Flocculation of heavy metal by functionalized starch-based bioflocculants: Characterization and process evaluation

Starch-based bio-membrane for water purification, biomedical waste, and environmental remediation

This review article explores the utilization of starch-based materials as smart materials for the removal of dyes and heavy metals from wastewater, highlighting their cost-effectiveness, biodegradability, and biocompatibility. It addresses the critical need for clean water, emphasizing the contamination caused by industrial activities, such as printing, textile, cosmetic, and leather tanning industries. Starch and its derivatives demonstrate significant potential in water purification technology, effectively removing toxicants through hydrogen bonding, electrostatic interactions, and complexation. The review also discusses the application of starch-based materials in the biomedical field, particularly as drug carriers. Starch-based microspheres, hydrogels, nano-spheres, and nano-composites exhibit sustained drug-release properties and are effective in transporting various drugs, including DOX, quercetin, 5-Fluorouracil, glycyrrhizic acid, paclitaxel, tetracycline hydrochloride, amoxicillin, ciprofloxacin, and moxifloxacin. These materials show good antimicrobial activity against a range of pathogens, including C. albicans, E. coli, S. aureus, C. neoformance, B. subtilis, A. niger, A. fumigatus, and A. terreus. While highlighting the significant achievements of starch-based materials, the review also discusses current limitations and areas for future development. Key weaknesses include the need for enhanced adsorption capacities and the challenge of scaling up production for industrial applications. The review concludes by identifying development directions, such as improving functionalization techniques and exploring new applications in water purification and drug delivery systems. This article aims to assist researchers in advancing the field of starch-based materials for environmental and biomedical applications.

Starch-based self-assembled three-dimensional network nanostructure materials for sustainable cascade adsorption

Toward the development of a sustainable utilization strategy for adsorption materials, a starch-based adsorbent starch-chitosan-tannic acid (St-CTS-TA) with a three-dimensional (3D) structure was fabricated in water via electrostatic and hydrogen bonding reactions between St, CTS, and TA without using toxic reducing agents or special instruments. St-CTS-TA demonstrated a high specific surface area of 37 m2/g as well as a mesoporous/macroporous distribution ranging from 30 to 80 nm, which enhanced the mass transfer of adsorbate and the exposure of catechol groups in TA. The Langmuir isotherm adsorption model revealed that the highest adsorption capacities of St-CTS-TA for Fe3+ and Co2+ were 1678.2 and 944.8 mg/g, respectively. Surprisingly, the specific surface area of St-CTS-TA increased from 37 to 87 and 42 m2/g after Fe3+ and Co2+ adsorption, respectively, and the resulting St-CTS-TA-Fe and St-CTS-TA-Co could continuously adsorb basic fuchsin (BF) and rhodamine B (RhB). The adsorption capacities of St-CTS-TA-Fe and St-CTS-TA-Co for BF/RhB were found to be 1854.79/401.19 mg/g and 2229.77/537.49 mg/g, respectively, based on the Langmuir isotherm adsorption model.

Photosystem modulation and extracellular silicification in green microalgae: Key strategies for lead tolerance and removal

The escalating contamination caused by lead ions (Pb2⁺) and its harmful effects on all life forms has raised global concerns. Certain microalgae thrive in metal mining sites characterized by low pH and high concentrations of Pb2⁺, which are usually prohibitive for many microorganisms. Little is known about the mechanisms underlying the adaptation of such microalgae to these hostile conditions. In this study, we elucidated the adaptive strategies of the green microalga Micractinium belenophorum strain AUMW, isolated from a lead mining site, and its application for the removal of Pb+2. Results revealed that strain AUMW can efficiently tolerate up to 200 ppm of Pb+2 in an F/2 medium. Further experimental variables were optimized through response surface methodology (RSM), and 99.6 % removal of Pb2⁺ was achieved. Novel adaptive responses of strain AUMW to high levels of Pb2⁺ include: (i) activation of metal-protective response by modulation of quantum yield (F v /F m ) and non-photochemical quenching (NPQ) of photosystem II; (ii) extracellular silicification encapsulated cells of strain AUMW and altered cell morphology from oval to hexagonal; (iii) silicification prevented intracellular translocation of Pb+2; (iv) silicification boosted adsorption of Pb+2, thus enhanced its removal. This study offers new insights into the protective role of silicification in green microalgae and its potential for the removal of metals from metal-polluted sites, waste from energy storage battery industries, and spent batteries. It also provides a solid base to explore the genetic and metabolic pathways involved in the adaptation of strain AUMW to elevated levels of Pb+2.

