Electroosmotic Dewatering Research Articles

Mathematical model and optimization of continuous electro-osmotic dewatering

A mathematical model was developed for continuous electrokinetic dewatering of phosphatic clay, a clay-water suspension generated as an effluent from processing of phosphate ores. The model, accounting for compressibility of the cake and for both electro-osmotic and hydraulic permeability, provided good agreement with experimental data obtained from a prototype that separated a 10 wt% phosphatic clay slurry into clear water and a cake with a solids content up to 35 wt%. A constrained optimization strategy was developed to identify optimal operation parameters for an industrial-scale electrokinetic dewatering process for processing the effluent generated by a typical phosphate mine.

The influence of pulp and interfacial chemistry and mode of electrical power input on electroosmotic dewatering of Na-exchanged smectite dispersions

Abstract In this study, pulp and interfacial chemistry, gravity settling/drainage and electroosmotic (EO) dewatering behaviour of two types of fine, Na-exchanged smectite clay (high and low Na content montmorillonites) slurries were investigated as a function of background electrolyte ionic strength and time at pH 7.5 with constant voltage (0.5 vs. 1 V/cm initial field strength) or current density (12.5 vs. 25 A/m2). The two smectite variants displayed significantly different mineral chemistry and particle zeta potential, the latter dependent on Ca(II) background. Suppressed swelling and marked reduction in zeta potential magnitude occurred at 0.03–0.3 M Ca(II) ionic strength, the extent of which was greater for low than high Na-smectite pulps. Ca(II) ionic strength of ~0.1 M improved pre-EO gravity dewatering from

Sewage sludge drying method combining pressurized electro-osmotic dewatering with subsequent bio-drying

In this study, pressurized electro-osmotic dewatering (PEOD) as a pretreatment process, instead of the conventional practice of adding bulking agents, for sewage sludge bio-drying was proposed. Initially, various parameters were optimized for obtaining dewatered sewage sludge (DSS), treated by an efficient, quick, and energy-saving PEOD process. The results show that the moisture content (MC) of sewage sludge could decrease from 83.41% to 60.0% within 7.5 min in the optimum conditions of the PEOD process. Subsequently, two DSS bio-drying tests were carried out to investigate the effects of inoculation. The highest temperature (68.1 °C) was obtained for T2 (inoculation), which was 3.6 °C higher than that for T1 (non- inoculation). The MC accumulative removal rate for T1 (41.49%) was slightly less than that for T2 (44.60%). Lastly, the volatile solid degradation dynamics model parameters were measured. The degradation rate constants (k) for T1 and T2 were 0.00501 and 0.00498, respectively.

Electroosmotic dewatering of cellulose nanocrystals

One of the main challenges for industrial production of cellulose nanocrystals is the high energy demand during the dewatering of dilute aqueous suspensions. It is addressed in this study by utilising electroosmotic dewatering to increase the solid content of suspensions of cellulose nanocrystals. The solid content was increased from 2.3 up to 15.3 wt%, i.e. removal of more than 85% of all the water present in the system, at a much lower energy demand than that of thermal drying. Increasing the strength of the electric field increased not only the dewatering rate but also the specific energy demand of the dewatering operation: the electric field strength used in potential industrial applications is thus a trade-off between the rate of dewatering and the energy demand. Additionally, it was found that high local current intensity had the potential of degrading cellulose nanocrystals in contact with the anode. The maximum strength of the electric field applied should therefore be limited depending on the equipment design and the suspension conditions.

Magnetic micro-particle conditioning–pressurized vertical electro-osmotic dewatering (MPEOD) of activated sludge: Role and behavior of moisture and organics

In this study, a magnetic micro-particle conditioning–pressurized vertical electro-osmotic dewatering (MPEOD) process with magnetic micro-particle conditioning–drainage under gravity–mechanical compression–electrical compression (MMPC–DG–MC–EC) stages was established to study the distribution and migration of water, extracellular polymeric substances (EPS), and other organic matter in the activated sludge (AS) matrix at each stage. Results showed that the MPEOD process could attain 53.52% water content (WC) in dewatered AS with bound water (BW) and free water (FW) reduction rates of 82.97% and 99.67%, respectively. The coagulation and time-delayed magnetic field effects of magnetic micro-particles (MMPs) along the MMPC–DG–MC stages initiated the transformation of partial BW to FW in AS. EC had a coupling driving effect of electro-osmosis and pressure on BW, and the changes in pH and temperature at EC stage induced the aggregation of AS flocs and the release of partial BW. Additionally, MMPs dosing further improved the dewatering performance of AS by acting as skeleton builders to provide water passages. Meanwhile, MMPs could disintegrate sludge cells and EPS fractions, thereby reducing tryptophan-like protein and byproduct-like material concentrations in LB-EPS as well as protein/polysaccharide ratio in AS matrix, which could improve AS filterability. At EC stage, the former four Ex/Em regions of fluorescence regional integration analysis for EPS were obviously reduced, especially the protein-like substances in LB- and TB-EPS, which contributed to improvement of AS dewaterability.

