Ion exchange extraction of heavy metals from wastewater sludges

A novel chitosan-glutamic acid membrane for multi-pollutant amputation: Investigational and RSM optimizations

The novel glutamic acid crosslinked chitosan membrane (CsG) was fabricated and tested for its adsorption capabilities for the removal of multiple pollutants like Cr (VI), cyanide, fluoride and diclofenac sodium from wastewater. This fabricated CsG membrane was characterized by various techniques like FT-IR, SEM, EDX and XRD, BET to assess its structural, compositional and morphological properties. The working parameters studied by batch experiments were solution pH, CsG dose, contact time, pollutant concentration and solution temperature. The CsG membrane exhibited maximum adsorption capacity of 410.7 mg/g, 310.2 mg/g, 14.3 mg/g, 132.7 mg/g for Cr (VI), cyanide, fluoride and diclofenac respectively. The validation of the operational parameters was performed by Response Surface Methodology (RSM). The experimental data fitted well with Langmuir isotherm model and followed pseudo second order kinetics for all the four targeted contaminants. The spontaneity of the process was checked by thermodynamics studies. The high partition coefficients of 7669 L/kg Cr(VI), 23,309 L/kg (CN-), 649 L/kg (F-) and 2613 L/kg (DFC) are the indicators of excellent attractive interaction between CsG membrane and target toxicants. The CsG membrane showed efficient regenerative adsorption properties up to 5 adsorption-desorption cycles. Overall, the developed novel CsG membrane promised as an effective material for the removal of multiple number of pollutants from water.

Functionalization of Shorea faguetiana biochar using Fe2O3 nanoparticles and MXene for rapid removal of methyl blue and lead from both single and binary systems

The synthesis of polymeric magnetic composites is a promising strategy for the rapid and efficient treatment of wastewater. Lead and methyl blue are extremely hazardous to living organisms. The sorption of Pb2+ and the dye methyl blue (MB) by biochar is an ecologically sustainable method to remediate this type of water pollution. We functionalized Shorea faguetiana biochar with Fe2O3 and MXene, resulting in Fe2O3/BC/MXene composites with an efficient, rapid, and selective adsorption performance. Based on X-ray photoelectron and Fourier transform infrared spectrometry, we found that the Fe2O3/BC/MXene composites had an increased number of surface functional groups (F-, C[double bond, length as m-dash]O, CN, NH, and OH-) compared with the original biochar. The batch sorption findings showed that the maximum sorption capacities for Pb2+ and MB at 293 K were 882.76 and 758.03 mg g-1, respectively. The sorption phenomena obeyed a pseudo-second-order (R2 = 1) model and the Langmuir isotherm. There was no competition between MB and Pb2+ in binary solutions, indicating that MB and Pb2+ did not influence each other as a result of their different adsorption mechanisms (electrostatic interaction for Pb2+ and hydrogen bonding for MB). This illustrates monolayer sorption on the Fe2O3/BC/MXene composite governed by chemical adsorption. Thermodynamic investigations indicated that the sorption process was spontaneous and exothermic at 293-313 K, suggesting that it is feasible for practical applications. Fe2O3/BC/MXene can selectively adsorb Pb2+ ions and MB from wastewater containing multiple interfering metal ions. The sorption capacities were still high after five reusability experiments. This work provides a novel Fe2O3/BC/MXene composite for the rapid and efficient removal of Pb2+ and MB.

Pollutants in aquatic system: a frontier perspective of emerging threat and strategies to solve the crisis for safe drinking water

Water is an indispensable natural resource and is the most vital substance for the existence of life on earth. However, due to anthropogenic activities, it is being polluted at an alarming rate which has led to serious concern about water shortage across the world. Moreover, toxic contaminants released into water bodies from various industrial and domestic activities negatively affect aquatic and terrestrial organisms and cause serious diseases such as cancer, renal problems, gastroenteritis, diarrhea, and nausea in humans. Therefore, water treatments that can eliminate toxins are very crucial. Unfortunately, pollution treatment remains a difficulty when four broad considerations are taken into account: effectiveness, reusability, environmental friendliness, and affordability. In this situation, protecting water from contamination or creating affordable remedial techniques has become a serious issue. Although traditional wastewater treatment technologies have existed since antiquity, they are both expensive and inefficient. Nowadays, advanced sustainable technical approaches are being created to replace traditional wastewater treatment processes. The present study reviews the sources, toxicity, and possible remediation techniques of the water contaminants.

