Hydrothermal Conditioning Research Articles

Hydrothermal conditioning of oleaginous yeast cells to enable recovery of lipids as potential drop-in fuel precursors

BackgroundLipids produced using oleaginous yeast cells are an emerging feedstock to manufacture commercially valuable oleochemicals ranging from pharmaceuticals to lipid-derived biofuels. Production of biofuels using oleaginous yeast is a multistep procedure that requires yeast cultivation and harvesting, lipid recovery, and conversion of the lipids to biofuels. The quantitative recovery of the total intracellular lipid from the yeast cells is a critical step during the development of a bioprocess. Their rigid cell walls often make them resistant to lysis. The existing methods include mechanical, chemical, biological and thermochemical lysis of yeast cell walls followed by solvent extraction. In this study, an aqueous thermal pretreatment was explored as a method for lysing the cell wall of the oleaginous yeast Rhodotorula toruloides for lipid recovery.ResultsHydrothermal pretreatment for 60 min at 121 °C with a dry cell weight of 7% (w/v) in the yeast slurry led to a recovery of 84.6 ± 3.2% (w/w) of the total lipids when extracted with organic solvents. The conventional sonication and acid-assisted thermal cell lysis led to a lipid recovery yield of 99.8 ± 0.03% (w/w) and 109.5 ± 1.9% (w/w), respectively. The fatty acid profiles of the hydrothermally pretreated cells and freeze-dried control were similar, suggesting that the thermal lysis of the cells did not degrade the lipids.ConclusionThis work demonstrates that hydrothermal pretreatment of yeast cell slurry at 121 °C for 60 min is a robust and sustainable method for cell conditioning to extract intracellular microbial lipids for biofuel production and provides a baseline for further scale-up and process integration.Graphical abstract

Effect of hygrothermal conditioning on compressive strength after impact in carbon fiber/epoxy composites

AbstractCarbon fiber‐reinforced polymers have been widely applied in structural parts and components in several sectors, in addition to being constantly used in environments with the presence of humidity and high temperatures, which can affect their density, hardness, and rigidity. In this work, the influence of hydrothermal conditioning on carbon fiber (CF)/epoxy composites was investigated using three types of epoxy resin and two different CF fabric reinforcements, that is, plain weave and eight harness satin (8HS) arrangements. The CF/epoxy composites were subjected to compression after impact (CAI) test by 28 and 40 J energy and then exposed to hydrothermal conditioning for 8 weeks. After the CAI tests, the visual analysis of all composites presented microbuckling mechanisms. The composites tested with 40 J energy absorbed only 2% more moisture compared with the other composites, nonimpacted, and tested with 28 J, indicating that the impact damage did not cause delamination between the layers of the composites, which could facilitate the absorption of water. All composites analyzed showed resistance to CAI even after exposure to humidity, with decreases ranging from 2.8% to 23.8% about the unconditioned specimens. The decrease in CAI also shows the influence of the type of epoxy matrix and the arrangement of the CF in fabrics.

An experimental implication of long‐term hot‐wet‐aged carbon fiber/polyether ketone ketone composites: The impact of automated fiber placement process parameters and process‐induced defects

AbstractDuring the service life of aerospace‐grade composites, process parameters and process‐induced defects may become crucial. Most studies in this field have mainly focused on the relationship between process‐induced defects and mechanical performance. However, the potential impact of process parameters and process‐induced defects on the service life of composites serving under severe service conditions has received little attention. In this work, the effects of hydrothermal conditioning on the mechanical performance of carbon fiber/polyether ketone ketone (CF/PEKK) composites are examined, along with the correlation between automated fiber placement (AFP) process parameters and process‐induced defects. For this, gap and overlap defects integrated CF/PEKK laminates were exposed to a long‐term (90 days) hot‐wet aging environment to simulate the actual service conditions. Defect‐induced composite samples reached saturation point at the end of 30 days with a mass gain of 0.2 wt%. The aging process resulted in an increase in the degree of crystallization by almost 14% without a change in the chemical structure, indicating the postcrystallization of the PEKK matrix. Even though the thermo‐mechanical performance diminished (~25%) with the aging process, storage modulus was slightly affected by process parameters and process‐induced defects. Considering the flexural and shear test results after the aging process, the impact of gap and overlap defects on the service life of AFP composites can be minimized with higher compaction forces (600 N) and lower lay‐up speeds (0.1 m/s).

