New trends in removing heavy metals from wastewater

With the development of researches, the treatments of wastewater have reached a certain level. Whereas, heavy metals in wastewater cause special concern in recent times due to their recalcitrance and persistence in the environment. Therefore, it is important to get rid of the heavy metals in wastewater. The previous studies have provided many alternative processes in removing heavy metals from wastewater. This paper reviews the recent developments and various methods for the removal of heavy metals from wastewater. It also evaluates the advantages and limitations in application of these techniques. A particular focus is given to innovative removal processes including adsorption on abiological adsorbents, biosorption, and photocatalysis. Because these processes have leaded the new trends and attracted more and more researches in removing heavy metals from wastewater due to their high efficency, pluripotency and availability in a copious amount. In general, the applicability, characteristic of wastewater, cost-effectiveness, and plant simplicity are the key factors in selecting the most suitable method for the contaminated wastewater.

Algae-facilitated chemical phosphorus removal during high-density Chlorella emersonii cultivation in a membrane bioreactor

An algae-based membrane bioreactor (A-MBR) was evaluated for high-density algae cultivation and phosphorus (P) removal. The A-MBR was seeded with Chlorella emersonii and operated at a hydraulic retention time of 1day with minimal biomass wastage for about 150days. The algae concentration increased from initially 385mg/L (or 315mg biomass COD/L) to a final of 4840mg/L (or 1664mg COD/L), yielding an average solids (algae biomass+minerals) production rate of 32.5gm(-3)d(-1) or 6.2gm(-2)d(-1). The A-MBR was able to remove 66±9% of the total P from the water while the algal biomass had an average of 7.5±0.2% extracellular P and 0.4% of intracellular P. The results suggest that algae-induced phosphate precipitation by algae is key to P removal and high-density algae cultivation produces P-rich algal biomass with excellent settling properties.

Plant-wide model-based analysis of iron dosage strategies for chemical phosphorus removal in wastewater treatment systems

Stringent phosphorus discharge standards (i.e. 0.15-0.3 g P.m^-3) in the Baltic area will compel wastewater treatment practice to augment enhanced biological phosphorus removal (EBPR) with chemical precipitation using metal salts. This study examines control of iron chemical dosing for phosphorus removal under dynamic loading conditions to optimize operational aspects of a membrane biological reactor (MBR) pilot plant. An upgraded version of the Benchmark Simulation Model No. 2 (BSM2) with an improved physico-chemical framework (PCF) is used to develop a plant-wide model for the pilot plant. The PCF consists of an equilibrium approach describing ion speciation and pairing, kinetic minerals precipitation (such as hydrous ferric oxides (HFO) and FePO₄) as well as adsorption and co-precipitation. Model performance is assessed against data sets from the pilot plant, evaluating the capability to describe water and sludge lines across the treatment process under steady-state operation. Simulated phosphorus differed as little as 5-10% (relative) from measured phosphorus, indicating that the model was representative of reality. The study also shows that environmental factors such as pH, as well operating conditions such as Fe/P molar ratios (1, 1.5 and 2), influence the concentration of dissolved phosphate in the effluent. The time constant of simultaneous precipitation in the calibrated model, due to a step change decrease/increase in FeSO₄ dosage, was found to be roughly 5 days, indicating a slow dynamic response due to a multi-step process involving dissolution, oxidation, precipitation, aging, adsorption and co-precipitation. The persistence effect of accumulated iron-precipitates (HFO particulates) in the activated sludge seemed important for phosphorus removal, and therefore solids retention time plays a crucial role according to the model. The aerobic tank was deemed to be the most suitable dosing location for FeSO₄ addition, due to high dissolved oxygen levels and good mixing conditions. Finally, dynamic model-based analyses show the benefits of using automatic control when dosing chemicals.

