Starch-based Flocculants Research Articles

Economic and environmentally friendly anionic flocculant synthesized by starch-acrylic acid-itaconic acid grafting and efficient treatment of cationic dye wastewater

Starch-based flocculants are environmentally friendly and high-performance products, potentially applied in wastewater treatment with low operation cost and ecological risk. In this study, we successfully synthesized a ternary anionic copolymer of starch-acrylic acid-itaconic acid (SAI) through graft copolymerization. The synthesis conditions were optimized based on flocculation efficiency against cationic crystal violet (CV), and subsequent applicability was conducted under various environmental conditions. The results indicate that SAI exhibited outstanding decolorization efficiency under wide scopes of pH, temperature, and ionic strength. Most importantly, SAI achieved a remarkable decolorization rate of 91.2 % for 100 mg/L CV dye at a low concentration of 25 mg/L, accounting for one-fourth of the cost operated with commercial polyacrylamide. Compared to binary flocculants, SAI demonstrates superior flocculation performance too. The flocculation mechanism is primarily attributed to the combined effects of charge neutralization, bridging, and sweeping. SAI flocculants possess characteristics of high efficiency, environmental friendliness, and cost-effectiveness, thus presenting broad prospects for the treatment of dye wastewater.

Residue-Free and Recyclable Starch-Based Flocculants for Dye Wastewater Flocculation.

Flocculants are crucial agents in wastewater treatment because they can remove oppositely charged impurities effectively and swiftly. However, flocculation also inevitably causes secondary contamination due to the residual properties, nonreusability, and nondegradability of traditional flocculant molecules. Herein, an ecofriendly starch-based flocculant, i.e., 2,4-bis(dimethylamino)-[1,3,5]-triazine-6-starch, was synthesized via a preactivation-etherification strategy. The large molecular weight property of the flocculant produced by this method enhances the intermolecular hydrophobic association, achieving complete phase separation of all flocculant molecules from water and residue-free flocculation for the first time. Importantly, a large molecular weight tertiary amine starch-based flocculant (LMTS) exhibits a remarkable flocculation capacity of over 1800 mg·g-1 for dye wastewater, which is significantly higher than that of traditional polyacrylamide and polyaluminum chloride flocculants. Furthermore, the LMTS flocculant could be recycled by pH adjustment, and its structural stability ensured sustained reusability. This high-performance residue-free biomass-based flocculant offers a green advance for wastewater treatment.

Production of Cationic Starch-Based Flocculants and Their Application in Thickening and Dewatering of the Municipal Sewage Sludge

Polymer flocculants are used to promote solid-liquid separation processes in wastewater treatment technologies, and bio-based flocculants possess many advantages over conventional synthetic polymers. Potato starch microgranules were chemically modified and mechanically sheared to produce modified starch flocculants. The effectiveness of produced cationic starch (CS) and cross-linked cationic starch (CCS) flocculants in the thickening and dewatering of surplus activated sewage sludge was evaluated and compared with that of synthetic cationic flocculants (SCFs) The flocculation efficiency of SCF, CS, and CCS in sludge thickening was determined by measuring the filtration rate of treated surplus activated sludge. Comparing the optimal dose of SCFs and CCS flocculants needed for thickening, the CCS dose was more than 10 times higher, but a wide flocculation window was determined. The impact of used flocculants on the dewatering performance of surplus activated sludge at optimal dose conditions was investigated by measuring capillary suction time. The filtration efficiencies (dewaterability) of surplus activated sludge using SCF, CS, and CCS were 69, 67, and 72%, respectively. The study results imply that mechanically processed cross-linked cationic starch has a great potential to be used as an alternative green flocculant in surplus activated sludge thickening and dewatering operations in municipal sewage sludge treatment processes.

A novel treatment for amelioration of sludge dewaterability using green starch-grafted flocculant and realized mechanism

