Comparison of heavy metal removal efficiencies in four activated sludge processes

The removal efficiencies of heavy metals(As, Cr, Cu, Ni, Pb and Zn) were investigated in the 17 operating municipal wastewater treatment plants(WWTPs) and compared with those in four main activated sludge processes. Significant differences of heavy metal removal efficiencies were observed among four activated sludge processes. The removal efficiency for As(75.5%) in the oxidation ditch(OD) process is significantly higher than that in the conventional activated sludge(CAS) process(38.6%) or sequencing batch reactor(SBR) process(51.4%). The mean removal efficiencies for Cu and Ni in the OD process are 90.5% and 46.7%, respectively, while low mean removal efficiencies are observed for Cu(69.9%) and Ni(16.5%), respectively, in the SBR process. The removal efficiencies for Cu and Ni in the OD process are significantly higher than those in the anaerobic-anoxic-oxic(A2-O) process. These results highlight the differences of removal efficiencies for heavy metals in different processes and should be considered when selecting a wastewater treatment process.

Study on the Heavy Metals Removal Efficiencies of Constructed Wetlands with Different Substrates

In this study constructed wetlands (CWs) were used to remove three heavy metals (Zn, Cu and Pb). The two tested substrates were made of coke and gravel, respectively. First order dynamic model was appropriate to describe removing of Zn and Cu. The experimental results showed that first dynamic removal rate constants of Zn in CWs with coke and gravel were 0.2326 h-1 and 0.1222 h-1, respectively. And those of Cu in CWs with coke and gravel were 0.2017 h-1 and 0.3739 h-1. However, removal efficiencies of Pb in the coke system and the gravel system were within 95-99%, so the first order dynamic model failed to fit the experimental data because the hydraulic resident times of Pb did not affect outlet concentration of Pb. From the removal rate constants, it is found that the coke and gravel system have different absorption efficiencies of heavy metal pollutants. Therefore, it is suggested that the removal efficiencies of heavy metals are influenced by the choice of substrates to some extent.

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 0.9484 and a small sum of square error of 0.0006.The maximum adsorption capacities(Qm)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.

Assessment of Sunflower (Helianthus annuus L.) for Phytoremediation of Heavy Metal Polluted Mine Tailings—A Case Study of Nampundwe Mine Tailings Dam, Zambia

Mining activities have led to a generation of large quantities of heavy metals laden wastes which are released into the environment in an unsustainable way causing the contamination of the ecosystems and posing a risk to human health. Most mining companies have not employed any rehabilitation or remediation program of the heavy metal laden waste. The aim of this study was to assess the potential of sunflower for phytoremediation of heavy metal polluted mine tailings. Phytoremediation is an emerging technology in the remediation of mine tailings that uses tolerant plant species to clean up contaminated sites. It uses plants with high biomass and sunflower has been identified as such. These plants can extract, transfer, sequester and stabilize a variety of metals through mechanisms such as phytoextraction, phytostabilization, phytoaccumulation and phytovolatilization. Pot experiments were conducted by growing sunflower (Helianthus annuus L.) in pyrite mine tailings and in agricultural soil as a control. The study showed that the concentration of Cu reduced from 40.76 mg/kg to 36.59 mg/kg, Zn reduced from 3.58 mg/kg to 3.49 mg/kg and Fe reduced from 23.70 mg/kg to 10 mg/kg respectively in the mine tailings after 6 weeks. Analysis of harvested sunflower (roots, stems, leaves) showed that sunflower could remove heavy metals from the tailings and the highest removal efficiency was 53.7% and the highest translocation factor was 0.25. It was concluded that sunflower has the potential to remediate contaminated mine tailings and that phytoremediation is a viable and efficient technology to treat soils contaminated with heavy metals.

脱硫废水烟道蒸干对脱硫废水和飞灰重金属浓度的影响

将脱硫废水回喷到烟道中蒸干是实现脱硫废水零排放的主要手段之一,烟气脱氯可以实现脱硫废水减量,从而改善大量脱硫废水回喷对设备的影响。脱硫废水含有大量氯离子和多种重金属,在烟道中蒸干后形成的固体颗粒部分被除尘器脱除,剩下的会再次进入脱硫系统,在多次循环后可能会在脱硫废水中形成重金属的富集。以某660 MW机组作为对象建立模型,考虑除尘器脱除率与烟气脱氯效率的变化,分析脱硫废水流量变化,以及脱硫废水蒸干形成的固体颗粒的迁移行为对脱硫废水与飞灰中重金属浓度的影响。结果表明:在控制脱硫浆液氯离子浓度一定的情况下,受除尘器脱除率的影响,脱硫废水循环利用都将导致脱硫废水流量增加;当烟气脱氯效率为70%时,除尘器脱除率在90%当基础上增减5%,脱硫废水流量分别变化-5%和6%,脱硫废水中的重金属浓度变化幅度可以忽略;烟气脱氯会导致脱硫废水中重金属浓度增加到3倍多,不过脱硫废水全部内部循环利用,重金属富集并不是关键问题;脱硫废水回喷烟道后给飞灰带来的重金属浓度增加幅度基本不到1%,对飞灰品质的影响几乎可以忽略。

