Floc Surface Research Articles

Study on the morphological characteristics of coal particle flocs under fractal theory

Based on fractal theory, the geometric size, surface morphology, and spatial structure of flocs in the hydrophobic flocculation process of coal particles were examined via particle size distribution detection, image analysis technology, and numerical simulation. The floc size distribution curve was classified and discussed via the dual-domain fractal rule, and the variation law of the composition and distribution of the coarse- and fine-grained coal particle flocs with the flocculation process was clarified. The various levels and characteristics of the floc growth geometry were explained by the analysis of the fractal dimension of the individual floc surface and the multiple spectra of the floc groups in the metallographic microscopy image. The hydrophobic flocculation process of coal particles was simulated via the diffusion-limited cluster aggregation model. The gyration fractal dimension was used to examine floc fragmentation and reconstruction and clarify the growth law of the floc spatial structure during the hydrophobic flocculation process.

Efficient, quick, and low-carbon removal mechanism of microplastics based on integrated gel coagulation-spontaneous flotation process

To address the problems of unstable efficiency, long treatment period, and high energy consumption during microplastics (MPs) removal by traditional coagulation–flotation technology, a gel coagulation–spontaneous flotation (GCSF) process is proposed that employs laminarin (LA) as the crosslinker and polyaluminum chloride (PAC)/polyaluminum ferric chloride (PAFC) as the coagulant to remove MPs. Herein, the effects of GCSF chemical conditions on microplastic-humic acid composite pollutants (MP-HAs) removal were investigated, and the removal mechanisms were analyzed through theoretical calculations and floc structure characterization. Results showed that an LA to PAC/PAFC ratio of 2.5:1 achieved the highest removal of HA (86 %) and MPs (93 %–99 %) in short coagulation (< 1 min) and spontaneous flotation (< 9 min) period. PAC-LA exhibited strong removal ability for MP-HAs while PAFC-LA induced fast flotation speed. The peak intensity and peak shift in Fourier-transformed infrared and X-ray photo-electron spectra indicated that the removal mechanisms of MPs include hydrogen bond adsorption and the sweeping effect, mainly relying on –OH/–C = O on the MPs surface and entrapment of gel flocs with a high degree of aggregation, respectively. The extended Derjaguin-Landau-Verwey-Overbeek calculation also revealed that interactions between PAC/PAFC-LA and MP-HAs were mainly polar interaction (hydrogen bonding) and intermolecular attraction interaction (Lifshitz-van der Waals force), and the sweep effect was reflected by intermolecular interaction. In addition, density function theory calculations indicated that –OH in LA mainly adsorbs DO through a double hydrogen bond configuration, and the crosslinking ligand FeO6/AlO6 assists in DO absorption by –OH.

Enhanced removal of nano-oil droplets utilizing polysilicate aluminum ferric (PSAF): Leveraging bridging and non-polar surface advantages.

Hydraulic oil leaks during mechanical maintenance, resulting in flushing wastewater contaminated with dispersed nano-oil droplets. In this study, 75 mg L-1 of polysilicate aluminum ferric (PSAF) was stirred at 350 rpm and the optimal chemical oxygen demand (COD) removal was 71%. The increase of PSAF led to more hydrolysis of Fe, and 1,175 cm-1 hydroxyl bridged with negative oil droplets. At the same molar concentration, PSAF hydrolyzes cationic metals more rapidly than polymeric aluminum chloride (PAC). PSAF forms flocs of smaller complex structures with greater bridging. The Al-O and Si-O peaks occurred at 611 and 1,138 cm-1, indicating the formation of Si-O-Fe and Si-O-Al bonds on the flocs surface. Higher stirring speeds did not change the free energy of the flocs surface γTot, mainly because the decrease in the van der Waals force (γLW) offset the increase of Lewis acid-base force (γAB). Preserving the non-polar surface, in summary, owing to its bridging abilities and affinity for non-polar surfaces, PSAF demonstrates superior efficiency over PAC in capturing and removing oil droplets.

