Removal of phosphate by Fe-coordinated amino-functionalized 3D mesoporous silicates hybrid materials

Phosphate removal from aqueous waste streams is an important approach to control the eutrophication downstream bodies of water. A Fe(III) coordinated amino-functionalized silicate adsorbent for phosphate adsorption was synthesized by a post-grafting and metal cation incorporation process. The surface structure of the adsorbent was characterized by X-ray di raction, N2 adsoropion/desoprotion technique, and Fourier transform infrared spectroscopy. The experimental results showed that the adsorption equilibrium data were well fitted to the Langmuir equation. The maximum adsorption capacity of the modified silicate material was 51.8 mg/g. The kinetic data from the adsorption of phosphate were fitted to pseudo second-order model. The phosphate adsorption was highly pH dependent and the relatively high removal of phosphate fell within the pH range 3.0–6.0. The coexistence of other anions in solutions has an adverse e ect on phosphate adsorption; a decrease in adsorption capacity followed the order of exogenous anions: F?? > SO2?? 4 > NO??3 > Cl??. In addition, the adsorbed phosphate could be desorbed by NaOH solutions. This silicate adsorbent with a large adsorption capacity and relatively high selectivity could be utilized for the removal of phosphate from aqueous waste streams or in aquatic environment.     

Removal of Cd2+ from water by Friedel’s salt (FS: 3CaO.Al2O3·CaCl2·10H2O): Sorption characteristics and mechanisms

The development of low-cost and efficient new mineral adsorbents has been a hot topic in recent years. In this study, Friedel’s salt (FS:3CaO·A12O3 ·CaCl2 ·10H2O), a hexagonal layered inorganic absorbent, was synthesized to remove Cd2+ from water. The adsorption process was simulated by Langmuir and Freundlich models. The adsorption mechanism was further analyzed with TEM, XRD, FT-IR analysis and monitoring of metal cations released and solution pH variation. The results indicated the adsorbent FS had an outstanding ability for Cd(Ⅱ) adsorption. The maximum adsorption capacity of the FS for Cd(Ⅱ) removal can reach up to 671.14 mg/g. The nearly equal numbers of Cd2+ adsorbed and Ca2+ released demonstrated that ion-exchange (both surface and inner) of the FS for Cd(Ⅱ) played an important role during the adsorption process. Furthermore, the surface of the FS after adsorption was microscopically disintegrated while the inner lamellar structure was almost unchanged. The behavior of Cd(Ⅱ) adsorption by FS was significantly affected by surface reactions. The mechanisms of Cd2+ adsorption by the FS mainly included surface complexation and surface precipitation. In the present study, the adsorption process was fitted better by the Langmuir isotherm model (R2 = 0.9999) than the Freundlich isotherm model (R2 = 0.8122). Finally, due to the high capacity for ion-exchange on the FS surface, FS is a promising layered inorganic adsorbent for the removal of Cd(Ⅱ) from water.     

Organic pollutants removal from 2,4,6-trinitrotoluene （TNT） red water using low cost activated coke

2,4,6-trinitrotoluene (TNT) red water from Chinese explosive industry was adsorbed by activated coke (AC) from lignite. Since the composition of TNT red water was very complicated, chemical oxygen demand (COD) was used as the index for evaluating the treatment efficiency. This study focused on the sorption kinetics and equilibrium sorption isotherms of AC for the removal of chemical oxygen demand (COD) from TNT red water, and the changes of water quality before and after adsorption were evaluated by using high performance liquid chromatograph (HPLC), UV-vis spectra and Gas Chromatography/Mass Spectroscopy (GC/MS). The results showed that the sorption kinetics of adsorbing COD from TNT red water onto AC was fitted well with the pseudo-second order model. The adsorption process was an exothermic and physical process. The sorption isotherm was in good agreement with Redlich–Peterson isotherm. At the conditions of initial pH, 20℃ and 3 hr of agitation, when the AC dosage was 160 g L-1, 64.8% of COD could be removed. The removal efficiencies of 2,4-dinitrotoluene-3-sulfonate (2,4-DNT-3-SO3-) and 2,4-dinitrotoluene-5-sulfonate (2,4-DNT-5-SO3-) were 80.5% and 84.3%, respectively. After adsorption, the acute toxicity of TNT red water reduced 81.8%, compared with that of unprocessed TNT red water.     

