down the amount of convolutional layers and fully connected layers in VGG-19, a lightweight network can be given. Meanwhile, the activation function of some convolutional layers is replaced to protect the network weight that can be updated successfully. After then, a multi-attention mechanism is introduced to the modified network architecture to result in improving the ability of extracting important features. Finally, a strategy based on transfer learning has been used to reduce the training time in the model training phase. Honestly, it is obvious that the proposed finger vein recognition algorithm has a good performance in recognition accuracy, robustness and speed. The experimental results show that the recognition accuracy can arrive at about 98.45%, which has had better performance in comparison with some existing algorithms.

Reservoir flood regulation affects nutrient transport through altering water and sediment conditions.

The effect of reservoir construction on nutrient dynamics is well recognized, at flood event-scale influence of reservoir flood regulation on nutrient transport however has received less attention. Taking the Three Gorges Reservoir (TGR) in the Changjiang River as an example, during the TGR's regulation on a flood in Sep., 2021, this study collected water samples along the mainstream of the reservoir as well as pre/post-dam, with the aim to identify the impact of flood regulation on nutrient (nitrogen and phosphorus) distribution and transportation. Results show that nitrate nitrogen (NO3N) and particulate phosphorus (PP) were the main fraction of the total nitrogen (TN) and total phosphorus (TP) with the proportion of 46.5%-95.6% and 57.4%-81.6%, respectively. N and P responded different to flood regulation: (i) along the stream P concentration significantly decreased due to PP deposited with sediment while N concentration barely changed during flood regulation; (ii) P concentration was significantly higher at post-dam section than at pre-dam section, while N concentration maintained the same. The diffed response to flood regulation caused TN/TP ratio increased from 4 to 8 in the reservoir tail to over 20 near the dam, which probably arise eutrophication in the reservoir head area. This study reveals the influence of flood regulation on nutrient transport in flood event and provides scientific basis for reservoir management.

Electrokinetic geosynthetics restrained nitrogen release from sediment to overlying water through porewater drainage.

Porewater is the primary carrier of sediment nitrogen and a crucial source of overlying water nitrogen; its separation thus is essential for restraining nitrogen release from sediment to overlying water. We developed a novel device using electrokinetic geosynthetics to drain porewater with nitrogen and restrain nitrogen release. A batch experiment lasted 1120 h (about 47 days) was conducted with 20 cm depth of overlying water under three conditions, i.e., undrained at 0 V/cm voltage gradient (control), drained at 0 V/cm, and drained at 0.5 V/cm. Under the pulsed direct current, once porewater drained, overlying water replenished sediment pore space and supplied porewater. Along with porewater drainage, sediment nitrogen concentration was reduced by 11%-30%, decreasing nitrogen release from sediment to overlying water from 83 mg/m2 in the first 100 h to -95 mg/m2 after about 600 h. Processes such as electroosmosis, electromigration, and redox reaction contributed to the restraint on nitrogen release. This research revealed the potentiality of applying electrokinetic geosynthetics to in-situ restraint on sediment nitrogen release in eutrophic waterbodies such as fishponds.

Spatial and temporal characteristics, influencing factors and prediction models of water quality and algae in early stage of Middle Route of South-North Water Diversion Project.

