Removal of Cr(VI) by magnetite nanoparticle.

Magnetite nanoparticles were synthesized by sol-gel method. The highly crystalline nature of the magnetite structure with diameter of around 10 nm was characterized with transmission electron microscopy and X-ray diffractometry. The surface area was determined to be 198 m2/g. Batch experiments were carried out to determine the adsorption kinetics and mechanism of Cr(VI) by these magnetite nanoparticles. The Cr(VI) uptake was mainly governed by physico-chemical adsorption. The adsorption process was found to be pH and temperature dependent. The adsorption data fit well with the Freundlich isotherm equation. The Freundlich constants were calculated at different temperatures. The adsorption capacity increased with rising temperature. Preliminary results indicate that magnetite nanoparticles may be used as an adsorbent for removal of Cr(VI) from wastewater.     

壳聚糖基印迹水凝微球对Cr (VI)的选择性吸附研究

目前水环境污染物成分复杂,常用的化学沉淀法已很难将重金属污染物分类去除并资源化利用,由此产生了大范围的危废污染环境,需要进行二次处理。利用离子印迹技术对壳聚糖基水凝微球进行改性,制备具有对Cr (VI)特异识别性能的吸附材料(CTS-IGB）,对其在单一Cr (VI)溶液和模拟电镀废水中的吸附行为特征进行研究。研究结果表明:在20 ℃、pH值为3时,CTS-IGB在单一Cr (VI)溶液和模拟电镀废水中Cr (VI)的吸附量在180 min内分别达到37.4 和44.3 mg/g,半饱和吸附时间仅分别为5.8和23.5 min;吸附行为符合准二级动力学。吸附等温线拟合表明吸附过程符合Freundlich模型;热力学参数表明吸附过程是放热反应,且吸附后无序度减小;相比于未改性壳聚糖水凝微球,CTS-IGB在共存离子（模拟电镀废液及其他双组份溶液）工况下对Cr (VI)的选择性提高32%~74%。该材料可作为潜在的吸附材料用于污染水环境中Cr (VI)的分离及回收。     

Efficient removal of Cr(VI) by polydopamine-modified lignin from aqueous solution: Batch and XAFS studies

Lignocellulose has the potential to become a bio-based adsorbent due to its biodegradability and renewability. In this study, a novel polydopamine-functionalized-lignin (lignin@PDA), prepared via self-polymerization of dopamine (PDA) on lignin, was used as a bio-based adsorbent for rapid scavenging of hexavalent chromium (Cr(VI)). The morphology, functional groups, crystalline structure, and chemical composition of lignin@PDA were characterized with a scanning electron microscope–energy dispersive spectrometer, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The Cr(VI) adsorption process of lignin@PDA was studied using batch experiments as a function of pH, ionic strength, adsorbent dose, and contact time at room temperature. The adsorption rate of lignin@PDA was five times greater than that of the unmodified lignin, with a maximum adsorption capacity of 102.6 mg/g in an acidic medium. The adsorption of Cr(VI) on lignin@PDA fit the pseudo-second-order equation and the Freundlich model, indicating that the adsorption process was mainly dominated by chemisorption and surface complexation. The thermodynamic parameters showed that adsorption of Cr(VI) on lignin@PDA was an endothermic and spontaneous process. The X-ray absorption fine structure results showed that sorption and reduction of Cr(VI) into Cr(III) occurred simultaneously on lignin. Moreover, PDA coating not only improved the reactivity of lignin but also promoted the complete reduction of Cr(VI) by lignin. According to these results, polydopamine-functionalized-lignin is a promising bio-based adsorbent for immobilization of Cr(VI) from wastewater.

     

纳米铁还原TNT红水中二硝基甲苯磺酸(钠)的影响因素研究

考察了纳米铁的投加量、二硝基甲苯磺酸钠(DNTS)初始浓度、初始pH、纳米铁超声、干燥处理等因素对纳米铁还原TNT红水中DNTS效果的影响。结果表明:考察范围内,纳米铁/DNTS质量比越大,DNTS的去除率越高,单位质量纳米铁去除DNTS总质量越小;当初始pH<10时,去除率受pH影响不大,但准一级反应速率常数随pH上升而接近直线下降,酸性条件下还原更彻底,碱性条件下吸附沉淀作用更明显;干燥处理使纳米铁被部分氧化,还原能力下降;超声有助于促进纳米铁的充分分散和表面氧化层的剥离,提高反应活性。去除率随时间变化曲线表明,2,4-DNT-5-SO3Na(H)比2,4-DNT-3-SO3Na(H)容易被还原。     

