Cationic starch-based flocculant for cyanobacteria harvesting and algal sludge dewatering: Mechanisms and full-process risk assessment

• Flocculation improves vacuum filtration of ultrafine-rich iron ore tailings. • Cationic flocculants increase cake permeability at 0.9 bar pressure vacuum. • Cationic polyacrylamide and tannin provide the best dewatering performance. • Cake moistures of 12–14 wt% are achieved for feeds with 20–30 wt% ultrafines (<10 µm) • Under vacuum, capillary forces impose a high moisture limit at ≥ 40 wt% ultrafines. Efficient dewatering of iron ore tailings is critical for safer tailings management via dry stacking in Brazil. Typical tailings streams comprise a coarse, siliceous fraction from reverse cationic flotation and an ultrafine slime fraction (<10 μm) generated during desliming before flotation. In industrial practice, both fractions are thickened with anionic polyacrylamides and blended before vacuum filtration at a pressure differential of approximately 0.9 bar. For feeds containing ∼ 10–30 wt% ultrafine particles, this configuration typically produces filter cakes with 16–20 wt% moisture, above the 12–14 wt% target generally required for geotechnically stable dry stacking. This study evaluates chemical pretreatment strategies to improve the vacuum filtration process/performance of typical Brazilian slime-rich iron ore tailings. Conditioning with cationic tannin and/or high-molecular-weight cationic polyacrylamides markedly enhanced dewatering, enabling residual cake moistures of 12–14 wt% for feeds containing up to 30 wt% ultrafine particles. Under optimised conditions (pH 8.0; 55 wt% solids), cationic polyacrylamide achieved 12.5 wt% cake moisture, with a cake formation time of ∼ 10 s, cake thickness of 24 mm, and permeability of ∼ 300–500 mD (vs ∼ 225 mD for the untreated reference). Scanning electron microscopy indicated that cationic conditioning increased cake porosity and was consistent with the observed permeability gains. Overall, cationic-flocculant pretreatment offers a practical route to meet dry-stacking moisture targets for slime-rich iron ore tailings under moderate vacuum pressures, addressing a persistent issue in Brazilian operations.

Bridging mechanism of a hydrophobically associating cationic flocculant in kaolinite settling during two-step flocculation

Prolonged use ofoil-based drilling fluids often leads to the accumulationof inferior solids, resulting in gradual performance degradation,requiring eventual disposal. Current recycling technologies exhibitsignificant limitations in terms of cost-effectiveness, operationalfeasibility, and removal efficiency. For efficient recycling and reuse,this study synthesized a cationic polymer flocculant (CPF) with anarrow molecular-weight distribution via free-radical solution polymerization,using lauryl methacrylate and methacrylatoethyl trimethylammoniumchloride as monomers. The chemical structure and molecular weightof CPF were systematically characterized via Fourier transform infraredspectroscopy, proton nuclear magnetic resonance, and gel permeationchromatography. Thermogravimetric analysis indicated that CPF exhibitsgood thermal stability, with a decomposition temperature of 226 °C.Based on fractal dimension analysis, the optimal dosage of CPF wasdetermined to be 1%. Mechanistic studies revealed that CPF acts throughelectrostatic adsorption on the surface of low-density solids, effectivelyneutralizing particle surface charges, reducing interparticle electrostaticrepulsion, promoting floc formation, and improving settling efficiency.Meanwhile, its bridging effect enhances adhesion, ensuring structuralstability of flocs under shear conditions. Performance evaluationresults demonstrated that, at a CPF dosage of 1%, the initial settlingvelocity of low-density solids in mineral oil increased to 0.3 mm/s,and the transmittance of the supernatant reached 60%. After CPF assistedflocculation centrifugation treatment, the density of the spent oil-baseddrilling fluid, solid content, and apparent viscosity decreased by0.54 g/cm3, 15%, and 25 mPa·s, respectively, indicatingsignificantly improved rheological properties. These results demonstratethat CPF shows promising potential for the treatment and recyclingof spent oil-based drilling fluids.