The Middle Route (MR) of the South-to-North Water Diversion Project (SNWDP) of China is one of the world's largest inter-basin water diversion projects. As an important source of drinking water in North China, its water quality safety determines the success or failure of a sizable water supply. At present, there is a lack of in-depth and systematic understanding of the interaction between hydrodynamics and the water environment as well as water ecological processes in the main canal at the early stages of operation. It is not currently possible to accurately predict water quality and algae status at the early stage of canal ecosystem succession. Change trends and distribution characteristics of the main water ecological environment elements in the main canal at the early MR stage are analyzed in this study. The main factors influencing algae are investigated by principal component analysis (PCA) to characterize the water quality and algae transport distribution in the main MR canal under the complex multi-sluice joint dispatching conditions. The relationship between environmental factors, hydrodynamic, water quality, and algae in the coupled canal-sluice system in the SNWDP MR is determined. Algae distributions under different water transmission conditions in a typical canal section are predicted accordingly. CODMn and algal density in the main canal are shown to increase from south to north along the canal. DO decreases from south to north; other water quality indexes do not significantly differ from north to south. Algal density along the canal differs to the greatest extent in summer, followed by spring and autumn, and is the weakest in winter. The predicted algae densities in the main canal under different water conveying conditions show that single sluice control and strong water flow from Taocha Head Section increase the flow velocity after passing through the sluice with a fixed opening. Algal density decreases flow rate increases under single sluice regulation conditions. The maximum rate of algal density change reaches 22.13% and 29.55% under double sluice and four sluice scheduling. Algae control effects grow significantly as the number of control sluices increases. The results of this work may provide technical support for water quality forecasting and algae risk warning in the SNWDP MR as well as a workable reference for similar projects.

Impacts of electrokinetic isolation of phosphorus through pore water drainage on sediment phosphorus storage dynamics.

Pore water is a crucial storage medium and a key source of sediment phosphorus. A novel equipment based on electrokinetic geosynthetics (EKGs) was used for isolating phosphorus from eutrophic lake sediments through pore water drainage. Three mutually independent indoor group experiments (A, B, and C) were conducted to investigate the effects of voltage gradient (0.00, 0.25, and 0.50 V/cm) on pore water drainage capacity, phosphorus removal performance, sediment physicochemical properties, and phosphorus storage dynamics. The average reduction in the sediment moisture and total phosphorus content was 2.5%, 4.3%, and 4.6% and 28.15, 75.95, and 112.65 mg/kg after 6 days of treatment for A, B and C, respectively. Efficient pore water drainage through gravity and electroosmotic flow and electromigration of phosphate were the main drivers of sediment-dissolved and mobilized phosphorus separation. A high voltage gradient facilitated the migration of pore water and the phosphorus in it. The maximal effluent total phosphorous (TP) concentration was up to 27.9 times that in the initial pore water samples, and negligible effluent TP was detected when the pore water pH was less than 2.5. The TP concentration was exponentially and linearly related to the pH and electronic conductivity of the electroosmotic flow, respectively. The migration of H+ within the sediment matrix promoted the liberation of metals bounded to phosphorus, particularly of Ca-P and Fe-P. Pore water drainage through an EKG resulted in Ex-P separation of up to 87.50% and a 13.84 mg/kg decrease in Ca-P and 125.35 mg/kg accumulation of low mobile Fe-P in the weak acid anode zone.

Cooperative identification for critical periods and critical source areas of nonpoint source pollution in a typical watershed in China.

Critical periods (CPs) and critical source areas (CSAs) refer to the high-risk periods and areas of nonpoint source (NPS) pollution in a watershed, respectively, and they play a significant role in NPS pollution control. The upstream Daning River Basin is a typical watershed in the Three Gorges Reservoir area. In this study, a Hydrological Simulation Program-Fortran (HSPF) model was used to simulate phosphorus loss in the upstream Daning River Basin. Co-analysis of critical periods and critical source areas (CACC) is a quantitative collaborative analysis method for the identification of CSAs in CPs, and it was used to classify the periods and areas of NPS pollution as CPs, sub-CPs, non-CPs, CSAs, and non-CSAs. The CPs occurred in months 5-7 and accounted for 53.7% of the total phosphorus (TP) loads, and the sub-CPs occurred in months 1, 3, 4, and 8 and accounted for 29.2% of the TP loads. In CSAs, 49.4% of the TP loads occurred in 26.8% of the basin. Furthermore, we proposed the following multilevel priority control measure for NPS pollution in the upstream Daning River Basin: CSAs in CPs (with load-area rate of 1.4), CSAs in sub-CPs (0.7), CSAs in non-CPs (0.4), non-CSAs in CPs (0.3), non-CSAs in sub-CPs (0.2), and non-CSAs in non-CPs (0.1). CSAs in CPs accounted for 25.8% of the TP loads from 19.0% of the areas in only 3 months while 49.4% of the TP loads from similar areas over an entire year. These findings indicated that the CSAs in CPs located in farmland along the Daning, Dongxi, and Houxi Rivers should be prioritized for pollution management measures.

