Enhanced flushing of polychlorinated biphenyls contaminated sands using surfactant foam: Effect of partition coefficient and sweep efficiency

Foam flushing is an in situ soil remediation technology based on the traditional surfactant flushing method. The contribution of mobility control to contaminant removal by foam is helpful for improving this technology. Foam flushing of polychlorinated biphenyl (PCB)-contaminated unconsolidated media was performed to evaluate the effect of the partition coefficient (PC) and sweep efficiency (SE) on PCB removal. Column flushing with surfactant solution and foam with different types and concentrations of surfactant was carried out for PCB removal. Two types of quartz sand were investigated to evaluate the Jamin effect on the SE value of the washing agent. The results demonstrate that a small PC value and large SE value are necessary to achieve high PCB removal for foam flushing. Compared with solution flushing, the introduction of foam can effectively control the mobility of the washing agent. Similar to solution flushing, solubilization is a key factor which dominates the removal of PCBs in foam flushing. In addition, the SE value and PCB removal by foam flushing is less affected by particle size. Therefore, foam flushing was proved to be more effective in porous media with low hydraulic conductivity and high porosity. An integrated flushing with water, surfactant solution and foam was performed and the results prove that this technology successfully combines the advantages of solution solubilization and mobility control by foam, and thus further increases the remediation efficiency of PCBs to 94.7% for coarse sand.     

Chlorine removal from MSWI fly ash by thermal treatment: Effects of iron/aluminum additives

The high content of alkali chlorides in municipal solid waste incineration(MSWI) fly ash limit its resource reuse due to the potential environmental risks.In this paper, with superheated steam as the gasifying agent and inducer, chlorides in fly ash were removed by thermal treatment within a moderate temperature range.Thermal treatment experiments were performed under different conditions: temperature(500–800℃), steam addition(mass ratio of steam to fly ash = 0.25–1) and residence time(0.5–3 hr).Iron and aluminum powders were added to fly ash to improve the chlorine removal efficiency.Water-soluble chlorides included Na Cl and KCl, and insoluble chlorides mainly included Ca(OH)Cl.The heating process with the addition of water steam was more efficient than that without steam in terms of the removal performance of water-soluble chlorides.The removal efficiency of soluble chlorides reached 75.25% for a mass ratio of 1:1 after 1-hr thermal treatment at 700℃.When the residence time was increased above 1 hr, the total dechlorination efficiency was not increased dramatically.Moreover, adding iron and aluminum powder into the fly ash improved the removal of water-insoluble chlorides, and the total dechlorination efficiency was increased by 11.41%–16.64%.     

Laboratory-scale column study for remediation of TCE-contaminated aquifers using three-section controlled-release potassium permanganate barriers

A laboratory-scale study with a sand column was designed to simulate trichloroethylene(TCE) pollution in the aquifer environment with three-section controlled-release potassium permanganate(CRP) barriers.The main objective of this study was to evaluate the feasibility of CRP barriers in remediation of TCE in aquifers in a long-term and controlled manner.CRP particles with a 1:3 molar ratio of KMnO 4 to stearic acid showed the best controlled-release properties in pure water,and the theoretical release time was 138.5 days.The results of TCE removal in the test column indicated that complete removal efficiency of TCE in a sand column by three-section CRP barriers could be reached within 15 days.The molar ratio of KMnO 4 to TCE in the three-section CRP barriers was 16:1,which was much lower than 82:1 as required when KMnO 4 solution is used directly to achieve complete destruction of TCE.This result revealed that the efficiency of CRP for remediation of TCE was highly improved after encapsulation.     

