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

Chitosan has the potential to improve water quality without negative effects on the coral, Porites lobata

Coral reefs off the coast of West Maui in Hawai'i are frequently subjected to highly turbid water, caused in part by terrigenous sediment inputs from stream gulches after rain events. Sediment has numerous deleterious consequences on scleractinian corals, including impacts on growth and survival. The finalized West Maui Watershed Management Plan includes recommendations to reduce sources and conveyance of land-based pollution to increase resiliency of coral reefs. This study investigated the use of the flocculant, chitosan, for potential use near sensitive coral reef ecosystems. In a laboratory-based experiment, chitosan did not impact growth of Porites lobata during a 30-day exposure. Additionally, chitosan significantly reduced turbidity within 1 h of addition in both seawater and freshwater. These data suggest that chitosan does not negatively impact one of Hawai'i's common coral species. This study provides the foundation for further research investigating the ecosystem effects of chitosan application when used as a potential mitigation action to reduce sedimentation in West Maui's coral reefs.

Adsorption of Bisphenol A from Water Using Chitosan-Based Gels

The comonomer bisphenol A (BPA) finds applications in the plastics industry, where it is used in the production of polycarbonates, plastics, PVC, thermal paper, epoxy and vinyl ester resins, and polyurethane. The water, with which many of these materials come into contact, is one of the main sources of human exposure to BPA. When ingested or touched, BPA can damage organs, disrupt the endocrine and immune systems, generate inflammatory responses, and be involved in genotoxic processes. Therefore, the need to develop effective techniques for removing BPA from aqueous environments is imperative. This paper provides a comprehensive review regarding the effective removal of BPA from water, focusing on the performance and adsorption mechanisms of various adsorbents based on chitosan and chitosan composites. The chemical and physical factors, adsorption kinetics and models governing the adsorption process of BPA in chitosan materials are also examined. This review outlines that, despite considerable progress in the absorption of bisphenol using chitosan gels, further research is necessary to assess the efficacy of these adsorbents in treating real wastewater and in large-scale manufacture.

Treatment of cold pressed Zanthoxylum schinifolium oil wastewater: Process, sludge characteristics, and microbial diversity analysis using biochemical methods

Cold-pressed Zanthoxylum schinifolium oil wastewater (ZOW), rich in organic pollutants, poses serious environmental challenges. This study examined ZOW treatment using a biochemical process, analyzing changes in activated sludge (AS) characteristics and microbial diversity to clarify pollutant removal pathways. Optimal parameters were established for biological treatment: a temperature of 30 °C, mixed liquor suspended solids (MLSS) of 4000 mg/L, initial pH of 7.5, rotational speed of 200 rpm, and a hydraulic retention time (HRT) of 48 h. For flocculation, 400 mg/L of polymeric aluminum sulfate and 60 mg/L of amphoteric polyacrylamide at pH 8 were identified as ideal. The biochemical process significantly reduced chemical oxygen demand (94.03 ± 0.31%), total phosphorus (93.33 ± 0.25%), total nitrogen (97.03 ± 0.26%), and turbidity (98.97 ± 0.02%). AS characterization showed enhanced sedimentation, larger particle size, increased extracellular polymer production indicating greater adsorption capacity, and higher biomass. 16S rRNA sequencing revealed Proteobacteria and Bacteroidota as dominant taxa (>50%), with aerobic denitrifiers such as Chryseobacterium and Pseudomonas showing strong adaptation to ZOW. Functional annotation confirmed the AS community's efficacy in pollutant removal.

Graft copolymerization synthesis of chitosan-polyferric sulfate composite coagulant to improve biogas slurry treatment toward effective irrigation

Biogas slurry from anaerobic digestion of organic wastes can be a potential biofertilizer for agricultural irrigation, which however, is challenged by suspended solids and contaminants. Thus, this study synthesized a composite coagulant and optimized its performance to advance biogas slurry treatment. A natural-synthetic polymer, chitosan (CTS), was modified by 2-methacryloxyethyltrimethyl ammonium chloride (DMC) via graft copolymerization and then combined with polyferric sulfate (PFS) to formulate the composite CTS-g(DMC)-PFS coagulant. Results show that CTS-g(DMC)-PFS exhibited stronger electrical neutralization and adsorption bridging to destabilize and aggregate colloidal particles, thus, exhibiting higher removal of suspended solids, heavy metals, and antibiotics over individual and pristine coagulants. Graft copolymerization of CTS with DMC at the mass ratio of 1:9 maximized its water solubility. Further blending this mixture with PFS at the mass ratio of 1:2 effectively improved the coagulation of biogas slurry, particularly for the removal of antibiotics and heavy metals (e.g. enrofloxacin and Cu). Moreover, CTS-g(DMC)-PFS produced dense and compact flocs for effective sedimentation. Detailed characterization attributed such improvement to the hydrolysis of cationic quaternary ammonium groups on grafted monomers and further coordinative effects between CTS-g(DMC) and Fe to enhance molecular chains and positive charges in CTS-g(DMC)-PFS to facilitate particle aggregation, contaminant adsorption, and then floc sedimentation.

Insight into enhancing the performance of sludge dewatering using a novel flocculant CS-TA prepared through free radical-mediated conjugation

Flocculation is one of the most significant conditioning methods for sludge dewatering. In the study, a novel flocculant CS-TA, prepared through free radical-mediated conjugation of tannic acid (TA) and chitosan (CS), was proposed to improve sludge dewatering. The characterisation using Fourier transform infra-red spectroscopy and X-ray diffraction analysis shows that the CS chain was the backbone of CS-TA, and the presence of CS-TA aromatic rings confirmed the conjugation of CS with TA. Moreover, the conditioning of CS-TA yielded the best dewatering performance at 30 mg g TS-1 with the water content of sludge cake by press filtration (Wsc) of 59.78% ± 0.3% and capillary suction time (CST) of 11.8s ± 0.35 s, compared to 98.2% ± 0.15% and 56.2 s ± 0.16 in raw sludge. The results of different influencing factors (e.g. pH and temperature) on flocculation efficiency indicated that CS-TA possessed the capacity for enhancing sludge dewaterability over a wide range of pH, and the optimal temperature was observed to be 35 °C. Furthermore, the increase of particle size and zeta potential implied the addition of CS-TA favoured the formation of larger particles charge neutralisation and adsorption bridging effect. In addition, extracellular polymer substances (EPS) analysis indicated that the decrease in the polysaccharide and protein contents in EPS after CS-TA addition could increase the relative hydrophobicity of sludge. Moreover, the contents of heavy metals in sludge and their leaching toxicity and environmental risk were reduced. This study provides comprehensive insights into the exploration of CS-TA for sludge dewatering and the maintenance of ecological security in an eco-friendly.

Removal and Recovery of AgNPs from Water by Sustainable Magnetic Nanoflocculants

The presence of silver nanoparticles (AgNPs) in water bodies has emerged as a new environmental concern and the efficient separation of these nanoparticles remains a critical challenge. Here, we developed novel magnetic nanoflocculants for the recovery of AgNPs from water. Alternating layers of biopolymers, in particular, chitosan, alginate, and polymeric bio-based soluble substances (BBS) derived from urban waste, were coated on magnetic nanoparticles via the layer-by-layer technique to prepare reusable magnetic nanoflocculants (MNFs). The MNFs obtained were characterized with diverse physicochemical techniques. Surface response methodology, based on the Doehlert matrix, has shown to be a useful tool to determine the effect of pH (in the range 5-9), concentration of AgNPs (7-20 mg L-1), and MNFs (50-1000 mg L-1) on the performance of AgNPs removal. The model predicts a high AgNPs removal percentage at low pH values and high MNF concentration. In particular, for the most efficient MNFs, 90% of AgNPs removal was obtained at pH 5 and 600 mg L-1 MNF concentration. Additionally, the effects of AgNPs size, ionic strength, the presence of humic acids, and two types of surfactants (LAS anionic and TWEEN 20 nonionic) on the AgNPs removal were evaluated. Finally, recovery and reuse experiments showed that MNF made of Chitosan-BBS can be reused in ten cycles, losing only 30% of the initial removal capacity. Therefore, magnetic flocculation could represent a sustainable alternative for AgNPs separation with potential applications in water treatment and remediation of nanoparticle contamination.

