Ultrasound-initiated synthesis of cationic polyacrylamide for oily wastewater treatment: Enhanced interaction between the flocculant and contaminants

Copolymers functionalized with quaternary ammonium compounds under template chain exhibit simultaneously efficient bactericidal and flocculation properties: Characterization, performance and mechanism

In this work, novel multifunctional cationic template copolymers with flocculation and sterilization capabilities were synthesized using a low-pressure ultraviolet (LP-UV) template polymerization method for the removal of kaolin and Escherichia coli (E. coli) from water. The influence of template agents on the structural performance of the copolymers was evaluated through characterization, which showed that template copolymer TPADM possesses a higher cationic charge density and a more complex rough surface, contributing to better flocculation performance than that of the non-template copolymer CPADM. Under optimal experimental conditions, TPADM-1 exhibited removal rates of 98.45% for kaolin and 99% for E. coli (OD600 =0.04), marginally outperforming the non-template copolymer. Simultaneously, TPADM-1 produced good adaptability to kaolin and E. coli wastewater in terms of wide pH, speculating that charge neutralization, adsorption bridging, patching, and sweeping simultaneously dominate the flocculation mechanism. Interestingly, SEM and 3D-EEM analysis confirm that the sterilization of E. coli occurs through two distinct functions: initially adsorption followed by subsequent cell membrane rupture and leakage of cellular contents, ultimately leading to cell death. This research further confirms the feasibility of the designed novel multifunctional copolymers for achieving simultaneous disinfection and turbidity removal, demonstrating practical applicability in real water treatment processes.

Understanding the Role of Surface Charge on Nanobubble Capillary Bridging during Particle-Particle Interaction

The interactions between particles due to long-range hydrophobic forces have been extensively investigated. The hydrophobic force is likely a capillary force that arises from the formation of capillary bridges due to the merging of nanobubbles. In this study, we aim to investigate the impact of the nanobubble surface charge on the capillary bridge and, subsequently, the interaction between particles. The surface charge of the nanobubbles was altered in the presence of various surfactants (cationic, anionic, and nonionic) and salts (mono-, di-, and trivalent). The particle-particle interaction was quantified by measuring the aggregate size of the hydrophobized glass particles. Both experimental and theoretical findings confirm that the interaction between particles was enhanced when the surface potential of the nanobubble was around the neutral regime. This is probably because, when the surface potential was close to neutral, the interaction between two surface-deposited nanobubbles dominated over electrostatic repulsion, which was more conducive to the formation of the nanobubble capillary bridge. The estimation of the constrained Gibbs potential also showed the capillary bridge to be more stable when surface charge density along the bridge gas-liquid interface was minimal.

Recent advances of ultrasound applications in the oil and gas industry

In the last two decades, ultrasound (US) technologies research has increasingly earned attention for applications in the oil and gas industry. Numerous laboratory and field research have proven ultrasonics as an efficient, sustainable and cost-effective technology for improving well productivity. This paper pursues the elaboration of a comprehensive review of the most recent research related to ultrasonic technologies for applications in the oil and gas industry. Statistical analysis of different functional categories and classification of the research publications were performed. Considering the research reviewed, there is a huge gap between numerical and field studies in comparison with the numerous laboratory studies, deeming it necessary to increase efforts on developing mathematical and numerical models and field-testing cases of the ultrasonic effect. A comprehensive review of the ultrasonic waves' mechanisms of action for enhanced oil recovery (EOR) and emulsification/demulsification was conducted. Despite the lack of consensus regarding the mechanisms, cavitation and thermal effects on wellbore fluid and formation rock have been widely accepted as two of the most influencing mechanisms. A compilation of the state-of-the-art research of numerical, laboratory and field studies in the last two decades was assembled. Most authors agreed that ultrasonics is a highly efficient method for EOR and emulsion treatment if the optimal conditions are identified and achieved. The development of screening criteria for the application of ultrasonic waves was recommended, as this technique and the same parameters should not be utilized for all reservoir types. Treatment with ultrasound waves has shown improvement of oil recovery efficiency rates of over 90% and viscosity reduction values over 80%. The most efficient results were observed when in combination with another conventional EOR method, where ultrasound boosts recovery efficiency. Potential new applications related to rock mechanics and additional research topics were also recommended.