Efficient removal of copper from wastewater by using mechanically activated calcium carbonate

Copper removal from aqueous solution is necessary from the stances of both environmental protection and copper resource recycling. It is important to develop a new chemical precipitation method suitable for removing copper particularly at low concentration as the case of waste mine water, with regards to the various problems related to the current precipitation methods by using strong alkalis or soluble sulfides. In this research, we studied a possible chemical precipitation of copper ions at concentration around 60 mg/L or lower by cogrinding copper sulfate in water with calcium carbonate (CaCO₃) using wet stirred ball milling. With the aid of ball milling, copper precipitation as a basic sulfate (posnjakite: Cu₄ (SO₄) (OH)₆·H₂O) occurred at a very high copper removal rate of 99.76%, to reduce the residual copper concentration in the solution less than 0.5 mg/L, reaching the discharge limit, even with the addition amount of CaCO₃ as a stoichiometric ratio of CaCO₃/Cu²⁺at 1:1. It is more interesting to notice that, at the same conditions, other heavy metals such as Ni, Mn, Zn and Cd do not precipitate obviously just with CaCO₃ addition at CaCO₃/M²⁺at 1:1 so that the precipitate without the impurities can be processed as good source to recover copper. This newly proposed concept can be further developed to treat wastewaters with other metals to serve both purposes of environmental purification and resource recovery in a similar way.

Removal of chloride from water and wastewater: Removal mechanisms and recent trends

Increased chloride concentration can cause salinization, which has become a serious and widespread environmental problem nowadays. This review aims at providing comprehensive and state-of-the-art knowledge and insights of technologies for chloride removal. Mechanisms for chloride removal mainly include chemical precipitation, adsorption, oxidation and membrane separation. In chemical precipitation, chloride removal by forming CuCl, AgCl, BiOCl and Friedel's salt. Adsorbents used in chloride removal mainly include ion exchangers, bimetal oxides and carbon-based electrodes. Oxidation for chloride removal contains ozone-based, electrochemical and sulfate radical-based oxidation. Membrane separation for chloride removal consists of diffusion dialysis, nanofiltration, reverse osmosis and electrodialysis. In this review, we specifically proposed the factors that affect chloride removal process and the corresponding strategies for improving removal efficiency. In the last section, the remaining challenges of method explorations and material developments were stated to provide guidelines for future development of chloride removal technologies.

Removal of high concentration of sulfate from pigment industry effluent by chemical precipitation using barium chloride: RSM and ANN modeling approach

Sulfate ions pose a major threat and challenge in the treatment of industrial effluents. The sample of wastewater obtained from a pigment industry contained large quantities of sulfate in the form of sodium sulfate which resulted in high TDS. As the removal of sulfate from pigment industry effluent was not reported previously, this work was focused on removing the sulfate ions from the effluent by chemical precipitation using barium chloride. The efficiency of sulfate removal was nearly 100% at an excess dosage of barium chloride, which precipitates the dissolved sulfate ions in the form of barium sulfate. Optimization of the parameters was done using Response Surface Methodology (RSM). This work is the first attempt for modeling the removal of sulfate from pigment industry effluent using RSM and Artificial Neural Network (ANN). Prediction by both the models was evaluated and both of them exhibited good performance (R² value > 0.99). It was observed that the prediction by RSM (R² value 0.9986) was closer to the experimental results than ANN prediction (R² value 0.9955). The influence on the pH and conductivity of the solution by dosage of precipitant was also studied. The formation of barium sulfate was confirmed by characterization of the precipitate. Therefore, the sulfate removed from the effluent was converted into a commercially valuable precipitate.

Evaluation of the treatability of a winery distillery (vinasse) wastewater by UASB, anoxic-aerobic UF-MBR and chemical precipitation/adsorption

