Insight into conditioning landfill sludge with ferric chloride and a Fenton reagent: Effects on the consolidation properties and advanced dewatering

Low-cost optimization of industrial textile landfill sludge re-dewatering using ferrous sulfate and blast furnace slag

This study was based on an industrial sludge landfill with a scale of 1 million cubic meters, which had been filled for more than 10 years. It focused on the secondary dewatering of industrial textile landfill sludge (LS) with a total organic carbon (TOC) content greater than 50% and a volatile suspended solids to suspended solids (VSS/SS) ratio of 0.59. A response surface methodology (RSM) model was established using the coagulant ferrous sulfate (FeSO4) and conditioning agents such as hydrated magnesium oxide (MgO), blast furnace slag (BFS), and calcium oxide (CaO). By solving the RSM equations for the respective indicators, the optimal dosages of FeSO4, MgO, and BFS were determined to be 90 mg/g of dry sludge (DS), and for CaO 174.85 mg/g DS. Further examinations of the dewatering performance, apparent properties, extracellular polymeric substances (EPS) components, rheological characteristics, moisture distribution, and pollutant content variation led to the development of a green waste-based dewatering agent composed of FeSO4 and BFS. In small-scale diaphragm plate and frame filter press tests, the optimal water content (WC) was 69.11%. In the final production-scale experiments, it was 65.72%, with the actual application cost being only 13.07 $/ton DS. Additionally, when FeSO4 and BFS were used together, the combined action of Fe and Si could significantly reduce the biotoxicity of heavy metals (HMs), cut down 75.2% of the LS's TOC, and effectively reduced the leaching of organic substances from the leachate, which was beneficial for subsequent disposal. In conclusion, the combined use of FeSO4 and BFS for the secondary dewatering of industrial textile LS was economically efficient, effective in dewatering, and had significant harm reduction effects, making it a worthwhile for waste treatment.

Physical conditioning methods for sludge deep dewatering: A critical review

Sludge is an inevitable waste product of sewage treatment with a high water content and large volume, it poses a significant threat of secondary pollution to both water and the atmosphere without proper disposal. In this regard, dewatering has emerged as an attractive method in sludge treatment, as it can reduce the sludge volume, enhance its transportability and calorific value, and even decrease the production of landfill leachate. In recent years, physical conditioning methods including non-chemical conditioners or energy input alone, have been extensively researched for their potential to enhance sludge dewatering efficiency, such as thermal treatment, freeze-thaw, microwave, ultrasonic, skeleton builders addition, and electro-dewatering, as well as combined methods. The main objective of this paper is to comprehensively evaluate the dewatering capacity of various physical conditioning methods, and identify key factors affecting sludge dewatering efficiency. In addition, future research anticipated directions and outlooks are proposed. This work is expected to provide valuable insights for developing efficient, eco-friendly, and low-energy consumption techniques for deep sludge dewatering.

Flocculating and dewatering of lake sediment: An in-situ pilot study comparing synthetic polymers and biopolymers for restoring lake water quality and reusing phosphorus

Dredging of lake sediment is a method to remove accumulated phosphorus and nitrogen in lakes and thereby reducing the risk of eutrophication. After dredging, the sediment is dewatered to reduce the volume. It is important to get a high dry matter content and ensure that the filtrate does not contain harmful compounds so it can be returned to the lake. A pilot-scale belt filter and flexible intermediate bulk containers (FIBC) were used for dewatering lake sediment with the sediment treated with a synthetic polymer or three different biopolymers. The goal of the study was to retain the phosphorus in the filter cake while returning the filtrate to the lake with a minimal phosphorus content. Results showed dry matter content of up to 16 % in the dewatered sediment and the sediment retained 96-99 % of the phosphorus. Furthermore, nitrogen was reduced by 27-71 % in the filtrate water. Toxicity tests found low ecotoxicity for most biopolymer filtrates, whereas synthetic polymer showed the highest potential ecotoxicity. Consequently, biopolymers provided satisfactory results, proving more environmentally friendly despite requiring longer filtration time.