Efficient dewatering of unclassified tailings with flocculant: role of ultrasound

Flocculants play an important role in the solid-liquid separation of tailings slurry, and its dosage directly impacts on the dewatering efficiency of tailings. Herein, the influence of ultrasonication on flocculant dosage in dehydration process of unclassified tailings was studied. The effects of flocculant dosage on initial settling rate (ISR), underflow concentration, and effective settling time in the process were investigated in detail. The directivity characteristics of ultrasound transducers with different frequencies in unclassified tailings slurry was simulated by MATLAB. The morphologies of underflow tailings at different flocculant dosages were detected by environmental scanning electron microscope (E-SEM). The relationship between flocculant dosage and fractal dimension (D_F) was quantitatively analyzed based on fractal theory. The influence mechanism of flocculant on the settling and thickening of unclassified tailings was revealed. The results show that the optimum flocculant dosage for the ultrasonically treated tailings slurry is 40 g/t, at which the ISR reach a maximum value of 0.262 cm/min and the final underflow concentration (FUC) reach a maximum value in 60 min. Compared with settling without ultrasonication, the optimum flocculant dosage is reduced by 10 g/t, the ISR increases by 10.45%, the effective settling time is reduced by 50 min, and the FUC increases by 1.65%. The fractal dimension of underflow tailings first increases and then decreases with the increase in flocculant dosage, the relationship of which is in accordance with Lorentz model.

Enhanced remediation of fracturing flowback fluids by the combined application of a bioflocculant/biosurfactant-producing Bacillus sp. SS15 and its metabolites

Fracturing flowback fluids (FFFs), which is generated from the process of oil and gas exploitation, is one of the major environmental concerns. In this study, a bacterial strain, Bacillus sp. SS15, capable of producing both bioflocculant (BF) and biosurfactant (BS), was isolated from oil-contaminated mudflat sediment. The BS produced by SS15 was identified as lipopeptide, which could reduce the surface tension of water from 74.2 mN/m to 36.6 mN/m with a critical micelle concentration of 44.4 mg/L. It also exhibited strong tolerance against a wide range of pH (2-12), temperature (4-60 °C), and salinity (0-100 g/L). Meanwhile, the BF produced by SS15 exhibited high flocculating activity (84.9%) for kaolin suspension, and was confirmed to be thermostable, salt-tolerant, and alkaliphilic. The combined treatment of bioremediation (introducing SS15 and BS) followed by flocculation (introducing BF) greatly promoted the removal of chroma (85.7% reduction), suspended solids (94.4% reduction), chemical oxygen demand (84.9% reduction), n-alkanes (50.0% reduction), and polycyclic aromatic hydrocarbons (66.5% reduction), respectively. The genome analysis showed that strain SS15 possessed abundant genes related to the synthesis of carbohydrate, protein, and lipid, which might play an important role in BF and BS synthesis. The findings in this study demonstrated that Bacillus sp. SS15 has promising prospect in the remediation of FFFs.

Optimizing the Conditions of Cationic Polyacrylamide Inverse Emulsion Synthesis Reaction to Obtain High–Molecular–Weight Polymers

Cationic polyacrylamide (CPAM) emulsifier is widely applied in the wastewater treatment industry, mining industry, paper industry, cosmetic chemistry, etc. However, optimization of input parameters in the synthesis of CPAM by using the traditional approach (i.e., changing one factor while leaving the others fixed at a particular set of conditions) would require a long time and a high cost of input materials. Onsite mass production of CPAM requires fast optimization of input parameters (i.e., stirring speed, reaction temperature and time, the amount of initiator, etc.) to minimize the production cost of specific–molecular–weight CPAM. Therefore, in this study, we synthesized CPAM using reverse emulsion copolymerization, and proposed response surface models for predicting the average molecular weight and reaction yield based on those input parameters. This study offers a time–saving tool for onsite mass production of specific–molecular–weight CPAM. Based on our response surface models, we obtained the optimal conditions for the synthesis of CPAM emulsions, which yielded medium–molecular–weight polymers and high conversion, with a reaction temperature of 60–62 °C, stirring speed of 2500–2600 rpm, and reaction time of 7 h. Quadratic models showed a good fit for predicting molecular weight (Adj.R2 = 0.9888, coefficient of variation = 2.08%) and reaction yield (Adj.R2 = 0.9982, coefficient of variation = 0.50%). The models suggested by our study would benefit the cost–minimization of CPAM mass production, where one could find optimal conditions for synthesizing different molecular weights of CPAM more quickly than via the traditional approach.