Water Quality Degradation Due to Heavy Metal Contamination: Health Impacts and Eco-Friendly Approaches for Heavy Metal Remediation

Water quality depends on its physicochemical and biological parameters. Changes in parameters such as pH, temperature, and essential and non-essential trace metals in water can render it unfit for human use. Moreover, the characteristics of the local environment, geological processes, geochemistry, and hydrological properties of water sources also affect water quality. Generally, groundwater is utilized for drinking purposes all over the globe. The surface is also utilized for human use and industrial purposes. There are several natural and anthropogenic activities responsible for the heavy metal contamination of water. Industrial sources, including coal washery, steel industry, food processing industry, plastic processing, metallic work, leather tanning, etc., are responsible for heavy metal contamination in water. Domestic and agricultural waste is also responsible for hazardous metallic contamination in water. Contaminated water with heavy metal ions like Cr (VI), Cd (II), Pb (II), As (V and III), Hg (II), Ni (II), and Cu (II) is responsible for several health issues in humans, like liver failure, kidney damage, gastric and skin cancer, mental disorders and harmful effects on the reproductive system. Hence, the evaluation of heavy metal contamination in water and its removal is needed. There are several physicochemical methods that are available for the removal of heavy metals from water, but these methods are expensive and generate large amounts of secondary pollutants. Biological methods are considered cost-effective and eco-friendly methods for the remediation of metallic contaminants from water. In this review, we focused on water contamination with toxic heavy metals and their toxicity and eco-friendly bioremediation approaches.

Review of Clay-Based Nanocomposites as Adsorbents for the Removal of Heavy Metals

Due to rapid industrialization, urbanization, and surge in modern human activities, water contamination is a major threat to humanity globally. Contaminants ranging from organic compounds, dyes, to inorganic heavy metals have been of major concern in recent years. This necessitates the development of affordable water remediation technologies to improve water quality. There is a growing interest in nanotechnology recently because of its application in eco-friendly, cost-effective, and durable material production. This study presents a review of recent nanocomposite technologies based on clay, applied in the removal of heavy metals from wastewater, and highlights the shortcomings of existing methods. Recently published reports, articles, and papers on clay-based nanocomposites for the removal of heavy metals have been reviewed. Currently, the most common methods utilized in the removal of heavy metals are reverse osmosis, electrodialysis, ion exchange, and activated carbon. These methods, however, suffer major shortcomings such as inefficiency when trace amounts of contaminant are involved, uneconomical costs of operation and maintenance, and production of contaminated sludge. The abundance of clay on the Earth’s surface and the ease of modification to improve adsorption capabilities have made it a viable candidate for the synthesis of nanocomposites. Organoclay nanocomposites such as polyacrylamide-bentonite, polyaniline-montmorillonite, and β-cyclodextrin-bentonite have been synthesized for the selective removal of various heavy metals such as Cu2+, Co2+, among others. Bacterial clay nanocomposites such as E. coli kaolinite nanocomposites have also been successfully synthesized and applied in the removal of heavy metals. Low-cost nanocomposites of clay using biopolymers like chitosan and cellulose are especially in demand due to the cumulative abundance of these materials in the environment. A comparative analysis of different synthetic processes to efficiently remove heavy metal contaminants with clay-based nanocomposite adsorbents is made.

