Salt Coagulants Research Articles

Efficient removal of per- and polyfluoroalkyl substances (PFASs) from stored rainwater by composite metal salt /polydimethyldiallylammonium chloride coagulants

Stored rainwater, the primary source of drinking water in the villages and towns of the Loess Plateau in northwest China, has been found to contain per- and polyfluoroalkyl substances (PFASs) and lacks necessary treatment measures. Coagulation is a common water treatment process, and enhancing its efficacy in removing PFASs can significantly improve treatment efficiency, reduce costs, and minimize the environmental and health risks associated with perfluorinated compounds. This study investigated the removal efficiency of perfluorobutanoic acid (PFBA), perfluorobutanesulfonic acid (PFBS), perfluorooctanoic acid (PFOA), and perfluorooctanesulfonic acid (PFOS) using inorganic salt coagulants alone and in combination with polydimethyldiallylammonium chloride (PDMDAAC). The results indicated that the removal efficiencies of the four PFASs by polyferric chloride (PFCl) and polyaluminum chloride (PACl) increased with alkalinity. PDMDAAC significantly enhanced the coagulation removal efficiency of the four PFASs. The removal efficiency of the four PFASs was highest when the raw water pH was near 7. Within the molecular weight range of 0–500,000 for PDMDAAC, the removal efficiency of the four PFASs increased with increasing molecular weight. Charge neutralization is the primary coagulation mechanism for the removal of anionic PFASs. Therefore, this study provides guidance for selecting coagulants to remove PFASs from stored rainwater.

A Review of Chitosan as a Coagulant of Health-Related Microorganisms in Water and Wastewater

The coagulation and flocculation properties of chitosan, an organic biopolymer derived from chitin, have been researched as an alternative to synthetic polymers and inorganic metal salt coagulants currently used in water and wastewater treatment. In an effort to encourage further research into the practical uses of chitosan as green chemistry in water and wastewater treatment and to promote the efficacious removal of microbial contaminants in drinking and wastewater, we have summarized the current state of research pertaining to the treatment of microorganisms in water and wastewater. A search of PubMed revealed 720 possible titles and abstracts, of which 44 full-text articles were identified as matching the eligibility criteria for inclusion in this systematic review. Results are presented based on the type of water matrix treated (i.e., drinking water, wastewater, and recreational waters) and a summary table providing details on the types and forms of chitosan utilized and the treatment mechanisms and processes described in the study. We find chitosan to be an effective coagulant, flocculant, and adsorbent for removing microbes from water and wastewater; some modified forms of chitosan can inactivate microbes and achieve disinfection, such as those containing metals like silver and antimicrobial chemicals like quaternary ammonium compounds or other strong oxidants, and use with filtration or electrochemical processes can achieve extensive reductions in microbes to meet performance targets of the World Health Organization.

In-situ generation of bifunctional reagents via Al/C microelectrolysis for efficient coagulation–Fenton oxidation treatment of leachate MBR effluent

Coagulation–Fenton oxidation stands as a prevalent method for organic pollutant removal from MBR effluent in landfill leachate. However, its dependence on intricate coagulant preparation and hazardous H2O2 handling presents challenges in logistics. Herein, a novel Al0/C–N, Cl composite was developed via high-energy ball milling and high-temperature sintering, which facilitates in situ generation of H2O2 and aluminum salt coagulant upon stirring in oxygen-containing aqueous solutions. Under conditions of 2 g/L Al0/C–N, Cl and initial pH 9, H2O2 production achieved 459 mg/L within 1 h, yielding an Al3+/H2O2 bifunctional reagent. Subsequent coagulation in MBR effluent and Fenton oxidation achieved removal efficiencies of 85.5 %, 76.4 %, and 99.3 % for UV254, total organic carbon, and chromaticity, respectively. The efficient degradation of refractory fulvic-like substances was obtained from this novel “coagulation–Fenton” hybrid process without additional coagulants and H2O2. These results illustrated that the hybrid process is a promising and efficient technology for the advanced treatment of landfill leachate.

