Sedimentation Of Suspended Solids Research Articles

The ADDRESS of a grain: Sediment particle tracking as an approach to assessing ecosystem quality in dammed reservoirs

The study integrates hydrodynamic modelling and geospatial analysis methods to describe the dynamic transport and sedimentation conditions of suspended solids (SS) in large lowland reservoirs. The method was tested on a dam reservoir on the Vistula River (Poland). Stochastic particle tracking was used with a Lagrangian approach, then geostatistical analyses to interpret the simulation results.It is shown that, excluding the backwater, SS sedimentation is greatest in distal parts of the reservoir's lacustrine and river sections. The reservoir retains an average of 79 % of inflowing SS. The primary process affecting the sedimentation of SS is a dam-wards increasing fineness of settling grains. Hydrodynamic simulation results showed deposition of clay fraction to also be possible in the reservoir's upper part, even during floods. Moreover, sand grains entered the dam even during very low flows. Interpretation of Particle Tracking Model (PTM) simulation results and geostatistical modelling reveals that the submerged bed of the pre-dam river still has a transport function, while fine SS accumulates in slow-flowing areas outside it. The anastomosing pre-dam riverbed still influences flow conditions and SS deposition in the upper and middle reservoir. PTM modelling and geostatistical analyses determined the influence of hydrodynamic conditions on the spatial variability of SS sedimentation in terms of the quantity and grain-size distribution of sedimenting matter.An original indicator (ADDRESS [A]; Accumulation or Discharge of Dam REservoir Suspended Solids) was developed determining the ability of polymictic reservoirs to either retain SS of different diameters or allow them through the reservoir to be discharged through the dam. The indicator quickly and simply determines particle behaviour under given hydrological conditions. Information on whether all or only some of grains of specific diameters will flow through the dam is important for explaining many natural processes affecting the reservoir ecosystem and the river ecosystem below the dam.

Investigation of the Effect of Pumping Depth and Frequency of Flapping Hydrofoil on Suspended Matter Discharge Characteristics

In order to study the effect of the pumping depth and pumping frequency of the flapping hydrofoil device on suspended solids in the waters, this paper takes raceway aquaculture as an example, and introduces a flapping hydrofoil device to improve the discharge of suspended solids in the raceway, in response to the problem of the deposition of suspended solids from fish faeces and bait residues in water. The CFD method was used to compare and analyze the discharge of suspended solids at different pumping depths, and the combined effect of the two was studied according to different combinations of pumping frequency and pumping depth. The results proved that the flapping hydrofoil motion can improve the bottom hydrodynamic insufficiency in ecological waters and thus enhance the discharge effect of suspended particles in water. In addition, the pumping depth of the flapping hydrofoil is too deep for the movement to be disturbed by the bottom surface, while the thrust generated by the flapping hydrofoil is weakened if the depth is too shallow. When the pump water depth is 1.1 H, the reversed Kármán vortex street is more stable under the balancing effect of the bottom surface and gravity, and the rate curve of the flapping hydrofoil acting on the discharge of suspended particles is better. From our comprehensive consideration of the joint effect of the pumping depth and pumping frequency, we recommend the use of a 1.1 H of pumping depth and 2.0 Hz pumping frequency in combination to achieve the best effect of discharging suspended particles. This study provides valuable insights into the actual engineering applications of flapping hydrofoil devices for improving water quality and ecological sustainability in raceway aquaculture.

Combined settlement and clogging in drainage sand layer for suspended solids, colloids and inorganic salts

Blockage of leachate drainage facilities is a common engineering problem in landfill operation. The key factors that cause blockage of drainage facilities in landfill leachate are the deposition of suspended solids (SS) with colloids and the precipitation of inorganic salts. To determine the combined sedimentation law of SS, colloids and inorganic salts, a combined sedimentation test of suspended solids, colloids and inorganic salts was conducted. To further clarify the resulting clogging characteristics of the water-conducting sand layers, a sand column blocking test were conducted, and mineral composition and grain characteristics of sediments were determined. The experimental results shown that the colloids (silver iodide) and inorganic salts (calcium chloride or aluminum sulfate) increased the sedimentation rate of SS by 8 to18 times. Among them, the effect of AgI colloid was the most significant, followed by effect of calcium chloride, while effect of aluminum sulfate was the weakest. Compared with sand column clogging caused by SS, this combined migration shortened the sand column clogging time by more than half and reduced hydraulic conductivity by nearly two to three orders of magnitude. This study contributes to the accurate assessment of the service performance of landfill leachate drainage systems.