Effect of initial water content on the dewatering performance of freeze-thaw preconditioned landfill sludge

Freeze-thawing (F/T) is an effective method of sludge dewatering preconditioning and has been studied in many studies. However, previous studies have taken landfill sludge from different regions, filled for different length of time or at different depth, resulting in large differences in initial water content and different treatment effects. Therefore, the effect of initial water content on the dewatering characteristics of F/T preconditioned landfill sludge has been investigated. The sludge with different initial water contents was firstly preconditioned by one F/T cycle. Then the F/T sludge was vacuum filtered and compared with the dewatering performance of FeCl3 preconditioned sludge with the same water content. Finally, the mechanism of the initial water content on the effect of F/T preconditioning was analyzed by the change of sludge internal composition. The results show that the higher the initial water content of the sludge, the greater the improvement of its dewatering performance after F/T preconditioning. The specific resistance and water content after filtration of sludge after F/T conditioning decreased greatly with the increase of the initial water content, reaching their respective minimum values of 13.3 × 1012 m/kg and 58.3% at 85% and 87.5%. These values are lower than the optimal values observed for the sludge conditioned by FeCl3. With the rise in initial water content, the driving force at the ice-water interface gains strength. Small particles aggregate into larger flocs, forming stable drainage channels that enhance the dewatering performance of sludge. Once the initial water content surpasses 85%, the squeezing force exerted by ice crystals amplifies the degree of cracking in sludge particles, releasing bound water and further decreasing the water content of sludge.

Effect of dewatering conditioners on phosphorus removal efficiency of sludge biochar

Based on the best dehydration effect, this study compared the adsorption phosphorus effect of sludge biochar after sludge conditioning with FeCl3, KMnO4, and cationic polyacrylamide (CPAM). This provided insights into the effects of chemical conditioning during the sludge dewatering stage on the overall phosphate adsorption of the dewatered sludge biochar. The phosphorus adsorption mechanism of the dewatering sludge biochar was analysed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. Under the optimal pyrolysis temperature (300°C), the phosphate adsorption capacity of FeCl3-conditioned sludge biochar (SB-FeCl3) was increased 77 times of the unconditioned sludge biochar. In different solution environments (e.g. pH and coexisting anions), Phosphate adsorption of SB-FeCl3 was srtrongest when the pH of 9 and contained CO32-. Through the analysis of surface elements and functional groups, it was explained that the phosphorus removal effect of SB-FeCl3 comes from abundant active sites containing iron. Phosphorus release occurred in sludge biochar (SB) during the study. SB-FeCl3 solved SB the release of phosphorus, and improved the adsorption capacity of phosphorus.

Effect of chemical regulation combined with mechanical filtration on deep dewatering and consolidation characteristics of sludge

To reveal the mechanism underlying deep dewatering of municipal sludge, this paper investigated the sludge characteristics from the perspective of soil mechanics, and analyzed the sludge physical and mechanical properties, stress as well as dewatering behavior during the dewatering process. Before and after cationic polyacrylamide (CPAM) and chitosan (HACC) conditioning, the pressure filtration dewatering time of treated sludge was shorter than that of raw sludge, and the water removal rate was greater than 70% at the 6 MPa pressure. However, with the increase in filter pressing time, the filtration resistance coefficient of sludge increased, and the water pressure in sludge pores rose up, and a longer time was needed for dissipation at the larger pressure, resulting in the slowdown of sludge consolidation. In addition, based on the three-stage Terzaghi Voigt model, when the pressure rose from 2 to 6 MPa, the time from filtration stage to compression stage of raw sludge was shortened, and the second stage played the most important role in the dewatering process. Compared with the raw sludge, the sludge filtration stage was shortened after CPAM or HACC conditioning, and the main dewatering mechanism changed from the second compression stage to the first compression stage, which means the bound water in sludge flocs was transformed into free water. This was also the reason why the dewatering, compression and consolidation rate of the conditioned sludge was faster than that of the raw sludge.

