Search Results (119)

Although coagulation can enhance sludge dewatering performance, it often leads to dense flocs, hindered water release, and secondary pollution of the sludge cake. In this study, three types of biochar-based skeleton materials, tea waste-derived biochar (TB), PAC sludge-derived biochar (PB), and their mixture (MB), were employed in combination with polyaluminum chloride (PAC) to improve sludge permeability and water release capacity. The results showed that PAC alone reduced the water content (Wc) and capillary suction time (CST) of raw sludge (RS) from 79.07% and 97.45 s to 69.45% and 42.30 s, respectively. In contrast, biochar–PAC composite conditioning achieved further enhancement. Among them, the TBP group (10% DS TB + 4% DS PAC) exhibited the best performance, with Wc and CST reduced to 58.73% and 55.65 s, reaching the threshold for deep dewatering (Wc < 60%). Low-field nuclear magnetic resonance (LF-NMR) analysis revealed an enhanced transformation from bound to free water, improving water mobility. Zeta potential and particle size analysis indicated that biochar promoted electrostatic neutralization and adsorption bridging. Rheological and EPS measurements demonstrated significant reductions in yield stress and apparent viscosity, alongside the enhanced release of proteins and polysaccharides into soluble EPS (S-EPS). Scanning electron microscopy and pore structure analysis further confirmed that biochar formed a stable porous skeleton (pore diameter up to 1.365 μm), improving sludge cake permeability. In summary, biochar synergizes with PAC through a “skeleton support–charge neutralization–adsorption bridging” mechanism, reconstructing sludge microstructure and significantly improving deep dewatering performance. Full article

A comparative study was conducted to investigate membrane fouling control and treatment performance using natural surface water as the feed source. The evaluated processes included: (1) direct filtration–tubular ceramic membrane (DF-TCM, control); (2) coagulation–tubular ceramic membrane (C-TCM); and (3) coagulation–tubular ceramic membrane with concentrate recycling (C-TCM-CR). Experimental results demonstrated that under constant flux operation at 75 L/(m²·h) for 8 h, the C-TCM-CR process reduced the transmembrane pressure (TMP) increase by 83% and 35% compared to DF-TCM and C-TCM, respectively. Floc size distribution analysis and cake layer characterization revealed that the C-TCM-CR process enhanced coagulation efficiency and formed high-porosity cake layers on membrane surfaces, thereby mitigating fouling development. Notably, the coagulation-assisted processes demonstrated improved organic matter removal, with 13%, 10%, and 10% enhancement in COD_Mn, UV₂₅₄, and medium molecular weight organics (2000–10,000 Da) removal compared to DF-TCM, along with a moderate enhancement in fluorescent substances removal efficiency. All three processes achieved over 99% turbidity removal efficiency, as the ceramic membranes demonstrate excellent filtration performance. Full article

HPMC, regulating slurry properties, is widely used in cement-based materials. Research on the application of HPMC in gangue slurry is still in its early stages. Moreover, the interactive effects of various factors on gangue slurry performance have not been thoroughly investigated. The work examined the effects of slurry concentration (X₁), maximum gangue particle size (X₂), and HPMC dosage (X₃) on slurry performance using response surface methodology (RSM). The microstructure of the slurry was characterized via scanning electron microscopy (SEM) and polarized light microscopy (PLM), while low-field nuclear magnetic resonance (LF-NMR) was employed to analyze water distribution. Additionally, industrial field tests were conducted. The results are presented below. (1) X₁ and X₃ exhibited a negative correlation with layering degree and slump flow, while X₂ showed a positive correlation. Slurry concentration had the greatest impact on slurry performance, followed by maximum particle size and HPMC dosage. HPMC significantly improved slurry stability, imposing the minimum negative influence on fluidity. Interaction terms X₁X₂ and X₁X₃ significantly affected layering degree and slump flow, while X₂X₃ significantly affected layering degree instead of slump flow. (2) Derived from the RSM, the statistical models for layering degree and slump flow define the optimal slurry mix proportions. The gangue gradation index ranged from 0.40 to 0.428, with different gradations requiring specific slurry concentration and HPMC dosages. (3) HPMC promoted the formation of a 3D floc network structure of fine particles through adsorption-bridging effects. The spatial supporting effect of the floc network inhibited the sedimentation of coarse particles, which enhanced the stability of the slurry. Meanwhile, HPMC only converted a small amount of free water into floc water, which had a minimal impact on fluidity. HPMC addition achieved the synergistic optimization of slurry stability and fluidity. (4) Field industrial trials confirmed that HPMC-optimized gangue slurry demonstrated significant improvements in both stability and flowability. The optimized slurry achieved blockage-free pipeline transportation, with a maximum spreading radius exceeding 60 m in the goaf and a maximum single-borehole backfilling volume of 2200 m³. Full article