Spatiotemporal distribution dynamics of heavy metals in water, sediment, and zoobenthos in mainstream sections of the middle and lower Changjiang River.

Water, sediment, and zoobenthos are crucial carriers and storage media for heavy metal migration and transformation. The distribution characteristics of heavy metals in water, sediment, and zoobenthos can reflect their pollution status and potential influences on the health of aquatic ecosystems. On the basis of monitoring data related to Cu, Zn, Pb, Cd, Ni, Mn, Hg, and As in mainstream water, surface sediment, and zoobenthos at eight sections-from Wuhan to Shanghai-of the Changjiang River (also known as the Yangtze River) and historical monitoring data on heavy metal distributions in different environmental media of the Changjiang River since the 1980s, this study undertook systematically analyzed the spatiotemporal distribution dynamics, pollution levels, and corresponding environmental risks related to heavy metals in water, sediment, and biota, and examined the effects of pollution source variations and water and sediment regimes on heavy metal distribution. Heavy metal concentrations in the waters were much lower than the water quality threshold of Grade III of the Chinese Surface Water Environmental Quality Standard (GB3838-2002); the concentrations of different heavy metals were irregularly distributed and varied significantly along the river mainstream; Cu, Cd, Zn, and Pb concentrations in sediment all exceeded their respective critical effect concentrations and exposed the ecosystem to pollution risks; the pollution levels of and ecosystem health risks posed by Zn and Cu in zoobenthos were high, with pollution concentrations ranked as shrimp > snails > crabs. In general, heavy metal concentrations in the three environmental mediums were ranked as sediment > zoobenthos > water. Finally, comparison with historical monitoring data revealed increasing Cd and Hg concentrations, with the average heavy metal concentration in sediment reaching its maximum value in the 2000s in the middle and lower reaches of the Changjiang River, which are subjected to the combined effect of pollutant emissions and changing water and sediment regimes.

Spatial-temporal distribution characteristics and health risk assessment of heavy metals in surface water of the Three Gorges Reservoir, China.

Heavy metal contamination in surface water of the Three Gorges Reservoir (TGR) is a distinctly important issue for the water security of the Yangtze River Basin in China. Surface water samples of 46 river sections in the main stream and tributaries of the entire TGR area were collected during high and low water level operation periods of 2015 to 2016 to investigate the spatial-temporal distribution characteristics of six heavy metals (As, Cd, Cr, Cu, Pb and Zn) and assess their health risks. Results indicated that average concentrations of heavy metals in the surface water were lower than the threshold values for the first-grade water quality based on the Chinese standard of GB3838-2002 except for Zn. Heavy metals concentrations at high water levels was slightly lower compared with that at the low water levels in the main stream, As, Cd, Cr and Cu exhibited certain inter-annual decline variations in 2015 and 2016. Heavy metals showed distinctly regional variation and mainly distributed in upstream urban sections of the TGR area. The total health risks caused by heavy metals at the low water level periods, most of which exceeded the maximum acceptable risk level recommended by ICRP (5×10-5 a-1), were slightly higher than that at the high water level periods. The average annual health risks caused by carcinogenic and non-carcinogenic heavy metals was ranked as Cr > As > Cd > Pb > Cu > Zn, meanwhile this value via drinking water ingestion was 2 to 3 orders of magnitude larger than that of dermal contact. Carcinogenic heavy metals of Cr and As were the main causes of health risk and should be prioritized as the main focus of aquatic environment risk management in the TGR area.

[Vertical Distribution Profiles and Release Potential of Mainstream Column Sediments in the Three Gorges Reservoir After Impoundment to 175 m].