Mechanistic insights into chemical conditioning on transformation of dissolved organic matter and plant biostimulants production during sludge aerobic composting

Inorganic coagulants (aluminum and iron salt) are widely used to improve sludge dewaterability, resulting in numerous residues in dewatered sludge. Composting refers to the controlled microbial process that converts organic wastes into fertilizer, and coagulant residues in dewatered sludge can affect subsequent compost efficiency and resource recycling, which remains unclear. This work investigated the effects of two typical metal salt coagulants (poly aluminum chloride [PAC] and poly ferric sulfate [PFS]) conditioning on sludge compost. Our results revealed that PAC conditioning inhibited composting with decreased peak temperature, microbial richness, enzymatic reaction intensities, and compost quality, associated with decreased pH and microbial toxicity of aluminum. Nevertheless, PFS conditioning selectively enriched Pseudoxanthomonas sp. and resulted in more fertile compost with increased peak temperature, enzymatic reaction intensities, and humification degree. Spectroscopy and mass difference analyses indicated that PFS conditioning enhanced reaction intensities of labile biopolymers at the thermophilic stage, mainly comprising hydrolyzation (H2O), dehydrogenation (-H2, -H4), oxidation (+O1H2), and other reactions (i.e., +CH2, C2H4O1, C2H6O1). Unlike the common composting process primarily conducts humification at the cooling stage, PFS conditioning changed the main occurrence stage to the thermophilic stage. Non-targeted metabolomics revealed that indole (a humification intermediate) is responsible for the increased humification degree and indoleacetic acid content in the PFS-conditioned compost, which then promoted compost quality. Plant growth experiments further confirmed that the dissolved organic matter (DOM) in PFS-conditioned compost produced the maximum plant biomass. This study provided molecular-level evidence that PFS conditioning can promote humification and compost fertility during sludge composting, enabling chemical conditioning optimization for sustainable management of sludge.

Insighting the interaction mechanism of zirconium xerogel coagulants with humic acid: the protective effect of acetylacetone

The use of efficient modification methods determines the wide application potential of zirconium salt coagulants.

Comparison of aluminum formate and traditional aluminum coagulants in structure, hydrolysates, coagulation behavior, and its corrosion resistance advantage

Aluminum formate (AF) has been considered as a superior coagulant that can decompose under the UV light without causing equipment corrosion during water treatment. The main components of the aluminum formate coagulant are aluminum formate (C3H3AlO6), aluminum formate hydrate (C3H3AlO6·3H2O), and aluminum hydrogen formate (C3H3AlO6·2H2O2). Analysis of the hydrolyzed products revealed that the content of added formic acid during the synthesis of aluminum formate is a crucial factor influencing its coagulation effectiveness. Increasing the HCOOH/Al ratio from 1.5 to 4.0 resulted in smaller mass-to-charge ratio (m/z) and higher positive charge for AF hydrolysates, with fewer undetected aluminum species present. Hydrolysates of AF 1.5 exhibited similar characteristics to those of aluminum polychloride, while AF 3.0 demonstrated optimal glucan removal efficiency (>55 %) through physical absorption rather than chemical bond bridging as the primary coagulation mechanism. The jar test results for bovine serum albumin (BSA) coagulation removal indicated a decrease in removal efficiency as the HCOOH/Al molar ratio increased from 1.5 to 4.0, accompanied by a decrease in pH conditions from 6.35 to 7.27. The highest BSA removal efficiency (58 %) was achieved using AF 1.5 at pH 6.35, suggesting that BSA molecules were captured by aluminum formate through chemical bonds such as NO-Al-, Al2(SO4)3, unlike the physical absorption effect observed in glucan coagulation process. Furthermore, it should be noted that compared to traditional aluminum salt coagulants, aluminum formate exhibits excellent pipeline corrosion resistance properties.

