Adsorption of heavy metals onto sewage sludge-derived materials

A critical review on emerging industrial applications of chars from thermal treatment of biosolids

Thermochemical treatment is rapidly emerging as an alternative method for the management of stabilised sewage sludges (biosolids) to effectively reduce waste volume, degrade contaminants, and generate valuable products, particularly biochar and hydrochar. Biosolids-derived char has a relatively high concentration of heavy metals compared with agricultural chars but is still applied to land due to its beneficial properties and ability to retain metals. However, non-agricultural applications can provide additional economic and environmental benefits, promote sustainability and support a circular economy. This review identifies extensive non-agricultural opportunity for biosolids biochar, including adsorption, catalysis, energy storage systems, biological process enhancement, and as additives for rubber compounding and construction. Biosolids chars have received limited attention vs agricultural char, and we draw on both areas of literature, as well as evaluating differences between agricultural and biosolids chars. A key opportunity for biosolids biochar in comparison with other materials and agricultural chars is its sustainable and low-cost nature, relatively high metals content, improving catalyst properties, and ability to modify in various stages to tune it to specific applications. The specific opportunities for hydrochar have only received limited attention. Research needs to include better understanding of the benefits and limitations for specific applications, as well as adjacent drivers, including society, regulation, and market and economics.

Application of common industrial solid waste in water treatment: a review

Industrial solid waste has a wide range of impacts, and it is directly or indirectly related to land, atmosphere, water, and other resources. Industrial solid waste has a large amount of production, complex and diverse components and contains a variety of harmful substances. However, as industrial by-products, it also has a lot of available value. Industrial solid waste has been continuously studied in water treatment due to its special composition and porous and loose structure. It is known that there are few reviews of various industrial solid wastes in the field of wastewater treatment, and most of them only discuss single industrial solid waste. This paper aims to sort out the different studies on various solid wastes such as fly ash, red mud, wastewater sludge, blast furnace slag and steel slag in dyeing, heavy metal, and phosphorus-containing wastewater. Based on the modification of industrial solid waste and the preparation of composite materials, adsorbents, coagulants, catalysts, filtration membranes, geological polymers, and other materials with high adsorption properties for pollutants in wastewater were formed; the prospect and development of these materials in the field of wastewater were discussed, which provides some ideas for the mutual balance of environment and society. Meanwhile, some limitations of solid waste applications for wastewater treatment have been put forward, such as a lack of further researches about environment-friendly modification methods, application costs, the heavy metal leaching, and toxicity assessment of industrial solid waste.

Cu(II) and Cd(II) Removal Efficiency of Microbially Redox-Activated Magnetite Nanoparticles

Heavy metal pollutants in the environment are of global concern due to their risk of contaminating drinking water and food supplies. Removal of these metals can be achieved by adsorption to mixed-valent magnetite nanoparticles (MNPs) due to their high surface area, reactivity, and ability for magnetic recovery. The adsorption capacity and overall efficiency of MNPs are influenced by redox state as well as surface charge, the latter of which is directly related to solution pH. However, the influence of microbial redox cycling of iron (Fe) in magnetite alongside the change of pH on the metal adsorption process by MNPs remains an open question. Here we investigated adsorption of Cd2+ and Cu2+ by MNPs at different pH values that were modified by microbial Fe(II) oxidation or Fe(III) reduction. We found that the maximum adsorption capacity increased with pH for Cd2+ from 256 μmol/g Fe at pH 5.0 to 478 μmol/g Fe at pH 7.3 and for Cu2+ from 229 μmol/g Fe at pH 5.0 to 274 μmol/g Fe at pH 5.5. Microbially reduced MNPs exhibited the greatest adsorption for both Cu2+ and Cd2+ (632 μmol/g Fe at pH 7.3 for Cd2+ and 530 μmol/g Fe at pH 5.5 for Cu2+). Magnetite oxidation also enhanced adsorption of Cu2+ but inhibited Cd2+. Our results show that microbial modification of MNPs has an important impact on the (im-)mobilization of aqueous contaminations like Cu2+ and Cd2+ and that a change in stoichiometry of the MNPs can have a greater influence than a change of pH.

Subsurface flow constructed wetlands for treating of simulated cadmium ions-wastewater with presence of Canna indica and Typha domingensis

The presence of toxic cadmium ions in the wastewater resulted from industrial sector forms the critical issue for public health and ecosystem. This study determines the ability of four vertical subsurface flow constructed wetlands units in the treatment of simulated wastewater laden with cadmium ions. This was achieved through using sewage sludge byproduct as alternative for the traditional sand to be substrate for aforementioned units in order to satisfy the sustainable concepts; however, Canna indica and Typha domingensis can apply to enhance the cadmium removal. The performance of constructed wetlands has been evaluated through monitoring of the pH, dissolved oxygen (DO), temperature, and concentrations of cadmium (Cd) in the effluents for retention time (0.5-120 h) and metal concentration (5-40 mg/L). The results demonstrated that the Cd removal percentage was exceeded 82% beyond 5 days and for concentration of 5 mg/L; however, this percentage was decreased with smaller retention time and higher metal concentration. The Grau second-order kinetic model accurately simulated the measurements of effluent Cd concentrations as a function of retention times. The FT-IR analysis indicated the existence of certain functional groups capable of enhancing the Cd removal. The treated wastewater's pH, DO, temperature, total dissolved solids (TDS), and electrical conductivity (EC) all meet the requirements for irrigation water.

Citrus fruit residues as alternative precursors to developing H2O and CO2 activated carbons and its application for Cu(II) adsorption

Due to its toxicity, the presence of Cu(II) ions released in aquatic environments presents a serious threat to the environment and human health. In search of sustainable and low-cost alternatives, there are citrus fruit residues, which are generated in large quantities by the juice industries and can be used to produce activated carbons. Therefore, the physical route was investigated for producing activated carbons to reuse citrus wastes. In this work, eight activated carbons were developed, varying the precursor (orange peel-OP, mandarine peel-MP, rangpur lime peel-RLP, and sweet lime peel-SLP) and the activating agent (CO₂ and H₂O) to remove Cu(II) ions of the aqueous medium. Results revealed promising activated carbons with a micro-mesoporous structure, a specific surface area of around 400 m² g^-1, and a pore volume of around 0.25 cm³ g^-1. In addition, Cu (II) adsorption was favored at pH 5.5. The kinetic study showed that the equilibrium was reached within 60 min removing about 80% of Cu(II) ions. The Sips model was the most suitable for the equilibrium data, providing maximum adsorption capacities (qmS) values of 69.69, 70.27, 88.04, 67.83 mg g^-1 for activated carbons (AC-CO₂) from OP, MP, RLP, and SLP, respectively. The thermodynamic behavior showed that the adsorption process of Cu(II) ions was spontaneous, favorable, and endothermic. It was suggested that the mechanism was controlled by surface complexation and Cu²⁺-π interaction. Desorption was possible with an HCl solution (0.5 mol L^-1). From the results obtained in this work, it is possible to infer that citrus residues could be successfully converted into efficient adsorbents to remove Cu(II) ions from aqueous solutions.