Compartmentalization of extracellular polymeric substances (EPS) solubilization and cake microstructure in relation to wastewater sludge dewatering behavior assisted by horizontal electric field: Effect of operating conditions

Sludge treatment and disposal have become important environmental issues in China. Mechanical dewatering is widely used to reduce the amount of sludge to be disposed and relieve the rapid growth pressure of waste sludge. In comparison to traditional sludge dewatering processes, pressure electro-osmotic dewatering has many advantages on sludge dewatering efficiency, low conditioner dosage and concentrated cake are both beneficial to further recycling of waste sludge. In general, complex electrochemical effects (eg. electrochemical oxidation, ohmic heating and pH gradient effect) are accompanied by the pressure electro-osmotic dewatering process. These electrochemical effects will inevitably cause solubilization and/or degradation of key constituents of wastewater sludge - extracellular polymeric substances (EPS). In this study, the effects of voltage, pH and ionic strength on sludge electro-osmotic dewatering performance and electrochemical effects were investigated. The solubilization and degradation of EPS were analyzed by examining the variation of dissolved organic matter (DOM) in the filtrate, and the relationships between microstructural properties of sludge cake and DOM and electro-osmosis dewatering performance in electro-dewatering process was examined. It was found that electro-dewatering properties were improved by raising the operating voltage or decreasing the pH value, while dewatering rate initially increased at low ionic strength it decreases with increased ionic strength. In addition, the porous structure of cathodic cake was more plentiful than that at the anode. At the cathode, the EPS dissolution was mainly related to alkalization, while the oxidation and acidification were responsible for release of EPS at the anode. Meanwhile, electrophoresis effect was able to promote migration of EPS toward the anode. The average electro-osmotic dewatering rate at the anode (R2.>0.79, p < 0.02) and at the cathode (R2.>0.87, p < 0.03) strongly correlated with the volume of pore of sludge cake. There was no correlation between the total content of anodic DOM (R2<0.31, p>0.08) and electro-osmotic dewatering rate at the anode, however, the content of cathodic DOM (R2 > 0.62, p < 0.09) negatively correlated with average electro-osmosis dewatering rate of cathode. Since cathode is the main water-permeable side in sludge electro-dewatering, and the sticky biopolymers (proteins and humic subtances) could not be converted into small molecules, higher EPS release was associated with worse sludge filterability. As for the anode, the biopolymers were degraded into small molecules due to electrochemical oxidation, which greatly reduced the impact of DOM on dewatering effect. Therefore, the operating conditions (voltage, pH and ionic strength) caused changes in electrochemical effects, which played a crucial role in compartmentalization of sludge EPS dissolution and consequently sludge electro-dewatering behavior.

Electric Field Induced Polarization Effects Measured by in Situ Neutron Spectroscopy

Despite the success of electrical stimulation in many areas, including clay or sludge dewatering, extraction of juices from fruit pulp, fracture healing and targeted drug delivery, the induced transport mechanisms are controlled by unknown factors. While electroosmotic dewatering of clays particles <10 μm is well known, understanding of how tightly bound water molecules are removed from within the clay interlayers is still incomplete. By performing quasielastic neutron scattering experiments with in-situ electric field stimuli on calcium montmorillonite (Ca-Mt) pre-hydrated at relative humidity (RH) of 58 and 85%, we observed an increase in the water mean residence time, suggesting that hydrogen bonding lifetimes are prolonged under electric field. Assuming that at these RH most all water present resides within the interlayer space of the Ca-Mt, this result indicates strong polarization of the water by the interlayer cation. This electroosmotic induced reorganization has important implications in terms of...