This study investigates the flocculation behaviour of feldspar suspension using a variety of anionic, cationic, and non-ionic flocculants (A.336, A.338, A.1011, A.5250, A.110, A.120, A.1858, C.573, N.333 and N.351) in single and two-step flocculation systems. Experiments have been performed at various dosages ranging from 0.2 to 12.5 mg/L. Flocculation performance is evaluated based on turbidity, settling rate, and efficiency. Of the flocculants tested, non-ionic flocculant N.351 demonstrated the most effective flocculation performance in terms of both turbidity reduction and flocculation efficiency. N.351 achieved a flocculation efficiency of 98.5% at a dosage of 0.8 mg/L, achieving the lowest turbidity value of 6.4 NTU (Nephelometric Turbidity Unit). Although N.351 demonstrated turbidity reduction and flocculation efficiency, the highest settling rates are observed in the two-step system employing the cationic-anionic flocculation combinations of C.573-A.338 and C.573-A.1011. These combinations achieved the highest settling rate of 2700 mm/min at dosages of 8.5 mg/L and 12.5 mg/L, respectively. This experimental study demonstrates that optimum flocculant dosages can vary significantly depending on the type of flocculant, the combination used, and the performance parameters. These results provide valuable information to optimize feldspar flocculation in industrial applications, which could improve process efficiency and product quality in feldspar using industries.

Experimental investigation and molecular dynamics simulation on the effect of ionic strength and pH on kaolinite flocculation using a novel cationic chitosan-based flocculant

ABSTRACT Efficient coal tailings slurry treatment relies on floc properties that control solid – liquid separation. The performances of cationic polyacrylamide (CPAM), nonionic polyacrylamide (NPAM), and a hydrophobic cationic flocculant (GgB14) were investigated under ultrapure and industrial water conditions. Flocculation efficiency was evaluated by sedimentation rate, supernatant transmittance, and floc moisture content. CPAM and GgB14 achieved superior clarification and sedimentation at 120–160 g/t, forming stable flocs with low moisture, while NPAM induced fast settling but poor dewatering under high ionic strength. Mechanistic analysis revealed that CPAM acted through charge neutralization and bridging, GgB14 enhanced these effects via hydrophobic interactions to promote water release, and NPAM relied mainly on physical bridging. These findings highlight the combined role of water chemistry and flocculant design in coal tailings slurry treatment and provide guidance for efficient flocculation – dewatering strategies.

The presence of organic matter can alter the dewatering characteristics of river-dredged silt and affect the dewatering efficiency. This study systematically compared the dewatering effects of cationic polyacrylamide (CPAM), ferric chloride (FeCl3), and composite flocculant (CPAM + FeCl3) for sludge with different organic matter contents by using the combined flocculation–electro-osmotic dewatering technology. The results show that the presence of organic matter significantly hinders the dewatering of silt. After the combined treatment of low-, medium-, and high-organic-matter river-dredging sludge with composite flocculants and electro-osmotic treatment, the final water content was 39.53%, 45.08%, and 47.28%, respectively. Compared with the use of CPAM alone, its dewatering efficiency increased by 66.98%, 5.39%, and 13.72%, respectively. Three-dimensional fluorescence spectroscopy analysis (3D-EEM) indicates that the combined dewatering of flocculation and electro-osmosis can improve the dewatering performance of sludge by promoting the transformation of organic matter. Scanning electron microscopy (SEM) analysis shows that under the action of the composite flocculant, the sludge particles aggregate significantly, and after electro-osmosis, the structure becomes more compact and channels are formed, which further improves the sludge dewatering efficiency. This study provides a theoretical basis for the optimization of dewatering processes for dredged silt with different organic matter contents.

Enhanced residual water quality in the dewatering process of dredged sediment slurry via flocculation: Intrinsic mechanisms of dissolved organic matter removal using cationic flocculants.