To investigate the vertical distribution characteristics of phosphorus in the main stream sediments of the Three Gorges Reservoir (TGR), column sediment samples were collected from 5 sites in October 2010, and sediment particle size, organic matter contents, and mineral compositions were analyzed. Investigation of the contribution rate of phosphorus released from column sediments in the TGR was also conducted. The results show that the sediment pH is between 7.3-7.8. The mainstream column sediment is mainly constituted by silt and clay, which account for 49.4%-78.6% and 20.6%-50.6% of total sediments, while sand represents less than 4.4%. Median grain size of each sampling site presented a phased increase or decrease trend. The organic matter content was between 12.94 g·kg-1 and 53.43 g·kg-1, and it tended to slightly increase from upstream to downstream. The C/N ratio in the sediment was between 4.00 and 11.64, and organic matter content was mainly affected by terrigenous input. Total phosphorus (TP) content was between 861.86 mg·kg-1 and 1024.54 mg·kg-1, and it exhibited negligible change in vertical distribution. There is no obvious enrichment phenomenon of phosphorus for column sediment. The major component of sediment TP is calcium bound phosphorus (Ca-P, 47.83%-73.90%), and there are various trends for phosphorus distribution in different sampling sites. Exchangeable phosphorus (Ex-P), aluminum-bound phosphorus (Al-P), and iron-bound phosphorus (Fe-P) in the 0-4 cm surface sediment of each sampling sites was relatively high. For most sampling sites, no obvious change of phosphorus fractions in 16-20 cm of sediment was detected. Bioavailable phosphorus (the sum of Ex-P, Al-P, and Fe-P) accounted for 2.78%-7.05% of TP, indicating that bioavailability of phosphorus in the column sediments is low. The contents of bioavailable phosphorus and organic matter were significantly and positively correlated (P<0.05, N=50). The distribution and transformation of organic matter will affect the migration and transformation of sediment phosphorus in the TGR.

Influence of turbid flood water release on sediment deposition and phosphorus distribution in the bed sediment of the Three Gorges Reservoir, China.

Excessive phosphorus (P) loading was identified as an urgent problem during the post-Three Gorges Reservoir (TGR) period. Turbid water with high suspended sediment loads has been periodically released during the flood season to mitigate sediment deposition in the TGR, but limited attention has been paid to its effect on the distribution of P in bed sediment within the reservoir. In this study, field surveys, historical monitoring data related to sediment deposition, and physiochemical properties and the fractional P content in the mainstream surface sediment and representative column sediment, were used to investigate the effect of turbid flood water release on P distribution in bed sediment. The results revealed that turbid flood water release could discharge approximately 20% of the suspended sediment inflow entering the TGR. Additionally, both the particle size of the inflow sediment and suspended sediment flux tended to decline, and the deposited sediment volume tended to constantly increase in the TGR at a rate of 0.117 billion tonnes per year between 2004 and 2016. The median particle size (MPS) was larger for surface sediment obtained in the flood season than for that obtained in the dry season, and the MPS tended to increase with an increase in the sediment depth from 0 to 20 cm. The total phosphorus (TP) content in sediment ranged from 2.6% to 17.5% lower in the flood water releasing period than in the non-flood water storing period. However, no consistent variation was detected for the vertical distribution of P fraction in the top 20 cm of bed sediment. Compared with lakes with slow deposition rates, the TGR showed a rapid sedimentation rate of >1.0 m/y, which mostly resulted in the uniform distribution of the surface sediment P fraction.

Phosphorus distribution and bioavailability dynamics in the mainstream water and surface sediment of the Three Gorges Reservoir between 2003 and 2010.