Water diffusion kinetics study at different hydrothermal bath temperatures and subsequent durability studies of CNT embedded fibrous polymeric composites: Roles of CNT content, functionalization and in‐situ testing temperature

AbstractAlthough structural polymers like epoxy are extensively used in marine applications over metallic structures, environmental water tends to ingress into this polymer which may affect its long‐term durability. The extent of degradation caused by the absorbed water on polymeric composite's mechanical properties depends on the water diffusion mechanism, environmental temperature and subsequent reversible and irreversible chemical restructuring of the polymer. In this study, hydrothermal conditioning behavior of glass fiber reinforced epoxy (GE) composites with varying (0.1, 0.3, and 0.5) wt.% of pristine and functionalized carbon nanotubes (CNTs and FCNTs) was studied at 15°C (Low‐Temperature Hydrothermal Conditioning (LTHC)) and 50°C (Elevated‐Temperature Hydrothermal Conditioning (ETHC)) water baths. The changes in chemical bonding characteristics and glass transition temperature of GE composite due to above mentioned factors have been studied by Fourier transformed infrared spectroscopy and differential scanning calorimetry. The gravimetric analysis was employed to monitor the water uptake kinetics of the composites and flexural strength of conditioned composites after 50 days of conditioning and saturation was study to understand the effect of water sorption. Experimental results revealed that, FCNTs greatly hinders the water absorption through the interfaces at LTHC, as the equilibrium water content of 0.1FCNT‐GE composite was ~9.5% and ~3.0% and Diffusion coefficient was ~60.0% and ~15.5% lower than the GE and 0.1CNT‐GE composites, respectively at LTHC. At LTHC, the water saturated 0.1FCNT‐GE composites exhibited superior flexural strength than GE and 0.1CNT‐GE composites. At ETHC, generation of hygroscopic stresses and unfavorable stresses at the weak CNT/polymer interface adversely affected the 0.1CNT‐GE composites water resistance compared to 0.1FCNT‐GE composites with stronger FCNT/polymer interface. The extent of recovery in the flexural strength was evaluated by complete desorption of water‐saturated specimens. Finally, a fractography study was conducted to understand the variation in the well‐being of the glass fiber/polymer and nanotube/polymer interface due to mentioned varying factors.

Failure modes in GFRP composites assessed with the aid of SEM fractographs

Abstract Hand-laid, 18 layered, E-Glass/Epoxy resin (GFRP) composite specimens were exposed to distilled water immersion at 65 °C (hydrothermal conditioning), a moist ambience with 95% relative humidity at 60 °C (hygrothermal conditioning) and sea water immersion (at room temperature) for different lengths of time. The treated samples were then exposed to both up and down thermal shocks. The specimens were also exposed to gamma irradiations pertaining to both high and low intensity gamma doses. Three-point Bend test of the samples so treated, was carried out in a universal testing machine and the failure modes as revealed from the SEM fractographs of the fractured specimens surfaces subjected to SEM analysis were recorded and analyzed. The samples conditioned differently for different lengths of time exhibited different extents of structural damages and adopted different modes for the ultimate failure. Any one or any combination of failure modes such as matrix-cracking, fibre pull-out, fibre–matrix de-bonding etc. indicating the interfacial failure were seen to be the chief mode of failure/disintegration of the GFRP composite specimens.

Enhanced hydrothermal stability of Cu MOF by post synthetic modification with amino acids

In this work, we report the solvothermal synthesis of copper metal organic framework (Cu MOF) also known as HKUST 1 and its functionalization with amino acids to increase hydrothermal stability. MOFs are porous materials made up of organic and inorganic components. Owing to properties like large surface area, tunable pore size, pore volume and desirable functionality via Post Synthetic Modification (PSM), MOFs are gaining attention in various applications such as catalysis, energy storage, pollutant removal and sensing. But most of the MOFs show poor hydrothermal stability that limits their applications in aqueous samples. Various characterization techniques such as Powder X-Ray Diffraction (PXRD), Fourier-Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), Zeta potential study indicated successful modification of Cu MOF with different amino acids. Thermogravimetric analysis (TGA), contact angle and SEM results after hydrothermal conditioning showed enhanced water stability for glycine, lysine and tyrosine functionalized Cu MOF compared to pristine MOF. The pristine Cu MOF possessed contact angle of 39.6° which got increased for modified Cu MOFs showing transition behaviour of Cu MOF from hydrophilic to hydrophobic after functionalization.