花生壳对模拟废水中Cr(Ⅵ)的动态吸附特性研究

采用废弃花生壳对质量浓度为20 mg/L的Cr(Ⅵ)模拟水样进行动态吸附实验研究。结果表明:在室温条件下,用粒径为1.6～2.5 mm花生壳作吸附剂,用量为5.0 g,介质pH值为1.0,流量为3 mL/min,吸附后水样中Cr(Ⅵ)的去除率可以达到99.08%,Cr(Ⅵ)质量浓度为0.184 mg/L,满足GB 8978—1996《污水综合排放标准》的标准。对模型的拟合结果表明,Thomas模型能较好地反映吸附过程特征,花生壳饱和吸附容量为9.4 mg/g。从动态吸附穿透曲线中可见,219 min时达到吸附穿透点,1312 min时达到吸附衰竭点。     

Removal of hexavalent chromium in aquatic solutions by pomelo peel

This study investigated the removal of hexavalent chromium(Cr(VI)) in aqueous solutions using pomelo peel(PP) and FeCl_3-modified pomelo peel(FPP) as novel biomass adsorbents.Batch adsorption experiments were performed to evaluate the effects of pH,time,temperature,initial concentration,and adsorbent dose on Cr(VI) removal by PP and FPP.The results show that the maximum adsorption capacity of Cr(VI)was 21.55 mg/g for FPP and 0.57 mg/g for PP at a pH of 2.0 and a temperature of 40℃.The surface shape,microstructure,and chemical composition of FPP were analyzed with scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),and energy dispersive spectroscopy(EDS),and compared with those of PP.The results show that the adsorption performance of FPP was much better than that of PP,indicating that FPP can be an alternative high-efficiency adsorbent for Cr(VI) removal.     

Adsorption of Cr(VI) in wastewater using magnetic multi-wall carbon nanotubes

Magnetic multi-wall carbon nanotubes were prepared with wet chemical treatments and characterized by a transmission electron microscope (TEM) and X-ray diffraction (XRD). They were used as adsorbents for the removal of Cr(VI) in aqueous solutions. The effects of adsorbent dosage, the concentration of Cr(VI) in aqueous solution, temperature, and pH value on the removal efficiency were studied. Results showed that the adsorption capacity of the magnetic multi-wall carbon nanotubes increased with the initial Cr(VI) concentration, but decreased with the increase of adsorbent dosage. The adsorption amount increased with contact time. The adsorption kinetics were best represented by the pseudo second-order kinetic model, and the adsorption isotherms indicated that the Langmuir model better reflected the adsorption process. The obtained calculation results for the Gibbs free energy revealed that the adsorption was a spontaneous and endothermic process. The enthalpy deviation was 3.835 kJ·mol⁻¹. The magnetic multi-wall carbon nanotubes showed significant potential for application in adsorption of heavy metal ions.     

Biosorption and bioreduction of Cr(VI) by locally isolated Cr-resistant bacteria.

Cr(VI) biosorption and bioreduction ability of locally isolated Cr-resistant bacteria was investigated using the shake-flask technique. A mixture of S. epidermidis and B. cereus showed the highest minimum inhibitory concentration (MIC) level at 750 mg/L Cr(VI) followed by S. aureus and Bacillus sp. of 250 mg/L, and A. haemolyticus of 70 mg/L. From the Langmuir adsorption isotherm, the treatment of cells with heat-acid resulted in the highest amount of Cr(VI) adsorped (78.25 mg/g dry wt. for S. epidermidis) compared to heat-acetone (67.93 mg/g dry wt. Bacillus sp.), heat only (36.05 mg/g dry wt. S. epidermidis) or untreated cells (45.40 mg/g dry wt. S. epidermidis and B. cereus). FTIR analysis showed the involvement of amine groups in Cr(VI) adsorption. In the bioreduction study, A. haemolyticus was able to completely reduce Cr(VI) up to 50 mg/L.     