A staged impoundment scheme was adopted for the Three Gorges Reservoir (TGR) to increase its maximal water level from 135 to 175 m between 2003 and 2010; however, the variation in phosphorus distribution and its bioavailability in the water column and surface sediment, during this period is still uncertain. Field surveys and historical monitoring data related to water column, surface sediment, total phosphorus (TP) and fractional contents, and water bloom characteristics were used to identify the effects of staged impoundment on phosphorus distribution and water eutrophication in the TGR. It is indicated that retention of particulate phosphorus (PP)-bounded suspended sediment (SS) caused an average of 4.69 %-12.28% decline in water column TP between 2004 and 2010 compared with that measured between 1998 and 2003. Phosphorus did not notably accumulate in the mainstream surface sediment when the impoundment water level increased from 135 to 175 m. The mainstream surface sediment was relatively clean, and the release of sediment bioavailable P (Bio-P) contributed to 0.013% of dissolved phosphorus (DP) concentrations in the water column when impoundment of the TGR was 175 m. An increase in dissolved Bio-P in the water column and weak hydrodynamic conditions stimulated the outburst of water bloom in more tributaries when the impoundment water level increased from 135 to 175 m, and the dominant algae gradually evolved from river-dominated species to lake-dominated species. Therefore, it is necessary to limit the entry of DP from the upstream and tributaries into the TGR and manage TP loads in the TGR as a lake rather than as a river in the future.

[Pollution Characteristics and Source Identification of Polycyclic Aromatic Hydrocarbons and Phthalic Acid Esters During High Water Level Periods in the Wuhan Section of the Yangtze River, China].

Persistent organic pollutants (POPs) have been detected extensively in water and sediments in China, causing potential risks to the environment and human beings. In this study, the content level, distribution characteristics, and pollution sources of PAHs and PAEs in the water and sediments collected from 15 sites in the Wuhan section of the Yangtze River in August of 2016 were analyzed systematically. The following conclusions were made. The total PAHs concentrations were 20.8-90.4 ng·L-1 (mean value 40.7 ng·L-1) in water and 46.1-424.0 ng·g-1 (mean value 191.8 ng·g-1) in the sediments, while for PAEs, they were 280.9-779.0 ng·L-1 (mean value 538.6 ng·L-1) in water and 1346.2-7641.1 ng·g-1 (mean value 3699.5 ng·g-1) in the sediment. Both PAH and PAE concentrations in water meet the Chinese national water environmental quality standard (GB 3838-2002) with a low degree of pollution. PAH monomers with two to three rings were dominant in water, while those with two to three rings and four rings were dominant in the sediment. DEHP and DBP were the dominant PAE pollutants in both the water and sediment. The ratio and principal component analysis showed that the main source of PAHs in water and the sediment were the emission from coal, biomass combustion, and petroleum sources, while the main sources of PAEs include the plastic and chemical industries and municipal solid wastes. Two types of POPs (PAHs and PAEs) in water and sediment have potentially detrimental effects on human health and monitoring needs to be strengthened. This research provides basic data and technical support for the protection of the Yangtze River.

[Assessment of Physico-chemical Properties and Phosphorus Fraction Distribution Characteristics in Sediments after Impounding of the Three Gorges Reservoir to 175 m].

In order to understand the characteristics of the distribution of sediment total phosphorus (TP) and phosphorus fractions in the mainstream sediments in the Three Gorges Reservoir (TGR) after impounding the water level to 175 m, 13 surface sediment samples were collected from the Wujiang to Maoping sections in October 2010. The physico-chemical properties, including organic matter content, particle grain size distribution, and major mineral analysis, as well as total phosphorus and its fractions in the sediment, were determined. Moreover, the relationships among phosphorus fractions, organic matter contents, and particle grain size were discussed, and the effect of the impoundment on sediment phosphorus accumulation and bioavailability was also evaluated. Results indicated that the sediment organic matter content of the TGR was between 7.79 g·kg-1 and 55.63 g·kg-1, and the main mineral components were chlorite, illite, and quartz. The sediments were dominated with clayey silt with a median diameter (d50) ranging from 3.84 µm to 23.65 µm. The measured total phosphorus content of the sediments were between 557.06 g·kg-1 and 837.92 g·kg-1, and the total phosphorus enrichment index of each sampling site is greater than 1, demonstrating a potential risk for phosphorus pollution. The calcium bound phosphorus (Ca-P) and the reductant soluble phosphorus (Oc-P) were the dominant sediment phosphorus fractions, while the exchangeable phosphorus (Ex-P), the iron bound phosphorus (Fe-P), and aluminum bound phosphorus (Al-P) content were relatively low. Bioavailable P only accounts for 2%-8% of the total phosphorus content. When referring to previous studies, the sediment particle size tended to be smaller and the content of comparatively easy-to-weather minerals slightly increased with the increase of the impoundment water level. However, the increase in the impoundment water level did not result in a significant increase tendency in sediment TP content. In the future, a reduction in sediment input and a decline in sediment particle size may facilitate the accumulation of phosphorus in the sediments in the broad valley section of the TGR. Moreover, large scale dry-wet alternation in the water level fluctuation zone and resuspension of floating mud near the dam both potentially impact the bioavailability of phosphorus in the sediments.