Gas Hydrate-Based Heavy Metal Ion Removal from Industrial Wastewater: A Review

Innovating methods for treating industrial wastewater containing heavy metals frequently incorporate toxicity-reduction technologies to keep up with regulatory requirements. This article reviews the latest advances, benefits, opportunities and drawbacks of several heavy metal removal treatment systems for industrial wastewater in detail. The conventional physicochemical techniques used in heavy metal removal processes with their advantages and limitations are evaluated. A particular focus is given to innovative gas hydrate-based separation of heavy metals from industrial effluent with their comparison, advantages and limitations in the direction of commercialization as well as prospective remedies. Clathrate hydrate-based removal is a potential technology for the treatment of metal-contaminated wastewater. In this work, a complete assessment of the literature is addressed based on removal efficiency, enrichment factor and water recovery, utilizing the gas hydrate approach. It is shown that gas hydrate-based treatment technology may be the way of the future for water management purposes, as the industrial treated water may be utilized for process industries, watering, irrigation and be safe to drink.

A review on recent trends in the removal of emerging contaminants from aquatic environment using low-cost adsorbents

Emerging contaminants (ECs), a class of contaminants with low concentrations but significant harm, have received a lot of attention in recent times. ECs comprises of various chemicals that enter the environment every day. In today's modern lifestyle, we use many chemical-based products. These persist in wastewater and ultimately enter the water bodies, causing serious problems to the human and aquatic ecosystem. This is because the conventional wastewater treatment methods are inefficient in identifying and removing such contaminants. Aiming for a long-term, effective solution to this issue, Adsorption was proposed. Although several adsorbents are already present in the market, which have proved beneficial in removing such ECs, not all are affordable. This article reviews replacing costly adsorbents with agriculture-based biomass that are abundant, inexpensive, and biodegradable and possess excellent adsorption capacity. The objectives of this article is to look at adsorption as a viable treatment option for emerging pollutants, as well as sophisticated and cost-effective emerging contaminants treatment options.

Adsorption of cupric, cadmium and cobalt ions from the aqueous stream using the composite of iron(II,III) oxide and zeolitic imidazole framework-8

In recent research, the composite of Fe₃O₄ and metal-organic frameworks have shown great potential in removing potentially toxic metals from water. We conducted the adsorption studies of potentially toxic metal ions (Cu²⁺, Co²⁺ and Cd²⁺) using the composite of Fe₃O₄ and zeolitic imidazole framework-8 (Fe₃O₄@ZIF-8) for the first time. The solvothermal technique was used to synthesize the Fe₃O₄. The magnetic ZIF-8 offers high thermal stability, greater adsorption surface, good removability, and high chemical and thermal stability. Characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) were used to characterize the synthesized samples. The SEM and XRD results revealed the high purity and structural integrity of ZIF-8 crystallites. To remove potentially toxic metals (Cu²⁺, Co²⁺ and Cd²⁺), the influence of adsorbent dosage, contact time, pH, and adsorbate concentration on the adsorption performance of Fe₃O₄@ZIF-8 was investigated. The Langmuir isotherm accurately represented the adsorption processes, with absorption magnitudes of Fe₃O₄@ZIF-8 determined to be 46.82 mg g^-1, 71.29 mg g^-1 and 54.49 mg g^-1 for Cu²⁺, Co²⁺ and Cd²⁺, respectively. According to the adsorption mechanism analysis, the primary Cu²⁺, Co²⁺ and Cd²⁺ removal methods of Fe₃O₄@ZIF-8 were ion exchange and coordination bonds. The uptake capacity of Cu²⁺, Co²⁺ and Cd²⁺ solution by Fe₃O₄@ZIF-8 were not significantly affected by the presence of counter ions. The material exhibited superior regenerative properties for Cu²⁺, Co²⁺ and Cd²⁺ ions from water for up to three cycles. This study concluded that the Fe₃O₄@ZIF-8 could be a viable candidate for eliminating potentially toxic metals (Cu²⁺, Co²⁺ and Cd²⁺).