Simultaneous removal of multiple heavy metals using single chamber microbial electrolysis cells with biocathode in the micro-aerobic environment

The simultaneous and efficient removal of various heavy metals from wastewater to satisfy the requirements of zero discharge has been a research hotspot and difficult point. In the laboratory scale (0.5 L), the biocathode microbial electrolytic cells (BCMECs) were constructed with the pre-screened heavy metal-tolerant electroactive bacterial, mainly of the Sphingomonas, Azospira and Cupriavidus. The BCMECs system showed a more satisfactory removal effect for multiple heavy metals and organic pollutants. At the auxiliary voltage of 0.9 V and initial concentration of 20 mg L^-1, the removal efficiency of Cu, Pb, Zn, Cd and COD were 98.76 ± 0.32%, 98.01 ± 0.76%, 73.58 ± 4.83%, 84.39 ± 5.95%, 77.55 ± 1.51%, respectively. It was found by various characterization techniques (CV, EIS, XPS et al.) that the constructed biocathode has the function of electrocatalytic reduction of heavy metal ions in a micro-aerobic, film-free environment. The positive shift (0.030-0.229 V) of the initial potential for heavy metal reduction and the absence of a significant increase (＜ 10 Ω) in the interfacial resistance indicated a reduction in the total free energy of the reduction reaction, which promotes the reaction and improves the efficiency of heavy metal removal. Bacterial community analysis revealed that the Proteobacteria has been dominant in different heavy metal environments. With the increase of heavy metal concentration, Sphingomonas, Azospira and Cupriavidus showed stronger tolerance and became the dominant genus. This study emphasized the important performance of biocathodes and the effective treatment of heavy metal wastewaters by BCMECs and provided a reasonable way for industrial and mining enterprises to innovate the water treatment process.

Kill two birds with one stone: The management of hazardous waste and the preparation of efficient adsorbents for Pb(II) were realized by the pyrolysis of penicillin mycelial dreg

The penicillin industry produces a large amount of penicillin mycelial dreg (PMD), potentially causing severe environmental problems without proper treatment and disposal. To achieve the goals of PMD management, the present work explored the potential of PMD as a novel feedstock to produce biochar with very high adsorption performance. PMD was pyrolyzed at 400-800 °C to prepare biochars (PMD-BCs), and the physical and chemical properties were characterized using various methods. The adsorption capacities of Pb²⁺ on PMD-BC400, PMD-BC600, and PMD-BC800 were 37.04, 62.89, and 107.53 mg/g, respectively, at a temperature of 25 °C and pH of 5.0. The adsorption process of Pb²⁺ on PMD-BCs can be well described by the Langmuir model and pseudo-second-order model. Mineral precipitation, ion exchange, functional group complexation and Pb²⁺-π interaction were involved in the adsorption of Pb²⁺ on PMD-BCs. Moreover, mineral precipitation and ion exchange dominated Pb²⁺ sorption on PMD-BCs (84.71-92.73%). This study indicates the transition of PMD to biochar for Pb²⁺ adsorption is a promising method for PMD utilization.

Removal of heavy metals from sewage sludge by chemical leaching with biodegradable chelator methyl glycine diacetic acid

The heavy metals (HMs) contained in sewage sludge are some of the largest obstacles that hamper the usage of sewage sludge in land application (e.g. fertilizer, soil improver). The conventional chelators, e.g., ethylenediaminetetraacetic acid (EDTA), were effective in the remediation of HMs polluted sewage sludge, but suffered from an evident drawback of low biodegradability. Therefore, the applicability of a new biodegradable chelator, methyl glycine diacetic acid (MGDA), to extract HMs from sewage sludge was carried out and compared with EDTA. The experimental parameters affecting the performance of MGDA were optimized. Leaching results showed that in general, MGDA exhibited higher Zn leaching efficiency and similar Cu, Ni and Cr leaching efficiencies with EDTA at same pH and dosage conditions. The maximum Zn, Cu, Ni and Cr leaching efficiencies of MGDA were 94.1% ± 4.5%, 58.2% ± 3.1%, 78.2% ± 2.3% and 54.6% ± 2.5%, respectively. The leaching efficiency plateaued within a reaction time of 4 h, but that of Cu and Ni showed a slightly decreasing trend during hours 4 to 10. In raw sewage sludge, the Zn and Cu were mainly presented in the organically bound fraction, i.e., 45.3 ± 3.2% of total Zn and 48.3 ± 1.4% of total Cu. The addition of MGDA and EDTA caused obvious distribution transformations in Zn and Cu from the organically bound fraction to soluble fraction. According to the reduced partition index calculation, the mobility of Zn, Cu, Ni, and Cr was not significantly lowered after the MGDA treatment. However, the HMs secondary pollution risk of the sludge was reduced due to the drop of the total HMs content after chelator leaching. Findings from this study suggest that MGDA could be a potential environment-friendly alternative for refractory chelators (e.g. EDTA) in the decontamination of HMs from sludge.

Pretreatment, modification and applications of sewage sludge-derived biochar for resource recovery- A review

With the quick increase in industrialization and urbanization, a mass of sludge has been produced on the account of increased wastewater treatment facilities. Sewage sludge (SS) management has become one of the most crucial environmental problems because of the existence of various pollutants. However, SS is a carbon-rich material, which has favored novel technologies for biochar production, which can be utilized for dissimilar applications. This review systematically analyzes and summarizes the pretreatment, modification, and especially application of sewage sludge-derived biochar (SSBC), based on published literature. The comparative assessment of pretreatment technology such as pyrolysis, hydrothermal carbonization, combustion, deashing, and co-feeding is presented to appraise their appropriateness for SS resource availability and the production of SSBC. In addition, the authors summarize and analyze the current modification methods and divide them into two categories: physical properties and surface chemical modifications. The applications of SSBC as absorbent, catalyst and catalyst support, electrode materials, gas storage, soil amendment, and sold biofuel are reviewed in detail. Furthermore, the discussion about the existing problems and the direction of future efforts are presented at the end of each section to envisage SS as a promising opportunity for resources rather than a nuisance.