Removal of cobalt(Ⅱ) ion from aqueous solution by chitosan-montmorillonite

Montmorillonite （MMT） modified with chitosan （CTS, molecular weight = S x 104） was applied to remove heavy metal cations by using Co2＋ as a model ion. An increase in MMT interlayer distance observed from X-ray diffraction indicates the intercalation of CTS into MMT. Together with the results of scanning electron microscopy and Fourier transform infrared spectroscopy, it was concluded that the composite material of CTS and MMT （CTS-- MMT） was prepared successfully. The mass ratio of CTS to MMT had a strong influence on the adsorption performance of CTS-MMT. The highest adsorption value of 150 mg/g was obtained over the composite material with CTS to MMT mass ratio of 0.25, which is much higher than those reported in other studies. The adsorption isotherms and kinetic results indicated that Co2＋ was adsorbed over CTS-MMT in a multilayer model, and the chemical sorption of Co2＋ was determined to be the rate-limiting step.     

Cadmium sorption by sodium and thiourea-modified zeolite-rich tuffs

In the present investigation, two zeolite-rich tuffs from Guaymas and El Cajon(State of Sonora), which were conditioned with a sodium chloride solution and subsequently modified with a thiourea solution, were chosen to evaluate the removal of Cd from aqueous systems. The zeolitic materials were characterized by scanning electron microscopy and X-ray diffraction. The surface area was also determined. The experiments were performed in a batch system, and the influences of p H, contact time between phases, and the concentration of Cd in the solution on the adsorption by sodium or thiourea-modified zeolite-rich tuff were investigated. It was found that the efficiency of Cd ion removal from aqueous solutions is influenced by the p H of the aqueous systems. The Cd adsorption kinetic data were well fitted to a pseudo-second-order model in all cases. The Langmuir and Langmuir–Freundlich isotherms adequately described the Cd sorption behavior by the zeolite from El Cajon pretreated with Na Cl and the zeolite from Guaymas modified with thiourea, respectively.     

One-step synthesis of Cu(II) metal–organic gel as recyclable material for rapid, efficient and size selective cationic dyes adsorption

Efficient removal of non-biodegradable and hazardous dyes from wastewater remains a hot research topic. Herein, a rationally designed a Cu(Ⅱ)-based metal–organic gel(Cu-MOG) with a nanoporous 3 D network structure prepared via a simple one-step mixing method was successfully employed for the removal of cationic dyes. The Cu-MOG exhibited high efficiency, with an adsorption capacity of up to 650.32 mg/g, and rapid adsorption efficiency, with the ability to adsorb 80% of Neutral Red within 1 min. The high adsorption efficiency was attributed to its large specific surface area, which enabled it to massively bind cationic dyes through electrostatic interaction, and a nanoporous structure that promoted intra-pore diffusion. Remarkably, the Cu-MOG displayed size-selective adsorption, based on adsorption studies concerning dyes of different sizes as calculated by density functional theory. Additionally, the adsorption performance of the Cu-MOG still maintained removal efficiency of 100% after three regeneration cycles. These results suggested that the Cu-MOG could be expected to be a promising and competitive candidate to conveniently process wastewater.     

Adsorption of 17β-estradiol from aqueous solution by raw and direct/pre/post-KOH treated lotus seedpod biochar

Five biochars derived from lotus seedpod(LSP) were applied to examine and compare the adsorption capacity of 17β-estradiol(E2) from aqueous solution.The effect of KOH activation and the order of activation steps on material properties were discussed.The effect of contact time,initial concentration,p H,ionic strength and humic acid on E2 adsorption were investigated in a batch adsorption process.Experimental results demonstrated that the pseudo second-order model fitted the experimental data best and that adsorption equilibrium was reached within 20 hr.The efficiency of E2 removal increased with increasing E2 concentration and decreased with the increase of ionic strength.E2 adsorption on LSP-derived biochar(BCs) was influenced little by humic acid,and slightly affected by the solution p H when its value ranged from 4.0 to 9.0,but considerably affected at p H 10.0.Low environmental temperature is favorable for E2 adsorption.Chemisorption,π–π interactions,monolayer adsorption and electrostatic interaction are the possible adsorption mechanisms.Comparative studies indicated that KOH activation and the order of activation steps had significant impacts on the material.Post-treated biochar exhibited better adsorption capacity for E2 than direct treated,pretreated,and raw LSP biochar.Pyrolyzed biochar at higher temperature improved E2 removal.The excellent performance of BCs in removing E2 suggested that BCs have potential in E2 treatment and that the biochar directly treated by KOH would be a good choice for the treatment of E2 in aqueous solution,with its advantages of good efficiency and simple technology.     