Recovering phosphorus as struvite from anaerobic digestate of pig manure with ferrochrome slag as a magnesium source

The circular economy initiative has driven the agriculture and agro-based industry to beneficiate from waste,thus closing the material loop towards enhancing economic and environmental performance. In this study, the aim was to recover phosphorus from anaerobic digestate of piggery wastewater (ADPW) using ferrochrome slag (FCSL) as the magnesium source to improve the environmental and economic sustainability of struvite precipitation. This was achieved by leaching 100 g L^-1 of ferrochrome slag with 5 M HCl where 14.02 g L^-1 of magnesium ions were extracted, and this acid-leachate of ferrochrome slag also contained 2650 mg L^-1 of total iron. To simultaneously remove both high concentrations of organic matters in ADPW and iron in FCSL which are known to be detrimental to struvite precipitation, hydrogen peroxide (H₂O₂) at an H₂O₂/Fe molar ratio of 0.75 and pH 4.0 was added to the mixture of ADPW and FCSL. After the Fenton reaction, removal efficiencies of chemical oxygen demand (COD) and total iron reached 95.06% and 94.00%, respectively. Then COD and an iron-reduced mixture of ADPW and FCSL were added with a satisfying Mg:N:P molar ratio of 1.2:1:1.15 at pH 9.5 to produce struvite in 1 h. From 1 L of ADPW (2.6 g NH₃-N), 0.5 L of FCSL (5.34 g Mg²⁺), and 6.62 g of PO₄ ^3- P, were consumed to produce 45.57 g of struvite precipitate. Additionally, the economic feasibility of ferrochrome slag was assessed by estimating the chemical costs of FCSL against that of magnesium chloride which is commercially used. It was observed that using FCSL was cheaper as compared to using commercial MgCl₂. Response surface methodology coupled with the central composite design was applied as a statistical tool to determine the effects of the key parameters (N:P; Mg:PO₄; pH) on phosphorus recovery. Second-order polynomial equations were determined to correlate the parameters. ANOVA was applied and showed that p values for all the investigated parameters were less than 0.05 showing that they had a statistically significant effect on the phosphorus recovery. The study confirmed that it was possible to recover phosphorus as struvite from anaerobic digestate of pig manure with ferrochrome slag as a magnesium source.

Anti-clogging mechanism of freeze-thaw combined with step vacuum preloading in treating landfill sludge

Globally, landfill sludge (LS) has accumulated in large quantities, and its reduction and dewatering are urgently needed. To address pollution problems and clogging of drainage boards caused by chemical conditioning combined with traditional vacuum preloading (TVP), a freeze-thaw combined with step vacuum preloading (F/T-SVP) method is proposed. A comparative experimental study was carried out between TVP and SVP to explore the anti-clogging mechanism of F/T-SVP in treating LS. As a result, the water discharge for the original sludge (OS) is 1840 ml, the water discharge for TVP is 8830 ml and for SVP is 10,010 ml; The total settlement of SVP is 16% higher than that of TVP; TVP has a volume reduction ratio of 57.6%, while SVP has 66.8%; the OS's water content was 86%, which was reduced to 57.6% by F/T-SVP; The center of the drainage board of TVP is seriously clogged, while the particles of SVP are evenly distributed; The tendency for small particles to undergo transport is relatively low at the beginning of SVP, which can effectively reduce clogging; TVP mainly focuses on the compression of large pores into small pores, and SVP mainly focuses on the compression of large into small pores and micropores. In SVP, there is more consolidation and a more compact structure. When F/T-SVP is used to treat LS, the pores are gradually penetrated, effectively avoiding the generation of clogging and improving LS's drainage and consolidation.