鼠李糖脂对水中重金属Cd的去除效率研究

此研究在纯水环境下,测定出鼠李糖脂的临界胶束浓度值,并通过正交实验的方法研究了鼠李糖脂对重金属Cd的去除效率以及影响因素。结果表明,在鼠李糖脂的临界胶束浓度下,可得到最佳的去除效率,鼠李糖脂的浓度、反应时间、温度、pH对去除效率均有影响,最优实验方案为:鼠李糖脂浓度为2 g/L,pH为10,温度为50℃时震荡3小时可达到最佳去除效率76.28%,无机盐K^(+)、Ca^(2+)的存在,可在一定程度上促进重金属的解脱附,同时二者存在一定竞争关系,表现为:Ca^(2+)>K^(+)。

不同水生植物对污染水体中重金属及有机污染物去除效果研究

研究了不同水生植物在去除污染水体中重金属和有机污染物的能力。通过实验考察了芦苇、水葫芦和睡莲在单一种植与套种模式下对铅、镉、汞、苯和甲苯等污染物的去除效率。结果表明,芦苇去除重金属有效,而水葫芦和睡莲可降低有机污染物和悬浮固体物浓度,且种植方式对去除效率有明显影响。此外,生态流量的变化对污染物去除率也有显著影响,高流量条件下去除效率更高。研究结论可为河流及其他水体的污染治理提供科学依据。

电解金属锰制液过程中的氧化锰除铁工艺优化

电解金属锰制液工艺中,常利用氧化锰粉将Fe^(2+)氧化成Fe^(3+),以便在后续中和过程中形成氢氧化铁胶体,实现铁的去除。针对低品位氧化锰粉在生产过程中存在除铁利用率低的问题,开展了氧化锰粉除铁工艺优化研究,结果表明:当除铁锰粉粒径≤125μm,初始酸的质量浓度为6.5 g/L,反应温度为60℃,反应时间为90 min时,除铁利用率达到98.4%,实现除铁氧化锰粉的高效利用。

化学萃取技术在重金属污染土壤修复中应用的研究

用HCl、Na2 EDTA、柠檬酸作为萃取剂在不同的萃取条件下对湘潭锰矿污染土壤进行萃取实验 ,研究 3种萃取剂对土壤中 3种重金属Mn、Pb和Cd的萃取效率。该研究表明 。

电絮凝法处理电镀废水中Cr^(n+)、Cu^(2+)、Zn^(2+)的试验

针对电镀废水对生态环境的严重污染问题,提出了铝板作为极板的电絮凝设备处理电镀废水中的重金属离子Crn+、Cu2+、Zn2+,研究了初始pH值、电流密度、电极间距等因素对处理效果的影响.试验结果表明,在电絮凝过程中,初始pH值在4～8之间时,金属离子的去除率最好,但当初始pH值超过8时,铬的去除率有所下降;并且随着电流密度、电解时间的增加,金属离子的去除率不断增加;电极间距的减小,使得重金属离子取得较好的去除效果.在初始pH为6,电流密度5.45A/dm2,电极间距为1 cm,通电时间为30 min的工艺条件下,电镀度水中Crn+去除率为96.22%,Cu2+去除率为99.86%,Zn2+去除率为99.13%.

行波磁场净化液态金属时矩形管及三角形管内夹杂物去除效率的理论解析

采用活塞流及轨线模型，对行波磁场净化液态金属时，三角形及矩形管中夹杂物的去除效率进行了理论分析，找出了提高夹杂物去除效率的途径；对两种形状管的夹杂物去除效率进行了比较；

淀粉黄原酸酯的合成及捕集重金属离子性能研究

以天然木薯淀粉为主要原料,环氧氯丙烷为交联剂制备交联淀粉,然后与CS2在碱性条件下发生黄原酸化反应制备改性淀粉黄原酸酯捕集剂,考察环氧氯丙烷用量、氢氧化钾用量、CS2浓度及反应温度、时间等诸因素对反应过程及产物捕集Cu2+性能的影响,确定了最佳的合成工艺条件。实验结果显示,合成捕集剂的最佳工艺条件为:环氧氯丙烷的用量为1.6 ml,KOH的用量为1.6 g,CS2用量11 ml,反应温度为35℃,反应时间为1.5 h。产物的含硫量可达9.02%,Cu2+去除率可达96.95%。

电磁过滤钢液中非金属夹杂物的运动速度和去除效率的理论分析

电磁过滤原理是根据非金属夹杂物与熔体导电性的差异，在电磁场作用下非金属夹杂物与熔体的运动规律不同，使非金属夹杂物与熔体分离．经流体力学分析、采用柱塞流及轨线模型研究电磁过滤水平流动钢液中非金属夹杂物的运动速度和去除效率．结果表明，非金用夹杂物的去除效率随着熔体流速（ｕ）和过滤器的高度（２ｈ）的降低而增加；随着电磁力（ｆ）、电磁力作用区长度（ｘ）和非金属夹杂物的粒径（ｄｐ）的增加而增加．经分析表明，采用电磁过滤法可有效去除粒径小于１０ ｍ的非金属夹杂物，该模型可用来设计过滤器的结构和确定电磁过滤工艺参数。

