Stable Flocs Research Articles

Depth filtration of dredged sediments via reduced iron driving persulfate sodium activation: Perspectives from technical viability, potential mechanism, and prospect assessment

The existing single-use conditioning agents for dredged sediments (DS) treatment were confronted with problems such as high cost, insufficient efficiency, or potential toxicity. The study, for the first time, utilized a heterogeneous process of reduced iron (RI)/Persulfate sodium (PS) to deeply filter DS and further uncovered the potential mechanism as well as raised the application prospect. The results showed that after 120 mg/g TSS RI with 40 mg/g TSS PS treatment, the water content (WC) of DS dropped from 75.4% (Blank) to 41.6%, which is obviously lower than that of traditional flocculant-treated DS reported. Mechanistic probe indicated that the strengthened filterability of DS is likely evoked by the sulfate radical (SO4●-)/hydroxyl radical (•OH) with the ferrous/ferric substances generated from RI/PS process. SO4●-/•OH damaged extracellular polymeric substances (EPS) along with their major ingredients and possibly disturbed cellulate physiology of DS, which further promoted the dissociation/liberation of bound-water and strengthened a trend toward fluidization but declined the hydrophilicity and stickiness of DS. Moreover, SO4●-/•OH may evoke the proteins conformation to unfold the hydrophobic spots, promoting the escape of untied water also. By extruding the electric-double layers and lowing the negative charge, Ferrous and/or ferric substances promotes the re-aggregation of disrupted DS particles, which potentially leads to the formation of dense & stable flocs through interaction of ferric substances with carboxyl and hydroxyl functional groups in DS, thus facilitating bound-water removal. The findings here not only deepen our understandings upon mechanisms of heterogeneous AOPs conditioning DS filterability but also offer a promising approach for DS treatment in the fields of solid waste management and water environment remediation.

Capture and flocculation of toxic cyanobacteria by amphiphilic peptide dendrimers for mitigating harmful blooms

Harmful and toxic cyanobacterial blooms in freshwater constitute critical environmental problems and are becoming more frequent as a consequence of global climate change. One mitigation strategy is flocculation, which could be achieved with treatment by highly efficient, non-toxic, and biodegradable agents. Here, we report two amphiphilic peptide dendrimers (AmPDs), KK2 and KK2K4, for the removal of the toxic and bloom-forming cyanobacterium Microcystis aeruginosa from freshwater. KK2 and KK2K4 are composed of a hydrophobic alkyl chain and a positively charged polylysine dendron of the first and second generation, respectively. Owing to electrostatic interactions with the negatively charged cell surface of M. aeruginosa, KK2 and KK2K4 could quickly capture the cyanobacterial cell population via flocculation at very low concentrations. When combined with the natural clay sepiolite, the two AmPDs were even more efficient in promoting cell flocculation. The most performant system, with 3.0 mg/L KK2K4 and sepiolite clay, could remove 97.1 % of M. aeruginosa within 15 min by forming stable flocs. Remarkably, such a system was able to trap toxin molecules released by cyanobacterial cells, thus limiting its destructive impact on ecosystems. This study demonstrates how self-assembling dendrimer materials can resolve cyanobacterial blooms, providing an innovative solution to this environmental challenge.

Polymeric Flocculation as a Sustainable Solution for Heavy Metal Removal from Leachate in Barka Landfill, Oman

Purpose: This study investigates the effectiveness of polymeric flocculation in removing heavy metals from leachate through filtration, sedimentation, and precipitation, aiming to separate and eliminate particulate matter. to separate and remove particulate matter. Method: This study investigated the use of alum and chitosan to remove heavy metals from leachate. The addition of a polymeric flocculant, chitosan, promoted the formation of stable flocs, which effectively removed heavy metals. Chitosan, a natural biopolymer, was found to be a promising alternative to synthetic polymers. Main Findings: The experimental results demonstrated that alum outperformed chitosan in terms of removing heavy metals. Under optimal conditions, an alum dosage of 6 mg/l at a pH of 6.23 resulted in copper and magnesium removal efficiencies of 84% and 92%, respectively. In contrast, the optimal chitosan dosage was 8 mg/l at a pH of 7.5, with copper and magnesium removal efficiencies of 43.1% and 91.8%, respectively. Implications: Leachate treatment reduces heavy metals and organic compounds, controls odors, and generates foam indicating the presence of gases like carbon dioxide and methane. These gases can be harnessed for clean energy production and green hydrogen development. harnessed for clean energy production and green hydrogen development. Novelty: This study is the first to scientifically analyze leachate treatment at the Barka landfill. Chitosan, a natural polymer, effectively removes suspended matter and heavy metals, reducing their concentrations. removes suspended matter and heavy metals, reducing their concentrations.