Oxidation-flocculation conditioning to improve the performance and mechanism of municipal sludge dewatering

In this study, ferrous iron (Fe2+)-catalyzed sodium percarbonate (2Na2CO3·3H2O2) was used for conditioning (referred to as F-N conditioning) municipal sludge. On this basis, Fe2+-catalyzed 2Na2CO3·3H2O2 was coupled with polymerized ferrous sulfate (PFS) conditioning (referred to as F-N-P conditioning) as well as coupled with the compounding of PFS and cationic polyacrylamide (CPAM) conditioning were explored (referred to as F-N-P-C conditioning) for municipal sludge. The results showed that the optimal dosages of Fe2+, 2Na2CO3·3H2O2, PFS and CPAM were 15, 40, 200 and 0.3 mg/g of absolutely dry sludge (DS), respectively, in which the specific resistance of the sludge (SRF) and the water content of the filtered sludge cake (WC) dropped from 2.1 × 1013 m/kg and 90.5 % to 2.9 × 1011 m/kg and 75.3 %, respectively. The mechanism study showed that the hydroxyl radicals (•OH) generated by F-N-P-C effectively cleaved the extracellular polymer (EPS) and remodeled the protein secondary structure by affecting the ratio of α-sheet and β-helix in the proteins secondary structure. PFS and CPAM neutralized the negative charge on the surface of municipal sludge flocs, and adsorbed-bridged with sludge flocs to improve the settling performance of sludge. Finally, the results of the plate and frame filter press dewatering tests verified that the F-N-P-C conditioning mode was the best formulation of sludge conditioning and determined the optimal working conditions: sludge feeding time, pressing time and pressing pressure were 5400 s, 5400 s and 1.2 MPa, respectively. The chemical cost of F-N-P-C conditioning was preliminarily estimated as 58.55 USD$/ton DS. Therefore, The F-N-P-C process had certain practical value and promotion significance.

The key role of hydrophobic forces during the electrocoagulation of perfluorooctanoic acid substitute (HFPO-TA) revealed by the interfacial thermodynamics

Per- and polyfluoroalkyl substances (PFASs) have been widely found in water bodies and may generate negative impacts on the ecosystem. Eectrocoagulation (EC) with a zinc anode is an effective technology to remove PFASs but the dominating interaction forces between zinc flocs and PFASs are still not well elucidated. In this study, we used hexafluoropropylene oxide trimer acid (HFPO-TA), a new perfluorooctanoic acid substitute, as a model to investigate the influence of EC operational parameters on its removal efficiency, including the current density, the pH value, and the electrolyte type. 99 % removal of 40 μM HFPO-TA were achieved in 3-h at optimal conditions. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was innovatively applied to reveal the interfacial free energies between zinc flocs and HFPO-TA and other PFASs. It was found that the hydrophobic force can significantly promote the adsorption of HFPO-TA on the surface of zinc flocs and a strong correlation may exist between the calculated total interfacial free energies and the pseudo-first-order kinetic constants of removing PFASs. FT-IR spectra indicated the specific interactions occurring between carboxylate head groups and zinc flocs. These findings advance the mechanistic understanding of PFASs removal by metal flocs and could support the development of electrocoagulation for removing PFASs.

Effects of agitation intensity and foam stability on the Floc-flotation of ultrafine minerals using a laboratory flotation column

In the present study flocculation flotation (floc-flotation) of ultrafine hematite and quartz was investigated in a laboratory-scale flotation column. A direct flotation scheme was used to float hematite using in-house synthesized n-octyl hydroxamic acid (OHA) as a collector. A polymer system containing tannic acid (TAN) and poly(ethylene oxide) (PEO) was used to flocculate quartz to reduce its entrainment. The effects of agitation intensity and foam stability on floc size distribution, entrainment reduction, and flotation kinetics/recovery were investigated. It was shown that the dual polymers TAN-PEO were effective in reducing quartz entrainment, and that the degree of entrainment reduction was affected by the intensity of agitation. A correlation was established between the mean floc size and a reduction in quartz entrainment. TAN-PEO dual polymer system also enhanced the flotation kinetics and recovery of hematite by OHA, originating from a synergistic effect between PEO and OHA. Therefore, higher separation efficiency was achieved from synthetic ultrafine hematite and quartz mixtures when TAN-PEO was added after OHA. The underlying mechanisms were studied by floc size distribution, surface tension, and foam height and decay time measurement. This work helps understand the relationship between hydrodynamic condition, flocs size, and mechanical entrainment when polymeric flocculation is used for entrainment reduction in fine and ultrafine minerals flotation.