A multi-stage pilot-scale treatment cycle consisting of an Upflow Anaerobic Sludge Blanket reactor (UASB) followed by an anoxic-aerobic Ultra Filtration Membrane Bio Reactor (UF-MBR) and a post treatment based on chemical precipitation with lime or adsorption on Granular Activated Carbons (GAC), was applied in order to evaluate the treatment feasibility of a real winery distillery wastewater at laboratory and bench scale. The wastewater was classified as high strength with acidic pH (3.8), and concentrations of 44,600, 254, 604 and 660 mg/l for COD_tot, total nitrogen, total phosphorous and phenols, respectively. The UASB reactor was operated at Organic Loading Rates (OLR) in the range 3.0-11.5 kgCOD_tot/m³/d achieving treatment efficiency up to 97%, with an observed methane production of 340 L of CH₄/kgCOD. The MBR system was operated with an organic load in the range 0.070-0.185 kgCOD/kgVSS/d, achieving a removal up to 48%, 67% and 65% of the influent COD, total nitrogen and phenols, respectively. The combination of UASB and UF-MBR treatment units was not effective in phosphate and colour removal assigning to further chemical precipitation and adsorption processes, respectively, their complete removal in order to comply with legal standards for wastewater discharge. Subsequently, the optimization of the investigated treatment chain was assessed by applying a chemical precipitation step upstream and downstream the UASB reactor, and a related treatment unit cost assessment is presented in view of a further technological scale-up.

Lithium recovery from salt-lake brine: Impact of competing cations, pretreatment and preconcentration

The global demand of lithium is rising steadily, and many industrially advanced countries may find it hard to secure an uninterrupted supply of lithium for meeting their manufacturing demands. Thus, innovative processes for lithium recovery from a wide range of natural reserves should be explored for meeting the future demands. In this study, a novel integrated approach was investigated by combining nanofiltration (NF), membrane distillation (MD) and precipitation processes for lithium recovery from salt-lake brines. Initially, the brine was filtered with an NF membrane for the separation of lithium ions (Li⁺) from competing ions such as Na⁺, K⁺, Ca²⁺ and Mg²⁺. The extent of permeation of metal ions by the NF membrane was governed by their hydrated ionic radii. Rejection by NF membrane was 42% for Li, 48% for Na and 61% for K, while both the divalent cations were effectively rejected (above 90%). Importantly, in the NF-permeate, Mg²⁺/Li⁺ mass ratio reduced to less than 6 (suggested for lithium recovery). The result showed that MD can enrich lithium with a concentration of 2.5 for raw brine and 5 for NF-treated brine. Following the enrichment of NF-permeate by the MD membrane, a two-stage precipitation method was used for the recovery of lithium. X-ray diffraction confirmed the precipitation of lithium as well as the formation of lithium carbonate crystals.

Aerobic granular sludge for simultaneous accumulation of mineral phosphorus and removal of nitrogen via nitrite in wastewater

Lab-scale experiments were conducted to investigate the aerobic granular sludge process for simultaneous phosphorus (P) accumulation by chemical precipitation and biological nitrogen removal via nitrite. The P-rich granules were successfully incubated in a sequencing batch reactor, in which simultaneous nitrification-denitrification occurred via nitrite. The average diameter of the P-rich granules was 2.47 mm and the P content in granules was much higher than that in other granular systems with enhanced biological phosphorus removal process. Filamentous bacteria (genus Thiothrix) in the granules and the long sludge retention time (30 d) of the granular system played a crucial role in accumulation of precipitated phosphate. X-ray diffraction analysis, scanning electron microscopy coupled with energy dispersive X-ray and the experimental design using response surface methodology confirmed that the main mineral patterns in P-rich granules were Ca-Mg phosphate and whitlockite.

Effects of sono-assisted modified precipitation on the crystallinity, size, morphology, and catalytic applications of hematite (α-Fe2O3) nanoparticles: A comparative study