A novel flocculant based on "happy molecules" for the efficient removal of NSAIDs and NOM complexes: Role of parallel π-π stacking force

Non-steroidal anti-inflammatory drugs (NSAIDs) pose potential risks to human health and ecosystems in the water cycle. Herein, Dopamine (DA), known as the "happy molecule" and "biological glue", it can interact with various drugs and " adhere " to them. In this study, DA was used as a monomer to modify chitosan (CS) under ultraviolet light through Michael addition and Schiff base reactions, resulting in a novel eco-friendly polymer (CS@PDA) with high flocculation activity for ibuprofen (IBU), representing NSAIDs. CS@PDA achieved the IBU flocculation removal rate of 91.6 %. The mechanism involves three primary forces: hydrophobic interactions, hydrogen bonding, π-π stacking among benzene rings, along with secondary forces like electrostatic neutralization. DFT calculations indicate that π-π interactions between partially parallel-stacked benzene rings are dominant in CS@PDA's flocculation of IBU. Notably, the removal efficiency of ibuprofen (IBU) in coflocculation with natural organic matter (NOM) reached 93.1 %, which was higher than that achieved by flocculating IBU alone (91.6 %). And the co-flocs exhibit greater resistance and re-flocculation capabilities under strong hydraulic stirring conditions. In this mixed mechanism, hydrogen bonding is enhanced while hydrophobic associations diminish. π-π stacking remains significant. The possible flocculation pathways among with three substances were further analyzed. This study employed a star rating methodology to quantify each force's intensity.

Innovative grease interceptor to enhance fat, oil and grease removal from the wastewater generated from food service establishments

Commercial grease interceptors (GIs), commonly used in food service establishments, are primarily designed to treat fat, oil and grease (FOG) from handwash sink (HS) wastewater. They are generally less effective for removing highly concentrated FOG from dishwasher (DW) effluents which contain highly emulsified FOG with complex long-chain fatty acids (LCFAs). Furthermore, standard testing of GIs uses diesel fuel to simulate FOG separation; however, the flow properties of typical cooking oils and animal fats differ significantly from diesel. We developed a novel GI (bench-scale with 72 L capacity) and examined the impact of various baffle configurations on FOG removal efficiency using samples containing representative FOG components of cooked oil, fat and food solids. The results demonstrated that the installation of two short baffles projecting from the top along with one short baffle projecting from the bottom in the first chamber, and another short baffle projecting from the top in the second chamber, led to FOG removal efficiencies of up to 88% and 40% for HS and DW effluents, respectively, at a hydraulic retention time (HRT) of 44 min. The short baffles acted as barriers, thus enhancing the loss of kinetic energy, subsequently ensuring a quiescent flow condition, resulting in an increased HRT for effective FOG separation. The addition of alum as coagulant at 200 mg/L (18.2 mg of Al3+/L) significantly enhanced the removal of FOG from treated DW effluents (up to 87%), effectively reducing the concentrations of various extra-LCFAs, such as paullinic (C20:1), arachidic (C20:0), eicosadienoic acid (C20:2), mead (C20:3), eicosapentaenoic (C20:5), erucic (C22:1), cervonic (C22:6), tricosanoic acid (C23:0), lignoceric (C24:0) and nervonic (C24:1) acid by up to 99%. These findings provide significant insights into the advanced GI design, offering a proactive solution to prevent fatberg formation while promoting a more sustainable and economically viable approach to sewer management.

Deep dewatering of oily sludge: Mechanism, characterization, and pretreatment technology

Oily sludge, characterized by its high organic pollution, poses significant challenges for treatment and disposal due to its high proportion of bound water and elevated viscosity from petroleum hydrocarbons. This study focuses on the deep dewatering of oily sludge, examining the role of internal bound water and the pretreatment mechanisms involved. The deep dewatering process is categorized into two main areas: liberation of bound water and modification of physicochemical properties. (1) Bound water is primarily found in two major categories: water bound within proteins, EPS, and cells through hydrophilic interactions, and water within an oil-water emulsion structure facilitated by inorganic particles. (2) Physicochemical properties: The formation of flocs in oily sludge is crucial for effective dewatering, while creating dewatering channels in later stages enhances efficiency. Advanced oxidation and emerging demulsification technologies are also discussed, summarizing the latest research. The significant potential of electric fields in the deep dewatering of oily sludge is emphasized, offering valuable insights for future advancements.

Enhancing resource recovery from acid whey through chitosan-based pretreatment and machine learning optimization

Acid whey, a dairy byproduct with low pH and high organic content, presents disposal challenges but also potential for resource recovery. In this study, chitosan gel was synthesized and evaluated for turbidity reduction of acid whey. Machine learning (ML) models were employed to predict and optimize the pretreatment process, with the Random Forest algorithm achieving a prediction accuracy of 0.78. Using the Simulated Annealing algorithm, optimal conditions were identified, applying a 2.2 % chitosan solution gel at a dosage of 24 g/L to acid whey at pH 4.6 for 12 h, achieving a 91 % turbidity reduction, a significant improvement over the 71 % obtained prior to optimization. Validation experiments confirmed its effectiveness in predicting and optimizing the pretreatment process. These findings highlight the feasibility of ML in optimizing chitosan pretreatment and demonstrate chitosan gel as a cost-effective, efficient option for acid whey, with potential to enhance resource recovery in the dairy industry.

Phosphorus removal in microalgal growth and harvesting using natural flocculant: Influence of microalgal characteristics and phosphorus forms

Phosphorus-induced harmful algae blooms elicited attention, and both microalgae harvesting and phosphorus removal are essential, especially preventing secondary pollution. In this study, starved Chlorella vulgaris removed 68.73 % of dissolved inorganic phosphorus (DIP) compared to 37.47 % of dissolved organic phosphorus (DOP). Microalgae growth promoted the increase of extracellular organic matter, which had little effect on phosphorus removal. As incubation time increased, the phosphorus rebound was even higher than the original, which was not consistent with the continued growth of the microalgae cells, indicating that phosphorus uptake by microalgae alone could not inhibit algal blooms. A starch-based flocculant fed after the phycoremediation process exhibited effective microalgae harvesting, reducing DIP and DOP by 72.06 % and 48.31 %, respectively. Only 1/3rd flocculant dose was needed to treat suspensions supplemented with DIP compared with DOP. The study offers an eco-friendly technology for simultaneous phosphorus removal and microalgae harvesting by combining Chlorella vulgaris with natural flocculants.

Algal-bacterial bioremediation of cyanide-containing wastewater in a continuous stirred photobioreactor

This study reports the isolation and characterization of highly resistant bacterial and microalgal strains from an Egyptian wastewater treatment station to cyanide-containing compounds. The bacterial strain was identified as Bacillus licheniformis by 16S rRNA gene sequencing. The isolate removed up to 1 g L-1 potassium cyanide, 3 g L-1 benzonitrile, and 1 g L-1 sodium salicylate when incubated as 10% v/v in MSM at 30 ℃. However, it failed to degrade potassium thiocyanate at all tested concentrations. The microalgal isolate was identified by electron microscopy as a strain of Chlorella spp.. Algal toxicity was tested by incubating the microalgae as 6% v/v in MSM containing 2 g L- 1 NaHCO3 with increasing concentrations of the pollutants. Results showed that 0.05 g L-1 KCN, 1.5 g L-1 benzonitrile, 5 g L -1 KSCN, and 5 g L-1 sodium salicylate inhibited 93%, 96%, 75%, and 21% of algal growth, respectively. In a continuous stirred photobioreactor, the bacterial-microalgal microcosm detoxified synthetic wastewater containing 0.2 g L-1 KCN, 0.1 g L-1 benzonitrile, and 0.5 g L-1 sodium salicylate in 3.5 days of hydraulic retention time. System failure was recorded when the KCN concentration was increased to 0.25 g L-1. The effluent had no inhibitory effect on the germination of Lepidium sativum seeds in phytotoxicity testing. Temperature, pH, and chitosan effects were assessed on the algal/bacterial settleability. Statistical analysis showed no significant difference between the tested parameters. The microcosm represents a potential candidate for the treatment of industrial wastewater containing cyanide compounds.

Three intertwining effects guide the mode of action of chitin deacetylase de- and N-acetylation reactions

Chitosans are promising multi-functional biomolecules for various applications whose performance is dependent on three key structural parameters, including the pattern of acetylation (PA). To date, chitin deacetylases (CDAs) are the only tool to control the PA of chitosan polymers via their specific mode of action during de- or N-acetylation. For a start, this review summarizes the current state of research on the classification of carbohydrate esterase 4 enzymes, the features in sequence and structure of CDAs, and the different PAs produced by different CDAs during de- or N-acetylation. In the main part, we introduce three effects that guide the mode of action of these enzymes: the already established subsite capping effect, the subsite occupation effect, and the subsite preference effect. We show how their interplay controls the PA of CDA products and describe their molecular basis. For one thing, this review aims to equip the reader with the knowledge to understand and analyze CDAs - including a guide for in silico and in vitro analyses. But more importantly, we intend to reform and extend the model explaining their mode of action on chitosans to facilitate a deeper understanding of these important enzymes for biology and biotechnology.

