A review on chitosan-based flocculants and their applications in water treatment

Flocculation of kaolin particles with cationic lignin polymers

Currently, lignin of black liquor is incinerated to generate energy in pulp mills; but it has potential to be valorized through different modification methods. In this work, kraft lignin (KL) was polymerized with 2-[(methacryloyloxy) ethyl] trimethylammonium chloride (DMC) to produce cationic water soluble polymers. After producing five polymers with different molecular weights and charge densities, their flocculation efficiency in kaolin suspensions was investigated. The adsorption, zeta potential and flocculation results confirmed that the polymer with the highest charge density and molecular weight (KLD5) was a more effective flocculant than other polymers. The structure and size of flocs formed from the interaction of kaolin with KLD were determined by a focused beam reflectance measurement (FBRM). The sedimentation studies, conducted under gravitational (by vertical scan analyzer) and centrifugal force (by Lumisizer analytical centrifuge), revealed that KLD5 was very effective in flocculating kaolin particles.

Evaluation of acidification and oxidation of sludge to improve the effect of a starch-based flocculant on the dewaterability of sewage sludge

Conditioning is essential for achieving effective sludge dewatering and easier disposal. In this study, a combined pretreatment of acidification and oxidation using potassium permanganate (KMnO₄) as oxidant was conducted to improve the effect of a cationic starch-based flocculant (St-WH) on the dewaterability of sewage sludge. Synergetic dewatering mechanisms by acidification, oxidation, and flocculation are discussed in detail according to the analysis of the changes in bound water content, extracellular polymeric substances (EPS) fractions and components, zeta potentials, floc size, and surface microstructures of sludge cakes in the dewatering process. Acidification and oxidation could destroy the sludge flocs, thereby causing the degradation of EPS and formation of fine particles. Original loosely and tightly bound EPS partially converted to soluble EPS, resulting in release of trapped water, which can be reflected by the significant correlation between loosely bound EPS and filter cake moisture content (FCMC) (R_s = 0.83, P < 0.05). Those fine particles, simultaneously produced, were adverse to filtration efficiency. In addition to enhancing the oxidation effect of KMnO₄, acidification treatment could still compress the protein-like materials in soluble EPS due to protonation effect, which was positively related to specific resistance to filtration (SRF) (R_s = 0.74, P < 0.05). The following flocculation using St-WH efficiently aggregated those fine particles and restrained the released EPS to bind with free water through charge neutralization and bridging effects, thereby resulting in improved filtration performance and enhanced removal of bound water (R_s = 0.88, P < 0.01). Response surface methodology was also applied to achieve an optimal condition and evaluate the effects of various environmental factors.

Efficient Harvesting of Nannochloropsis Microalgae via Optimized Chitosan-Mediated Flocculation

Food-grade rather than synthetic or chemical flocculants are needed for microalgae harvesting by settling, if used for food products. Chitosan is effective in harvesting freshwater microalgae, but it is expensive and typically not suitable for marine microalgae like Nannochloropsis. To minimize costs for food-grade flocculation, a number of potentially important parameters are considered, including chitosan solubility and optimized chitosan-mediated flocculation of Nannochloropsis sp. BR2 by a five-factor central composite design experiment. Results show that an optical density (440 nm) of 2 (0.23 g dry weight L-1), initial pH of 6, final pH of 10, and 22 ppm chitosan with a viscosity of 1808 cP provide optimum flocculation efficiency, which is predicted to be in the range of 97.01% to 99.93%. These predictions are verified on 4.5 and 8 L Nannochloropsis sp. BR2 cultures.