Softening of seawater by ionic flocculation using surfactants derived from vegetable oils and its application in textile industry processes

The object of this study is the process of thickening and dewatering excess activated sludge from municipal wastewater treatment plants in sedimentation centrifuges. The subject of the study is the conditions and factors that affect the efficiency of sludge dewatering, taking into account environmental safety, energy efficiency, and the possibility of reusing resources. The study is aimed at solving the problem of the efficiency and environmental safety of dewatering excess activated sludge. The results of studies on the centrifugation of samples of excess and stabilized activated sludge in a laboratory centrifuge showed that effective separation into sediment and clarified liquid is achieved at a separation factor of 200–600 with the use of a flocculant. In an industrial centrifuge under a flow mode, the best results were obtained at a separation factor of 450 and a flow rate of 9.4 m3/h: the solid phase content in the thickened product was 12.8 g/l, at an input concentration of 4.2 g/l and the residual in the clarified liquid – 0.3 g/l. The proposed scheme for thickening and dewatering sludge stabilizes the process and improves the quality of the product for further use or disposal. For effective dewatering, mixing the thickened sludge with thickened activated sludge is recommended due to the need for a mineral component. It has been established that thickening of activated sludge is possible using centrifuges in a weak centrifugal field (Fr = 200–600), with a cationic flocculant consumption of 5 kg/t. The second stage – dehydration – is implemented using sedimentation centrifuges. The results could be used at municipal treatment plants to optimize the processes of thickening and dewatering of excess activated sludge, taking into account energy efficiency and environmental safety. The proposed centrifuge operating modes and the technological scheme enable process stability, reduce sludge volumes, and improve the quality of the final product for further use or disposal

The energy intensive nature of harvesting microalgaeby centrifugationand drying results in a low energy profit ratio for biofuel productionfrom wet microalgae. To address this, microalgal cultures can be flocculatedby polymers to reduce energy consumption and avoid centrifugation.Additionally, lipids can be directly extracted from wet microalgaeharvested by centrifugation using liquefied dimethyl ether (DME) toreduce energy consumption. In this study, we investigated the lipidextraction from the green alga, Chlorella sorokiniana (C. sorokiniana), flocculated withamphoteric and cationic polymers using liquefied DME, without centrifugationand drying pretreatment. Although the addition of amphoteric polymerdid not interfere with lipid extraction by liquefied DME, the amountof lipids extracted by ethanol from flocculated C.sorokiniana decreased. The addition of cationic polymersalso interferes with lipid extraction using liquefied DME, chloroform–methanolmixtures, and ethanol. Surface functional group measurements revealedthat the amphoteric and cationic polymer flocculants were insolublein these solvents, remained in the residue, and did not contaminatethe extracted lipids. Thus, the amphoteric flocculant KA305BH wasfound to be effective for lipid extraction with liquefied DME from C. sorokiniana. The proposed approach can facilitatethe energy efficient production of biofuel from wet microalgae.

This review summarizes the literature data on the use of water-soluble ammonium-containing ionene flocculants for water purification from dyes (including in compositions with coagulants). The influence of the type of dyes, the molecular weight of ionenes, their concentration, the pH of solutions, and other parameters on the purifi cation efficiency is considered.

Flocculants are essential for removing pollutants from wastewater, yet conventional organic and inorganic types often lack renewability and pose risks of secondary pollution. In this study, a cationic cellulose nanofiber (CCNF) flocculant was developed from rice straw, offering enhanced flocculation performance, sustainability, and environmental compatibility. The cellulose nanofiber was extracted and cationically modified under mild conditions. Optimized modification enhanced cationic substitution, yielding a maximum SS removal of 98.9%. CCNF maintained stable performance under both acidic and alkaline conditions and was particularly effective in removing nanoscale SS and treating actual agricultural wastewater. Moreover, cationic modification did not significantly alter the biodegradability of cellulose, with CCNF showing a weight loss similar to that of unmodified CNF after 180 days in soil. The estimated cost of CCNF-3 was approximately 1.13 yuan/g, slightly higher than conventional flocculants, but with considerable environmental benefits.