Simultaneous chelated heavy metals removal and sludge recovery through titanium coagulation: From waste to resource

Green methods for chelated heavy metals treatment and recovery are essential for coordinated development of resources and environment. Herein, a simple and competent method, titanium salt (TiCl4) coagulation was developed to remove and recycle chelated heavy metals. Our results revealed that this method proved to be effective for metals-citrate [Cu(II), Ni(II), Zn(II) and Cr(VI)], achieving removal efficiencies of 95 %, 92 %, 99 %, and 99 % within 30 min, surpassing direct alkaline precipitation and well-used Fe(III) coagulation. Whereafter, the copper-containing sludge was successfully transformed into copper-doped titanium dioxide (TiO2) photocatalysts by facile calcination. Through comprehensively investigating physicochemical properties by a suite of characterization techniques, we confirmed that doping of Cu induced bandgap narrowing, high specific surface area as well as the formation of oxygen vacancy. Accordingly, the recycling photocatalysts showed remarkable enhanced photocatalytic performance than the pristine TiO2, achieving improvement in the degradation efficiency of 82 %, 61 % and 67 % for carbamazepine(CBZ), bisphenol A (BPA) and methyl orange (MO). In addition, both radical (OH and O2−) and non-radical (1O2 and h+) pathways synergistically contributed to the removal of organic pollutants during photocatalysis. Ultimately, based on economic feasibility assessment and life cycle assessment (LCA), the copper-containing titanium coagulation sludge reuse for photocatalyst could bring lower carbon emissions, reduced environmental risks and higher economic benefits. The elucidation of this study provides new insights into the removal and recycle of chelated heavy metals from wastewater by using an environment-friendly and cost-effective method.

Application of a novel zirconium coagulant in the coagulation-ultrafiltration process: Fluoride removal and membrane fouling alleviation

Groundwater fluoride pollution is a worldwide problem that threatens human health and drinking water. Economical and efficient coagulation is the most widely used defluorination technology. The fluoride removal efficiency depends on the complexation and adsorption capacities of the hydrolyzed metal salt coagulant, so the development of new metal coagulants is the key to coagulation defluorination technology. In this study, novel polymeric zirconium salt coagulants (ZXCs) were prepared by the sol-gel method. Their capabilities in coagulation and coagulation-ultrafiltration processes were evaluated and compared with those of the traditional polyaluminum chloride (PAC) and polyferric sulfate (PFS) coagulants. ZXC exhibited more effective fluoride removal than PAC and PFS, and the fluoride removal rates of ZXC, PAC and PFS were 81.0 %, 24.7 % and 5.4 % with the optimized dosages of 0.30 mM and pHs of 5.0, 6.0 and 5.0, respectively. With an initial fluoride concentration of 4.0 mg/L, 0.30 and 1.5 mM doses of ZXC reduced the fluoride concentrations to 0.76 and 0.13 mg/L. The structures and properties of ZXC and the flocs were characterized with Fourier Transform Infrared spectroscopy (FT-IR), X-ray Diffraction (XRD), X-ray photoelectron Spectroscopy (XPS), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface area determinations. The series characterization and hydrolysis precipitation area map showed that adsorption onto hydroxyl groups and ion exchange with surface hydroxyl groups were the main pathways for fluoride removal by ZXC. In the coagulation-ultrafiltration defluorination process, the highly polymerized ZXC was fully hydrolyzed under acidic conditions to form larger and looser flocs with almost no dissolved residue, which substantially reduced membrane fouling. This work provides new insights into the development of materials and technologies for fluoride removal from drinking water.