Light scattering study of algal floc growth and structure: alum vs. polymeric plant-derived flocculant.

The flocculation dynamics of Microcystis aeruginosa algal cultures using alum and aqueous Moringa oleifera seed extracts as flocculants were analyzed through light scattering and fractal analysis. Floc growth in continuously stirred M. aeruginosa suspensions, with cell densities ranging from 200 to 800 μg L-1 chlorophyll a (Chl a), exhibited distinct patterns in fractal dimension (dF) evolution relative to floc size: a smooth, monotonic increase; stochastic increase; and stabilization or leveling off. dF values ranged from 1.3 to 2.6, with floc diameters (D4,3 volume-weighted mean) spanning 30 to 300 μm. Alum (0.1 to 0.4 g L-1) induced fast diffusion-limited flocculation, initially producing lower dF values, which progressively increased due to structural rearrangement at a slower rate. In contrast, at sufficiently high concentrations (0.1 to 0.2 g L-1 BSA equivalent), M. oleifera seed proteins facilitated stable, high dF ≈ 2.0 early on, evidently through patch charge interactions. Flocs formed with alum were prone to shear-induced breakage, limiting both their size and stability, whereas M. oleifera extract produced larger, more stable flocs with greater resilience to shear due to robust particle network formation by the polymer. Both flocculants effectively treated 800 μg L-1 Chl a M. aeruginosa suspensions, but M. oleifera extract demonstrated better performance in terms of floc size at similar mass concentrations. These findings highlight the potential of Moringa seed extract as a sustainable and effective alternative to conventional flocculants like alum, offering insights into their mechanisms and performance in flocculation processes.

Chelated heavy metals removal by in-situ formed Fe(II) and Fe(III) iron (oxy)hydroxides: Mechanism and performance

For more than a century, coagulation-precipitation using Fe(II) and Fe(III) are ubiquitous in wastewater treatment, however, a systematic understanding of the underlying mechanism and their performance toward chelated heavy metals (e.g. CuII-EDTA) is still lacking. In this study, we therefore investigate the efficiency of Fe(II) and Fe(III) salts coagulation-precipitation, the properties (coagulation and crystallization behavior) of in-situ formed iron (oxy)hydroxides and explore the reaction mechanism using a suite of characterization techniques. Our results reveal that no matter Fe(II) and Fe(III) exhibited an exceptional removal performance for Cu(II) in terms of kinetics and iron dosage along with pH. Impressively, under optimal condition, over 95 % of chelated Cu(II) was removed within 10 min from Fe(II) while about 85 % from Fe(III) dosing. The highly reductive structural Fe(II) existing on mixed-valent iron bearing mineral results in reductive decomplexation of CuII-EDTA in the Fe(II) coagulation-precipitation process in compare with replacement decomplexation in the Fe(III) coagulation-precipitation process, and then released free metal ions (Cu(I) and Cu(II)) can be removed by adsorption and coprecipitation. In addition, the in-situ formed Fe(III) (oxy)hydroxides were amorphous 2-line ferrihydrite with stable flocs and better sedimentation behavior than crystalline lepidocrocite from Fe(II) dosing, and these factors are crucial to the subsequent retention of heavy metals. The elucidation of this study has highlighted the great potential of using in-situ formed iron (oxy)hydroxides for cost-effective treatment of chelated heavy metal-bearing industrial wastewaters.

Persistent reshaping of cohesive sediment towards stable flocs by turbulence

Cohesive sediment forms flocs of various sizes and structures in the natural turbulent environment. Understanding flocculation is critical in accurately predicting sediment transport and biogeochemical cycles. In addition to aggregation and breakup, turbulence also reshapes flocs toward more stable structures. An Eulerian–Lagrangian framework has been implemented to investigate the effect of turbulence on flocculation by capturing the time-evolution of individual flocs. We have identified two floc reshaping mechanisms, namely breakage-regrowth and restructuring by hydrodynamic drag. Surface erosion is found to be the primary breakup mechanism for strong flocs, while fragile flocs tend to split into fragments of similar sizes. Aggregation of flocs of sizes comparable to or greater than the Kolmogorov scale is modulated by turbulence with lower aggregation efficiency. Our findings highlight the limiting effects of turbulence on both floc size and structure.