A review of flocculants as an efficient method for increasing the efficiency of municipal sludge dewatering: Mechanisms, performances, influencing factors and perspectives

Mechanical sludge dewatering is one of the stages of the municipal wastewater treatment process, which allows the amount of generated sludge and the cost of its transport and management to be reduced. Achieving a high degree of dewatering is possible thanks to the use of flocculation technology. The article presents issues related to the theory of flocculation, sewage sludge, and its dewatering. The main mechanisms of flocculation, the kinetics of the process, the division of flocculants, and flocculation in dual systems are discussed. The influence of particular parameters on the efficiency of flocculation and the dewatering of sewage sludge was analyed. The assessed parameters are: pH, the presence of salt, the mixing process, the structure and ionicity of chains, and the dose. The results of experimental studies on the dewatering of various types of sludge were compared. The literature review included in the paper helps to better understand the process of flocculation and sludge dewatering, and presents the progress to date and the possible directions for further development in this field.

Removal of emulsified oil from water by using recyclable chitosan based covalently bonded composite magnetic flocculant: Performance and mechanism

In this work, a novel recyclable covalently bonded magnetic flocculant (FS-MC) was successfully prepared by combining chitosan-based modified polymers (MCS) with Fe₃O₄@SiO₂ through a silane coupling agent. The covalent bond Fe-O-Si-O-C and the core-shell structure of FS-MC were confirmed through several characterization methods. The emulsified oily wastewater flocculation performance and mechanism by using FS-MC were evaluated and studied. Results showed that 94.47%, 93.95%, and 92.98% of emulsified oil could be removed by using FS-MC1, FS-MC2 and FS-MC3 at dosages of 2.0, 2.5, and 2.0 mg/L, respectively. Furthermore, FS-MC exhibited an excellent behavior on the removal of organic compounds with molecular weight > 10 kDa, including long chain alkanes, cycloalkanes, and aromatic hydrocarbon compounds. In addition, triple-phase separation of oil, water and flocculants was achieved by using magnetic FS-MC. Due to the introduction of cationic and hydrophobic groups in FS-MC, charge neutralization, compression double electric-layer action, hydrophobic interaction, interfacial adsorption bridging and sweep-flocculation synergistically contributed and enhanced the removal of emulsified oil. Recycling experiments also showed that no obvious decrease of oil removal rate was observed by using magnetic FS-MC flocculants in five cycles.

Oily Wastewater Treatment: Overview of Conventional and Modern Methods, Challenges, and Future Opportunities

Industrial developments in the oil and gas, petrochemical, pharmaceutical and food sector have contributed to the large production of oily wastewater worldwide. Oily wastewater pollution affects drinking water and groundwater resources, endangers aquatic life and human health, causes atmospheric pollution, and affects crop production. Several traditional and conventional methods were widely reported, and the advantages and limitations were discussed. However, with the technology innovation, new trends of coupling between techniques, use of new materials, optimization of the cleaning process, and multiphysical approach present new paths for improvement. Despite these trends of improvement and the encouraging laboratory results of modern and green methods, many challenges remain to be raised, particularly the commercialization and the global aspect of these solutions and the reliability to reduce the system’s maintenance and operational cost. In this review, the well-known oily wastewater cleaning methods and approaches are being highlighted, and the obstacles faced in the practical use of these technologies are discussed. A critical review on the technologies and future direction as the road to commercialization is also presented to persevere water resources for the benefit of mankind and all living things.