Enhanced removal of organic arsenic by using potassium ferrate coupled with metal coagulants: Role of iron species and effect of AlCl3 and FeCl3

This study investigated the removal performance and synergistic mechanism of p-arsanilic acid (p-ASA) using a pre-oxidative coagulation system of potassium permanganate (K2FeO4) with aluminum chloride (AlCl3) or ferric chloride (FeCl3). The arsenic removal efficiencies of K2FeO4-AlCl3 and K2FeO4-FeCl3 reached 93.46% and 98.58%, respectively. K2FeO4 could alter the distribution of hydrolysis products of the coagulants and the addition of the coagulants directly or indirectly influenced the generation of intermediate valence iron (Fe(IV) and Fe(V)), interestingly, the mechanisms of aluminum and iron salts enhancing the removal of p-ASA by potassium ferrate were different. During the coupling process, AlCl3 and FeCl3 enhanced the self-decomposition rate of K2FeO4 with △kAl = 3.0530 and △kFe = 0.0912, respectively, resulting in difference on the generation of Fe(IV) and Fe(V). FeCl3 facilitated more effective Fe(IV) and Fe(V) production (FeCl3eff/AlCl3eff＞1), and multiple active iron species degraded p-ASA into inorganic arsenic, p-aminophenol (p-AP), nitarsone (NIA), and other products. Additionally, in the presence of K2FeO4, the hydrolytic dominant species of AlCl3 and FeCl3 were influenced under near-neutral conditions (pH 6–8), and Al13 and polynuclear Fe-hydroxides (PnFe-H) effectively improved the removal efficiency of inorganic arsenic and other organic products. The in-situ generation of nanoiron particles by K2FeO4 altered the original floc structure of the coagulants, with the specific surface areas of the flocs being 8733.176 cm2/cm3 for K2FeO4-AlCl3 and 7232.856 cm2/cm3 for K2FeO4-FeCl3. The coupling of K2FeO4 with metal salt coagulants not only enhanced p-ASA removal but also effectively improved the floc structure.

Effect of ultrasound treatment on thawing process of frozen tofu prepared with different salt coagulants

This study investigated the effects of ultrasound-assisted water thawing (UWT) at different power levels (0, 100, 150, 200, and 250 W) on the thawing rate and gel properties of frozen tofu made using three different salt coagulants (CaCl2, CaSO4, and MgCl2). Tofu produced with CaCl2 and CaSO4 elicited gel structures with dense and homogeneous networks, while that with MgCl2 had rough pores and irregular networks. UWT treatment significantly decreased thawing time by 30.9–53.5% compared to the control. Water holding capacity and scanning electron microscopy analyses demonstrated that UWT-100, UWT-150, and UWT-200 should be used to increase the amount of fixed water for CaCl2, CaSO4, and MgCl2. These findings suggest that appropriate ultrasonic treatment could improve the water retention capacity of the tofu network and make the gel network structure more compact. Additionally, protein structural analysis showed a decrease in the exposure of hydrophobic groups and reduced protein denaturation when tofu prepared with all the coagulants were thawed with UWT energies of 100–200 W ultrasonication. These findings offer theoretical support for improving the frozen tofu thawing process while ensuring optimal final product quality.

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.

Enhanced removal of trace pesticides and alleviation of membrane fouling using hydrophobic-modified inorganic-organic hybrid flocculants in the flocculation-sedimentation-ultrafiltration process for surface water treatment

