Coagulation and sludge recovery using titanium tetrachloride as coagulant for real water treatment: A comparison against traditional aluminum and iron salts

Performance study of fly-ash-derived coagulant in removing natural organic matter from drinking water: synthesis, characterization, and modelling

This study is an attempt to develop a liquid coagulant using fly ash (FAC) for removing natural organic matter (NOM) from drinking water systems. Acid-alkali leaching and polymerization technique was used for developing FAC. Characterization of FAC was performed using Fourier-transform infrared spectroscopy (FESEM), field emission scanning electron microscopy (FTIR), and X-ray diffraction (XRD) to assess the surface morphology and functional groups present. FE SEM analysis revealed uneven, coarse, and irregular structure with numerous pores, an indicative of their high adsorption capacity. XRD study revealed that Al, Fe, and Si are the major constituent group of FAC. FAC demonstrated excellent potential in removing THMs precursors: dissolved organic carbon (84.46%), UV₂₅₄ (90.57%), and turbidity (96.85%) from the drinking water systems. Charge neutralization followed by adsorption is the main mechanism behind NOM removal. Moreover, FAC also showed good capability in minimizing the reactivity of NOM (ASI-72.86%) towards THM formation. FAC proved to be a good alternative for conventional coagulant used in drinking water treatment and can be effectively used for reducing NOM content of raw water which leads to the formation of THMs on chlorination.

The influence of environmental factor on the coagulation enhanced ultrafiltration of algae-laden water: Role of two anionic surfactants to the separation performance

With the acceleration of urbanization and the improvement of people's living standards, more chemicals that humans rely on are entering the city and surrounding water bodies. Anionic surfactants are one of the essential products for human beings. It is also one of the inducements that cause the eutrophication. The algae-laden water caused by eutrophication is a headache in the traditional water treatment process. To solve the problem, ultrafitration combined process was widely investigated to treat the algae-laden water. The presence of stimuli, low concentration anionic surfactant, probably interfere the performance of ultrafiltration process during algae-laden water treatment. In this study, the influence of two typical anionic surfactants, sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (LAS), on the performance of coagulation-enhanced ultrafiltration was investigated. The aluminum sulfate hydrate and iron sulfate hydrate were respectively employed as coagulant. Based on the residual turbidity and zeta potential, 4 mg/L Al and 8 mg/L Fe were determined as the optimal coagulant dosage. The floc morphology confirmed that Al-algae flocs with lower fractal dimension (D_f) were looser and more porous compared to Fe-algae flocs. More coagulant was depleted by LAS due to the better hydrophobicity of LAS. During the filtration process, LAS caused a larger flux reduction compared with SDS regardless of the coagulant that was used. More organic compounds penetrate into membrane pores and block the pores with the presence of LAS since algal cell aggregation was weakened. Finally, the rejection of organic compounds by the coagulation-enhanced ultrafiltration process was studied, and the co-existing surfactants can cause effluent deterioration. Therefore, the presence of surfactants has a negative effect to the ultrafiltration treatment of algae-laden water.

Titanium-Containing Coagulants in Wastewater Treatment Processes in the Alcohol Industry

As part of the work, studies of the quality of wastewater from alcohol production were carried out; the main characteristics were determined, such as the charge of dispersed particles and the content of organic compounds and fats. A comparison is made of the effectiveness of titanium salts, traditional aluminum, and iron-containing coagulants. It has been established that titanium salts are much more effective than traditional reagents, but their high cost significantly limits the scope of their application. The possibility of increasing the efficiency of traditional coagulants by adding various titanium salts in an amount of up to 10% of the mass has been proved. It has been established that the addition of titanium compounds to aluminum or iron-containing coagulants makes it possible to increase the cleaning efficiency by an average of 10–20% while a significant reduction in the dose of reagents is possible, which will have a positive effect on the cost of the cleaning process. It was found that the addition of titanium salts to a coagulant based on aluminum sulfate allows not only an increase in the cleaning efficiency but also further intensifies the processes of sedimentation and filtration of coagulation sludge, which will significantly reduce the size of the treatment equipment and reduce capital costs.