Removal of Pb(II) from aqueous solution by hydrous manganese dioxide: Adsorption behavior and mechanism

Hydrous manganese dioxide (HMO) synthesized by redox of potassium permanganate and hydrogen peroxide was used as an adsorbent for Pb(Ⅱ) removal.The specific surface area,pore volume and BJH pore diameter of the HMO were 79.31m2/g,0.07cm3/g and 3.38 nm,respectively.The adsorption equilibrium at 298K could be well described by the Langmuir isotherm equation with q max value of 352.55mg/g.The negative values of G and the positive values of H and S indicated the adsorption process was spontaneous and endothermic.The pseudo second-order equation could best fit the adsorption data.The value of the calculated activation energy for Pb(Ⅱ) adsorption onto the HMO was 38.23 kJ/mol.The uptake of Pb(Ⅱ) by HMO was correlated with increasing surface hydroxyl group content and the main adsorbed speciation was PbOH+.The final chemical state of Pb(Ⅱ) on the surface of HMO was similar to PbO.HMO was a promising candidate for Pb(Ⅱ) removal from aqueous solution.     

Adsorption behavior of sulfamethazine in an activated sludge process treating swine wastewater

Swine wastewater is an important pollution source of antibiotics entering the aquatic environment. In this work,the adsorption behavior of sulfamethazine(SMN),a commonlyused sulfonamide antibiotic,on activated sludge from a sequencing batch reactor treating swine wastewater was investigated. The results show that the adsorption of SMN on activated sludge was an initially rapid process and reached equilibrium after 6 hr. The removal efficiency of SMN from the water phase increased with an increasing concentration of mixed liquor suspended solids,while the adsorbed concentration of SMN decreased. Solution pH influenced both the speciation of SMN and the surface properties of activated sludge,thus significantly impacting the adsorption process. A linear partition model could give a good fit for the equilibrium concentrations of SMN at the test temperatures(i.e.,10,20 and 30°C). The partition coefficient(Kd) was determined to be 100.5 L/kg at 20°C,indicating a quite high adsorption capacity for SMN. Thermodynamic analysis revealed that SMN adsorption on activated sludge was an exothermic process. This study could help to clarify the fate and behavior of sulfonamide antibiotics in the activated sludge process and assess consequent environmental risks arising from sludge disposal as well.     

Biosorption of Cu(II) on extracellular polymers from Bacillus sp. F19

Biosorption can be an effective process for the removal of heavy metals from aqueous solutions. The adsorption of Cu(Ⅱ) from aqueous solution on the extracellular polymers (EPS) from Bacillus sp. (named MBFF19) with respect to pH, incubation time,concentration of initial Cu(Ⅱ), and biosorbent dose was studied. Biosorption of Cu(Ⅱ) is highly pH dependent. The maximum uptake of Cu(Ⅱ) (89.62 mg/g) was obtained at pH 4.8. Biosorption equilibrium was established in approximately 10 min. The correlation coefficient of more than 0.90 turned out that the adsorption process of Cu(Ⅱ) on MBFF19 was in accordance with both Langmuir and Freundlich isotherms. The pseudo-first and second order models were applied to examine the kinetics of the adsorption, whereas the latter was found to be in harmony with the kinetic data better. Because of the outstanding uptake capacity of Cu(Ⅱ), MBFF19 produced by Bacillus sp. was proved to be an excellent biosorbent for removing Cu(Ⅱ) from aqueous solutions.     