High capacity Pb(II) adsorption characteristics onto raw- and chemically activated waste activated sludge

The Pb(II) adsorption characteristics of chemically activated waste activated sewage sludge (WAS) were compared to raw WAS. Adsorption kinetics and equilibrium isotherm parameters were fit using classic adsorption models. HCl and H₂SO₄ activation terminated any significant sludge-based adsorption. Raw and ZnCl₂ activated WAS displayed Langmuir adsorption capacities of 307 mg/g and 274 mg/g, respectively. Surface characterization revealed that chemical activation with ZnCl₂ increased the BET surface area for raw WAS from 0.97 m²/g to 1.78 m²/g, but did not significantly change the surface structure. FTIR analyzes and XPS were used to further investigate the nature of lead binding. The relationships between equilibrium ion concentration and Pb(II) adsorption suggest cationic exchange with hydrogen, calcium, and zinc as a significant mechanism of Pb(II) removal alongside electrostatic attraction. The pH_PZC was determined as 2.58 and 2.30 for ZnCl₂ activated WAS and raw WAS respectively. HNO₃ and Ca(NO₃)₂ demonstrated sufficient elution properties for WAS recovery. For authentic industrial effluent both raw and ZnCl₂ activated WAS displayed Pb(II) removal behavior comparable to simulated Pb(II) solutions. In comparison with modified and unmodified sludges from literature, this study demonstrates the auspicious potential of raw WAS as an effective Pb(II) adsorbent independent of pyrolytic or chemical activation.

Preparation of ultrahigh-surface-area sludge biopolymers-based carbon using alkali treatment for organic matters recovery coupled to catalytic pyrolysis

In this work, we employed waste activated sludge (WAS) as carbon source to prepare ultrahigh specific surface area (SSA) biopolymers-based carbons (BBCs) through alkali (KOH) treatment coupled to pyrolysis strategy. Before the pyrolysis process, the involvement of KOH made a great recovery of soluble biopolymers from WAS, resulting in highly-efficient catalytic pyrolysis. The Brunner-Emmett-Teller and pore volume of BBCs prepared at 800°C (BBC₈₀₀) reached the maximum at 2633.89 m²·g^-1 and 2.919 m³·g^-1, respectively. X-ray photoelectron spectroscopy suggested that aromatic carbon in the form of C=C was the dominant fraction of C element in BBCs. The N element in BBCs were composed of pyrrolic nitrogen and pyridinic nitrogen at 700°C, while a new graphitic nitrogen appeared over 800°C. As a refractory pollutant of wastewater treatment plants, tetracycline (TC) was selected to evaluate adsorption performance of BBCs. The adsorption behavior of BBCs towards TC was conformed to the pseudo-second-order kinetic and the Langmuir models, signifying that chemisorption of monolayers was dominant in TC adsorption. The adsorption capacity of BBC₈₀₀ reached the maximum at 877.19 mg·g^-1 for 90 min at 298 K. Thermodynamic analysis indicated that the adsorption process was endothermic and spontaneous. Hydrogen bonding and π-π stacking interaction were mainly responsible for TC adsorption, and interfacial diffusion was the main rate-control step in adsorption process. The presence of soluble microbial products (SMPs) enhanced TC removal. This work provided a novel strategy to prepare bio-carbon with ultrahigh SSA using WAS for highly-efficient removal of organic pollutants.

Removal of ammonia nitrogen and phosphorus by biochar prepared from sludge residue after rusty scrap iron and reduced iron powder enhanced fermentation

The rusty scrap iron (RSI) or a mixture of rusty scrap iron and reduced iron powder (RSI-RIP) can be used as an exogenous additive to enhance the anaerobic fermentation of sewage sludge. In order to make rational use of the fermentation residue, the sludge after intensified fermentation was pyrolyzed to produce biochar in this study, which was used in the adsorption of ammonia and phosphorus from the anaerobic fermentation broth. The experimental results demonstrated that the pore structure of the sludge biochar was greatly improved after enhanced fermentation with RSI and RIP. Meanwhile, there was an increase in the proportion of metallic elements such as Ca, Fe and Mg. On the other hand, the RSI-RIP co-enhanced fermented biochar (ES600) prepared at 600 °C showed a higher adsorption capacity, which was comparable to the commercially activated carbon. Neutral or weakly alkaline environments were preferred during the adsorption process. At a suitable pH condition, the maximum removal efficiency of ammonia nitrogen (NH₄⁺-N) and total phosphorus (TP) on ES600 reached 91.3% and 98.6%, respectively. In addition, the saturated ES600 was regenerated by simple washing with ammonia-free water. After three cycles, the removal efficiency of NH₄⁺-N and TP remained at 71.3% and 83.2%, respectively. As a result, the biochar prepared from RSI-RIP enhanced fermented sludge can be used as a promising low-cost adsorbent.

Biochar produced from the co-pyrolysis of sewage sludge and waste tires for cadmium and tetracycline adsorption from water

Application of sewage sludge biochar as an adsorbent for pollutant removal has obtained special attention due to their low cost and surface functionality. In this research, sludge-tire composite biochar (STB) was successfully prepared through co-pyrolysis at 300, 500 and 700 °C, respectively. Cadmium (Cd) and tetracycline (TC) were selected as the target pollutant. The results indicated that STB has the highest surface area (49.71 m²/g), more inorganic minerals (Kaolinite) as well as relatively stable physicochemical properties with 10% tire particles (TP) at 700 °C. The adsorption results indicated that the pseudo-second-order equation and Langmuir isotherm model could better describe the adsorption of Cd²⁺ and TC by STB. The maximum adsorption capacity of Cd²⁺ and TC was 50.25 mg/g and 90.09 mg/g, respectively. The main mechanism of the adsorption process of STB for Cd mainly involves anion binding adsorption and ion exchange. The main mechanism of the adsorption process of STB for TC mainly involves complexation and cation exchange. The present study could set a scientific foundation for further research on the recycle of sewage sludge and tires.

A review of the application of sea material shells as low cost and effective bio-adsorbent for removal of heavy metals from wastewater

The pollution caused by heavy metal ions in industrial wastewater is of a great concern. Applying effective and low-cost methods is an urgent need for treatment of polluted water and aqueous solutions. Biosorption have received the most attention among the various methods. It has become an alternative technique to conventional technologies due to low cost, simple operation and treatment for heavy metal recovery, and high selectivity. In recent years, sea material shells have been applied as one of the most cost-effective bio-adsorbents due to their special properties. They are environmentally friendly, low cost, and easy to access and have high adsorption capacity. The purpose of this review is to present the application of oyster shell, snail shell, and shrimp shell as low-cost and effective biosorbents for removal of noxious heavy metals from aqueous solutions. In addition, heavy metals, their sources, and ways to remediate them from waste streams and various factors affecting the biosorption process with sea materials shells are also reviewed. Moreover, a brief description and literature review of the equilibrium, kinetic, and thermodynamic behaviors of the heavy metal ion adsorption process on sea material shells have been studied. Finally, further applications of sea materials shell for waste effluents treatment are specially focused.