Hydrogen generation from polyvinyl alcohol-contaminated wastewater by a process of supercritical water gasification

Gasification of polyvinyl alcohol(PVA)-contaminated wastewater in supercritical water(SCW)was investigated in a continuous flow reactor at 723-873 K,20-36 MPa and residence time of 20-60 s.The gas and liquid products were analyzed by GC/TCD,and TOC analyzer.The main gas products were H_2,CH_4,CO and CO_2.Pressure change had no significant influence on gasification efficiency. Higher temperature and longer residence time enhanced gasification efficiency,and lower temperature favored the production of H_2. The effects of KOH catalyst on gas product composition were studied,and gasification efficiency were analyzed.The TOC removal efficiency(R_(TOC)),carbon gasification ratio(R_(CG))and hydrogen gasification ratio(R_(HG))were up to 96.00%,95.92% and 126.40% at 873 K and 60 s,respectively,which suggests PVA can be completely gasified in SCW.The results indicate supercritical water gasification for hydrogen generation is a promising process for the treatment of PVA wastewater.     

Catalytic reductive dechlorination of p–chlorophenol in water using Ni/Fe nanoscale particles

Nanoscale bimetallic Ni/Fe particles were synthesized from the reaction of sodium borohydride （NaBH4） with reduction of Ni^2＋ and Fe^2＋ in aqueous solution. The obtained Ni/Fe particles were characterized by TEM （transmission electron microscope）, XRD （X-ray diffractometer）, and N2-BET. The dechlorination activity of the Ni/Fe was investigated using p-chlorophenol （p-CP） as a probe agent. Results demonstrated that the nanoscale Ni/Fe could effectively dechlorinate p-CP at relatively low metal to solution ratio of 0.4 g/L （Ni 5 wt%）. The target with initial concentration ofp-CP 0.625 mmol/L was dechlorinted completely in 60 rain under ambient temperature and pressure. Factors affecting dechlorination efficiency, including reaction temperature, pH, Ni loading percentage over Fe, and metal to solution ratio, were investigated. The possible mechanism of dechlorination ofp-CP was proposed and discussed. The pseudo-first- order reaction took place on the surface of the Ni/Fe bimetallic particles, and the activation energy of the dechlorination reaction was determined to be 21.2 kJ/mol at the temperature rang of 287-313 K.     

Response surface method for modeling the removal of carbon dioxide from a simulated gas using water absorption enhanced with a liquid-film-forming device

This paper presents the results from using a physical absorption process to absorb gaseous CO_2mixed with N_2using water by producing tiny bubbles via a liquid-film-forming device(LFFD)that improves the solubility of CO_2in water.The influence of various parameters—pressure,initial CO_2concentration,gas-to-liquid ratios,and temperature—on the CO_2removal efficiency and its absorption rate in water were investigated and estimated thoroughly by statistical polynomial models obtained by the utilization of the response surface method(RSM)with a central composite design(CCD).Based on the analysis,a high efficiency of CO_2capture can be reached in conditions such as low pressure,high CO_2concentration at the inlet,low gas/liquid ratio,and low temperature.For instance,the highest removal efficiency in the RSM–CCD experimental matrix of nearly 80%occurred for run number 20,which was conducted at 0.30 MPa,CO_2concentration of 35%,gas/liquid ratio of 0.71,and temperature of 15°C.Furthermore,the coefficients of determination,R~2,were 0.996 for the removal rate and 0.982 for the absorption rate,implying that the predicted values computed by the constructed models correlate strongly and fit well with the experimental values.The results obtained provide essential information for implementing this method properly and effectively and contribute a promising approach to the problem of CO_2capture in air pollution treatment.     

Iron and lead ion adsorption by microbial flocculants in synthetic wastewater and their related carbonate formation

Although microbial treatments of heavy metal ions in wastewater have been studied, the removal of these metals through incorporation into carbonate minerals has rarely been reported. To investigate the removal of Fe^3＋ and Pb^2＋, two representative metals in wastewater, through the precipitation of carbonate minerals by a microbial flocculant （MBF） produced by Bacillus mucilaginosus. MBF was added to synthetic wastewater containing different Fe^3＋ and Pb^2＋ concentrations, and the extent of flocculation was analyzed. CO2 was bubbled into the mixture of MBF and Fe^3＋/Pb^2＋ to initiate the reaction. The solid substrates were analyzed via X-ray diffraction, transmission electron microscopy and energy dispersive spectroscopy. The results showed that the removal efficiency decreased and the MBF adsorption capacity for metals increased with increasing heavy metal concentration. In the system containing MBF, metals （Fe^3＋ and Pb^2＋）, and CO2, the concentrated metals adsorbed onto the MBF combined with the dissolved CO2, resulting in oversaturation of metal carbonate minerals to form iron carbonate and lead carbonates. These results may be used in designing a method in which microbes can be utilized to combine CO2 with wastewater heavy metals to form carbonates, with the aim of mitigating environmental problems.     