The key role of crystal boron in enhanced degradation of refractory contaminants using heterogeneous Fe3+/SPC system

An origin Fenton-like system was discussed for the abatement of refractory contaminants. Sodium percarbonate (SPC) was utilized as the source of H2O2 and crystal boron (C-boron) was applied to enhance the activation of H2O2. Under the conditions of 0.50 mM Fe3+, 0.34 mM SPC, and heterogeneous catalysis using 100 mg L-1 C-boron, four target pollutants, at the initial concentrations of 20 μM, could be efficiently degraded by the Fenton-like system, with a degradation rate within 20 min up to 81.1% (aspirin, ASA), 92.8% (nitrobenzene, NB), 94.7% (flunixin meglumine, FMME), and 94.3% (benzoic acid, BA) respectively and total organic carbon removal up to 25.0%. The increase of Fe2+ concentration indicated that the conversion of Fe2+/Fe3+ was remarkably promoted by C-boron. Degradation reactions at acidic pH were comparatively fast, with pH-dependent kobs of 9.9 × 10-2 min-1 (ASA), 1.5 × 10-1 min-1 (NB), 1.7 × 10-1 min-1 (FMME), and 1.9 × 10-1 min-1 (BA), whereas those at neutral and alkaline pH were slower. Furthermore, reactive oxygen species including ·OH, 1O2, and O2·- were identified by in-situ electron paramagnetic resonance tests. The contribution ratios of ·OH turned out to be about 71.3-86.7% for the decomposition of four contaminants. The elimination of natural organic matter and the performance of material recycling highlighted the potential for its application in water treatment. The inhibition rate of Chlorella pyrenoidosa reached 211.9% in the C-boron/Fe3+/SPC system. The relatively high algae toxicity limited its application scope, which requires additional research to resolve.

Enhancing the Dewaterability of Oily Cold Rolling Mill Sludge Using Quicklime as a Conditioning Agent

The high moisture and viscosity characteristics of oily cold rolling mill (CRM) sludge led to limitations in its recycling. In this paper, the results of using quicklime as a conditioning agent to improve the dewaterability of the oily CRM sludge cake were reported. Quicklime was selected as the best conditioning agent through conditioning-dewatering experiments because it could effectively reduce the viscosity of oily CRM sludge and improve the dewaterability of the oil sludge filter cake. The optimal conditioning effect was obtained when the quicklime dosage was 10%, the temperature was 60 °C, the liquid/solid ratio was 1.5:1, and the time was 30 min. The reduction of specific resistance to filtration was 95.9%, and the coefficient of compressibility of the filter cake decreased from 1.11 to 0.89. The dewatering rate increased from 9.0 to 52.6%. The oily CRM sludge cake formed an incompressible rigid porous structure because of conditioning with quicklime. In addition, after conditioning with quicklime, the oil content, chemical oxygen demand, and turbidity of the filtrate decreased, and the composition of the dried filter cake met the requirements of ironmaking raw materials. Using quicklime to condition the oily CRM sludge provided a green approach to waste recovery and sustainable management.

Effect of freezing temperature on dewatering, consolidation properties, and microstructure of landfill sludge

There is currently a considerable amount of landfill sludge (LS) accumulating worldwide, threatening the surrounding environment and land safety. It is urgent to dewater and reduce LS. Chemical conditioning is the most common treatment for LS, which can pollute the environment and limit resource exploitation. Therefore, a more environmentally friendly and efficient freeze-thaw combined vacuum preloading method is proposed. Experimental studies were conducted to investigate the influence of different freezing temperatures on the dewatering properties, compression and consolidation features, and the mechanism of microstructural change in LS. The results show that the freezing temperature has an important influence on the dewatering, compression, vacuum drainage, consolidation, and microstructure characteristics of LS. The compressibility of LS does not improve when the freezing rate is too high. Freeze-thaw cycles can improve sludge's permeability and consolidation properties by one to two orders of magnitude, and a suitable freezing temperature can significantly improve sludge's permeability and consolidation properties. After vacuum drainage and consolidation, the maximum volume reduction ratio of sludge can reach 55.3%, and the water content of LS can be reduced from 86% to 66%. The distribution of large pores and mesopores in LS increases as the freezing temperature decreases, reaching a maximum of -15 °C, which can substantially improve permeability, drainage, and consolidation efficiency.