To clarify the effect of extracellular polymeric substances (EPS), protein and hydrophilic substances on the dewatering efficiency during starch-grafted flocculant (SBF) conditioning, a green and cost-saving SBF was synthesized. Dewatering performance of sludge, secondary structure of protein, change of hydrophobic substances and removal of bound water were investigated. Results showed that after SBF conditioning, filter cake moisture content and specific resistance to filtration decreased from 75.63 % and 2.31 × 1012 m/kg to 66.76 % and 5.68 × 1011 m/kg, respectively. SBF neutralized the negative charges from the sludge system, promoting the increase of sludge flocs size and EPS decomposition, decreasing the compressibility of sludge and constructing a channel for water release. Moreover, the secondary structures of protein were changed through the interaction between SBF and the oxygen-containing functional groups in EPS, resulting in the reduction of hydrophilic substances and the increase of hydrophobic substances, which increased the hydrophobicity of molecules and thus improved the dewatering capacity of sludge. Meanwhile, the construction of sludge skeleton channels, charge neutralization, hydrophobic association effect were the primary mechanisms of SBF conditioning sludge dewatering. Additionally, SBF has an excellent economy as a sludge conditioner. This paper provided a new ideal for starch-based flocculants for improving the dewatering capacity of sludge treatment.

Synthesized cationic starch grafted tannin as a novel flocculant for efficient microalgae harvesting

Owing to low cost and excellent biodegradability, cationic starch-based flocculants (CCs) have been researched in the field of harvesting microalgae, however lacking of targeted affinity to microalgae cells limited their flocculation performance. In present study, tannin was used in the synthesis of a novel CCs grafted tannin-based flocculant (TCCs). SEM, XRD, FTIR, 1H-NMR, zeta potential and UV–Vis analysis proved the successful graft of tannin on CCs skeleton. TCCs exhibited outstanding harvesting performance at 4.0 mg/L dosage, much better than CCs (20.0 mg/L) and flocs formed by TCCs possessed higher reflocculation ability. The flocs size, flocs shape and zeta potential changing regulation indicated that both CCs and TCCs can flocculate microalgae cells through charge neutralization and bridging flocculation. To further explore the flocculation mechanisms, effects of flocculants on microalgal dissolved and/or bound extracellular organic matter were systematically tested. Results suggested that the introduction of tannin make TCCs targeted to combine with proteins in the bound extracellular organic matter and then form compact flocs through hydrogen bonds and hydrophobic bonds, thus saving the flocculant dosage and improving the harvesting efficiency. Additionally, harvesting per ton microalgae by TCCs costs only 19.4 USD, which is more economic saving than CCs and some traditional flocculants.

Efficient removal of both positively and negatively charged colloidal contaminants using amphoteric starch-based flocculants synthesized by low-pressure UV initiation

• Amphoteric starch-based flocculants were synthesized by low-pressure UV initiation. • Amphoteric starch-based flocculants show high flocculation performance. • Amphoteric starch-based flocculants exhibit low salts sensitivity. • Flocculation mechanism includes charge neutralization, patching and bridging. Surface charges of the suspended colloidal particles in real water can be either negative or positive. Flocculation is one of the most widely used technologies in water treatment. A series of amphoteric starch-based flocculants (denoted as ASBFs) with the same chemically modified functional groups but different charge degrees and intrinsic viscosities were successfully via low-pressure ultraviolet initiation and used for the removal of different charged contaminants from water. The characterization results confirmed the successful grafting acrylamide (AM) and 2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC) onto carboxymethyl starch. Different influencing factors, including flocculant dosage, contaminants concentration, pH of solution, stirring speed, sedimentation time and various salts, were investigated systematically. ASBFs with eco-friendliness exhibited high flocculation property, low optimal dosage and low salts sensitivity, for not only kaolin, but also hematite suspensions. The zeta potential (ZP) measurement suggested that the removal mechanism mainly includes charge neutralization, patching and bridging.

The Use of Chitosan and Starch-Based Flocculants for Filter Backwash Water Treatment

Inorganic aluminum or iron salts supported with synthetic polymers are commonly used to eradicate colloidal particles from water in coagulation and flocculation processes. Nevertheless, these agents have several disadvantages, such as large volumes of sludge produced or environmental toxicity. Recently biodegradable polymers have been suggested as eco-friendly flocculants for water treatment. This study aimed to investigate the possibilities of using starch and chitosan and their oxidized derivatives as flocculants for filter backwash water treatment. Dialdehyde starch (DST) and dialdehyde chitosan (DCT) were synthesized by periodate oxidization of natural starch from corn and low molecular weight chitosan. The obtained materials have been characterized with scanning electron microscopy (SEM), ATR-FTIR spectroscopy, and thermogravimetric analysis (TGA). Furthermore, we studied the flocculation properties of polysaccharide flocculants in a series of jar tests. The effectiveness of chitosan and starched-based flocculants was compared to synthetic polymers commonly used to treat iron ions-rich filter backwash water. The environmental aspects of these chemicals, particularly the biodegradability of post-flocculation residues, were also addressed. It was found that oxidized starch and chitosan derivatives can be used as ecological flocculating materials to treat potable water or sludge.