Due to the lack of sophisticated instruments for monitoring sludge dewatering performance in certain wastewater treatment plants, there is an urgent need to develop cost-effective and rapidly deployable technologies for assessing sludge dewaterability. This study proposed an image-based approach to evaluate sludge dewaterability. Flocculation images of sludge were captured using a smartphone under controlled conditions and processed via MATLAB for grayscale adjustment, contrast enhancement, and size standardization. Fractal image analysis was employed to justify the selection of floc area (rather than floc equivalent diameter) for downstream analyses. Significant correlations were observed between the number of different sludge floc area range and key dewaterability parameters: The number of flocs in area range of 10⁻⁶–10⁻⁵ cm² showed a negative correlation with capillary suction time (CST) (regression coefficient (R) = −0.511, probability (p) < 0.05) and a positive correlation with median particle size (R = 0.470, p < 0.05); the number of flocs in area range of 10⁻⁵–10⁻⁴ cm² exhibited a stronger negative correlation with CST (R = −0.538, p < 0.05) and a positive correlation with median particle size (R = 0.480, p < 0.05). Further validation experiments using a laboratory-scale diaphragm filter press demonstrated that when the proportion of the number of flocs in area range of 10⁻⁵–10⁻⁴ cm² relative to the total number of flocs for conditioned sludge fell below 70%, the dewatered sludge cake achieved a water content of less than 60%. This study highlights the feasibility of using commercially available smartphones as a practical tool for evaluating sludge dewaterability. Full article

This study evaluated the combined effect of a cationic coagulant (Magnafloc 1727^®) and a high molecular weight anionic flocculant (SNF 604^®) on the settling properties, aggregate structure, and rheological behavior of synthetic tailings suspensions composed of kaolinite and quartz in industrial water at pH 11. Settling tests, focused beam reflectance measurement (FBRM), zeta potential measurement, and rheological characterization were used to analyze the system’s performance under different coagulant dosages (0–150 g/t), while keeping the flocculant dosage constant (20 g/t). The results indicated that the coagulant favored surface charge neutralization, shifting the zeta potential from −13.2 mV to +4.0 mV. This resulted in larger, more efficient flocs capturing fines, with a 46% turbidity reduction. FBRM analysis revealed a significant increase in aggregate size and a slight decrease in fractal dimension (from 2.35 to 2.20), consistent with larger volume structures and lower bulk density. Rheologically, a substantial increase in yield stress was observed, especially in 50 wt% suspensions, suggesting the development of a continuous flocculated network with greater mechanical strength. These findings highlight the importance of sequential chemical conditioning in clayey tailings and its impact on clarification efficiency and water recovery under alkaline conditions representative of industrial mining processes. Full article

Boehmite is an aluminum oxyhydroxide (AlO(OH)) and one of bauxite’s main mineral phases. This mineral is highly valued as an important source of aluminum for the metallurgical industry. However, the formation of synthetic boehmite has been observed in water treatment when aluminum anodes are used for electrocoagulation. This boehmite occurs in flocs that capture impurities from the water, but removing these flocs is a slow process. Therefore, the froth-flotation method was employed in the present study to float synthetic boehmite. This was achieved by evaluating the particle size of synthetic boehmite, generating microbubbles, and using an anionic collector system in a novel experimental setup. The results show that the surfactants sodium dodecyl sulfate (SDS) and potassium oleate (PO) favor the recovery of synthetic boehmite in different particle sizes, with the particle size favored related to the bubble size generated. It was noted that increasing the SDS concentration enabled the microbubbles to recover up to 95% of boehmite particles with diameters of less than 30 microns. Full article

The majority of microplastics (MPs) removed from urban wastewater during conventional treatments end up in sewage sludge (around 95%). There are not many studies focused on the retention of MPs in secondary sewage sludge. This study explores the amount and kind of MPs retained in secondary sludge from a municipal wastewater treatment plant (WWTP) and the factors affecting the entrapment of MPs within the sludge flocs. The most abundant MPs in the sludges were fibres (61%), and the majority were within the size range of 250–500 μm. In addition, the effect of solid concentration on MP retention in settled sludge was analysed by carrying out a mixing–settling test. Without the addition of any chemicals, a maximum MP retention efficacy of 63% was obtained for a total suspended solids (TSS) concentration of 5.33 g/L. The effect of adding FeCl₃ and non-ionic polyacrylamide (PAM) was also investigated, and the percentage of retained MPs increased to values of 82% and 70%, respectively (with only 0.63 g TSS/L). This improvement occurred predominantly in the case of fibres. The results suggest the possibility of adding chemicals before the secondary settling stage as a means of reducing MP contamination in treated water. Full article