The present study reports a new approach to improve the adsorption and catalytic properties of hematite nanoparticles (HNPs) synthesized via the chemical precipitation technique as one of the most applicable and preferable synthesis methods. This could be performed through controlling the particles' crystallinity where a facile ultrasonic pathway (UP) modification was introduced as a hybrid replacement for the conventionally-used magnetic stirring pathway (MP) using different precursor concentrations. The X-ray diffraction and Raman spectra define the pristine phase of α-Fe₂O₃ crystal with lower crystallinity and higher degrees of structural disorder for UP products. UP also shows smaller nanosized particles with lower bundles of aggregations and lumps formation in addition to lesser values of polydispersity index compared to the MP products. The catalytic performance supported by the reaction kinetics for the degradation of hazardous Rose Bengal and Congo Red dyes in light and dark, respectively, were examined. It revealed superior efficiencies for all of the UP products within a short span against the conventional MP and previous studies. Moreover, it was confirmed that UP products could catalyze the biodegradation reactions of green algae (Enteromorpha) and induced higher rates of biogas production. In addition to this, decreasing the precursor concentrations was found to be another key factor reducing the produced particles' crystallinity, size, and lumps formation as well as affecting the morphology development. Thus, the synergetic effects of applying the UP at low precursor concentrations could show a practical pathway for the synthesis of low-crystalline HNPs with enhanced properties for green applications over the conventional MP products. Hence, the obtained findings are of vital importance to show the improved catalytic efficiency of HNPs by shedding new light on controlling the crystallinity and developing the surface features in the conventional precipitation process via the proposed modification.

Cancer Cells Treated by Clusters of Copper Oxide Doped Calcium Silicate

Purpose: Different compositions of copper oxide (CuO)-doped calcium silicate clusters were used to treat the cancer cells. Methods: The influence of CuO content on the morphology, drug delivering ability, physicochemical properties and cytotoxicity was investigated. Results: The microcrystalline structure revealed the decrement of the size from (20-36 nm) to (5-7 nm) depending on the copper content percentages. Drug delivering ability of doxycycline hyclate (Dox) was down regulated from 58% to 28%in the presence of the CuO. The inclusion of CuO and Dox didn't show any remarkable changes on the physicochemical properties of the CuO-doped calcium silicate nanoparticles. Conclusion: The CuO-doped calcium silicate sample (5 weight %) exhibited great cytotoxicity against the tested cell lines compared to the CuO-free sample. CuO-doped materials displayed significant anticancer effect; this sheds light on its implication in the treatment of cancer.

Voltammetric determination of levofloxacin using silver nanoparticles deposited on a thin nickel oxide porous film

The authors describe a simplified chemical precipitation method and silver mirror reaction to synthesize a nanocomposite consiting of silver nanoparticles on a thin and porous nickel oxide film. Placed on a glassy carbon electrode (GCE), it allows for the determination of levofloxacin (LEV) via square wave voltammetry (SWV). Under optimal detection conditions, the voltammetric signal (typically measured at around 0.96 V vs. SCE) increases linearly in the 0.25-100 μM LEV concentration range. And the detection limit was calculated as 27 nM (at S/N = 3). The sensor is highly selective, stable and repeatable. It was applied to the determination of LEV in spiked human serum samples, and the satisfactory results confirm the applicability of this sensor to practical analyses. Graphical abstract Schematic of a two-step method to synthesize a nanocomposite consisting of nickel oxide porous thin-film supported silver nanoparticles. The composite was used for improved voltammetric determination of levofloxacin.

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.

A critical updated review of the hydrometallurgical routes for recycling zinc and manganese from spent zinc-based batteries

This review paper aims to present and analyse data from the most recent literature (between 2007 and 2019) published on the topic of manganese (Mn) and zinc (Zn) recovery from zinc-based spent batteries through hydrometallurgical methods. In a first attempt, a detailed comparative assessment of the metals leaching performance (as well as the experimental variables that influence its performance) reported in the various studies with strong acid or bases, potentially supplemented by complexing or reducing agents, as well as the reactions involved, are reviewed and discussed. All data point out that the use of a reductant is needed to fully solubilize Mn from spent batteries during the leaching process. Comparison of the data seem to indicate that most reductants have similar performance and, therefore, the choice of a reductant should be focused on low cost or even waste materials. In a second attempt, the separative processes mostly described in the literature to recover Mn and Zn from leachates are reviewed emphasizing the strengths and weaknesses of each technique. Solvent extraction is the most widely tested process for this aim. A thorough comparison of existing data indicates that, in general, neutral extractants have higher potential for selective separation of Zn and Mn. Furthermore, although chemical precipitation is a simple process, low pure final metal hydroxide products are expected to be achieved when alkaline precipitation is implemented comparatively to the Mn oxidative precipitation where Mn can be recovered selectively as a solid of manganese (IV) oxide.

