Impact of Dewatering on the Spatio-Temporal Distribution of Benthic Macroinvertebrate Communities in the Okpara River, Benin

Surface watercourses are areas of very high ecological and heritage value. Macroinvertebrates are bioindicators of the health of aquatic ecosystems. The aim of this study was to assess the effects of dewatering and re-watering cycles on benthic macroinvertebrate (BMI) communities. Two data collections were carried out at two stations (Okpara 1 and Okpara 2) on the Okpara river before and after dewatering. Thus, 8 samples of benthic macroinvertebrates and 12 physico-chemical parameters (T°C, pH, Transparency, Depth, Conductivity, Dissolved Oxygen that were measured in situ, and BOD5, COD, NH4+, NO3-, NO2- and PO43-) were assayed in the laboratory. Canonical Correspondence Analysis (CCA) was used to match physico-chemical data to MIB families. Shannon and Piélou diversity indices were used to determine the effects of dewatering on MIBs. The increase in temperature values of pH, BOD5, COD, NH4+, NO3-, NO2- and PO43-, after re-watering indicates the effect of dewatering on the quality of Okpara aquatic ecosystems. The benthic macrofauna collected consisted of 62.42% insects, 0.65% crustaceans, 6.48% molluscs, 0.72% worms and 0.14% arachnids. Whereas after re-watering, 21.67% insects, 0% crustaceans, 0.22% molluscs, 7.56% worms and 0.29% arachnids were recorded. Insects, crustaceans and molluscs were more abundant before dewatering than after. This was revealed by low abundances and taxonomic richness, as well as low Shannon index values of samples collected after re-watering.

Comparative filtration and dewatering behavior of vitrinite and inertinite of bituminous coal:Experiment and simulation study

The filtration and dewatering of fine clean coal not only ensure industrial water recycle in coal washing plant,but also reduce the moisture of coal product in order to meet the requirements of combustion or coking industry.Fine clean coal is mainly composed by organic matter,and the property difference of different organic matter determines the filtration and dewatering behavior.In this investigation,vitrinite and inertinite were separated from a clean bituminous coal,and the comparative filtration and dewatering behavior of vitrinite and inertinite were conducted.The results showed that inertinite has lower dewatering rate and higher filter cake moisture than vitrinite.The analysis of filter cake structure showed that inertinite particle is easier to be broken into small particles due to the difference of mechanical properties,thus forming more compact filter cake than vitrinite.The analysis of particle surface properties showed that vitrinite is more hydrophobic than inertinite,which makes water easier drained from filter cake.The simulation study showed that the structure of inertinite is more porous than that of vitrinite,and the interaction between inertinite and water is stronger than that between vitrinite and water.This study provides a theoretical basis for improving coal dewatering by selectively improving coal maceral hydrophobicity.

Reconstructed rheometer for direct monitoring of dewatering performance and torque in tailings thickening process

To further clarify the dewatering performance and torque evolution during the tailings thickening process,a self-made rake was connected to a rheometer to monitor the shear stress and torque.The dewatering performance of the total tailings was greatly improved to a solid mass fraction of 75.33%in 240 min.The dewatering process could be divided into three stages:the rapid torque growth period,damping torque growth period,and constant torque thickening zone.The machine restart was found to have a significant effect on the rake torque;it could result in rake blockage.Furthermore,the simultaneous evolution of the torque and solid mass fraction of thickened tailings was analyzed.A relationship between the torque and the solid mass fraction was established,which followed a power function.Both the experimental and theoretical results provide a reference for the deep cone thickener design and operation to enhance the dewatering performance.

Calculation of groundwater head distribution with a close barrier during excavation dewatering in confined aquifer

When pumping is conducted in confined aquifer inside excavation pit(waterproof curtain),the direction of the groundwater seepage outside the excavation changes from horizontal to vertical owing to the existence of the curtain barrier.There is no analytical calculation method for the groundwater head distribution induced by dewatering inside excavation.This paper first analyses the mechanism of the blocking effects from a close barrier in confined aquifer.Then,a simple equation based on analytical solution is proposed to calculate groundwater heads inside and outside of the excavation pit with waterproof curtain(hereafter refer to close barrier)in a confined aquifer.The distribution of groundwater head is derived according to two conditions:(i)pumping with a constant water head,and(ii)pumping with a constant flow rate.The proposed calculation equation is verified by both numerical simulation and experimental results.The comparisons demonstrate that the proposed model can be applied in engineering practice of excavation.