Estuarine benthos, among other lifeforms of interest to water quality, can be sensitive to size-distributed suspended cohesive flocs. In such a context, tide-dependent floc mass distributions in the Tamar Estuary in the UK are revisited. At the field site close to maximum turbidity, time-series of the water level, current velocity, salinity, and suspended sediment concentration (SSC) were recorded in 1998 over several tidal cycles. Concurrently, at selected times and elevation, floc mass distributions were derived from in situ observations of the SSC, floc diameters, and settling velocities. A previously developed time-dependent model, revised to account for both multiclass floc aggregation/disaggregation and bed sediment exchange by erosion and deposition, is applied to simulate mass distributions during ebb/flood cycles on 24 June and 5 August. Although the model does not account for the density effects of salinity or sediment advection, limited comparisons between simulated and observed mass distributions indicate generally good agreement in median diameter prediction on both days. This concurrence is due to the primary role of suspended floc dynamics and only a secondary contribution from bed sediment exchange in governing floc properties. For a better prediction of the SSC variation with the tide, the effects of salinity and advection can be incorporated by coupling the modeled floc dynamics with a suitable multi-dimensional hydrodynamic code. Full article

The tubular flocculation reactor is a new and efficient device for treating algae-containing wastewater. The introduction of bubbles during the reaction process can effectively shorten the time required for floc separation. However, the impact of bubbles on floc formation and removal in the tubular flocculation reactor is not well understood. To further clarify the effect of bubbles on the reactor’s operation, this study employed a uniform experimental design, varying the flow rate, chemical dosage, bubble reaction distance, and bubble injection rate in the reactor to examine the influence of bubbles under different operating conditions. The results indicated that as the bubble reaction distance increased from 0 m to 7.6 m, the removal efficiency increased from 60% to 70%, the floc size increased from 160 μm to 165 μm, and the fractal dimension decreased from 2.1 to 1.9. When the bubble volume increased from 5% to 30%, the removal efficiency increased from 50% to 80%. Under constant bubble conditions, the rising speed of the flocs increased from 0.4 mm·s⁻¹ to 1.2 mm·s⁻¹, while the removal efficiency increased from 30% to 90%. A logarithmic correlation was observed between the rising speed and removal efficiency. A linear relationship was found between the floc rising speed and the floc size, with floc size increasing from 200 μm to 800 μm and the rising speed increasing from 0.4 mm·s⁻¹ to 2.3 mm·s⁻¹. An exponential relationship was found between the fractal dimension and the rising speed, with the rising speed decreasing from 2.3 mm·s⁻¹ to 0.4 mm·s⁻¹, while the fractal dimension increased from 1.93 to 2.02. Full article

The high-efficiency dewatering of ultra-fine tailings is one of the most prominent challenges in tailings thickening. The two-step shear flocculation process represents a promising practical method to achieve the dewatering of ultra-fine tailings. In this paper, a small self-made experimental device was used to simulate the two-step shear flocculation process of ultra-fine tailings, strengthening the effect of shear failure and shear coagulation, and we explored the mass fraction of ultra-fine tailings, floc structure size, floc strength, and regeneration performance of tailings slurry according to the variation in shear action in different stages. In addition, the synergistic mechanism of shear failure and shear coagulation in the two-step high-efficiency dewatering process of ultra-fine tailings was proposed. The results show that the dewatering of ultra-fine tailings was significantly improved by two-step flocculation, and the mass fraction of tailings can reach more than 71%. In the primary floc failure stage, the value of G₁T₁ should be higher than 100,000, and in the secondary floc regeneration stage, the value of G₂T₂ should be in the range of 7000~11,000. This paper provides a reference for the regulation of the shear mode and action range in the two-step flocculation process of ultra-fine tailings. Full article

Floc size distribution and settling velocities are crucial parameters for characterising cohesive sediments, as they influence how these sediments behave in various environmental settings. The accurate measurement of these properties is essential, with different methods available depending on the scope of the study. For long-term monitoring, in situ techniques based on laser diffraction are commonly used, while video microscopy techniques are preferred for shorter studies due to their ability to provide detailed information on individual particles. This study compares two high-magnification digital video camera setups, LabSFLOC-2 and FLOCCAM, to investigate the impact of particle concentration on settling velocity in flocculated sediments. Flocculated clay was introduced into settling columns, where both the size and settling velocities of the flocs were measured. The results obtained from both setups are in line with each other, even though the FLOCCAM was slightly more efficient at capturing images of small particles (of size less than 50 microns) and LabsFLOC-2 was better at detecting large size fraction particles (having a low contrast due to the presence of organic matter). Floc size and settling velocity measurements from both setups however exhibit mostly similar trends as a function of clay concentration and the same order of magnitudes for the recorded settling velocities. Full article

