Dewatering Mechanism Research Articles

Depth dewatering of kaolinite cake by SDBS/PEI synergy and a mesoscopic mechanism study

The objective of this study was to elucidate the synergistic dewatering mechanism of mixed sodium dodecylbenzene sulfonate (SDBS) and polyethyleneimine (PEI) on kaolinite filter cakes and to test the dewatering effectiveness of a custom-built pressure dewatering device. The dewatering experiments showed that while the reagent dose was reduced by 50%, the dewatering rate decreased to 19.78%, surpassing the optimal dose of a single reagent. During the natural compression stage of the filter cake, the deformation reached its maximum under the same pressure difference. During the transitional period, the closure of the filter cake pores occurred at a slower rate, facilitating better moisture drainage. Under strong compression, the ultimate deformation reached its maximum. PEI acted as a bridging agent for kaolin flocculation and served as a medium for SDBS on the kaolin surface. A small amount of PEI reduced the electrostatic repulsion of SDBS, increasing its adsorption capacity. PEI adsorbed on the kaolin surface through electrostatic and hydrogen bonding, while SDBS could adsorb onto the PEI reagent layer through electrostatic and polar interactions, exposing its alkyl chains on the surface and thereby facilitating flocculation and generating a hydrophobic reagent layer. This study could provide a new method and insights for the efficient pressurized dewatering of kaolin.

Effective dewatering and resourceful utilization of high-viscosity waste slurry through magnetic flocculation

When a slurry shield tunnel traverses through extensive deposits of silty clay stratum, a considerable amount of high-viscosity waste slurry with elevated particle content is inevitably generated. Failure to promptly address this waste slurry could have a severe impact on project progress and the surrounding environment. To address the challenge of rapid dewatering for high-moisture and high clay-content waste slurry, this paper introduces an efficient waste slurry dewatering technique: magnetic flocculation dewatering technology. Additionally, the paper explores avenues for the resource utilization of waste slurry containing magnetic particles Through conducting flocculation settling experiments, a comparative analysis was carried out on the dewatering effects of traditional flocculation and magnetic flocculation technologies. The paper discusses the dewatering mechanism of magnetic flocculation and determines the optimal process conditions for treating waste slurry utilizing magnetic flocculation. The results indicate: (1) The flocculation and dewatering process of waste slurry can be divided into two stages: a rapid flocculation settling stage and a slow consolidation stage, with the rapid flocculation settling stage playing a dominant role. (2) Under magnetic flocculation, the time required for the rapid flocculation settling stage is only 1/3 of that in traditional flocculation, and the slurry dewatering rate is 1.4 times higher than traditional flocculation. (3) The optimal sequence for adding material under magnetic flocculation is to add magnetic powder first and then the flocculant. The optimum dosage of magnetic powder is 1.0 g/L, and the most suitable magnetic field intensity is 92.0 mT. (4) The magnetically flocculated sludge obtained after magnetic flocculation treatment can be utilized for the production of construction bricks that comply with standard specifications. The research findings of this paper provide a basis and guidance for the efficient reduction and resource utilization of waste slurry.

In-situ generation of iron activated percarbonate for sustainable sludge dewatering

Effective dewatering of sewage sludge could potentially address the issues of high energy consumption and large carbon footprint inherent in the sludge treatment process, advancing toward carbon neutrality in environmental remediation. Yet, the surface hydrophilic characteristics and water-holding interfacial affinity in sludge led to dwindled sludge-water separation performance. Here, the integration of in-situ generation of iron from zero-valent scrap iron (ZVSI) and sodium percarbonate (SPC) was attempted to attenuate the water-retaining interfacial affinity within sludge, thus achieving superior sludge dewatering performance. Results showed that under the optimal conditions, the ZVSI + SPC system led to a remarkable decline of 76.09 % in the specific resistance to filtration of the sludge, accompanied by a notable decline of 34.96 % in the water content. Moreover, the utilization of ZVSI + SPC system could be a viable alternative to the traditional strategies in terms of enhanced sludge dewaterability, offering application potential with stable operating performance, economic feasibility, and reduced carbon emissions. Investigation into dewatering mechanism revealed that ZVSI could maintain the Fe3+/Fe2+ in a stable dynamic cycle and continuously in-situ generate Fe2+, thereby efficaciously fostering the SPC activation for the ceaseless yield of reactive oxygen species. The predominant •OH and 1O2 efficiently decomposed the hydrophilic biopolymers, therefore minimizing the hydrophilic protein secondary structures, along with the hydrogen and disulfide bonds within proteins. Subsequently, the water-holding interfacial affinity was profoundly diminished, leading to intensified hydrophobicity, self-flocculation, and dewaterability. These findings have important implications for the advancement of efficacious ZVSI + SPC conditioning techniques toward sustainable energy and low-carbon prospects.