Enhanced phosphate removal from wastewater by using in situ generated fresh trivalent Fe composition through the interaction of Fe(II) on CaCO3

Excessive existences of nutrients such as phosphate in the aqueous environment remain as a heavy concern although many researches have been reported for dealing with their removal. Based on the understanding toward the interactions of Fe compounds with phosphate and carbonate from many available researches, we designed a very simple and efficient approach for phosphate removal by using in situ generated fresh trivalent Fe composition through the interaction of Fe(II) as FeSO₄ on CaCO₃. Addition and agitation of Fe(II) and CaCO₃ simultaneously to phosphate solution allowed an amorphous Fe(III)-P or Ca-Fe(III)-P precipitation, with a phosphate removal rate close to 100%, to reduce the residual phosphorus concentration less than 0.03 mg/L from 100 mg/L, reaching the discharge limit, even with the addition amounts of CaCO₃ as low as a stoichiometric ratio of CaCO₃/PO₄^3- at 0.9 and ratio of Fe(II)/PO₄^3- at 1.5, and the percent of P₂O₅ in the precipitate was as high as 19.4% enough as phosphate source for fertilizer production. Different from the alkaline process with enough OH^- group, the slow hydrolysis of CaCO₃ resulting in low concentration of OH^- group for the formation of Fe(OH)₂, which was oxidized soon by air into trivalent Fe, achieved a continuous generation of fresh ferric composition for phosphate precipitation and could avoid its rapid formation and subsequent transformation into stable FeOOH of large particle size to lose the activity. These results based on the synergistic effect of using CaCO₃ and Fe(II) together may have applications in the treatment of eutrophic wastewater through a process with many advantages of easy operation and low-cost besides the high removal efficiency with phosphate percentage inside the precipitate high enough to serve for fertilizer production.

Recovering chemical sludge from the zero liquid discharge system of flue gas desulfurization wastewater as flame retardants by a stepwise precipitation process

In this study, a five-stage stepwise precipitation process, including pre-sedimentation, magnesium removal, gypsum precipitation, ettringite precipitation and calcium removal, was proposed as a softening pretreatment for zero liquid discharge system for flue gas desulfurization wastewater. Batch tests and long-term bench-scale experiment showed that magnesium, sulfate and calcium were efficiently removed with efficiencies all above 98.0%, leaving a clean effluent majorly containing NaCl and NaOH. The precipitated CaSO₄, CaCO₃, Mg(OH)₂ and ettringite were completely separated by stepwise precipitation, and the purity of Mg(OH)₂ and ettringite were further enhanced by washing and soaking treatment. CaSO₄ and CaCO₃ can be directly recycled as gypsum product and desulfurizing agent within the power plant, while Mg(OH)₂ and ettringite presented proper particle size and excellent thermal properties as a synergistic flame retardant. The flame retardancy of ethylene vinyl acetate copolymer were greatly improved when blended with recovered Mg(OH)₂ and ettringite, and possessed better performance by blending them together because ettringite could act as a dispersing and compatible agent of Mg(OH)₂, and relieve the intensity of smoke releasing. Chemical sludge recovery compensates the total cost of the five-stage process by 45.0%, and makes the process technically versatile, economically beneficial and environmentally friendly without solid waste production.