Dehydration effect of freeze-thaw on sludge: Temperature spatio-temporal distribution and multi-scale evaluation

The freeze-thaw vacuum method for conditioning pretreated sludge has been proved that it not only has greater dewatering efficiency but also is more ecologically friendly. In this paper, the experiment is improved to address shortcomings in previous freeze-thaw vacuum approach for sludge treatment. The spatio-temporal distribution relationship of distance-time-temperature is developed and divided into two stages by numerically fitting the temperature change of freezing tubes in the sludge. It is expected to guide the time control of large-scale frozen sludge in practical engineering applications to achieve optimal dewatering treatment. Furthermore, the performance of dehydration after the model test is evaluated on multi-scale: settlement and mechanical properties (macroscopic perspective), mean particle size (mesoscopic perspective), and SEM microstructure (microscopic perspective). The results reveal that the improved sludge treatment method of alternating freeze-thaw vacuum procedures, using both prefabricated horizontal drains (PHDs) and prefabricated vertical drains (PVDs), substantially benefits the sludge dewatering and reduction. This method results in an unparalleled volume reduction of 63.51% and a water content reduction to 58.54%. Moreover, in-situ vane shearing strength of the sludge obtained from the improved test meets the strength requirement for the landfill final cover soil, demonstrating that the method is superior in improving mechanical properties.

Enhanced technology for sewage sludge advanced dewatering from an engineering practice perspective: A review

The increasing production of sludge poses significant environmental risks. Sludge disposal and transport are costly because of the high water content (WC). Reducing the WC of sludge is the most efficient strategy to decrease treatment costs. However, the sludge contains a large amount of hydrophilic organic matter, causing poor dewaterability. Therefore, research on preconditioning and mechanical dewatering has great significance for advanced sludge dewatering. In this study, the features of sludge, the advantages and disadvantages of preconditioning methods, and the action mechanisms (including physical, chemical, and biological preconditioning) are thoroughly described. In addition, the dewatering principle and engineering applications of mechanical dewatering techniques are introduced in this manuscript, especially the application of vacuum preloading as an in-situ dewatering technology in sludge. Finally, cost analysis of different conditioning and mechanical dewatering methods is conducted to explore their application feasibility. This manuscript provides new insights for engineering applications of preconditioning methods and mechanical dewatering technology.

Experimental investigation on a combination of soil electrokinetic consolidation and remediation of drained water using composite nanofiber-based electrodes

A novel electrokinetic geosynthetic (EKG) can be efficient in achieving multiple objectives. In this study, a new EKG as an electrode and a drainage channel in the electro-osmotic consolidation was fabricated by electrospun nanofibers containing graphene nanoparticles (GNs) attached to a carbon fiber substrate. To investigate the effectiveness of the fabricated electrodes in electro-osmotic consolidation and remediation of water drained from the system, an experimental apparatus was constructed while considering loading capability in expanded ranges and applying the electric field, and was filled with copper (Cu)-contaminated kaolinite. Experiments were divided into control (CT) and EKG groups, and three categories, C-EK, ES₁-EK, and ES₂-EK (using carbon fiber, electrospun nanofibers containing 1 wt% GNs, and electrospun nanofibers consisting of 2 wt% GNs, respectively). All the experiments were conducted with the same conditions, loading, drainage condition, and duration. However, EKG experiments were performed by employing the electric field under the vertical pressure in the range of 7-113 kPa, while the CT was conducted without the electric field. According to experimental results, 18 wt% polymethyl methacrylate in the dimethylformamide solvent containing 1 and 2 wt% GNs was selected for making a nanofibrous layer on the carbon fiber. The average diameters of the fibers were 404 ± 36 and 690 ± 62 nm and yielded at 1 and 2 wt% GNs, respectively. The results revealed that using the EKG accelerated kaolinite consolidation. The average degree of consolidation was 68 and 85% in the CT and EKG experiments, respectively. Furthermore, the fabricated electrodes were highly effective as a drainage channel for remediating water drained from the system. Moreover, the highest Cu removal efficiency was obtained in ES₂-EK (97%) and ES₁-EK (92%), respectively. Conversely, the lowest Cu removal efficiency was observed in the C-EK group (85%).