A review of the application of adsorbents for landfill leachate treatment: Focus on magnetic adsorption

Landfill leachate is a significant environmental threat due to the complexity and variety of its pollutants. There are various physical, chemical, and biological treatment methods proposed for leachate treatment. Adsorption with conventional adsorbents such as activated carbon is a process which has been widely employed with relative success. Magnetic adsorbents are a special type of adsorbents with favorable stability, high adsorption capacities, and excellent recycling and reuse capabilities when compared to conventional sorbents. Research regarding the synthesis and use of magnetic adsorbents has been growing at a rapid pace, exhibiting >8-fold increase in publications in the decade of 2010 to 2020. In the current study, both conventional and magnetic adsorbents for landfill leachate treatment have been comprehensively reviewed and discussed. The application of magnetic adsorbents for landfill leachate treatment is relatively new, with numerous avenues of research open to study. Although the production of magnetic adsorbents is significantly more expensive than conventional adsorbents, when taking into consideration all life cycle costs, they are much more competitive than it initially appears. If environmental impacts are of concern, research should shift towards the use of greener chemicals and processes for magnetic adsorbent synthesis, because preliminary analysis of the current synthesis processes shows a much higher environmental impact compared to conventional adsorbents, in particular in terms of global warming potential and energy use.

Biosorption Characteristics of Hg(II) from Aqueous Solution by the Biopolymer from Waste Activated Sludge

The divalent mercury ion (Hg(II)) is one of the most hazardous toxic heavy-metal ions, and an important industrial material as well. It is essential to remove and recover Hg(II) from wastewater before it is released into the environment. In this study, the biosorption characteristics of Hg(II) from aqueous solution by the biopolymer from waste activated sludge (WAS) are investigated. The major components of the biopolymer consisted of proteins, carbohydrates, and nucleic acids. The adsorption kinetics fit for the pseudo-second-order kinetic model, and the adsorption isotherms were well described by Langmuir equation. The adsorption capacity of the biopolymer increased along with rising temperature, and the maximal adsorption capacity was up to 477.0 mg Hg(II)/g biopolymer at 308 K. The infrared spectroscopy analyses showed that the complexation of Hg(II) by the biopolymer was achieved by the functional groups in the biopolymer, including hydroxyl (-OH), amino (-NH2), and carboxylic (-COOH). From the surface morphology, the special reticulate structure enabled the biopolymer to easily capture the metal ions. From the elemental components analyses, a part of Hg(II) ions was removed due to ion exchange with the Na+, K+, and Ca2+, in the biopolymer. Both complexation and ion exchange played key roles in the adsorption of Hg(II) by the biopolymer. These results are of major significance for removal and recovery of Hg(II) from wastewater.

Adsorption Properties of Magnetic Magnetite Nanoparticle for Coexistent Cr(VI) and Cu(II) in Mixed Solution

The adsorption properties of coexistent Cr(VI) and Cu(II) in mixed solution on magnetic magnetite (Fe3O4) nanoparticle were studied in batch experiments. The influences of various factors, such as pH, adsorbent dose, temperature, initial concentration of metal ions, and coexisting ions in water were investigated. At the same time, the adsorption kinetics and adsorption isotherms were studied. The mechanism of adsorption for Cr(VI) and Cu(II) was investigated through the study of surface properties of Fe3O4, the presence of ions, and the influence of pH and zeta potential. The results indicate that pH has an influence on adsorption for Cr(VI) and Cu(II), and the optimal pH value for Cr(VI) and Cu(II) adsorption is 4.0. The adsorption efficiency increased with the increase of the adsorbent dose. Temperature under experimental design had no obvious effect. With 2.0 g/dm3 Fe3O4, the maximum adsorption capacity for Cr(VI) and Cu(II) reached 8.67 mg/g and 18.61 mg/g in mixed solution of 80 mg/dm3 Cr(VI) and Cu(II), respectively. Phosphorus had some influence on the adsorption for Cr(VI), and other coexisting anions and cations had no influence on the adsorption for Cr(VI) and Cu(II). The adsorption data for Cr(VI) and Cu(II) were nicely fit to the Langmuir adsorption equation and the pseudo-second-order model. As a multifunctional material, nano-Fe3O4 exhibited good adsorption performance for coexistent Cr(VI) and Cu(II) and could easily be separated and recovered under magnetic field.

Biochar produced from the co-pyrolysis of sewage sludge and walnut shell for ammonium and phosphate adsorption from water

Pyrolysis of sewage sludge to obtain biochar is an environmentally friendly method of sewage sludge utilization. In this study, sewage sludge and walnut shell were co-pyrolyzed to produce biochar, which was utilized in the adsorption of ammonium and phosphate from water. Brunauer-Emmett-Teller analysis, X-ray diffraction spectroscopy, scanning electron microscopy, and Fourier transform infrared techniques were applied to analyze the physical and chemical properties of the biochar. The sewage sludge-based biochar consisted of rich metal oxides and functional groups, and the addition of walnut shell was beneficial for the development of porous structure. When the mixing ratio of sewage sludge and walnut shell was 3:1, the derived biochar (MBC3-1) showed a high adsorption capacity for NH₄⁺ in neutral or weak alkaline water. Pure sewage sludge biochar (SBC) was the best option for the adsorption of PO₄^3- in a wide pH range of water. The adsorption of NH₄⁺ and v on MBC3-1 and SBC were controlled by intraparticle diffusion and pseudo-second-order kinetic models, respectively. Isothermal studies indicated that multiple adsorption processes occurred in the adsorption of NH₄⁺ and PO₄^3-, and the maximum adsorption capacity of NH₄⁺ and PO₄^3- reached 22.85 mg/g and 303.49 mg/g on MBC3-1 and SBC, respectively. Thermodynamic analysis confirmed the exothermic and endothermic nature for NH₄⁺ and PO₄^3- adsorption on biochar, respectively.