Modelling sludge dewatering in treatment reed bed considering sludge deposit formation

AbstractThe accumulation of sludge deposits is a crucial factor in the dewatering efficiency of sludge treatment reed bed (STRB). This paper presents an improved one-dimensional process-based mathematical model to simulate the dewatering mechanism in STRBs, in which the compressible cake filtration (CCF) theory was implemented to simulate the sludge deposits accumulation on the surface of the reed bed, while the varying sludge deposit thickness was accounted for using the moving mesh method. The proposed model also included the dual porosity variably saturated flow model and the Penman–Monteith equation to describe the dewatering through gravity drainage and evapotranspiration, respectively. The results from the model were validated with experimental data from laboratory-scale STRBs treating septage. The simulation results showed that considering the sludge deposit layer as a specific flow resistance effectively avoids the overprediction of water infiltration rate in the reed bed. The predicted results showed excellent agreement with the actual data, where only five cases of the root mean square error were above 10% compared to the average effluent flux. Further, the effect of evapotranspiration was found to be insignificant within a short-term simulation. The consideration of the influence of sludge deposit formation on drainage dewatering using the CCF model and moving mesh model has delivered a more robust simulation for sludge dewatering in STRBs, and the proposed model is capable of facilitating the understanding of the interactions between the sludge dewatering in STRB with respect to the bed characteristics, hydraulic load, and solid load.

Achievement of waste sludge deep dehydration under acidic conditions with polydimethyldiallylammonium chloride and ferric chloride: performance and mechanism.

The biological treatment of wastewater generates a substantial amount of waste sludge that requires dewatering before final disposal. Efficient sludge dewatering is essential to minimize storage and transportation costs. In this study, the sludge conditioners polydimethyldiallylammonium chloride (PDMDAAC) and ferric chloride (FeCl3) were sequentially dosed, and the pH was adjusted to 3. As a result, the sludge moisture content (MC) was reduced to 59.4%, achieving deep dewatering. After conditioning, the tightly bound extracellular polymeric substances (TB-EPS) were reduced from 34.5 to 10.2 mg g-1 VSS, with the majority of the reduced fractions being composed of protein (PN). In contrast, soluble EPS increased more than 8 times. Subsequent studies revealed that the decrease in PN from TB-EPS primarily involved tryptophan and tyrosine proteins, accompanied by a significant reduction in the N-H and C[double bond, length as m-dash]C absorption peaks. These results highlight the critical role of TB-EPS dissolution in achieving deep dehydration, with the N-H in PN was identified as the key group influencing sludge dewatering. Combined with the changes in sludge particle size and morphology, the dewatering mechanism can be summarized as follows: PDMDAAC dissolves TB-EPS, simultaneously disrupting the floc structure and refining the sludge. Subsequently, FeCl3 reconstructs these elements, forming larger particle sizes. Finally, hydrochloric acid reduces TB-EPS once again, releasing bound water. This study offers alternative methods and new insights for achieving deep dewatering of waste sludge.

Beyond filterability: Understanding the complexities of sludge dewatering through typical coagulation and advanced oxidation

Coagulation and advanced oxidation process (AOP) are the two most significant conditioning methods in sludge dewatering. However, previous studies mainly focus on their differences and overlook their similarities in dewatering mechanisms. In this study, PAC and Fe3+ were selected as typical coagulants, and Fenton and Fenton-like reactions as typical AOP. By regulating the reagent dosage to achieve basically the CST-based filterability (CST = 22.9 ± 1.5 s), AOP had superior dewatering efficiency (59.54–63.04 wt%) compared to coagulation (68.84–69.16 wt%). Obviously, the filterability of sludge could not accurately reflect its dewatering performance. The mechanism revealed that AOP had both “extracellular oxidation” and “intracellular oxidation”, whereas coagulation mainly affected the properties of extracellular organic matter. Both processes improved the sludge's relative hydrophobicity and reduced its interfacial free energy. AOP was superior to coagulation in improving sludge fluidity, hydrophobicity, permeability, cell disintegration and reducing bound water content. While coagulation had a better effect on electric neutralization, floc particle size growth and colloidal structure strength. Moreover, this study emphasized the significance of considering the vector-based relationship between sludge dewatering performance and various influencing factors for analyzing the dewatering mechanism. These findings are expected to deepen our understanding of the similarities and disparities in dewatering efficacy and the related mechanisms between the these two pretreatments.