Insights into the dewatering of excavated landfill sludge conditioned by polyferric silicate sulfate

Large quantities of landfill sludge (LS) with higher water content (WC) were stored underground, and excavation and re-dewatering of LS is a sustainable and economic strategy to save landfill space and reduce the leaching of contaminants. In this study, polyferric silicate sulfate (PFSS) was first applied in the conditioning of excavated LS, and the effects of the Si/Fe mass ratio and PFSS dosage on physicochemical properties, dewaterability and rheological properties were investigated. At the best Si/Fe of 0.18, PFSS conditioning obtained compact aggregates with the strongest internal structure, thus achieving the lowest WC. Large sludge flocs were formed, and slime and loosely-bound extracellular polymeric substances were effectively removed with the PFSS dosage above 100 mg/g dried solids, which made the WC to be lower than 51.4%. The whole mechanical compression process of conditioned LS can be described by the modified Terzaghi-Voigt model, and increasing the PFSS dosage induced the release of bound water and migration of the consolidation stage from ternary to secondary. PFSS is an economically sustainable conditioner for LS, integrating multiple functions such as charge neutralization, particle aggregation, interparticle bridging and skeleton building in one chemical.

Synergistic effect of combined hydrothermal carbonization of Fenton's reagent and biomass enhances the adsorption and combustion characteristics of sludge towards eco-friendly and efficient sludge treatment

The amount of lignocellulose biomass and sludge is enormous, so it is of great significance to find a treatment combining the two substances. Co-hydrothermal carbonization (Co-HTC) has emerged as an efficient approach to dispose sludge. However, the improvement of sludge upgrading and combustion performance remains an important challenge during the Co-HTC of sludge. In this work, the Co-HTC of sludge and Fenton's reagent at different mixing ratios was proposed to achieve sludge reduction. Moreover, the addition of two kinds of biomass improved the adsorption capacity and combustion performance of hydrochars. When sludge and sawdust were the Co-HTC at the mass ratio of 1:3, the liquid phase Pb concentration decreased notably to 18.06%. Furthermore, the adsorption capacity of hydrochars was further improved by modification, which was in accordance with pseudo-second-order kinetics. Particularly, the hydrochars derived from the Co-HTC had higher heating value (HHV) and could be used as a clean fuel. This study proposed a new technical route of combining the HTC with Fenton's reagent and lignocellulose biomass, which could be served as a cleaner and eco-friendly treatment of sludge.

Insights into vacuum preloading consolidation of landfill sludge based on Fe2+-activated sodium persulfate

To further reduce the in-situ sludge from landfill, Fe²⁺-activated sodium persulfate combined with vacuum preloading was first proposed. Firstly, the effects of optimal Na₂S₂O₈ dosage on the landfill sludge (LS) were investigated by the vacuum filtration experiments. Then, vacuum preloading experiments were conducted on the sludge with different Na₂S₂O₈ dosages to study the water content, water discharge, and settlement. Besides, sludge particle size diversification was carried out by particle size distribution and scanning electron microscopy (SEM) tests. The results were summarized as follows: the specific resistance of filtration (SRF) of LS could be reduced by 98.5% mostly when the Na₂S₂O₈ dosage was 30%; the particle size became significantly smaller, and large particles were converted to small particles; the water content dropped from 86.9 to 58.3%; and the SEM test manifested the oxidation of sodium persulfate caused the destruction of the glial structure of the sludge and the recombination of partial particles.