Comparison of biochars derived from different types of feedstock and their potential for heavy metal removal in multiple-metal solutions

Three different types of feedstocks and their biochars were used to remove Cr(III), Cd(II), Cu(II) and Pb(II) ions from a mixture of multiple heavy metals. The effect of the initial concentration of heavy metals in solution has been analysed, and kinetics modelling and a comparison of the adsorption capacity of such materials have been performed to elucidate the possible adsorption mechanisms. The results show that the adsorption capacity is dependent on the type of feedstock and on the pyrolysis conditions. The adsorption capacity of the biomass types is ranked as follows: FO (from sewage sludge)>> LO > ZO (both from agriculture biomass waste)>> CO (from wood biomass waste). Biochars, which are the product of the pyrolysis of feedstocks, clearly improve the adsorption efficiency in the case of those derived from wood and agricultural biomasses. Complexation and cation exchange have been found to be the two main adsorption mechanisms in systems containing multiple heavy metals, with cation exchange being the most significant. The pore structure of biomass/biochar cannot be neglected when investigating the adsorption mechanism of each material. All the disposal biomasses presented here are good alternatives for heavy metal removal from wastewaters.

The effect of biochar mild air oxidation on the optimization of lead(II) adsorption from wastewater

In the present study, the effects of mild air oxidation of a biochar produced by the Pyrovac Inc. pyrolysis process, on the adsorption of lead(II) from synthetic wastewater under batch experimental conditions have been investigated. The adsorption experiments were performed under several conditions suggested by the response surface methodology, which allowed finding the optimal conditions, in order to maximize the adsorption capacity (Q(mgg^-1)), as well as the extraction efficiency (E (%)). The optimal conditions of lead ions adsorption were as follows: pH = 5, agitation time = 300 min, adsorbent mass = 0.5 g (per 50 cm³ of solution), and lead initial concentration = 100gm^-3, resulted in an adsorption capacity of 7.9 mg g^-1. Equilibrium adsorption was then obtained by keeping pH and adsorbent mass at the optimal values and changing the lead initial concentration for a sufficient agitation time. Results showed that mild air oxidation increased the equilibrium adsorption capacity of biochar from 2.5 to 44 mg g^-1. Oxidized biochar after equilibrium adsorption was submitted to SEM/EDX and XPS analysis. From SEM it was found that lead particles were distributed heterogeneously after adsorption. From XPS analysis, it was revealed that the external surface of oxidized biochar particles becomes saturated for the initial point of equilibrium diagram, obtained at lead initial concentration of 100gm^-3, suggesting that for a higher concentration, the internal surfaces of particles participate in the cations adsorption. The participation of surface functional groups in the adsorption process showed that carbonyl, carboxylic, and aromatic rings of oxidized biochar were involved in the adsorption. This work suggests that the very simple process of mild air oxidation can be used instead of the usual costly chemical activation, in order to improve biochar cation exchange capacity.

Enhanced Capture Ability of Sludge-Derived Mesoporous Biochar with a Template-like Method

Sewage sludge-derived mesoporous biochars (SS-MBCs) were prepared by using cationic polyacrylamide (PAM⁺) as a template agent through a template-like method under high temperature and employed for getting rid of methylene blue (MB) from water. Textural evolution, mesostructured morphology, thermodynamic properties, and surface chemical groups of SS-MBCs were analyzed. It showed that PAM⁺ not only played an important role in good nucleation that brought well-developed texture and novel pore size distribution to SS-MBCs but also improved the MB adsorption capacities of SS-MBCs by increasing the specific surface area and the content of oxygen functional groups, especially the lactone. Preparation factor analysis indicated that PAM⁺ concentration, dosage of additive sludge, and carbonization temperature had distinct effects on material structure and adsorption performance especially above the pyrolytic temperature of 800 °C. The adsorption kinetics and isotherms were analyzed in detail, and it revealed that the kinetics and equilibrium adsorptions of SS-MBCs could be well-described by the Langmuir isotherm model and pseudo-second-order kinetics, respectively. Remarkably, the SS-MBCs showed higher removal efficiency and adsorption capacity than commercial activated carbon and most reported sludge-based adsorbents.

A novel waste activated sludge multistage utilization strategy for preparing carbon-based Fenton-like catalysts: Catalytic performance assessment and micro-interfacial mechanisms

Waste activated sludge (WAS) contains many anionic functional groups which can interact with heavy metal ions through electrostatic action and complexation reactions. The transition metals adsorbed in WAS can catalyze sludge pyrolysis in anaerobic conditions and improve structural properties of organic matter. In this work, a multistage WAS utilization process for preparing the carbon-based Fenton-like catalysis materials is proposed. More specifically, WAS is firstly used as an adsorbent for heavy metals (Cu and Ni) removal, and then complexes are converted into heterogeneous Fenton-like carbon-based catalysts through oxygen-free pyrolysis. The mechanisms of interactions between extracellular polymeric substances (EPS) and metals are investigated, and the physicochemical properties of sludge-based carbons (SBC) are comprehensively characterized using varies techniques. It is found that WAS is an excellent adsorbent for Cu and Ni removal, which is mainly due to the coordination and electrostatic interactions between EPS and heavy metals. Cu and Ni adsorbed in WAS significantly improved the porous structure of SBC. Both adsorption and catalytic oxidization of Cu/Ni-SBC contribute the removal of E2 in real wastewater. The E2 removal mechanism is explored by electron-spin resonance spectroscopy (ESR) analysis, and it is found that both of ^.O₂^- and ^.OH radicals are responsible for E2 degradation in Cu(II)-SBC-H₂O₂, while ^.O₂^- radicals contributes to E2 degradation in Ni(II)-SBC-H₂O₂ system, so the former performed better than the latter in total removal of E2. Besides, Cu(II) and Cu(I) are both formed in Cu(II)-SBC during the oxidation process, while only Ni(II) is found in the Ni(II)-SBC-H₂O₂ process, confirming that different catalytic oxidation reactions are occurred in the Cu(II)-SBC-H₂O₂ and Ni(II)-SBC-H₂O₂ processes. This study facilitates a great strategy to the sludge multi-stage circulating utilization and a better understanding about the role of the Cu/Ni existed in SBC during the estrogens removal process.