Clogging index: A tool to quantify filter bed clogging in horizontal subsurface flow macrophyte-assisted vermifilter.

This study aimed to develop a mathematical index for quantifying filter bed clogging in horizontal subsurface flow macrophyte-assisted vermifilter (HSSF-MAVF). The developed clogging index (CI) simulates the porosity reduction in the HSSF-MAVF bed due to the combined actions of deposition of suspended solids, biofilm generation, and plant growth. A series of experiments based on HSSF-MAVF were conducted to examine the key parameters related to clogging of the vermifilter such as hydraulic loading rates (HLR), organic strength (COD), and total suspended solid (TSS) at different operating conditions for the treatment of synthetic dairy wastewaters. The index was then validated using the data collected from the experiments. The predicted CI was observed to be highly capable of replicating the clogging phenomenon, as observed in this experimental study within the error range of 2-8%. Based on the visual observation and value of CI, filter beds can be grouped as unclogged (CI < 25), partially clogged (25 < CI < 40), and clogged (40 < CI). Clogged filter beds with higher CI resulted in a 5-15% reduction in the COD removal performance of HSSF-MAVFs. Moreover, the CI also envisages one to understand the individual contributions of biofilm growth, suspended solid deposition, and plant roots growth on the filter bed clogging during the operation of vermifilter and thus helps in deciding the proper setting of operational conditions to prolong the time of HSSF-MAVF operations within the acceptable range of bed materials clogging. PRACTITIONER POINTS: A mathematical index was developed to quantify clogging of the HSSF-MAVF. Flow is the most sensitive parameter based upon the sensitivity analysis. Dairy wastewater was used for the validation of CI.

The use of a composite mix to remove metals from acidic drainage waters at tailings facilities

This paper describes various studies on the possibility of using MSW incineration waste for treating acidic drainage waters at tailings facilities. It has been shown that the required water purity for its recycling into the process is observed when using a composite mix containing MSW incineration waste and quicklime at the ratio of 10 to 1. The kinetics of sedimentation of suspended solids and the resulting colloidal compounds indicates that the acceptable particle concentration is achieved after 2&ndash;3 minutes. The expected economic effect of using this composite mix consists in the prevention of the general environmental damage from pollution of the aquatic environment, land, and bioresources with metals, as well as from the impact of waste storage sites during MSW incineration on various components of the natural environment. The settled sludge may then be disposed into the tailings facilities to ensure the storage of respective valuable components for subsequent recovery. The use of MSW incineration waste as part of the composite mix for the treatment of acidic drainage waters at mining enterprises solves a set of urgent problems:&mdash; enables environmentally efficient treatment to prevent environmental damage caused by the ingress of acidic drainage waters contaminated with metals into the ground and natural watercourses;&mdash; ensures cost-effective use of MSW incineration waste;&mdash; reduces the volume of accumulated MSW incineration waste and ensures conservation of natural resources;&mdash; enables the storage of valuable components for subsequent recovery through disposal of the settled sludge in the tailings facilities.

Analysis of Flow Channel Structure Parameter and Optimization Study on Tooth Spacing of Drip Irrigation Tape