A three-stage process of Mn(VII)-Fe(III)/PDS system for enhancing sludge dewaterability: Effective driving of Fe(II)/Fe(III) cycle and adequate assurance of ROS

Sludge dewatering helps to reduce the cost of sewage treatment plants and environmental impact. Hence, we used a type of permanganate (Mn(IV)) activated ferric chloride (Fe(III))/ peroxydisulfate (PDS) system to enhance sludge dewaterability. At optimal dose, the simultaneous addition of Mn(IV), Fe(III) and PDS (MFP treatment) reduced the value of specific resistance to filtration (SRF) from 6.76 × 108 s2/g to 2.01 × 108 s2/g. There is a three-stage process during MFP conditioning: oxidation/flocculation, adsorption/oxidation, and reflocculation. X-ray photoelectron spectroscopy (XPS) and Electron spin resonance (ESR) analyses were employed to investigate the oxidation mechanism. Meanwhile, the analysis of Mn valence was improved by considering metal leaching rates. The cycles of Mn(II)/Mn(III)/Mn(IV) were initiated under the reaction between Mn(VII) and extracellular polymeric substances (EPS)/PDS. This process sustained the cycle of Fe(II)/Fe(III) to promote activation of PDS, which continuously promoted to generate OH•, SO4-•, •O2–, 1O2 and Fe(IV). Additionally, sludge EPS was proven to be the primary electron donor of Fe(II)/Fe(III) cycle, resulting in the increasing of Fe(II) proportion. Notably, the hydrophilicity and water-holding capacity of EPS declined significantly following excellent oxidation, which promoted the conversion of bound water. The effective destruction of hydrogen bonds and protein secondary structures explained the outstanding effects. Meanwhile, XDLVO calculation revealed that sludge coagulation performance enhanced through Fe(III) flocculation, MnO2 adsorption and hydrophobic flocculation. Raw and converted free water would be effectively removed through the more hydrophobic surface of large and tough drain pores formed after the reflocculation process. The efficient drainage of sludge water created strong sludge dewaterability. This study verified the practicality of MFP treatment by exploring the oxidation and coagulation mechanisms to clarify the dewatering mechanism.

Sustainable use of rice husk powder and bamboo powder as sludge deep dewatering conditioners in pilot-scale application: Feasibility for incineration and potential application for land use

Conventional conditioners are not conducive to the sludge separate incineration process. The agricultural wastes bamboo powder (BP) and rice husk powder (RHP) have strong toughness and porosity, which has the potential to replace quicklime as a sludge conditioner. When the dosage of BP and RHP is 30 % of the sludge dry solids, the dewatering performance of sludge was greatly improved after sludge was conditioned with BP and RHP respectively, where the specific resistance of sludge was reduced from 4.6 × 1012 m/kg to 1.3 × 1012 and 0.9 × 1012 m/kg. In addition, the sludge conditioned by BP and RHP acquired better filtrate quality, which is conducive to the stable operation of the wastewater treatment plants (WWTPs). The components of extracellular polymer substances (EPS) showed that the tightly bound-EPS (TB-EPS) decreased by 36.6 % after conditioning with quicklime, while the TB-EPS maintained with BP and RHP conditioning, indicating that the dewatering mechanism of BP and RHP involves physical activities to work as the skeleton builder. The use of BP and RHP increased the enrichment effect of nitrogen and phosphorus in the sludge cake, yet the contents of heavy metals Cd, Pb and Zn were below the sludge land use limit. Combined with the ecological risk assessment by the methods of the Geoaccumulation index (Igeo), the Nemerow pollution index (PI) and the potential ecological risk index (RI), the ecological risk index of quicklime-conditioned sludge is higher when the dewatered sludge is composted and applied for land use, while the ecological risk after conditioning by BP and RHP is in a slightly polluted or non-polluted state, therefore the application of BP and RHP as the deep dewatering conditioners possesses practical potential for land use.