Preparation of thiol-functionalized activated carbon from sewage sludge with coal blending for heavy metal removal from contaminated water

Sewage sludge produced from wastewater treatment is a pressing environmental issue. Mismanagement of the massive amount of sewage sludge would threat our valuble surface and shallow ground water resources. Use of activated carbon prepared from carbonization of these sludges for heavy metal removal can not only minimize and stabilize these hazardous materials but also realize resources reuse. In this study, thiol-functionalized activated carbon was synthesized from coal-blended sewage sludge, and its capacity was examined for removing Cu(II), Pb(II), Cd(II) and Ni(II) from water. Pyrolysis conditions to prepare activated carbons from the sludge and coal mixture were examined, and the synthesized material was found to achieve the highest BET surface area of 1094 m²/g under 500 °C and 30 min. Batch equilibrium tests indicated that the thiol-functionalized activated carbon had a maximum sorption capacity of 238.1, 96.2, 87.7 and 52.4 mg/g for Pb(II), Cd(II), Cu(II) and Ni(II) removal from water, respectively. Findings of this study suggest that thiol-functionalized activated carbon prepared from coal-blended sewage sludge would be a promising sorbent material for heavy metal removal from waters contaminated with Cu(II), Pb(II), Cd(II) and Ni(II).

Tuning role and mechanism of paint sludge for characteristics of sewage sludge carbon: Paint sludge as a new macro-pores forming agent

For the first time, paint sludge waste (PS) was used as a pore forming agent in the preparation of sewage sludge derived carbon (SC). The tuning role and mechanism of PS for characteristics of SC were explored. It was found that a sludge carbon (SC_PS-Zn) with rich macro-, meso- and micro- porous could be produced by one-step pyrolytic process of sludge in the presence of PS and ZnCl_2. Its surface area could reach as high as 680.5m²g^-1 as 88.4 times and 4.8 times of sludge carbon without addition of PS and ZnCl₂ (SC) and only addition of ZnCl₂ (SC_Zn)_, respectively. The macro- pores fabricated by PS provided much inner-space for ZnCl₂ to generate meso- and micro- porous, leading to a hierarchical porous structure. SC_PS-Zn showed a high adsorption capacity of 685.4mgg^-1 for Chrysophenine, which is 1.3 and 1.7 times that of SC_PS and SC_Zn respectively. The adsorption difference could be simply attributed to the fact that the great molecules were difficult to enter micro- pores of SC_Zn. It was also found that the difference was also dependent on orientation of Chrysophenine, which was related to pH value of solution.

Unexpected nitrile formation in bio-based mesoporous materials (Starbons®)

The bio-based mesoporous materials made from polysaccharides, Starbons® can be modified by two different routes to give high levels of N-content, unexpectedly including significant quantities of nitrile groups which can improve the materials performance in applications including metal capture.

Surface characteristics and potential ecological risk evaluation of heavy metals in the bio-char produced by co-pyrolysis from municipal sewage sludge and hazelnut shell with zinc chloride

Municipal sewage sludge (MSS) and hazelnut shell were used for co-pyrolysis by chemical activation with ZnCl₂. The surface characteristics and potential ecological risk evaluation of heavy metals in the bio-char produced by co-pyrolysis were analyzed by surface analyzer and BCR sequential extraction. When raw materials with ZnCl₂ (3mol/L) were co-pyrolyzed at 500°C for 90min, specific surface area of the bio-char is 598.73m²/g, and iodine absorption number is 607.85mg/g. For microcosmic surface of the bio-char, the ratio of micropore area is stabilized from 0.74 to 0.80 of the total specific surface area, and hazelnut shell is effective to generate microporous construction. For the migration and transformation behavior of heavy metals, pyrolysis promoted mobile fraction (F1 and F2) to stable fraction (F3 and F4) with increasing pyrolysis temperature. The potential ecological risk of heavy metals transforms from considerable risk to low risk after pyrolysis at 500°C.

Sustainable pyrolytic sludge-char preparation on improvement of closed-loop sewage sludge treatment: Characterization and combined in-situ application

Aiming at closed-loop sustainable sewage sludge treatment, an optimal and economical pyrolytic temperature was found at 400-450 °C considering its pyrolysis efficiency of 65%, fast cracking of hydrocarbons, proteins and lipids and development of aromatized porous structure. Fourier-transform infrared (FTIR) and X-ray diffraction (XRD) tests demonstrated the development of adsorptive functional groups and crystallographic phases of adsorptive minerals. The optimal sludge-char, with a medium specific surface area of 39.6 m² g^-1 and an iodine number of 327 mgI₂ g^-1, performed low heavy metals lixiviation. The application of sludge-char in raw sewage could remove 30% of soluble chemical oxygen demand (SCOD), along with an acetic acid adsorption capacity of 18.0 mg g^-1. The developed mesopore and/or macropore structures, containing rich acidic and basic functional groups, led to good biofilm matrices for enhanced microbial activities and improved autotrophic nitrification in anoxic stage of an A/O reactor through adsorbed extra carbon source, and hence achieved the total nitrogen (TN) removal up to 50.3%. It is demonstrated that the closed-loop sewage sludge treatment that incorporates pyrolytic sludge-char into in-situ biological sewage treatment can be a promising sustainable strategy by further optimization.

Long-term Cu stabilization and biomass yields of Giant reed and poplar after adding a biochar, alone or with iron grit, into a contaminated soil from a wood preservation site

A 2-year pot experiment was carried out to examine the aging effect of biochar (B), alone or combined with iron grit (Z), on Cu stabilization and plant growth in a contaminated soil (964mg Cu kg^-1) from a wood preservation site. The experiment consisted in 3 soil treatments, either planted with Arundo donax L. (Ad) or Populus nigra L. (Pn): (1) untreated Cu-contaminated soil (Ad, Pn); (2) Unt+1% (w/w) B (AdB, PnB), and (3) Unt+1% B+1% Z (AdBZ, PnBZ). After 22months, the soil pore water (SPW) was sampled and roots and shoots were harvested. The SPW compositions at 3 and 22months were compared, showing that the SPW Cu²⁺ concentration increased again in the PnB and PnBZ soils. Cultivation of A. donax enhanced the dissolved organic matter concentration in the SPW, which decreased its Cu²⁺ concentration but promoted its total Cu concentration in the Ad and AdB soils. Adding Z with B reduced both SPW Cu²⁺ and Cu concentrations in the pots cultivated by A. donax and P. nigra as compared to B alone. The B and BZ treatments did not enhance root and shoot yields of both plant species as compared to the Unt soil but their shoot Cu concentrations were in the range of common values.

Utilization of sludge based adsorbents for the removal of various pollutants: A review

Sludge based adsorbents are widely used for the removal of various pollutants from water and wastewater systems and the available data is much diversified. The purpose of this review is to organize and critically review the scattered available information on the potential of use of sludge based adsorbents for the removal of various pollutants. It was observed that performance of the sludge based adsorbents varies depending on the type of pollutants, type of precursor sludge, carbonization time-temperature profile and the type of activation conditions used. The variation in pyrolysis and activation conditions found to directly affect the adsorbent properties, adsorption capacity and the mechanism of pollutant removal by sludge based adsorbents. The interaction mechanisms of pollutants with adsorbent surface found to have a detrimental effect on desorption and regeneration of the adsorbents and its recycling potential. Therefore, desorption and regeneration technique used for recycle of the adsorbents is also discussed in detail. Moreover, life cycle and cost analysis of sludge based adsorbents is assessed to ensure the cost effectiveness of their application in water treatment operations.