Photoreductive degradation of sulfur hexafluoride in the presence of styrene

Sulfur hexafluoride （SF6） is known as one of the most powerful greenhouse gases in the atmosphere. Reductive photodegradation of SF6 by styrene has been studied with the purpose of developing a novel remediation for sulfur hexafluoride pollution. Effects of reaction conditions on the destruction and removal efficiency （DRE） of SF6 are examined in this study. Both initial styrene-to-SF6 ratio and initial oxygen concentration exert a significant influence on DRE. SF6 removal efficiency reaches a maximum value at the initial styrene-to-SF6 ratio of 0.2. It is found that DRE increases with oxygen concentration over the range of 0 to 0.09 mol/m^3 and then decreases with increasing oxygen concentration. When water vapor is fed into the gas mixture, DRE is slightly enhanced over the whole studied time scale. The X-ray Photoelectron Spectroscopy （XPS） analysis, together with gas chromatography-mass spectrometry （GC-MS） and Fourier Transform Infrared spectroscopy （FT-IR） analysis, prove that nearly all the initial fluorine residing in the gas phase is in the form of SiF4, whereas, the initial sulfur is deposited in the form of elemental sulfur, after photodegradation. Free from toxic byproducts, photodegradation in the presence of styrene may serve as a promising technique for SF6 abatement.     

Interference of iron as a coagulant on MIB removal by powdered activated carbon adsorption for low turbidity waters

Powered activated carbon (PAC) is widely used in water treatment plants to minimize odors in drinking water. This study investigated the removal of 2-methylisoborneol (MIB) by PAC adsorption, combined with coagulation using iron as a coagulant. The adsorption and coagulation process were studied through different case scenarios of jar tests. The analysis evaluated the effect of PAC dosing in the liquid phase immediately before or after the coagulant addition. Ferric sulphate was used as the coagulant with dosages from 10 to 30 mg/L, and PAC dosages varied from 10 to 40 mg/L. The highest MIB removal efficiency (about 70%) was achieved without the coagulant addition and with the highest PAC dosage (40 mg/L). Lower MIB removal efficiencies were observed in the presence of coagulant, showing a clear interference of the iron precipitate or coagulant in the adsorption process. The degree of interference of the coagulation process in the MIB removal was proportional to the ratio of ferric hydroxide mass to the PAC mass. For both cases of PAC dosing, upstream and downstream of the coagulant injection point, the MIB removal efficiency was similar. However, MIB removal efficiency was 15% lower when compared with experiments without the coagulant application. This interference in the MIB adsorption occurs potentially because the coagulant coats the surface of the carbon and interferes with the MIB coming in contact with the carbon’s surface and pores. This constraint requires an increase of the PAC dosage to provide the same efficiency observed without coagulation.     

Absorption characteristics of elemental mercury in mercury chloride solutions

Elemental mercury （Hg^0） in flue gases can be efficiently captured by mercury chloride （HgCl2） solution. However, the absorption behaviors and the influencing effects are still poorly understood. The mechanism of Hg^0 absorption by HgCl2 and the factors that control the removal were studied in this paper. It was found that when the mole ratio of Cl^- to HgCl2 is 10：1, the Hg^0 removal efficiency is the highest. Among the main mercury chloride species, HgCl3^- is the most efficient ion for Hg^0 removal in the HgCl2 absorption system when moderate concentrations of chloride ions exist. The Hg^0 absorption reactions in the aqueous phase were investigated computationaIIy using Moller-Plesset perturbation theory. The calculated Gibbs free energies and energy barriers are in excellent agreement with the results obtained from experiments. In the presence of SO3^2- and SO2, Hg^2＋ reduction occurred and Hg^0 removal efficiency decreased. The reduced Hg^0 removal can be controlled through increased chloride concentration to some degree. Low pH value in HgCla solution enhanced the Hg^0 removal efficiency, and the effect was more significant in dilute HgCl2 solutions. The presence of SO4^2- and NO3^- did not affect Hg^0 removal by HgCl2.     