When an electric field is applied to or removed from colloidal particle aqueous dispersions, a reversible increase in sedimentation velocity of the colloidal particles, referred to as the Electrically Induced Rapid Separation (ERS) effect, is observed. While electrophoresis and other interfacial electrokinetic phenomena under applied electric fields are well-studied, the phenomena of particle aggregation and re-dispersion caused by the application and removal of the field remain largely unexplored despite their significance. Experiments using mixed aqueous dispersions of poly (methyl methacrylate) (PMMA) particles of different sizes revealed that applying an electric field induced the formation of co-flocs involving both large and small particles, significantly enhancing the sedimentation velocity. It was also observed that slight vibrational deformation hindered the ERS effect. Under uniform electrolyte concentration conditions, the ERS effect was found to depend on pH, with a stronger effect observed when the absolute value of the zeta potential was larger. These findings indicate that the presence of the electric double layer plays a crucial role in the manifestation of the ERS effect. The results of this study provide critical insights for the further application of the ERS effect. Full article

Biofloc technology (BFT) is an advanced aquaculture method that uses microbial communities to enhance water quality and support aquatic species cultivation. Our research aims to delve into the pivotal role of aeration intensity within BFT systems, revealing its influence on microbial community structures, water quality, and nutrient cycling for L. vannamei culture. Three aeration levels were set with intensities of V75 (75 L/min), V35 (35 L/min), and V10 (10 L/min). The results showed that the lowest aeration intensity (V10) resulted in larger floc sizes and a reduction in the 2D-fractal dimensions, indicating a decreased overall structural complexity of the bioflocs. In addition, water quality parameters, including total ammonia nitrogen and nitrite, remained low across all treatments, highlighting the water-purifying capacity of biofloc. While protein and lipid contents in biofloc did not differ significantly among treatments, docosahexaenoic acid (DHA) levels were highest in the V75 treatment, suggesting that higher aeration promotes the accumulation of essential fatty acids. RDA analysis revealed that microorganisms like Ruegeria sp. and Sulfitobacter mediterraneus negatively correlated with ammonia and nitrite levels, suggesting their key role in converting ammonia to nitrite and nitrate in marine nitrogen cycles. The functional annotation of metagenomes across different aeration levels showed the similarly active roles of microorganisms in nitrogen metabolism and protein synthesis. In conclusion, while variations in aeration intensity affect floc size and the accumulation of essential fatty acids in biofloc, they do not significantly impact overall water quality or core microbial functions in L. vannamei aquaculture. Future research should focus on the effects of aeration strategies on microbial community dynamics and the integration of these data with performance metrics in L. vannamei. These insights can help optimize biofloc cultivation and enhance environmental sustainability in the aquaculture industry. Full article

Effective coal slurry water solid–liquid separation is indispensable for the recycling and sustainable development of coal resources. The interaction between bubble and coal particles plays a critical role in the process of dewatering for clean coal. In this study, we firstly conducted a comprehensive investigation of the impact of froth on the interactions between coal particles by rheological measurement and particle aggregation behavior. Furthermore, the macroscopic dewatering performance of coal slurry in the presence of froth and its microscopic cake structure were investigated using the filtration test and X-ray microtomography (CT). It was found that the interaction between coal particles in the presence of froth was enhanced as a result of the dynamic shear value, combined with the large floc size and compact structure, which led to a higher cake moisture and higher filtration velocity. The CT results indicated that the enhanced interaction of particles in the presence of froth also led to a dense microstructure of the filter cake. The porosity of the filter cake decreased to 2.05% when the aeration time increased from 0 s to 90 s, the throat radius in the filter cake was reduced to 1.32 μm, and the number of throat passages was reduced to one third. Multiple blind pores and low coordination numbers led to a poor connectivity of the pore network and high moisture content. Full article

Turbidity flows are known to be affected by the density difference between sediment plumes and the surrounding water. However, besides density, other factors could lead to changes in flow propagation. Such a factor is the presence of suspended organic matter. Recently, it was found that flocculation does occur within plumes upon release of a sediment/organic matter mixture in a lock exchange flume. In the present study, mineral sediment (illite clay) was released into the outflow compartment containing water and synthetic organic matter (polyacrylamide flocculant). Even though the density of water was barely affected by the presence of flocculant, flow head velocity was observed to be larger in the presence of flocculant than without. Samples taken at different positions in the flume indicated that flocs were created during the small current propagation time (about 30–60 s) and that their sizes were larger with higher flocculant dosage. The size of flocs depended on their positions in the flow: flocs sampled in the body part of the flow were larger than the ones sampled at the bottom. All these properties are discussed as a function of sediment–flocculant interactions. Full article