Investigation of the Effects of Molecular Parameters on the Hemostatic Properties of Chitosan

Hemorrhea is one of the major problems in war, trauma care, and surgical operation that threaten the life of the injured and patients. As a novel polymeric hemostatic agent, biodegradable chitosan can stop bleeding through a variety of approaches. In this paper, chitosan with various molecular parameters was prepared from chitin as raw material through deacetylation, oxidative degradation, hydrophilic modification, and salt formation reactions. The influence of different polymer parameters on the hemostatic effects of chitosan was investigated by in vitro coagulation time and dynamic coagulation assay. The results showed that when the molecular weights were high (10⁵⁻10⁶) and approximate, the coagulation effect of chitosan improved with a decrease of the deacetylation degree and achieved a prominent level in a moderate degree of deacetylation (68.36%). With the same degree of deacetylation, the higher the molecular weight of chitosan, the better the procoagulant effect. The substituent derivatives and acid salts of chitosan showed significant procoagulant effects, especially the acid salts of chitosan. In addition, the hemostasis mechanism of chitosan with various parameters was preliminarily explored by analyzing the plasma recalcification time (PRT). The efforts in this paper laid a basis for further study of the structure⁻activity relationship and the mechanism of chitosan hemostasis.

pH-responsive chitosan-based flocculant for precise dye flocculation control and the recycling of textile dyeing effluents

In this work, we introduce a simple and effective method for the controlled release of dye from dye saturation flocs by a well-designed pH responsive chitosan-based flocculant. The dye flocculation capacities could be precisely controlled from 0.5 to 2 g g-1 by simply adjusting the pH of the desorption solution. A series of flocs with different dye flocculation capacities was prepared and used as nitrogen-rich precursors to prepare nitrogen-doped carbon materials through one-step carbonization. The results demonstrate that the specific surface areas, pore structures and supercapacitance performance of the resulting N-doped carbon materials could be readily controlled by varying the dye flocculation capacity. By using a dye sludge floc with an appropriate dye flocculation capacity (1.5 g g-1) as a precursor, the resulting N-doped material exhibited a high specific capacity and good cycling performance for a supercapacitor electrode. The unique pH-responsive properties of the chitosan-based flocculant facilitated easy tuning of the surface cationic degree and deprotonation behavior by varying pH. This work presents a new concept for balancing between environmental capacity and energy capacity using a smart pH-responsive carrier system based on modified chitosan, which is highly promising for the recycling of industrial wastewater to produce energy materials.

Radical Scavenging Activities of Novel Cationic Inulin Derivatives

Many saccharides are attractive targets for biomaterial applications, due to their abundance, biocompatibility, and biodegradability. In this article, a synthesis process of 6-N-substituted cationic inulin derivatives, including 6-pyridyl-6-deoxyinulin bromide (PIL), 6-(2-amino-pyridyl)-6-deoxyinulin bromide (2APIL), 6-(3-amino-pyridyl)-6-deoxyinulin bromide (3APIL), 6-(4-amino-pyridyl)-6-deoxyinulin bromide (4APIL), 6-(2,3-diamino-pyridyl)-6-deoxyinulin bromide (2,3DAPIL), 6-(3,4-diamino-pyridyl)-6-deoxyinulin bromide (3,4DAPIL), and 6-(2,6-diamino-pyridyl)-6-deoxyinulin bromide (2,6DAPIL) was described. The C₆-OH of inulin was first activated by PPh₃/N-bromosuccinimide (NBS) bromination. Then, pyridine and different kinds of amino-pyridine groups (different position and different numbers of amino) were grafted onto inulin, respectively, via nucleophilic substitution. Then, we confirmed their structure by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. After this, their radical scavenging activities against hydroxyl radical and diphenylpicryl phenylhydrazine (DPPH) radical were tested in vitro. Each derivative showed a distinct improvement in radical scavenging activity when compared to inulin. The hydroxyl-radical scavenging effect decreased in the following order: 3APIL > PIL > 3,4DAPIL > 4APIL > 2,3DAPIL > 2,6DAPIL > 2APIL. Amongst them, 3APIL revealed the most powerful scavenging effect on hydroxyl radicals, as well as DPPH radicals. At 1.6 mg/mL, it could completely eliminate hydroxyl radicals and could clear 65% of DPPH radicals. The results also showed that the steric hindrance effect and the substitute position of the amino group had an effect on the radical scavenging activity. Moreover, the application prospects of inulin derivatives as natural antioxidant biomaterials are scientifically proven in this paper.