Study on the dewatering process for water treatment residuals: Applicability of freezing–thawing, compression, and electro-osmotic treatment

ABSTRACTThe applicability of freezing–thawing, compression, and electro-osmotic unit on dewatering water treatment residuals (WTRs) was studied through freezing–thawing conditioning followed by a pressurized electro-osmotic dewatering (PEOD) process. Results showed that 86.12% of bound water was released after freezing–thawing treatment at the optimum freezing temperature of −10°C and duration of 22 h. At optimized mechanical pressure of 811 kPa and voltage of 30 V, the subsequent PEOD could lead to a water content of 58.70% in WTRs with estimated energy consumption of 0.107 kWh/kg (water removed), and free water was obviously removed by compression, while bound water content (BWC) remained stable. Moreover, freezing–thawing treatment remarkably reduced the PEOD duration from 200 to 20 min. Electro-osmotic treatment could accelerate dewatering rate and improve dewatering efficiency especially for raw WTRs. Therefore, direct compression on raw WTRs could be suited to warm regions, while natural freezing–thawing treatment combined with compression/electrical compression will be selected in cold regions.

Performance of electro-osmotic dewatering on different types of sewage sludge

The feasibility of pressure-driven electro-dewatering (EDW) on sludge samples taken after different biological processes, stabilisation methods or mechanical dewatering techniques was assessed. First, the influence of potential values on EDW of anaerobically and aerobically stabilised, mechanically dewatered, sludge samples was investigated. Preliminary tests carried out by applying a constant potential (10, 15 and 20V) in a lab-scale device confirmed the possibility to reach a dry solid (DS) content of up to 42.9%, which corresponds to an increase of 15% of the dry content in dewatered sludge without the application of the electrical field. Dewatering increased with the applied potential but at the expense of a higher energy consumption. A potential equal to 15V was chosen as the best compromise for EDW performance, in terms of DS content and energy consumption. Then, the influence of the mechanical dewatering was studied on aerobically stabilised sludge samples with a lower initial DS content: the higher initial water content led to a lower final DS content but with a considerable reduction of energy consumption. Finally, the biological process, studied by comparing sludge samples from conventional activated sludge and membrane bioreactor processes, didn’t evidence any influence on EDW. Experimental results shown that DS obtained after mechanical dewatering, volatile solids and conductivity are the main factors influencing EDW. Anaerobically digested sludge reached the highest DS content, thanks to lower organic fraction.

Soil vapor extraction of wet gasoline-contaminated soil made possible by electroosmotic dewatering\u2013lab simulations applied at a field site

PurposeSoil restoration is still mainly carried out ex situ by excavating and replacing the contaminated soil. In situ remediation would reduce the costs of soil transportation and this way, the problem is not merely transferred elsewhere. The present study introduces a field case where the aged, oil-contaminated soil in a former fuel station in Finland was treated in situ sequentially with different methods.Materials and methodsSeveral approaches, including soil vapor extraction and biostimulation with electrokinetic pumping, were performed in the field. After these treatments, the dense original portion of the soil beneath the gasoline pump location, ca 100 m3, was still contaminated with petroleum-derived volatile organic compounds (VOCs), with concentrations of nearly 10,000 mg kg−1 measured at some hotspots. After a period of electroosmotic water circulation, the electrical field (0.5 V cm−1, DC) was kept connected for 6 months without addition of water, leading to dewatering and warming of the soil.Results and discussionIn contrast to the situation with the original wet soil, VOCs, in lab conditions, were found to volatilize very efficiently from the dewatered soil. When the soil vapor extraction treatment was renewed using perforated tubing installed horizontally at ca 1 m depth in the dewatered soil at the contaminated site, the treatment was efficient and the soil was decontaminated in 5 months. The final VOC concentrations were on average 190 mg kg−1 (n = 13) with the highest value of 700 mg kg−1 at one hotspot. After a risk evaluation, the site was concluded to be sufficiently clean for industrial use.ConclusionsSince with many former fuel stations, the contamination consists of both volatile fractions that are difficult to degrade by biological means and heavier compounds for which biostimulation is often suitable, a combination of different methods may be worth pursuing.