双金属和多金属系统对零价铁利用效率的改进

为解决Fe0-PRB(零价铁-渗透反应格栅)中Fe0利用效率低、易板结堵塞的问题,分别采用粒径为0.074 mm的试剂铁粉和0.150～0.270 mm的工业铁粉为反应介质,在铁粉表面负载不同比例的Cu或Ni制备Cu/Fe、Ni/Fe双金属和Cu/Ni/Fe多金属颗粒,研究Fe0、双金属和多金属系统去除Cr(Ⅵ)的性能、机制.结果表明:双金属和多金属系统的Cr(Ⅵ)去除率明显高于Fe0,试剂铁粉的Cr(Ⅵ)去除率明显高于工业铁粉.反应8 h达到平衡后,试剂铁粉和工业铁粉的Cr(Ⅵ)去除率仅为45%和20%,Cu/Fe双金属、Cu/Ni/Fe多金属的Cr(Ⅵ)去除率均能达到90%以上,以试剂铁粉和工业铁粉制备的Ni/Fe双金属的Cr(Ⅵ)去除率最高分别为76.6%和44.0%.不同负载率的双金属和多金属系统反应过程中可溶的ρ〔Cr(Ⅲ)〕较低.反应后溶液的pH从反应前的5.0升至10.0左右.反应初期ρ(TFe)(TFe为总铁)超过了0.30 mg/L,其余时间均达标.反应过程中ρ(Cu2+)均在0.40 mg/L以下,均未检测出Ni2+.研究显示,双金属和多金属系统显著提高了Fe0利用效率.      

Evaluation of remediation process with soapberry derived saponin for removal of heavy metals from contaminated soils in Hai-Pu, Taiwan

The use of a biodegradable natural plant-based surfactant extracted from soapberry is proposed for the remediation of Ni, Cr and Mn from industrial soil site in Hai-Pu, Taiwan. Batch experiments were performed under variation of fundamental factors (saponin concentration, pH, and incubation time) for metal remediation. Removal of Ni and Mn were increased with increasing saponin concentration (0.015-0.150 g/L), whereas the removal of Cr was increased upto 0.075 g/L saponin. The Ni, Cr and Mn were removed significantly (p ≤q 0.05) at near to the neutral and slightly acidic (pH 5 to 8) conditions. Removal efficiency of Ni (99%) from the soil was found to be greater than that of Cr (73%) or Mn (25%) in the presence of saponin at a concentration of 0.150 g/L at pH 5. The removal percentage increased with incubation time where the removal of Ni was faster than that of Cr and Mn. The result indicates the feasibility of eco-friendly removal of heavy metal (Ni, Cr and Mn) from industrial soil by soil washing process in presence of plant derived saponin.     

Enhanced remediation of Cr（Ⅵ）-contaminated groundwater by coupling electrokinetics with ZVI/Fe3O4/AC-based permeable reactive barrier

Although widely used in permeation reaction barrier（PRB） for strengthening the removal of various heavy metals, zero-valent iron（ZVI） is limited by various inherent drawbacks, such as easy passivation and poor electron transfer. As a solution, a synergistic system with PRB and electrokinetics（PRB-EK） was established and applied for the efficient removal of Cr（Ⅵ）-contaminated groundwater. As the filling material of PRB, ZVI/Fe₃O₄/activated carbon（ZVI/Fe₃O₄     