Produced water re-injection (PWRI) is the water management strategy with least environmental impact during petroleum recovery. A major challenge, however, is clogging of pores in the injection reservoir by particles suspended in the produced water. Basic understanding of transport and retention of particles in porous media is required to better handle this injectivity decline. Here, a microfluidic technique was used to study the transport and retention of monodisperse silica particles in a porous network. The amount of particle retained in the network, the distribution of the particles in the network and the aggregation state of the particles depended on particle–particle and particle–pore wall interactions. These interactions were modulated by varying the salinity of the suspension introduced into the network and by adsorbing surface-active additives (a non-ionic surfactant, a cationic flocculant and an anionic flocculant) onto the particles. The latter was done to mimic how adsorption of production chemicals onto solid particles in produced water influence their transport in reservoirs. In accordance with the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, high-energy barriers prevented both aggregation of particles and retention of particles in the pore network at low salinities. A threshold salinity was reached, where the energy barriers were reduced so that individual particles were retained in the pore network. Further increase in the salinity resulted in aggregation of particles prior to the network and most of the aggregates were accumulated close the entrance of the network. Adsorption of a non-ionic surfactant provided sufficient steric hindrance to prevent aggregation of particles at high salinities, and the retention of particles became more evenly distributed in the network. The adsorption of the anionic flocculant resulted in steric hindrances that reduced the retention of particles in the network, while the opposite was seen when the cationic flocculant was adsorbed onto the particles. The extent of re-mobilization of retained particles indicated the strength of the particle–pore wall interactions.

Efficient alleviation of ultrafiltration membrane fouling in treatment of dye effluent by a novel cationic dendritic starch-based flocculant.

ABSTRACT The starch-grafted cationic flocculant is a nontoxic and environmentally friendly natural polymer flocculant that has been extensively utilized in wastewater treatment. Despite its widespread application, the efficient grafting of cationic monomers onto starch for the preparation of flocculants remains a significant challenge. Previous research has demonstrated that acrylamide (AM) can enhance the binding of certain cationic monomers to starch. However, the effect of AM on starch grafted with quaternary ammonium salts remains unclear. Therefore, this study utilized hydroxypropyl starch (HPS) as the raw material, with potassium persulfate-sodium sulfite (K2S2O8-Na2SO3) serving as the initiator, AM and dimethyldiallylammonium chloride (DMDAAC) as grafting monomers. The investigation focused on the effects of various parameters, including initiator concentration, monomer ratio, total monomer-to-starch mass ratio, reaction time, and reaction temperature, on the grafting efficiency. The optimal process conditions were determined to be an initiator concentration of 3 mmol/L, an AM/DMDAAC mass ratio of 9:1, a total monomer-to-hydroxypropyl starch mass ratio of 5:1, a reaction time of 3 hours, and a reaction temperature of 70°C. Under these conditions, the grafting efficiency reached approximately 96.50%, and the degree of cationic substitution was about 16.55%. When applied to the flocculation process of coal slime water, it was found that HPS-AM-DMDAAC exhibited superior performance compared to nonionic flocculant (HPS-AM) and cationic polyacrylamide (CPAM). HPS-AM-DMDAAC demonstrated higher flocculation efficiency, flocculation kinetics and produced flocs with a greater fractal dimension. At a dosage of 32 mg/L, HPS-AM-DMDAAC achieved a flocculation efficiency of 91.69%.

Preparation of cationic starch flocculants by etherification, esterification and grafting approach for removal of textile dyes

Enhanced flocculation performance and coal slurry water by using starch-based flocculant with rich charges and its flocculation mechanism.

Impacts of cationic polyacrylamide flocculant and elevated pH on the harvesting of the diatom Phaeodactylum tricornutum