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.

Application of Chitosan Composite Flocculant in Tap Water Treatment

The chitosan is a good flocculant for tap water treatment because of its properties such as faster deposition rate and higher removal efficiency for COD (organic matter), SS (suspended solids), and metal ions. However, its high price limits the use in tap water treatment. In this paper, in order to reduce costs, chitosan (CTS), polyaluminum chloride (CF-PAC), and modified rectorite (Al(OH)3 + HCl) were combined to prepare the flocculant for tap water treatment. In order to get the optimal composite flocculant formula, first, we combined these flocculants in two-by-two schema and then we combined all the three flocculants together with various dosing amounts. Through comparison between different combination schemas, the best formula of the composite chitosan flocculant was found to be CTS (ml) : CF-PAC (ml) : modified rectorite (Al(OH)3 + HCl) (ml) = 1 : 30 : 5, with a turbidity removal rate of 96.38% and a removal rate of aluminum up to 80.1%, while the treatment cost is the lowest. In addition, we have designed a cost-effective method for the treatment cost evaluation. As raw water, we used water from the Han River, which is used as raw water at Zonguan Waterworks. In order to show the effectiveness of our optimal composite chitosan formula, we have compared our treatment results to those of the aluminum polyaluminum chloride flocculant currently used in Zonguan’s water treatment plants.

Fabrication of Bifunctional Chitosan-Based Flocculants: Characterization, Assessment of Flocculation, and Sterilization Performance

In this study, a series of chitosan-based quaternary ammonium graft flocculants, namely chitosan-graft-poly(acrylamide and methacryloyl ethyl trimethyl ammonium chloride) [CTS-g-P(AM-DMC)], was successfully synthesized by plasma initiation, and the as-prepared [CTS-g-P(AM-DMC)] had both flocculation and sterilization functions. Various characterization techniques were used to study the structure and physicochemical properties of the chitosan-based flocculants. ¹H nuclear magnetic resonance spectroscopy (¹H NMR), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD), and thermogravimetric analysis/differential scanning calorimetry (TG/DSC) confirmed the successful synthesis of CTS-g-P(AM-DMC). Scanning electron microscopy (SEM) analysis exhibited that CTS-g-P(AM-DMC) contained a smooth convex and porous structure with an enormous surface area. CTS-g-P(AM-DMC) was then used to flocculate the simulated wastewater of the kaolin suspension and the Salmonella suspension. Besides external factors, such as the dosage of flocculant and pH, the effect of the internal factor graft ratio was also evaluated. The experimental results showed that CTS-g-P(AM-DMC) also revealed a strong sterilization effect, aside from the excellent flocculation effect. Moreover, the sterilization mechanism was investigated through a series of conductivity measurements and the analysis of fluorescence-based cell live/dead tests. The results indicated that CTS-g-P(AM-DMC) destroyed the cell membrane of Salmonella through its grafted quaternary ammonium salt, thereby exhibiting sterilization property.

Coagulation/flocculation in dewatering of sludge: A review

Sludge disposal is an integral part of wastewater treatment systems, and its cost usually accounts for more than half of the total operation cost. Sludge disposal technology is facing challenges and opportunities simultaneously and can still be improved. Sludge dewatering is an essential process in sludge disposal, and it is important for the effective reduction of the final processing cost. Coagulation/flocculation is a relatively mature, cost-effective, user-friendly sludge dewatering technology. In this work, coagulation/flocculation and their combinations with other pretreatments, including dewatering mechanisms, are reviewed. Various coagulants/flocculants used in sludge dewatering, including inorganic coagulants, organic synthetic and natural polymeric flocculants, and bioflocculants, are introduced in detail because coagulants/flocculants are the key in coagulation/flocculation. The different factors that influence the dewatering performance of these coagulants/flocculants are also presented briefly. Moreover, aiming at the complicated composition of sludge and its treatment difficulty, the prospects and technical developments of coagulation/flocculation in sludge dewatering are discussed.