Dual Porosity Filtration for treatment of stormwater runoff: first proof of concept from Copenhagen pilot plant

Dual Porosity Filtration (DPF) is designed for sedimentation-based removal of suspended solids (SS) and adsorption-based removal of dissolved contaminants from stormwater runoff. It consists of shallow (10 mm) low-porosity layers for contaminant retention, interlaid with high-porosity layers for horizontal, gravity-driven flow. First proof of concept was obtained in a 10 m by 60 m pilot plant receiving stormwater runoff from 1.3 hectares of trafficked area in Copenhagen. The pilot plant contains two versions of DPF-designs, a cheaper one with 6 pairs of low- and high-porosity layers ('DPF-6-layers'), and a more expensive one with 18 such pairs ('DPF-18-layers'). Both versions are designed for a flow capacity of 9 m(3)/h. The DPF-designs were tested on the basis of 25 rain events. Flow proportional event mean concentrations showed the concentration of SS to be on averaged reduced from 123 mg/L in the inlet to 10.4 mg/L in the outlet from the DPF-6-layers, and 1.4 mg/L from DPF-18-layers, Zn from 98 to 29 and 12.5 μg/L, Cu from 25 to 12.2 and 9.6 μg/L, Cr from 18 to 10.9 and 10 μg/L, Pb from 9 to 1.0 and 0.2 μg/L, and P from 178 μg/L to 47.4 μg/L and 38 μg/L, respectively for the DPF-6-layers and DFF-18-layers. Based on the observed hydraulic performance and contaminant removal rates the concept of DPF appears to hold a potential for treatment of road runoff to high water quality standards. Cu and Cr fate must be further studied. Suggestions for optimized full scale DPF-designs are given.     

无机柱撑膨润土对有机锡废水COD的吸附研究

利用原土、羟基铁膨润土和羟基铁铝柱撑膨润土,进行了吸附有机锡废水中CODcr的试验.研究了膨润土投加量、吸附pH、时间和等温线的变化规律.结果表明,达到吸附平衡的时间为2 h;随着吸附pH由小到大的变化,CODCr的吸附去除率在一定范围内波动;膨润土的投加量宜大于4 g/L;吸附符合Henry等温式;膨润土的层间距、吸附位的数量及活性是决定对吸附性能的关键因素;吸附容量的大小和吸附作用的强弱顺序为:羟基铁铝膨润土＞羟基铁膨润土＞原土.     

改性活性炭对饮用水中铬酸盐的去除特性研究

研究了阳离子聚合物十六烷基三甲基氯化铵(CTAC)、癸基三甲基溴化铵(MTAB)以及三甲基正十四烷溴化铵(DTAB)对颗粒活性炭的改性特点以及改性后活性炭对饮用水中六价铬的去除效果。目的在于开发一种能有效去除饮用水中铬盐离子的吸附材料。研究中首先利用吸附平衡实验比较了未改性活性炭以及三种阳离子聚合物改性后活性炭对铬的吸附能力。结果表明:阳离子聚合物改性能有效提高活性炭对铬的吸附,同时CTAC改性后活性炭对铬盐的吸附效果要好于MTAB和DTAB。另外,活性炭对六价铬的吸附过程符合Langm iur吸附平衡模型以及二级动力学模型。阳离子聚合物在活性炭上的稳定性也是个重要的问题。对其检测的结果表明聚合物和活性炭的结合非常稳定,改性活性炭吸附六价铬的过程中阳离子聚合物的脱附量少于3%。     

特定污泥对铬(Ⅵ)的吸附容量研究

接种了高效菌种A、B的驯化污泥在前期的生物滤床系统中体现了良好的铬(Ⅵ)去除效率,为了解决系统放大后污泥再生与使用周期等问题,对污泥的铬(Ⅵ)吸附容量进行了测定,测定项目包括一次连续吸附总量、营养添加前后吸附容量的变化等。以铬(Ⅵ)质量浓度为100mg/L的废水进行实验,得到该污泥吸附最佳时间为40min,此时污泥对铬的吸附能力为污泥自身干重的14 94%。一次连续吸附总量为27～28mg/g干污泥。营养液的加入使得污泥吸附能力提高了29 68%。     

Characterization of cobalt ferrite-supported activated carbon for removal of chromium and lead ions from tannery wastewater via adsorption equilibrium