Distribution, sedimentation, and bioavailability of particulate phosphorus in the mainstream of the Three Gorges Reservoir.

The transportation and sedimentation of particulate phosphorus (PP) in a huge reservoir such as the Three Gorges Reservoir (TGR) are closely related to the phosphorus distribution characteristics and nutritional status of the water body. In this study, the PP distribution, sedimentation, and bioavailability in the mainstream section of the TGR were investigated through a field survey, indoor simulated settlement experiment, and historical data analysis. The results indicated that PP was the major component of the total phosphorus (TP) and that the Three Gorges Dam (TGD) trapped nearly 76.25% of suspended sediment (SS) and 75.35% of PP in the TGR, even during the flood season. A decline in flow velocity promoted the deposition of PP; additionally, PP concentrations gradually dropped from 0.35 mg/L in Chongqing to 0.02 mg/L in Zigui. The static PP sedimentation process adequately fitted a pseudo-second-order kinetic equation with a maximum correlation coefficient of 0.97. Moreover, more than half of the PP sedimentation process was achieved in less than 60 min for samples collected from the upper river reaches within simulated sedimentation process. The median particle size of SS and absolute value of the water column's zeta potential were negatively and positively related to the t12 values of PP sedimentation, respectively. Compared with the concentration and particle size of SS obtained in the pre-TGR period, the values in the mainstream section of the TGR were lower. However, the TP and Fe/Al-P contents in SS increased several times. Due to the combined effects of flow velocity reduction and SS trapping, the water transparency and bioavailability of water column phosphorus were enhanced. Thus, the risk of water bloom outburst significantly increased when the impounded water level of 175 m in the TGR became the normal state.

Enhanced nitrate-nitrogen removal by modified attapulgite-supported nanoscale zero-valent iron treating simulated groundwater.

Attapulgite (or palygorskite) is a magnesium aluminium phyllosilicate. Modified attapulgite-supported nanoscale zero-valent iron (NZVI) was created by a liquid-phase reduction method and then applied for nitrate-nitrogen (NO3-N) removal (transformation) in simulated groundwater. Nanoscale zero-valent iron was sufficiently dispersed on the surface of thermally modified attapulgite. The NO3-N removal efficiency reached up to approximately 83.8% with an initial pH values of 7.0. The corresponding thermally modified attapulgite-supported nanoscale zero-valent iron (TATP-NZVI) and NO3-N concentrations were 2.0 g/L and 20 mg/L respectively. Moreover, 72.1% of the water column NO3-N was converted to ammonium-nitrogen (NH4-N) within 6 h. The influence of environmental boundary conditions including dissolved oxygen (DO) concentration, light illumination and water temperature on NO3-N removal was also investigated with batch experiments. The results indicated that the DO concentration greatly impacted on NO3-N removal in the TATP-NZVI-contained solution, and the NO3-N removal efficiencies were 58.5% and 83.3% with the corresponding DO concentrations of 9.0 and 0.3 mg/L after 6 h of treatment, respectively. Compared to DO concentrations, no significant (p > 0.05) effect of light illumination on NO3-N removal and NH4-N generation was detected. The water temperature also has great importance concerning NO3-N reduction, and the removal efficiency of NO3-N at 25 °C was 1.25 times than that at 15 °C. For groundwater, therefore, environmental factors such as water temperature, anaerobic conditions and darkness could influence the NO3-N removal efficiency when TATP-NZVI is present. This study also demonstrated that TATP-NZVI has the potential to be developed as a suitable material for direct remediation of NO3-N-contaminated groundwater.