A Comprehensive Review for Groundwater Contamination and Remediation: Occurrence, Migration and Adsorption Modelling

The provision of safe water for people is a human right; historically, a major number of people depend on groundwater as a source of water for their needs, such as agricultural, industrial or human activities. Water resources have recently been affected by organic and/or inorganic contaminants as a result of population growth and increased anthropogenic activity, soil leaching and pollution. Water resource remediation has become a serious environmental concern, since it has a direct impact on many aspects of people's lives. For decades, the pump-and-treat method has been considered the predominant treatment process for the remediation of contaminated groundwater with organic and inorganic contaminants. On the other side, this technique missed sustainability and the new concept of using renewable energy. Permeable reactive barriers (PRBs) have been implemented as an alternative to conventional pump-and-treat systems for remediating polluted groundwater because of their effectiveness and ease of implementation. In this paper, a review of the importance of groundwater, contamination and biological, physical as well as chemical remediation techniques have been discussed. In this review, the principles of the permeable reactive barrier's use as a remediation technique have been introduced along with commonly used reactive materials and the recent applications of the permeable reactive barrier in the remediation of different contaminants, such as heavy metals, chlorinated solvents and pesticides. This paper also discusses the characteristics of reactive media and contaminants' uptake mechanisms. Finally, remediation isotherms, the breakthrough curves and kinetic sorption models are also being presented. It has been found that groundwater could be contaminated by different pollutants and must be remediated to fit human, agricultural and industrial needs. The PRB technique is an efficient treatment process that is an inexpensive alternative for the pump-and-treat procedure and represents a promising technique to treat groundwater pollution.

Marble Waste Sludges as Effective Nanomaterials for Cu (II) Adsorption in Aqueous Media

This study evaluated the waste generated by a Spanish marble-producing company as adsorbent for the removal of copper (Cu [II]) from aqueous media. Six marble waste sludge samples were studied, and the following operational parameters were analyzed in discontinuous regime, including pollutant concentration, pH, temperature, nature of aqueous medium, and ionic strength. The applicability of the adsorbent material was assessed with experiments in both continuous and discontinuous regimes under close-to-real-life conditions. A pseudo-second order model yielded a better fit to the kinetic data. Application of the intraparticle diffusion model revealed two well-differentiated adsorption stages, in which the external material transfer is negligible and intraparticle diffusion is the controlling stage. The equilibrium study was better fitted to a Freundlich-type isotherm, predicting elevated maximum adsorption values (22.7 mg g⁻¹) at a relatively low initial Cu (II) concentration (25 ppm), yielding a highly favorable chemisorption process (n >> 1). X-ray fluorescence study identified calcite (CaCO₃) as the main component of marble waste sludges. According to X-ray diffraction analysis, Cu (II) ion adsorption occurred by intercalation of the metallic cation between CaCO₃ layers and by the formation of surface complexes such as CaCO₃ and Cu₂(CO₃)(OH)₂. Cu (II) was more effectively removed at medium pH, lower temperature, and lower ionic strength of the aqueous medium. The salinity and dissolved organic matter in surface, ground-, and waste-waters negatively affected the Cu (II) removal process in both continuous and discontinuous regimes by competing for active adsorption sites. These findings demonstrate the applicability and effectiveness of marble-derived waste sludges as low-cost and readily available adsorbents for the treatment of waters polluted by Cu (II) under close-to-real-life conditions.

Heavy metal removal with magnetic coffee grain

The presence of heavy metals in environmental waters having an important place in the industrial waste is a major threat to viability. Heavy metals are transported to humans through the ecological cycle, damaging many tissues and organs. In recent years, agricultural and food waste can be used to remove heavy metals. At the present study, magnetically modified coffee grains which are alternative to conventional particle systems were prepared and heavy metal removal performances were investigated. The coffee grains used were magnetically modified by contact with water-based magnetic fluid. Magnetically modified coffee grains were characterized by scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analysis and electron spin resonance (ESR). Adsorption studies are made with four different heavy metal ions, namely Cu(II), Pb(II), Cd(II) and Zn(II). Adsorption isotherms were determined and heavy metal removal performance of magnetic coffee grains were investigated from synthetic waste water.