In this experiment, cobalt ferrite-supported activated carbon (CF-AC) was developed and characterized via the wet impregnation method for the removal of Cr and Pb(II) ions from tannery wastewater. Batch adsorption was carried out to evaluate the effect of experimental operating conditions (pH of solution, contact time, adsorbent dose, and temperature), and the removal efficiencies of Cr and Pb(II) ions by the developed adsorbents were calculated and recorded for all experimental conditions. These variables were estimated and reported as removal efficiencies of 98.2% for Cr and 96.4% for Pb(II) ions at the optimal conditions of 5, 0.8 g, 80 min, and 333 K for pH, adsorbent dose, contact time, and temperature, respectively. The equilibrium for the sorption of Cr and Pb(II) ions was studied using four widely used isotherm models (the Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherm models). It was found that the Freundlich isotherm model fit better with the coefficient of determination (R²) of 0.948 4 and a small sum of square error of 0.000 6. The maximum adsorption capacities (Q_m) of Pb(II) and Cr adsorbed onto CF-AC were determined to be 6.27 and 23.6 mg/g, respectively. The adsorption process conformed well to pseudo-second order kinetics as revealed by the high R² values obtained for both metals. The thermodynamic parameters showed that adsorption of Cr and Pb(II) ions onto CF-AC was spontaneous, feasible, and endothermic under the studied conditions. The mean adsorption energy (E) values revealed that the adsorption mechanism of Cr and Pb(II) by CF-AC is physical in nature. The results of the study showed that adsorbent developed from CF-AC can be efficiently used as an environmentally friendly alternative adsorbent, for removal of Cr and Pb(II) ions in tannery wastewater.     

Domestic wastewater reclamation by submerged membrane bioreactor with high concentration powdered activated carbon for stream restoration.

This study focuses on the practical application of high concentration powdered activated carbon coupled membrane bio-reactor to domestic wastewater reclamation. The study was conducted in three parts, such as analysis of secondary domestic wastewater effluent, design and operation parameter evaluation and reclaimed water quality estimation for stream restoration. The organic concentration was 25.2-80.2 mgCOD(Cr)/L for the effluent of three domestic wastewater treatment plants. Around 50-75% of the COD was low molecular substances less than 1,000 which were quite biodegradable. The sawdust PAC was estimated to be proper adsorbent for the organics in the secondary effluents. Its Freundlich constant, K value was 5.847 and 1/n, 0.36. Using a system consists of single reactor with high concentration PAC (80 g/L) and submerged hollow fiber MF membrane module with nominal pore size of 0.1 microm, design and operation parameters were obtained, such as HRT of the bioreactor (2.5 hr), PAC concentration (80 g/L), the initial flux (less than 0.5 m/day) and intermittent suction cycle (12 min. suction and 3 min. idling). Organic removal by the system was high enough to produce reclaimed water for urban stream restoration The effluent organic concentration was at the level of 2 mg/L in terms of TOC (around 5 mg/L as COD(Cr)). Substances with molecular weight cut off < 1,000 were removed mostly by adsorption and biodegradation. Those above 1,000 were rejected at PAC cake layer on the membrane and gradually degraded by microorganisms during extended contact.     

Fabrication of graphene oxide-keratin-chitosan nanocomposite as an adsorbent to remove turbidity from tannery wastewater

Excessive turbidity in water is aesthetically unappealing and severely malfunctions the photosynthesis process of aquatic ecosystems. This study aimed to evaluate the effectiveness of a nanocomposite adsorbent made of graphene oxide-keratin-chitosan for removing turbidity from tannery influent. The nanocomposite was fabricated with simple solution casting methods. Material dispersibility, bonding between composite materials (amide linkage), and the surface morphology of the nanocomposite were analyzed with the ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. At pH of 6, 2 g/L of adsorbent and a 25-min contact time resulted in about 88% of turbidity elimination. After the adsorption process, the total suspended solids, total dissolved solids, salinity, biochemical oxygen demand, and chemical oxygen demand of the tannery wastewater were reduced by 55%, 29%, 12%, 58%, and 75%, respectively. The optimum dosage of the nanocomposite with the maximum turbidity removal capacity was 12.62 mg/g. According the adsorption kinetic and isotherm models, the graphene oxide-keratin-chitosan nanocomposite played a key role in the turbidity removal process with chemisorption and electrostatic multilayer adsorption. This study provided methodological and mechanistic insights into the procedures of investigating the removal of turbidity from tannery wastewater with a novel composite material.     