Functionalization of seaweed bloom-derived Ulvan using response surface methodology with application in flocculation of oil-in-water pollution

Utilizing macroalgal waste biomass for pollution management is a highly efficient method for addressing the environmental difficulties associated with its disposal. To accomplish this, we have attempted to synthesize a graft copolymer by combining ulvan, a sulfated polysaccharide isolated from seaweed, with acrylates. A one-pot synthesis method using UV-initiated graft polymerization with V-50 as the photoinitiator resulted in the production of a distinctive, high-performance, and eco-friendly flocculant, Ulvan-g-Poly (acrylamide-co-acrylic acid) referred as P(U_AAm_AAc). The synthesis was optimized using the CCD-RSM approach, employing molecular weight and inherent viscosity as indicators to optimize the parameters. The structural and physio-chemical properties of the synthesized P(U_AAm_AAc) were characterized utilizing XRD, ATR-FTIR, ζ-potential, and H1 NMR spectroscopy. The flocculation performance of P(U_AAm_AAc) was further examined for the removal of oils from samples with high neem oil in urea solution and low crude oil in seawater. By employing a coagulant-flocculant combination of poly-aluminium chloride (PAC) and P(U_AAm_AAc), it was noted that more than 94% of oil was effectively eliminated in both samples. Optimization of the dosage of P(U_AAm_AAc) resulted in enhanced turbidity reduction and improved dewatering efficiency of the filter cake generated following flocculation. An evaluation of performance was conducted using the commercial flocculant APAM, where synthesized P(U_AAm_AAc) demonstrated similar results. In conclusion, the findings of this research highlight the potential of P(U_AAm_AAc) as a sustainable alternative to commercial flocculants with multifaceted solution to coastal waste management, paving the way for a cleaner and healthier marine ecosystem to mitigate oil emulsion pollution.

Sustainable wastewater treatment by RO and hybrid organic polyamide membrane nanofiltration system for clean environment

One of the environmental pollution is happened by the discharge of industrial wastewater that needs to be adequately filtered. Given that the effluent from the leather industry contains high levels of chromium, heavy metals, lipids, and Sulphur, it is one of the wastewater disposals that are most damaging. This experimental study focuses on reverse osmosis and hybrid organic polyimide membrane for nanofiltration for sustainable wastewater treatment. In the RO and organic polyamide Nano-porous membranes, a thin film of polyamide membrane was used for efficient filtration. Taguchi analysis optimized process parameters such as pressure, temperature, pH, and volume reduction factor. The outcome shows an 89% reduction in total wastewater hardness, an 88% reduction in sulfate, and an 89% efficiency reduction in COD. As a result, the proposed technology significantly increased filtration efficiency.

Integrating Ultrafiltration Membranes with Flocculation and Activated Carbon Pretreatment Processes for Membrane Fouling Mitigation and Metal Ion Removal from Wastewater

The presence of metal ions in an aqueous medium is an ongoing challenge throughout the world. Processes employed for metal ion removal are developed continuously with the integration of these processes taking center stage. Herein, an integrated system consisting of flocculation, activated carbon (AC), and an ultrafiltration (UF) membrane was assessed for the removal of multiple metal ions contained in wastewater generated from a university chemistry research laboratory. The quality of the wastewater was established before and further determined after treatment with inductively coupled plasma optical emission spectrometry (ICP-OES) for metal content, total dissolved solids (TDS), turbidity, electrical conductivity (EC), and pH. Assessing the spent AC indicated minimal structural changes, indicating a potential for further reuse; for instance, the BET for both the pristine and spent AC exhibited type I isotherms with a mesoporous structure, indicating no major structural changes due to metal complexation. The relative performance of the integrated system indicated that the use of flocculation improved the water quality of metal-laden wastewater for safe disposal. The integrated treatment systems exhibited high removal efficiencies between 80 and 99.99% for all the metal ions except for Mn (<0.008 mg L^-1) and Cr (<0.016 mg L^-1) both at ca. 70%, indicative of the positive influence of the polyelectrolyte in the treatment process. The fabricated UiO-66-NH₂@GO membranes (Z4 and Z5) exhibited high fouling resistance and reusability potential as well as relatively high pure water flux. Consequently, the integrated process employed for the treatment of laboratory metal-containing wastewater is promising as a generic approach to improving the quality of metal-containing wastewater to meet the standards of discharging limits in South Africa.