Visible light activation of photocatalysts formed from the heterojunction of sludge-generated TiO2 and g-CN towards NO removal

The feasibility of preparing TiO₂/g-CN heterojunction from Ti-incorporated dried dye wastewater sludge is explored in this study. Two reaction routes of composite formation were evaluated. In the initial approach, one-step calcination of dried sludge and melamine mixture @600 °C was carried out. Detailed morphological and chemical characterizations showed that the one-step calcination route did not create TiO₂/g-CN composites; instead, only N-doped anatase TiO₂ composites were formed. Moreover, due to the non-uniform composition of organic content in the dried sludge, it was not easy to control the N doping level by varying melamine content (0-100%) in the precursor mix. However, successful formation of anatase TiO₂ and g-CN was observed when a two-step calcination route was followed, i.e., via synthesis of anatase TiO₂ from dried sludge, and later development of heterojunction by calcining (@550 °C) the TiO₂ and melamine mixture. X-ray diffraction along with infrared and X-ray photoelectron spectroscopy verified the effective heterojunction. In addition, maximum atmospheric NO removal under UV and visible light were observed for the prepared composite when the melamine content in the precursor mixture was 70%. After 1 h of UV and visible light irradiation, the best TiO₂/g-CN composite removed 25.71% and 13.50% of NO, respectively. Optical characterization suggested that the enhanced NO oxidation under UV/visible light was due to the bandgap narrowing and diminished photogenerated electron-hole recombination.

Pilot-scale field study for vanadium removal from mining-influenced waters using an iron-based sorbent

This study investigated the removal of vanadium from mining waters at a closed mine site (Mustavaara, Finland) using granular ferric oxyhydroxide (CFH-12) on pilot scale. Two filter systems, pilot A and pilot B, were placed in different streams, where the influent in pilot A contained a higher and very variable vanadium concentration (6.46-99.1 mg/L), while the pilot B treated influent had lower vanadium concentrations (0.443-2.33 mg/L). The operation periods were 51 days for pilot A and 127 days for pilot B. Water quality analyses revealed that vanadium was efficiently captured in the filter system in both pilots. X-ray fluorescence analysis revealed that the filter beds were not fully saturated with vanadium. X-ray photoelectron spectroscopy confirmed that oxidised vanadium (5⁺) existed in the used CFH-12 and the carbon content in the used material had increased due to the adsorbed organic compounds. For comparison, lab-scale coagulation experiments were conducted using ferric sulphate for the influent of pilot A (the sampled batch contained 15.9 mg/L V). The optimum coagulant dosage was 350 mg/L (>93% vanadium removal) at the original pH (7.8-7.9) of the influent, whereas the required coagulant amount decreased when the influent pH was adjusted to 4.6-4.8.

Characterization of titanium oxide optical band gap produced from leachate sludge treatment with titanium tetrachloride

This study investigated the coagulation performance of titanium tetrachloride (TiCl₄) for leachate treatment and preparation of titanium oxide (TiO₂) from generated sludge through calcination process at different temperatures and times. TiCl₄ with chitosan as coagulant aid employed to perform coagulation process on Alor Ponhsu Landfill leachate. Further calcination process was done to synthesize TiO₂ from produced sludge for photocatalytic applications. The studied factors included pH, TiCl₄ dosage, and chitosan dosage. The results indicated that maximum reduction in suspended solids was 92.02% at pH 4, 1200 mg/L TiCl₄, and 250 mg/L chitosan addition, and maximum reduction in chemical oxygen demand was 71.92% at experimental condition of 1200 mg/L TiCl₄ and 500 mg/L chitosan with pH 10. The maximum and minimum band gaps of prepared TiO₂ achieved at 3.35 eV and 2.75 eV, respectively. Morphology and phase analysis of prepared TiO₂ characterized using scanning electron microscope (SEM) and X-ray diffraction (XRD). The XRD spectrums showed the anatase phase at lower calcination temperature and the rutile phase at elevated temperature. The photocatalysis activity of produced TiO₂ investigated under UV irradiation and showed almost fast degradation similar to commercial TiO₂. The results indicated that TiO₂ powder was successfully prepared from generated sludge from TiCl₄ coagulation for photocatalytic applications.