Sulphur compounds removal from an industrial landfill leachate by catalytic oxidation and chemical precipitation: From a hazardous effluent to a value-added product

This study focused on the removal of sulphur compounds from a high-strength leachate of a hazardous industrial waste landfill. Firstly, sulphides (0.5 g L^-1) and sulphites (2.5 g L^-1) were catalytic oxidised at natural pH (8.7). Air or H₂O₂ were applied as oxidants and metals present in the leachate were used as catalysts. Distinct air flow rates and H₂O₂:sulphur molar ratios were tested. Concentrations of sulphide and sulphite lower than 1.0 mg L^-1 (emission limit value - ELV) were obtained after 5-h oxygenation or 1-min peroxidation under the best conditions, i.e. air flow rate of 1 L_air L_leachate^-1 min^-1 and H₂O₂:sulphur stoichiometric ratio. Aeration was considered unsafe since >33 volatile organic compounds (VOCs) and hydrogen sulphide (H₂S) were released to the atmosphere. Thus, only the H₂O₂-oxidised leachate pursued treatment. Sulphates (13 g L^-1) were removed by chemical precipitation as ettringite or barite applying different reactants contents and pH values. Without pH correction, sulphate contents below 2.0 g L^-1 (ELV) were achieved using a [Ca²⁺]:[Al³⁺]:[SO₄^2-] molar ratio of 12:4:3 (2-fold stoichiometry) and a [Ba²⁺]:[SO₄^2-] molar ratio of 1.0:1.0 (1-fold stoichiometry). The analysis of precipitates by X-ray diffraction (XRD) showed a three-phase ettringite (only 67% corresponding to ettringite itself) and single-phase barite. Barite precipitation proved to be more appealing since a value-added product was obtained and, furthermore, less reactants were required. After sulphur compounds removal using H₂O₂-driven catalytic oxidation and chemical precipitation through barite, the leachate was suitable for biological treatment, despite the high salinity, and a high fraction of the organic load (46%) could be biologically oxidised.

Comparison of biological and chemical treatment processes as cost-effective methods for elimination of benzoate in saline wastewaters

Eight mixed cultures able to degrade benzoic acid under saline conditions were established and kinetic parameters were determined in batch processes with cultures SBM002 (0.5 g d(-1)·g oDM(-1)), SBM003 (0.7 g d(-1)·g oDM(-1)) and SBM007 (2.2 g d(-1)·g oDM(-1)) showing the highest degradation rates. Treatability of an industrial waste water (12 g L(-1) benzoic acid, 82 g L(-1) NaCl) by these cultures was proven in a fed-batch system (SBM002 & SBM003) and a continuous flow reactor (SBM007). The performance of the continuous flow reactor was 15-times higher compared to the fed-batch system due to the change of inocula, higher concentration of ammonia as nutrient and less accumulation of possibly toxic catecholic compounds. Average DOC reduction was found to be 98% at 100 g L(-1) NaCl and 1.2 g L(-1) benzoic acid under these conditions. Pre-treatment of the waste water via chemical precipitation by acidification to pH 3.5 diminished the concentration of benzoic acid to 2.1 g L(-1). In a combined chemical-biological process the volume of the bioreactor is reduced to 15% compared to a pure biological process. A comparison of operational costs for these three alternatives is presented.

Metallic iron (Fe0)-based materials for aqueous phosphate removal: A critical review

The discharge of excessive phosphate from wastewater sources into the aquatic environment has been identified as a major environmental threat responsible for eutrophication. It has become essential to develop efficient but affordable techniques to remove excess phosphate from wastewater before discharging into freshwater bodies. The use of metallic iron (Fe⁰) as a reactive agent for aqueous phosphate removal has received a wide attention. Fe⁰ in-situ generates positively charged iron corrosion products (FeCPs) at pH > 4.5, with high binding affinity for anionic phosphate. This study critically reviews the literature that focuses on the utilization of Fe⁰-based materials for aqueous phosphate removal. The fundamental science of aqueous iron corrosion and historical background of the application of Fe⁰ for phosphate removal are elucidated. The main mechanisms for phosphate removal are identified and extensively discussed based on the chemistry of the Fe⁰/H₂O system. This critical evaluation confirms that the removal process is highly influenced by several operational factors including contact time, Fe⁰ type, influent geochemistry, initial phosphate concentration, mixing conditions, and pH value. The difficulty in comparing independent results owing to diverse experimental conditions is highlighted. Moreover, contemporary research in progress including Fe⁰/oxidant systems, nano-Fe⁰ application, Fe⁰ material selection, desorption studies, and proper design of Fe⁰-based systems for improved phosphate removal have been discussed. Finally, potential strategies to close the loop in Fe⁰-based phosphate remediation systems are discussed. This review presents a science-based guide to optimize the efficient design of Fe⁰-based systems for phosphate removal.