The influence of hydrophobicity on sludge dewatering associated with cationic starch-based flocculants

Coagulation/flocculation is an extensive and effective pretreatment technology for improving the sludge dewaterability. A series of hydrophobically associated cationic starch-based flocculants (CS-DMRs) with different degrees of hydrophobicity but similar charge densities were designed and synthesized. The CS-DMRs exhibited excellent sludge dewatering performance. The dewaterability of sludge increased with the hydrophobicity of the CS-DMRs, and the filter cake moisture content (FCMC) and specific resistance to filtration (SRF) could be reduced from 95.47% and 7.09 × 1012 m/kg to 79.26% and 2.258 × 1012 m/kg, respectively, at a constant pressure of 0.05 MPa after conditioned by the starch-based flocculant with the highest hydrophobicity at its optimal dose. Moreover, due to their amphiphilic structures, CS-DMRs could closely interact with the negatively charged extracellular polymeric substances (EPS), efficiently compress the protein and polysaccharide in EPS, and release the bound water. A second-order polynomial model was proposed according to the phenomenological theory to quantitatively analyze the effect of hydrophobicity in these starch-based flocculants on the sludge dewaterability. The structure–activity relationship was built, and the optimal dose and corresponding FCMC could be theoretically estimated accordingly. The results were in good agreement with the experimental results. The dewatering mechanisms were also discussed in detail on the basis of the changes in the FCMC, SRF, capillary suction time, properties of sludge flocs, compression coefficient, microstructures of sludge cakes, EPS fractions and components, and spatial distributions of the proteins and polysaccharides. In addition to charge neutralization, the hydrophobic association effects of CS-DMRs played an important role in the formation of drainage channels and net-like porous structures in the sludge cake to improve its permeability and filterability. This study thus provided a good understanding of the structural effects of the starch-based flocculants on the sludge dewaterability. The results are greatly beneficial to the fabrication and utilization of environment-friendly and high-performance natural polymeric conditioners for sludge treatment.

Environmental friendly flocculants for drinking water treatment

Coagulation-flocculation is an important step for the treatment of drinking water obtained from surface water sources. Various types of flocculants are available in the drinking water treatment market but only some of them are friendly for the environment due to their specific structure, which includes natural compounds. Starch-based flocculants are included in this category and some types of them were tested in our research work, in similar conditions with ordinary polyelectrolytes, in order to prove their efficiencies for turbidity and organic load (COD-Mn) removal. Five types of flocculants based on starch and acrylamide were tested during the classic treatment flow coagulation-flocculation-settling with aluminum sulfate as coagulant (1-10 mg Al/L) and 0.5-10 mL/L flocculant dose (0.2% active substance). Better removal efficiencies of turbidity and organic load (COD-Mn) in case of flocculants based on starch and acrylamide copolymers: over 99% for turbidity and ~90% for COD-Mn in case of 300-400 NTU initial surface water turbidity were registered.

Evaluation of hydrophobically associating cationic starch-based flocculants in sludge dewatering

Two series of binary graft cationic starch-based flocculants (CS-DMCs and CS-DMLs) with different hydrophilicity and charge density (CD) were prepared by graft copolymerization of acrylamide with 2-(Methacryloyloxy)-N,N,N-trimethylethanaminium chloride and methacrylic acid 2-(benzyldimethylaminio) ethyl chloride, respectively, on the starch (St) backbone. The sludge dewatering performance of CS-DMCs and CS-DMLs were evaluated and compared based on the changes in filter cake moisture content (FCMC), specific resistance of filtration (SRF), fractions and components of extracellular polymeric substances, and various physiochemical characteristics of sludge flocs and cakes. Increase in CD of the St-based flocculants caused improved sludge dewaterability. Under the similar CD, CS-DML with relatively high hydrophobicity exhibited lower FCMC and SRF, larger and denser sludge flocs, and better permeability of sludge cakes than CS-DMCs due to the synergistic effects of charge neutralization, bridging flocculation and hydrophobic association. Furthermore, a second-order polynomial model on the basis of phenomenological theory was successfully applied to quantitatively evaluate the influences of the two important structural factors of these St-based flocculants, i.e., hydrophobicity and CD, on the sludge dewaterability. The structure–activity relationship of the St-based flocculants in sludge dewatering was obtained according to the theoretic simulation. The dewatering mechanisms was discussed in depth on the basis of the experimental and simulated results; besides, the FCMC and optimal dose can be predicted by the established structure–activity relationship. This current work offered a novel and valuable way to exploit and design of low-cost and high-performance graft natural polymeric flocculants applied in efficient conditioning of sludge.