Optimization of synthesis of cationic starches for wastewater sludge and microalgae separation

The implementation of stricter water protection legislation requires the development of novel environmentally friendly water treatment materials. A new method for the preparation of water soluble cationic starch flocculants using potato starch, 3-chloro-2-hydroxypropyltrimethylammonium chloride and CaO additive was developed and surface response methodology was successfully utilized for the optimization of degree of substitution in the cationization of potato starch with and without CaO additive. Based on the results of destabilization studies of model kaolin, wastewater sludge, and microalgae dispersion systems, optimized conditions ware proposed for obtaining an efficient, soluble, and biodegradable cationic starch flocculant with optimal structure. The duration of starch etherification reaction was reduced to <12 h to obtain soluble cationic starch derivatives with a degree of substitution of quaternary ammonium groups of 0.25, which retained the granular structure during synthesis. An efficient flocculation technology using anionic polymer and high content of biodegradable cationic flocculant was proposed. The highly efficient flocculation of microalgae suspensions using developed cationic starch derivative with the degree of substitution of cationic groups of 0.25 has been also achieved. The developed environmentally friendly cationic starches with tailored flocculation properties proofed to have a great potential in various water cleaning and separation technologies with prospects in wastewater treatment, agriculture or energy sectors.

Precisely controlled electrostatically sprayed sodium alginate/carboxymethyl chitosan hydrogel microbeads as super-adsorbent for adsorption of cationic dye

In this pioneering study, electrostatic spraying (ES) technology with high voltages is proposed to reduce the size of hydrogel microbeads further, aiming to enhance the adsorption rate of cationic methylene blue (MB) dye. The increased voltages, ranging from 0.0 to 13.0 kV, further decreased the size of electrostatically sprayed hydrogel microbeads crosslinked by hydrogen bonds between sodium alginate (SA) and carboxymethyl chitosan (CMCS) in hydrochloric acid. The size of SA/CMCS hydrogel microbeads was successfully reduced from 2000 ± 121 μm (SC-2000) to 400 ± 15 μm (SC-400). Notably, SC-400 exhibits the highest maximum adsorption capacity (qm) and rate constant (k2) at 840.3 mg/g and 0.0598 g/mg/min, respectively, at pH 9.0 and a temperature of 25 °C in the absence of ionic compounds, which is three times higher than that of SC-2000, due to their high specific surface area and pore volume. Through a series of adsorption studies and characterization analyses, SA/CMCS hydrogel microbeads displayed heterogeneous adsorption behaviors towards MB dye through electrostatic interactions between the deprotonated carboxylic groups and cationic MB molecules, where MB adsorption efficiency could be significantly influenced by pH and ionic strength. These findings suggest that ES technology is effective in synthesizing smaller SA/CMCS hydrogel microbeads with enhanced MB removal rates and stable adsorption capacities and their applications could be further explored for removing other organic dyes and toxic metals in subsequent research studies.

Preparation, characterization and application of a composite bioflocculant

Composite flocculant PAFS-PDM was prepared from Polymeric aluminium ferric sulphate (PAFS) and Poly (diallyl dimethyl ammonium chloride) (PDM) in this study. A bacterium was selected from the soil near the shale gas exploitation platform as a bioflocculant-producing bacterium, and polysaccharide was extracted and combined with PAFS-PDM to obtain composite bioflocculant (CBF) to treat shale gas fracturing flowback fluid. The prepared CBF was characterized and the results showed that the prepared PAFS-PDM contained aluminium-iron hydroxyl polymer, which was a cationic flocculant. By measuring the turbidity removal rate and chemical oxygen demand (COD) removal efficiency, the function mechanism of CBF on the shale gas fracturing flowback fluid was discussed. The results showed that CBF had a stable treatment effect on fracturing flowback fluid when the pH value was about 7.0. With the increase of dosage, the coagulation efficiency increased first and then decreased. When the dosage of the CBF was 2500 mg·L-1, the treatment effect of shale gas fracturing flowback fluid was the best, and COD removal rate reached 89.43%. Through Zeta potential analysis, it was concluded that one of the coagulation mechanisms was electrical neutralization. According to the characterization results, it could be concluded that both adsorption bridging and charge neutralization mechanisms played important roles in the treatment of shale gas fracturing flowback fluids.

Flocculation of Micractinium reisseri for successful harvesting and potential use

This study includes Micractinium reisseri cultivation in artificial saline medium (ASM). With the aim of harvesting the bulk M. reisseri biomass, an experiment was set up at a bench scale to evaluate the best flocculation technique with the least compromising biomass and lipid loss. The flocculation efficiencies for the M. reisseri biomass have been studied using the auto-, bio-, and chemical-flocculation methods. Different concentrations of chitosan for the biological method and alum for the chemical method were added in M. reisseri culture growing in the liquid ASM. The optimal concentration with the highest biomass and oil collection was determined for each method. In the biological method, the highest (96.44%) and lowest (67.88%) flocculation efficiencies were observed by adding 15 and 2 mg of chitosan, respectively, and in the chemical method, the highest (97.2%) and lowest (35.4%) flocculation efficiencies were observed by adding 150 and 50 mg of alum, respectively. The auto-flocculation method shows the highest efficiency (97.8%) among all the tests. The oil yield from the three highest biomasses was 2.60, 1.51, and 1.08% in the auto-, bio-, and chemical-flocculation methods, respectively. The time taken for auto-, bio-, and chemical-flocculation was 48, 4, and 1 h, respectively.

Development and evaluation of amine-functionalized β-cyclodextrin grafted starch as a natural flocculant for turbidity removal in water treatment

Recently, biopolymers have been used as coagulants/flocculants due to their biodegradability, low cost, and renewability. In this study, an environmentally friendly amine-functionalized starch-based flocculant was successfully prepared. Initially, β-cyclodextrin was grafted onto the starch backbone to increase the number of hydroxyl groups, and this composite was named CD-starch. Subsequently, in order to introduce cationic properties and enhance effective flocculation, CD-starch was modified using amine functional groups. The surface functional groups were engineered by introducing different amine to CD-starch ratios (0.5:1, 1:1, 2:1 w/w), named A-CD-starch 0.5, 1 and 2, respectively. Following the characterization of the synthesized substrate, its performance in the flocculation process of a kaolin suspension was investigated. The effects of different parameters, including pH, flocculant dosage, and initial turbidity on wastewater turbidity removal, was investigated. The results showed that a higher ratio of amine to CD-starch leads to a better amination reaction due to the greater availability of nitrogen for alkylation. Jar experiments showed that for initial turbidities of 50, 150 and 300 NTU, the appropriate doses of flocculant were 0.070, 0.085 and 0.130 mg/mL, respectively. For these initial turbidities, the maximum turbidity removal was achieved 80.1 %, 92 %, and 97.8 %, respectively. This work provides an innovative natural flocculant based on starch which can effectively treat turbid wastewaters.

Electrocoagulation treatment of wastewater collected from Haldia industrial region: Performance evaluation and comparison of process optimization

This study investigates the treatment of oil-contaminated wastewater with high levels of inorganic substances, suspended solids and turbidity, collected from the Haldia industrial region of India in February 2023. The wastewater, originating from industries such as chemical, petrochemical, textile, and battery manufacturing, presents a complex pollutant load that challenges traditional treatment methods. Electrocoagulation was employed as the treatment technique, with process optimization conducted using Box-Behnken design (BBD) and central composite design (CCD) for key parameters: pH, initial oil concentration, current density, and electrolysis time. The study comprehensively examined the effects of these parameters on turbidity removal. The optimal conditions were determined to be a pH of 7.5, an initial oil concentration of 275 mg/L, a current density of 17.5 mA/cm², and an electrolysis time of 20 min. Under these conditions, CCD outperformed BBD, achieving a desirability score of 93 % compared to 80 % for BBD. The process successfully reduced turbidity from 450 NTU to 56 NTU and total suspended solids (TSS) from 300 mg/L to 102 mg/L. The operation cost of the process was found to range from ₹0.904/m³ to ₹2.71/m³ as the electrolysis time increased from 0.17 to 0.5 h. The study presents a viable solution for industrial wastewater treatment in this region, aligning with the United Nations Sustainable Development Goal (UN SDG) 2030. Additionally, combining electrocoagulation with membrane filtration may enhance comprehensive pollutant removal.