Use of Fe/Al drinking water treatment residuals as amendments for enhancing the retention capacity of glyphosate in agricultural soils

Fe/Al drinking water treatment residuals (WTRs), ubiquitous and non-hazardous by-products of drinking water purification, are cost-effective adsorbents for glyphosate. Given that repeated glyphosate applications could significantly decrease glyphosate retention by soils and that the adsorbed glyphosate is potentially mobile, high sorption capacity and stability of glyphosate in agricultural soils are needed to prevent pollution of water by glyphosate. Therefore, we investigated the feasibility of reusing Fe/Al WTR as a soil amendment to enhance the retention capacity of glyphosate in two agricultural soils. The results of batch experiments showed that the Fe/Al WTR amendment significantly enhanced the glyphosate sorption capacity of both soils (p < 0.001). Up to 30% of the previously adsorbed glyphosate desorbed from the non-amended soils, and the Fe/Al WTR amendment effectively decreased the proportion of glyphosate desorbed. Fractionation analyses further demonstrated that glyphosate adsorbed to non-amended soils was primarily retained in the readily labile fraction (NaHCO₃-glyphosate). The WTR amendment significantly increased the relative proportion of the moderately labile fraction (HCl-glyphosate) and concomitantly reduced that of the NaHCO₃-glyphosate, hence reducing the potential for the release of soil-adsorbed glyphosate into the aqueous phase. Furthermore, Fe/Al WTR amendment minimized the inhibitory effect of increasing solution pH on glyphosate sorption by soils and mitigated the effects of increasing solution ionic strength. The present results indicate that Fe/Al WTR is suitable for use as a soil amendment to prevent glyphosate pollution of aquatic ecosystems by enhancing the glyphosate retention capacity in soils.     

Removal of veterinary antibiotics from anaerobically digested swine wastewater using an intermittently aerated sequencing batch reactor

A lab-scale intermittently aerated sequencing batch reactor(IASBR)was applied to treat anaerobically digested swine wastewater(ADSW)to explore the removal characteristics of veterinary antibiotics.The removal rates of 11 veterinary antibiotics in the reactor were investigated under different chemical organic demand(COD)volumetric loadings,solid retention times(SRT)and ratios of COD to total nitrogen(TN)or COD/TN.Both sludge sorption and biodegradation were found to be the major contributors to the removal of veterinary antibiotics.Mass balance analysis revealed that greater than 60%of antibiotics in the influent were biodegraded in the IASBR,whereas averagely 24%were adsorbed by sludge under the condition that sludge sorption gradually reached its equilibrium.Results showed that the removal of antibiotics was greatly influenced by chemical oxygen demand(COD)volumetric loadings,which could achieve up to 85.1%±1.4%at 0.17±0.041 kg COD/m-3/day,while dropped to 75.9%±1.3%and 49.3%±12.1%when COD volumetric loading increased to 0.65±0.032 and1.07±0.073 kg COD/m-3/day,respectively.Tetracyclines,the dominant antibiotics in ADSW,were removed by 87.9%in total at the lowest COD loading,of which 30.4%were contributed by sludge sorption and 57.5%by biodegradation,respectively.In contrast,sulfonamides were removed about 96.2%,almost by biodegradation.Long SRT seemed to have little obvious impact on antibiotics removal,while a shorter SRT of 30–40 day could reduce the accumulated amount of antibiotics and the balanced antibiotics sorption capacity of sludge.Influent COD/TN ratio was found not a key impact factor for veterinary antibiotics removal in this work.     

Rapid adsorption of toxic Pb(Ⅱ) ions from aqueous solution using multiwall carbon nanotubes synthesized by microwave chemical vapor deposition technique