Comparison analysis of cationic-polyacrylamide as flocculant aid in titanium salt coagulants

The combination of organic and inorganic coagulants is considered to be an effective strategy for Humic Acid (HA) removal. In this study, the performance of Titanium-based coagulants aided by Cationic-Polyacrylamide (CPAM) to HA molecules was compared. It was found that CPAM had a higher promotion effect in the TXC system. The reason for why CPAM was more suitable for the TXC system could be explained by analyzing Zeta potential, FTIR, and XPS. By comparing the coagulation mechanism of TiCl4 (TC) and Poly-Titanium Chloride (PTC), we found that complexation was the main mechanism of TC and PTC in acidic and neutral environments. The C-O-Ti Bond was formed by complexing the Ti-OH with the C-OH and -COOH functional groups of HA molecules. Sweeping was the most important removal mechanism of TXC in the neutral and alkaline environment, and CPAM bridged floc through hydrogen bond force for enhancing the sweeping effect. In addition, the role of CPAM in TXC system was further demonstrated by Zeta potential analysis. Both TC and PTC were positively charged in the measured pH range, so the removal of Humic acid was limited by increasing zeta potential. In both neutral and alkaline environments, TXC kept a negative surface charge and CPAM significantly enhanced the adsorption of HA on the TXC floc surface. This study provided clues for the interaction mechanism between titanium salt coagulants and HA, and it also provided a reference for the application of TXC coagulant combined with CPAM flocculant for the removal of HA molecules.

Application of laminarin as a novel coagulant aid to improve coagulation-ultrafiltration efficiency

Polyacrylamide (PAM) is the most commonly used coagulant aid in coagulation-ultrafiltration (C-UF) systems; however, its hydrolyzed monomer is harmful to the human nervous system. In this study, laminarin (LA), was extracted from Laminaria japonica and used as a novel coagulant aid to improve coagulation efficiency and reduce membrane fouling during the C-UF process. Optimal LA usage conditions were systematically examined and compared with those of PAM to evaluate their potential for industrial applications. The results revealed that coagulation efficiency could be enhanced by 15–35% with moderate LA addition, which exhibited comparable aid effects to PAM. LA exhibited the highest coagulation aid effect at pH 8–9, and under this condition, turbidity and natural organic matter (NOM) removal achieved 82% and 54%, respectively. Compared with a one-time LA dosing strategy, the pollutant removal capacity of batch dosing was superior. Even in lower water temperatures (5–15 °C), coagulation efficiency was still satisfied, which exhibited a good practical application perspective. The coagulation aid role of LA should be attributed to its long-chain molecular structure, which enhances the bridging role between micro flocs and assists floc growth, thus facilitating the formation of large flocs. In addition, LA adsorption on floc surface was conducive to the direct electrostatic repulsion effect of electronegative membrane, which resulted in a more porous cake layer and higher membrane flux. Therefore, LA exhibits excellent application potential for eliminating NOM while simultaneously reducing membrane fouling through the C-UF process.

Insights on enhanced antibiotic sulfamethoxazole removal by magnetic activated carbon-ballasted coagulation: Efficacy and floc properties

Removal of antibiotics from wastewater is extremely important for the reduction of antibiotic resistance-related risk and safe water reuse. Coagulation is a promising approach for this purpose, but its practical implementation requires further upgrades in coagulation performances and antibiotics targeting. Here, the magnetic activated carbon ballasted coagulation (MAC-BC) process was proposed to enhance the coagulation process and antibiotic sulfamethoxazole (SMX) removal. Response surface curves indicated that MAC played a dominant role in SMX removal rather than coagulant. The MAC ballasting promoted the removal of DOC and SMX in the coagulation process by 1.4 and 1.6 times, which was attributed to hydrogen bonding interaction, π-π electro-donor-accepter interaction, and surface complexation introduced by COOH/C–O, CC, and Fe–O/Al–O in the MAC flocs, respectively. MAC could serve as nuclei and readily bound to the hydrolyzed Al species, resulting in the formation of larger Al-species-induced primary clusters. The ratio of OH/Al on the surface of MAC-BC flocs was higher than that of the flocs generated in the single coagulation process. The higher binding ability with MAC addition facilitated the aggregation of primary clusters and increased the floc size by 1.3 times, which further accelerated floc settling and separation. The multiple functions of MAC ballasting enhanced the coagulation process and promoted SMX removal. This study opens a new avenue to upgrade traditional coagulation and adsorption processes.