Recent Advances in the Preparation, Antibacterial Mechanisms, and Applications of Chitosan

Chitosan, a cationic polysaccharide derived from the deacetylation of chitin, is widely distributed in nature. Its antibacterial activity, biocompatibility, biodegradability, and non-toxicity have given it extensive uses in medicine, food, and cosmetics. However, the significant impact of variations in the physicochemical properties of chitosan extracted from different sources on its application efficacy, as well as the considerable differences in its antimicrobial mechanisms under varying conditions, limit the full realization of its biological functions. Therefore, this paper provides a comprehensive review of the structural characteristics of chitosan, its preparation methods from different sources, its antimicrobial mechanisms, and the factors influencing its antimicrobial efficacy. Furthermore, we highlight the latest applications of chitosan and its derivatives across various fields. We found that the use of microbial extraction shows promise as a new method for producing high-quality chitosan. By analyzing the different physicochemical properties of chitosan from various sources and the application of chitosan-based materials (such as nanoparticles, films, sponges, and hydrogels) prepared using different methods in biomedicine, food, agriculture, and cosmetics, we expect these findings to provide theoretical support for the broader utilization of chitosan.

Osteogenic citric acid linked chitosan coating of 3D-printed PLA scaffolds for preventing implant-associated infections

>25 % of the patients who receive orthopedic implants have been reported with implant-associated osteomyelitis, which can result in inflammation, osteolysis, and aseptic loosening of implants. Current treatment methods doesn't ensure defect healing and prevention from reinfection. Thermoplastic-based 3D-printed scaffolds offer a bioresorbable, biocompatible, and mechanical strong implant system. However, the hydrophobicity and bio-inertness of these polymers prevent their use in clinics. In this study, we developed dual functionalized scaffolds with osteogenic and antibacterial properties by immobilizing citric acid-linked chitosan on oxygen plasma etched 3D-printed PLA scaffolds through an EDC-NHS coupling reaction. Acellular mineralization of these scaffolds in DMEM demonstrated the deposition of crystalline hydroxyapatite. In addition, the antibacterial properties of these surface-modified scaffolds have been determined against E. coli and S. aureus, where the citric-linked chitosan biofunctionalized 3D-printed PLA scaffolds showed significantly higher antibacterial activity in comparison to oxygen-etched PLA and PLA scaffolds due to the synergistic effect of citric acid and chitosan functionalities. MG-63 cells exhibited increased proliferation and osteogenic activity on the modified scaffolds compared to the PLA and OP-PLA. These 3D-printed scaffolds, coated with citric-linked chitosan, can be a potential solution to orthopedic complications such as critical-sized bone defects and implant-associated osteomyelitis.

Insights into water insecurity in Indigenous communities in Canada: assessing microbial risks and innovative solutions, a multifaceted review

Canada is considered a freshwater-rich country, despite this, several Indigenous reserves struggle with household water insecurity. In fact, some of these communities have lacked access to safe water for almost 30 years. Water quality in Canadian Indigenous reserves is influenced by several factors including source water quality, drinking water treatments applied, water distribution systems, and water storage tanks when piped water is unavailable. The objective of this multifaceted review is to spot the challenges and consequences of inadequate drinking water systems (DWS) and the available technical and microbiological alternatives to address water sanitation coverage in Indigenous reserves of Canada, North America (also known as Turtle Island). A comprehensive literature review was conducted using national web portals from both federal and provincial governments, as well as academic databases to identify the following topics: The status of water insecurity in Indigenous communities across Canada; Microbiological, chemical, and natural causes contributing to water insecurity; Limitations of applying urban-style drinking water systems in Indigenous reserves in Canada and the management of DWS for Indigenous communities in other high-income countries; and the importance of determining the microbiome inhabiting drinking water systems along with the cutting-edge technology available for its analysis. A total of 169 scientific articles matched the inclusion criteria. The major themes discussed include: The status of water insecurity and water advisories in Canada; the risks of pathogenic microorganisms (i.e., Escherichia coli and total coliforms) and other chemicals (i.e., disinfection by-products) found in water storage tanks; the most common technologies available for water treatment including coagulation, high- and low-pressure membrane filtration procedures, ozone, ion exchange, and biological ion exchange and their limitations when applying them in remote Indigenous communities. Furthermore, we reviewed the benefits and drawbacks that high throughput tools such as metagenomics (the study of genomes of microbial communities), culturomics (a high-efficiency culture approach), and microfluidics devices (microminiaturized instruments) and what they could represent for water monitoring in Indigenous reserves. This multifaceted review demonstrates that water insecurity in Canada is a reflection of the institutional structures of marginalization that persist in the country and other parts of Turtle Island. DWS on Indigenous reserves are in urgent need of upgrades. Source water protection, and drinking water monitoring plus a comprehensive design of culturally adapted, and sustainable water services are required. Collaborative efforts between First Nations authorities and federal, provincial, and territorial governments are imperative to ensure equitable access to safe drinking water in Indigenous reserves.

Advanced treatment and reuse of dye wastewater using thermo-irreversible on/off switch starch with disruption of dissolution/precipitation dynamic equilibrium

The development of irreversible on/off switching materials is a potential strategy for unidirectional capture and encapsulation of pollutants, preventing the pollutant leakage problem resulting from the reversible dissolution of flocculants. Herein, a thermo-irreversible on/off switch starch (TISS) is prepared through modifying starch by etherification grafting glycidyl phenyl ether and 2,4-bis(dimethylamino)-6-chloro-[1,3,5]-triazine. It breaks the dissolution/precipitation dynamic equilibrium across heating-cooling cycles by thermal-induced irreversible coil-to-globule self-assembly of polymer chains, resulting in a 50-fold decrease in polymer solubility. Particularly, TISS shows a superior double-locking effect on pollutants and flocculants through its unique irreversible conformation memory capability, leading to a high-quality reuse water. 99.9 % of reactive brilliant red dye and 97.9 % of TISS remain fixed within sludge flocs even after prolonged immersion in cold water at 24 °C for 60 days. Furthermore, direct recycling and reuse of dye-bath energy can be realized through the isothermal flocculation and dyeing method, showing a 75 % decrease in energy consumption after three cycles compared to traditional dyeing techniques. This work presents a novel approach to constructing an irreversible pollutant delivery system using thermo-irreversible on/off switch starch, addressing the problems of high energy dissipation and water quality fluctuations during wastewater treatment.

Enhancement of alkaline pretreatment-anaerobically digested sludge dewaterability by chitosan and rice husk powder for land use of biogas slurry

Alkaline pretreatment can improve the methane yields and dewatering performance of anaerobically digested sludge, but it still needs to be coupled with other conditioning methods in the practical dewatering process. This study utilized four different flocculants and a skeleton builder for conditioning of alkaline pretreatment-anaerobically digested sludge. Chitosan was found to be the most effective in dewatering the sludge. Chitosan coupled with rice husk powder further improved the dewatering performance, which reduced normalized capillary suction time, specific resistance to filtration, and moisture content by 98.7%, 82.0%, and 12.1%. For land use of biogas slurry as a fertilizer, chitosan conditioning promoted the growth of corn seedlings, while the other three flocculants diminished the growth of corn seedlings. Chitosan coupled with rice husk powder further promoted the growth of corn seedlings by 103.5%, 65.0%, and 53.7% in fresh weight, dry weight, and root length, respectively. Overall, chitosan coupled with rice husk powder not only enhanced the dewaterability of alkaline pretreatment-anaerobically digested sludge but also realized the resource utilization of agricultural waste.

Effective removal of Cu(II) from water by three-dimensional composite microspheres based on chitosan/sodium alginate/silicon dioxide: Adsorption performance and mechanism

Chitosan (CS) is commonly used as an adsorbent for removing Cu(II) from water, but it has drawbacks such as solubility in dilute acid, difficulty in recycling in powder form, and short service life. This study utilized sodium alginate (SA) as a gel carrier to encapsulate CS, combined with silicon dioxide (SiO2) to improve mechanical stability. The preparation of CS/SA/SiO2 (SSC1.0) involved physical blending, CaCl2 cross-linking, and freeze-drying. Characterization methods such as SEM-EDS, FTIR, BET, and XRD were used to analyze the structural composition of SSC1.0. The material exhibited a folded surface, porous internal cross-section, nitrogen/oxygen-containing functional groups, and thermal stability in high temperatures and various aqueous environments. The adsorption performance of SSC1.0 on Cu(II) was evaluated under different conditions, showing a maximum adsorption capacity of 47.50 mg/g. The material maintained a removal rate above 70 % after 5 cycles. SSC1.0 also showed the highest removal rate of Cu(II) when applied to mine wastewater treatment. Adsorption modeling indicated that the process was driven by chemical reactions and was spontaneous and heat-absorbing.'