Damage of Hygrothermally Conditioned Carbon Epoxy Composites under High-Velocity Impact.

The influence of hygrothermal aging on high-velocity impact damage of carbon fiber-reinforced polymer (CFRP) laminates is investigated. Composite laminate specimens were preconditioned in water at 70 °C. The laminates were subsequently impacted by flat-, sphere-, and cone- ended projectiles with velocities of 45, 68, and 86 m/s. The incident and residual velocities were collected during the impact test. The impact-induced damages were measured by ultrasonic C-scan, a digital microscope system, and a scanning electron microscope. The results show that the hygrothermally conditioned laminates offer a higher energy absorption during high-velocity impact. Due to the weakening of the interlaminar properties, the hygrothermally conditioned laminates are more susceptible to delamination failure, and shear-induced debonding dominates. The projected delamination area increases with the increment of impact velocity. The damaged region becomes close to a circular shape after hydrothermal conditioning, and close to a rhomboidal shape for the dry specimens.

Advantages of Separated Silage for Bioenergy Applications without Material Washing

In order to guarantee the sufficient efficiency using biomass for the anaerobic digestion (AD) process, lower mineral solid fuels production, saving same time most of fertilizing elements the silage mechanical separation process can be applied. Press liquids (PL) from separation in fact shows tendency to higher biogas yield per dry-matter (DM) on AD process and press cake (PC) gives comparable biogas yields with silage. The separation includes as pretreatment positive impact to biomethane yields on AD process. The period of fermentation of PL from silage is shorter than the duration of the cycle of fermentation process when silage is used as untreated substrate for AD. Based on these trends it is possible to reduce the volume of the reactor, reducing investment costs and to simplify the technology as the substrates can be easier injected in the reactor with a lower need of maintenance. The separation of the solid-liquid phases of the silage enables to produce solid fuels from press cake (PC), or can be used in fluidized bed boiler houses because of high enough dry DM content in range of 43–49%. Solid biofuels, as the result of separation process have less ashes and elements which can cause problems in furnace chemistry and physical performance. Separation of silage enables number of advantages as faster AD process, feedstock specific methane yield per DM, possibility to produce higher quality solid biofuels and save most of nutrients in PL (digestate) as fertilizers on case of using PC as solid fuels. Feedstock mashing with water or hydro-thermal conditioning is not used.

Effects of UV irradiation and condensation on poly(ether-ether-ketone)/carbon fiber composites from nano- to macro-scale

Durability and damage mechanism of carbon fiber–reinforced poly(ether-ether-ketone) composites (T300/PEEK) have been investigated under ultraviolet (UV) and water condensation conditions for 1560 h. The tensile modulus decreased by 5.4% after 1560 h of exposure, while no significant changes were found in tensile strength. The microhardness and elastic modulus of the resin measured by atomic force microscope–based nanoindentation were found to be dramatically increased after 240 h treatment and then decreased after longer treatment. The thermal decomposition temperature decreased from 549° to 522° after 840 h of exposure due to the formation of side chains and low molecular products induced by UV. The damage of resin was attributed to chain scission and recombined cross-linking by UV irradiation and hydrolytic deterioration by hydrothermal conditioning, where the decomposition led to the formation of carbonyl groups and hydroxyl groups, as well as the reduction of ether groups determined by Fourier transform infrared spectroscope. Scanning electron microscopy analysis on tensile fractures near the exposed surface indicated fiber/matrix debonding. The resin on the surface degraded rapidly, and its roughness increased continuously from 30.8 ± 4.1 nm to 88.8 ± 6.8 nm after 840 h of degradation, with the formation of microholes and microcracks. A degradation mechanism was proposed, and the accelerated weather aging affected only the surface region of T300/PEEK.

Effect of Hydrothermal immersion and Hygrothermal Conditioning on Mechanical Properties of GRE Composite

Glass fibre reinforced epoxy (GRE) composite meet several degrading agents like moisture and temperature while its use in real time applications in civil infrastructures. Keeping this in mind, the short beam shear (SBS) specimens of GRE composite were exposed to such laboratory created stringent environment as a combination of moisture and elevated temperature for several periods. The environments are as: immersion in distilled water coupled with 65oC as hydrothermal conditioning and an ambience containing 95% relative humidity at 60oC as hygrothermal conditioning. Moisture treated SBS specimens were subjected to 3-point bend test to reveal inter laminar shear strength (ILSS), stress/strain at rupture and modulus values with periods of exposures. The concerned sample suffered 23% of degradation in ILSS values after 120 days of hydrothermal immersion and 25% after 90 days of hygrothermal conditioning. Samples at some optimum exposing conditions of both the exposures are thermally characterized by adopting differential scanning calorimetry (DSC) test. Glass transition temperature (Tg) of such representing samples were determined from the DSC thermograms. About 8 % reduction in Tg values was observed for the GRE composite sample, expectedly, due to moisture induced matrix plasticization and swelling. The fractographs as obtained through scanning electron microscope (SEM) revealed some causes of failures indicating the prime modes of failure of the treated GRE samples with optimum duration of both the exposures.