Recycling of titanium-coagulated algae-rich sludge for enhanced photocatalytic oxidation of phenolic contaminants through oxygen vacancy

In the 21st century, sludge disposal and resource recycling are global issues. Titanium coagulation has received increasing attention due its strong coagulation capability and sludge recycling. Titanium coagulation is highly efficient for the treatment of algae-laden micro-polluted surface water; however, the safe disposal of titanium-coagulated algae-rich sludge remains a challenge. Here, we report on the recycling of titanium-coagulated algae-rich sludge for the production of functional TiO₂ nanoflowers (TNFs) through a simple hydrothermal and calcination process. Anatase TNFs (particle size of 10-15 nm) with petal-like structures (mesoporous), relatively high specific surface areas, i.e. 299.4 m²g^-1, and low band gaps, i.e. 2.67 eV (compared to P-25), were obtained. Additionally, oxygen vacancy (OV) was generated on the surface of the recycled TNFs based on electron paramagnetic resonance (EPR) results, which were verified by the first-principles calculations within density-functional theory. These TNFs display high photocatalytic performance for the degradation of diverse phenolic organic contaminants, such as bisphenol A, diphenyl phenol, p-tert-butyl phenol, and resorcinol, i.e. > 95%, under mild ultraviolet light irradiation and without any sacrificial reagents. Formation of OV on TNFs not only efficiently inhibited the recombination of photo-generated electrons and holes but also facilitated contaminant adsorption and photo-generated electron transfer on the surface of the recycled TNFs, thereby promoting the generation of holes and hydroxyl and superoxide radicals which were regarded as the reactive oxygen species for attacking contaminants in the reactions. This study proposes a new perspective on recycling chemical-coagulated sludge for producing functional nanomaterials as photocatalysts.

Preparation and Characterization of Photoactive Anatase TiO2 from Algae Bloomed Surface Water

The purpose of the study was to effectively treat algae bloomed water while using a Ti-based coagulant (TiCl4) and recover photoactive novel anatase TiO2 from the flocculated sludge. Conventional jar tests were conducted in order to evaluate the coagulation efficiency, and TiCl4 was found superior compared to commercially available poly aluminum chloride (PAC). At a dose of 0.3 g Ti/L, the removal rate of turbidity, chemical oxygen demand (COD), and total phosphorus (TP) were measured as 99.8%, 66.7%, and 96.9%, respectively. Besides, TiO2 nanoparticles (NPs) were recovered from the flocculated sludge and scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX), and X-ray diffraction (XRD) analysis confirmed the presence of only anatase phase. The recovered TiO2 was found to be effective in removing gaseous CH3CHO and NOx under UV-A lamp at a light intensity of 10 W/m2. Additionally, the TiO2 mixed mortar blocks that were prepared in this study successfully removed atmospheric nitrogen oxide (NOx) under UV irradiance. This study is one of the first to prepare anatase TiO2 from flocculated algal sludge and it showed promising results. Further research on this novel TiO2 concerning internal chemical bonds and shift in the absorbance spectrum could explore several practical implications.

Preparation and characterization of TiO2 generated from synthetic wastewater using TiCl4 based coagulation/flocculation aided with Ca(OH)2

This study focused on the preparation of undoped and Ca-doped titania from flocculation generated sludge. Initially, TiCl₄ was utilised to perform coagulation and flocculation in synthetic wastewater and an optimised dose of coagulant was determined by evaluating the turbidity, dissolved organic carbon (DOC) and zeta potential of the treated water. Later, using Ca(OH)₂ as a coagulant aid, the effects on effluent pH, turbidity and DOC removal were investigated. Both Ca-doped and undoped anatase TiO₂ were prepared from the flocculated sludge for morphological and photocatalytic evaluation. During the standalone use of TiCl₄, maximum turbidity and DOC removal were found at 11.63 and 14.54 mg Ti/L, respectively. At the corresponding coagulant dose, rapid deprotonation of water caused the pH of the effluent to reach below 3.77 mg Ti/L. Whereas, when using Ca(OH)₂ as a coagulant aid, a neutral pH (7.26) was attained at a simultaneous dosing of 32.40 mg Ca/L and 14.54 mg Ti/L. When aided with Ca(OH)₂, the turbidity removal was further increased by 54.28% and the DOC removal was somewhat similar to the standalone use of TiCl₄. TiO₂ was prepared by incinerating the collected sludge at 600 °C for 2 h. Both XRD and SEM analysis were conducted to observe the morphology of the prepared titania. The XRD pattern of the TiO₂ showed only an anatase phase along with the presence of a high atomic proportion of Ca (4.14%). Consequently, a high amount of Ca atoms inhibited the level of TiO₂ phase and no obvious presence of CaO was observed. The prepared Ca-doped TiO₂ at the optimised dose of Ca(OH)₂ was found to be inferior to the undoped TiO₂ during the photodegradation of acetaldehyde. However, a reduced dose of Ca(OH)₂ (<15 mg Ca/L) exhibited a substantial increase in photoactivity under UV irradiance.

