Coagulation-ultrafiltration efficiency of polymeric Al-, Fe-, and Ti- coagulant with or without polyacrylamide composition

Preparation and Application of Polyaluminum Ferric Sulfate from Red Mud: Behaviors of Leaching, Polymerizing, and Coagulation

Red mud is a solid waste containing valuable components, such as aluminum and iron. This paper aims to recover aluminum and iron from red mud by acid leaching and prepare polyaluminum ferric sulfate (PAFS) to apply for the turbidity reduction treatment of coal slurry water. The behaviors of leaching, polymerizing, and coagulation were analyzed by leaching thermodynamics and advanced micro-detection methods. More than 90% of aluminum and 60% of iron in red mud were dissolved into the leaching solution by using 50% sulfuric acid (v/v) with 7 mL/g at 100 °C for 2 h, where the crystal lattice of cancrinite was significantly destroyed to promote the dissolution of aluminum. The low polymerization (Al + Fe)a, medium polymerization (Al + Fe)b, and high polymerization (Al + Fe)c could be generated in PAFS by adjusting the basicity of the leaching solution with 0.7-0.9. The removal efficiency of turbidity of wastewater could reach more than 95% by using PAFS at 25 mg/L in the pH range of 6.0-7.0. The turbidity reduction mechanism included not only the electric neutralization of (Al + Fe)a but also the adsorption of (Al + Fe)b and the entrapment effect of (Al + Fe)c. This current study contributes to the future development of red mud based on flocculants containing aluminum and iron for wastewater treatment.

Preparation of composite coagulant for the removal of microplastics in water

In this work, a composite flocculant (polyferric titanium sulfate-polydimethyldiallylammonium chloride [PFTS-PDMDAAC]) with a rich spatial network structure was prepared for the treatment of simulated wastewater containing polystyrene (PS) micro-nanoparticles. Characterization results showed that the surface of the PFTS-PDMDAAC was a three-dimensional network polymer of chain molecules that exhibited good thermal stability and formed an amorphous polymer containing multiply hydroxyl-bridged titanium and iron. When n(OH- ) : n(Fe) = 1:2, n(PO4 3- ) : n(Fe) = 0.35, n(Ti) : n(Fe) = 1:8, n(DMDAAC) : n(Fe) = 5:100, and the polymerization temperature is 60°C, the prepared composite flocculant has the best effect. The effects of dosage, pH, and agitation intensity on the flocculation properties of PFTS-PDMDAAC were also studied. The optimal removal rates of PS-μm and haze by PFTS-PDMDAAC were 85.60% and 90.10%, respectively, at a stirring intensity of 200 rpm, a pH of 9.0, and a PFTS-PDMDAAC dosage of 20 mg/L. The flocs produced by the PFTS-PDMDAAC flocculation were large and compact in structure, and the flocculation mechanism was mainly based on adsorption bridging. Kaolin played a promoting role in the process of PS-μm removal by PFTS-PDMDAAC floc and accelerated the formation of large and dense flocs. This study provided a reference for the coagulation method to remove micro-nanopollutants in the actual water treatment process. PRACTITIONER POINTS: A composite flocculant with rich spatial network structure (PFTS-PDMDAAC) was prepared. PFTS-PDMDAAC can effectively remove micro-nano polystyrene (PS) in wastewater. The floc produced by PFTS-PDMDAAC is large and compact in structure. The flocculation mechanism of PFTS-PDMDAAC is mainly adsorption bridging.

Role of inorganic foulants in the aging and deterioration of low-pressure membranes during the chemical cleaning process in surface water treatment: A review

Low-pressure membrane (LPM) filtration, including microfiltration (MF) and ultrafiltration (UF), is a promising technology for the treatment of surface water for drinking and other purposes. Various configurations and operational sequences have been developed to ensure the sustainable provision of clean water by overcoming fouling problems. In the literature, various periodic physical and/or chemical approaches to the cleaning of LPMs have been reported, but little data is available on the aging of MF/UF membranes that results from the interaction between the foulants and the cleaning agent. Periodic physical cleaning of the membrane is expected to return the membrane to its original performance capacity, but it only recovers to a certain level because the remaining foulants cause irreversible fouling. Chemical cleaning can then be employed to recover the membrane from this irreversible fouling but, in the process, it can cause irrecoverable damage to the membrane. In this review, the foulants responsible for irrecoverable damage to MF/UF membranes are summarized, and their interaction with cleaning agents and other foulants is described. The impact of these foulants on various membrane parameters, including filtration efficiency, flux decline, permeability, membrane characterization, and membrane integrity are also summarized and discussed in detail. In addition, mitigation options and future prospects are also discussed with regard to increasing the operational life span of a membrane in a cost-effective manner. Ultimately, this review suggests an advanced control system based on membrane-foulant interactions under the impact of various operational parameters to mitigate the integrity loss of membranes.

Removal behaviors and mechanism of polystyrene microplastics by coagulation/ultrafiltration process: Co-effects of humic acid

Microplastics (MPs) have been detected in drinking water, which could absorb or accumulate humic acid (HA) and threaten the water quality. Coagulation-ultrafiltration (CUF) is a common drinking water treatment technology, but its behavior and mechanism of removing MPs and MPs-HA remain unclear. In this study, the removal mechanism of polystyrene (PS)-MPs coagulated by Al- and Fe-based salts with or without HA was investigated to optimize the CUF process. The results showed that Al-based salt (92.7 %) was better than Fe-based salt (91.2 %) in the removal efficiency of PS or HA, and the optimal coagulants dosage of PS-HA composite system (12 mg·L^-1) was higher than that of the individual PS system (9 mg·L^-1). Moreover, the coagulation mechanism was studied by Fourier transform infrared spectroscope (FTIR) and X-ray photoelectron spectroscopy (XPS). The oxygen group in PS and PS-HA was the main binding site of Al and Fe hydrolysate, and the effects of charge neutralization, adsorption bridging, and sweep flocculation became weaker in turn at the optimal dosage. In addition, the cake layer formed by coagulation and the presence of HA alleviated the irreversible membrane fouling by intercepting flow and re-adsorption. This study guides the improvement of the traditional drinking water treatment process to remove MPs.

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.

Reduction of Ultrafiltration Membrane Fouling by the Pretreatment Removal of Emerging Pollutants: A Review

Ultrafiltration (UF) processes exhibit high removal efficiencies for suspended solids and organic macromolecules, while UF membrane fouling is the biggest obstacle affecting the wide application of UF technology. To solve this problem, various pretreatment measures, including coagulation, adsorption, and advanced oxidation, for application prior to UF processes have been proposed and applied in actual water treatment processes. Previously, researchers mainly focused on the contribution of natural macromolecular pollutants to UF membrane fouling, while the mechanisms of the influence of emerging pollutants (EPs) in UF processes (such as antibiotics, microplastics, antibiotic resistance genes, etc.) on membrane fouling still need to be determined. This review introduces the removal efficiency and separation mechanism for EPs for pretreatments combined with UF membrane separation technology and evaluates the degree of membrane fouling based on the UF membrane's materials/pores and the structural characteristics of the cake layer. This paper shows that the current membrane separation process should be actively developed with the aim of overcoming specific problems in order to meet the technical requirements for the efficient separation of EPs.