The pretreatment effects of various target pollutant in real coal gasification gray water by coupling pulse electrocoagulation with chemical precipitation methods

To prevent the scale formation in the equipments and pipelines after pre-treated coal gasification gray water (CGGW) entering the reuse system and reduce the influence of various pollutants in the effluent on subsequent biochemical treatment, this study presented a coupled use of pulse electrocoagulation (PEC) and chemical precipitation (CP) coupling method for the pretreatment of coal gasification gray water (CGGW). In addition, the operation parameters of PEC and the reaction conditions of PEC-CP were optimized based on iron plate as electrode and total hardness, turbidity and sludge yield as assessment indicators. Due to the formation of multi-hydroxyl iron by several minutes of pulse current, and the addition of pH regulator and coagulant aid, the efficient removal of various ions, hardness and turbidity was significantly reduced via various mechanism such as redox, precipitation, adsorption and coagulation reaction. The result indicated that under the optimal operation conditions, the total hardness, turbidity, and Feⁿ⁺ of PEC-CP effluents were 275.0 mg/L, 3.0 NTU and 5.6 mg/L, respectively and sludge amount was 0.88 kg/m³. The removal rates of Si, B, Mn, Ba, COD, NPOC and NH₄⁺-N by PEC-CP reached 80.0%, 75.4%, 97.0%, 99.8%, 35.0%, 33.6% and 23.8%, respectively. The present results suggested that the CGGW pretreatment effluents could be not only reused directly, but also greatly alleviate the scaling problem of water pipeline and coal gasification production facilities.

The Effect of Contact Non-equilibrium Plasma on Structural and Magnetic Properties of Mn Х Fe3 - X О4 Spinels

Nano-sized manganese ferrites Mn х Fe3 - х О4 (х = 0-1.3) were prepared using contact non-equilibrium plasma (CNP) in two different pH (11.5 and 12.5). The influence of synthesis conditions (e.g., cation ratio and initial pH) on phase composition, crystallite size, and magnetic properties were investigated employing X-ray diffraction (XRD), differential thermal analysis (DTA), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and magnetic measurement techniques. The formation of monodispersed faceted ferrite particles at х = 0-0.8 was shown. The FTIR spectra revealed reflection in region 1200-1700 cm-1 caused by the presence of water adsorbed on the surface of Fe3 - x Mn x O4 micro-granules or embedded into their crystal lattice. The most sensitivity of reflection spectra to the composition changes takes place within a 400-1200 cm-1 range, typical to the stretching vibrations of Fe(Mn)-O (up to 700 cm-1 ), Fe(Mn)-OH, and Fe(Mn)-OH2 bonds (over 700 cm-1). The XRD results showed that the nanocrystalline Mn х Fe3 - х О4 (0 < x < 1.0) had cubic spinel crystal structure with average crystallite size 48-49 A. The decrease of crystalline size with the x increase was also observed.

Detailed analysis of size-separation of silver nanoparticles by density gradient centrifugation method

In this research, silver nanoparticles were synthesized by chemical precipitation method and stabilized by chitosan biopolymer in the range of 15 to 235 nm. Then, the silver nanoparticles were separated by density gradient centrifugation method at different gradients and centrifuged at various duration and speed. The best separation was done with the gradient chosen at 10%, 20%, 30% and 40% for a duration of 2 h at 6000 rpm. The UV-visible spectra demonstrated the proper synthesis of silver nanoparticles, while FTIR spectrum and XRD data revealed the structure of prepared Ag-NPs. The FESEM and TEM analysis were used to check for the exact shape and size of Ag-NPs, respectively. However, the separation of silver nanoparticles was assessed making use of DLS analysis.