Heterogeneously deacetylated chitosans possess an unexpected regular pattern favoring acetylation at every third position

Chitosans are promising biopolymers for diverse applications, with material properties and bioactivities depending i.a. on their pattern of acetylation (PA). Commercial chitosans are typically produced by heterogeneous deacetylation of chitin, but whether this process yields chitosans with a random or block-wise PA has been debated for decades. Using a combination of recently developed in vitro assays and in silico modeling surprisingly revealed that both hypotheses are wrong; instead, we found a more regular PA in heterogeneously deacetylated chitosans, with acetylated units overrepresented at every third position in the polymer chain. Compared to random-PA chitosans produced by homogeneous deacetylation of chitin or chemical N-acetylation of polyglucosamine, this regular PA increases the elicitation activity in plants, and generates different product profiles and distributions after enzymatic and chemical cleavage. A regular PA may be beneficial for some applications but detrimental for others, stressing the relevance of the production process for product development.

Comprehensive strategies for microcystin degradation: A review of the physical, chemical, and biological methods and genetic engineering

Addressing the threat of harmful cyanobacterial blooms (CyanoHABs) and their associated microcystins (MCs) is crucial for global drinking water safety. In this review, we comprehensively analyze and compares the physical, chemical, and biological methods and genetic engineering for MCs degradation in aquatic environments. Physical methods, such as UV treatments and photocatalytic reactions, have a high efficiency in breaking down MCs, with the potential for further enhancement in performance and reduction of hazardous byproducts. Chemical treatments using chlorine dioxide and potassium permanganate can reduce MC levels but require careful dosage management to avoid toxic by-products and protect aquatic ecosystems. Biological methods, including microbial degradation and phytoremediation techniques, show promise for the biodegradation of MCs, offering reduced environmental impact and increased sustainability. Genetic engineering, such as immobilization of microcystinase A (MlrA) in Escherichia coli and its expression in Synechocystis sp., has proven effective in decomposing MCs such as MC-LR. However, challenges related to specific environmental conditions such as temperature variations, pH levels, presence of other contaminants, nutrient availability, oxygen levels, and light exposure, as well as scalability of biological systems, necessitate further exploration. We provide a comprehensive evaluation of MCs degradation techniques, delving into their practicality, assessing the environmental impacts, and scrutinizing their efficiency to offer crucial insights into the multifaceted nature of these methods in various environmental contexts. The integration of various methodologies to enhance degradation efficiency is vital in the field of water safety, underscoring the need for ongoing innovation.

Natural flocculant chitosan inhibits short-chain fatty acid production in anaerobic fermentation of waste activated sludge

Chitosan (CTS) serves as an excellent natural flocculant in wastewater purification and sludge conditioning, but its potential impact on anaerobic fermentation of waste-activated sludge is unclear. The current study investigated the role of CTS in short-chain fatty acids (SCFAs) generation via sludge alkaline anaerobic fermentation. The results showed a drastic reduction in SCFA production with CTS, showing a maximum inhibition of 33 % at 6 mg/g of total suspended solids. CTS hindered sludge solubilization through flocculation, and acted as a humus precursor, promoting humus formation, and consequently reduced the amount of available substrates. Further, CTS promoted free ammonia production, posing a challenge to enzymes and cell viability. Additionally, CTS increased the population of Rikenellaceae sp. and weakened the dominance of hydrolyzing and acidifying bacteria. This study deepens the understanding of the potential impact of CTS on anaerobic fermentation and provides a theoretical basis for reducing the risk of polymeric flocculants.

Recycling and 3D-Printing Biodegradable Membranes for Gas Separation-toward a Membrane Circular Economy

Polymer membranes employed in gas separation play a pivotal role in advancing environmental sustainability, energy production, and gas purification technologies. Despite their significance, the current design and manufacturing of these membranes lack cradle-to-cradle approaches, contributing to plastic waste pollution. This study explores emerging solutions, including the use of biodegradable biopolymers such as polyhydroxybutyrate (PHB) and membrane recycling, with a focus on the specific impact of mechanical recycling on the performance of biodegradable gas separation membranes. This research represents the first systematic exploration of recycling biodegradable membranes for gas separation. Demonstrating that PHB membranes can be recycled and remanufactured without solvents using hot-melt extrusion and 3D printing, the research highlights PHB's promising performance in developing more sustainable CO2 separations, despite an increase in gas permeability with successive recycling steps due to reduced polymer molecular weight. The study emphasizes the excellent thermal, chemical, and mechanical stability of PHB membranes, albeit with a marginal reduction in gas selectivity upon recycling. However, limitations in PHB's molecular weight affecting extrudability and processability restrict the recycling to three cycles. Anticipating that this study will serve as a foundational exploration, we foresee more sophisticated recycling studies for gas separation membranes, paving the way for a circular economy in future membrane technologies.

Influence of chitosan properties and operating parameters on the flocculation efficiency and harvesting of microalgae (Scenedesmus sp.)

Physicochemical and structural characteristics of chitosan prepared from Deep-sea shrimp (DCs), including degree of deacetylation (DD), molecular weight (Mw), viscosity, crystallinity index (CrI) and surface morphology were compared with a commercial chitosan (CCs). The DCs had a higher DD of 81.33 ± 0.40 %, whereas the CCs had a lower DD of 74.62 ± 0.64 %. Additionally, the DCs exhibited a lower Mw of 192.47 ± 2.5 kDa and viscosity of 646.00 ± 4.00 cP compared to the CCs, which had a Mw of 202.44 ± 0.28 kDa and viscosity of 689.67 ± 5.91 cP. This study investigated the influence of chitosan properties, particularly DD and Mw on the harvesting of Scenedesmus sp. along with the chitosan dosage, pH of the culture medium, mixing speed and time. Under optimal operating conditions, the microalgae removal efficiency of the DCs reached a significantly higher level (94.71 ± 0.20 %) compared to that of CCs (88.25 ± 0.41 %). Chitosan with a higher DD and low Mw demonstrated superior flocculation efficiency. The results highlight the significance of DD and Mw of chitosan and its influence on the flocculation of microalgae, providing valuable insights for optimizing the harvesting process with the non-toxic and natural flocculent, chitosan.

Comprehensive assessment of enhancing dewaterability of dredged sediments by starch-based flocculant

Dredged sediment poses significant challenges for transportation and subsequent treatment due to its high water content and large volume. Coagulation, a common method of dewatering, can significantly enhance the dewatering performance of dredged sediment. This study synthesized a cationic starch-based flocculant [starch-3-chloro-2-hydroxypropyl trimethylammonium chloride (St-CTA)] through etherification for the flocculation dewatering of dredged sediment. The effectiveness and mechanism of St-CTA as a dewatering flocculant for dredged sediment were investigated. The results demonstrated that when the dosage of St-CTA was 12 mg g-1 TSS (total suspended solids), the dehydration property of dredged sediment substantially improved, with the specific resistance to filtration (SRF) decreasing by 93.3%, the capillary suction time (CST) by 93.5%, and the water content of the filter cake (WC) by 9.7%. The removal rate of turbidity of the supernatant from the conditioned dredged sediment reached 99.6%, accelerating the settling speed and effectively capturing and separating fine particles from the sediment. St-CTA significantly increased the median particle size (D50), altered the microstructure and extracellular polymeric substances (EPS) of the flocs, and increased the fractal dimension of the flocs, making them more compact and conducive to the formation of drainage channels. These findings confirm the feasibility of using potentially environmentally friendly St-CTA as a rapid dewatering conditioning agent for sediment.

Coagulation in combination with anaerobic digestion for enhancement of resource recovery from faecal sludge

Poorly managed faecal sludge (FS) poses significant challenges to public health and the environment. Anaerobic digestion (AD) of FS provides an effective method for energy recovery while reducing FS associated threats. Recognizing the critical role of the dewatering process before AD, this study investigates the synergistic application of chemical coagulation and mesophilic AD for synthetic FS treatment. FeCl3, AlCl3, Fe2(SO4)3, poly ferric sulfate (PFS) and poly aluminium ferric chloride (PAFC) were utilized at varying dosages to examine their impact on FS properties and subsequent biogas production from the dewatered FS. It was found that coagulation enhances sedimentation efficiencies and dewaterability through mechanisms such as charge neutralization, charge patching and bridging, thereby improving the FS feasibility for AD. Notably, polymer coagulant PFS showed good performance in balancing pollutant removal and methane recovery, contributing to facilitating the hydrolysis and acidogenesis microorganisms involved in the AD process. Optimal dosage was identified at 150 mg/g TS (1.7 g/L FS), achieving prominent removal efficiencies for total COD (67%), turbidity (85%), and total phosphorus (60%), while simultaneously enhancing AD performance with specific CH4 production reaching 517 ml CH₄/g VS or 24.8 ml CH₄/g AD wet feedstock compared to 309 ml CH₄/g VS or 2.7 ml CH₄/g AD wet feedstock in untreated FS.