The flow channel structure is the main factor affecting the hydraulic performance, anti-clogging and energy dissipation performance of drip irrigation tape. Proper exploring of the performance-related but hard-to-measure structure parameters in the flow channel emitter of drip irrigation tape is imperative. However, the traditional studying methods may lead to large systematic errors and human errors, resulting in inaccurate estimations of the parameters and an unreasonable design. This paper aims to find an effective way to optimize the most significant channel structural parameter through studying 18 kinds of drip irrigation belts commonly used in the agricultural irrigation field. Unigraphics NX and Spaceclaim were applied to measure the eight main structure parameters of the selected drip irrigation tapes. The one critical parameter that affects the emitter hydraulic performance—tooth spacing—was found by Principal Component Analysis (PCA). Therefore, we designed three plans where the tooth spacing decreased by 0.1, 0.2, and 0.29 mm to 1.36, 1.26, and 1.17 mm, respectively, and, finally, formed two types of flow channels. Flow channel 1 with a tooth base is represented by Plan 1 and Plan 2, and flow channel 2 without a tooth base is represented by Plan 3. Then, computational fluid dynamics (CFD) was used to simulate the flow characteristics of the emitters in the three plans. The results demonstrate that flow channel 2 without a tooth base, represented by Plan 3, has a greater kinetic energy and hydraulic performance than flow channel 1. Compared with the control group, the changes in Plan 3 were the most obvious, with the changes in the flow index, flow coefficient, and average flow rate by −14.50%, −5.08%, and 12.50%, respectively. The flow indexes in the three plans are all less than 0.5, while the smallest of Plan 3 is 0.395. Therefore, the hydraulic performance of flow channel 2 represented by Plan 3 is better. The narrowing of the tooth spacing makes the space for vortexing between the serrated teeth smaller. The flow velocity in Plan 3 is generally increased by 3 m/s from 2.3 to 4.1 m/s, becoming more uniform. Due to a high velocity of the water flow and less vortexing, the deposition of suspended solids in the flow channel is avoided to a certain extent, and for the flow channel in Plan 3, the improvement in the hydraulic performance is greater than the reduction in the energy dissipation performance. The ratio of the decrease in the flow index to the increase in the average outflow of the emitter in Plan 3 is 1.16:1. In conclusion, the overall performance of Plan 3 is optimal for all schemes. Flow channel 2 can improve the hydraulic performance and reduce the production costs. Therefore, this study could provide a theoretical induction for inner drip irrigation tape application and production.

Imaging of particle deposition and resulting flow field during flocculation filtration within a granulated activated carbon filter

Flocculation filtration onto granulated activated carbon (GAC) filters is an advanced treatment method to achieve lower phosphorous and micropollutant discharge in wastewater treatment plants. However, the suitability is put into question as the deposition of suspended solids (SS) onto a GAC filter is aligned with more frequent backwashing ongoing with abrasion of GAC and downtimes. To evaluate the filtration process of SS onto GAC filters on the pore scale, we resolved the particle deposition in a timely and spatially resolved image series by means of magnetic resonance imaging (MRI). Besides structural images, flow measurements were acquired to evaluate the impact of SS accumulation onto the local flow field. The column had an inner surface area of 1.54 cm2 and was filled with GAC up to 10 cm in height. In total, 6.4 L of wastewater originating from a secondary clarifier were added to the GAC filter in steps of 0.2 L. The wastewater contained approximately 8.4 mg/L TSS after flocculation and precipitation. Results of one experimental run are presented. Particle accumulations within the GAC filter as well as a formation of a deposit layer was found. During the filtration process preferential inflow points into the GAC filter were recognizable. The transition of a preferential inflow point to another was often aligned with the redistribution of upper parts of the GAC filter and a compaction of accumulated SS. Analysis of flow distributions revealed that the equivalent filter velocity of 28.8 m/h is 2.3 times higher compared to the average filter velocity (12.5 m/h including porosity). Further, the equivalent filter velocity increased up to 100.8 m/h at the end of the experiment. As particles do not distribute equally over the filter height, those velocities are not representative for the whole height of GAC filters. The current study provides insights into a real flocculation filtration process without using artificial materials for imaging purposes.