Flocculation of emulsified oily wastewater by using functional grafting modified chitosan: The effect of cationic and hydrophobic structure

In this work, modified chitosan flocculants (MCS) was synthesized by using chitosan (CS), acrylamide, cationic monomers and hydrophobic monomers via low-pressure UV-initiated copolymerization. The flocculation performance of MCS was evaluated in emulsified oily wastewater treatment. The effect of cationic and hydrophobic structure on oil removal was studied, and the interactions between these functional groups and the components in oil were also analyzed. Results suggested that MCS flocculants exhibited excellent oil removal efficiency in a wide pH range (2.0‒10). The flocculation efficiency of 91 % was achieved at the dosages of 0.6 mL/L (6 mg/L). During pH of 2.0-10, the optimal cationic and hydrophobic monomer was DMC and VT, respectively. Silane groups were favorable for oil removal than the other hydrophobic structures. The cationic groups expanded the optimal pH range of MCS in flocculation, whereas hydrophobic groups considerably reduced the dosage of MCS. The experimental results showed that alkane, cyclic aromatic hydrocarbon compounds in oil can be easily removed by using MC4, whereas cycloalkanes compounds was effectively removed by MC6 and MC7 because of preferable demulsification capacity, and the hydrophobic interaction, interfacial adsorption and electrostatic attraction played the dominant in flocculation. Thus, the synthesized MCS is favorable for emulsified oily wastewater treatment.

Recent advances in applications of power ultrasound for petroleum industry

Power ultrasound, as an emerging green technology has received increasing attention of the petroleum industry. The physical and chemical effects of the periodic oscillation and implosion of acoustic cavitation bubbles can be employed to perform a variety of functions. Herein, the mechanisms and effects of acoustic cavitation are presented. In addition, the applications of power ultrasound in the petroleum industry are discussed in detail, including enhanced oil recovery, oil sand extraction, demulsification, viscosity reduction, oily wastewater treatment and oily sludge treatment. From the perspective of industrial background, key issue and resolution mechanism, current applications and future development of power ultrasound are discussed. In addition, the effects of acoustic parameters on treatment efficiency, such as frequency, acoustic intensity and treatment time are analyzed. Finally, the challenges and outlook for industrial application of power ultrasound are discussed.

Preparation of a hydrophobically associated cationic polyacrylamide and its regulation of the sludge dewatering performance

A hydrophobically associating cationic polyacrylamide (HACPAM) was prepared by using a micellar polymerization method with V-50 (azobisisobutyramidine hydrochloride) as the initiator and acrylamide, acryloyloxyethyl trimethylammonium chloride and butyl methacrylate as substrates under ultraviolet light irradiation. Structural analysis using Fourier transform infrared spectroscopy, proton nuclear magnetic resonance and X-ray photoelectron spectroscopy analyses showed that the substrates were successfully polymerized. HACPAM was used to condition sludge to improve its dewatering performance, and the results showed that as the amount of HACPAM increases, the sludge dewatering performance is significantly improved, and 3.532 kg/t dry solids of HACPAM is regarded as the optimal amount. Compared with the commercially available cationic polyacrylamide (CPAM), HACPAM has a stronger hydrophobic group association effect, with better promotion of the conversion of bound water in sludge flocs into free water, thereby improving the sewage dewatering performance. The 3D spatial structure of dewatered sludge cakes analyzed by computed tomography technology showed that the number of pores of the dewatered sludge cake treated by HACPAM 3 was smaller than that of the cake treated by CPAM, with a reduction in the porosity of 68.8%, resulting in a better hydrophobic effect. In addition, the mechanism of HACPAM improving the dewatering performance is discussed.

Nanofibrous, Emulsion-Templated Syndiotactic Polystyrenes with Superhydrophobicity for Oil Spill Cleanup

A series of syndiotactic polystyrene (sPS) monoliths with controllable shapes, nanofibrous structures, hierarchical pores, superhydrophobicity, high specific surface area, and high strength have been fabricated for the first time by solidifying nonaqueous high internal phase emulsions (HIPEs) through crystallization-induced gelation. The nonaqueous HIPEs were formed by dispersing glycerol in 1,2,4-trichlorobenzene stabilized by sulfonated sPS at a high temperature of 120 °C, and with sPS in the continuous phase, these HIPEs were solidified by cooling at room temperature to obtain sPS monoliths. The shapes of the sPS monoliths were controllable, and excitedly, nanofibrous structures were found at void walls, with fiber diameters ranging from 20 to 100 nm. The sPS monoliths exhibited pores in different scales: emulsion-templated voids at nearly 10 μm with pore throats ranging from 1 to 2 μm and macropores and mesopores between nanofibers, enabling the monoliths to exhibit extremely high specific surface area of up to 420 m²·g^-1. The porous sPS monoliths were robust, and they did not fail even at a compressive strain of 70%, with Young's moduli ranging from 157.7 to 2638.0 kPa. The monoliths were superhydrophobic and oleophilic, with water contact angles over 150° and with oils absorbed rapidly. The superhydrophobicity and oleophilicity enabled the porous sPS monoliths to absorb bulk oils on the water surface, underwater oils, and even oils within oil-in-water emulsions. The monoliths absorbed a large amount of organic solvents, edible oils, and fuel oils with equilibrium liquid uptakes up to 81.3, 44.4, and 41.9 g·g^-1 for chloroform, olive oil, and diesel, respectively. The liquid absorption was rapid, and the monoliths exhibited a relatively high reusability. These porous sPS monoliths were demonstrated to be a candidate for the applications of oil/water separation and/or oil spill cleanup.