Treatment of electroplating industry wastewater: a review on the various techniques

Water pollution by recalcitrant compounds is an increasingly important problem due to the continuous introduction of new chemicals into the environment. Choosing appropriate measures and developing successful strategies for eliminating hazardous wastewater contaminants from industrial processes is currently a primary goal. Electroplating industry wastewater involves highly toxic cyanide (CN), heavy metal ions, oils and greases, organic solvents, and the complicated composition of effluents and may also contain biological oxygen demand (BOD), chemical oxygen demand (COD), SS, DS, TS, and turbidity. The availability of these metal ions in electroplating industry wastewater makes the water so toxic and corrosive. Because these heavy metals are harmful to living things, they must be removed to prevent them from being absorbed by plants, animals, and humans. As a result, exposure to electroplating wastewater can induce necrosis and nephritis in humans and lung cancer, digestive system cancer, anemia, hepatitis, and maxillary sinus cancer with prolonged exposure. For the safe discharge of electroplating industry effluents, appropriate wastewater treatment has to be provided. This article examines and assesses new approaches such as coagulation and flocculation, chemical precipitation, ion exchange, membrane filtration, adsorption, electrochemical treatment, and advanced oxidation process (AOP) for treating the electroplating industry wastewater. On the other hand, these physicochemical approaches have significant drawbacks, including a high initial investment and operating cost due to costly chemical reagents, the production of metal complexes sludge that needs additional treatment, and a long recovery process. At the same time, advanced techniques such as electrochemical treatment can remove various kinds of organic and inorganic contaminants such as BOD, COD, and heavy metals. The electrochemical treatment process has several advantages over traditional technologies, including complete removal of persistent organic pollutants, environmental friendliness, ease of integration with other conventional technologies, less sludge production, high separation, and shorter residence time. The effectiveness of the electrochemical treatment process depends on various parameters, including pH, electrode material, operation time, electrode gap, and current density. This review mainly emphasizes the removal of heavy metals and another pollutant such as CN from electroplating discharge. This paper will be helpful in the selection of efficient techniques for treatment based on the quantity and characteristics of the effluent produced.

Removal of hazardous ions from aqueous solutions: Current methods, with a focus on green ion flotation

Hazardous ions, like those of heavy metals, cause significant health and environmental problems when they are discharged into water resources naturally or through various industrial processes. Removing these ions from water is of significant importance in the provision of high-quality water for drinking and agricultural usage. This work discusses current techniques that are frequently used for the removal of heavy-metal ions from aqueous solutions by absorption, particularly the use of biodegradable surfactants in ion flotation. Certain new surfactants promise high efficiency in their use in the ion-flotation process and in their application in industrial-water treatment to remove heavy metals. As an example, this work demonstrates the high efficiency of surfactants based on an amino-acid (L-cysteine) in removing a range of heavy-metal ions in a simple, single-stage ion-flotation process. High foaming ability, the ability to operate in various temperatures and pHs, decomposing into natural products and high binding affinity for heavy-metal ions make the cysteine-based surfactants a highly suitable compound to replace current commercial surfactants in ion- and froth-flotation processes. Removal of particular ions can also be achieved in ion flotation; a suitable choice of parameters, such as pH and surfactant concentration, favours the surfactant binding to those ions. Further intensive work is required to develop an optimal process to recover valuable elements from waste solutions.

Optimized preparation and performance evaluation of a bifunctional chitosan-modified flocculant

In view of the diversification of pollutants in current sewage, further improving the application efficiency of water treatment agents and realizing multi-functionalization are important directions for the research of water treatment agents. In this paper, on the basis of the natural polymer flocculant chitosan, MAPTAC and AM were used as modified monomers to improve its solubility and also enhance its flocculation and bactericidal properties. Furthermore, the preparation conditions of chitosan flocculant poly(CTS-g-AM-MAPTAC) were optimized by response surface methodology, and its flocculation and sterilization functions were evaluated in detail. The experimental results showed that the significance order of the factors in the preparation process was illumination time, mass ratio of total monomer to chitosan, molar ratio of monomers, and initiator concentration. The optimum conditions for preparing poly(CTS-g-AM-MAPTAC) were 6 moL L-1 for initiator concentration, 4 for mass ratio of total monomer to chitosan, 25% for monomer molar ratio, and 60 min for illumination time. The intrinsic viscosity and grafting rate of poly(CTS-g-AM-MAPTAC) prepared under optimum conditions were 5.4965 dL g-1 and 220.34%. The obtained poly(CTS-g-AM-MAPTAC) had good solubility, which could fully expose the active sites in wastewater with different acidity and had good flocculation effect. The performance evaluation results showed that the flocculant had a good combination of flocculation and sterilization, and had the advantages of high turbidity removal and sterilization efficiency, good biodegradability and low reagent consumption.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Enhanced treatment of organic matters in starch wastewater through Bacillus subtilis strain with polyethylene glycol-modified polyvinyl alcohol/sodium alginate hydrogel microspheres