Combined vacuum-assisted geotextile and geomembrane tubes for sludge dewatering: a theoretical switching point

Treating the high water-content sludge with vacuum-assisted prefabricated horizontal drains (PHDs) placed inside, geotextile tubes have the advantage of multiple drainage paths, and geomembrane tubes have the superiority of high vacuum maintenance. Therefore, converting the geotextile tube into a geomembrane tube during slurry dewatering is an effective measure for greater dewatering efficiency and better dehydration effect. In this study, a profound plane-strain consolidation model considering two-dimensional seepage is developed for explaining the dewatering mechanism of sludge in the geo-tubes. Analytical solutions are given and validated by the experiment. The impact of major variables on tube efficiency is further discussed to reference the practice design. Parametric analyses reveal the critical time corresponding to the optimal efficiency of the geotextile tube, after which its consolidation efficiency decreases significantly. However, the consolidation efficiency of a geomembrane tube increases throughout the duration. Consequently, a switching point corresponding to the iso-efficiency state of the geotextile tube and geomembrane tube can be determined for the tube conversion.

Understanding mechanism of improved-dewatering of waste activated sludge by multi-stage pressurized vertical electro-osmotic

A multi-stage pressurized vertical electro-osmotic dewatering (MS-PVEOD) were designed to break through the dewaterability limit of pressurized vertical electro-osmotic dewatering (PVEOD) process and reduce energy consumption (EC). The effects of mechanical pressure and voltage on sludge moisture content (MC) are studied. The sludge MC can be reduced to 44.6 % and 54.7 % respectively after MS-PVEOD (0–2–3.5 MPa) and PVEOD (2–2–2 MPa) process dewatering under 40 V, and the total EC of the former is 33 % lower than that of the latter. The sludge morphology, electric current, protein (PN) and polysaccharide (PS) content and fluorescence spectrum of extracellular polymeric substances (EPS) were analyzed. The PN/PS of the sludge treated by the MS-PVEOD process is 16.3 % higher than that of the PVEOD process, and 20.0 % higher than that of the raw sludge (RS). The three-dimensional fluorescence spectrum (3D-EEM) showed that the fluorescence of hydrophilic fulvic acid and humus decreased more than that of hydrophobic tryptophan protein and tyrosine protein. The present work may be helpful to understand the dewatering mechanism of MS-PVEOD and provides some useful technical guidance for the industrial application of efficient deep dewatering of sludge.

Influence of alternating electric field on deep dewatering of municipal sludge and changes of extracellular polymeric substance during dewatering

A self-prepared experimental device made of plexiglass with alternating power supply system was used to study the deep dewatering of municipal dewatered sludge. Considering the reduction rate of sludge water content (Wr) as the index, factors affecting enhanced electric settlement of sludge such as exchange electrode method, voltage gradient, sludge thickness, and mechanical pressure were studied, and the dewatering mechanism was elucidated. The single-factor experiment combined with the surface response method based on the Box–Behnken central experimental design was performed. With Wr as the response value, the voltage gradient conditions, time ratio, and sludge thickness were optimized. Pearson correlation analysis showed that the reduction of proteins/polysaccharides was beneficial to improving the sludge dewatering effect. Tightly bound extracellular polymeric substances (TB-EPSs) showed a significant influence on the sludge dewatering effect. Under the action of the external electric field, particles with negative charge moved toward the anode sludge, water with partial positive charge flowed to the cathode, and the sludge cellular structure was damaged. This resulted in the dissolution of a large number of EPSs and the release of bound water. The anode sludge cake got thickened due to the accumulation of the sludge particles, leading to the increase in resistance. The TB-EPS was deconstructed by the ohmic heating to improve the sludge dewatering effect and achieve deep dewatering. Scanning electron microscopy results showed that the drying problem of anode sludge was alleviated during the dewatering process.