Preparation of terpyridine-functionalized paramagnetic nickel-zinc ferrite microspheres for adsorbing Pb(ii), Hg(ii), and Cd(ii) from water

A paramagnetic microsphere combining special functional groups may be one kind of the most promising methods for heavy metal adsorption, due to their specific separation capacity, selectivity and reusability. In this study, a novel terpyridine-based magnetic solid-phase adsorbent (TPY-M) is successfully constructed. The paramagnetic Ni_0.25Zn_0.75Fe₂O₄ microsphere (M) is synthesized and applied as a magnetic core, and is functionalized by terpyridine (TPY) groups. The naked magnetic core and TPY-M are characterized by vibration sample magnetism (VSM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and Fourier-transform infrared spectroscopy (FT-IR) techniques. Some parameters of the TPY-M samples are evaluated as potential adsorbents for heavy metal ions in various aqueous solutions. The adsorption capacities of TPY-M for Pb(ii), Hg(ii) and Cd(ii) were 64.75 mg g⁻¹, 33.94 mg g⁻¹ and 24.64 mg g⁻¹ under given conditions, respectively. In the case of Pb(ii), some influencing factors on the TPY-M adsorbent are investigated, including the pH, adsorption time, and ion concentrations. The adsorbent can be easily regenerated by HCl solution after use. The adsorbent revealed good adsorption performance in some real water samples.

A paramagnetic microsphere combining special functional groups may be one kind of the most promising methods for heavy metal adsorption, due to their specific separation capacity, selectivity and reusability.

Bio-removal of Pb, Cu, and Ni from solutions as nano-carbonates using a plant-derived urease enzyme-urea mixture

This study focuses on utilizing a plant-derived urease enzyme (PDUE)-urea mixture to remove heavy metals from water as constituents of nano-carbonate minerals. The bio-removal process was conducted by individually mixing PbCl₂, CuCl₂, and NiCl₂ solutions with a PDUE-urea mixture, followed by incubation for 24 h at 23 ± 2 °C. The preliminary results revealed that the proposed method exhibited high Pb removal efficiency (˃ 99%) in a short time (8 h); meanwhile, moderate Cu and Ni removal efficiencies (67.91% and 58.49%, respectively) were obtained at the same incubation time. The concentration of heavy metals (50-200 mM) had an insignificant effect on the bio-removal rate, indicating that the PDUE-urea mixture is highly effective for the removal of heavy metals at different concentrations. The bio-removal process involved the transformation of soluble heavy metals into insoluble carbonate materials. A spherically shaped nano-cerussite (4-15 nm), a malachite hexahydrate nanosheet (thickness 8 nm), and an ultrafine micro-hellyerite (thickness 0.3 μm) were the main minerals produced by the Pb, Cu, and Ni bio-removal processes, respectively. As a beneficial application, nano-cerussite was used as an additive in an alkali-activated slag/ceramic waste-based geopolymeric coating. A preliminary study proved that increasing the nano-cerussite content enhanced the resistance of the geopolymeric coating to sulfur-oxidizing bacteria, which is detrimental to normal concrete, particularly in sewer systems.

New effective 3-aminopropyltrimethoxysilane functionalized magnetic sporopollenin-based silica coated graphene oxide adsorbent for removal of Pb(II) from aqueous environment

A new effective adsorbent, 3-aminopropyltrimethoxysilane functionalized magnetic sporopollenin (MSp@SiO₂NH₂) based silica-coated graphene oxide (GO), (GO@SiO₂-MSp@SiO₂NH₂) was successfully synthesized and applied for the first time in the removal of hazardous Pb(II) ions from aqueous solution. The properties of the composite were characterized using Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX) and vibrating-sample magnetometery (VSM). Evaluation of GO@SiO₂-MSp@SiO₂NH₂ adsorption performance at optimum conditions revealed that the adsorbent has a maximum adsorption capacity of 323.5 mg/g for Pb(II) using 50-200 mg/L initial Pb(II) ions concentrations. Initial and final concentrations of Pb(II) ions in aqueous solution were analyzed using graphite furnace atomic absorption spectroscopy (GF-ASS). The adsorption behavior of Pb(II) ions onto GO@SiO₂-MSp@SiO₂NH₂ was studied using Langmuir, Freundlich and Temkin isotherms models. The values of coefficient of determination showed that the adsorption best fitted the Langmuir model (R² = 0.9994). Kinetic studies suggested that the adsorption of Pb(II) ion followed a pseudo-second-order rate model (R² = 1.00) and thermodynamic studies revealed that the adsorption process is endothermic and spontaneous. The effect of co-existing ions on Pb(II) ion adsorption were also studied and found to have considerable effects only at higher matrix concentration. The adsorbent can be reused up to ten times and retain its good adsorption capacity. In addition, GO@SiO₂-MSp@SiO₂NH₂ showed great potential for Pb(II)removal from industrial wastewater samples.

