Competitive adsorption of toxic metals on bentonite and use of chitosan as flocculent coagulant to speed up the settling of generated clay suspensions

Full biomass-based multifunctional flocculant from lignin and cationic starch

Flocculation is a common process for wastewater treatment. However, the most commonly used organic synthetic flocculants such as polyacrylamide are petroleum-based. In this work, biomass lignin was grafted with cationic starch to synthesize low-cost, green and fully biomass-based multifunctional flocculants. The cationic polyacrylamide was replaced by cheap industrial cationic starch. Hyperbranched multifunctional lignin-grafted cationic starch flocculant (CS-L) was successfully prepared via ring-opening reaction with epichlorohydrin. The mass content of lignin in the grafted product was between 16.6 % and 70.1 %. With the dosage of CS-L between 4.0 and 7.5 mg/l, the turbidity removal rate for 500 mg/l kaolin suspension reached more than 97 %. When the dosage of CS-L was 24 mg/l, the removal rate of 50 mg/l Cu2+ reached 85.7 %. Importantly, when the mixed solution of kaolin particles and Cu2+ was treated, the synchronous removal rates of kaolin and Cu2+ reached 90 % and 72 % respectively in the range of 8.0-12.0 mg/l flocculant addition. The synthesized lignin-grafted cationic starch flocculant showed an excellent multifunctional flocculation function.

Highly efficient functionalized MOF-LIC-1 for extraction of U(VI) and Th(IV) from aqueous solution: experimental and theoretical studies

A set of four new functionalized MOFs, namely MOF-LIC-DPPC, MOF-LIC-GA, MOF-LIC-PCA and MOF-LIC-SA, were synthesized via the post-synthetic modification (PSM) strategy using MOF-LIC-1 for efficient extraction of U(VI) and Th(IV) from an aqueous medium. FTIR, powder XRD, TGA and SEM-EDX were employed for characterization of the functionalized MOFs. Sorption studies for U(VI) and Th(IV) were performed by monitoring the pH and contact time. Interestingly, the modified MOF-LIC-SA displayed rapid (∼5 min) and efficient extraction towards U(VI) and Th(IV) from an aqueous medium and modified MOF-LIC-DPPC displayed enhanced thermal stability (600 °C) compared with the parent MOF-LIC-1 (450 °C). These studies revealed that the grafted functionalities on MOF-LIC-1 possess enhanced sorption efficiency towards U(VI) and Th(IV) as well as thermal stability. MOF-LIC-SA exhibited the highest sorption capacity towards U(VI) and Th(IV), viz. 298 mg g^-1 (pH 6) and 149 mg g^-1 (pH 6), respectively. Leaching, recyclability, and radiation stability studies were also performed using MOF-LIC-1 MOFs. Additionally, we investigated the nature of U(VI) interactions on MOFs by applying density functional theory (DFT). PSM MOFs with various functionalities display high selectivity and efficient extraction of U(VI) and Th(IV) over a wide pH range (2-9) and also exhibit easy recovery of metal ions from MOFs. These studies reveal that U(VI) and Th(IV) can be extracted from aqueous streams in a pH range from 6 to 8 and potential applications of these MOFs include recovery of U(VI) and Th(IV) from mine water, sea water, etc. The studies reported in the present work also have extensive potential applications for environmental concerns as well as in the nuclear industry.

Influence of Cr (VI) concentration on Cr (VI) reduction and electricity production in microbial fuel cell

Microbial fuel cell is an efficient technology to reduce pollutants of the heavy metal ions. Herein, a dual-chamber microbial fuel cell (MFC) coupled with abio-cathode and electrochemically active bacteria is fabricated to treat Cr (VI) containing wastewater and harvest bioelectricity simultaneously. To investigate the wide application of MFC for various industries, four different concentrations of Cr (VI) (6 mg/L, 15 mg/L, 40 mg/L, 100 mg/L) are used to explore the removal efficiency of Cr (VI) and the corresponding power performance. We find that the power performance gradually increases with the increment of the initial Cr (VI) concentration. Significantly, a maximum power density of 35.3 mW/m² can be achieved with the initial concentration of 100mg/L Cr (VI), while MFC only generate negligible power density (2.6 mW/m²) without the presence of Cr (VI). Meanwhile, MFC combined with the initial Cr (VI) concentration of 15 mg/L shows the highest Cr (VI) removal of 66.5%. Moreover, partial precipitates are found on the cathode surface and X-ray photoelectron spectroscopy (XPS) analysis has demonstrated that the Cr (VI) is successfully reduced into Cr (III). This study offers an alternative technology to remove Cr (VI) and synchronous electricity generation.