Comparison of two starch-based flocculants with polyacrylamide for the simultaneous removal of phosphorus and turbidity from simulated and actual wastewater samples in combination with FeCl3

Two laboratory-made cationic starch-based flocculants (St-CTA and St-AD) with different chain architectures were used to simultaneously remove phosphorus and turbidity from two simulated wastewaters and one actual wastewater with laboratory and pilot scales, respectively, in conjunction with FeCl3. A commercial polyacrylamide (PAM) has been also tried and compared with aforementioned starch-based flocculants. The removal extents of phosphorus and turbidity increased, the required dosages of FeCl3 decreased, and floc properties improved after dosing each polymeric flocculant after FeCl3 in all tested wastewaters due to their synergistic effects. However, the three flocculants exhibited different improvement efficiencies on the treated wastewaters containing different forms of phosphorus and showed various synergistic mechanisms owing to their distinct structural features. In inorganic–phosphorus-simulated wastewater, the linear nonionic PAM with a high molecular weight had a more notable contribution than the two starch-based flocculants due to its efficient bridging flocculation effect. Given the branched-chain structure and high positive charge density of St-AD, it had a higher efficiency in treating real wastewater and organic–phosphorus-simulated wastewater than PAM and linear cationic St-CTA. These results may serve as references for the design and selection of a suitable flocculant in treating target wastewaters.

Synthesis of Polymer Grafted Starches and Their Flocculation Properties in Clay Suspension

Starch-based flocculants have been emerged as a promising alternative to conventional synthetic flocculants in wastewater treatment, especially for the treatment of oil sand tailings, as they are low cost, safe, biodegradable, fairly shear-stable, readily available from reproducible agricultural resources, and do not result in secondary pollution. In this paper, three types of polymer-grafted starches (St-g-Polymer) with different charge properties were synthesized and their molecular structures were controlled by atom transfer radical polymerization (ATRP). The correlations between the charge properties of starch-based flocculants, external environmental parameters, and flocculation performance were systematically investigated by conducting jar tests under various environmental conditions. It was found that the charge properties of the branch chain had a significant impact on flocculation performance. The cationic St-g-Polymer demonstrated the best performance due to the grafting of the cationic monomer to the starch backbone which improved the solubility of the copolymer and aided in the removal of small/water-soluble particles. The results obtained could assist in guiding the selection and design of suitable biodegradable flocculants when treating targeted wastewater.

Preparation of amphoteric starch-based flocculants by reactive extrusion for removing useless solids from water-based drilling fluids

In drilling operations, the removal of drill cuttings from recirculating drilling fluids is one of the most important procedures. The high cost and low efficiency of present solid control technologies are two crucial problems that need to be solved urgently. In this work, a series of amphoteric starch-based flocculants (CS-g-DC) were developed to remove useless solids from drilling fluids. These flocculants were synthesized by grafting diallyldimethylammonium chloride (DADMAC) onto carboxymethyl starch (CMS) with different grafting frequencies through reactive extrusion. The physicochemical property of the CS-g-DC products was measured by Fourier-transform infrared (FT-IR) spectroscopy, proton nuclear magnetic resonance (1H NMR) spectroscopy, and zeta potential analysis. It has been found that DMDAAC had been successfully grafted onto the starch backbone and the isoelectric points (IEP) of different CS-g-DC samples increased with grafting degree of DMDAAC (G(DMDAAC)). Three types of clay suspensions (kaolinite, smectite and illite) were used to study the flocculation performance and mechanism of CS-g-DC by turbidity and particle size distribution. The results of these analyses showed that CS-g-DC samples with a G(DMDAAC) higher than 98% flocculated well all three clay suspensions depending on charge attraction and bridging mechanism. The flocculation performance of CS-g-DC was also evaluated in drilling fluids from a drilling site by mineral content analysis. The results showed that these CS-g-DC samples with appropriate G(DMDAAC) could remove useless solids from the drilling fluids effectively, indicating it could be used as flocculants for drilling fluids reuse or recirculation during drilling operation.