Effect of carbon source on lipid accumulation and biodiesel production of Yarrowia lipolytica

Yarrowia lipolytica (Y. lipolytica) is an oleaginous yeast that can utilize hydrophobic substrates as carbon source to produce single-cell lipids for biodiesel production. This study attempts to increase the lipid accumulation ability of Y. lipolytica by first gradually elevating pure oil substrate concentration during the cultivation and then adding short-chain carbon compounds, such as glucose and sodium acetate, to a culture substance according to the optimal oil concentration. Results showed that Y. lipolytica cultured under 40.0 g L^-1 oil concentration showed higher lipids (2.97 g L^-1) and lipid content (37.35%, DW) compared with that cultured under 20.0 g L^-1, where the corresponding values were 1.91 g L^-1 and 24.46%. By contrast, the lipid content of Y. lipolytica increased from 37.35 to 41.50% when the substrate was changed from 40.0 g L^-1 pure oil to 5% sodium acetate combined with 95% oil under the same total carbon concentration. However, lipid accumulation did not increase even though 15% sodium acetate or 5% glucose, or 15% glucose was added to the combined substrate. Moreover, the lipid biomodification of Y. lipolytica was evident when it was cultured under the oil concentration of 20.0 g L^-1. Therefore, the lipid accumulation of Y. lipolytica can be elevated through the gradient increase of oil concentration and by adding a suitable amount of easily degradable carbon source. Furthermore, the lipid biomodification of Y. lipolytica improves biodiesel quality.

Flocculation of a High-Turbidity Kaolin Suspension Using Hydrophobic Modified Quaternary Ammonium Salt Polyacrylamide

In this work, a novel cationic polyacrylamide (PAMD) was synthesized by acrylamide (AM) diallyl dimethyl ammonium chloride (DMD) and dodecyl polyglucoside (DPL) under low-pressure ultraviolet (UV) initiation. The intrinsic viscosity and cationic degree of PAMD were optimized in copolymerization. The optimum synthesis conditions that affect polymerization were determined to be solid content 30%, DPL content 25%, DMD content 30%, illumination time 135 min, and pH 9. The flocculation performance of flocculant PAMD with a high cationic degree was investigated in the purification of high-turbidity water. The flocculation mechanism was correspondingly studied and summarized based on Fourier transform-infrared (FTIR) analysis. Finally, the results of an experimental simulation using the response surface method show that 98.9% supernatant transmittance was achieved under dosage 4 mg/L, fast stirring time 20 min, pH 7, and stirring speed 320 rpm.

Evaluation of a novel dextran-based flocculant on treatment of dye wastewater: Effect of kaolin particles

Graft modified flocculants have recently received increasing attention in the field of water treatment as they have the combinative advantages of synthetic and natural polymeric flocculants. In this work, surface-active monomer benzyl(methacryloyloxyethyl)dimethylammonium chloride (BMDAC) was selected to graft on dextran (DX) with high molecular weight (10.3 × 10⁶ g/mol) produced through enzyme-catalyzed process in order to remove dissolved dyes from wastewater. The flocculant (DAB) was fabricated by ultrasound initiated polymerization technique, and the structure characterization of FTIR, ¹H/¹²C NMR, XRD and XPS spectrum confirmed the successful grafting. Then the Congo red (CR) removal efficiency by DAB was optimized based on the flocculation conditions, including wastewater initial pH, flocculant dosage and initial dye concentration. The effect of suspended solids on the removal of dyes was evaluated in kaolin-CR simulated wastewater. The results indicated that the optimal removal efficiency of CR was 68.1% and 88.2% in single CR and kaolin-CR flocculation system, respectively. The improvement of removal efficiency was attributed to the fact that partial CR molecules were adsorbed onto kaolin particles before flocculation, and were synergistically flocculated accompanied by kaolin particles. Finally, the flocculation mechanism was discussed by a detailed investigation of the zeta potentials, FTIR and XPS spectra of flocs, which can provide important reference for optimizing the flocculation conditions and designing novel high-performance flocculants.