Feasibility of membrane distillation brine assistant anaerobic fermentation for enhancing carbon migration and recovery from excess sludge: Two wastes into one resource

The carbon recovery from excess sludge has received rising attentions. This study developed an innovative membrane distillation (MD) brine assistant anaerobic fermentation. The Na+, instead of other ions in MD brine, disrupted O-H stretching and N-H/C-N stretches of amide I in proteins for loosening protein structure and reducing hydrophilic functional groups, which triggered considerable sludge disintegration and microbial cell lysis with plicated floc surface structure and organic fragment stripping. Thereby, the carbon sources of 785.90 mg/L were released, among which the tyrosine-like protein and soluble microbial by-products were identified as the crucial dissolved organic matters relating to enhancing anaerobic fermentation. As such, the volatile fatty acids (VFAs) production was improved to 1689.65 mg COD/L (55.93 mg C/g VSS) through 4-day MD brine assistant anaerobic fermentation, which was mainly composed by acetic and propionic acids (58.96–84.16%), while the acetoxylation was also facilitated by MD brine. Correspondingly, the carbon source biodegradation towards micromolecule shift was promoted, considerable carbon release and recovery rates of 18.27% and 13.31% were achievable, respectively. The VFAs and proteins were dominant soluble carbon sources, while the pretty high C/N of 10.4 was achieved in fermentation liquid, demonstrating the bio-availability of recovered carbon sources. The economic and carbon-emission reduction benefits of 167.94–412.26 CNY and 0.0726 ton CO2 were obtained by carbon recovery from each ton excess sludge solid.

Removal of colloidal impurities by thermal softening-coagulation-flocculation-sedimentation in steam assisted gravity drainage (SAGD) produced water: Performance, interaction effects and mechanism study

Effective removal of colloidal impurities from steam-assisted gravity drainage (SAGD) produced water is essential for enhancing water recycling in industry. Response surface methodology (RSM) was employed to optimize the thermal softening-coagulation-flocculation-sedimentation process with softeners (Ca(OH)2, MgO and Na2CO3), poly-DADMAC as coagulant, and cationic polyacrylamide (PAM) as flocculant, and assess the interaction effects of operational variables for sludge volume index (SVI) and the removal efficiency of turbidity (TSS), particulate hardness, silica, total organic carbon (TOC) and total inorganic carbon (TIC) in synthetic SAGD produced water. The optimal conditions at 0.93 desirability were 67 mg/L poly-DADMAC dose, 14 min mixing time with softeners only, 200 rpm coagulation speed, and 16 min flocculation time. At this condition, the predicted maximum removal of turbidity, TSS, particulate hardness, silica, TOC and TIC were 99.2 %, 99.1 %, 99.4 %, 27.0 %, 69.0 %, and 30.3 %, respectively, and the value of SVI was 38.1 mL/g. Our results indicated that poly-DADMAC dose and mixing time with softeners only were the most influential factors for the treatment process. Furthermore, the temperature effect on removal mechanisms was investigated at optimal conditions under room temperature and high temperature (80 °C). The results of floc characterization and surface force measurement indicated that temperature could facilitate the removal of colloidal impurities via forming larger and denser flocs and changing their surface composition. The results also provided confirmation that adsorption and subsequent bridging are the main removal mechanisms in the coagulation-flocculation process. This study illuminates the importance of the interactions among operational variables and provides in-depth insights into the mechanism for the removal of colloidal impurities under high temperature.