Starch wastewater is a wide range of environmental issues with organic pollutants. A high efficiency and stability hydrogel-organic degradation system was designed via Bacillus Subtilis with Polyethylene glycol (PEG)-modified Polyvinyl alcohol (PVA)/Sodium alginate (SA) hydrogel microspheres. Bacillus subtilis was immobilized on the surface or inside of PEG-modified PVA/SA hydrogels microspheres via physical adsorption. Results showed PEG-modified PVA/SA microspheres had an effect of adsorption on Bacillus subtilis with enhancing bearing rate to 54.22% compared to the blank control group. The effect of microspheres on degradation was remarkable in simulation starch wastewater with a maximum COD removal rate of 93.35% and compared in reality starch wastewater with 90.02% under the optimal condition of pH = 6, 35℃, 20% dosage, 180 rpm. This novel biological method on starch wastewater enhanced tolerance of microorganisms and degradation effect, reflecting safety, effectiveness, and economy with great significance to environmental protection.

Wastewater Treatment in Mineral Processing of Non-Ferrous Metal Resources: A Review

Water used by mining enterprises needs to be comprehensively recovered and utilized to achieve clean production. This requires the effective treatment of mineral processing wastewater. Wastewater produced during non-ferrous metal mineral processing contains a complex mixture of pollutants at high concentrations, making comprehensive treatment difficult. Here, the sources of and hazards posed by wastewater produced during non-ferrous metal mineral processing are introduced and the techniques for removing heavy metal ions and organic chemicals are reviewed. Chemical precipitation and adsorption methods are often used to remove heavy metal ions. Chemical precipitation methods can be divided into hydroxide and sulfide precipitation methods. Organic chemicals are mainly removed using oxidation methods, including electrochemical oxidation, photocatalytic oxidation, and ultrasonic synergistic oxidation. External and internal cyclic utilization methods for treating wastewater produced by mineral processing plants are introduced, and a feasibility analysis is performed.

Kinetics, thermodynamics, equilibrium, surface modelling, and atomic absorption analysis of selective Cu(ii) removal from aqueous solutions and rivers water using silica-2-(pyridin-2-ylmethoxy)ethan-1-ol hybrid material

The removal of heavy metals is attracting considerable attention due to their undesirable effects on the environment. In this investigation, a new adsorbent based on silica functionalized with pyridin-2-ylmethanol (SiPy) was successfully synthesized to yield to a hybrid material. FTIR, SEM, TGA, and specific surface area analysis were used to characterize the structure and morphology of the SiPy hybrid material. Various heavy metal ions such as Cu(ii), Zn(ii), Cd(ii), and Pb(ii) were selected to examine the adsorption efficiency of the newly prepared adsorbent, optimized at varying solution pH, contact time, concentration, and temperature. The adsorbent SiPy displayed good adsorption capacity of 90.25, 75.38, 55.23, and 35.12 mg g⁻¹ for Cu(ii), Zn(ii), Cd(ii), and Pb(ii), respectively, at 25 min and pH = 6. The adsorption behaviors of metal ions onto the SiPy adsorbent fitted well with the pseudo-second-order kinetic mode and the isotherm was better described by the Langmuir isotherm. The thermodynamic studies disclose spontaneous and endothermic adsorption process. Furthermore, the SiPy adsorbent retained good selectivity and regeneration properties after five adsorption–desorption cycles of Cu(ii). A computational investigation of the adsorption mechanism indicates that the N-pyridine, O-hydroxyl, and ether O-atoms play a predominant role during the capture of Cu(ii), Zn(ii), Cd(ii), and Pb(ii). This study proposes the SiPy adsorbent as an attractive material for the selective removal of Cu(ii) from real river water and real industrial wastewater.