A novel carboxyl-rich chitosan-based polymer and its application for clay flocculation and cationic dye removal

Due to the complexity of contaminants, the effectiveness of traditional flocculants toward water purification is insufficient. To break the limitation, a novel polymer flocculant [chitosan grafted poly (acrylamide-itaconic acid), CS-g-P(AM-IA)] was synthesized via ultraviolet-initiated graft copolymerization reaction. Characterization results revealed that the graft copolymers were successfully synthesized and with rougher surface structure. The solubility of CS-g-P(AM-IA) and chitosan grafted polyacrylamide (CS-g-PAM) were greatly improved and they can dissolve in the wide pH range of 2.0-12.0. CaCl₂ was used as a source of cation bridge to enhance the flocculation of kaolin particles, and its optimum dosage was 150 mg·L^-1. At dosage of 30 mg·L^-1 and pH of 5.0, the turbidity removal efficiency of CS-g-P(AM-IA) reached the maximum of 93.8%, whereas those of CS-g-PAM and CS were 96.7% and 76.9%, respectively. The patchwise adsorption of ionic groups embedded in the molecular chain on Ca²⁺-clay complexes took effect to generate flocs with larger particle size. Besides, the decolorization ability of cationic dyes by CS-g-P(AM-IA) was greatly enhanced due to the role of abundant carboxyl groups. In the crystal violet (CV) adsorption experiment, the maximum CV dye removal efficiency for CS-g-P(AM-IA) reached the maximum of 81.6% at dosage of 0.7 mg·mL^-1 and pH of 9.0, while those for CS-g-PAM and CS were 51.7% and 36.5%, respectively.

Magnetic flocculants synthesized by Fe3O4 coated with cationic polyacrylamide for high turbid water flocculation

A novel magnetic flocculant (CPAMF) was synthesized by using Fe₃O₄ coated with cationic polyacrylamide (CPAM) for flocculation of high turbid water. The surface morphology and chemical structures of CPAMF were confirmed by Fourier transform infrared spectroscopy (FTIR) and thermo-gravimetric analysis (TGA). X-ray diffraction (XRD) was employed to verify the crystal structure of CPAMF. The magnetic property of CPAMF was compared with Fe₃O₄ in this study. The flocculation performance by using flocculants CPAMF was evaluated in high turbid water treatment. The maximum transmittance 92.4% of kaolin suspension was achieved at corresponding optimal flocculation conditions. The result indicated that CPAMF was efficient in high turbid water flocculation. Analysis of FTIR, XRD of flocs, and zeta potential (ZP) of supernatant were accomplished for flocculation mechanism investigation. Because of low recovery factor in reflocculation under the effect of shear force on flocs, the bridging effect was found to be dominant in both acidic and alkaline conditions. Sedimentation experiments under the role of permanent magnet indicated that nano-Fe₃O₄ could effectively improve the settling property of CPAM. Graphical abstract ᅟ.

Screening of physicochemical treatment processes for reducing toxicity of hair care products wastewaters