Improved isolation of cadmium from paddy soil by novel technology based on pore water drainage with graphite-contained electro-kinetic geosynthetics.

Novel soil remediation equipment based on electro-kinetic geosynthetics (EKG) was developed for in situ isolation of metals from paddy soil. Two mutually independent field plot experiments A and B (with and without electric current applied) were conducted. After saturation using ferric chloride (FeCl3) and calcium chloride (CaCl2), soil water drainage capacity, soil cadmium (Cd) removal performance, energy consumption as well as soil residual of iron (Fe) and chloride (Cl) were assessed. Cadmium dissolved in the soil matrix and resulted in a 100% increase of diethylenetriamine-pentaacetic acid (DTPA) extracted phyto-available Cd. The total soil Cd content reductions were 15.20% and 26.58% for groups A and B, respectively, and electric field applications resulted in a 74.87% increase of soil total Cd removal. The electric energy consumption was only 2.17 kWh/m3 for group B. Drainage by gravity contributed to > 90% of the overall soil dewatering capacity. Compared to conventional electro-kinetic technology, excellent and fast soil water drainage resulted in negligible hydrogen ion (H+) and hydroxide ion (OH-) accumulation at nearby electrode zones, which addressed the challenge of anode corrosion and cathode precipitation of soil metals. External addition of FeCl3 and CaCl2 caused soil Fe and Cl residuals and led to 4.33-7.59% and 139-172% acceptable augments in soil total Fe and Cl content, correspondingly, if compared to original untreated soils. Therefore, the novel soil remediation equipment developed based on EKG can be regarded as a promising new in situ technology for thoroughly isolating metals from large-scale paddy soil fields.

Enhanced phosphorus removal using acid-treated magnesium slag particles.

Magnesium-enriched magnesium slag particles (MSPs) can be used as an adsorption substrate as well as the magnesium source for struvite precipitation. In this study, an HCl treatment was used to enhance MSPs for phosphorus removal. After soaking in 1 mol/L HCl, an 11.27% decrease in median diameter (D50) and a 6.73% increase in specific surface area were observed when compared with the original MSPs. The improvement of the MSP surface properties resulted in 188.96 mg/kg increase in the PO43- adsorption capacity. Irrespective of HCl treatment, the phosphorus adsorption process followed the Dubinin-Radushkevich (D-R) model much more accurately than the Langmuir and Freundlich equations with correlation coefficients higher than 0.94. The adsorption free energy obtained through the D-R model revealed a 9.75% decrease after HCl treatment. Sequential fraction extraction results indicated that 96% of the Mg2+ released from the HCl-treated MSPs came from acid-soluble magnesium (exchangeable and carbonate-bound). Mg2+ obtained from HCl-treated solutions provided a reliable magnesium source for struvite precipitation. The PO43- removal rate can reach 53.63% with the optimal pH value of 10.0 and molar ratio of NH4+ to PO43- of 1:1. Struvite precipitation and adsorption can simultaneously occur in HCl-treated MSP solution. It contributed 63.19% to the overall PO43- removal and is a major contributor compared with adsorption. Thus, HCl treatment greatly enhanced the potential of MSPs for phosphorus removal due to an improved adsorption capacity and is a reliable Mg2+ source for struvite precipitation.

Polycyclic aromatic hydrocarbons and organochlorine pesticides in surface water from the Yongding River basin, China: Seasonal distribution, source apportionment, and potential risk assessment.