Insight into the purification of algael water by a novel flocculant with enhanced branched nanochitosan structure

For improving inadequate nanostructural stability and promote algal removal efficiency, a novel nanochitosan-grafted flocculant (PAD-g-MNC) with an enhanced branched nanostructure and high molecular weight (MW) was fabricated via maleic anhydride acylation polymerization. Characterization results verified the successful synthesis of the flocculant and the formation of an irregular particle nanostructure. PAD-g-MNC exhibited superior algal and extracellular organic matter (EOM) removal and obtained the turbidity and chlorophyll-a removal rates of 93.46%–95.39% and 95.10%–97.31%, respectively, at the dosage of 4–5 mg L−1. The growth rate, strength factor, and recovery factor of algal flocs flocculated by PAD-g-MNC were 90.36, 0.63, and 0.27 (100 rpm), respectively, and were higher than other flocculants prepared through conventional methods. Results indicated that the high intrinsic viscosity and stability branched nanostructure promoted the formation of stable flocs and regeneration ability of flocs. MW distribution and three-dimensional fluorescence analyses revealed that the special structure of PAD-g-MNC was beneficial to the removal of tryptophan-like proteins in EOM. Strong adsorption–adhesion and bridging–netting effects of the nanostructure chain were the dominated mechanisms in the improvement of flocculation efficiency. This study provided theoretical and experimental guidance for the design of flocculants with superior performance and efficient algal water purification performance.

Reducing disinfection byproduct precursors through coagulation enhancement as particle weight and size control using potassium permanganate.

The widespread use of chlorine pre-oxidation in water purification has been limited in several countries owing to the production of carcinogenic byproducts when combined with naturally occurring organic matter. This study investigates the efficient use of potassium permanganate (KMnO4) pretreatment and coagulation enhancement as particle size and molecular weight distribution controlling parameters. KMnO4 pretreatment significantly reduced the apparent molecular weight of humic acid due to KMnO4 reduction and the continuous generation of manganese dioxide (MnO2) formed in situ under neutral and alkaline conditions. The MnO2 formed in situ had adsorption characteristics that enabled it to form large and stable flocs with the hydrolysis products of aluminum sulfate. However, under acidic conditions, KMnO4 pretreatment exhibited strong oxidation characteristics due to Mn(VII) reduction to Mn(II), and the mean particle floc size was the same as without KMnO4 pretreatment. Overall, KMnO4 pretreatment is a useful alternative strategy for traditional pre-oxidation using chlorine and a good coagulant enhancement agent in neutral and basic media.

Aluminum-based electrocoagulation for residual fluoride removal during per- and polyfluoroalkyl substances (PFASs) wastewater treatment

The residual fluorion (F–) generated during per- and polyfluoroalkyl substances (PFASs) treatment presents a new environmental burden, while minimum attention has been redirected to its removal. In this study, Al-based electrocoagulation (EC) technique was optimized to effectively remove the residual F– during PFASs wastewater treatment. At EC’s optimal operating conditions, it can achieve over 81.7 % removal efficiency within 30 min. Furthermore, EC exhibited a stable performance on removing F– across a wide range of pH (3–11), and could form stable flocs under neutral pH conditions. The in-depth characterization of flocs has revealed the dynamic change of Al-F species along the EC process, and removal mechanisms were proved to be a combination of complexation, ion exchange, hydrogen bonding and precipitation. In addition, the optimized EC showed stable removal efficiency of F– with the co-existence of multiple PFASs. Hence, we have effectively removed the residual F– during PFASs wastewater treatment, and provide new insights to better understand the defluorination mechanisms in the EC process.