Removal of suspended solids from weathered tungsten-ore beneficiation wastewater by electroneutralization and chemical precipitation

The direct reuse of weathered tungsten-ore beneficiation wastewater (WTBW) in tungsten-flotation system seriously deteriorates the flotation index of tungsten because of its high content of suspended solids (SS). In the present study, an innovative technology using calcium chloride (CaCl2) to remove SS from WTBW was established based on the theory of electroneutralization and chemical precipitation. A series of laboratory tests was performed to determine the optimal conditions for SS removal from WTBW. Species-distribution calculation, zeta potential, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy were used to analyze the underlying mechanism. Results showed that the content of SS in WTBW decreased from 25.16×103 mg/L to 22.56 mg/L after CaCl2 treatment. A concentrate with tungsten grade and recovery of 1.93% and 74.81%, respectively, was obtained by reusing the treated wastewater in the tungsten-flotation system. Compared with untreated wastewater, the tungsten grade and recovery of concentrate increased by 0.45% and 12.20%, respectively. Moreover, the Ca2+ supplied by CaCl2 can neutralize the negative charge on SS surface and further react with CO32– and SiO32– in solution to form CaCO3(S) and CaSiO3(S), which explained why CaCl2 can promote the aggregation and sedimentation of SS.

Development and simulation of the operation of a two-tier sedimentation tank for urban wastewater treatment

One of the main reasons for the increase in the ecological tension of aquatic ecosystems remains the discharge into water bodies of domestic wastewater containing toxic substances and pathogenic microorganisms. This is due to the imperfection of water treatment technologies, including due to wear and tear of utility networks and violations in the technological process, accompanied by salvo emissions. Reducing the anthropogenic load on water bodies is possible by retechnologizing various stages of wastewater treatment. The paper describes the design of a sedimentation tank with aeration elements for clarification of urban wastewater, providing an increase in the efficiency of sedimentation of suspended solids. Spraying fine air bubbles contributes to the collision and enlargement of aggregate-unstable elements without the use of coagulants and flocculants. The paper presents a mathematical algorithm for calculating the required deposition surface, taking into account the wastewater flow rate, the nominal diameter of the dispersed phase particles and the required degree of purification. Numerical experiments have shown that for a settlement with a population of 100,000 people, a treatment plant with a standard sedimentation tank is required, the area of which is 130 m2. The use of a sedimentation tank with aeration elements in similar conditions allows reducing the required clarification surface to 120.9 m2 without reducing the clarification efficiency. It has been proven that the spraying of finely dispersed air bubbles helps to reduce the required settling area of the sump by 8%.

Effect of Fe3+ on the sludge properties and microbial community structure in a lab-scale A2O process.

During biological wastewater treatment, ferric salt (Fe3+) usually serves as an inorganic flocculant to improve the agglomeration and sedimentation of suspended solids, and thus the removal efficiency of pollutants to meet the increasing strictly regulated wastewater discharge standards. In this study, we investigated the effects of Fe3+ on the removal efficiencies of pollutants, sludge properties, dominant flora and metabolic pathways of bacterial community in a classical anaerobic-anoxic-oxic (A2O) process. The results showed that a Fe3+ concentration lower than 10mg·L-1 could improve the removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN), while an inhibition effect was exerted at concentration higher than 10mg·L-1. The maximum removal efficiencies of COD and TN were 97% and 89%, respectively, under the critical Fe3+ concentration of 10mg·L-1. Total phosphorous (TP) removal was constantly positively correlated with Fe3+ concentration, due to the enhanced adsorption of phosphorus on activated sludge with the increase of surface roughness. Thauera displayed the highest relative abundance, and certain bacteria in Proteobacteria, Dehloromonas and Candidatus-Competibacter exhibited good adaptability to high concentration of Fe3+. In the context of metabolic collaterals, the most abundant functional gene families were identified to be Carbohydrate Metabolism, Amino Acid Metabolism, Cell Motility, Membrane Transport, and Replication and Repair. This study provides an extensive mechanistic insight into the impact of Fe3+ on the A2O process, which is of fundamental significance to exploit the contributions of inorganic salts to biological wastewater treatment.

Influence of Storm Runoff on the Spectral Characteristics of Dissolved Organic Matter (DOM) in a Drinking Water Reservoir During the Flood Season