Carbon microspheres derived from walnut shell: Rapid and remarkable uptake of heavy metal ions, molecular computational study and surface modeling

Carbon microspheres were synthesized under nitrogen flow from walnut shells (WS) and then used as an adsorbent for the removal of Pb (II), Cu(II), Cr(III) and Cd(II) metals. The prepared material was characterized using X-ray photoelectron spectroscopy, scanning electron microscopy, Brounauer-emett-teller surface, Fourier transform infrared and Raman spectroscopy. SEM micrographs showed homogenous sphere-like structure with an average diameter of 4.55 μm. The prepared carbon microspheres exhibit selective and rapid removal of hazardous metals from synthetic water samples. The effects of solution pH, contact time and temperatures on the removal process have been systematically investigated. The material used in this present work present the highest adsorption capacities ever reported for Cr(III), Pb(II), Cd(II) and Cu(II) at an optimum pH of 5, the adsorption capacities reached 792, 638, 574 and 345 mg g^-1 for Cr(III), Pb(II), Cd(II) and Cu(II), respectively. Density functional calculations (DFT) showed an agreement with the adsorption process results, Cr(III) had stronger binding ability to the OH and/or COOH functional groups followed by Pb, Cu and Cd. The adsorption mechanism was discussed based on the experimental and theoretical results. Finally, the response surface methodology was used to optimize the adsorption conditions.

A facile synthesis of hydroxyapatite for effective removal strontium ion

Hydroxyapatite (HA) with perforated porous structure was successfully synthesized using shell powder as the raw material by double interfacial diffusion method. The structure of obtained products was examined by X-ray diffraction, Fourier transform infrared spectrograph, field-emission scanning electron microscopy, transmission electron microscopy, particle size, thermogravimetry and nitrogen adsorption-desorption analysis etc. Results indicate that the perforated porous structure is composed of nanosheets and has high specific surface area (up to 188.5 m² g^-1). Thus, investigation of adsorbing Sr²⁺ in solution was further examined by discussing factors such as initial pH, ion strength, adsorbent dosage, contact time, initial Sr²⁺ concentration and temperature. The kinetics and equilibrium adsorption data followed the nonlinear pseudo-second-order kinetic and Liu isotherm models. The maximum removal (%) was up to 98.94% at 313.15 K, and the adsorption process of Sr²⁺ was endothermic, feasible, and spontaneous in nature as studied via thermodynamic analysis (ΔG° < 0, ΔH° > 0, and ΔS° > 0). A possible adsorption mechanism was proposed. Meanwhile, leaching and desorption experiments was used to evaluate recycling capacity. All the outcomes effectively reveal that the synthesized HA shows great potential in removing Sr²⁺ from nuclear effluents.

Dopamine crosslinked graphene oxide membrane for simultaneous removal of organic pollutants and trace heavy metals from aqueous solution

A graphene oxide-polydopamine-(β-cyclodextrin) (GPC) ultrafiltration membrane was fabricated by using the method of drop-coating combined with vacuum filtration. The prepared GPC membrane was characterized with FTIR and XPS spectrophotometry and evaluated for its performances for the rejection of organic molecules (methylene blue) and adsorption of trace heavy metals (Pb²⁺) from aqueous solutions. The membrane exhibited an excellent rejection coefficient of 99.2% for methylene blue and the permeation flux was 12 L m^-2 h^-1 at 0.1 bar. The membrane also exhibited fast adsorption kinetics for Pb²⁺ and the adsorption capacity was 101.6 mg g^-1 at a solution pH of 6. The performance of the membrane could almost be completely recovered after a simple clean and regeneration process. These results indicate that the GPC membrane has potential applications in treatment of complex industrial wastewater streams.