Adsorption of Cr(VI) from aqueous solution by adsorbent prepared from paper mill sludge: Kinetics and thermodynamics studies

In the present work, a new low-cost activated carbon was prepared from paper mill sludge in order to remove Cr(VI) ions from aqueous solution. The effects of adsorbent dosage, pH, contact time, metal ion concentrations, and temperature on adsorption efficiency were studied by experimental tests. The maximum equilibrium uptake of Cr(VI) by the adsorbent was 23.18 mg g−1 at optimum pH = 4.0, contact time of 180 min, and temperature of 45℃. Analysis of equilibrium adsorption data in terms of several isotherm models revealed that Langmuir isotherm with respect to Freundlich isotherm indicates better agreement with the experimental data. The kinetics of Cr(VI) adsorption onto activated carbon was described with the pseudo-second-order model which indicates the dominance of chemisorption mechanism. Thermodynamic parameters indicated that the Cr(VI) adsorption onto adsorbent was feasible in nature, spontaneous, and endothermic.

Carbonization of heavy metal impregnated sewage sludge oriented towards potential co-disposal

Sewage sludge (SS) is adopted as a stabilizer to immobilize externally impregnated heavy metals through carbonization oriented towards the co-disposal of SS and some hazardous wastes. Firstly Cu and Pb were impregnated into SS to ascertain the impregnating capacity and leaching behaviours of heavy metals in the resulting sewage sludge char (SSC). Meanwhile, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to detect the heavy metal phase in the SSC. The results showed that within 400-800°C and an impregnating concentration ≨0.5wt%, more than 90% of the externally impregnated Cu and Pb were remained in the SSC and immobilized. And higher temperatures helped produce non-hazardous SSC. In addition, SEM and XRD analyses revealed that externally impregnated heavy metals could be converted into stable forms and evenly distributed throughout the SSC. In the second step municipal solid waste incineration fly ash (FA) was kneaded into SS and subjected to carbonization; it has been proved that the heavy metals in FA can be well immobilized in the resulting char when FA: SS mass ratio is 1:5. Those results show that sewage sludge can be co-carbonized with wastes contaminated with heavy metals to achieve co-disposal.

Functionalized magnetic Fe3O4 nanoparticles for removal of heavy metal ions from aqueous solutions

Fe3O4 nanoparticles (MNP) were coated with 3-aminopropyltriethoxy-silane (APTES), resulting in anchoring of primary amine groups on the surface of the particles, then four kinds of novel magnetic adsorbents (Fe3O4@SiO2-NH-HCGs) were formed by grafting of different heterocyclic groups (HCG) on amino groups via substitution reaction. These Fe3O4@SiO2-NH-HCGs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and energy disperse spectroscopy (EDS). The results confirmed the formation of Fe3O4@SiO2-NH-HCGs nanoparticles and the Fe3O4 core possessed superparamagnetism. Batch experiments were performed to evaluate adsorption conditions of Cu2+, Hg2+, Pb2+ and Cd2+. Under normal temperature and neutral condition, just 20 min, the removal efficiency of any Fe3O4@SiO2-NH-HCGs is more than 96%. In addition, these Fe3O4@SiO2-NH-HCGs have good stability and reusability. Their removal efficiency has no obvious decrease after being used seven times. After the experiments were finished, Fe3O4@SiO2-NH-HCGs were conveniently separated via an external magnetic field due to superparamagnetism. These results indicate that these Fe3O4@SiO2-NH-HCGs are potentially attractive materials for the removal of heavy metal ions from industrial wastewater.

New insight into adsorption characteristics and mechanisms of the biosorbent from waste activated sludge for heavy metals

The adsorption characteristics and mechanisms of the biosorbent from waste activated sludge were investigated by adsorbing Pb(2+) and Zn(2+) in aqueous single-metal solutions. A pH value of the metal solutions at 6.0 was beneficial to the high adsorption quantity of the biosorbent. The optimal mass ratio of the biosorbent to metal ions was found to be 2. A higher adsorption quantity of the biosorbent was achieved by keeping the reaction temperature below 55°C. Response surface methodology was applied to optimize the biosorption processes, and the developed mathematical equations showed high determination coefficients (above 0.99 for both metal ions) and insignificant lack of fit (p=0.0838 and 0.0782 for Pb(2+) and Zn(2+), respectively). Atomic force microscopy analyses suggested that the metal elements were adsorbed onto the biosorbent surface via electrostatic interaction. X-ray photoelectron spectroscopy analyses indicated the presence of complexation (between -NH2, -CN and metal ions) and ion-exchange (between -COOH and metal ions). The adsorption mechanisms could be the combined action of electrostatic interaction, complexation and ion-exchange between functional groups and metal ions.

Nanoscale zero valent supported by Zeolite and Montmorillonite: Template effect of the removal of lead ion from an aqueous solution

In this work, we have studied the Pb(2+) sorption capacity of Zeolite (Z) and Montmorillonite (Mt) functionalized with nanoscale zero-valent iron (nZVI), at 50% w/w, obtained by means of an impregnating process with a solvent excess. The composites were characterized by several techniques including X-ray diffraction; scanning electron microscopy (SEM); BET area; isoelectric point (IEP); and, finally a magnetic response. Comparatively significant differences in terms of electrophoretic and magnetic characteristics were found between the pristine materials and the composites. Both structures show a high efficiency and velocity in the removal of Pb(2+) up to 99.0% (200.0 ppm) after 40 min of reaction time. The removal kinetics of Pb(2+) is adequately described by the pseudo second-order kinetic model, and the maximum adsorbed amounts (q(e)) of this analyte are in close accordance with the experimental results. The intraparticle diffusion model shows that this is not the only rate-limiting step, this being the Langmuir model which was well adjusted to our experimental data. Therefore, maximum sorption capacities were found to be 115.1±11.0, 105.5±9.0, 68.3±1.3, 54.2±1.3, and 50.3±4.2 mg g(-1), for Mt-nZVI, Z-nZVI, Zeolite, Mt, and nZVI, respectively. The higher sorption capacities can be attributed to the synergetic behavior between the clay and iron nanoparticles, as a consequence of the clay coating process with nZVI. These results suggest that both composites could be used as an efficient adsorbent for the removal of lead from contaminated water sources.