Destabilization of polystyrene nanoplastics with different surface charge and particle size by Fe electrocoagulation

Nanoplastics (NPs) discharged from wastewater could pose a major threat to organisms in aquatic environments. Effective removal of NPs by the current conventional coagulation-sedimentation process is not yet satisfactory. This study aimed to investigate the destabilization mechanism of polystyrene NPs (PS-NPs) with different surface properties and sizes (i.e., 90 nm, 200 nm, and 500 nm) by Fe electrocoagulation (EC). Two types of PS-NPs were prepared by a nanoprecipitation method using sodium dodecyl sulfate and cetrimonium bromide solutions to produce negatively-charged SDS-NPs and positively-charged CTAB-NPs. For both NPs, obvious floc aggregation from 7 μm to 14 μm was observed only at pH 7 with particulate Fe accounted for >90 %. At pH 7, Fe EC removed 85.3 %, 82.8 %, and 74.7 % of the negatively-charged SDS-NPs at small-, mid-, and large-sizes from 90 nm, 200 nm, to 500 nm, respectively. Small-size SDS-NPs(90 nm) were destabilized through physical adsorption on the surface of Fe flocs, while the main removal mechanism of mid- and large-SDS-NPs(200 nm and 500 nm) involved the enmeshment of large Fe flocs. Compared to SDS-NPs(200 nm and 500 nm), Fe EC performed similar destabilization behavior to two CTAB-NPs(200 nm and 500 nm), but it resulted in much lower removal rates of 54.8 % - 77.9 %. The Fe EC also exhibited no removal (<1 %) ability toward the small-size and positively-charged CTAB-NPs(90 nm) due to insufficient formation of effective Fe flocs. Our results provide insight into the destabilization of PS in nano-scale with different sizes and surface properties, which clarifies the behavior of complex NPs in a Fe EC-system.

Influence of the hydrophobicity of the starch-based coagulant on the coagulation of various pollutants in water and the study of its mechanism

<p indent="0mm">Parts of surface water in China, including some rivers and lakes, show the characteristics of micropollution containing excessive dissolved organic matter, which has become a key factor in restricting the improvement of water quality. Coagulation is one of the most popular technologies in the purification of surface water owing to its low cost and simple operation. However, traditional coagulants, including inorganic and organic synthetic polymer coagulants, usually show a low efficiency in removing organic micropollutants from surface water and pose the risk of secondary pollution. Furthermore, the molecular structures of organic micropollutants contain hydrophilic and a large number of hydrophobic groups. Considering these facts, in this study, starch (St), a natural polymer with the characteristics of environmental friendliness, wide source, and low cost, was used as the raw material and acrylamide and various quaternary ammonium salts containing different lengths of carbon chains were used as modifiers. Accordingly, four modified starch coagulants (CS-DMRCs) with the same charge density and good water solubility but different degrees of hydrophobicity were designed and fabricated using graft copolymerization. Kaolin particles, sodium humate (NaHA), and bovine serum albumin (BSA) were used as the simulated sources of inorganic colloids and different organic pollutants in the micropolluted turbid surface water. The effects of the hydrophobicity of four St-based coagulants on the removal of kaolin particles, NaHA, and BSA from their single, binary, and ternary pollutant aqueous systems were investigated systematically. Based on the apparent coagulation performance, the floc properties, including floc size, compactness, surface morphology, breakage and recovery behaviors, and the zeta potentials of the supernatants after coagulation, the coagulation mechanisms associated with the structural features of the St-based coagulants and treated pollutants were explored and discussed in detail. The St-based coagulants with a higher hydrophobicity showed better coagulation performance owing to the synergistic effects of charge neutralization, bridging flocculation, and hydrophobic association. In addition to these simulated water samples, a real micropolluted turbid surface water sample from the Jiuxiang River of Nanjing was tested and compared with the simulated water samples, further confirming the practicality of the hydrophobically modified cationic St-based coagulants. In summary, CS-DMRCs should have broad prospects in practical applications owing to their easy and simple fabrication and high efficiency in the purification of organic micropolluted turbid surface water.