Freeze-thaw vacuum treatment of landfill sludge: Mechanism of uneven frost heaving and dewatering performance

The method of freeze-thaw combined with vacuum pretreatment for landfill sludge (LS) has attracted extensive attention. However, most of the existing approaches are based on small-scale laboratory testing, and further testing studies must be performed to realize in situ treatment. To enhance the practicality of such approaches, the range of temperature effects on LS was analysed after field freeze-thaw model testing. After the freeze-thaw model test, samples were transported to the laboratory for unidirectional oedometer tests, and the remaining samples were retained in the field to continue vacuum model testing for exploring the differences in the consolidation and drainage effect of the LS. Results show that temperature changes during freeze-thaw process affect the distribution of sludge and water in the model boxes, resulting in frost heave and the appearance of "extrusion rings". In addition, the coefficient of consolidation obtained from the unidirectional oedometer test shows that the consolidation coefficient is generally larger near the freezing tubes at a lower temperature. The settlement determined from the field vacuum preloading test shows that the subsequent vacuum consolidation settlement is larger at the position with a lower elevation of the frozen sludge surface. The comparison indicates that the consolidation and drainage effect in the field is not as significant as that in the laboratory. The findings can provide reference to optimize the field conditions during the in situ engineering practice of sludge treatment.

Improvement of sewage sludge dewatering by piezoelectric effect driven directly with pressure from pressure filtration: Towards understanding piezo-dewatering mechanism

Piezoelectric effect was firstly employed to improve dewatering efficiency of sludge. It was found that the piezoelectric effect could be driven directly by the pressure of pressure filtration process, without any additional energy. This piezo-dewatering process coupled piezoelectric effect with pressure filtration could efficiently remove moisture of sludge. Under 0.6 MPa for 2 h, moisture content (MC) and weight of sludge could be reduced to 63.9% and 3.2 g from 96.7% and 50 g by the piezo-dewatering process with 0.45 g t-BaTiO3. This piezo-dewatering efficiency was much higher than that of usual conditioning-pressure filtrations using CaO, FeCl3 or polyacrylamide (PAM) as the conditioners. And the piezo-dewatering process assisted by PAM could further decrease MC and weight of the sludge to 54.9% and 2.1 g, correspondingly, which complied to the advanced dewatering requirement (MC < 60%). The favorable piezo-dewatering efficiency was contributed to the piezo-catalytic oxidation and the electric role of remnant piezo-field. The finding of this piezo-dewatering mechanism offered an inspiring look at developing the emerging dewatering technology.

Novel insights into enhanced dewaterability and consolidation characteristics of landfill sludge and fresh sludge conditioned by Fe2+ activated sodium persulfate

Considering the reduction and resource utilization of landfill sludge (LS) and fresh sludge (FS), Fe²⁺ activated Na₂S₂O₈ is proposed. The effects of the molar ratio of Fe²⁺/S₂O₈^2- and the addition of Na₂S₂O₈ on the dewatering performance of sludge were studied by vacuum filtration experiments. Consolidation tests were conducted on the sludge with different Na₂S₂O₈ dosage, and the compression, consolidation, and permeability characteristics of the sludge were researched. Besides, via particle size distribution (PSD) and scanning electron microscope (SEM) test, the variation of particle size of sludge was studied from the microscopic perspective. The results are as follows: the specific resistance of filtration (SRF) of LS and FS decreases by 99.3%, 95.2% at an optimal dosage (the molar ratio of (Fe²⁺/S₂O₈^2-) = 1, 30% Na₂S₂O₈); the particle size of LS and FS is significantly smaller; the consolidation and permeability coefficients are increased by 1-2 orders of magnitude compared with non-conditioned sludge; the water content of LS and FS drops from 86.5% to 58.4%, 82.4%-59.7%. The research results have certain guiding significance for the in-situ treatment of sludge deep dewatering.