Brazilian bentonite and a new modified bentonite material, BAC302, reduce zearalenone-induced cell death

Bentonite clays exhibit high adsorptive capacity for contaminants and is frequently used as a feed additive to reduce the bioavailability and thus the toxicity of several mycotoxins. Zearalenone (ZEN) is a secondary Fusarium toxic metabolite that can contaminate a wide range of food- and feedstuff. Since organophilic treatments is known to increase the adsorption capacity of bentonites, the aim of study was to evaluate and compare the ability of natural bentonite and bentonite treated with BAC302 to protect against ZEN-induced cytotoxicity in the epithelial colorectal adenocarcinoma (Caco-2) and human leukemia monocytic (THP-1) cell lines. The two materials were not toxic to the cell lines at lower concentrations. Furthermore, the results indicate that the two materials protect the Caco-2 and THP-1 cells against ZEN-induced cytotoxicity, probably by extracellular adsorption of ZEN. The tested natural bentonite shows potential for in vivo testing to evaluate if it is suitable for intoxication in ZEN contaminated animal feeds.

Carboxymethylcellulose-chitosan film modified magnetic alkaline Ca-bentonite for the efficient removal of Pb(II) and Cd(II) from aqueous solution

In order to endow alkaline Ca-bentonite (ACB) with magnetic separation ability, simultaneously obtain better magnetic stability and stronger removal capacity of heavy metal cations; magnetic alkaline Ca-bentonite/carboxymethylcellulose-chitosan film (MACB/C-C) was prepared by organic modification of magnetic alkaline Ca-bentonite (MACB) using non-toxic carboxymethylcellulose and chitosan. Textural characterization results revealed that magnetic Fe3O4 nanoparticles were successfully immobilized on ACB and modified with C-C. The functionalized layer of C-C concurrently enhanced the stability of Fe3O4 and removal performances of heavy metal cations. Adsorption results indicated that MACB/C-C exhibited thorough separation from aqueous solution and greater uptake ability for Pb(II) and Cd(II) (483 mg·g-1 and 123 mg·g-1) than the nascent MACB (335 mg·g-1 and 76 mg·g-1), respectively, at pH 5 and 25 °C temperature. The adsorption of Pb(II) and Cd(II) on MACB/C-C mainly occurred via surface precipitation and complexation when pH > 2. MACB/C-C could be efficiently recycled with marginal decrease in adsorption capacity. The current approach credited to the convenient operation, simplified synthesis, and high efficiency of MACB/C-C could be deemed as a promising alternative for the removal of heavy metal cations from wastewater.

Copper release from waste rocks in an abandoned mine (NE, Brazil) and its impacts on ecosystem environmental quality

This study aimed to estimate the impact of an abandoned copper (Cu) mine on ecosystem environmental quality, using integrated ecological and biogeochemical analyses. Through a controlled experiment, the amount of Cu released by waste rocks, Cu adsorbed in soils, Cu geochemical behaviour and its leached amount were measured. Furthermore, to investigate the impacts of mine drainage on the adjacent ecosystem, samples of sediments, water and aquatic macroinvertebrates were analysed. We found that waste rocks still have high Cu concentration even after 30 years under weathering, ranging from 7782 to 8717 mg kg^-1, associated mainly with carbonates, amorphous oxides and sulphides. It was estimated that 7.2 tonnes of Cu were released by waste rocks into the environment over last 30 years. The concentration of Cu observed in Ubari stream water was (<dl to 90 μg L^-1), in sediments (28.0-1185 mg kg^-1) and in macroinvertebrates (1.3-28.9 mg kg^-1 d/w). The ecological indexes showed that near mine discharge a significance decrease in the density of aquatic macroinvertebrates and a significance increase of Cu in biological tissues occurs, causing disturbances in biodiversity. The results showed that, even after long periods, the waste rocks from abandoned mines still contain high levels of metal, that are gradually released into the environment through weathering and erosion, representing a potential source of environmental pollution and a clear threat to the environmental quality of adjacent ecosystems.