Synthesis of chitosan-based grafting magnetic flocculants for flocculation of kaolin suspensions

A series of novel chitosan-based magnetic flocculants FS@CTS-P(AM-DMC) was prepared by molecular structure control. The characterization results showed that FS@CTS-P(AM-DMC) had a uniform size of about 21.46 nm, featuring a typical core-shell structure, and the average coating layer thickness of CTS-P(AM-DMC) was about 5.03 nm. FS@CTS-P(AM-DMC) exhibited excellent flocculation performance for kaolin suspension, achieved 92.54% turbidity removal efficiency under dosage of 150 mg/L, pH 7.0, even at high turbidity (2000 NTU) with a removal efficiency of 96.96%. The flocculation mechanism was revealed to be dominated by charge neutralization under acidic and neutral conditions, while adsorption and bridging effects play an important role in alkaline environments. The properties of magnetic aggregates during flocculation, breakage, and regeneration were studied at different pH levels and dosages. In the process of magnetophoretic, magnetic particles collide and adsorb with kaolin particles continuously due to magnetic and electrostatic attraction, transform into magnetic chain clusters, and then further form three-dimensional network magnetic aggregates that can capture free kaolin particles and other chain clusters. Particle image velocimetry confirmed the formation of eddy current of magnetic flocs and experienced three stages: acceleration, stabilization, and deceleration.

Unveiling the mechanisms of Fe(III)-loaded chitosan composite (CTS-Fe) in enhancing anaerobic digestion of waste activated sludge

Anaerobic digestion (AD) of waste activated sludge (WAS) is usually limited by the low generation efficiency of methane. Fe(III)-loaded chitosan composite (CTS-Fe) have been reported to effectively enhanced the digestion of WAS, but its role in promoting anaerobic sludge digestion remains unclear. In present study, the effects of CTS-Fe on the hydrolysis and methanogenesis stages of WAS anaerobic digestion were investigated. The addition of CTS-Fe increased methane production potential by 8%-23% under the tested conditions with the addition of 5-20 g/L CTS-Fe. Besides, the results demonstrate that the addition of CTS-Fe could effectively promote the hydrolysis of WAS, evidenced by lower protein or polysaccharides concentration, higher soluble organic carbon in rector adding CTS-Fe, as well as the increased activity of extracellular hydrolase with higher CTS-Fe concentration. Meanwhile, the enrichment of Clostridia abundance (iron-reducing bacteria (IRBs)) was observed in CTS-Fe adding reactor (8.9%-13.8%), which was higher than that in the control reactor (7.9%). The observation further suggesting the acceleration of hydrolysis through dissimilatory iron reduction (DIR) process, thus providing abundant substrates for methanogenesis. However, the presence of CTS-Fe was inhibited the acetoclastic and hydrogenotrophic methanogenesis process, which could be ascribed to the Fe(III) act as electron acceptor coupled to methane for anaerobic oxidation. Furthermore, coenzyme F420 activity in the CTS-Fe added reactor was 34.9% lower than in the blank, also abundance of microorganisms involved in hydrogenotrophic methanogenesis was decreased. Results from this study could provide theoretical support for the practical applications of CTS-Fe.

Insight into the role of chitosan in rapid recovery and re-stabilization of disintegrated aerobic granular sludge

The disintegration and instability of aerobic granular sludge (AGS) systems during long-term operation pose significant challenges to its practical implementation, and rapid recovery strategies for disintegrated AGS are gaining more attention. In this study, the recovery and re-stabilization of disintegrated AGS was investigated by adding chitosan to a sequencing batch reactor and simultaneously adjusting the pH to slightly acidic condition. Within 7 days, chitosan addition under slight acidity led to the re-aggregation of disintegrated granules, increasing the average particle size from 166.4 μm to 485.9 μm. Notably, sludge volume indexes at 5 min (SVI5) and 30 min (SVI30) decreased remarkably from 404.6 mL/g and 215.1 mL/g (SVI30/SVI5 = 0.53) to 49.1 mL/g and 47.6 mL/g (SVI30/SVI5 = 0.97), respectively. Subsequent operation for 43 days successfully re-stabilized previous collapsed AGS system, resulting in an average particle size of 750.2 μm. These mature and re-stabilized granules exhibited characteristics of large particle size, excellent settleability, compact structure, and high biomass retention. Furthermore, chitosan facilitated the recovery of COD and nitrogen removal performances within 17-23 days of operation. It effectively facilitated the rapid aggregation of disintegrated granules by charge neutralization and bridging effects under a slightly acidic environment. Moreover, the precipitated chitosan acted as carriers, promoting the adhesion of microorganisms once pH control was discontinued. The results of batch tests and microbial community analysis confirmed that chitosan addition increased sludge retention time, enriching slow-growing microorganisms and enhancing the stability and pollutant removal efficiency of the AGS system.

The Chemical Modification to Improve Solubility of Chitosan and Its Derivatives Application, Preparation Method, Toxicity as a Nanoparticles

Chitosan is a functional polymer in the pharmaceutical field, including for nanoparticle drug delivery systems. Chitosan-based nanoparticles are a promising carrier for a wide range of therapeutic agents and can be administered in various routes. Solubility is the main problem for its production and utilization in large-scale industries. Chitosan modifications have been employed to enhance its solubility, including chemical modification. Many reviews have reported the chemical modification but have not focused on the specific characteristics obtained. This review focused on the modification to improve chitosan solubility. Additionally, this review also focused on the application of chitosan derivatives in nanoparticle drug delivery systems since very few similar reviews have been reported. The specific method for chitosan derivative-based nanoparticles was also reported and the latest report of chitosan, chitosan derivative, and chitosan toxicity were also described.

Co-fermentation of titanium-flocculated-sludge with food waste towards simultaneous water purification and resource recovery

Recovery of resources from domestic sewage and food waste has always been an international-thorny problem. Titanium-based flocculation can achieve high-efficient destabilization, quick concentration and separation of organic matter from sewage to sludge. This study proposed co-fermentation of the titanium-flocculated sludge (Ti-loaded sludge) and food waste towards resource recovery by converting organic matter to value-added volatile fatty acids (VFAs) and inorganic matter to struvite and TiO2 nanoparticles. When Ti-loaded sludge and food waste were co-fermented at a mass ratio of 3:1, the VFAs yield reached 3725.2 mg-COD/L (VFAs/SCOD 91.0%), which was more than 4 times higher than the case of the sludge alone. The 48-day semicontinuous co-fermentation demonstrated stable long-term operation, yielding VFAs at 2529.0 mg-COD/L (VFAs/SCOD 89.8%) and achieving a high CODVFAs/NNH4 of 58.9. Food waste provided sufficient organic substrate, enriching plenty of acid-producing fermentation bacteria (such as Prevotella 7 about 21.0% and Bacteroides about 9.4%). Moreover, metagenomic sequencing analysis evidenced the significant increase of the relative gene abundance corresponding to enzymes in pathways, such as extracellular hydrolysis, substrates metabolism, and VFAs biosynthesis. After fermentation, the precious element P (≥ 99.0%) and extra-added element Ti (≥99.0%) retained in fermented residues, without releasing to VFAs supernatant, which facilitated the direct re-use of VFAs as resource. Through simple and commonly used calcination and acid leaching methodologies, 80.9% of element P and 82.1% of element Ti could be successfully recovered as struvite and TiO2 nanoparticles, respectively. This research provides a strategy for the co-utilization of domestic sludge and food waste, which can realize both reduction of sludge and recovery of resources.