Removal of natural organic matter for wetland saline water desalination by coagulation-pervaporation

The high number of natural organic matter contain in wetland water may cause its water has brown color and not consumable. In other hand, intrusion of sea water through wetland aquifer create water become saline, notably on hot season. Coagulation is effective method to applied for removing of natural organic matter. However, it could not be used for salinity removal. Hence combination of coagulation and pervaporation process is attractive method to removing both of natural organic matter and conductivity of wetland saline water. The objective of this works is to investigate optimum coagulant doses for removing organic matter by coagulation process as pretreatment and to analysis performance of coagulation-pervaporation silica-pectin membrane for removing of organic matter and conductivity of wetland saline water. Coagulation process in this work carried out under varied aluminum sulfate dose 10-60 mg.L-1. Silica-pectin membrane was used for pervaporation process at feed temperature ~25 °C (room temperature). Optimum condition of pretreatment coagulation set as alum dose at 30 mg.L-1 with maximum removal efficiency 81,8 % (UV254) and 40 % (conductivity). In other hand, combining of coagulation-pervaporation silica-pectin membrane shows both of UV254 and salt rejection extremely good instead without pretreatment coagulation of 86,8 % and 99,9 % for UV254 and salt rejection respectively. Moreover, water flux of silica-pectin membrane pervaporation with coagulation pretreatment shown higher 17,7 % over water flux of wetland saline water without pretreatment coagulation. Combining of coagulation and pervaporation silica-pectin membrane is effective to removing both of organic matter and salinity of wetland saline water at room temperature.

Reduction of organic matter and disinfection byproducts formation potential by titanium, aluminum and ferric salts coagulation for micro-polluted source water treatment

Typical Chinese source water has high content of low molecular weight and aromatic protein-like organic matter which is difficult to remove and poses a great challenge to conventional coagulation/flocculation. To investigate coagulation performance of this typical water, this research focused on organic matter removal characteristics and the associated disinfection byproducts formation potentials (DBPFPs) during the coagulation process by titanium salts compared with traditional aluminum and ferric salts. Results showed that based on the dissolved organic matter (DOM) removal, the optimal coagulant dosages of AlCl₃, FeCl₃ and TiCl₄ were 0.5 mM and the optimal initial pH values were 8, indicating that the DOM in the typical Chinese water could be effectively removed through sweeping and adsorption by metal hydroxides rather than the complexation and charge neutralization effect under acidic conditions. Compared these three coagulants, the highest ultra violet absorbance at 254 nm removal rate of 72.9% was achieved by TiCl₄. The three-dimensional excitation emission matrix results showed that the removal ability of humic acids by AlCl₃ was poorer than FeCl₃ and TiCl₄. The removal rate of low molecular weight components (1600 Da) by TiCl₄ was 20% higher than using AlCl₃ and 14% higher than FeCl₃. Comparing with AlCl₃ and FeCl₃, TiCl₄ had a better performance on the control of DBPFPs, especially for chloroform and dichloroacetic acid, due to its higher removal ability of aromatic organics. The trihalomethane formation potentials removal rate by TiCl₄ was three times higher than that by AlCl₃ and twice by FeCl₃, by which could be inferred that titanium salts achieved better removal of low molecular weight organic matter than aluminum and ferric salts.

Wet flue gas desulfurization wastewater treatment with reclaimed water treatment plant sludge: a case study

To upgrade a wet flue gas desulfurization (FGD) wastewater treatment process in a typical thermal power plant (TPP) in Hunan province, China, a new concept for reusing polyaluminum chloride (PAC)-based water treatment plant sludge (WTPS) as a coagulant is proposed. Results show that, for an optimal WTPS dosage of 1,000 mg/L, the corresponding removal capacities for suspended solids (SS) and chemical oxygen demand (COD) from the practical FGD wastewater were 58.3% and 40.3%, respectively. Through an advanced treatment with a dosage of 50 mg/L of PAC, pH of 9, and stirring of 150 r/min for 60 s and 50 r/min for 15 min, the total removal efficiencies of SS, COD, and total cadmium (Cd) from the FGD wastewater were 93.7%, 88.8%, and 84.6%, respectively. Therefore, a new modification process (that involves mixing with WTPS - slag cleaner - neutralization - coagulation - sedimentation) was proposed. The proposed process is economically superior, and the average cost for the FGD wastewater treatment was only 1.08 USD/t. This could provide a cost-effective alternative process for upgrading FGD wastewater treatment facilities of TPPs.