Sludge dewaterability of a starch-based flocculant and its combined usage with ferric chloride

A series of cationized starch-based flocculants [i.e., starch-3-chloro-2-hydroxypropyl trimethylammonium chloride (St-WH)] with different charge densities (CDs) was synthesized by etherification and used as sludge dewatering conditioners. In this series of St-WH samples, St-WH4, with the highest CD, exhibited the optimal sludge dewaterability properties, including specific resistance of filtration, filter cake moisture content, and floc properties, because of the enhanced dual effects of charge neutralization and bridging flocculation. An inorganic coagulant, namely, FeCl3, was combined with the organic flocculant (St-WH) at different dosing sequences to improve the dewatering performance. In comparison with St-WH4, FeCl3, and polyacrylamide, used individually, as well as St-WH4 dosed before and at the same time as FeCl3, the combination of the starch-based flocculant fed after FeCl3 showed better sludge dewaterability and less compressible property because of the synergistic effects of FeCl3 followed by St-WH4. FeCl3 and St-WH4 exhibited good coagulation effects and functioned as skeleton builders. The Pearson correlation between various components of extracellular polymeric substances (EPS) and sludge dewaterability showed that FeCl3 could efficiently compress the protein-like components in EPS. The starch-based flocculant might exhibit not only effective bridging flocculation effects but also good affinity to polysaccharide components in EPS because of their similar structures besides to protein-like components. Thus, sludge dewaterability was substantially improved by using the combination of St-WH and FeCl3.

Amphoteric starch derivatives as reusable flocculant for heavy-metal removal.

A pH-responsive amphoteric starch derivative (PRAS) bearing dual functional groups (amino and carboxyl groups) was prepared through etherification of starch with 2-chloro-4,6-diglycino-[1,3,5]-triazine. PRAS exhibits a reversible pH-response property in aqueous solution. The attractive property of PRAS is that it could be used as an effective flocculant for heavy metal-ion (e.g. Cu(ii) and Zn(ii)) removal from wastewater by changing pH. The transition of hydrophobicity–hydrophilicity would produce shrinkage of the polymer matrix, facilitating the release of heavy-metal ions from the saturated flocculant. As an ideal flocculant PRAS displayed outstanding stability and reproducibility, whose remove rate for Cu(ii) and Zn(ii) remained at 93% and 91% after three flocculation/regeneration cycles.

Dual starch–polyacrylamide polymer system for improved flocculation

Organic polyelectrolytes such as polyacrylamide (PAM) are commonly used in the water industry to improve flocculation. However, potential adverse health effects may arise from the use of PAM owing to the presence of trace acrylamide monomers in commercial products. Hence, there is growing interest in replacing synthetic polyelectrolytes with natural and sustainable alternatives, which would eliminate risks related to the presence of toxic monomers/impurities and oxidation by-products from the interaction of polymers and common disinfectants such chlorine and ozone. Starch-based flocculants are recognized to offer fairly good flocculation performance, but require higher polymer dosages than conventional high-molecular-weight PAM. To reduce exposure to acrylamide monomers, this study examined the combination of an activated starch-based polymer with PAM to determine whether synergistic effects can be achieved using a dual polymer system. Flocculation performance (floc size, density and rate of aggregation) was monitored using jar tests. Turbidity removal was also assessed to confirm settling performance. Single PAM/starch mixture injection and sequential dual polymer injection were compared in order to simplify practical industrial applications. For the tested samples of surface water and wastewater, jar tests showed that the PAM dosage can be significantly reduced (50–70% for surface water) for both conventional and ballasted flocculation if a dual starch–PAM polymer system is used.

Evaluation of the starch-based flocculants on flocculation of hairwork wastewater