Progress of improving waste activated sludge dewaterability: Influence factors, conditioning technologies and implications and perspectives

Large amounts of waste activated sludge (WAS) as a by-product generated from the biological treatment in wastewater treatment plants (WWTPs) is of high moisture content (MC), organic pollutants, heavy metals and pathogenic bacteria, it may cause serious environmental ecological risk without appropriate disposal. More than one half of the total operation cost is accounted for sludge disposal in a WWTP. Dewatering is an essential and important step during the sludge treatment and disposal process for it could efficiently reduce its volume, and be beneficial to the subsequent treatment and disposal of sludge. However, sludge should be conditioned before mechanical dewatering because of its high hydrophilicity. In this work, it presented a comprehensive review on sludge dewatering including summarizing the dewaterability measurement indexes, affecting factors, conditioning technologies, the improvement mechanisms. Finally, based on the eventual disposal and low carbon emission target, the implications and perspectives development of sludge conditioning were discussed. Based on the above discussion, there is no unified theoretical insight of the improvement mechanism of sludge dewaterability. In addition, the relationship between the microstructure of organic matters in sludge floc and the dewaterability should be deepened. Especially, how to choose the optimal conditioning technology for sludge dewatering lies in the physical and chemical properties of sludge, however, the carbon emission of the conditioning and dewatering process also needs to be considered. Accordingly, green, low-cost and organic conditioning agents are the direction of future research, and the establishment of automatic operating system and real-time evaluation index system is the key challenge.

Simultaneous chelated heavy metals removal and sludge recovery through titanium coagulation: From waste to resource

Green methods for chelated heavy metals treatment and recovery are essential for coordinated development of resources and environment. Herein, a simple and competent method, titanium salt (TiCl4) coagulation was developed to remove and recycle chelated heavy metals. Our results revealed that this method proved to be effective for metals-citrate [Cu(II), Ni(II), Zn(II) and Cr(VI)], achieving removal efficiencies of 95 %, 92 %, 99 %, and 99 % within 30 min, surpassing direct alkaline precipitation and well-used Fe(III) coagulation. Whereafter, the copper-containing sludge was successfully transformed into copper-doped titanium dioxide (TiO2) photocatalysts by facile calcination. Through comprehensively investigating physicochemical properties by a suite of characterization techniques, we confirmed that doping of Cu induced bandgap narrowing, high specific surface area as well as the formation of oxygen vacancy. Accordingly, the recycling photocatalysts showed remarkable enhanced photocatalytic performance than the pristine TiO2, achieving improvement in the degradation efficiency of 82 %, 61 % and 67 % for carbamazepine(CBZ), bisphenol A (BPA) and methyl orange (MO). In addition, both radical (OH and O2-) and non-radical (1O2 and h+) pathways synergistically contributed to the removal of organic pollutants during photocatalysis. Ultimately, based on economic feasibility assessment and life cycle assessment (LCA), the copper-containing titanium coagulation sludge reuse for photocatalyst could bring lower carbon emissions, reduced environmental risks and higher economic benefits. The elucidation of this study provides new insights into the removal and recycle of chelated heavy metals from wastewater by using an environment-friendly and cost-effective method.

Chitosan in the treatment of mine spoil rainwater - An approach to protect the aquatic biota

The mining industry suppresses vegetation, exposing large soil areas in its ordinary operation. Water pollution and turbidity are caused by the carrying of solids, mainly colloidal particles, to the watercourses due to the effect of rainfall events. Therefore, the discharge of those effluents will lead to failure with watercourse quality parameters. Thus, there is a need to treat drainages (rainwaters) from the mining industry. However, using common coagulants and flocculants can result in acute or chronic ecotoxicity for aquatic biota. In this scenario, this research aimed to evaluate using a natural coagulant, the biopolymer Chitosan, to remove turbidity from mining industry spoiled water through bio-coagulation. The ecotoxicity of the natural coagulant was compared to the commonly used coagulants. For this purpose, we used synthetic rainwater (SRW) from the dispersion of fine (colloidal) particles in natural waters. Materials (water and soil) were collected in the mining area's sumps (sedimentation basins). The turbidity of the produced SRW ranged from between 500 and 4000 NTU. Jar Tests using Chitosan (CTS), polyaluminum chloride (PAC®12), and Superfloc®N100 variable doses were carried out to compare the effects of the coagulating/flocculating agents on the SRW turbidity reduction. The obtained results demonstrated the efficiency of CHS on turbidity reduction. The results were encouraging for low turbidity samples (<1000 NTU), making it possible to meet the limit parameters recommended by the Brazilian legislation. In addition, it was possible to conclude both CHS and the effluents treated with this coagulant have lower toxicity to aquatic biota than the combination of PAC®12 and Superfloc®N100.

Fast insights into chitosan-cleaving enzymes by simultaneous analysis of polymers and oligomers through size exclusion chromatography

The thorough characterization of chitosan-cleaving enzymes is crucial to unveil structure-function relationships of this promising class of biomolecules for both, enzymatic fingerprinting analyses and to use the enzymes as biotechnological tools to produce tailor-made chitosans for diverse applications. Analyzing polymeric substrates as well as oligomeric products has been established as an effective way to understand the actions of enzymes, but it currently requires separate, rather laborious methods to obtain the full picture. Here, we present ultra high performance size exclusion chromatography coupled to refractive index and mass spectrometry detection (UHPSEC-RI-MS) as a straightforward method for the semi-quantitative analysis of chitosan oligomers of up to ten monomers in length. Additionally, the method allows to determine the average molecular weight of the remaining polymers and its distribution. By sampling live from an ongoing enzymatic reaction, UHPSEC-RI-MS offers the unique opportunity to analyze polymers and oligomers simultaneously-i.e., to monitor the molecular weight reduction of the polymeric substrate over the course of the digestion, while at the same time analyzing the emerging oligomeric products in a semi-quantitative manner. In this way, a single simple analysis yields detailed insights into an enzyme's action on a given substrate.

Efficient Removal of Tetracyclines and Quinolones Enabled by Polyphenol-Mediated Supramolecular Coagulation

Ubiquitous antibiotics threaten human health and ecosystem sustainability, and existing removal strategies, especially conventional multistep water treatments, are primarily limited by the antibiotic-specific removal capability. Here, we explore the natural biomass, plant polyphenols, in the capture of various antibiotics with a facile treatment─polyphenol-mediated antibiotic-independent supramolecular coagulation (PMAC). The PMAC shows a superior performance in removing five tetracyclines and quinolones (up to 98.54%), even under complex environmental parameters, including different pH, the presence of inorganic particles and ionic strength, and the presence of conventional colloid-associated contaminants. Our mechanistic studies suggested that PMAC is capable of exerting multiple molecular interactions with various antibiotics, and the coordination-driven self-assembly further destabilizes the phenolic-antibiotic nanocomplexes, enabling an antibiotic-independent coagulation. Collectively, the combination of efficient remediation with inexpensive biomass suggests a simple and scalable method for the sustainable removal of antibiotics. Our strategy shows great promise as a cost-effective, facile approach to eliminate antibiotics capable of being integrated into the currently existing water treatment systems.

A review on versatile applications of biomaterial/polycationic chitosan: An insight into the structure-property relationship

Chitosan is a versatile and generous biopolymer obtained by alkaline deacetylation of naturally occurring chitin, the second most abundant biopolymer after cellulose. The excellent physicochemical properties of polycationic chitosan are attributed to the presence of varied functional groups such as amino, hydroxyl, and acetamido groups enabling researchers to tailor the structure and properties of chitosan by different methods such as crosslinking, grafting, copolymerization, composites, and molecular imprinting techniques. The prepared derivatives have diverse applications in the food industry, water treatment, cosmetics, pharmaceuticals, agriculture, textiles, and biomedical applications. In this review, numerous applications of chitosan and its derivatives in various fields have been discussed in detail with an insight into their structure-property relationship. This review article concludes and explains the chitosan's biocompatibility and efficiency that has been done so far with future usage and applications as well. Moreover, the possible mechanism of chitosan's activity towards several emerging fields such as energy storage, biodegradable packaging, photocatalysis, biorefinery, and environmental bioremediation are also discussed. Overall, this comprehensive review discusses the science and complete information behind chitosan's wonder function to improve our understanding which is much needful as well as will pave the way towards a sustainable future.

Harnessing the Potential of Chitosan and Its Derivatives for Enhanced Functionalities in Food Applications

As one of the most abundant natural polysaccharides that possess good biological activity, chitosan is extracted from chitin. Its application in the food field is being increasingly valued. However, chitosan extraction is difficult, and its poor solubility limits its application. At present, the extraction methods include the acid-base method, new chemical methods, and biological methods. The extraction rates of chitin/chitosan are 4-55%, 13-14%, and 15-28%, respectively. Different chemical modifications have different effects on chitosan, making it applicable in different fields. This article reviews and compares the extraction and chemical modification methods of chitosan, emphasizing the importance of green extraction methods. Finally, the application prospects of chitosan in the food industry are discussed. This will promote the understanding of the advantages and disadvantages of different extraction methods for chitosan as well as the relationship between modification and application, providing valuable insights for the future development of chitosan.