Effects of dissolved oxygen on the sludge dewaterability and extracellular polymeric substances distribution by bioleaching

Bioleaching is a biological conditioning technology for sludge, which not only improves sludge dewatering performance but also removes heavy metals from sludge. As the bioleaching process is a comprehensive biological and chemical process, it is necessary to explore the effects of dissolved oxygen (DO) concentrations on bioleaching efficiency. Three bioleaching experiments with different DO concentrations (T1: 0.8-3.1 mg/L, T2: 3.1-5.5 mg/L, T3: 5.5-7.5 mg/L) were conducted for five days. The sludge dewatering efficiency was evaluated using capillary suction time (CST) and specific resistance to filtration (SRF). The relationship between sludge dewaterability and extracellular polymeric substance (EPS) fraction distribution was investigated. In the treatment with the highest DO concentration, the minimum values of SRF and CST were 4.31 × 10¹¹ m/kg and 13.5 s, which occurred earlier than the treatment with the lower DO concentrations by approximately 24-48 h. A significant decrease (83.4-93.2%) in tightly bound EPS (TB-EPS) protein (PN) was observed in all treatments, while a positive correlation (r = 0.924, P < 0.01) was observed between SRF and PN content in TB-EPS. A relatively higher abundance of Acidithiobacillus was found with the increase in DO concentration. Additionally, other genera including Metallibacterium, Alicyclobacillus, Acidibacter, Acidocella, and Luteococcus also played important roles in EPS biodegradation. These results revealed that increasing the DO concentration could improve sludge dewatering performance and heavy metal removal by enhancing bioleaching microbial activity, the degradation of PN in TB-EPS, and sludge floc fragmentation, but only if sufficient energy sources were provided.

New methods for quantification of Fenton's reagent addition based on aged sludge indicators to improve filterability

Fenton oxidation can effectively improve the dewaterability of aged sludge. Quantification of the addition of optimal reagents is central to the conditioning and dewatering of aged sludge. Improving the accuracy of quantification is significant to promote cost effectiveness. The effects of reagent addition and the mechanism governing the improved filterability of the aged sludge need to be understood uniformly. In this study, the optimal reagent additions have been determined using the response surface method (RSM) for five out of the eight aged sludges that were investigated. The physicochemical characteristics of eight aged sludges, including the extracellular polymer substance, undissolved organic matter, and suspension structure network, were investigated. Meanwhile, a comprehensive correlation analysis of critical indicators was conducted to investigate the interactions among the properties of the aged sludge. The effects of these interactions on the conditioning and filtration processes were examined, and a unified understanding of the combination of factors affecting the optimal reagent addition was obtained. The key factors were aggregate size, dewatering extent, yield stress, and organic substance content. Based on these results, a new reagent addition quantification method was developed along with an empirical model of the relationship between physicochemical properties and the economically optimal reagent addition.

Experimental study on treating landfill sludge by preconditioning combined with vacuum preloading: Effects of freeze-thaw and FeCl3 preconditioning

The deep dewatering of landfill sludge (LS) mainly uses the methods of chemical preconditioning and mechanical dewatering, which is easy to cause environmental pollution and is not conducive to the subsequent recycling treatment of sludge. To find a more environment-friendly and efficient method for LS's deep dewatering and volume reduction, an in-situ sludge treatment method combining freeze-thaw (F/T) preconditioning and vacuum preloading was proposed. Firstly, the F/T test of LS was carried out to explore the optimum freezing temperature. FeCl₃, the most widely used agent, was selected as the chemical preconditioning. Then carry out vacuum preloading model box test. The data were compared after the test. The mechanisms of the two different sludge preconditioning methods on the LS's consolidation were analyzed. The results show that: after freezing, the specific resistance of LS decreases obviously, the overall particle size increases, the content of small particles decreases. Too fast freezing rate is not conducive to the LS's dewatering. After preconditioning (F/T and FeCl₃) combined with vacuum preloading, the volume reduction ratio was 57.1% and 41.1% respectively, the water content was reduced from 73.4% to 53.7% and 58.1%, and the unconfined compressive strength(UCS) was improved from 15.5 kPa to 50.9 kPa and 77.3 kPa. The total water discharge, drainage rate, volume reduction, and water content of freeze-thaw preconditioned LS are better than FeCl₃ preconditioned, while FeCl₃ preconditioned LS has higher UCS. F/T can aggregate small sludge particles but the acidification and hydrolysis of FeCl₃ always produce small particle, which is not conducive to the consolidation of LS during vacuum preloading.