Overcoming Interfacial Scaling Using Engineered Nanocelluloses: A QCM-D Study

Nucleation of sparingly soluble species, such as the inorganic salts of calcium, magnesium, and phosphorous, followed by their growth at solid-liquid interfaces has turned into a major concern in water-based industries. Increased resistance against heat, mass, and momentum transfer is the main drawback of the so-called scaling phenomenon. Although phosphorous-, nitrogen-, and sulfur-based antiscaling macromolecules offer adequate antiscaling performance, their potential negative environmental impacts render them less desirable. Despite recent efforts in developing green antiscalants, there has been no promising green solution based on biomass due to its chemical inertness. Here, we use quartz crystal microbalance with dissipation monitoring (QCM-D) to evaluate the real-time performance of an emerging family of nanoengineered anionic hairy cellulose crystals, bearing dicarboxylated amorphous cellulose chains, with a charge density of more than 5.5 mequiv per g, in preventing the nucleation and growth of calcium carbonate, the most common industrial scale. Remarkably, a CaCO₃ mass deposition rate ∼0 (complete scale inhibition) is obtained when less than 10 ppm of the hairy nanocellulose is added to an already scaled surface under a harsh supersaturated condition at 50 °C. Motivated by their threshold antiscaling effect, we show that coating planar silica surfaces with hairy nanocelluloses may result in scale-resistant interfaces. This research envisions how engineered hairy nanocelluloses may have practical implications for developing scale-resistant interfaces based on the most abundant biopolymer in the world.

Removing Escherichia coli from water using zinc oxide-coated zeolite

The removal of Escherichia coli (E. coli) from water by zinc oxide-coated zeolite (ZOCZ) and ZOCZ's antibacterial properties were examined in laboratory experiments using plate counting method and tests of cell apoptosis. Batch experiments showed that ZOCZ has a maximum removal capacity for E. coli of about 4.34 × 10⁶ CFU g^-1 at 25 °C. Element mappings confirm that zinc ions accumulate in the E. coli cells causing cell death. Pseudo-second-order kinetics and Freundlich isotherms were found to best describe the removal of E. coli, suggesting that a multilayer of E. coli cells forms on the surface of ZOCZ particles.

Combination of bioleaching by gross bacterial biosurfactants and flocculation: A potential remediation for the heavy metal contaminated soils

Combining bioleaching by the gross biosurfactants of Burkholderia sp. Z-90 and flocculation by poly aluminium chloride (PAC) was proposed to develop a potential environment-friendly and cost-effective technique to remediate the severely contaminated soils by heavy metals. The factors affecting soil bioleaching by the gross biosurfactants of Burkholderia sp. Z-90 were optimized. The results showed the optimal removing efficiencies of Zn, Pb, Mn, Cd, Cu, and As by the Burkholderia sp. Z-90 leachate were 44.0, 32.5, 52.2, 37.7, 24.1 and 31.6%, respectively at soil liquid ratio of 1:20 (w/v) for 5 d, which were more efficient than that by 0.1% of rhamnolipid. The amounts of the bioleached heavy metals by the Burkholderia sp. Z-90 leachate were higher than that by other biosurfactants in the previous studies, although the removal efficiencies of the metals by the leachate were relatively lower. It was suggested that more heavy metals caused more competitive to chelate with function groups of the gross biosurfactants and the metal removal efficiencies by biosurfactants in natural soils were lower than in the artificially contaminated soils. Moreover, the Burkholderia sp. Z-90 leachate facilitated the metals to be transformed to the easily migrating speciation fractions. Additional, the results showed that PAC was efficient in the following flocculation to remove heavy metals in the waste bio-leachates. Our study will provide support for developing a bioleaching technique model to remediate the soils extremely contaminated by heavy metals.