Natural organic matter as precursor to disinfection byproducts and its removal using conventional and advanced processes: state of the art review

Natural organic matter (NOM) is ubiquitous in the aquatic environment and if present can cause varied drinking water quality issues, the major one being disinfection byproduct (DBP) formation. Trihalomethanes (THMs) are major classes of DBP that are formed during chlorination of NOM. The best way to remove DBPs is to target the precursors (NOM) directly. The main aim of this review is to study conventional as well as advanced ways of treating NOM, with a broad focus on NOM removal using advanced oxidation processes (AOPs) and biofiltration. The first part of the paper focuses on THM formation and removal using conventional processes and the second part focuses on the studies carried out during the years 2000-2018, specifically on NOM removal using AOPs and AOP-biofiltration. Considering the proven carcinogenic nature of THMs and their diverse health effects, it becomes important for any drinking water treatment industry to ameliorate the current water treatment practices and focus on techniques like AOP or synergy of AOP-biofiltration which showed up to 50-60% NOM reduction. The use of AOP alone provides a cost barrier which can be compensated by the use of biofiltration along with AOP with low energy inputs, making it a techno-economically feasible option for NOM removal.

Characterization and treatment of landfill leachate membrane concentrate by Fe2+/NaClO combined with advanced oxidation processes

Landfill leachate membrane concentrate (LLMC) is a type of non-biodegradable wastewater intercepted by the membrane filtration of the landfill leachate membrane bioreactor (MBR) effluent. The concentrations of chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N) in the LLMC collected from a landfill in Beijing were determined to be 4700 mg/L and 487 mg/L, 2–5 times higher than those in the MBR effluent. The photoelectro oxidation (PEO) followed with the NaClO enhanced Fe²⁺ coagulation were more effective for the removal of COD than the Fenton oxidation followed with the enhanced coagulation. The final removal efficiencies of COD, UV₂₅₄, NH₄⁺-N and color degree were 86%, 95%, 93% and 95% with Fe²⁺ (90 mmol/L) and NaClO (60 mmol/L, Fe²⁺:NaClO = 1.5:1), and PEO for 3 hours with a current density of 400 A/m². Due to the existence of Cl⁻, the chlorinated intermediates, which would be more toxic, were detected in the PEO treatment. However, the intermediates could be eliminated finally. As a result, the NaClO enhanced Fe²⁺ coagulation treatment combined with PEO treatment was efficient for the treatment of LLMC.

The removal of silver nanoparticle by titanium tetrachloride and modified sodium alginate composite coagulants: floc properties, membrane fouling, and floc recycle

In this study, a modified sodium alginate (MSA) composited with TiCl₄ was used to treat the synthetic Ag nanoparticles (AgNPs) water in coagulation-ultrafiltration process. The floc properties and membrane fouling of TiCl₄ and MSA composite coagulants (TiCl₄ + MSA) were investigated by a laser diffraction instrument and ultrafiltration fouling model. The recycle of the AgNP-containing flocs was evaluated by XRD and photocatalytic experiments. The results showed that TiCl₄ + MSA could achieve better coagulation performance than TiCl₄ alone with AgNP and DOC removal up to 97 and 59% at the optimum condition (pH = 5 and dosage = 12 mg TiCl₄/L). TiCl₄ + MSA produced larger and looser flocs than TiCl₄ and TiCl₄ + SA composite coagulant (TiCl₄ + SA), which was benefit for the inhibition of subsequence membrane fouling. The strongly attached external fouling resistance (R_ef-s) and the reversible internal fouling resistance (R_if-r) of TiCl₄ + MSA were only 43 and 39.2% of those achieved by TiCl₄ at the optimal coagulation condition. Besides, the adopted AgCl-TiO₂ could be recycled from AgNP-containing flocs. And MSA could promote the form of TiO₂ anatase. It gives us a possible way for silver nanoparticle recycle.