Hydrothermal Conditioning of Physical Hydrogels Prepared from a Midblock‐Sulfonated Multiblock Copolymer

Since nanostructured amphiphilic macromolecules capable of affording high ion and water transport are becoming increasingly important in a wide range of contemporary energy and environmental technologies, the swelling kinetics and temperature dependence of water uptake are investigated in a series of midblock-sulfonated thermoplastic elastomers. Upon self-assembly, these materials maintain a stable hydrogel network in the presence of a polar liquid. In this study, real-time water-sorption kinetics in copolymer films prepared by different casting solvents are elucidated by synchrotron small-angle X-ray scattering and gravimetric measurements, which directly correlate nanostructural changes with macroscopic swelling to establish fundamental structure-property behavior. By monitoring the equilibrium swelling capacity of these materials over a range of temperatures, an unexpected transition in the vicinity of 50 °C has been discovered. Depending on copolymer morphology and degree of sulfonation, hydrothermal conditioning of specimens to temperatures above this transition permits retention of superabsorbent swelling at ambient temperature.

Recovered spinel MnCo2O4 from spent lithium-ion batteries for enhanced electrocatalytic oxygen evolution in alkaline medium.

A facile way of recovering 3d transition metals of industrial importance from spent lithium-ion batteries (LIBs) without using any surfactants has been developed. Mn- and Co-rich spent LIBs were chosen as sustainable sources for recovering the oxides of the respective elements. The physical dismantling of Li-ion batteries, chemical leaching with 2 M acetic acid, precipitation with ammonium carbonate, hydrothermal conditioning and calcination at 650 °C led to the facile formation of spherical spinel MnCo2O4 with very high morphological selectivity. The obtained spherical MnCo2O4 was identified by various advanced characterization techniques. Detailed electrochemical characterization revealed that the recovered spheres of spinel MnCo2O4 were effective in catalyzing the oxygen evolution reaction (OER) in 1 M KOH and required an overpotential of 358 and 400 mV to generate a current density of 5 and 10 mA cm-2, respectively, with a relatively low catalyst loading (0.001025 g cm-2). Comparative electrocatalytic studies carried out with recovered LiCoO2, recovered LiXMnOX+1 and commercially available catalysts such as RuO2 (c-RuO2), Co3O4 (c-Co3O4) and MnO2 (c-MnO2) revealed that the recovered spheres of spinel MnCo2O4 were more effective OER catalysts than the recovered LiCoO2, recovered LiXMnOX+1, c-Co3O4 and c-MnO2 and exhibited comparable activity to that of c-RuO2 with very little difference in overpotential (∼50 mV) at current densities of 5 and 10 mA cm-2. With such a low catalyst loading, the observed electrocatalytic performance in water oxidation of a material recovered from waste is highly significant and will surely attain greater industrial importance when the recycling of spent LIBs from electronic wastes is considered.

The Effect of the Invasive Plant Species Lupinus polyphyllus Lindl. on Energy Recovery Parameters of Semi-Natural Grassland Biomass

Biodiversity of semi-natural grasslands is increasingly endangered by successful invasive plant species such as the legume Lupinus polyphyllus Lindl. In order to contain the propagation of this plant species, early and regular harvesting needs to be applied. Therefore, a form of utilization for the harvested biomass has to be developed. One opportunity could be the use of the biomass as a feedstock for biogas and solid fuel production. This study investigates the effect of L. polyphyllus on the nutrient and mineral composition in a mixture series with semi-natural grassland biomass and examines the changes in nutrient and mineral content through hydrothermal conditioning and mechanical dewatering of silage. Untreated lupine-invaded biomass has higher N and Mg concentrations, but lower Cl, K and S concentrations compared to the semi-natural grassland biomass. The mineral concentrations in the biomass exceeded recommendations for combustion. However, with the proposed pre-treatment of hydrothermal conditioning and subsequent dewatering, both lupine-containing and lupine-free semi-natural grassland biomass could achieve adequate values for combustion, given that a state-of-the-art combustion technique is used, including measures to reduce emissions of NOx and particulate matter. Thus, solid fuel production through hydrothermal conditioning and mechanical separation may offer a practical solution for the containment of lupine or other invasive species in semi-natural grasslands and may constitute an important element for sustainable bioenergy production.