Electro-osmotic dewatering of soaked hemp stems

ABSTRACTHemp stems were immersed in water as a pretreatment to enhance the production of hemp fiber. To reduce the high moisture content, the soaked hemp stems were dewatered using a bench-type electro-osmotic roller press. Variables like applied voltage (12, 24, and 36 V), roller pressure (1000, 2000, and 3000 kPa), and duration of soaking of hemp stems (12, 24, and 36 h) were subjected to investigation and the percentage of total water expelled due to electro-osmotic dewatering (EOD) at various levels of experiments was recorded. Hemp stems soaked for 24 h treated at a roller pressure of 2,000 kPa at an applied voltage of 36 V showed the maximum water removal after EOD process. The water removal was found to be increasing with increase in applied voltage and roller pressure. Soaking time up to 32 h leads to an increase in water removal and then it started decreasing. The probable reason for that was the penetration of surface water into micropores and its adhesion to the lignocellulosic bonds. Electro-osmotic permeability of hemp stems at various levels of voltages, roller pressures, and soaking times was studied and the result proved that electro-osmotic permeability was inversely proportional to applied voltage and it was independent of the applied pressure.

The characteristics of electric vertical drains in electro-osmotic dewatering

ABSTRACTThe product performance and drainage effect of electric vertical drains (EVDs) were evaluated by implementing field tests. A small number of electrodes were inserted into the field site and were electrified with different operation modes. The results of the field tests show that the largest range of the current for each pair of electrodes is 1.5–2 A in this dredger fill. A high-concentration salt solution injected into the soil can significantly improve the electro-osmotic drainage effect, for there are no corrosion problems with the electrodes. The electroconductive filter cloth of the EVD does not have much impact on drainage effect and can be replaced by nonwoven fabric cloth. Suggestion is given in this paper that the operation way of electro-osmosis is to provide low energy for the soil in the early stage and then constantly improve the energy when the drainage rate is significantly reduced.

ELECTRO-OSMOSIS DEWATERING OF COAL SLUDGE

In waste treatment process, decreasing of water load from the coal sludge is economical and feasible before disposal. Electroosmosis dewatering (EOD) is more energy saving and effective process over other conventional dewatering process. Draining of water from the sludge by generating potential gradient in between two electrodes which were placed in the sludge; is called electro-osmotic dewatering process. A direct current (DC) was used to create that potential difference. This experiment was done by dewatering fine coal sludge using two copper disks as electrodes. It is reported that the flow rate of dewater is proportional to the potential difference between two electrodes and the zeta potential of the sludge particle [2] . In this study, the voltage is increased from 40V to 100V with constant current (1.1 Amp) supply. The zeta potential of the coal particle is increased by adding 1%, 2% and 5% (w/v) sodium hydroxide (NaOH) solution, respectively. The volume of water removed, % moisture content of coal slurry after EOD, volume of water evaporated from the hot electrode surface, and energy consumption are measured for each case. It is observed that as the increasing NaOH concentration and the potential difference in the slurry, the % moisture content of slurry is reduced after EOD. The moisture content of the slurry is measured at 5% NaOH for 100V is around 19.7% which is approximately 6% lower than as compared to without using caustic solution under same operating condition. The energy used for the removal of above moisture content (19.7%) is around 5KWh/Kg of dewater, which is 54% less than the thermal processing of sludge.

Effect of flow path structure on solid/liquid separation under electric field

Electroosmosis is especially effective in removing liquid from a highly compressible difficult-to-filter solid/liquid mixture. The extent of solid/liquid separation depends on the electroosmotic pressure gradient (Epg) which is a combination of applied electric field, the surface charge density of solid particles and the flow path structure in the mixture. The larger the Epg value, the higher the solid content of the treated mixture. A theoretical equation of Epg for a capillary flow is derived from the Navier–Stokes equation, and its extensions to a flow through porous materials are examined by using experimental Epg values from constant-current electroosmotic dewatering (EOD), electroosmotic permeation (EOP) and electro-forced sedimentation (EFS) tests. It has been clarified that the specific hydrodynamic resistance α has the most effect on the Epg value. The larger the α value of the material, the larger its Epg value. Modifications to the existing theories were suggested to understand the effect of solid/liquid mixture concentration on the separation under electric field more precisely.

Electro-osmotic dewatering of high moisture flax stems

Retted flax stems contained high amounts of water from the pre-soaking and retting processes. Electro-osmotic dewatering was investigated as a pre-drying process for high-moisture flax stems using a bench electro-osmotic roller press. The various parameters affecting electroosmotic dewatering were cylinder pressure (1000 kPa–3000 kPa), applied voltage (12 V–36 V) and pre-soaking time of the flax stem (12 h–36 h). An experiment was designed using central composite design. From the experiments, a maximum of 38.34% of the total water contained in the stem was removed using 12 h soaking; 1000 kPa cylinder pressure and 36 V applied voltage during the electro-osmotic treatment. For a given soaking time, at 36 V with 3000 kPa cylinder pressure the maximum water removal occurred. The electro-osmotic permeability of the stems at various conditions was studied. In all the treatments, electro-osmotic permeability ranged between 3.32 × 10−5 m2 V−1 s−1 and 1.22 × 10−4 m2 V−1 s−1. Electro-osmotic permeability was found to increase with increasing water removal and decreased with increasing applied voltage.