Mechanism of real-time capture of organics by in-situ-formed microbubble flocs to enhance organics removal in hybrid ozonation-coagulation process

The over-oxidation of organic pollutants by pre-ozonation leads to a decreased removal efficiency of coagulation. In this study, it was demonstrated that organics modified by ozonation can be captured in real time by microbubble flocs mediated by the interaction among ozone, Al species, and other organics using the hybrid ozonation-coagulation (HOC) process, which avoids further oxidation of the modified organics. Compared with the pre-ozonation-coagulation process, this real-time capture strategy during the HOC process can increase organics removal efficiency, and broaden the ozone dosing range. The synergistic effect of Al species and ozone enhanced hydroxyl radicals (·OH) formation, which increased the content of carboxyl and hydroxyl groups in the modified intermediates while retaining their original macro aromatic structure. That modified intermediates can be captured and complexed by Al species in the HOC process in real time was verified by differential absorbance spectroscopy (DAS). Al species are complexed with carboxyl and hydroxyl groups of organic compounds to form Al-organic complexes that have COAl coordination bonds. These complex structures protect the modified organic compounds during immediate contact with and decomposition by ozone. The existence of ozone can increase the formation of poly Al species via hydroxyl bridges, thus causing the soluble small-scale metal complex to form insoluble flocs. The surface of flocs can be oxidized and modified, thus strengthening the surface coordination of residual organics in water and further improving their removal efficiency.

Mechanism of thermally activated sodium persulfate–biochar skeleton treatment to improve the dewaterability of waste activated sludge

Sludge dewatering is a necessary process in the disposal of waste activated sludge (WAS). In this study, thermally activated sodium persulfate–biochar skeleton pretreatment was performed to improve the dewaterability of sludge, and its internal mechanism was systematically elucidated. The experimental results showed that, under optimal operating conditions, the water content of WAS could be reduced from 89.7% to 61.3% of the raw sludge. Under these conditions, the capillary suction time and specific resistance to filtration were roughly 23.23% and 59.57% of those in the raw sludge, respectively. This study proposes a relationship between organic matter migration and sludge physical structure that explains the dewaterability improvement mechanism. Separate thermal treatment caused organic matter such as proteins, polysaccharides, and humic substances to dissolve, releasing their bound water. Simultaneously, changes in the surface structure (pore size reductions and BET surface area increases) deteriorated the dewaterability of WAS. The reactive oxygen species generated by the thermally activated sodium persulfate further mineralized the organic matter, simplifying the floc surface structure (pore size increases and BET surface area decreases) and finally improving the dewaterability. Under these conditions, the addition of biochar increased the pore size, and further improved sludge dewaterability.

Surface Chemical Groups of Flocs Are Key Factors for the Growth of Flocs in Sweep Coagulation: A Case Study of Surface Occupation by Humic Acid

Coagulation is one of the most common processes in water treatment. Charge neutralization and sweep flocculation are recognized as the primary coagulation mechanisms. However, in-depth understanding on floc growth, breakage, and regrowth is still unclear. In this study, the formation, breakage, and regrowth of alum flocs with humic acid (HA) added either before coagulant addition or during the floc breakage stage were investigated. The floc size continuously decreased with the increase in floc breakage events, and eventually, to a stable value. The floc growth was not affected by the addition of HA before coagulant addition. However, it was prevented as HA was added during the breakage stage, and the prevention extent increased with HA dose. Similar results were also found for natural organic matter (NOM) from real surface water. These results suggested that HA/NOM can cover the active site on the floc surface, and the coverage differed for fresh flocs (newly precipitated) and old flocs (after breakage), which, respectively, represent the case in conventional coagulation and sludge recirculation. Based on these findings, the illustration of floc growth, breakage, and regrowth processes was put forward. We concluded that the charge neutralization and sweep flocculation mechanisms only explained the possibility of flocs approaching each other; whether flocs can connect to each other depends on the activated functional groups on the floc surface. The results in this study revealed the underlying mechanism of “collision effectiveness” in coagulation, complementing the existing understanding of the coagulation process.