Effect of Suspended Solids and Organic Matter in Water on the Removal of ZnO-NPs by Coagulation

Background: Zinc oxide nanoparticles (ZnO-NPs) have been shown to have a non-negligible impact on the environment Objective: Kaolin and humic acid were used in the aqueous environment to study their effects on the removal of ZnO-NPs. Method: In this work, polyaluminum ferric chloride (PAFC)/cationic polyacrylamide (CPAM) coagulants were used together with kaolin and humic acid were used to study their effects on the removal of ZnO-NPs and to analyze their mechanism of action. Results: The results showed that the removal rate of ZnO-NPs in the humic acid system decreased by about 30% compared to that in the pure water system, and increasing the ionic strength and humic acid concentration was not conducive to removing ZnO-NPs. On the other hand, the ZnO-NPs removal rate in the kaolin system was up to 96.28%, and increasing the ionic strength and kaolin concentration contributed to the removal of ZnO-NPs. In the humic acid and kaolin systems, the effects of coagulant dosage and pH on the removal of ZnO-NPs were about the same as in the pure water system. Moreover, 5 mg/L humic acid inhibited floc growth during removal of ZnO-NPs by coagulation with PAFC/CPAM. In contrast, 5 mg/L kaolin promoted flocs growth, resulting in stronger and more stable flocs and a 5.25% increase in the fractal dimension compared to the pure water system. Conclusion: These results suggested that suspended solids and natural organic matter in the water could directly affect the effectiveness of coagulation to remove ZnO-NPs.

Natural Flocculant from a Combination of Moringa oleifera Seeds and Cactus Cladodes (Opuntia ficus-indica) to Optimize Flocculation Properties

The lack of access to clean water worldwide and organic, inorganic as well as biological contamination of existing freshwater sources are a major problem for around 2 billion people, especially in the countries of the global south. One sign of polluted water is turbidity. It is generally caused by colloidal and particulate suspended solids. Chemical flocculants are often used to reduce turbidity and thus eliminate the mostly harmful substances that cause it. However, these have some disadvantages, such as cost and availability, so increasingly natural plant-based flocculants are coming into focus and are considered as an alternative option. In this study, Moringa seeds (Moringa oleifera) and cactus cladodes (Opuntia ficus-indica) were investigated as innovative and environmentally friendly flocculants for water treatment. The parameters investigated included absolute turbidity reduction and flocculation activity, as well as shear strength of the resulting flocs. The flocculation experiments were conducted as simultaneous tests in beakers. Experiments were conducted using both a laboratory-prepared model suspension with an initial turbidity of approximately 139 NTU and natural surface water with an initial turbidity of approximately 136 NTU. The flocculant dosages used ranged from 100 to 300 mg/L. The results show that although Moringa seeds had the highest flocculation activity (up to 93%), the flocs were very fragile and were destroyed again even at low induced shear forces. Flocculants from cactus yielded stable flocs, but the flocculation activity (maximum at 54%) was not as high as that of Moringa. The combination of the two materials resulted in a flocculant with sufficiently high flocculation activity (76%) and stable flocs, which could withstand higher shear forces potentially induced in further treatment steps.

Elucidating the role of solids content in low-temperature thermal hydrolysis and anaerobic digestion of sewage sludge

The role of total solids content in low-temperature thermal hydrolysis and anaerobic digestion of sewage sludge was investigated. Increasing total solids from 2% to 6% improved thermal hydrolysis and anaerobic digestion performance, while increasing it further to 12% decreased methane production. Maximum sludge solubility (22.9% ± 0.6%) and methane production (320 ± 7 mL/g volatile solids) were achieved at 6% solids. The increase in solids content from 2% to 6% improved heating efficiency and volatile fraction content, which facilitated sludge solubilization and enrichment of methanogens. However, further increases in solids content resulted in a stable floc structure with excess ammonia nitrogen and volatile fatty acids, which limited the release of substrates and reduced the abundance of acidifying bacteria and methanogens, ultimately leading to reduced methane production. An in-depth understanding of the role of solids content opens up new avenues for improved low-temperature thermal hydrolysis of sludge.