Toxicity reduction in wastewaters from small hair care products manufacturing companies using coagulation/flocculation/sedimentation or flotation, membrane separation and powdered activated charcoal adsorption was evaluated. Raw wastewater composition varied widely within and especially between companies, but all exhibited high acute toxicity to Daphnia similis (EC(I)50; 48 h < 0.02-0.33%). Coagulation with aluminum sulfate and polyaluminum chloride aided by cationic or anionic polymers, as well as filtration on ultra (UF) and nanofiltration (NF) membranes efficiently removed turbidity (>99%) and oil and grease (>99%) and all treated samples exhibited similar dissolved organic matter contents. However, elimination of acute toxicity was only achieved after UF on submerged hollow fiber membrane, while other membrane modules (tubular UF and NF) produced filtrates with residual toxicities equal to or higher than the wastewater samples treated by coagulation processes. Adsorption removed up to 90% of the soluble COD remaining after coagulation or membrane processes, but did not eliminate acute toxicity, possibly because of the presence of activated charcoal or substances leached from it in the treated samples. The results indicate the need for further studies to develop treatment strategies that can guarantee non-toxic effluents at costs compatible with those of the simple manufacturing processes used at small-scale cosmetics manufacturing plants.

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

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

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

Effective treatment of emulsified oil wastewater by the coagulation–flotation process

Ship emulsified oil wastewater was used as the research object in this study. The highly efficient coagulant demulsification degreasing mechanism and microbubble flotation technology were combined and the effects of coagulant type and dosage amount on the demulsification of emulsified oil wastewater were evaluated. The influence of the mixed coagulation effect of pH values, temperature, and hydraulic condition parameters were determined and water intake, air intake, and oil content were regulated. The coagulant for the demulsification of emulsified oil wastewater was screened; the dosage was 500 mg L⁻¹, and the removal capacity of the coagulant was in the following order: polyaluminum ferric chloride (PAFC) > polyaluminum chloride (PAC) > polysilicate aluminum ferric sulfate (PSAFS) > alum > Al₂(SO₄)₃ > polyferric sulfate > FeCl₃. Polyacrylamide (PAM) with added water was used to further reduce the oil content. The PAFC, PAC, and PSAFS were selected as coagulation–air flotation dynamic test alternative agents. The investment quantities of PAFC, PSAFS and PAM were 300 mg L⁻¹, 300 mg L⁻¹ and 30 mg L⁻¹, respectively. The stirring time was 5 min, the pH value was 6.5–6.9, the flow rate was 0.25 m³ h⁻¹, the oil content of the emulsified oil wastewater was 3000–5000 mg L⁻¹ and the effluent oil was stable below 15 ppm. The microbubble generation device using air flotation effluent was used in the two air flotation treatments to enhance the device efficiency. The air flotation device adopted the structural design of the upper part of the water inlet and the lower part of the micro-air bubble, which can increase the collision probability of the microbubble and improve the efficiency of oil removal.

Ship emulsified oil wastewater was used as the research object in this study.

The investigation of the specific behavior of a cationic block structure and its excellent flocculation performance in high-turbidity water treatment

The fabrication of a cationic polyacrylamide (CPAM) with high efficiency and economy has been highly desired in the field of high-turbidity water treatment. This study introduced an ultrasound (US)-initiated template polymerization (UTP) method to develop a novel cationic templated polyacrylamide (TPAA) with a microblock structure. TPAA was prepared using acrylamide (AM) and sodium (3-acrylamidopropyl)trimethylammonium chloride (ATAC) as the monomers and sodium polyacrylate (NaPAA) as the template. Factors that affected polymerization such as the ultrasound power, ultrasound time, initiator concentration, pH, and m_AM : m_ATAC and n_NaPAA : n_ATAC values were investigated. The properties of the polymers were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance spectroscopy (¹H NMR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results indicated the successful formation of a cationic microblock structure in TPAA. In addition, TPAA displayed favorable thermal decomposition properties and a rough and coarse surface morphology, as shown by analyses using TGA and SEM, respectively. Moreover, a zip (type I) template polymerization mechanism was identified via analyses of the association constant (K_M), conversion (C_v) and polymerization rate (R_p). The flocculation performance of the templated copolymer TPAA was evaluated by treating high-turbidity water. According to the results for the zeta potentials and FTIR spectra of the generated flocs, it was indicated that the cationic microblocks in the templated copolymer could greatly enhance its charge neutralization, patching and bridging ability, and therefore excellent flocculation performance (residual turbidity: 5.8 NTU, D_f: 1.89, floc size d₅₀: 608.404 μm and floc kinetic: 15.86 × 10⁻⁴ s⁻¹) for treating high-turbidity water was achieved.

The fabrication of a cationic polyacrylamide (CPAM) with high efficiency and economy has been highly desired in the field of high-turbidity water treatment.