Rapid Room-Temperature Preparation of Hierarchically Porous Metal-Organic Frameworks for Efficient Uranium Removal from Aqueous Solutions

The effective removal of uranium from an aqueous solution is a highly valuable process for the environment and health. In this study, we developed a facile and rapid method to synthesize hierarchically porous Cu-BTC (RT-Cu-BTC) using a cooperative template strategy. The as-synthesized RT-Cu-BTC exhibited hierarchically porous structure and excellent thermostability, as revealed by X-ray powder diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Compared with conventional metal-organic frameworks (MOFs) and zeolites, the obtained RT-Cu-BTC exhibited enhanced adsorption capacity (839.7 mg·g-1) and high removal efficiency (99.8%) in the capture of uranium (VI) from aqueous solutions. Furthermore, the conditions such as adsorbent dose, contact time, and temperature in adsorption of uranium (VI) by RT-Cu-BTC were investigated in detail. The thermodynamics data demonstrated the spontaneous and endothermic nature of the uranium (VI) adsorption process. The Langmuir isotherm and pseudo-second-order models could better reflect the adsorption process of uranium (VI) onto RT-Cu-BTC. In addition, the as-synthesized RT-Cu-BTC showed excellent stability in removing uranium (VI) from an aqueous solution. This work provides a facile and rapid approach for fabricating hierarchically porous MOFs to realize a highly efficient removal of uranium (VI) from aqueous systems.

Carboxylated graphene oxide-chitosan spheres immobilize Cu2+ in soil and reduce its bioaccumulation in wheat plants

Due to the strong interaction with pollutants and the huge adsorption capacity, graphene adsorbents are widely applied in water decontamination. However, graphene adsorbents are seldom used in soil remediation, because the adsorptive sites on graphene would be occupied by soil components. In this study, we prepared carboxylated graphene oxide-chitosan (GO-COOH/CS) spheres for the immobilization of Cu²⁺ from water and soil. The pores in GO-COOH/CS allowed the internal diffusion of Cu²⁺ solution, while they blocked the direct contact between the solid soil and the adsorptive sites on graphene sheets. Therefore, the high adsorption capacity of GO-COOH/CS spheres (78 mg/g) was largely retained for the soil Cu²⁺ fixation. The partition coefficient (PC) for Cu²⁺ adsorption onto GO-COOH/CS spheres was 4.2 mg/g/μM at C_e of 0.48 mg/L and q_e of 31 mg/g, while the PC value decreased to 0.096 mg/g/μM at C_e of 91.4 mg/L and q_e of 78 mg/g. At initial Cu²⁺ concentrations of 120 mg/L and lower, the fixation efficiencies were all higher than 99% and the corresponding free Cu²⁺ concentrations in leachates were lower than 1.0 mg/L. The Cu²⁺ fixation on GO-COOH/CS spheres largely reduced its bioaccumulation in wheat roots from 127.8 μg/g to 51.2 μg/g. The toxicity evaluations suggested that GO-COOH/CS spheres were of low toxicity to wheat seedlings and did not amplify the toxicity of Cu²⁺. The implications to the design of graphene adsorbents for soil remediation are discussed. Overall, our results collectively indicated that porous GO-COOH/CS spheres were high-performance adsorbents for the immobilization of Cu²⁺ to reduce Cu²⁺ bioaccumulation in plants.

ZnO, AgCl and AgCl/ZnO nanocomposites incorporated chitosan in the form of hydrogel beads for photocatalytic degradation of MB, E. coli and S. aureus

Significant improvement of effective and low-cost decolorization and disinfecting technologies is required to address the problems created by dyes and dangerous microorganisms from water and wastewaters. This article expresses the degradation of methylene blue (MB), Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as gram negative and positive bacteria via a chitosan/AgCl/ZnO (CS/AgCl/ZnO) nanocomposite hydrogel beads system as a photocatalyst under visible light irradiation. The techniques such as FT-IR, SEM, EDAX, TGA, and XRD were applied to recognize the synthesized beads. Decolorization and disinfection experimental results revealed that the hydrogel beads system effectively degrade MB and bacteria. Also, the effects of the initial amount of catalysts, pH, coions and initial concentration of dye on the photocatalytic decolorization were investigated. Moreover, kinetics analysis indicates that the photocatalytic degradation rate of MB and bacteria can be described by Langmuir-Hinshelwood (L-H) and Weibull inactivation models, respectively. We provide a reusable and recoverable effective organic/inorganic photocatalyst in the form of beads that could solve the disadvantages of powder photocatalytic, without reducing the efficiency.