Variations in NOM during floc aging: Effect of typical Al-based coagulants and different particle sizes

Most studies on the interaction between coagulation and NOM (natural organic matter) currently focus on pollutant removal and coagulant species distribution, while studies on floc aging are lacking. Investigation onto the effects of floc aging could guide further processes that utilize flocs, such as densadeg sludge recirculation, floc predeposition for ultrafiltration, sludge condensation, and other traditional sludge reflux processes. In this study, flocs generated by Al13 and AlCl3 in microparticle- and nanoparticle-containing water were investigated, and the effect of floc aging on NOM was quantified based on several organic matter characterization techniques. Flocs absorb and release organics during aging. The flocs generated from micro-SiO2 have a significant absorbing effect for LWM-N (low-molecular-weight neutral substances) and protein-like substances, while the absorption of NOM by flocs generated from nano-SiO2 is insignificant. HS (humic substances) with high aromaticity are released during floc aging. From the molecular perspective, the molecules released during floc aging are those with higher double bond equivalents and higher aromaticity, while the absorbed molecules are those with lower double bond equivalents and lower aromaticity. 2D-COS (two-dimensional correlation spectroscopy) demonstrated that the flocs generated by Al13 and AlCl3 had the same organic release patterns but different intensities, while the flocs generated in the micro-SiO2 and nano-SiO2 systems had different organics release patterns. Abundant aluminum hydrolysates with low polymerization and amorphous Al(OH)3 would be produced from AlCl3 during the coagulation process and then undergo hydroxyl‑bridging reaction and crystallization during floc aging, thus releasing more HS with high aromaticity into the supernatant; in comparison, prehydrolyzed Al13 produces a more stable floc and releases less HS during aging. The flocs produced by nano-SiO2 and Al-based coagulants release higher aromaticity HS into the water than those produced by micro-SiO2, which may be related to the formation of more highly polymerized degree hydrolysates and nanocrystalline Al(OH)3 in the nano-SiO2 system. The flocs generated in water with micro-SiO2 may contain a large amount of Al-OH and have a loose structure, thus further absorbing NOM, such as protein-like substances and LWM-N. In contrast, the flocs generated from nano-SiO2 possess abundant adsorbed water and a denser structure; thus, organic matter cannot be absorbed stably.

Synthesis and evaluation of cationic polyacrylamide and polyacrylate flocculants for harvesting freshwater and marine microalgae

• Cationic PAETAC & PAmPTAC were synthesized by UV-induced radical polymerization. • New polymers showed good flocculation performance of freshwater & marine microalgae. • Optimal doses of PAETAC were 50 and 4.8 mg/g for C. vulgaris & P. purpureum. • PAETAC and PAmPTAC produced stable flocs, supporting simple dewatering step. This study addresses the challenge of microalgae harvesting through the development of flocculants. Two positively charged cationic polymers including poly[2 (acryloyloxy)ethyl]trimethylammonium chloride (PAETAC) and poly(3 acrylamidopropyl)trimethylammonium chloride (PAmPTAC) were synthesized using the UV-induced radical polymerization, for harvesting both freshwater and marine microalgae. The results show that the synthesized polymers have excellent flocculation performance for both freshwater green microalgae ( Chlorella vulgaris) and marine red microalgae ( Porphyridium purpureum). PAETAC outperformed PAmPTAC for both Chlorella vulgaris and Porphyridium purpureum microalgae. The optimal PAETAC doses for Chlorella vulgaris and Porphyridium purpureum microalgae were 50 and 4.8 mg/g of dry biomass while the optimal PAmPTAC doses were 252 and 35 mg/g of dry biomass respectively. Additionally, the floc formation with the PAETAC was more stable than PAmPTAC, which supported the dewatering step via sieving. The superior performance can be attributed to the higher molecular weight of the PAETAC polymer when compared to the PAmPTAC polymer. In comparison to commercially available polydiallyldimethylammonium chloride (PolyDADMAC), the newly synthesised PAETAC and PAmPTAC polymers demonstrated superior flocculation efficiency at a lower dose. The findings of this study established a platform technology for designing and synthesising cationic flocculants for use in microalgae harvesting.

Evaluating the performance of bridging-assembly chelating flocculant for heavy metals removal: Role of branched architectures