Multiwall carbon nanotubes(MWCNTs) were synthesized using a tubular microwave chemical vapor deposition technique, using acetylene and hydrogen as the precursor gases and ferrocene as catalyst. The novel MWCNT samples were tested for their performance in terms of Pb(Ⅱ)binding. The synthesized MWCNT samples were characterized using Fourier Transform Infrared(FT-IR), Brunauer, Emmett and Teller(BET), Field Emission Scanning Electron Microscopy(FESEM) analysis, and the adsorption of Pb(Ⅱ) was studied as a function of p H,initial Pb(Ⅱ) concentration, MWCNT dosage, agitation speed, and adsorption time, and process parameters were optimized. The adsorption data followed both Freundlich and Langmuir isotherms. On the basis of the Langmuir model, Qmaxwas calculated to be 104.2 mg/g for the microwave-synthesized MWCNTs. In order to investigate the dynamic behavior of MWCNTs as an adsorbent, the kinetic data were modeled using pseudo first-order and pseudo second-order equations. Different thermodynamic parameters, viz., ΔH0, ΔS0and ΔG0were evaluated and it was found that the adsorption was feasible, spontaneous and endothermic in nature. The statistical analysis revealed that the optimum conditions for the highest removal(99.9%) of Pb(Ⅱ) are at p H 5, MWCNT dosage 0.1 g, agitation speed 160 r/min and time of 22.5 min with the initial concentration of 10 mg/L. Our results proved that microwave-synthesized MWCNTs can be used as an effective Pb(Ⅱ) adsorbent due to their high adsorption capacity as well as the short adsorption time needed to achieve equilibrium.     

腐殖酸对苯并三唑的吸附动力学及热力学研究

HA(腐殖酸)是土壤和沉积物中有机质的重要组成部分,能在很大程度上影响有机污染物的环境行为和毒理效应. 采用批量平衡法研究了BT(苯并三唑)在HA上的吸附动力学、等温吸附和吸附热力学等内容,结果表明:拟二级动力学能较好地描述BT在HA上的吸附行为,吸附过程分为快速吸附阶段和慢速吸附阶段,但主要以快速吸附为主;0~40min为快速吸附阶段,吸附总量占平衡吸附量的89.0%以上. 吸附等温线较好地符合Freundlich模型,R2均在0.9996以上. 初始ρ(BT)为300.0mg/L时,温度由288.15K升至308.15K,吸附量从15.70g/kg降至11.58g/kg,减少了26.24%. 此外,ΔH0(吸附焓变)为-30.19kJ/mol,说明吸附过程为放热反应;ΔG0(吉布斯自由能变)小于零,说明反应是自发的. 吸附反应的E_a(活化能)为19.35kJ/mol,表明吸附属于物理吸附.      

Simultaneous removal of Cu(II) and Cr(VI) by Mg–Al–Cl layered double hydroxide and mechanism insight

Mg–Al–Cl layered double hydroxide (Cl-LDH) was prepared to simultaneously remove Cu(II) and Cr(VI) from aqueous solution. The coexisting Cu(II) (20 mg/L) and Cr(VI) (40 mg/L) were completely removed within 30 min by Cl-LDH in a dosage of 2.0 g/L; the removal rate of Cu(II) was accelerated in the presence of Cr(VI). Moreover, compared with the adsorption of single Cu(II) or Cr(VI), the adsorption capacities of Cl-LDH for Cu(II) and Cr(VI) can be improved by 81.05% and 49.56%, respectively, in the case of coexisting Cu(II) (200 mg/L) and Cr(VI) (400 mg/L). The affecting factors (such as solution initial pH, adsorbent dosage, and contact time) have been systematically investigated. Besides, the changes of pH values and the concentrations of Mg²⁺ and Al³⁺ in relevant solutions were monitored. To get the underlying mechanism, the Cl-LDH samples before and after adsorption were thoroughly characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. On the basis of these analyses, a possible mechanism was proposed. The coadsorption process involves anion exchange of Cr(VI) with Cl⁻ in Cl-LDH interlayer, isomorphic substitution of Mg²⁺ with Cu²⁺, formation of Cu₂Cl(OH)₃ precipitation, and the adsorption of Cr(VI) by Cu₂Cl(OH)₃. This work provides a new insight into simultaneous removal of heavy metal cations and anions from wastewater by Cl-LDH.     