Experimental Study of the Electro-osmotic Dewatering in Hangbag

In recent years, geotube began to be widely used in treatment of coastal reclamation projects. However, the dewatering of sludge in geotube is inefficient. In this paper, for improving dewatering efficiency and laying a basis for the further study of large-scale electro-osmotic dewatering in geotube, electroosmosis has been applied to silt dewatering experiments in small hangbag. By measuring the change of moisture content, electricity current, voltage and comparing with other experiments under different conditions, the following conclusions have been obtained: the electro-osmotic dewatering speed is much faster than the natural dewatering. The non-woven fabric bag is easier to dewater than the high strength fabric bag which is made by the company of Royal Tencate.

Vacuum Preloading Combined with Electro-Osmotic Dewatering of Dredger Fill Using Electric Vertical Drains

Based on the vacuum preloading combined electro-osmotic consolidation method, a site comparison trial of vacuum preloading and vacuum preloading in combination with electro-osmotic consolidation was performed on Li Island, Hubei Province. The performance and drainage effects of electric vertical drains were evaluated. The problems were analyzed by monitoring test results. Test results from the field showed that the water content of the dredger fill was greatly reduced and the physico-mechanical properties and bearing capacity were improved significantly after 28 days of treatment by vacuum preloading in combination with electro-osmotic consolidation. Compared with the vacuum preloading method, vacuum preloading in combination with the electro-osmotic consolidation method using electric vertical drains reduced the construction time, saved energy, and achieved an ideal reinforcement effect.

Dynamic changes in the characteristics and components of activated sludge and filtrate during the pressurized electro-osmotic dewatering process

The performance and process of pressurized electro-osmotic dewatering (PEOD) technology for activated sludge (AS) were investigated. In PEOD process, a single pressure of 600kPa only removed a small amount of free water and bound water in AS, whereas both kinds of water further decreased to 0.24gg−1dry solid and 0.25gg−1dry solid after the application of 50V voltage at electrical compression (EC) stage. During the PEOD process, the loosely network structure was gradually ruined, and a quantity of narrow and parallel slits generated in dewatered AS at EC stage. The contents of organic matters in filtrate increased at all PEOD stages and humic acid-like organics formed at EC stage. Using the response surface method (RSM), the optimum dewatering conditions were determined as a combination of 401kPa pressure and 50V voltage, which gave a dry solids content and energy consumption of 41.90% (wt%) and 0.153kWh per kg removed water.

Regrowth of bacterial pathogen indicators after advanced electro-osmotic dewatering of biosolids

Applying an electrical field for 10 min to mechanically dewatered biosolids increased dryness to 35 to 45% and reduced Escherichia coli levels to/close to detection limits. Possible reasons for the regrowth of bacterial pathogens impacted by electro-osmotic dewatering are biosolids dryness, low pH and the generation of bacterial oxidants on the anode due to high temperatures. Testing for this with aerobic and anaerobic incubations resulted in more than four logs of E. coli regrowth in 2011, when biosolids harboured higher initial counts; whereas regrowth was not observed in 2012, when biosolids had lower E. coli counts. In 2011 experiments, however, addition of a nitrate salt prior to anaerobic incubations reduced regrowth by 1.4 logs. This indicates that other NO3−-respiring organisms could be competing with E. coli and diverting electrons away from the E. coli population. These results suggest that electro-osmotic dewatering and nitrate can play a role in controlling E. coli regrowth.

Application of Electro-Technologies in Processing of Flax Fiber

Flax fibers used for various applications are obtained from flax stems. Retting followed by drying and mechanical separation leads to the production of fibers. This review article discusses the application of electro-technologies in the production of bast fibers from the flax stem. In these technologies, flax stems harvested from the field are subjected to microwave assisted retting, followed by electro–osmotic dewatering which reduces the water content of the stems. Dewatered stems are transferred to a microwave chamber for further drying, thus retted stems are obtained for further processing.