To explore the influence of storm runoff on reservoir organic matter during the flood season, the Lijiahe Reservoir was selected to analyze variations in the content and components of dissolved organic matter (DOM) during four periods (before runoff, flood peak period, 1 week after runoff, and 6 weeks after runoff) using three-dimensional fluorescence spectroscopy parallel factor analysis (EEMs-PARAFAC) and ultraviolet-visible (UV-Vis) spectra. The results showed that:① the turbidity and DOC content of the reservoir increased significantly during the flood peak period (P<0.01) and gradually decreased thereafter; ② the UV-Vis spectrum characteristics showed that a(254) and a(355) were significantly increased in the flood peak period (P<0.01) while E2/E3 and E3/E4 were significantly decreased (P<0.01), indicating that the concentration, relative molecular weight, and degree of DOM humification in the reservoir were increased by storm runoff; ③ four DOM components were identified as terrestrial humus (C1 and C2), microbial humus (C3), and a tryptophan-like component (C4). The fluorescence intensity of the C1-C3 components increased significantly during the flood peak period (P<0.05), indicating that the increase in the DOM humic-like component was caused by the storm runoff. At the same time, a decrease in the fluorescence intensity of the C1-C4 components was observed after the flood peak period, indicating that DOM continuously settled and degraded after runoff; and ④ Pearson's correlation analyses showed that DOM fluorescence intensity and turbidity were significantly correlated (r>0.467, P<0.05), indicating that the observed decrease in DOM content was related to the sedimentation of suspended solids. A principal component analysis (PCA) showed that the water quality in the reservoir reflected the observed characteristics during the different runoff periods. Overall, this study reveals the effects of the storm runoff on DOM content and its components over the short and long term, providing scientific support for the management of drinking water quality.

Revealing the Surge Phenomena Contribution of the Heavy Metals Inflow to the River Don Delta

Purpose. The aim of the study is to evaluate the surge phenomena effect on the heavy metals inflow to the Don Delta based on the archival and expedition data analysis, as well as using mathematical modeling. Methods and Results. To achieve the purpose, the Hydrologic Engineering Center River Analysis System (HEC-RAS) mathematical hydrodynamic model and the original model of the heavy metal compounds’ transfer and transformation in the Don Delta, developed by S. V. Berdnikov were applied. The models included the irregular grid for the Don Delta region with the average resolution 100 × 100 m. The grid cells were grouped into the compartments according to the hydrological principle. Twelve scenarios of dynamics of the suspended solids, and the dissolved and suspended forms of Ni, Cu, Pb and Cd were calculated for the surges of various intensity under the conditions of variable water content and seasonal dynamics of near-water vegetation. In accordance with the scenarios, the graphs showing the changes in the suspended matter content and accumulation, and the maps of the deposited substance distribution resulted from the surges in the delta were constructed. During two days the calculations for which include the surges of varying repeatability and the variable water content, about 0.3–3 t of nickel compounds, 0.1–1.8 t of copper compounds, 0.2–1.8 t of lead compounds and 0.01–0.04 t of cadmium ones deposit in Don. The obtained results made it possible to reveal two regions where the increased accumulation of the precipitated suspended matter and the heightened concentrations of the heavy metal dissolved forms were observed: the interfluve of the Don shipping channel, and the systems of the Kalancha and Kuterma river branches. Conclusions. As for their influence upon formation of the flow of the heavy metal suspended forms, the surge phenomena surpass the river flow. The suspended matter concentration in the Taganrog Bay waters during the surges is the governing factor for the heavy metals inflow to the Don Delta. At the same time, the regions characterized by the highest suspended solids sedimentation and the increased concentrations of the heavy metal dissolved forms are the closest to the Taganrog Bay areas covered by reed vegetation.

Vyyavleniye vklada nagonnykh yavleniy v postupleniye tyazhelykh metallov v del'tu Dona