Fuel Properties and Combustion Kinetics of Hydrochar Prepared by Hydrothermal Carbonization of Corn Straw

The potential of using hydrothermal carbonization (HTC) on corn straw (CS) was studied for the production of solid fuel. The effects of hydrothermal conditioning on the mass yield, energy yield, higher heating value (HHV), H/C and O/C atomic ratios, the morphology, and equilibrium moisture content (EMC) of hydrochars were examined by varying the reaction temperature (170 °C, 200 °C, 230 °C, and 260 °C) and the residence time (15 min and 30 min). The results demonstrated that the solid fuel properties of hydrochar produced at 230 °C for 30 min had an appropriate HHV of 20.51 MJ/kg, a mass yield of 64.80%, and an energy yield of 77.41%. The physical structure changed because of hydrothermal carbonization and the hydrophobicity of hydrochar increased in comparison to raw corn straw after hydrothermal carbonization. The combustion characteristics and kinetic parameters of raw corn straw and hydrochar were calculated based on the thermogravimetric curves according to Arrhenius equation. The activation energies of hydrochars were larger than that of raw corn straw. The comprehensive combustibility index (S) of raw corn straw was greater than that of hydrochar when the reaction temperature and residence time were 230 °C and 30 min, respectively.

Water diffusion and swelling stresses in highly crosslinked epoxy matrices

The present work investigates the swelling induced stresses arising in two epoxy systems during water uptake. The analysed systems are two epoxy resin based on DGEBA monomer and DGEBF monomer respectively, both fully cured by DDS amine. The systems achieve different cross-link density degrees, and are characterised by high glass transition temperatures ranging between 200 and 230 °C. Both epoxies have been conditioned in deionized water baths at two different temperatures (50 °C and 80 °C). A desorption process at room temperature in a dry airborne environment was performed after saturation. Dynamic Mechanical Thermal Analysis, carried out at the various stages of hydrothermal conditioning, has allowed to characterise the modifications occurring in the network structures during aging. Photoelastic Stress Analysis is adopted to monitor the evolution of stresses on rectangular beam samples during absorption and desorption of water. Correlation of water uptake, dynamic mechanical behaviour and transitory stress fields, has allowed to make some assumptions about the influence of the epoxy network on the swelling behaviour.

Mild hydrothermal conditioning prior to torrefaction and slow pyrolysis of low-value biomass

The aim of this research was to establish whether hydrothermal conditioning and subsequent thermochemical processing via batch torrefaction or slow pyrolysis may improve the fuel quality of grass residues. A comparison in terms of fuel quality was made of the direct thermochemical processing of the feedstock versus hydrothermal conditioning as a pretreatment prior to thermochemical processing. Hydrothermal conditioning reduced ash content, and particularly nitrogen, potassium and chlorine contents in the biomass. The removal of volatile organic matter associated with thermochemical processes can increase the HHV to levels of volatile bituminous coal. However, slow pyrolysis only increased the HHV of biomass provided a low ash content (<6%) feedstock was used. In conclusion, hydrothermal conditioning can have a highly positive influence on the efficiency of thermochemical processes for upgrading low-value (high-ash) biomass to a higher quality fuel.

The influence of a thermoplastic toughening interlayer and hydrothermal conditioning on the Mode-II interlaminar fracture toughness of Carbon/Benzoxazine composites

Carbon fibre/Benzoxazine laminates with and without non-woven polyamide (PA) fibre veils at the interlaminar regions were manufactured using vacuum assisted resin transfer moulding (VARTM). The effect of the interlaminar thermoplastic veils on the Mode-II critical strain energy release rate (GIIC), under both wet and dry conditions, was determined using two commercially available Benzoxazine resins: a toughened system and an untoughened system. In all samples the toughened system outperformed the untoughened system. The overall resistance to Mode-II crack growth was significantly improved by the inclusion of the interlaminar veils due to an increase in the thickness of the matrix-rich interlaminar region, plastic deformation of the PA fibres and a crack-pinning mechanism. Moisture caused an increase in matrix ductility, which improved the resistance to crack initiation; however, this was counteracted by a reduction in fibre/matrix interfacial strength causing a reduction in resistance to crack growth.