A novel chelating flocculant with branched architectures, polyacrylamide grafted maleoyl chitosan-mercaptoacetic acid (PAM-g-M(CS-MA)), was successfully fabricated using maleic anhydride as the “bridge” between chitosan and polyacrylamide. The functional groups and structural characteristic information of copolymers were obtained via characterization analysis. Flocculation performance was systematically investigated via purifying a series of simulated wastewater containing Cu or Cd. The properties of the flocs were studied to give in-depth evidences for the role of chelation groups and branched architectures in flocculation. Results indicated that PAM-g-M(CS-MA) showed excellent flocculation capacity for heavy metals in high concentrations and was superior to other chelating flocculants. The maximum flocculation efficiency of Cu (93.90%) and Cd (92.47%) was achieved by PAM-g-M(CS-MA) at pH 7, dosage of 100 mg L−1 and stirring speed of 90 rpm. The flocculation mechanisms of PAM-g-M(CS-MA) were deeply explored through the analyses of floc properties. The strong synergistic chelation of mercapto, carboxyl, amide and hydroxyl groups predominated for the capturing of heavy metals; and the branched architectures facilitated the formation of large and stable flocs via adsorption and bridging-furl effect. This study provided a solid foundation for the fabrication of flocculants for heavy metal wastewater treatment.

In situ conversion of goethite to erdite nanorods to improve the performance of doxycycline hydrochloride adsorption

Goethite is the major component of solid waste from surface de-rusting and zinc-electrolysis processes, and such waste is conventionally disposed of in landfills. A new conversion method of goethite to nanorod erdite was investigated in this study to develop an alternative route for reutilising goethite-bearing waste. The application performance of nanorod erdite was also determined. Results showed that raw goethite was interlaced with spicula. After hydrothermal treatment at 160 °C for 10 h, goethite was converted to hexahedral pyrite (named as E-0) without NaOH whilst to nanorod erdite (named as E-2) with corresponding diameter and length of 0.2 and 1–2 μm in the presence of 2 M NaOH. The formed erdite nanorod (E-4) grew longer from 1 to 2 μm to 2–5 μm when the NaOH concentration increased from 2 M to 4 M. NaOH is important for the dissolution of structural Fe on goethite as Fe(OH)4−. NaOH enabled the replacement of the OH− of Fe(OH)4− by HS−, followed by polymerisation and crystallisation of (FeS2)nn-, thus resulting in erdite production. Erdite was not observed when NaOH was replaced by KOH, Ca(OH)2 and ammonia liquid, respectively forming KFeS2, portlandite and pyrite. The erdite-bearing products were effective in doxycycline hydrochloride (DCH) adsorption. The adsorption data of DCH fitted well with Jovanovich and pseudo-second order models, and the maximum adsorption capacity of DCH was in the following order: goethite < E-0 < E-2 < E-4. Particularly, E-4 exhibited an optimal DCH adsorption capacity of 1520.46 mg/L, which is 15 times that of raw goethite. The DCH adsorption increased with ionic strength and phosphate concentration; DCH became superior at pH < 5 but weakened in the pH range of 6–9. The formed erdite was metastable in a weakly acidic solution and spontaneously hydrolysed to Fe/S-bearing flocs, which exhibited numerous functional groups (e.g. Fe-SH/Fe-OH) to complex DCH. The major mechanism was the complexation reaction between the -NH2 group on the side chain of DCH and the Fe-SH/Fe-OH, which generated stable flocs–DCH ligand. This study exhibited an acceptable route for the resource reutilisation of goethite-bearing waste as nanorod erdite, and the produced erdite-bearing product was effective in the adsorption of DCH from wastewater.

Shear driven vorticity aligned flocs in a suspension of attractive rigid rods.

A combination of rheology, optical microscopy and computer simulations was used to investigate the microstructural changes of a semi-dilute suspension of attractive rigid rods in an imposed shear flow. The aim is to understand the relation of the microstructure with the viscoelastic response, and the yielding and flow behaviour in different shear regimes of gels built from rodlike colloids. A semi-dilute suspension of micron sized, rodlike silica particles suspended in 11 M CsCl salt solution was used as a model system for attractive rods' gel. Upon application of steady shear the gel microstructure rearranges in different states and exhibits flow instabilities depending on shear rate, attraction strength, volume fraction and geometrical confinement. At low rod volume fractions, the suspension forms large, vorticity aligned, particle rich flocs that roll in the flow-vorticity plane, an effect that is due to an interplay between hydrodynamic interactions and geometrical confinement as suggested by computer simulations. Experimental data allow the creation of a state diagram, as a function of volume fraction and shear rates, identifying regimes of stable (or unstable) floc formation and of homogeneous gel or broken clusters. The transition is related to dimensionless Mason number, defined as the ratio of shear forces to interparticle attractive force.