Nitrogen removal from sludge dewatering effluent through anaerobic ammonia oxidation process

Anaerobic ammonia oxidation（Anammox） process is a novel and promising wastewater nitrogen removal process. The feasibility of transition of Anammox from denitrification and the performance of lab-scale Anammox biofilm reactor were investigated with sludge dewatering effluent. The results showed that Anammox process could be successfully started up after cultivation of denitrification biofilm and using it as inoculum. The transition of Anammox from denitrification was accomplished within 85 d. Anammox process was found suitable to remove ammonia from sludge dewatering effluent. The effluent ammonia concentration was detected to be 23.11 mgN/L at HRT of 28 h when influent ammonia concentration was fed 245 mgN/L, which was less than that for the national discharge standard Ⅱ （25 rngN/L） of China. Volumetric total nitrogen loading rate was up to 584.99 mg TN/（L. d） at HRT of 17 h, while influent concentrations were kept 243.25 mg NH4＊ -N/L and 288.31 mg NO2^- -N/L.

Study on Deep Well Dewatering Optimization Design in Deep Foundation Pit and Engineering Application

Based on analyses of the theories of groundwater unsteady flow in deep well dewatering in the deep foundation pit, Theis equations are chosen to calculate and analyze the relationship between water level drawdown of confined aquifer and dewatering duration. In order to reduce engineering cost and diminish detrimental effect on ambient surrounding, optimization design target function based on the control of confined water drawdown and four restriction requisitions based on the control of safe water level, resistance to throwing up from the bottom of foundation pit, avoiding excessively great subsidence and unequal surface subsidence are proposed. A deep well dewatering project in the deep foundation pit is optimally designed. The calculated results including confined water level drawdown and surface subsidence are in close agreement with the measured results, and the optimization design can effectively control both surface subsidence outside foundation pit and unequal subsidence as a result of dewatering.

Optimization of dewatering schemes for a deep foundation pit near the Yangtze River, China

A deep foundation pit constructed for an underground transportation hub was excavated near the Yangtze River. Among the strata, there are two confined aquifers, between which lies an aquiclude that is partially missing. To guarantee the safety of pit excavation, the piezometric head of the upper confined aquifer, where the pit bottom is located, should be 1 m below the pit bottom, while that of the lower confined aquifer should be dewatered down to a safe water level to avoid uplift problem. The Yangtze River levee is notably close to the pit, and its deformation caused by dewatering should be controlled. A pumping test was performed to obtain the hydraulic conductivity of the upper confined aquifer. The average value of the hydraulic conductivity obtained from analytical calculation is 20.45 m/d, which is larger than the values from numerical simulation（horizontal hydraulic conductivity K_H = 16 m/d and vertical hydraulic conductivity K_V = S m/d）. The difference between K_H and K_V indicates the anisotropy of the aquifer. Two dewatering schemes were designed for the construction and simulated by the numerical models for comparison purposes. The results show that though the first scheme could meet the dewatering requirements, the largest accumulated settlement and differential settlement would be94.64 mm and 3.3‰, respectively, greatly exceeding the limited values. Meanwhile, the second scheme,in which the bottoms of the waterproof curtains in ramp B and the river side of ramp A are installed at a deeper elevation of-28 m above sea level, and 27 recharge wells are set along the levee, can control the deformation of the levee significantly.

Application of Screw Press Filter for Oily Sludge Dewatering

In order to find suitable oily sludge treatment equipment for a produced water treatment station of an oilfield in Iraq,the widely used mechanical dewatering equipments overseas including plate and frame filter,belt press filter,centrifugal filter and screw press filter were compared and analyzed,and the application situation of screw press filter was investigated at site. The site survey showed that,screw press filter was an integrated equipment combined with functions of concentrating and dewatering,which was characterized by low water content of filter cake,small occupied area,easy to separate,no blocking and can realize self-cleaning,which is suitable to low concentration sludge. Screw press filter can simplify oily sludge treatment process,and save engineering construction and operation cost,which is a better choice for oily sludge dewatering. The design of screw press filter adopted in the produced water treatment station of an oilfield in Iraq was introduced here.