Pesticide concentrations in surface water occasionally exceed regulated values due to seasonal events (rainy season in high intensity agricultural areas) or intermittent discharges (leakage, spillage, or other emergency events). The need to remove pesticide compounds in these situations poses a challenge for drinking water treatment plants (DWTPs). In this work, the performance of dosing hydrophobic-modified inorganic-organic hybrid flocculants (HOC-M; lower acute toxicity than corresponding metal salt coagulants; acceptable economic costs when M=Al or Fe; prepared in large-scale quantities), for the removal of four different pesticides (each initial concentration: 0.25 μg/L) from Yangtze River water, and in mitigating membrane fouling, by an integrated flocculation-sedimentation-ultrafiltration (FSUF) process, was evaluated over a period of 40 days; the FSUF is well-established in many DWTPs. The mechanisms underlying the treatment were unveiled by employing a combination of instrumental characterizations, chemical computations, material flow analyses, and statistical analyses. Efficient pesticide removal (80.3%∼94.3%) and membrane fouling reduction (26.6%∼37.3% and 28.3%∼57.6% for reversible and irreversible membrane resistance, respectively) in the FSUF process were achieved by dosing HOC-M, whereas conventional inorganic coagulants were substantially inferior for pesticide removal (< 50%) and displayed more severe fouling development. Hydrophobic association between the pesticides and the hydrophobic organic chain of HOC-M played a predominant role in the improvement in pesticide removal; coexisting particulate/colloid inorganic minerals and natural organic matter with HOC-M adsorbed on the surface, acting as floc building materials, provided sites for the indirect combination of pesticides into flocs. The observed fouling alleviation from dosing HOC-M was ascribed to both the pre-removal of fouling-causing materials in the flocculation-sedimentation prior to UF, and a stable hydrophilization modification effect of residual HOC-M in the UF unit. The latter effect resulted from a hydrophobic association between the PVDF substrate of the membranes and the hydrophobic organic chains of the HOC-M, causing the hydrophilic ends of the HOC-M to be exposed away from the membrane surface, thereby inhibiting foulant accumulation. This work has not only demonstrated the superior performance of dosing HOC-M in the FSUF process for trace pesticide removal in DWTPs, but also clarified the underlying mechanisms.

Delivering Phenolic Acids in Soy Protein Gels: Noncovalent Interactions Control Gastrointestinal Bioaccessibility

This study aimed to explore how the delivery of added phenolic acids was affected by the soy protein gel matrix using the INFOGEST static in vitro digestion protocol. Gels were prepared by two consecutive heating steps and by adding glucono–delta–lactone (GDL) as an acidifier or magnesium sulphate (MgSO_{4}) as a salt coagulant. The addition of phenolic acids in GDL gels doubled their elastic modulus (G’) (p<0.05), without showing the same effect on MgSO_{4} gels. Nevertheless, the bioaccessibility of phenolic acids was not significantly different between the gel matrices (p>0.05). The release of all phenolics was almost complete (>80%) at the oral phase (pH 7) and significantly lower at gastric phase (pH 3), then at intestinal phase, the release was either increased or significantly reduced depending on the phenolic acid structure. The results of this study suggest that the bioaccessibility of the added phenolic acids is controlled by their interactions with the soy protein gels rather than the protein digestion kinetics of the gels.

Methods for enrichment and nucleic acid detection of SARS-CoV-2 in sewage

Since the outbreak of COVID-19, SARS-CoV-2 surveillance in sewage based on sewage epidemiology has been established in many countries around the world, while there is a lack of a standard detection method for SARS-CoV-2 in sewage in China. This standard provides three methods for the enrichment of SARS-CoV-2 in sewage, namely polyethylene glycol precipitation, aluminum salt coagulation precipitation and centrifugal ultrafiltration, which are suitable for the enrichment and nucleic acid detection of SARS-CoV-2 in domestic sewage and sewage from medical institutions. This standard is of great significance for standardizing the SARS-CoV-2 detection in sewage and ensuring the scientific and effective detection of SARS-CoV-2 in sewage.

An effective titanium salt dosing strategy for phosphorus removal from wastewater: Synergistic enhancement of chemical and biological treatment

Titanium salt coagulant, as a new type of water treatment agent, has been widely studied, but most researches do not consider its effect on the biological treatment. In this study, different doses of TiCl4 were added to the biological phosphorus removal (BPR) system to investigate the impact of TiCl4 on BPR. The results showed that the addition of TiCl4 not only significantly reduced the phosphorus concentration in effluent (below 0.5 mg/L), but also kept it stable. Moreover, the sedimentation performance of activated sludge was improved, which was superior to the control group. According to the results of flow cytometry (FCM), a small amount of TiCl4 significantly improved the bioactivities, but excessive dosage caused inhibition. When the dosage of TiCl4 below 20 mg/L, polyphosphate accumulating metabolism (PAM) was strengthened. In addition, the richness of microbial community and the relative abundance of Candidatus Accumulibacter clades also increased. However, when the dosage reached 60 mg/L, the relative abundance of Candidatus Competibacter increased and the BPR system was deteriorated. This study suggests that the addition of appropriate concentration of TiCl4 can realize the synergistic enhancement of biological and chemical phosphorus removal in sewage treatment.