The presence of 17 polycyclic aromatic hydrocarbons (PAHs) and 15 persistent organochlorine pesticides (OCPs) in surface water of the Yongding River Basin was analyzed through GC/MS/MS during the spring and summer at 46 sampling sites. The goal was to investigate their seasonal distribution, possible sources, and potential risk. Our results showed that the total PAH concentration in surface water of Yongding River Basin ranged from 41.60 to 1482.60ng/L with a mean value of 137.85ng/L in the spring, and from 53.53 to 506.53ng/L with a mean value of 124.43ng/L in the summer. The total OCP concentration ranged from <0.08 to 197.71ng/L with a mean value of 7.69ng/L in the spring, and from <0.08 to 93.58ng/L with a mean value of 7.92ng/L in the summer. Moreover, the total PAH concentration was slightly lower in the spring than in the summer, whereas the total OCP concentration was similar between seasons. Source analysis indicated that combustion sources and petroleum sources both contributed to the presence of PAHs. Historical environmental residues and long range atmospheric transport were the major sources of HCH and DDT contamination. The concentrations of total PAHs and single PAHs including benz(a)anthracene, benzo(a)pyrene, benz(b)fluoranthene, and benz(k)fluoranthene in surface water at some sampling sites exceeded the water environmental quality standards of China and several other countries or organizations. This indicated a potential threat to human health from the consumption of aquatic organisms due to PAH bioaccumulation. The concentrations of α-HCH, p,p'-DDE, and p,p'-DDD at several sampling sites exceeded the limit for human health specified in the ambient water quality criteria developed by the US Environmental Protection Agency, which indicated that these pollutants provide potential hazards to the residents around the sampling sites.

Prospect of recovering phosphorus in magnesium slag-packed wetland filter.

Phosphorus recovery from wastewater not only reduces the unbearable impacts of excessive nutrient discharge on environmental systems but also favor the reuse of phosphorus resource. Based on the mechanism as well as technical analysis for major phosphorus recovery techniques including struvite precipitation and wetland substrate adsorption, a novel magnesium slag-packed wetland filter and corresponding operational procedures are proposed, which aim to reduce the dependence of using magnesium-containing chemical reagent as magnesium sources for struvite precipitation, and improve the accumulation and recovery performance for struvite precipitation within porous wetland substrate. Results from preliminary experiments indicated that magnesium slag particles with approximately 2 mm in diameter can recover 43.20-72.39% phosphorus from 1-25 mol/L PO43- solution, and the presence of 5-50 mol/L NH4+ contributed to 11.71-29.11% enhancement of phosphorus recovery mainly due to struvite precipitation. The detected generation of struvite via XRD spectrum analysis partly demonstrated the potential of phosphorus recovery in magnesium slag-packed wetland filter. The proposed phosphorus recovery technology is free of secondary pollution and solid waste generation; phosphorus-saturated (mainly due to struvite precipitation and adsorption) magnesium slag particles can be potentially used as phosphorus fertilizer and thus partly solved the traditional shortages of disposing phosphorus-saturated substrate due to low phosphorus contents.

Arsenic(V) Removal in Wetland Filters Treating Drinking Water with Different Substrates and Plants.

Constructed wetlands are an attractive choice for removing arsenic (As) within water resources used for drinking water production. The role of substrate and vegetation in As removal processes is still poorly understood. In this study, gravel, zeolite (microporous aluminosilicate mineral), ceramsite (lightweight expanded clay aggregate) and manganese sand were tested as prospective substrates while aquatic Juncus effuses (Soft Rush or Common Rush) and terrestrial Pteris vittata L. (Chinese Ladder Brake; known as As hyperaccumulator) were tested as potential wetland plants. Indoor batch adsorption experiments combined with outdoor column experiments were conducted to assess the As removal performances and process mechanisms. Batch adsorption results indicated that manganese sand had the maximum As(V) adsorption rate of 4.55 h-1 and an adsorption capacity of 42.37 µg/g compared to the other three aggregates. The adsorption process followed the pseudo-first-order kinetic model and Freundlich isotherm equations better than other kinetic and isotherm models. Film-diffusion was the rate-limiting step. Mean adsorption energy calculation results indicated that chemical forces, particle diffusion and physical processes dominated As adsorption to manganese sand, zeolite and gravel, respectively. During the whole running period, manganese sand-packed wetland filters were associated with constantly 90% higher As(V) reduction of approximate 500 µg/L influent loads regardless if planted or not. The presence of P. vittata contributed to no more than 13.5% of the total As removal. In contrast, J. effuses was associated with a 24% As removal efficiency.