Phosphate adsorption performance of a novel filter substrate made from drinking water treatment residuals

Phosphate is one of the most predominant pollutants in natural waters. Laboratory experiments were conducted to investigate the phosphate adsorption performance of a(NFS) made from drinking water treatment residuals. The adsorption of phosphate on the NFS fitted well with the Freundlich isotherm and pseudo second-order kinetic models. At p H 7.0, the maximum adsorption capacity of 1.03 mg/g was achieved at 15°C corresponding to the wastewater temperature in cold months, and increased notably to 1.31 mg/g at 35°C.Under both acidic conditions(part of the adsorption sites was consumed) and basic conditions(negative charges formed on the surface of NFS, which led to a static repulsion of PO43-and HPO42-), the adsorption of phosphate was slightly inhibited. Further study showed that part of the adsorption sites could be recovered by 0.25 mol/L Na OH. The activation energy was calculated to be above 8.0 k J/mol, indicating that the adsorption of phosphate on NFS was probably a chemical process. Considering the strong phosphate adsorption capacity and recoverability, NFS showed great promise on enhancing phosphate removal from the secondary treated wastewater in the filtration process.     

给水厂污泥改良生物滞留填料除磷效果的研究

通过静态吸附实验研究了土壤、给水厂污泥对磷的吸附特性,采用生物滞留模拟柱,考察生物滞留技术对城市径流中磷的去除效果,评价以给水厂污泥改良填料的可行性.结果表明,给水厂污泥对磷的吸附能力远大于土壤.在进水磷浓度为1.0 mg·L-1条件下,传统填料模拟柱出水总磷随着进水量的增加浓度逐渐增大,而改良填料模拟柱表现出稳定的长期去除效果,经7个月的连续运行,改良填料模拟柱出水总磷的浓度仍小于0.050 mg·L-1,满足地表水Ⅲ类水质标准.根据静态吸附实验估算结果,相同的控制条件下,添加4%给水厂污泥的改良填料对磷的吸附能力约为传统填料的4倍.无定型铁铝的沉淀、吸附作用是改良填料截留进水中磷的主要机制,工程应用中可在填料中添加4%~5%比例的给水厂污泥以提高生物滞留设施控制受纳水体富营养化的效果.     

Investigation on the eco-toxicity of lake sediments with the addition of drinking water treatment residuals

Drinking water treatment residuals(WTRs) have a potential to realize eutrophication control objectives by reducing the internal phosphorus(P) load of lake sediments. Information regarding the ecological risk of dewatered WTR reuse in aquatic environments is generally lacking, however. In this study, we analyzed the eco-toxicity of leachates from sediments with or without dewatered WTRs toward algae Chlorella vulgaris via algal growth inhibition testing with algal cell density, chlorophyll content, malondialdehyde content, antioxidant enzyme superoxide dismutase activity, and subcellular structure indices. The results suggested that leachates from sediments unanimously inhibited algal growth, with or without the addition of different WTR doses(10% or 50% of the sediment in dry weight) at different p H values(8–9), as well as from sediments treated for different durations(10 or 180 days). The inhibition was primarily the result of P deficiency in the leachates owing to WTR P adsorption, however, our results suggest that the dewatered WTRs were considered as a favorable potential material for internal P loading control in lake restoration projects, as it shows acceptably low risk toward aquatic plants.     

Removal of ammonium ion from water by Na-rich birnessite: Performance and mechanisms

Na-rich birnessite (NRB) was synthesized by a simple synthesis method and used as a high-efficiency adsorbent for the removal of ammonium ion (NH₄⁺) from aqueous solution. In order to demonstrate the adsorption performance of the synthesized material, the effects of contact time, pH, initial ammonium ion concentration, and temperature were investigated. Adsorption kinetics showed that the adsorption behavior followed the pseudo second-order kinetic model. The equilibrium adsorption data were fitted to Langmuir and Freundlich adsorption models and the model parameters were evaluated. The monolayer adsorption capacity of the adsorbent, as obtained from the Langmuir isotherm, was 22.61 mg NH₄⁺-N/g at 283 K. Thermodynamic analyses showed that the adsorption was spontaneous and that it was also a physisorption process. Our data revealed that the higher NH₄⁺ adsorption capacity could be primarily attributed to the water absorption process and electrostatic interaction. Particularly, the high surface hydroxyl-content of NRB enables strong interactions with ammonium ion. The results obtained in this study illustrate that the NRB is expected to be an effective and economically viable adsorbent for ammonium ion removal from aqueous system.