曲霉对水中重金属的吸附去除

利用2种曲霉A.sojae M146和A.oryzae M149的菌体,作为吸附剂对水中Pb^(2+)和Cd^(2+)进行去除实验。结果表明,曲霉菌体的最佳培养时间为72h,吸附的最佳pH为5.5、温度为30℃、时间为1h。在最佳实验条件下,A.sojae M146对Pb^(2+)和Cd^(2+)的吸附率,分别为69.76％和72.28％;A.oryzae M149对Pb^(2+)和Cd^(2+)的吸附率,分别为60.64％和81.34％。使用稀碱溶液对曲霉菌体进行浸泡预处理后,可提高对重金属的吸附去除效果;而使用稀酸、乙醇水溶液以及蒸馏水对菌体浸泡后,明显降低了重金属的去除效果。Na_2CO_3和EDTA溶液,可以有效地将重金属从曲霉体上解吸下来,从而达到重复利用菌体作为吸附剂的目的。

重金属污染土壤的电动力学修复试验研究

采用自制的实验装置研究重金属污染土壤的电动力学修复性能,通过间歇断电法和提高电压法提高单一重金属污染土壤的重金属去除率,取得了良好的效果,并且对多离子污染土壤的电动修复进行了研究.结果表明:间歇断电法和提高电压法与相同试验条件下的普通试验相比,Cd去除率分别提高了6.17%和0.56%,电能消耗分别节省了51.86%和12.4%.多离子污染土壤Cu,Pb,Cd的去除率分别为68.56%,75.31%,69.90%,相对于单一离子Cd的电动试验,修复效果降低不少.电能消耗为5.061 2kJ.g-1,比单一离子的电能消耗高出许多.

采用硫化铵去除冶炼烟气中的重金属

以管式气氛炉作发生器,通过加热重金属氧化物,模拟冶炼厂重金属烟气。采用硫化铵沉淀化处理含铅、镉、汞的冶炼烟气,考察了硫化铵溶液的浓度、pH及SO2等条件对铝、镉、汞去除效果的影响。结果表明:硫化铵法吸收净化含铅、镉、汞烟气的最佳浓度分别为0.2、0.2和0.8 mol/L,最佳反应pH均为10。在最佳反应条件下,铅、镉、汞的净化效率可分别达到95.5%、93.2%、99.9%,烟气出口铅、镉、汞浓度均达到《大气污染物综合排放标准》(GB16297—1996)。此外,SO2对硫化铵吸收净化重金属有抑制作用。

烧结金属丝网高温煤气除尘

进行了烧结金属丝网管在热态下除尘试验。对滤管除尘效率、压降及反吹清灰特性作了考察。提出了适宜的操作条件。

聚硅酸金属盐处理含氟废水的实验研究

含氟工业废水危害大,处理困难,采用高效无机絮凝剂——聚硅硫酸金属盐能有效降低废水中的氟。对影响三种絮凝剂聚硅酸硫酸铝(PSAS)、聚硅酸硫酸铁(PSFS)和聚硅酸硫酸铁铝(PSFAS)絮凝效果的主要因素进行实验研究,并对絮凝机理进行了深入探讨。研究表明,pH值、絮凝剂用量、沉降时间和Fe(Al)/Si摩尔比对絮凝剂除氟率的影响很大。硅的加入能有效提高絮凝剂中有效成分Alb和Feb的含量,使絮凝效果大大提高。

影响铝熔体电磁净化效果因素的分析

从液态金属电磁净化技术的原理出发,在理论上分析了当夹杂物与金属熔体密度接近的情况下,可以利用两者之间的电性能与磁性能的差异来实现夹杂物的分离,达到金属熔体净化的效果.综述了影响电磁分离效率和效果的因素.表明在电磁净化过程中,通电时间越长、磁感应强度越大、管半径与集肤程度比值在1.5～2.0之间、分离管为异型管、夹杂颗粒越大且近于球形,分离效果越理想,分离效率越高.

电絮凝法处理电镀废水中重金属的研究

采用电絮凝法处理电镀废水中的重金属,考察了电极种类、溶液初始p H值、电流强度、电絮凝时间等因素对重金属离子去除效果的影响。结果表明:金属铁、铝分别作为电极,铝电极对重金属的的处理效果优于铁电极的处理效果;初始p H值在6~9时,重金属离子去除率最高,当p H值低于6或高于9时,去除率下降;随电流强度和电絮凝时间增加,金属离子的去除率增加;在初始p H=6、电流强度为30 A、电絮凝时间为2 min的条件下,电镀废水中Cu2+和Ni2+的去除率分别为98.98%和95.29%,出水重金属离子质量浓度均满足GB21900—2008《电镀污染物排放标准》的规定;以金属铝作为电极,电絮凝时间为2 min时,吨水处理电耗为6 k W·h/m^3。