Enhanced coagulation and oxidation by the Mn(VII)-Fe(III)/peroxymonosulfate process: Performance and mechanisms

To improve the performance of the conventional coagulation process, a permanganate (Mn(VII)) pre-oxidation combined with Fe(III)/peroxymonosulfate (PMS) coagulation process (Mn(VII)-Fe(III)/PMS) that can significantly improve the removal of dissolved organic carbon (DOC), turbidity, and micropollutants is proposed in this study. Compared with conventional Fe(III) coagulation, the Mn(VII)-Fe(III)/PMS process can also significantly enhance the removal of iohexol and sulfamethoxazole in raw water. During this process, the primary reduction product, Mn(IV), after Mn(VII) pre-oxidation was adsorbed on the floc surfaces and involved in the Fe(III)/PMS process. The natural organic matter (NOM) in raw water mediated the redox cycle of iron. The synergistic effect of NOM, Fe, and Mn facilitated the redox cycle of Mn(III)/Mn(IV) and Fe(III)/Fe(II) to promote the activation of PMS. The sulfate radical (SO4•−) played an important role in the degradation of micropollutants. The formation potential of the detected volatile disinfection by-product (DBP) during the subsequent chlorination was reduced by 21.9% after the Mn(VII)-Fe(III)/PMS process. This study demonstrated the promising application of the Mn(VII)-Fe(III)/PMS process for coagulation and micropollutant control and illustrated the reaction mechanism. This study provides guidance for improving conventional drinking water treatment processes.

The removal efficiency and reaction mechanism of the aluminum coagulant on phenolic compounds in the presence of hardness salts

This study is the evaluation of the coagulation efficiency of the aluminum sulfate on the removal of catechol and pyrogallol. The study has focused on the impact of inorganic components of hardness Algerian waters. Jar-test trials were conducted on the two phenolic compounds dissolved in distilled water only, which was later enriched with minerals. Several reaction parameters varied, including the effect of pH and the influence of the salt content, and this approach yielded a better understanding of interaction between phenolic compounds and calcium/magnesium salts. The results indicate that the process efficiency depends on the number and position of OH in molecules. The main mechanisms would be either a physical adsorption, an exchange of ligand, or complexation on the floc surface of aluminum hydroxide. Moreover, the addition of inorganic salts appears to improve removal efficiency of tested phenolic compounds and have an effect on the optimal pH range for coagulation.

Modern techniques for sludge dewaterability improvement

Since sludge mitigation requires new strategies for enhanced dewaterablity, several scientific and technological advancements in conditioning, dewatering and drying technologies for a variety of sludges are being developed continuously. Grappling with the problem of ever-increasing sludge volume, it is important to critically assess the new concepts to assist in rapid technological developments in this area. This paper provides a concise state-of-the-art discussion focused on the effects of the key parameters including affected dewatering performance according to the sludge type, source and its physicochemical characteristics, rheological factors, particle size distribution, floc surface charge and endogenic polymeric substances (EPS), on the dewatering performance. Since initial conditioning is highly critical on the following dewatering and drying steps, innovative methods, e.g., physical conditioning, sonication, hydrodynamic cavitation, thermal treatment, microwave, electrical treatment, photocatalytic treatment and chemical coagulation/flocculation have been included in this review. Furthermore, latest developments in dewatering and drying technologies are also discussed in terms of their advantages/disadvantages and energy demands. This paper includes a capsule discussion of control of industrial sludges and the application of advanced oxidation processes (AOP(s)) in sludge conditioning and dewatering.

Ultrafiltration membrane fouling control by two-stage coagulant dosing with moderate pH adjustment

For the coagulation-ultrafiltration process, it has been recognized that coagulation under acidic condition could greatly alleviate membrane fouling, but the high chemical consumption for pH adjustment and the diminished alkalinity of effluent severely restrict the practical application of this operation. In this study, it was found that two-stage coagulant dosing (separate dosing during rapid mixing and medium speed mixing) with pH adjusted to 6.5 could alleviate membrane fouling as that by one-time coagulant dosing at pH 5.5, which could significantly lower the chemical consumption for pH adjustment. Both the favorable aluminum hydrolysis speciation on the floc surface and the reduced interface interaction between membrane and foulant at pH 6.5 contributed to the effectiveness of this method on membrane fouling control. Compared with the scenarios at pH 5.5 and 7.5, the two-stage dosing at pH 6.5 could promote more aluminum species transformation to amorphous Al(OH)3 on the surface of flocs, resulting in less residual Al in the effluent. The acid-base interaction between foulant and membrane dominated membrane fouling. The degree of membrane fouling by separate dosage ratio of 3:7 at pH 6.5 was as low as that by one-time dosing at pH 5.5 because of the similarly low acid-base interaction energy.