Solidification Efficiency and Mechanism of Conventional Curing Agents for Sewage Sludge Stabilization and Dewatering

One of the challenges faced by sewage sludge treatment and disposal is its higher water content,and how to efficient dewater those hazardous materials properly is welcome in practice. This study stabilized the sewage sludge via the using of conventional curing agents and calcined aluminum salts,and the corresponding dewatering mechanisms and structural changes of the stabilized sludge were further comparable analyzed.Experimental results showed that wollastonite and kaolin exhibit a relative higher dewatering efficiency as compared to other conventional curing agents; however the releasing rate of heavy metals of Cu,Cr,Ni for kaolin solidification and Zn,Pb for wollastonite solidification is higher than the sludge samples solidified by other curing agents. For comparison,the sludge samples solidified by calcined aluminum salts (AS),calcium ash,Mg-based curing agent,tricalcium aluminate( C_3A) show a lower heavy metals leaching potential and unconfined compressive strength. In addition,the economic characteristics and local availability of AS,calcium ash,C_3A and CaO makes it have a broad prospect in extension and application. These findings are of great significance for stabilization and dewatering of sewage sludge.

Numerical simulation and land subsidence control for deep foundation pit dewatering of Longyang Road Station on Shanghai Metro Line 18

In terms of controlling groundwater in deep foundation pit projects, the usual methods include increasing the curtain depth, reducing the amount of pumped groundwater, and implementing integrated control, in order to reduce the drawdown and land subsidence outside pits. In dewatering design for confined water, factors including drawdown requirements, the thickness of aquifers, the depth of dewatering wells and the depth of cutoff curtains have to be considered comprehensively and numerical simulations are generally conducted for calculation and analysis. Longyang Road Station on Shanghai Metro Line 18 is taken as the case study subject in this paper, a groundwater seepage model is developed according to the on-site engineering geological conditions and hydrogeological conditions, the excavation depth of the foundation pit as well as the design depth of the enclosure, hydrogeological parameters are determined via the pumping test, and the foundation pit dewatering is simulated by means of the three-dimensional finite difference method, which produces numerical results that consistent with real monitoring data as to the groundwater table. Besides, the drawdown and the land subsidence both inside and outside the pit caused by foundation pit dewatering are calculated and analyzed for various curtain depths. This study reveals that the drawdown and the land subsidence change faster near the curtain with the increase in the curtain depth, and the gradient of drawdown and land subsidence changes dwindles beyond certain depths. In this project, the curtain depth of 47/49 m is adopted, and a drawdown-land subsidence verification test is completed given hanging curtains before the excavation. The result turns out that the real measurements basically match the calculation results from the numerical simulation, and by increasing the depth of curtains, the land subsidence resulting from dewatering is effectively controlled.

Characterisation of pore fluid salinity dependent evaporative dewatering of kaolin using dielectric spectroscopy

Realising the importance of pore fluid salinity on the dewatering behaviour of fine-grained porous systems,the present study systematically investigated such impacts on temporal moisture dynamics of kaolin subjected to evaporative dewatering.A detailed discussion is provided pertaining to the background processes dictating evaporative dewatering response and corresponding alterations in the dielectric behaviour of kaolin.Frequency dependent dielectric spectra of soil,which can be considered as the fingerprint of the transient changes in the condition of water phase within the pore system of the soil and associated densification,are monitored in real time during dewatering using an open-ended coaxial probe with a vector network analyser.The spatial sensitivity of the coaxial probe has been quantified through layered media approach.Combining the results of volume change behaviour of the material along with its moisture loss response,the study characterised the hydro-mechanical response of the material from the windows of frequency dependent dielectric spectroscopy.

Application of Water-Soluble Polymer in Dewatering of Fine Coal

The addition of water-soluble polymer to a fine coal slurry to enhance dewatering process is considered to be one of the most effective ways of solving the problems of dewatering of fine coal. A series of tests are conducted with a vacuum dewatering apparatus to study the effects of various factors such as the species of polymer, polymer dosage and its ways of addition, and the pH of fine coal slurry on filtrating and dewatering of fine coal.

Use of Surfactant in the Dewatering of Coal Flotation Concentrate

For reducing moisture content of cake, the attempt is made by the use of surfactant in the dewatering of flotation concentrate. Different kinds of surfactant have been tested in laboratory and tbe factors which influence dewatering effect are investigated. Four of the surfactants have good dewatering efficiency.The moisture content is decreased by 5% or so. Two of them have been used in commercial process. The method is very simple and may solve a moisture problem of coal preparation plant.