The influence of hydrothermal conditioning on the Mode-I, thermal and flexural properties of Carbon/Benzoxazine composites with a thermoplastic toughening interlayer

Carbon/Benzoxazine laminates with and without non-woven thermoplastic fibrous polyamide (PA) veils at the interlaminar regions were manufactured using Vacuum Assisted Resin Transfer Moulding (VARTM). The effect of the interlaminar thermoplastic veils on the Mode-I strain energy release rate (GIC), flexural stiffness, glass transition temperature (Tg) and water absorption behaviour was determined using two commercially available Benzoxazine resins. Despite an increase in the maximum moisture content, the veils greatly enhanced GIC by an increase in fibre bridging of PA fibres, with concurrent reductions in flexural stiffness. Water ingress resulted in large reductions in the Tg, although no significant change was observed due to the PA interlayers. Fibre bridging and fibre pull-out were the main mechanisms by which the veils assisted in resisting delamination. The presence of the water was observed to degrade mechanical properties due to a reduction in fibre/matrix interfacial strength, molecular degradation and plasticisation of the matrix.

Effects of hydrothermal conditioning and mechanical dewatering on ash melting behaviour of solid fuel produced from European semi-natural grasslands

Biomass from high nature value grasslands is a potential resource for renewable energy production, since its use as forage is declining due to decreasing livestock levels in many European regions. This study investigated silages and the derived press cakes after hydrothermal conditioning and mechanical dewatering from 18 European grassland sites on fuel relevant parameters. Through silage treatment high reductions of the concentration in the fuel of more than 73% of Cl, K and Na were obtained. Experimental investigation of the ash melting behaviour showed an increase of the ash softening temperature (AST) from approximately 1000°C for the ash from the silage to 1050°C for the press cake ashes. At the spherical, hemisphere and flow temperature differences between silage and press cake ashes were even bigger and ranged from 63 to 67K. Linear regression models, which were based on the fuel content of K, Ca, Si, Al and Na, were able to predict the AST with high accuracy (R2=0.88–0.89). Models showed that an increasing content of K led to decreasing AST. By contrast, AST was positively influenced by increasing contents of Ca. The effect of Si depended on the content of alkalis and earth alkalis.

Enhancing sewage sludge dewaterability by bioleaching approach with comparison to other physical and chemical conditioning methods

The sewage sludge conditioning process is critical to improve the sludge dewaterability prior to mechanical dewatering. Traditionally, sludge is conditioned by physical or chemical approaches, mostly with the addition of inorganic or organic chemicals. Here we report that bioleaching, an efficient and economical microbial method for the removal of sludge-borne heavy metals, also plays a significant role in enhancing sludge dewaterability. The effects of bioleaching and physical or chemical approaches on sludge dewaterability were compared. The conditioning result of bioleaching by Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans on sludge dewatering was investigated and compared with the effects of hydrothermal (121°C for 2 hr), microwave (1050 W for 50 sec), ultrasonic (250 W for 2 min), and chemical conditioning (24% ferric chloride and 68% calcium oxide; dry basis). The results show that the specific resistance to filtration (SRF) or capillary suction time (CST) of sludge is decreased by 93.1% or 74.1%, respectively, after fresh sludge is conditioned by bioleaching, which is similar to chemical conditioning treatment with ferric chloride and calcium oxide but much more effective than other conditioning approaches including hydrothermal, microwave, and ultrasonic conditioning. Furthermore, after sludge dewatering, bioleached sludge filtrate contains the lowest concentrations of chroma (18 times), COD (542 mg/L), total N (TN, 300 mg/L), NH4+-N (208 mg/L), and total P (TP, 2 mg/L) while the hydrothermal process resulted in the highest concentration of chroma (660 times), COD (18,155 mg/L), TN (472 mg/L), NH4+-N (381 mg/L), and TP (191 mg/L) among these selected conditioning methods. Moreover, unlike chemical conditioning, sludge bioleaching does not result in a significant reduction of organic matter, TN, and TP in the resulting dewatered sludge cake. Therefore, considering sludge dewaterability and the chemical properties of sludge filtrate and resulting dewatered sludge cakes, bioleaching has potential as an approach for improving sludge dewaterability and reducing the cost of subsequent reutilization or disposal of dewatered sludge.