Synthesis of a cationic polyacrylamide by a photocatalytic surface-initiated method and evaluation of its flocculation and dewatering performance: nano-TiO2 as a photo initiator

In the face of complex water quality changes, the application of existing cationic polyacrylamide has been largely limited. In this study, a series of cationic polyacrylamides (TPADs) with excellent flocculation/dewatering performance and low dosage were synthesized through photocatalytic surface initiation using acrylamide (AM) and acryloyloxyethyl trimethylammonium chloride (DAC) as monomers and nano-TiO₂ as an initiator. Characterization using Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (¹H NMR) spectroscopy, thermogravimetric/differential scanning calorimetry (TG/DSC) and scanning electron microscopy (SEM) was used to analyze the structural and morphological properties of TPADs. The initiation mechanism was described and the study on the properties of TPADs shows that the initiation method could obtain the copolymer with extra-high intrinsic viscosity. Furthermore, the flocculation and dewatering performance of TPADs and PADs were investigated in the micro-polluted low turbidity water flocculation test and sludge dewatering test. The application experimental results indicated that TPADs showed satisfactory turbidity removal and sludge dewatering performance by virtue of strong charge neutralization and a bridging effect. The excellent flocculation/dewatering performance was attributed to the photocatalytic surface-initiated method and the nano-TiO₂ initiator. Therefore, it is expected to open up new initiation methods in the synthesis of polymeric flocculants for a broad variety of applications.

In the face of complex water quality changes, the application of existing cationic polyacrylamide has been largely limited.

Removal of natural organic matter in drinking water treatment by coagulation: A comprehensive review

Natural organic matter (NOM) is a complex matrix of organic substances produced in (or channeled to) aquatic ecosystems via various biological, geological and hydrological cycles. Such variability is posing a serious challenge to most water treatment technologies, especially the ones designed to treat drinking water supplies. Lately, in addition to the fluctuating composition of NOM, a substantial increase of its concentration in fresh waters, and also municipal wastewater effluents, has been reported worldwide, which justifies the urgent need to develop highly efficient and versatile water treatment processes. Coagulation is among the most applied processes for water and wastewater treatment. The application of coagulation to remove NOM from drinking water supplies has received a great deal of attention from researchers around the world because it was efficient and helped avoiding the formation of disinfection by products (DBPs). Nonetheless, with the increased fluctuation of NOM in water (concentration and composition), the efficiency of conventional coagulation was substantially reduced, hence the need to develop enhanced coagulation processes by optimizing the operating conditions (mainly the amount coagulants and pH), developing more efficient inorganic or organic coagulants, as well as coupling coagulation with other water treatment technologies. In the present review, recent research studies dealing with the application of coagulation for NOM removal from drinking water supplies are presented and compared. In addition, integration schemes combining coagulation and other water treatment processes are presented, including membrane filtration, oxidation, adsorption and others processes.

Effects of ultrasound pretreatment on the characteristic evolutions of drinking water treatment sludge and its impact on coagulation property of sludge recycling process

Large amounts of drinking water treatment sludge (DWTS) are produced during the flocculation or flotation process. The recycling of DWTS is important for reducing and reclaiming the waste residues from drinking water treatment. To improve the coagulation step of the DWTS recycling process, power ultrasound was used as a pretreatment to disintegrate the DWTS and degrade or inactivate the constituents that are difficult to remove by coagulation. The effects of ultrasound pretreatment on the characteristics of DWTS, including the extent of disintegration, variation in DWTS floc characteristics, and DWTS dewaterability, were investigated. The capacity of the recycling process to remove particulates and organic matter from low-turbidity surface water compared to a control treatment process without DWTS was subsequently evaluated. The coagulation mechanism was further investigated by analyzing the formation, breakage, and re-growth of re-coagulated flocs. Our results indicated that under the low energy density applied (0.03-0.033 W/mL) for less than 15 min at a frequency of 160 kHz, the level of organic solubilization was less elevated, which was evidenced by the lower release of proteins and polysaccharides and lower fluorescence intensities of humic- and protein-like substances. The applied ultrasound conditions had an adverse effect on the dewaterability of the DWTS. Ultrasound pretreatment had no significant impact on the pH or surface charge of the DWTS flocs, whereas particle size decreased slightly and the specific surface area was moderately increased. The pollution removal capacity decreased somewhat for the recycled sonicated DWTS treatment, which was primarily ascribed to organic solubilization rather than variability in the floc characteristics of sonicated DWTS. The main coagulation mechanism was floc sweeping and physical adsorption. The breakage process of the flocs formed by the recycling process displayed distinct irreversibility, and the flocs were stronger and more resistant to breakage compared to those from the control treatment.