Review on recent progress in chitosan-based hydrogels for wastewater treatment application

Recently, chitosan has been used as a raw material for synthesis of hydrogels in a wide range of potential and practical applications like wastewater treatment, drug delivery, and tissue engineering. This review represents an overview of the application of chitosan-based hydrogels for wastewater treatment and helps researchers to better understand the potential of these adsorbents for wastewater treatment. It covers recently used and prospected methods for synthesis and modification of these hydrogels. Chitosan-based hydrogels are modified physically and chemically through crosslinking, grafting, impregnation, incorporating of hard fillers, blending, interpenetrating, and ion-imprinting methods to improve adsorption and mechanical properties. Understanding of these methods provides useful information in the design of efficient chitosan-based hydrogels and the select of appropriate pollutants for removal. This review provides a brief outlook on future prospects of chitosan-based hydrogels for wastewater application.

Removal of the commercial pesticides Novadim Progress, Bordeaux mixture and Karate Zeon by pullulan derivatives based flocculants

Cationic pullulan derivatives have been synthesized and evaluated, for the first time, as flocculants for the separation of the commercial pesticides, Novadim Progress (organophosphoric type), Bordeax mixture and Karate Zeon (pyrethroid type) from synthetic wastewater. The investigated polymer samples contained either pendent tertiary amine or quaternary ammonium salts groups. The separation efficiency was followed by UV-Vis spectroscopy, while the information regarding the mechanism involved in the separation of pesticide particles have been obtained by zeta potential. UV-Vis spectroscopy data showed strong pesticide particles/polycation interactions in case of Novadim Progress and Bordeaux mixture (maximum pesticide removal between 90% and 98%). Good separation efficiency (around 80%) of Karate Zeon emulsion was also noticed. The zeta potential measurements indicated that the charge neutralization was the common flocculation mechanism for the removal of these pesticides. In addition, the hydrogen bondings and chelation of copper ions by amide and/or tertiary amino groups of the polycations had a noteworthy contribution to the pesticide removal.

A review on acrylic based hydrogels and their applications in wastewater treatment

The acrylic based hydrogels have attracted the attention of many researchers in the field of pollutants adsorption such as dyes and metal cations due to their high swelling and adsorption capacities. This review introduces acrylic based hydrogels and focuses on their adsorption properties. We first described the methods for synthesizing hydrogels. Usual methods of characterization of acrylic based hydrogels such as swelling, adsorption capacity and desorption efficiency of the pollutants have been investigated. In addition, the adsorption isotherm and kinetic models which determine the mechanism of pollutants' adsorption by hydrogels have been introduced and relations that determine the values of thermodynamic parameters which define accomplishment of adsorption process have been investigated. In the following sections, a perfect insight has been provided on natural and synthetic acrylic based hydrogels. The effective parameters of swelling and adsorption by acrylic based hydrogels have been reviewed and the mechanism of pollutant's adsorption by acrylic based hydrogels has been discussed.

Changes in Microcystis aeruginosa cell integrity and variation in microcystin-LR and proteins during Tanfloc flocculation and floc storage

The objective of this study was to determine the influence of Tanfloc on Microcystis aeruginosa cell integrity, microcystin-LR (MC-LR), and proteins during flocculation and floc storage. The effects of Tanfloc addition, stirring, and floc storage time were considered to minimize cell damage and the release of MC-LR and proteins. Optimal flocculation conditions (Tanfloc dosage 10.42 mg L^-1, rapid agitation for 0.36 min at 568.88 rpm and slow agitation for 14.14 min at 12.1 rpm) were obtained using the response surface methodology. Up to 98.9% of the M. aeruginosa cells were removed intact at low Tanfloc dosage. During floc storage, Tanfloc initially protected the cells. After 8 d, large-scale cell lysis occurred because Tanfloc had substantially decomposed. Nevertheless, Tanfloc also extended the extracellular MC-LR and protein release time to 8 d. This delay ensured adequate time to decontaminate sludge containing the algae, thereby reducing the risk of secondary pollution. In addition, the low cost of Tanfloc facilitates its widespread application in the management of harmful algal blooms.

Remediation of water and wastewater by using engineered nanomaterials: A review

Nanotechnology is currently a fast-rising socioeconomic and political knowledge-based technology owing to the unique characteristics of its engineered nanomaterials. This branch of technology is useful for water and wastewater remediation. Many scientists and researchers have been conducting different studies and experiments on the applications of engineered nanomaterials at the local to international level. This review mainly aims to provide a current overview of existing knowledge on engineered nanomaterials and their applications in water and wastewater remediation. Furthermore, the present risks and challenges of nanotechnology are examined.