S-NZVI/PS凝胶反应带修复硝基苯污染地下水

采用前置硫化法合成制备硫化纳米铁,研究其与过硫酸盐对硝基苯的联合降解效果,检测反应前后溶液中铁离子和TOC浓度变化,对反应前后的S-NZVI进行表征,分析S-NZVI和PS对NB的联合降解机制.以纳米硅胶溶液为胶结剂,以PS为活性成分,制备缓释PS溶胶,注入砂柱中扩散形成凝胶,与S-NZVI构成S-NZVI/PS组合反应带,研究其对模拟硝基苯污染地下水的原位修复效果.结果表明,S-NZVI能够高效去除NB并生成大量苯胺（AN）,S-NZVI被PS氧化产生的Fe²⁺与PS组成活化过硫酸盐,对AN具有较好的降解和矿化效果.当NB浓度为100mg/L、S-NZVI和PS的投加量分别为0.5,2.5g/L时,NB去除率达91%,AN出水浓度为1.96mg/L,TOC去除率达64.09%.反应后S-NZVI的主要铁氧化产物为Fe₃O₄和FeO（OH）.反应带实验结果表明,S-NZVI/PS组合反应带可有效去除地下水的NB并高效消减NB还原产生的AN,当进水中NB浓度为100mg/L,流量为0.4mL/min,注入S-NZVI含量为1200mg/L的浆液200mL,二氧化硅含量为30%、PS含量为12.5%的PS凝胶4.8g时,S-NZVI/PS组合反应带7d内对AN的去除率最高达97.6%,NB当量累计去除率为83.7%.     

Rapid treatment of atrazine-contaminated water by nickel/iron bimetallic system

The utility of nickel/iron in the remediation of atraz.ine-contaminated water was investigated. The experimental results showed that nickel/iron had effective catalytic activity in dechlorinating atraz.ine under acidic conditions. The dechlonnation reaction approximately followed the first-order kinetics under the experimental conditions( nickel/iron: 1.0 g/250 ml: Ca~r~ = 20.0 mg/L), the reaction rate increased with decreasing pH value of the reaction solution and increasing the proportion of Ni: Fe within 2.95 %. For condition with 2.95% nickel/iron, the reaction rate constants were 0.07518( R = 0.9927), 0.06212( R = 0.9846) and 0.00131 min^-1 ( R = 0.9.565) at pH = 2.0, 3.0 and 4.0, respectively. HPLC analysis was used to monitor the decline of atraz.ine concentration.     

生物炭负载纳米零价铁对污染土壤中铜钴镍铬的协同去除

合成了一种低成本、高效生物炭负载纳米零价铁的复合材料(ZVI-SM)并应用于铜、钴、镍、铬污染土壤的修复。采用X射线衍射(XRD)、X射线光电子能谱(XPS)和金属吸附实验等方法,考察了不同碳化温度下制备的生物炭前驱体和生物炭复合材料对复合重金属污染修复的影响及去除作用机制。其中,吸附-还原后形成的FeCr₂O₄极大地降低了铬的毒性,同时提高了铜、钴、镍的去除率。Fe0的引入既提高了生物炭对重金属的吸附量,又解决了Cr(Ⅵ)毒性的问题;XPS的结果进一步阐明了生物炭可以作为电子传递介质,通过表面官能团得失电子与Fe0间形成强相互作用,增强了复合材料对多重金属离子的去除效果。除ZVI-SM500外,ZVI-SM100、300、400、700 4种材料对于铜、钴、镍、铬的去除率要远高于商用纳米Fe0和单纯的生物炭材料,表现为对铬和铜有较强的亲和力和反应性,均能在5 min内完全去除铜和铬,钴和镍也能在180 min内达到80%以上的去除率。在反应过程中存在显著的离子竞争效应:铬≥铜>钴>镍,这与金属离子的标准还原电位大小的趋势一致。土壤修复实验表明:ZNI-SM300用于污染土壤的修复,15 d后,Cr(Ⅵ)含量从480 mg/kg降至0.52 mg/kg,水溶态Cr总量从500 mg/kg降至1.2 mg/kg,两者的固定化效率均达到99%以上,并能达到完全去除水溶态的铜、钴、镍、Cr(Ⅵ)的效果。因此,以SM300为载体的纳米零价铁可作为复合重金属污染土壤修复的理想材料。     