Numerical analysis of asphaltene particles evolution and flocs morphology using DEM-CFD approach

The agglomeration and fragmentation of asphaltenes which dictate particle size distribution (PSD) play an important role in deposition behavior of asphaltene. However, the physics underlying the agglomeration/fragmentation processes is grossly missing in the available literature. In this paper, Discrete Element Method (DEM) in combination with a coalescence model is coupled with Computational Fluid Dynamics (CFD) to simulate agglomeration/fragmentation considering asphaltene particles as real/irregular objects in the absence of deposition process. The evolution of asphaltene particles, asphaltene particle size distribution (PSD), and morphology of asphaltene flocs have been examined during the simulation. Also, the effect of fluid velocity (Vf), primary particle concentration (N0), inter-particle bond strength (Fb), and energy barrier (Ub) have been investigated. During asphaltene flocculation, mean floc size increases until a steady-state condition is attained where floc size and mass fractal dimension approximately remains unchanged. The size of asphaltene flocs increases up to 40 μm and fractal dimension values change in the range of 1.45–1.75. Higher Vf leads to the steady-state condition is attained more rapidly along with smaller floc sizes and higher fractal dimensions. Increasing N0 results in faster growth of asphaltene flocs, however, the stable mean asphaltene floc size is approximately insensitive to N0. The presence of larger flocs at higher N0 eventuates the smaller fractal dimensions. As Fb increases, the frequency of small particles decreases, and PSD shifts to larger sizes. Consequently, smaller fractal dimensions are obtained. The floc growth is insensitive to Ub at initial times, whereas the steady-state condition is reached more quickly with a smaller stable floc size for higher values of Ub. The fractal dimension shows a weak dependency on the energy barrier.

Effect of saltwater intrusion on activated sludge flocculation.

Saltwater addition negatively impacted the settling properties of the activated sludge in a sequencing batch reactor, which in turn caused the effluent quality and the dewatering properties to deteriorate. Experiments showed that increasing sodium ion concentrations above 1meq/L interfered with bio-flocculation by ion exchange of calcium ions displaced by sodium in mixed liquor flocs, causing increases in the sludge volume index, total suspended solids, and chemical oxygen demand concentrations of the final effluent and in the times of the time to filter test of the mixed liquor. Experiments were also conducted to reverse mixed liquor de-flocculation by adding calcium ions in wastewater with different sodium chloride concentrations and a positive relationship was found between calcium ion added and improved effluent quality. Calcium ion concentrations above 1.6meq/L proved to be beneficial for adhesion of microbial aggregates leading to the formation of stable flocs and improved sludge dewatering by reversing the ion exchange phenomenon observed with sodium concentrations above 1meq/L. Monovalent-to-divalent ratios did not provide predictive information on de-flocculation. Hence, individual ion concentrations in addition to monovalent-to-divalent cation ratios are important in the onset of de-flocculation effects while a system-specific concentration threshold was measured under which no adverse effects were observed. PRACTITIONER POINTS: The adverse effects of varying concentrations of sodium chloride on the biological process affecting bioflocculation and effluent quality. Impact of sodium on the health of the mixed liquor as well as on dewatering processes. Prediction of sea level rise due to climate change will impact utilities situated along the coast with saltwater intrusion problems. Management of dewatered flows containing saltwater from onsite construction Identify management practices to reduce the impact of saltwater on the wastewater treatment plant.

Enhanced Biomass Properties In Sludge Bulking: Impact of Static Magnetic Field

Occurrence of sludge bulking with regard to prolong sludge age declines the removal performances attributable to the failure of aggregation by the floc-formers and insufficient adhesion among cells’ surfaces. Approach of sufficiently minimizing the sludge age had been taken most of the times. This approach, however, eliminated the floc-formers although it was found to inhibit the bulking. The aim of the present study, therefore, is to investigate the potential of magnetic field application as an alternative approach to control the sludge bulking. Two sequencing batch reactors, Reactor A (SBRA) and Reactor B (SBRB), were operated in long sludge age to induce the bulking. SBRA was subjected to 88.0 mT magnetic field intensity while SBRB served as a control system. The findings showed that the magnetic field was able to enhance the biomass properties including the aggregation ability, relative hydrophobicity and maintain significant negative surface charge under an adverse effect of long sludge age thus led to more stable flocs been formed. This had resulted with consistent high removal of SBRA compared to SBRB. Consequently, this approach minimizes the occurrence of sludge bulking.