A critical review of cast-off crab shell recycling from the perspective of functional and versatile biomaterials

Shellfish cultivation is an expanding economic activity worldwide. However, the rapid development of crab farming and processing result in a large number of crab shells (CS). Utilizing CS could not only benefit the environment and economy but also promote the sustainable development of aquaculture. In this work, it reviews and analyzes recent attempts in CS recycling, including extracting chitin and its derivatives, for use as adsorbent and flocculant and for preparing polymer composites and catalysts, as well as medical applications. The challenges in these utilizations are discussed, and future research directions are proposed as well. Extracting chitin and its derivates, for use as adsorbent and flocculant, are recent major recycling approaches. Preparing polymer composites and carbon materials has gained more and more attentions. Biotechnology is an alternative method for extracting chitin and its derivates from CS, and high-efficiency desalted and deproteinized bacteria need to be screened. Immobilizing the CS-based adsorbents is the key of treating wastewater in continuous systems. Using CS as a biofiller to prepare polymer composites is promising, and surface modification to improve the interfacial compatibility between CS-based fillers and matrix needs to be further studied.

Highly efficient removal of surfactant from industrial effluents using flaxseed mucilage in coagulation/photo-Fenton oxidation process

In this study, flaxseed mucilage (FSM) has been used as a green coagulant in the pretreatment stage of a combined process for the removal of an anionic surfactant, sodium dodecyl sulfate (SDS). In the post-treatment stage, heterogeneous photo-Fenton-like oxidation using MnFe₂O₄ nanocatalyst was applied to remove the remained SDS. Using response surface methodological approach, optimum condition in the coagulation process was obtained at pH 7.0, FSM dose of 100 mg L^-1 and 30 min. In the photo-Fenton oxidation process, complete SDS removal was achieved using 76 mg of the nanocatalyst, 1.07 mL of H₂O₂ at 17 min. Application of the combined process on the real wastewater samples indicates that the proposed method can be used effectively for the treatment of industrial effluents containing surfactants.

Comparative performance of green rusts generated in Fe0-electrocoagulation for Cd2+ removal from high salinity wastewater: Mechanisms and optimization

The treatment of wastewater containing high concentration of inorganic salts has always been one of the focuses of environmental researchers. In this work, the effect of Cl^- and SO₄^2- on the removal of Cd²⁺ from wastewater using Fe⁰-electrocoagulation (Fe⁰-EC) were investigated by evaluating the transformation of Fe mineral. The experimental results indicated that the removal of Cd²⁺ from wastewater was depended on the property of Fe minerals. The generation of sulfate green rust (GRSO₄) produced in the presence of SO₄^2- showed stronger adsorption than the chloride green rust (GRCl) for Cd²⁺, and GRSO₄ was obtained even in the mixture Cl^- and SO₄^2- solutions, because Fe(II)-Fe(III) GRs (layered double hydroxides, LDHs) showed stronger affinity for divalent SO₄^2- than monovalent Cl^-. High concentration of inorganic anions in wastewater resulted in the negative charged Fe flocs. High concentration of Cl^- promoted the oxidation of Fe(II) to Fe(III) by chlorine-containing oxidants, and increased the proportion of Fe(III)/Fe(II) in Fe flocs, secondary Fe mineral magnetite (Fe₃O₄) was formed because of the increase of pH. Therefore, the presence of GRSO₄ intermediate increased the Cd²⁺ removal by adsorption (coagulation and coprecipitation), and then the generated GRSO₄ were gradually transformed into lepidocrocite (γ-FeOOH) by oxygen from air. Finally, the parameter optimization were conducted by adjusting the ratio of Cl^- and SO₄^2- (R_C:S), current density (j), initial pH (pH_i), initial Cd²⁺ concentration (C₀), and temperature (T₀). The removal efficiency of Cd²⁺ reached 99.5% after 10 min Fe⁰-EC under the optimal parameters: R_C:S = 25:50 mmoL/mmol, j = 6 mA/cm², pH_i = 7-9, and T₀ = 40 °C.

Organo-modification of montmorillonite for enhancing the adsorption efficiency of cobalt radionuclides from aqueous solutions