Characterization, Recovery Opportunities, and Valuation of Metals in Municipal Sludges from U.S. Wastewater Treatment Plants Nationwide

U.S. sewage sludges were analyzed for 58 regulated and nonregulated elements by ICP-MS and electron microscopy to explore opportunities for removal and recovery. Sludge/water distribution coefficients (KD, L/kg dry weight) spanned 5 orders of magnitude, indicating significant metal accumulation in biosolids. Rare-earth elements and minor metals (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) detected in sludges showed enrichment factors (EFs) near unity, suggesting dust or soils as likely dominant sources. In contrast, most platinum group elements (i.e., Ru, Rh, Pd, Pt) showed high EF and KD values, indicating anthropogenic sources. Numerous metallic and metal oxide colloids (<100-500 nm diameter) were detected; the morphology of abundant aggregates of primary particles measuring <100 nm provided clues to their origin. For a community of 1 million people, metals in biosolids were valued at up to US$13 million annually. A model incorporating a parameter (KD × EF × $Value) to capture the relative potential for economic value from biosolids revealed the identity of the 13 most lucrative elements (Ag, Cu, Au, P, Fe, Pd, Mn, Zn, Ir, Al, Cd, Ti, Ga, and Cr) with a combined value of US $280/ton of sludge.

Determination of iron in drinking water after its flotation concentration by two new dithiocarbamate collectors

Two new methods for the determination of iron by atomic absorption spectrometry (AAS) are proposed for drinking water. The determination was made after flotation concentration of Fe by using of two new flotation collectors: lead(II) heptyldithiocarbamate, Pb(HpDTC)2 and cobalt(III) heptyldithiocarbamate Co(HpDTC)3. All important parameters for the two proposed procedures were optimised (pH, mass of Pb, mass of Co, amount of HpDTC(-), type of surfactant, induction time, etc.). Flotation recovery (R) of Fe was very high (from 94.4 to 104.4%) for the two proposed procedures. The detection limit of the methods was 2.17 μg L(-1) for Pb(HpDTC)2 and 2.39 μg L(-1) for Co(HpDTC)3, respectively. The proposed methods have been applied for the analysis of five samples of drinking water. The acquired AAS results for Fe by both new methods were compared with those obtained by inductively coupled plasma-atomic emission spectrometry (AES-ICP). It is shown that they are in good agreement. The results are also confirmed by the method of standard additions.

Control of metal toxicity, effluent COD and regeneration of gel beads by immobilized sulfate-reducing bacteria

Over the last few decades, the use of sulfate-reducing bacteria (SRB) in the treatment of heavy-metal containing wastewaters including acid mine drainage has become a topic of scientific and commercial interest. However, technical difficulties such as the sensitivity of SRB to toxic metals and high effluent COD limit the widespread use of SRB in high heavy-metal containing wastewater. The aim of this study was to clarify the reasons why the immobilized SRB sludge with inner cohesive carbon source (ISIS) process can endure high metal toxicity and decrease effluent COD. The ISIS process can physically set apart SRB and free the system of external influences such as the surrounding toxic metallic ions, as well as form inner carbon sources to avoid high effluent COD. Metal toxicity and bead durability are the two major factors which influence the regeneration and reuse of gel beads. Reuse of suspended SRB sludge and beads crosslinked with boric acid were unsuccessful due to metal toxicity and agglomeration of beads, respectively. However, beads crosslinked with ammonium sulfate prevented agglomeration of beads allowing successful bead regeneration and reuse. The result of four cyclic trials showed that over 99% of zinc was removed in each trial using these beads.

Removal of arsenic as arsenite from groundwater/wastewater as stable metal ferrite

This paper summarizes the results of the study on removal of arsenite ions in liquid medium at an ambient temperature by ferritization and its application in wastewater/groundwater treatment. X-ray Diffractometry (XRD), thermal analysis and dc resistivity measurement have characterized the ferruginous material (Arsenic ferrite) precipitated by both the aeration and ageing procedures. The laboratory scale experiments conducted with synthetic solution of arsenite at different concentration suggest that the arsenite ions can be effectively retrieved > 99%. The recovered arsenic ferrites may find commercial application as semiconductors, catalysts, metal scavengers, etc.