Effect of calcium magnesium acetate on the forming property and fractal dimension of sludge pore structure during combustion

The changes in pore structure characteristics of sewage sludge particles under effect of calcium magnesium acetate (CMA) during combustion were investigated, the samples were characterized by N2 isothermal absorption method, and the data were used to analyze the fractal properties of the obtained samples. Results show that reaction time and the mole ratio of calcium to sulfur (Ca/S ratio) have notable impact on the pore structure and morphology of solid sample. The Brunauer-Emmett-Teller (BET) specific surface area (SBET) of sample increases with Ca/S ratio, while significant decreases with reaction time. The fractal dimension D has the similar trend with that of SBET, indicating that the surface roughness of sludge increases under the effect of CMA adding, resulting in improved the sludge combustion and the desulfurization process.

Zero-valent iron doped carbons readily developed from sewage sludge for lead removal from aqueous solution

Low-cost but high-efficiency composites of iron-containing porous carbons were prepared using sewage sludge and ferric salts as raw materials. Unlike previous time- and energy-consuming manufacturing procedures, this study shows that pyrolyzing a mixture of sludge and ferric salt can produce suitable composites for lead adsorption. The specific surface area, the total pore volume and the average pore width of the optimal composite were 321m(2)/g, 0.25cm(3)/g, and 3.17nm, respectively. X-ray diffraction analysis indicated that ferric salt favored the formation of metallic iron, while Fourier transform infrared spectroscopy revealed the formation of hydroxyl and carboxylic groups. The result of batch tests indicated that the adsorption capacity of carbons activated with ferric salt could be as high as 128.9mg/g, while that of carbons without activation was 79.1mg/g. The new manufacturing procedure used in this study could save at least 19.5kJ of energy per gram of activated carbon.

Biomass based activated carbon obtained from sludge and sugarcane bagasse for removing lead ion from wastewater

Sewage sludge and bagasse were used as raw materials to produce cheap and efficient adsorbent with great adsorption capacity of Pb(2+). By pyrolysis at 800 °C for 0.5 h, the largest surface area (806.57 m(2)/g) of the adsorbent was obtained, enriched with organic functional groups. The optimal conditions for production of the adsorbent and adsorption of Pb(2+) were investigated. The results of adsorb-ability fitted the Langmuir isotherm and pseudo-second-order model well. The highest Pb(2+) (at pH = 4.0) adsorption capacity was achieved by treating with 60% (v/v) HNO3. This is a promising approach for metal removal from wastewater, as well as recycling sewage sludge and bagasse to ease their disposal pressure.

Sewage-sludge-derived carbonaceous materials for catalytic wet hydrogen peroxide oxidation of m-cresol in batch and continuous reactors

In this study, four sewage-sludge-derived carbonaceous materials (SWs) were evaluated for their catalytic wet hydrogen peroxide oxidation (CWPO) performance of m-cresol in batch reactor and continuous reactor, respectively. The SWs were produced by carbonization (SW); carbonization with the addition of CaO (CaO-SW); HNO3 pretreatment (HNO3-SW) and steam activation (Activated-SW). The properties of SW catalysts were assessed by thermogravimetric analysis, Brunauer-Emmett-Teller, Fourier Transform Infrared Spectroscopy, X-ray Fluorescence, Scanning electron microscopy, energy dispersive X-ray analysis and zeta potential. The results showed that SW treated by HNO3 (HNO3-SW) had a high conversion of m-cresol in batch reactor and continuous reactor, respectively. Under the conditions of batch reaction (Cm-cresol = 100 mg L(-1), CH2O2 = 15.7 mmol L(-1), initial pH=7.0, 0.5 g L(-1) catalyst, 80°C, 180 min adsorption and 210 min oxidation), the conversion of m-cresol reached 100% and total organic carbon removal was 67.1%. It had a high catalytic activity and stability on the treatment of m-cresol in CWPO for more than 1100 h. Furthermore, a possible reaction mechanism for the oxidation of m-cresol to 2-methyl-p-benzoquinone by CWPO was proposed.

Development of sludge-based adsorbents: preparation, characterization, utilization and its feasibility assessment

The increasing generation of sludge and its subsequent treatment are very sensitive environmental problems. For a more stable and sustainable treatment of sludge, there have been many studies, including the conversion of sludge into sludge-based adsorbents (SBAs) for pollutants removal. In this review, current SBAs preparation conditions and use as adsorbent for contaminant removal in water treatment are summarized and discussed. Carbonization, physical activation and chemical activation are three common preparation methods. The controlling key parameters include pyrolysis temperature, dwell time, heating rate, activator and feedstock type. The efficacy of SBAs in contaminant adsorption depends on their surface area, pore size distribution, surface functional groups and ion-exchange capacity. It has been demonstrated that SBAs can attain high uptakes of dyes and metal ions due to their high cation exchange capacity; whereas the strong antibiotics adsorption performance of SBAs derives from high degree of mesoporosity. In addition, thermal treatment significantly stabilizes heavy metals contained in sludge. The paper also discusses the economic feasibility and environmental safety of preparation and application of SBAs. Further research will include investigations on the migration and transformation of element in sludge by thermal treatment, more economical and efficient chemical activation reagents, obtaining SBAs for designated application, combination of coagulation and SBAs adsorption, regeneration of SBAs and full-scale tests.

Immobilization and phytotoxicity of Pb in contaminated soil amended with γ-polyglutamic acid, phosphate rock, and γ-polyglutamic acid-activated phosphate rock

Pot experiments were conducted to investigate the effects of γ-polyglutamic acid (γ-PGA), phosphate rock (PR), and γ-PGA-activated PR (γ-PGA-PR) on the immobilization and phytotoxicity of Pb in a contaminated soil. The proportion of residual Pb (Re-Pb) in soil was reduced by the addition of γ-PGA but was increased by the application of PR and γ-PGA-PR. The addition of γ-PGA in soil improved the accumulation of Pb in pak choi and decreased the growth of pak choi, suggesting the intensification of Pb phytotoxicity to pak choi. However, opposite effects of PR and γ-PGA-PR on the phytotoxicity of Pb to pak choi in soil were observed. Moreover, in the examined range, γ-PGA-PR activated by a higher amount of γ-PGA resulted in a greater proportion of Re-Pb in soil and weaker phytotoxicity of Pb to pak choi. The predominance of γ-PGA-PR in relieving the phytotoxicity of Pb was ascribed mainly to the increase of soil pH and available phosphate after the amendment, which could facilitate the precipitation of Pb in soil and provide pak choi with more phosphorus nutrient.