Synthesis of chitosan-based flocculant by dielectric barrier discharge modification and its flocculation performance in wastewater treatment

As a typical type of organic flocculant, chitosan is limited by its poor water solubility and narrow pH range application. Grafting modification can improve chitosan's solubility and availability through linking macromolecular chains with other types of water-soluble groups or functional side groups. In this study, dielectric barrier discharge (DBD) was used to active the surface of chitosan, then activated chitosan was polymerized with acrylamide to synthesize a chitosan-based flocculant, chitosan-acrylamide (CS-AM). During the synthesis of CS-AM, the optimal conditions were determined as follows: discharge time of 5 min, discharge power of 60 W, total monomer mass concentration of 80 g L-1, polymerization time of 3 h, polymerization temperature of 70 °C, and m(CS) : m(AM) ratio of 1 : 3. The structure and morphological characteristics of CS-AM were investigated and analyzed by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD) and N2 physical adsorption, respectively. The removal efficiency of kaolin suspension and CNTs suspension can reach up to 95.9% and 90.2% after flocculation of CS-AM. Furthermore, the zeta potential of the supernatant from the CS-AM treated kaolin suspension at different pH values was examined, and the flocculation mechanism of CS-AM was analyzed. This study provides new ideas for the preparation and development of modified chitosan and broadens its application in water treatment.

Interaction of chitosan with nanoplastic in water: The effect of environmental conditions, particle properties, and potential for in situ remediation

Micro- and nanoplastic (MNP) pollution in aquatic ecosystems requires investigation on its source, transport, and extent to assess and mitigate its risks. Chitosan is a potential biomolecule for water treatment, but its interaction with MNP is undefined. In this work, chitosan-nanoplastic interaction was explored in the laboratory under environmentally relevant conditions using polystyrene (PS) nanoplastic (NP) as model particle to identify conditions at which PS-chitosan interaction resulted in aggregation. Aggregation limits NP transport and allows separation of NP for targeted remediation. The effect of environmental conditions (pH, salinity, dissolved organic matter (DOM) content), chitosan particle size and NP surface modification on chitosan-NP interaction was studied at various chitosan doses. PS aggregated at chitosan doses as low as 0.2 % w/w, while higher doses of chitosan resulted in re-stabilization of NP in solution, restoring the particle size to its initial value. Increasing pH, DOM, or carboxyl modification of the NP surface also improved NP stability in solution. Increased salinity of the solution caused aggregation of unmodified PS independent of chitosan, but carboxyl-modified PS remained stable and aggregated at the same chitosan doses across all salinity levels. Chitosan with low molecular weight promoted PS aggregation at lower doses. Notably, zeta potential (ZP) alone did not indicate chitosan-induced PS aggregation, which occurred independently of changes in ZP. DLVO calculations based on ZP, however, still indicated attractive interaction due to charge differences, albeit with less contrast at high pH, salinity, and DOM content. Additional insights gained in the work recommend caution when using spectrophotometric methods to assess NP removal. Overall, this study demonstrates that chitosan impacts NP transport and holds potential for water remediation of NP.

Chitosan-based Schiff bases: Promising materials for biomedical and industrial applications

There is plenty of scope for modifying chitosan, an only polycationic natural polysaccharide, owing to its reactive functional groups, namely hydroxyl and amino groups. Although innumerable numbers of chitosan derivatives have been synthesized by modifying these groups and reported elsewhere, in this review article, an attempt has been exclusively made to demonstrate the syntheses of various chitosan-based Schiff bases (CSBs) simply by allowing the reactions of reactive amino groups of chitosan with different aldehydes/ketones of interest. Due to their very peculiar and unique characteristics, such as biodegradability, biocompatibility, metal-binding capability, etc., they are found to be very useful for diversified applications. Thus, we have also attempted to showcase their very specific biomedical fields, including tissue engineering, drug delivery, and wound healing, to name a few. In addition, we have also discussed the utilization of CSBs for industrial applications such as wastewater treatment, catalysis, corrosion inhibition, sensors, etc.

Anionic polyacrylamide alleviates cadmium inhibition on anaerobic digestion of waste activated sludge

The uncontrolled discharge of industrial wastewater leads to a significant cadmium (Cd) accumulation in waste activated sludge (WAS), posing a serious threat to the steady operation of the anaerobic digestion (AD) system in wastewater treatment plants (WWTPs). Therefore, developing a viable approach to cope with the adverse effects of high-concentration Cd on the AD system is urgently required. This study aims to investigate the potential of using anionic polyacrylamide (APAM), a commonly used agent in WWTPs, to mitigate the adverse effects of Cd in a toxic amount (i.e., 5.0 mg per g total suspended solids (TSS)) on AD of WAS. The results showed that the effectiveness of higher APAM on Cd toxicity alleviation was less than that of lower APAM at the studied level (i.e., the effectiveness order was 1.5 mg APAM per g TSS > 3.0 mg APAM per g TSS > 6.0 mg APAM per g TSS). The moderate supplement of APAM (i.e., 1.5 mg per g TSS) recovered the accumulative methane yield from 190.5 ± 3.6 to 228.9 ± 4.1 mL per g volatile solids by promoting solubilization, hydrolysis, and acidification processes related to methane production. The application of APAM also increased the abundance of key microbes in the AD system, especially Methanolinea among methanogens and Caldilineaceae among hydrolyzers. Furthermore, APAM facilitated the key enzyme activities involved in AD processes and reduced reactive oxygen species (induced by Cd) production via adsorption/enmeshment of Cd by APAM. These findings demonstrate the feasibility of using moderate APAM to mitigate Cd toxicity during AD, providing a promising solution for controlling Cd or other heavy metal toxicity in WWTPs.

N-lauric-O-carboxymethyl chitosan: Synthesis, characterization and application as a pH-responsive carrier for curcumin particles

A pH-responsive amphiphilic chitosan derivative, N-lauric-O-carboxymethyl chitosan (LA-CMCh), is synthesized. Its molecular structures are characterized by FTIR, 1H NMR, and XRD methods. The influencing factors are investigated, including the amount of lauric acid (LA), carboxymethyl chitosan (CMCh), N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC), and N-hydroxysuccinimide (NHS), and their molar ratio, reaction time, and reaction temperature on the substitution. The degrees of substitution (DS) of the lauric groups on the -NH2 groups are calculated based on the integrated data of 1H NMR spectra. The optimum reaction condition is obtained as a reaction time of 6 h, a reaction temperature of 80 °C, and a molar ratio of lauric acid to O-carboxymethyl chitosan to N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride to N-hydroxysuccinimide of 1:3:4.5:4.5, respectively. The crystallinity and initial decomposition temperature of LA-CMCh decrease, but the maximum decomposition temperature increases. The crystallinity is reduced due to the introduction of LA and the degree of hydrogen bonding among LA-CMCh molecules. LA-CMCh could self-aggregate into particles, which size and critical aggregation concentration depend on the degree of substitution and medium pH. LA-CMCh aggregates could load curcumin up to 21.70 %, and continuously release curcumin for >200 min. LA-CMCh shows nontoxicity to fibroblast HFF-1 cells and good antibacterial activity against S. aureus and E. coli, indicating that it could be used as an oil-soluble-drug carrier.

Microplastic Removal in Wastewater Treatment Plants (WWTPs) by Natural Coagulation: A Literature Review

Urban industrialization has caused a ubiquity of microplastics in the environment. A large percentage of plastic waste originated from Southeast Asian countries. Microplastics arising from the primary sources of personal care items and industrial uses and the fragmentation of larger plastics have recently garnered attention due to their ubiquity. Due to the rising level of plastic waste in the environment, the bioaccumulation and biomagnification of plastics threaten aquatic and human life. Wastewater treatment plant (WWTP) effluents are one of the major sources of these plastic fragments. WWTPs in Southeast Asia contribute largely to microplastic pollution in the marine environment, and thus, further technological improvements are required to ensure the complete and efficient removal of microplastics. Coagulation is a significant process in removing microplastics, and natural coagulants are far superior to their chemical equivalents due to their non-toxicity and cost-effectiveness. A focused literature search was conducted on journal repository platforms, mainly ScienceDirect and Elsevier, and on scientific databases such as Google Scholar using the keywords Wastewater Treatment Plant, Coagulation, Microplastics, Marine Environment and Southeast Asia. The contents and results of numerous papers and research articles were reviewed, and the relevant papers were selected. The relevant findings and research data are summarized in this paper. The paper reviews (1) natural coagulants for microplastic removal and their effectiveness in removing microplastics and (2) the potential use of natural coagulants in Southeast Asian wastewater treatment plants as the abundance of natural materials readily available in the region makes it a feasible option for microplastic removal.