Purpose. The aim of the investigation is to evaluate the surge phenomena effect upon the heavy metals inflow to the Don Delta based on analysis of the archival and expedition data, as well as using mathematical modeling. Methods and Results. To achieve the purpose, the Hydrologic Engineering Center River Analysis System (HEC-RAS) mathematical hydrodynamic model and the original model of the heavy metal compounds’ transfer and transformation in the Don Delta, developed by S. V. Berdnikov were applied. The models included the irregular grid for the Don Delta region with the average resolution 100 × 100 m. The grid cells were grouped into the compartments according to the hydrological principle. Twelve scenarios of dynamics of the suspended solids, and the dissolved and suspended forms of Ni, Cu, Pb and Cd were calculated for the surges of various intensity under the conditions of variable water content and seasonal dynamics of near-water vegetation. In accordance with the scenarios, the graphs showing the changes in the suspended matter content and accumulation, and the maps of the deposited substance distribution resulted from the surges in the delta were constructed. During two days the calculations for which include the surges of varying repeatability and the variable water content, about 0.3–3 t of nickel compounds, 0.1–1.8 t of copper compounds, 0.2–1.8 t of lead compounds and 0.01–0.04 t of cadmium ones deposit in Don. The obtained results made it possible to reveal two regions where the increased accumulation of the precipitated suspended matter and the heightened concentrations of the heavy metal dissolved forms were observed: the interfluve of the Don shipping channel, and the systems of the rivers Kalancha and Kuterma branches. Conclusions. As for their influence upon formation of the flow of the heavy metal suspended forms, the surge phenomena surpass the river flow. The suspended matter concentration in the Taganrog Bay waters during the surges is the governing factor for the heavy metals inflow to the Don Delta. At the same time, the regions characterized by the highest suspended solids sedimentation and the increased concentrations of the heavy metal dissolved forms are the closest to the Taganrog Bay areas covered by reed vegetation.

The optimization on distributions of flow field and suspended solids in a full-scale high-rate clarifier using computational fluid dynamics

Suspended solids (SS) are one of major pollutants that deteriorate water quality. The high-rate clarifier is commonly used as the tertiary treatment by coagulation to agglomerate particles, thus achieving a high SS removal and making effluents acceptable for discharge. Currently the control of average residence time in operation of high-rate clarifier is challenging: With limited residence time, the particles fail to form flocs in the mixing tank, causing inefficient solid/liquid separation; while with prolonged residence time, SS sedimentation would accumulate at the bottom of the tank. In this study, a liquid-solid two-phase computational fluid dynamics (CFD) model has been developed to simulate the distributions of flow field and SS in a high-rate clarifier. The CFD model was successfully validated against experimental results in a full-scale operation, with the normalized standard error on SS less than 1.24 %. The results showed that the height of under-through channel affected the flow field more significantly rather than its width. This study also indicated that with the height of under-through channel decreasing from 2000 to 500 mm and the height of baffle increasing from 3300 to 5213 mm, the average SS concentration at the bottom of reaction tank would decrease by 34.95 % and the average residence time would be shortened by 4.77 %, which can be helpful for prolonging dredging cycle and avoiding unnecessary dredging costs.

ПОВЫШЕНИЕ ЭНЕРГЕТИЧЕСКОЙ И ЭКОЛОГИЧЕСКОЙ ЭФФЕКТИВНОСТИ СИСТЕМ ГАЗООЧИСТКИ НА ТЭС

Актуальность исследования обусловлена необходимостью повышения энергетической и экологической эффективности систем очистки выбросов систем пылеприготовления и дымовых газов ТЭС при угольной генерации и систем подготовки газа при газовой генерации, во исполнение Федерального закона № 261-ФЗ от 23.11.2009 г. (ред. от 29.07.2017) «Об энергосбережении и о повышении энергетической эффективности и о внесении изменений в отдельные законодательные акты Российской Федерации», а также требований по контролю за выбросом парниковых газов (напр., приказа № 330 от 29.06.2017 года «Об утверждении методических указаний по количественному определению объёма косвенных энергетических выбросов парниковых газов» и др.) выбросов систем пылеприготовления и дымовых газов ТЭС с угольной генерацией и в системе подготовки газа с газовой генерацией. Цель: разработка устройства циклонной фильтрации для повышения эффективности систем газоочистки на ТЭС, снижения выбросов взвешенных частиц в атмосферу от систем пылеприготовления и дымовых газов при угольной генерации и увеличения надежности работы агрегатов газотурбинных и парогазовых установок ТЭС вследствие снижения износа рабочих поверхностей поршневых и винтовых дожимающих компрессоров дожимных компрессорных станций, предотвращения попадания продуктов внутренней коррозии газопроводов в газотурбинных установках, в соответствии с п.п. 93, 94 ФНиП в области промышленной безопасности «Правила безопасности сетей газораспределения и газопотребления» (Серия 12, вып. 13). Объект: модель циклона на базе ЦН-11-200, обеспечивающая повышение энергетической и экологической эффективности систем газоочистки на ТЭС. Методы: стендовые испытания циклонного фильтра, изготовленного путем модернизации циклона ЦН-11-200, аэродинамические расчёты; численное моделирование аэродинамических параметров работы циклона-фильтра на основе методов вычислительной гидродинамики. Для математического моделирования процесса сепарации использована система уравнений, состоящая из осредненных по Рейнольдсу уравнений движения однофазного потока Навье–Стокса и уравнения движения частиц, основанного на законе Ньютона. Для определения эффективности отделения взвешенной части потока в циклоне-фильтре использован безразмерный комплекс Rer, с помощью которого численные значения параметров осаждения взвеси из многофазного потока в сепараторе найдены расчетным путем. Результаты. Анализ литературных источников показал отсутствие конструкций циклонов-фильтров, которые обеспечивали бы надлежащую (более 98 %) степень очистки выбросов без резкого увеличения энергозатрат на обработку выбросов. Проведенные опыты показали целесообразность конструктивного дополнения возвратно-поточных циклонов фильтрующей вставкой в зоне, где происходит инерционное осаждение пыли. Для определения эффективности отделения взвешенной части потока в данном циклоне-фильтре был использован безразмерный комплекс Rer. Расчеты показали соответствие результатов теоретических и натурных исследований.