Insights into cetyl trimethyl ammonium bromide improving dewaterability of anaerobically fermented sludge

Cetyl trimethyl ammonium bromide (CTAB) is considered a promising sludge dewatering conditioner, but its potential dewatering mechanism has not been thoroughly understood. This study, therefore, aims to fully investigate how CTAB improves sludge dewaterability. Experimental results showed that after sludge was conditioned by 75 mg/g TSS CTAB, capillary suction time (CST), specific resistance to filtration (SRF), and the water content of sludge cake (WCSC) by vacuum filtration decreased from 164.1 ± 10.7 s, 1.90 ± 0.05 × 1012 m/kg, and 97.36 ± 0.12 % to 32.1 ± 1.4 s, 0.18 ± 0.01 × 1012 m/kg, and 70.55 ± 0.21 %, respectively. Mechanism revelations showed that CTAB could neutralize the negative charges on EPS surface and reduce the repulsive force between sludge particles to reduce the Zeta potential; CTAB could also enhance the hydrophobicity and the adhesion among the sludge particles to reduce the surface energy, and CTAB could release the intracellular water by damaging the outer membrane of sludge cells. The presence of CTAB also decreased the concentrations of PO43-, humic acid, and proteins in the liquid phase through electrostatic attractive or hydrophobic interactions. All these CTAB-caused variations in either the solid or liquid phase of sludge could result in the enhancement of sludge dewaterability. The findings deepen our understanding of CTAB affecting sludge dewatering and also might guide engineers to exploit promising strategies to facilitate sludge dewatering in the future.

Verification of the mechanism and effect of secondary advanced dewatering promoted by selective oxidative decomposition: On pilot scale

In the sewage treatment industry of China, there is a huge market demand for direct secondary advanced dewatering technology to reduce the water content of municipal dewatered sludge from approximately 80% to below 60%. In this study, three typical oxidants (Fenton’s reagent, H2O2 and KMnO4) were applied to pre-treat dewatered sludge, which was then dewatered further using a PFFP we manufactured on pilot-scale. Only high-dose H2O2 and Fenton’s reagent gave flow values of 4.5 cm and ratios of free water/ (dry matter + bound water) of greater than 1.1, which allowed for successful transfer of dewatered sludge into the chambers by a diaphragm pump. The dewatering mechanism involved injection and squeezing of the dewatered sludge which was not exactly similar to that of concentrated sludge. The overall advanced dewatering performance was improved after conversion of bound water to free water. The final moisture content was less than 50% under the optimal conditions when the Fenton’s reagent dose was 2257 mol/t·db. The reaction of less oxidizing other biomass and intensively selective oxidizing polysaccharide was also verified in our experiment.

A comprehensive study on simultaneous enhancement of sludge dewaterability and elimination of polycyclic aromatic hydrocarbons by Fe2+ catalyzing O3 process

Simultaneous removal of polycyclic aromatic hydrocarbons (PAHs) in the process of enhancement of sludge dewaterability via oxidation of hydroxyl radicals (•OH) and flocculation of Fe3+ by Fe2+-catalyzing O3 were investigated as a novel research focus. The results showed that capillary suction time (CST) and water content of dewatered sludge cake (Wc) were reduced from 57.9 s and 85.1% to 13.6 s and 69.65% under the optimum usage of 60 mg/g dry solids (DS) O3 and 80 mg/g DS FeSO4, respectively. The relevant dewatering mechanism of Fe2+-catalyzing O3 treatment was elucidated. It was found that extracellular polymeric substances-bound (EPS-bound) and intracellular water was dramatically released through destroying sludge cells and EPS gel-like structure by produced •OH. In addition, the results of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and 13C NMR spectroscopy revealed that •OH oxidized and mineralized hydrophilic organic matters intensifying hydrophobicity of sludge surface. Moreover, Fe3+ generated by oxidation of Fe2+ agglomerated fragmented fine particles into large aggregates and decreased exposure of hydrophilic sites by neutralizing negative charge, which promoted water-solids separation. Meanwhile, sludge surface roughness was decreased which was determined by material type upright confocal laser microscope (CLM). As a consequence, •OH and Fe3+ were mainly responsible for enhancement of sludge dewaterability. Moreover, more than 40% of removal rate of PAHs was accomplished by Fe2+-catalyzed O3 treatment mitigating the environmental risks of PAHs spread.