高铁酸盐溶液的制备与去除氨氮的实验研究

根据现场制备要求,优化传统高铁制备工艺,得出工业化现场制备液体高铁的最佳工艺条件,进而用于水库水氨氮的去除研究。实验结果表明,通过优化工艺所制得高铁浓度为24 g/L左右,铁转化率为80%左右。高铁对氨氮的去除效果随高铁与氨氮的摩尔比增大而增大,当摩尔比为0.45时,高铁对水源水中氨氮的去除率可达75%;在保证高去除率的基础上,通过延长絮凝反应时间,可降低高铁投加量;如果采用高铁预氧化,聚合铝或三氯化铁作絮凝剂,可提高对氨氮的去除率,还能大幅度降低高铁投加量,缩短反应时间。     

纳米镍/铁和铜/铁双金属对四氯乙烯脱氯研究

以实验室合成的纳米双金属颗粒(Ni/Fe和Cu/Fe)为反应材料,对四氯乙烯(PCE)进行脱氯试验研究.纳米金属颗粒(直径范围在1～100nm)比表面积比微米级铁颗粒高数十倍.结果表明,纳米Ni/Fe和Cu/Fe对四氯乙烯有明显的脱氯作用,且脱氯反应符合准一级反应动力学方程;在作为还原剂的铁表面镀上一薄层起催化作用的金属Ni或Cu,催化剂的存在大大降低脱氯反应活化能,提高了脱氯速率,并减少氯代副产物的产量.与零价铁及微米级双金属系统(Ni/Fe,Cu/Fe)相比,纳米颗粒对PCE的脱氯速率有明显提高,尤其是纳米Ni/Fe,标准化反应速率常数KSA为4.283 mL·m-2·h-1,分别比零价铁和微米级Ni/Fe系统快33.23倍和11.59倍.纳米Cu/Fe标准化反应速率常数KSA为1.194 mL·m-2·h-1,分别比零价铁和微米级Cu/Fe双金属系统快9.26倍和5.24倍.在相同条件下,纳米Ni/Fe脱氯速率常数KSA是纳米Cu/Fe的3.59倍.     

煤系硫铁矿处理含镍废水的实验研究

在煤系硫铁矿在处理含镍废水中,废水的pH值,反应时间,粒度,加入量,温度,搅拌等对Ni2+的去除率影响较大。在煤系硫铁矿中加入不同配比的还原铁粉进行改性处理实验。结果表明煤系硫铁矿与还原铁粉的比例为100:10时,加热温度为200℃时,对镍的去除率明显提高。     

硫化纳米铁反应带修复硝基苯污染地下水

采用前置硫化合成法制备硫化纳米铁（S-NZVI）并进行表征,采用模拟砂柱创建S-NZVI原位反应带,研究其对硝基苯（NB）污染地下水的修复效能.X射线衍射（XRD）、X射线光电子能谱（XPS）、透射电子显微镜（TEM）表征结果表明,S-NZVI是以Fe（0）为核心,硫铁化合物为外壳的颗粒,可以有效抑制S-NZVI颗粒的团聚,具有较好的分散性.与NZVI相比,S-NZVI对NB的去除效率更高,最高去除率可达99.65%,在砂柱中具有更强的穿透能力.S-NZVI对NB的去除过程符合准一级动力学模式.S-NZVI对NB的去除机理是先将NB快速吸附于表面,然后再进一步通过化学还原降解,因此NB去除较快而苯胺生成较慢.S-NZVI反应带对NB泄露区的削减幅度较大,增加单井S-NZVI注入量和增加注入井均可提高修复效果,7d内NB累计去除率最高达87.43%,但前2d出水NB浓度仍然较高;S-NZVI反应带对NB传输区具有较好的修复效果,增加注入井比增加单井S-NZVI注入量具有更好的持续性和更高的NB去除率,7d内NB累计去除率最高达99.90%.