Optimizing dewatering design for a metro station on the Chengdu Metro Line 7

At present, most calculation results regarding foundation pit dewatering are ideal values, making construction resources prone to being wasted. In order to optimize the traditional pipe well design of large wells, the linear programming solution module in Excel is used, with the total water inflow taken as the objective function, the water level drawdown used as the constraint and test condition, and a station project on the Chengdu Metro Line 7 serving as the subject of this study. The total water inflow of the traditional pipe well design is optimized by the simplex method, producing a total water inflow of 4 040.65 m^3/d, which, compared with 4 829.79 m^3/d, the total water inflow calculated by means of the traditional design optimization method, engenders a reduction of roughly 16% per day. The feasibility of the optimization methodology is verified by the drawdown constraint, which reveals the decrease of construction costs and the diminution of the influence that the lowered groundwater level has on the surroundings of the metro station. Finally, references are provided as to optimizing the dewatering designs for other metro stations in similar engineering and hydrogeological conditions.

Foundation pit dewatering optimization design based on GMW-2005 and LGR technique

The slope instability and uneven settlement caused by the foundation pit dewatering pose a great threat to the project and surrounding environment.Thus,it is necessary to carry out optimization design of the foundation pit dewatering project.To solve this problem,this paper introduces the simulation-optimization method and establishes the groundwater model based on MODFLOW-2005.The local grid refinement(LGR)technique is employed to achieve the refinement of dewatering area.Under the premise of construction safety,the minimum cost of the project is set as the objective function to solve the optimization problem of foundation pit engineering with GWM-2005.The results show that the optimization with GWM-2005 will be more accurate combined with the LGR model,but the improvement of the optimization is not obvious.It is necessary to choose a suitable local refinement model considering the engineering requirement.

Reed Beds for Sludge Dewatering and Stabilization

In urban and peri-urban areas of developing countries decentralized wastewater treatment using septic tanks as pretreatment is common. One challenge of decentralized wastewater treatment systems (DEWATS) is handling and utilization of the generated sludge. Sludge drying reed beds (SDRBs) are a robust method for dewatering and stabilization of sludge. Constructed wetlands (CWs) and SDRBs can be integrated to treat both wastewater and sludge. SDRBs require more area than most other sludge treatment options, but have low operational cost and energy requirements. The land area required for SDRB’s can be optimized by the selection of an appropriate loading rate, sludge application frequency and resting phase. This paper gives a review regarding the use of SDRB’s as well as presenting a pilot scale experiment comparing planted and unplanted sludge drying beds in Kathmandu. The planted beds showed a higher dewatering capability and higher reduction of volatile solids (VS). A short-term pilot-scale experiment can give valuable input to the design and operation of full-scale systems and for sub-tropical climate as that of Kathmandu Nepal, an initial sludge loading rate (SLR) of 100 kg total solids (TS)/m2/year is suggested with a gradual increase to up to 250 kg TS/m2/year.

Dewatering Techniques for Gas Recovery in Sichuan Gas Fields

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DEWATERING MEASURE APPLIED TO SOLVE LANDSLIDE PROBLEM IN EXPANSIVE SOIL AREA

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Drainage Bed:A Natural System for WTP Sludge Dewatering and Drying with Different Coagulant Chemicals in Tropical Countries

This study seeks to evaluate the mechanisms for dewatering sludge from Water Treatment Plants (WTP) in a natural system that uses nonwoven polyester geotextile blankets named Drainage Bed (DB). Dewatering mechanisms are divided into two stages: Drainage and Drying Phases. For the Drainage Phase, the results showed that the solids content of the Aluminum Sulfate sludge reached 8.9% to 18.3% and the PACl sludge 1.8% to 6.5%, the volume reduction on this phase exceeding 50% and 74%, respectively. The final solids content, after the Drying Phase, was greater than 28%, reaching 90%. In the Drainage Phase the lower the Surface Application Rate—SAR [kg/m2] is, the greater the drainage flow will be. In the Drying Phase, moisture and insolation were key factors in drying sludge. Thus, the Drying Phase in the DB takes special attention for being virtually nonexistent in dewatering technologies in a closed system (confined) without exposure to solar energy. The use of the DB as a natural system for dewatering WTP sludge in tropical countries proved to be a promising alternative, because of its efficient removal of water from sludge coupled with operational simplicity and low costs, provided there is area available.