Understanding the effect of residual aluminum salt coagulant on activated sludge in sequencing batch reactor: Performance response, activity restoration and microbial community evolution

To investigate the effect of residual coagulant after coagulation pretreatment on activated sludge system of wastewater treatment plants (WWTPs), comparative evaluation of lab-scale sequencing batch reactors under different poly-aluminum chloride (PAC) concentrations (20 and 55 mg/L), presenting the performance differences of reactors. Results showed that the PAC concentration of 20 mg/L slightly enhanced the average removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN), up to 93.43% and 72.52%. Whereas, an inhibition effect was exerted at the PAC concentration of 55 mg/L, the average removal efficiencies decreased to 88.56% and 57.80% respectively. Similarly, the residual aluminum salts showed a concentration effect of low promotion and high inhibition on sludge activity index. The content of specific oxygen utilization rate (SOUR) and dehydrogenase (DHA) sharply decreased by 30.17% and 53.56% under the high PAC concentration of 55 mg/L. Activity recovery phase showed that the suppression of aluminum salt coagulant on biological system was reversible. High-throughput sequencing presented that the relative abundance of microbes showed obvious variations at different PAC concentrations, and certain bacteria in Chloroflexi and Bacteroidota exhibited better adaptability to the high PAC concentration environment. Nevertheless, the antagonism action between denitrifying genera and other genera as well as the downregulation of functional enzymes regarding nitrogen metabolism gave rise to the deterioration of denitrification under the high PAC concentration of 55 mg/L. This study revealed the influence mechanism of residual aluminum salt coagulant on activated sludge system, providing strategies for efficient decontamination and long-term stable operation of biological system in wastewater treatment plant under the condition of adding PAC.

Failure analysis of ammonium chloride salt coagulation corrosion of U-tube heat exchanger in diesel hydrogenation unit

Diesel hydrogenation unit is an important equipment for processing inferior oil in petroleum refining enterprises. Among them, the U-tube heat exchanger has been in high temperature and corrosive environment containing chlorine for a long time. Serious problem of tube bundle corrosion failure caused by ammonium chloride salt deposit. Anatomy of the diesel hydrogenation heat exchanger showed that the leakage part mainly appeared in the outermost bundle of the heat exchanger tube near the exit section, and the local area showed a large area of gully damage. Metallographic and XRD results show that the failure tube bundle material does not have manufacturing defects, and the corrosion location scale contains NH4Cl and iron oxides. The process flow analysis based on PR-NRTL model showed that the heat exchanger was in the NH4Cl crystallization temperature range, and the crystallization temperature increased with the increase of N and Cl contents in raw materials. Fluid simulation analysis of inlet tube box and single U-tube is carried out by using component transport equation and condensation model. Computational fluid dynamics (CFD) results indicate that there is a low velocity zone with high volume fraction of gas phase in the tube box. The higher gas volume fraction results in the formation of more NH4Cl particles into the U-tube bundle during heat transfer cooling. With the decrease of temperature, liquid water content in U-tube increases gradually and mainly distributes at both sides and bottom of tube bundle. The gas phase gradually fills the top of the tube bundle, and the oil and gas stratification becomes more obvious. The mass transfer rate and corrosion rate were the highest at the bottom and both sides of the tube bundle. With the temperature decreases, the NH4Cl particles generated in the tube continue to increase. The particles were deposited at 2000–3000 mm near the outlet section of the U-tube tube. NH4Cl particles absorbed liquid water, resulting in under-deposit corrosion of the tube bundle, and eventually led to the thinning and leakage of the heat exchanger tube bundle.