Electroassisted Filtration of Microfibrillated Cellulose: Insights Gained from Experimental and Simulation Studies

An electroassisted filtration technique has been employed to improve dewatering of a suspension of microfibrillated cellulose (MFC) produced via 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxidation. In addition, all-atom molecular dynamic (MD) simulations were performed to deepen the understanding of the complicated dewatering mechanism on a molecular level. Both the experimental and the simulation results implied that the dewatering rate was not only improved when electroassisted filtration was used but also found to be proportional to the strength of the electric field. A channeled dewatered structure was observed for these experiments and may have contributed to enhanced dewatering by providing high overall permeability. The MD simulations revealed that the electric field had a significant impact on the fibril movement, whereas the impact of pressure was limited. The simulations also suggested that the increased filtrate flow upon the application of an electric field was not only due to electroosmotic flow but also due to electrophoretic movement of the fibrils toward the anode that led to the release of water that had been trapped between the fibrils, allowing it to be pressed out together with the rest of the bulk water. This study shows that electroassisted filtration has the potential to improve the dewatering of TEMPO-MFC, and the MD simulations provide further insights into the dewatering mechanism.

Mechanism insights into hydrothermal dewatering of food waste digestate for products valorization

Poor dewaterability is a bottleneck of the disposal of digestate from food waste (DFW). However, the dewatering mechanism remains unclear due to the complex composition of DFW. Understanding the dewatering mechanism, as well as the transformation of organic/inorganic matters is essential for the DFW management and valorization. In this study, the distribution, transformation, and complex interplay of organic and inorganic matters at different Hydrothermal treatment (HTT) temperatures were comprehensively analyzed to explore the hydrothermal dewatering mechanism of DFW. When HTT was conducted in the temperature range of 120–180 °C, the interstitial water was released as surface or free water because of membrane breaking and size reduction of the solid substrate. Releasing divalent cations increased the Zeta potential of the bulk solution. The weaker electrostatic repulsion between suspended particles made them easier to settle as the centrifugation cake. When the temperature of HTT was above 180 °C, polymerization and aromatization reactions took place gradually for organic matters, and the bound water was further removed. The generated humic substances were more hydrophobic than the raw material. In addition, the humic substance could combine with cationic metals, which decreased the zeta potential of the bulk solution but promoted the aggregation of nanoparticles and enhance the dewaterability of DFW.

Research and application of polyethylene glycol solution dialysis combined with vacuum pressure in sludge dewatering

A sludge dewatering method based on polyethylene glycol (PEG) solution dialysis effectively reduced the moisture content in sludge to under 60%, which realized the aim of deep dehydration. However, it remains difficult to apply to marketization and industrialization due to the limited influence range of dialysis. Therefore, this study develops a new sludge dewatering technology using the PEG solution dialysis method combined with vacuum pressure. By applying vacuum pressure to the dialysis process, the sludge structure is compacted, which reduces the internal voids between the sludge particles and promotes water that had not been removed to find suitable drainage channels to continue to discharge. The results showed that the dehydration effect of this method was observably improved as compared to single dialysis, and the influence range of dialysis significantly increased. Compared with 0 kPa, the influence range of dialysis at 100 kPa increased by 183%. X-ray computed tomography (X-ray CT) was used to establish the 3D reconstruction images of the sludge and analyze the change law of the sludge microstructure under different vacuum pressures. The relationships between the final moisture content and pore characteristics were obtained, which proved the effectiveness of the dehydration method using PEG solution dialysis combined with vacuum pressure. This study investigates the positive influence of vacuum pressure on dialysis dehydration, and further reveals the dewatering mechanism of this method during the sludge dialysis process. This study provides new insights for sludge volume reduction and propels the market-oriented and industrial application of sludge dialysis dewatering.

Dewaterability improvement and environmental risk mitigation of waste activated sludge using peroxymonosulfate activated by zero-valent metals: Fe0 vs. Al0