Responses of wastewater biofilms to chronic CeO2 nanoparticles exposure: Structural, physicochemical and microbial properties and potential mechanism

With the accelerated application of CeO₂ nanoparticles (NPs), wastewater treatment plants will increasingly receive CeO₂ NPs, thus inevitably causing CeO₂ NPs to encounter microaggregates. Here, we comprehensively elucidate the responses in the structural, physicochemical and microbial properties of wastewater biofilms to chronic exposure (75 days) to different CeO₂ NPs concentrations, with a particular emphasis on the protective mechanisms of stratified extracellular polymeric substances (EPSs). Chronic exposure to 0.1 mg/L CeO₂ NPs boosted the content and broadened the distribution of α-d-glucopyranose polysaccharides (PS), while the sharply increased production and breadth of β-d-glucopyranose PS, forming a formidable shield, was a response to 10 mg/L CeO₂ NPs. After the bacteria were exposed to CeO₂ NPs, loosely bound EPSs (LB-EPSs) aggregated into macromolecules (increasing in apparent molecular weight (AMW)) but at a lower abundance, whereas the average AMW in tightly bound EPSs (TB-EPSs) decreased. The acetyl content and (α-helix+3-turn helix)/β-sheet value of TB-EPSs increased to resist CeO₂ NPs. Furthermore, long-term exposure to CeO₂ NPs decreased cell viability, reduced microbial diversity and shifted the microbial composition. N-acylated-l-homoserine lactone concentrations increased with increased density of Pseudomonas, which was associated with PS-regulated control, thus promoting PS production in EPSs in response to CeO₂ NPs. These results expand the understanding of how microaggregates resist environmental stress caused by NPs.

Application of Chitin/Chitosan and Their Derivatives in the Papermaking Industry

Chitin/chitosan and their derivatives have become of great interest as functional materials in many fields within the papermaking industry. They have been employed in papermaking wet-end, paper surface coating, papermaking wastewater treatment, and other sections of the papermaking industry due to their structure and chemical properties. The purpose of this paper is to briefly discuss the application of chitin/chitosan and their derivatives in the papermaking industry. The development of their application in the papermaking area will be reviewed and summarized.

Scale-inhibition and flocculation dual-functionality of poly(acrylic acid) grafted starch

Natural-polymer based water treatment agents have recently received much more attention due to their environmental friendliness, widespread availability, and prominent structural features. Starch-graft-poly(acrylic acid) (St-g-PAA) is a simple natural-polymer based material that can be obtained easily by a one-step graft copolymerization. When used as a water treatment agent, St-g-PAA exhibits both effective scale-inhibition performance and high turbidity removal efficiency. The scale-inhibition efficiency of St-g-PAA against calcium carbonate (CaCO₃) is approximately 94% at the optimal dose in a static test of approximately 40 mg/L. Dispersion, crystal lattice distortion, and chelating effects all play important roles in the scale inhibition. When St-g-PAA is used as a coagulant aid for polyaluminum chloride (PAC) in the flocculation of a real hairwork wastewater, the highest reduction of the optimal PAC dose is more than 30% while the turbidity reduction is about 97% at the same time, both floc size and compactness increase, and the final settling efficiency also improves evidently. The efficient bridging flocculation effects account for the effective turbidity removal. The prominent scale-inhibition and flocculation dual-functionality of St-g-PAA is intrinsically ascribed to its distinct anionic linear branched-chain structure.