China is the world's largest producer of wigs, and the manufacturing generates large quantities of hairwork effluents. Coagulation/flocculation is an important step in the water treatment process. In this study, two versions of starch-based flocculants were successfully prepared through etherification and graft copolymerization, respectively. Starch-3-chloro-2-hydroxypropyl triethyl ammonium chloride (St-CTA-DQ) and starch-graft-poly[(2-methacryloyloxyethyl) trimethyl ammonium chloride] (St-g-PDMC-DQ) both contain strongly cationic quaternary ammonium salt groups, but have differing cationic contents, specifically, the degree of substitution (DS) and grafting ratio (G). Furthermore, the additional functional groups were distributed on different chain sites (the starch backbone for St-CTA-DQ, and the branch chains for St-g-PDMC-DQ). These two flocculants demonstrated superior efficiency for turbidity and UV254 removal in hairwork wastewater as well as better floc properties compared to polyaluminum chloride. The effects of pH, flocculant dose, and cationic group contents (DS and G) were systematically investigated. Consequently, it was determined that a higher cationic content in both the flocculants led to better flocculation performance as well as increased removal rates of both turbidity and UV254. This was primarily due to improved charge neutralization, which highlighted the preference towards a lower optimal dose. In addition, flocculation performance worsened as the pH level increased. Overall, St-g-PDMC-DQ exhibited similar flocculation performance to St-CTA-DQ. However, the wastewater treated by St-g-PDMC-DQ showed lower residual turbidity than when treated by St-CTA-DQ. This was attributed to the distinct branch chain architecture of St-g-PDMC-DQ, which was beneficial for coagulating the uneasily flocculated contaminants in water, such as smaller-sized colloids and water-soluble organic substances. Flocculant structural factors, specifically charge properties and chain architecture, heavily affected the final flocculation performance.

Flocculation and antimicrobial properties of a cationized starch

In this study, a series of cationized starch-based flocculants (starch-3-chloro-2-hydroxypropyl triethyl ammonium chloride, St-CTA) containing various quaternary ammonium salt groups on the starch backbone were prepared using a simple etherification reaction. All of the prepared starch-based flocculants show effective performance for the flocculation of kaolin suspension, two bacterial (Escherichia coli and Staphylococcus aureus) suspensions, and two contaminant mixtures (kaolin and each bacterium) under most pH conditions. St-CTA with a high substitution degree of CTA demonstrates improved contaminant removal efficiency because of the strong cationic nature of the grafted quaternary ammonium salt groups and the charge naturalization flocculation effect. The antibacterial effects of St-CTA were also evaluated, considering that many quaternary ammonium salt compounds elicit bactericidal effects. Three-dimensional excitation–emission matrix spectra and direct cell morphological observation under scanning electron microscopy reveal that the starch-based flocculants exhibit better antibacterial effects on the Gram-negative bacterium E. coli than on the Gram-positive bacterium S. aureus. The thicker cell wall due to the presence of abundant peptidoglycan and teichoic acids of S. aureus than E. coli explains the uneasy breakage of S. aureus cell wall after being attacked by the cationized starch-based flocculants.

Evaluation of structural effects on the flocculation performance of a co-graft starch-based flocculant

The molecular structure of a material substantially determines its final application performance. In this work, a series of starch-based flocculants with different charge densities and average graft chain lengths were prepared by the co-graft polymerization of acrylamide and [(2-methacryloyloxyethyl) trimethyl ammonium chloride] (St-g-PAM-co-PDMC). The flocculation performance of St-g-PAM-co-PDMC was studied systematically at neutral pH using kaolin suspension and sodium humate (NaHA) aqueous solution as synthetic wastewaters. The effects of the two structural factors on the flocculation efficiency of the starch-based flocculants have been investigated. The experimental results showed that the charge density and average graft chain length contributed distinctly to flocculation performance during the removal of both kaolin particles and NaHA under insufficient and excessive flocculant dose conditions. The flocculation mechanisms of this starch-based flocculant were discussed in detail on the basis of the structure-activity relationship, which are significant to optimize the flocculation conditions and guide the development of novel high-performance flocculants.

Dual functionality of a graft starch flocculant: Flocculation and antibacterial performance

In this work, a series of quaternary ammonium salt grafted starch flocculant, starch-graft-poly(2-methacryloyloxyethyl) trimethyl ammonium chloride (St-g-PDMC), with different grafting ratios was prepared by a simple method. Various characterization techniques were employed to investigate the structure and charge property of the starch-based flocculants. The efficiencies of St-g-PDMC for flocculation of kaolin and Escherichia coli suspensions as well as their mixtures were systematically examined in laboratory scale. In addition to environmental factors, such as flocculant dose and pH, the effects of grafting ratio were also evaluated. Results indicated that St-g-PDMCs exhibited dual functionality of high flocculation effects and antibacterial properties. Moreover, the flocculation and antibacterial mechanisms were investigated in detail based on apparent flocculation performance, charge properties, floc structures (floc size and its two-dimensional fractal dimension), and cell surface morphology, respectively.