The effect of coagulation on the removal of algogenic organic matter and the optical parameters for predicting disinfection byproducts

Algae-derived disinfection byproducts (DBPs) are receiving increasing attention. Coagulation is the first water treatment section in removing algogenic organic matter (AOM). However, there is a significant knowledge gap in the effects of coagulation on DBPs produced from AOM. In this study, in view of the multi-component AOM, several analysis methods were combined to investigate the changes in AOM of Microcystic aeruginosa during the coagulation treatment, including ultraviolet–visible absorbance, multi-peaks Gaussian fitting method based on differential absorption spectroscopy, Excitation-emission matrix, and Fourier transform infrared spectroscopic analysis. To identify the characteristic parameters that could indicate the formation of DBPs, the yields of twenty-one DBP species produced from the residual AOM after the coagulation treatment were investigated. The correlations between DBPs and the spectral parameters were also analyzed. The results showed that aluminum salt coagulant could significantly remove protein-like compounds, chlorophyll, and phycocyanin in AOM, but it had a limited ability to precipitate AOM. With the increase of aluminum sulfate coagulant, the yields of DBPs produced from the residual extracellular organic matter decreased, while those produced from the residual intracellular organic matter decreased firstly and then gradually increased. The Pearson’s correlation results showed that the combination of fluorescent regions of protein-like and humic acid-like could be used as an optical surrogate for predicting the formation of DBPs.

Simultaneous mitigation of disinfection by-product formation and odor compounds by peroxide/Fe(II)-based process: Combination of oxidation and coagulation

To remove disinfection by-product (DBP) precursors and mitigate odor compounds, peroxide (peroxymonosulfate and persulfate)/Fe(II)-based process was applied as a combination of coagulation and oxidation. Compared with traditional Fe-based salt coagulation (FeSO4 and FeCl3), peroxide/Fe(II)-based process was more efficient in dissolved organic carbon, UV254 and turbidity removal, and peroxymonosulfate showed better performance than persulfate. The better coagulation performance arose from a combination of enhanced neutralization and different characteristics of flocs. Even though the combined process would increase the bromine substitution factor of DBPs, DBP formation and DBP-associated toxicity after peroxide/Fe(II)-based process were 9.2–38.8% and 5.2–27.2% lower than that after conventional Fe(III) coagulation. Both enhanced dissolved organic matter removal and oxidation of DBP precursors played vital roles in DBP control. Conventional Fe-based salt coagulation could hardly remove odor compounds (less than 10%, generally), whereas 28.2–84.9% of odor compounds were degraded during peroxide/Fe(II)-based process, due to free radical formation. This study demonstrated that PMS/Fe(II)-based process might be a promising treatment process for simultaneous DBP control and odor removal in source water.

Analysis of key factors in the coagulation of metal salts based on the calculation of hydrolysis-precipitation distribution

Hydrolysis and precipitation are the key processes that determine the coagulation performance of inorganic metal salts. The valence and concentration of metal salts, ligands, and solution pH all influence the coagulation performance. In order to get a full picture on the pros and cons of various inorganic metal salts as coagulants, this paper conducted thermodynamic equilibrium calculations and coagulation experiments to analyze and verify the hydrolysis-precipitation areas and speciation of four inorganic metal salts (aluminum, iron, titanium, and zirconium) in the absence and presence of ligands. In addition, the contributions of polynuclear hydrolysates in the hydrolysis and precipitation of the four metal ions were quantitatively described. Furthermore, the underlying mechanisms of the effects of common aquatic ligands on coagulation performance were discussed from the perspective of solution chemistry. The above results provide a theoretical basis for the development and application of inorganic metal salt coagulants, and are of great significance for understanding the coagulation performance and mechanisms accurately.