Montmorillonite clay was organically modified with thoron (TH) and was employed as an adsorbent for removal of cobalt(II) radionuclides from aqueous solutions. Batch adsorption experiments, under several operational parameters such as pH, contact time, initial adsorbate concentration, adsorbent dosage, ionic strength, and temperature, were conducted to determine the optimum conditions for efficient removal of cobalt(II) radionuclides. The obtained data showed that almost complete removals were achieved for cobalt(II) at pH values ≥ 3.5 using TH-modified montmorillonite (TMM), while only 63% were obtained by unmodified clay at pH ≥ 5.4. Adsorption kinetic data of cobalt(II) were better fitted by the pseudo-second order kinetic model and its adsorption rate was controlled by film diffusion. Both Langmuir and Freundlich models had the ability to well describe the equilibrium data of cobalt(II) radionuclides at the studied temperatures. The adsorption capacity of TMM (0.85 mmol/g) was found to be not only nine times that of unmodified montmorillonite (0.097 mmol/g), but also higher than those reported in literature using various unmodified and modified clays. Thermodynamic parameters (ΔH°, ΔS°, and ΔG°) were calculated. Among the examined desorbing agents, both Al³⁺ and EDTA were succeeded to desorb most of cobalt(II) radionuclides (desorption % ~ 90%) loaded onto TMM. The results of this study clarified that TMM can be considered as an effective adsorbent for removal of cobalt(II) radionuclides from aqueous solutions.

Solid-liquid separation: an emerging issue in heavy metal wastewater treatment

Solid-liquid separation (SLS) plays a dominant role in various chemical industries. Nowadays, low efficiency of SLS also become a significant problem in heavy metal (HM) wastewater treatment, affecting the effluent quality (HM concentration and turbidity) and overall process economy. In this context, we summarize here the occurrence of solids in HM wastewater, as well as typical SLS operations used in HM wastewater treatment, including sedimentation, flotation, and centrifugation. More important, this article reviews the improvement of the SLS operations by some technologies, including coagulation, flocculation, ballasted method, seeding method, granular sludge strategy, and external field enhancement. It is noted that abiological granular sludge strategy and magnetic field enhancement often possess higher SLS efficiency (faster settling velocity or shorter separation time) than other methods. Hence, the two strategies stand out as promising tools for improving SLS in HM wastewater treatment, but further research is required regarding scalability, economy, and reliability.

Single, simultaneous and consecutive biosorption of Cr(VI) and Orange II onto chemically modified masau stones

Novel and low cost chemically modified masau stone (CMMS) was investigated for its biosorption of an anionic azo dye, Orange II (OII), and toxic hexavalent chromium (Cr(VI)) from aqueous systems: individually, simultaneously and consecutively. XPS and FTIR analyses indicated the introduction of quaternary-Nitrogen to the CMMS surface after activation with epichlorohydrin (etherifying agent) and diethylenetriamine (crosslinking agent). The effects of pH, contact time and initial concentration (C_o), and loading order on mechanisms of biosorption/reduction of OII and Cr(VI) onto CMMS were examined in detail. Several analytical techniques were employed to characterise the physio-chemical properties of the CMMS and determine the biosorption mechanisms. The pseudo second order and redox models were able to adequately predict the kinetics of biosorption. The Langmuir maximum OII biosorption capacity (q_max) was calculated as 136.8 mg/g for the dye onto the Cr(VI)-loaded CMMS consecutive system at C_o = 100 mg/dm³. The q_max for the Cr(VI) system was found to be 87.32 mg/g at the same C_o max. This reveals that the biosorption of OII and Cr(VI) mainly takes place via two different mechanisms i.e. hydrogen bonding and electrostatic attraction for the dye, and biosorption-coupled reduction for Cr(VI).

Treatment of oilfield wastewater by combined process of micro-electrolysis, Fenton oxidation and coagulation

In this study, a combined process was developed that included micro-electrolysis, Fenton oxidation and coagulation to treat oilfield fracturing wastewater. Micro-electrolysis and Fenton oxidation were applied to reduce chemical oxygen demand (COD) organic load and to enhance organic components gradability, respectively. Orthogonal experiment were employed to investigate the influence factors of micro-electrolysis and Fenton oxidation on COD removal efficiency. For micro-electrolysis, the optimum conditions were: pH, 3; iron-carbon dosage, 50 mg/L; mass ratio of iron-carbon, 2:3; reaction time, 60 min. For Fenton oxidation, a total reaction time of 90 min, a H₂O₂ dosage of 12 mg/L, with a H₂O₂/Fe²⁺ mole ratio of 30, pH of 3 were selected to achieve optimum oxidation. The optimum conditions in coagulation process: pH, cationic polyacrylamide dosage, mixing speed and time is 4.3, 2 mg/L, 150 rpm and 30 s, respectively. In the continuous treatment process under optimized conditions, the COD of oily wastewater fell 56.95%, 46.23%, 30.67%, respectively, from last stage and the total COD removal efficiency reached 83.94% (from 4,314 to 693 mg/L). In the overall treatment process under optimized conditions, the COD of oily wastewater was reduced from 4,314 to 637 mg/L, and the COD removal efficiency reached 85.23%. The contribution of each stage is 68.45% (micro-electrolysis), 24.07% (Fenton oxidation), 7.48% (coagulation), respectively. Micro-electrolysis is the uppermost influencing process on COD removal. Compared with the COD removal efficiency of three processes on raw wastewater under optimized conditions: the COD removal efficiency of single micro-electrolysis, single Fenton oxidation, single coagulation is 58.34%, 44.88% and 39.72%, respectively. Experiments proved the effect of combined process is marvelous and the overall water quality of the final effluent could meet the class III national wastewater discharge standard of petrochemical industry of China (GB8978-1996).