Removal of textile dyes by benefited marine shells wastes: From circular economy to multi-phenomenological modeling

Marine shell wastes were thermally activated and characterized as aragonite and calcite phases and were used in the removal of synthetic anionic dyes, Bright Blue Acid (NB180) and Reactive Red 133 (RR133). Benefited marine shells were classified as low-cost (USD 0.33/g of adsorbent) in comparison with other reported materials. Furthermore, the absence of chemicals in the adsorbent preparation allows its further employment in economic activities. The coexistence of adsorption and exchange-precipitation reaction was responsible for up to 93% of dye removal, whilst the maximum adsorption capacities were 225 mg g^-1 for NB180 and 36 mg g^-1 for RR133. The observed kinetic behavior of the dye removal by the adsorbent allowed the proposal of a mechanism for dye-adsorbent interaction in liquid-solid interface considering both adsorption and exchange-precipitation reaction. Contribution of the exchange-precipitation reaction in the removal process was quantified as being approximately 75% for NB180 and 25% for RR133. The mathematical model that phenomenologically described the kinetic behavior of the dye removals gave the magnitude order of the kinetic parameters as k_ads = 8.67-9.49 min^-1 and k_p = 1.18-2.84 min^-1, due to the adsorption and the (exchange-reaction)-precipitation, respectively. This work indicates the step (exchange reaction)-precipitation as an additional contribution to improve the dye removal from aqueous effluents, achieving in the evolution of the process up to 24% in terms of kinetic selectivity of removal.

Incorporation of an anaerobic digestion step in a multistage treatment system for sanitary landfill leachate

A combined process of anaerobic digestion (AD), lime precipitation (P), microfiltration (MF) and reverse osmosis (RO) was developed for the treatment of landfill leachate (LFL). The raw LFL contained high amount of organic matter with an elevated humic acids concentration. During the anaerobic digestion step, the organic loading rate was increased progressively up to 3.3gCODL(-1)d(-1). The upflow anaerobic fixed bed reactor showed a great performance in terms of COD removal efficiency and biogas production. During precipitation experiments, lime dose was optimized to obtain the maximum reduction of conductivity to prevent the fouling of RO membranes. This process was compared to a second one in which the AD step was eliminated. Both treatment plans achieved similar removal efficiencies. However, AD step significantly improved the process by reducing the needed lime dose by 50%. It has also increased MF and RO fluxes by 35% and 40% at a steady state, respectively. The dominant fouling mechanism was cake layer formation during both MF tests. This process seems to be a promising approach for the treatment of LFL and its industrial application should be further investigated.

Trace level monitoring of Cu(II) ion using CuS particles based membrane electrochemical sensor

Cu(II) monitoring is a matter of great interest to researchers due to its toxicity and adverse environmental effects. Among different methods for detecting Cu(II), ion-selective electrode (ISE) is more advantageous as they are low-cost, easy to fabricate, and highly selective. Here, we report a simple, inexpensive, and reproducible procedure for the fabrication of Cu(II) ion-selective electrodes using CuS particles and polyvinyl chloride (PVC) as a matrix. CuS particles, obtained by chemical precipitation, were characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, ultraviolet-visible spectroscopy (UV-Vis), scanning electron microscopy (SEM), and energy-dispersive X-Ray spectroscopy (EDX). Optimization of the membrane compositions was done to get a well-behaved sensor by varying amounts of CuS, PVC, and acetophenone (AP). A membrane composition of 0.4 g CuS, 0.5 g PVC, and 1.0 mL AP in 5.0 mL tetrahydrofuran (THF) gave a Nernstian slope of 27.31 mV per decade change of Cu(II) ion over a wide range of concentration down to 64 ppb (1 × 10⁻⁶ M). The sensor gave a fast response time of 25 s, and it indicated the endpoint in a potentiometric titration of Cu(II) with standard EDTA solution. A pH-independent potential response was obtained in the pH 4.0–6.0.