HDTMA改性沸石吸附水中Cr（VI）研究

摘要：研究以阳离子表面活性剂HDTMA改性天然斜发沸石,制得HDTMA改性沸石,进而研究HDTMA改性沸石对废水中Cr（VI）的吸附特征。结果表明：HDTMAL改性沸石对cr（VI）吸附符合Langmuir等温式和拟二级动力学方程,饱和吸附量为10．99mg／g,吸附主要为化学吸附,但温度、pH值和干扰离-~HDTMA沸石吸附cr（VI）具有明显影响。     

洗浴废水处理工艺中混凝预处理的作用与效果研究

采用混凝沉淀—过滤—固定化生物活性炭—膜滤—UV 消毒工艺处理洗浴废水,整体试验结果比较理想,在物化处理过程中混凝环节至关重要。为此研究了混凝对浊度、LAS、COD_(Cr)、洗浴浴香的处理效果。研究结果表明：当投药量大于25mg/L 时,混凝沉淀可以把平均浊度为65NTU的原水降低到15NTU 以下,对 LAS、COD_(Cr)的去除率可达62%和50%以上,因此混凝是去除洗浴废水中悬浮物质、LAS 和有机污染物有效的物化处理单元;但是混凝不能有效地去除洗浴废水中的浴香。     

The removal of residual organic matter from biologically treated swine wastewater using membrane bioreactor process with powdered activated carbon.

The objective of this study was to characterize the mechanisms of the COD removal in the membrane bioreactor (MBR) process with powdered activated carbon (PAC) addition and to determine its optimal operation, for the removal of residual organic matters (ROM) from biologically treated swine wastewater. The MBR process with PAC showed higher removal efficiency of chemical oxygen demand (COD(Mn)) than that without PAC. When the average COD(Mn) concentration of the influent was 217 mg/L, the average COD(Mn) concentration of the permeate from the MBR with PAC was about 41.5 mg/L, indicating an approximate removal efficiency of 81%. On the other hand, the average COD(Mn) concentration of the permeate from the MBR without PAC was 172 mg/L. The PAC dosage estimated to obtain the above removal efficiency was about 0.74 g per litre of influent. Among the total residual organics removed by PAC-added MBR, 46.5% was removed by PAC adsorption, 20.8% by biodegradation, 4.4% by membrane separation, and 9.3% by enhanced microorganism activity. From these results, the MBR process with PAC was considered as a very useful treatment process for the reduction of COD(Mn) in biologically treated swine wastewater.     

Removal of hexavalent chromium in soil and groundwater by supported nano zero-valent iron on silica fume

Silica fume supported-Fe(0) nanoparticles (SF-Fe(0)) were prepared using commercial silica fume as a support. The feasibility of using this SF-Fe(0) for reductive immobilization of Cr(VI) was investigated through batch tests. Compared with unsupported Fe(0), SF-Fe(0) was significantly more active in Cr(VI) removal especially in 84 wt% silica fume loading. Silica fume had also been found to inhibit the formation of Fe(III)/Cr(III) precipitation on Fe nanoparticles' surface, which was increasing the deactivation resistance of iron. Cr(VI) was removed through physical adsorption of Cr(VI) onto the SF-Fe(0) surface and subsequent reduction of Cr(VI) to Cr(III). The rate of reduction of Cr(VI) could be expressed by pseudo first-order reaction kinetics. The rate constant increased with the increase in iron loading but decreased with the increase in initial Cr(VI) concentration. Furthermore, column tests showed that the SF-Fe(0) could be readily transported in model soil.     

Development of adsorbent for the simultaneous removal of organic and inorganic contaminants from aqueous solution

In this study, a modified adsorbent, alginate complex beads, was prepared and applied to the removal of mixed contaminants from wastewater. The alginate complex beads were generated by the immobilization of powdered activated carbon and synthetic zeolites onto alginate gel beads, which were then dried at 110 °C for 20 h until the diameter had been reduced to 1 mm. This dry technique increased the hardness of the adsorbent to assure its durability and application. The adsorption onto the alginate complex beads of organic and inorganic compounds, as target contaminants, was investigated by performing both equilibrium and kinetic batch experiments. From the adsorption isotherms, according to the Langmuir equation, the alginate complex bead was capable of effectively removing benzene, toluene, zinc and cadmium. From kinetic batch experiments, the removal efficiencies of benzene, toluene, zinc and cadmium were found to be 66.5, 92.4, 74.1 and 76.7%, respectively, for initial solution concentrations of 100 mg L(-1). The results indicated that the adsorbent developed in this study has the potential to be a promising material for the removal of mixed pollutants from industrial wastewater or contaminated groundwater.