Study on adsorption properties and mechanism of Pb2+ with different carbon based adsorbents

Different activated carbon materials are prepared from a series of solid wastes (sawdust, acrylic fabric, tire powder and rice husk) by combination of the KOH activation method and steam activation method. The influences of several parameters such as pH, contact time, adsorbent dosage and temperature on adsorption performance of Pb²⁺ with those different carbon adsorbents are investigated. The results demonstrate that C_{rice husk} performance well in the adsorption process. In the following, the C_{rice husk} is used to explain the adsorption mechanism of Pb²⁺ by SEM-EDS, FT-IR and XPS. The results illustrate that the surface oxygen-containing functional groups such as carboxyl, lactone group, phenolic hydroxyl and other alkaline metal ions like Na⁺ and K⁺ have significant effect on the adsorption process. A reasonable mechanism of Pb²⁺ adsorption is proposed that the ion exchange play key roles in the adsorption process. In addition, the effects of Cu²⁺, Zn²⁺ on the Pb²⁺ adsorption capacity with the four carbon adsorbents are also studied and the results demonstrate that other heavy metals play positive effects on the adsorption of Pb²⁺.

Granulation and microbial community dynamics in the chitosan-supplemented anaerobic treatment of wastewater polluted with organic solvents

The effect of chitosan on the development of granular sludge in upflow anaerobic sludge blanket reactors (UASB) when treating wastewater polluted with the organic solvents ethanol, ethyl acetate, and 1-ethoxy-2-propanol was evaluated. Three UASB reactors were operated for 219 days at ambient temperature with an organic loading rate (OLR) of between 0.3 kg COD m^-3 d^-1 and 20 kg COD m^-3 d^-1. One reactor was operated without the addition of chitosan, while the other two were operated with the addition of chitosan doses of 2.4 mg gVSS^-1 two times. The three reactors were all able to treat the OLR tested with COD removal efficiencies greater than 90%. However, the time required to reach stable operation was considerably reduced in the chitosan-assisted reactors. The development of granules in the reactors with chitosan was accelerated and granules larger than 2000 μm were only observed in these reactors. In addition, these granules exhibited better physicochemical characteristics: the mean particle diameter (540 and 613 μm) was approximately two times greater than in the control reactor (300 μm), and the settling velocities exceeded 35 m h^-1. The extracellular polymeric substances (EPS) in the reactors with the chitosan was found to be higher than in the control reactor. The protein-EPS content has been correlated with the granule size. The analyses of the microbial communities, performed through denaturing gradient gel electrophoresis and high-throughput sequencing, revealed that the syntrophic microorganisms belonging to genus Geobacter and the hydrogenotrophic methanogen Methanocorpusculum labreanum were predominant in the granules. Other methanogens like Methanosaeta species were found earlier in the chitosan-assisted reactors than in the control reactor.

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.

A pH-responsive starch-based flocculants containing both cationic and anionic functional groups has been developed. The saturated flocculant can be facilely regenerated and separated from the solution by applying an external pH stimulus.

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.

A new triazine-based covalent organic polymer for efficient photodegradation of both acidic and basic dyes under visible light

COP-NT can be used as an efficient photocatalyst for the degradation of methyl orange (MO), rhodamine B (RhB) and methylene blue (MB).

Flocculation of coal washing wastewater using polysaccharide produced by Paenibacillus mucilaginosus WL412

Natural polymeric flocculant shows effectiveness in wastewater treatment without increasing the environmental burden. The extracellular substance produced by Paenibacillus mucilaginosus WL412 was identified as an anionic polysaccharide composed of five types of monosaccharides, namely, D-mannose, D-glucuronic acid, D-glucose, D-galactose, and L-fucose with the molar ratio of 2.8:1.2:2.0:1.8:0.8. The purified polysaccharide, POS412, presented high efficiency in flocculating coal washing wastewater and kaolin suspension without the assistance of inorganic coagulants. Addition of POS412 resulted in the polymer bridging phenomenon in suspensions, which was observed by means of scanning electron microscopic imaging, size grading, and ζ-potential analyses. More importantly, POS412 exhibited satisfactory stability after storage in various conditions. The flocculation rate was more than 91% for coal washing wastewater when POS412 was stored for 264 h in the wide range of pH (3-11) and temperature (20-50 °C) before use. Results indicate that POS412 is a competent bioflocculant for wastewater treatment.

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.