Spatial variations and periodic changes in heavy metals in surface water and sediments of the Three Gorges Reservoir, China

Substantial changes have occurred in hydrological situation of the Three Gorges Reservoir (TGR) after the operation of the Three Gorges project, as have the heavy metals (HMs) pollution characteristics. In this study, concentrations of Cu, Zn, Pb, Cr, and Cd in surface water and sediments of the TGR were determined during the water impoundment period (December 2015) and water drawdown period (June 2016). The index of geoaccumulation, principal component analysis (PCA), and correlation analysis were used to analyze HMs pollution characteristics. Results showed that HMs concentrations in surface water were much lower than the quality standards for drinking water and surface water of China. The pollution levels of HMs in sediments were nonpolluted for Cr, nonpolluted to moderately polluted for Cu, Zn, Pb, and moderately polluted for Cd. In the fluctuating backflow zone, HMs concentrations in sediments during the water drawdown period were lower than those during the water impoundment period, which was attributed to that faster flow velocity during the water drawdown period resulted in less deposition of suspended solids and faster release of HMs pollutants from sediments to water. HMs concentrations of sediments at sites M14 and M17 showed similar periodic changes to those at the fluctuating backflow zone, which might be attributed to the density-stratified flow in the adjacent upstream tributaries (Meixi River and Qinggan River, respectively). Correlation analysis and PCA analysis results showed that for the sediments, Cr came from natural sources, while Cu, Zn, Pb, and Cd mainly came from anthropogenic sources.

Groundwater Quality Assessment Using Fuzzy-AHP in An Giang Province of Vietnam

Along with rapid population growth in Vietnam, there is an increasing dependence on groundwater for various activities. An Giang province is known to be one of the agricultural intensification areas of The Vietnamese Mekong Delta (VMD). This study aimed to evaluate the spatiotemporal variation of groundwater quality for a period of ten years from 2009 to 2018 in An Giang. The weighted groundwater quality index (GWQI) was developed based on the fuzzy analytic hierarchy process (Fuzzy-AHP) for assigning weighted parameters. The results show that that shallow wells in the Northeast and Southeast regions of An Giang were mostly categorized under “bad water” quality with high arsenic (As) concentration over the years partly due to huge amounts of sediment deposition in monsoon season. Overall, the reason for the poor groundwater quality in An Giang was the combined effect of both natural and human activities. On the other hand, we detected high values of GWQI links with high As concentration in areas where people extract more groundwater for irrigation. Temporal variation of GWQI suggested that groundwater quality at eight wells has improved from 2009 to 2018 in the wet season as compared to the dry season. The reason behind the improvement of groundwater quality during wet season was the decrease in river discharge, which causes less deposition of suspended solids near the flood plains. Moreover, the filling of unused wells can reduce the movement of pollutants from unused wells to groundwater aquifers. Although there was not sufficient evidence to show the relationship between As and sediment concentration, the temporal reduction trend in river discharge and suspended solids was detected in An Giang. The understanding of groundwater quality can help policymakers protect and manage limited water resources in the long-term.