The stabilization and dewaterability of waste activated sludge (WAS) are essential factors for downstream disposal or reuse. Herein, two types of zero-valent metals, zero-valent iron (Fe0) and zero-valent aluminum (Al0), were compared for their ability to activate peroxymonosulfate (PMS) during the WAS conditioning process, with the effects of PMS activation by these two metals on WAS dewaterability and the potential environmental risks evaluated. Results showed that compared to Al0/PMS treatment, Fe0/PMS treatment achieved superior WAS dewaterability and reduced operational costs. Using PMS combined with Fe0 and Al0 treatments under optimal conditions, the water content (Wc) of dewatered sludge decreased to 55.7 ± 2.7 wt% and 59.4 ± 1.3 wt%, respectively. Meanwhile, application of the Fe0/PMS treatment system reduced the total annual cost by approximately 33.1%, compared to the Al0/PMS treatment. Analysis of the dewatering mechanism demonstrated that in the Fe0/PMS treatment, Fe3+/Fe2+ flocculation played an important role in the enhancement of WAS dewatering, while sulfate radical (SO4•−) oxidation was the dominant factor for WAS dewaterability improvement in Al0/PMS treatment. The greater enhancement of WAS dewaterability by Fe0/PMS treatment, was mainly attributed to more efficient reduction of hydrophilic extracellular polymeric substances (EPS) and an increase in surface charge neutralization. Environmental risk evaluation results indicated that Fe0/PMS and Al0/PMS treatments both effectively alleviated the environmental risks of heavy metals and faecal coliforms in dewatered sludge. Overall, this study proposes a novel perspective for the selection of an optimal PMS activator in sludge treatment.

Pore Structure Characterization of Tailing Bed and Dewatering Mechanism at nm-µm Scales Under Shearing.

The preparation of high-density tailings is a prerequisite for cemented paste backfill technology, and the flocculated fine tailings of sealed water leads to challenges in the slurry thickening of tailings. Shearing conditions can compact the micro floc structure to improve the underflow concentration. The nm-μm scales of pore characteristics and connectivity are essential for the dewatering process. The computed tomography (CT) results show that the underflow concentration increases from 62.3 wt% to 68.6 wt% after undergoing rake shearing at 2 rpm, and the porosity decreases from 42.7% to 35.54%. The shearing conditions reduces the spheres and sticks by 43.14% and 43.3%, respectively, from the pore network model (PNM). The seepage flow states were affected by the changes in the pore structure. The maximum surface velocity and the maximum internal pressure decrease after undergoing shearing. Shearing conditions can break the micro floc structures, and the fine particles can fill in the micron-scale pores by gravity and shearing conditions, resulting in the forced drainage of water into the pores. Shearing conditions can break the thickening floc network structures; natural fine particles can fill the micron-scale pores by gravity and shearing conditions. The upward seepage of sealed water along the μm-scale pore channel causes a higher bed concentration. However, the sealed water in the nm-scale pores cannot flow upward due to water cohesion and particle adhesion resistance.

Comprehensive assessment of flocculation conditioning of dredged sediment using organic polymers: Dredged sediment dewaterability and release of pollutants

Dredged sediment contains various contaminants that are released during the process of dewatering and subsequent utilization. In this study, two organic polymers—chitosan (CS) and cationic polyacrylamide (CPAM) both in samples of varying molecular weights (MWs)—were used as flocculants to improve dewatering and rheological behaviors of dredged sediment, and floc properties were characterized to unravel the mechanisms of flocculation treatment. Moreover, pollutant transfer and release in the flocculation-dewatering process was investigated. Compared to CPAM, CS had better performance in dredged sediment dewatering, and more compact flocs were produced after treatment. The flocculated sediment belonged to the type of yield dilatant fluid and showed good shear resistance. Three-dimensional excitation–emission matrix spectroscopy and PARAFAC showed that protein-like substances were removed after treatment. The MW of CS had insignificant effects on flocculation performance, whereas CPAM removal efficiency for protein-like substances was increased at higher MWs, which may be related to the adsorption bridging effect of CPAM polymer chains. There were significant correlations between the dewatering performance of sediments, MW distribution of organics and rheological properties. CS and CPAM treatments caused the transformation of Fe/Al-P into CaP, which could reduce phosphorus release and its ecological risk. The flocculants contributed to the formation of carbonate-bound forms of As, Cr, Pb, and Ni. Ecological risk assessment results of the geo-accumulation index showed that medium- and low-MW CS reduced risk of sediment contamination, whereas CPAM and high-MW CS increased the ecological risk. CS had a greater effect on the release of VOCs than CPAM, with an increased release of total VOCs at higher flocculant MWs. The study was helpful to understand the dewatering mechanism of dredged sediment and provided a new strategy for pollution release management in sediment dewatering.