Novel Metal-Organic Framework (MOF) Based Composite Material for the Sequestration of U(VI) and Th(IV) Metal Ions from Aqueous Environment

The combination of magnetic nanoparticles and metal-organic frameworks (MOFs) has demonstrated their prospective for pollutant sequestration. In this work, a magnetic metal-organic framework nanocomposite (Fe₃O₄@AMCA-MIL53(Al) was prepared and used for the removal of U(VI) and Th(IV) metal ions from aqueous environment. Fe₃O₄@AMCA-MIL53(Al) nanocomposite was characterized by TGA, FTIR, SEM-EDX, XRD, HRTEM, BET, VSM (vibrating sample magnetometry), and XPS analyses. A batch technique was applied for the removal of the aforesaid metal ions using Fe₃O₄@AMCA-MIL53(Al) at different operating parameters. The isotherm and kinetic data were accurately described by the Langmuir and pseudo-second-order models. The adsorption capacity was calculated to be 227.3 and 285.7 mg/g for U(VI) and Th(IV), respectively, by fitting the equilibrium data to the Langmuir model. The kinetic studies demonstrated that the equilibrium time was 90 min for each metal ion. Various thermodynamic parameters were evaluated which indicated the endothermic and spontaneous nature of adsorption. The collected outcomes showed that Fe₃O₄@AMCA-MIL53(Al) was a good material for the exclusion of these metal ions from aqueous medium. The adsorbed metals were easily recovered by desorption in 0.01 M HCl. The excellent adsorption capacity and the response to the magnetic field made this novel material an auspicious candidate for environmental remediation technologies.

Impact of chitosan and polyacrylamide on formation of carbonaceous and nitrogenous disinfection by-products

Coagulation is one of the most commonly used practices in water treatment to remove natural organic matter, which can serve as precursors for disinfection by-products (DBPs). Furthermore, some coagulant aids, particularly amine-based polymers, could foster the formation of both carbonaceous and nitrogenous DBPs (C-DBPs and N-DBPs, respectively). In this study, we evaluated the formation potentials of 11 C-DBPs and N-DBPs during chloramination when two coagulant aids, chitosan and polyacrylamide (PAM), were used under typical water treatment conditions. Our results suggest that both chitosan and PAM promote the formation of N-DBPs, while neither affects the formation of C-DBPs. We further investigated a potential method to mitigate the formation of N-DBPs. Methyl iodide (MeI), an alkylating agent, was effective at reducing the formation of N-DBPs by converting amine to quaternary ammonium groups in chitosan. ¹H-NMR results confirmed that the quaternarization reaction did take place. This study reports that chitosan, a natural coagulant, and PAM contribute to the formation of toxic DBPs. More importantly, it provides a preventative strategy for curbing the formation of DBPs through chemical structural modification.

Production of Chitin from Penaeus vannamei By-Products to Pilot Plant Scale Using a Combination of Enzymatic and Chemical Processes and Subsequent Optimization of the Chemical Production of Chitosan by Response Surface Methodology

The waste generated from shrimp processing contains valuable materials such as protein, carotenoids, and chitin. The present study describes a process at pilot plant scale to recover chitin from the cephalothorax of Penaeus vannamei using mild conditions. The application of a sequential enzymatic-acid-alkaline treatment yields 30% chitin of comparable purity to commercial sources. Effluents from the process are rich in protein and astaxanthin, and represent inputs for further by-product recovery. As a last step, chitin is deacetylated to produce chitosan; the optimal conditions are established by applying a response surface methodology (RSM). Under these conditions, deacetylation reaches 92% as determined by Proton Nuclear Magnetic Resonance (¹H-NMR), and the molecular weight (Mw) of chitosan is estimated at 82 KDa by gel permeation chromatography (GPC). Chitin and chitosan microstructures are characterized by Scanning Electron Microscopy (SEM).