Three-dimensional Eulerian-Lagrangian simulation of particle settling in inclined water columns

We present three-dimensional simulations of sedimentation of suspended solids in inclined vessels using a Eulerian-Lagrangian model developed specifically for the study of solid-liquid mixtures. The simulation results reveal the three-dimensional vortical flow structures that follow the occurrence of flow instability and induce strong mixing between the particle-laden and clear-fluid layers. We show that the tubes exhibit significant spanwise variation due to the presence of wall boundary layers and are subsequently transformed into three-dimensional turbulent structures. The vortices and turbulence result in significant resuspension from the particle-laden layer and weaken the convective effect that enhances sedimentation. We show that for the present flow condition and particle size, particle inertia plays an important role in particle resuspension. Analysis of the release of potential energy is presented to examine the sedimentation efficiency under different flow conditions. We show that the time history for a typical case can be divided into development, convection, and deposition stages. The analysis for cases with different particle sizes shows that the faster settling associated with larger particles stabilizes the flow by reducing the interfacial shear while settling. From simulation results using various angles of inclination, we can find the optimal angle of inclination to achieve the greatest efficiency in settling enhancement. Finally, critical modeling aspects, including the importance of different forcing terms and two- or three-dimensional considerations, are discussed.

A modified QWASI model for fate and transport modeling of Zn and Pb in a shallow lake during the ice-free period

Heavy metal pollution in lakes is becoming increasingly of interest to researchers. Because heavy metals have high mobility and do not degrade, they migrate easily between different environmental mediums through processes such as suspended solids deposition, sediment resuspension, and diffusion, among others. These processes are particularly pronounced in shallow lakes since the hydrodynamism is higher in bodies of water with minimal depth. Lake Ulansuhai—a typical shallow lake in the Hetao irrigation district in Inner Mongolia—also experiences intense sandstorm activity, which compounds the suspended solids exchange intensity between water and sediment, strengthening the migration of heavy metals in the lake system. This study examines the fate and transport of two heavy metals—Zn and Pb—within this lake, using a field experiment to determine the flux of sediment re-suspension and deposition and a laboratory experiment to modify the QWASI model for shallow bodies of water. The aquivalence and mass balance approaches were used to develop this modified QWASI model. The margins of error between the modeled and the measured average concentrations of Zn and Pb in water were 5.0%–30.6% and 5.8%–29.5%, respectively, and in sediment were 0.3%–4.9% and 0.9–5.5%, respectively. These results suggest that the modified QWASI model developed here could indeed be used to more accurately represent the fate and transport of Zn and Pb during the icefree period of a shallow lake.

Sequestration of heavy metal by glomalin-related soil protein: Implication for water quality improvement in mangrove wetlands

Glomalin-related soil protein (GRSP) is a widespread glycoprotein found to have strong ability of sequestering heavy metals in soils. However, the underlying mechanism for metal and metalloid removal as well as water quality improvement and the ecological role played by GRSP are still not well documented. This study was initiated to investigate the interconnection of metal loading in GRSP between sediments and suspended solids, focusing on the mobilization mechanisms of GRSP in the coastal mangrove wetland. Combined indicators of nine heavy metals were significantly positively correlated with GRSP concentration by Principal Component Analysis, indicating that GRSP could act as an indicator of contamination level in the mangrove wetlands. Large distribution of GRSP in sediments and suspended solids elevated sequestration potential of heavy metals (Fe, Mn, Cr, Cu, Zn, Ni, Cd, Pb) and metalloid arsenic in the mangrove aquatic ecosystem. GRSP mobilized and sequestered heavy metals in sediment profiles, which reduced the bioavailability of heavy metals. GRSP was also a significant contributor for suspended solids to adsorb heavy metals, enhancing suspended solids deposition and burial process in sediments. This new finding provided insights into the ecological functions of GRSP and the heavy metal cycling in wetland environments.