The removal of heavy metals is attracting considerable attention due to their undesirable effects on the environment.

Flocculation of combined contaminants of dye and heavy metal by nano-chitosan flocculants

In this study, two multifunctional nano-chitosan flocculants (CPAM-NCS1 and CPAM-NCS2) were made through the graft modification of cationic monomer and carboxymethylchitosan (CMCTS) to remove combined contaminants. The effects of various factors (pH, flocculant dosage and hydraulic mixing conditions) on the flocculation performance under single and composite pollution conditions were systematically investigated, the optimal chemical oxygen demand (COD) and the chromaticity removal rates in the dye wastewater were 79.9% and 83.9% at wastewater pH 7, the fast stirring rate 300 rpm, the fast stirring time 8 min, and the dosage of CPAM-NCS1 80 mg/L, respectively. The optimal removal rates of Cu (II) obtained by CPAM-NCS1 and CPAM-NCS2 at were 80.3% and 75.2% at 60 mg/L and the wastewater pH 7, respectively. The optimal removal rates of Cu (II) and disperse orange were 85.3% and 89.4%, respectively, in a composite pollutant system in which Cu (II) and disperse orange coexisted when the pH of the composite system was 9 and the dosage of CPAM -NCS1 was 60 mg/L. This study proved that nanoflocculants made by modifying CMCTS with different structures can demonstrate ideal flocculation removal performance for dye and heavy metal wastewaters.

Removal of copper ions by functionalized biochar based on a multicomponent Ugi reaction

Copper is widely present in the natural environment and inevitably poses a risk to both human health and the natural environment. Biochar is an inexpensive, clean and sustainable sorbent material that can be used as a resource for copper removal, and there is interest in new ways to chemically treat biochar to tune its unique properties and modify its atomic structure. In this study, biochar was oxidized, and then polyethyleneimine (PEI) modified chitosan and carboxylated biochar were economically compounded through a multicomponent Ugi reaction to effectively remove Cu(ii). PEI enhances the adsorption of Cu(ii) within an optimum solution pH range of 3.5–5.5. The adsorption process follows a pseudo-second-order kinetic model. When the dosage of BC-NH2 was 4 g L⁻¹ and the temperature was 303 K, the maximum adsorption capacity calculated by the Langmuir model was 26.67 mg g⁻¹. The adsorption process of Cu(ii) on BC-NH2 was heat-trapping and spontaneous. BC-NH2 showed good selectivity for K⁺ and Mg²⁺, and BC-NH2 desorbed by NaOH showed better adsorption performance than H₂SO₄ in the adsorption–desorption cycle. Characterization by SEM, EDS, BET, FTIR, TGA and XPS showed successful coupling and that the amide group of BC-NH2 had chelated with Cu(ii). This atomically economical multicomponent Ugi reaction provides a new option for preparing composite materials that effectively remove heavy metals.

Polyethyleneimine-modified chitosan and carboxylated biochar were economically compounded by a multicomponent Ugi reaction to produce products rich in amide functional groups.

Preparation and Characterization of High-Efficiency Magnetic Heavy Metal Capture Flocculants

In this study, a high-efficiency magnetic heavy metal flocculant MF@AA was prepared based on carboxymethyl chitosan and magnetic Fe3O4. It was characterized by SEM, FTIR, XPS, XRD and VSM, and the Cu(II) removal rate was used as the evaluation basis for the preparation process. The effects of AMPS content, total monomer concentration, photoinitiator concentration and reaction time on the performance of MF@AA flocculation to remove Cu(II) were studied. The characterization results show that MF@AA has been successfully prepared and exhibits good magnetic induction characteristics. The synthesis results show that under the conditions of 10% AMPS content, 35% total monomer concentration, 0.04% photoinitiator concentration, and 1.5 h reaction time, the best yield of MF@AA is 77.69%. The best removal rate is 87.65%. In addition, the response surface optimization of the synthesis process of MF@AA was performed. The optimal synthesis ratio was finally determined as iron content 6.5%, CMFS: 29.5%, AM: 53.9%, AMPS: 10.1%. High-efficiency magnetic heavy metal flocculant MF@AA shows excellent flocculation performance in removing Cu(II). This research provides guidance and ideas for the development of efficient and low-cost flocculation technology to remove Cu(II) in wastewater.