Comparison of the defluoridation efficiency of calcium phosphate and chitin in the exoskeleton of Antarctic krill

Calcium （Ca）, phosphorus （P）, and chitin are the main components of the exoskeleton of krill. Defluoridation of a solution of sodium fluoride （NaF） using calcium phosphate （Ca3（PO4）2） and chitin as defluoridation agents was studied. Orthogonal experiments were designed to find the optimum reaction conditions for defluoridation, to obtain the maximum defluoridation efficiency and fluoride removal capacity of calcium phosphate and chitin. At the same time, a comparison of the capacity of the two defluoridation agents was made. The results suggest that calcium phosphate has a far greater capability than chitin for the removal of fluoride （F） from water under similar reaction conditions. It is also suggested that Antarctic krill is likely to adsorb fluoride via compounds such as calcium phosphate, hydroxyapatite, and other compounds of Ca and P with the general form （Ca, X）x（PO4, HPO4, Y）y（OH, Z）z, in addition to chitin.

Defluoridation of water using biosorbents

Contamination of drinking water due to fluoride is a severe health hazard problem. Excess of fluoride (>1.5 mg/l) in drinking water is harmful to human health. Various treatment technologies for removing fluoride from groundwater have been investigated. The present study showed that Vetiveria zizanioides, a herbal plant of Kerala—commonly known as Vetiver is an effective adsorbent for the removal of fluoride from aqueous solution. Phosphoric acid activated Vetiver root showed good adsorption capacity than the fresh powdered Vetiver root. Batch sorptive defluoridation was conducted under variable experimental conditions such as pH, agitation time, dose of adsorbent and particle size. Maximum defluoridation was achieved at pH 6;there is a greater possibility of columbic interaction between fluoride ion and adsorbent surface at this pH. The percentage of fluoride removal in- creases with adsorbent dose and time at a given initial solute concentration. The surface and sorption characteristics were analyzed using SEM techniques. Freundlich as well as Langmuir isotherm were plotted and kinetic constants were determined.

Defluoridation of Water by a Biomass: <i>Tinospora cordifolia</i>

This research is focused on the search of a biomass for the sequestration of fluoride from drinking water. Defluoridation of water was studied by batch experiments in biosorption process. The biomass was found to reduce fluoride to permissible limit 1.5 mg/L as prescribed by WHO. The efficiency of the sorption process was investigated under different experimental parameters such as pH 7, standing time 120 min and biomass doses 7.0 g with 5 mg/L concentration of fluoride. Neutral pH was identified as the optimum condition of the medium and 120 minutes was the best contact time for maximum fluoride adsorption. The experimental data was found good fitting to Langmuir and Freundlich isotherm models. In interference study tolerable effect was found with 50 mg/L concentration of co-ions, whereas increasing the concentration of co-ions retarded the fluoride removal capacity in some extent. FT-IR spectrum analysis showed fluoride binding in the different frequency ranges of the biomass. Eventually, this plant biomass is recommended as a suitable and low cost adsorbent to reduce fluoride into standard permissible limit.

Sorption Kinetics, Isotherm and Thermodynamic Modeling of Defluoridation of Ground Water Using Natural Adsorbents

The aim of study is to investigate the removal ability of some natural adsorbents for fluoride ion from aqueous solution. The batch dynamic adsorption method was carried out at neutral pH as the functions of contact time, adsorbent dose, adsorbate concentration, temperature and effect of co-anions, which are commonly present in water. The sorption kinetics and equilibrium adsorption isotherms of fluoride on natural adsorbing materials had been investigated at afore-mentioned optimized. Equilibrium adsorption isotherms, viz., Freundlich and Langmuir isotherms were investigated. Lagergren and Morris-Weber kinetic equations were employed to find the rate constants. The negative enthalpy ΔH = -46.54 KJ·mol-1 and Gibbs free energy calculated was ΔG288-333—(2.07785, 3.08966, 4.1064, 4.90716 and 5.38036 KJ·mol-1) respectively, envisage exothermic and spontaneous nature of sorption.

Measuring the Accessibility of Safe Drinking-water： From Millennium Development Goals Experience to Sustainable Development Goals Prospects

The access to safe drinking-water is a global priority for sustainable development, as it has been recognized within the MDGs （Millennium Development Goals）. Although the MDG’s target of halving the proportion of people without sustainable access to safe drinking-water was met in 2010, the measurement method of the monitoring and evaluation indicator used ignored certain elements including the quality of water that should be underlined. Starting with a review of drinking-water and improved water source concepts, this study examines the limitations of measuring access to safe drinking-water in the context of the MDGs, and learns from the lessons to ensure a better performance in achieving the SDGs （Sustainable Development Goals）.

Nutrient-Induced Growth of Coliform and HPC Bacteria in Drinking-Water Pipes

We conducted a study on a model drinking water distribution system to evaluate the impact of nutrient in the form of sodium acetate on the growth and survival of coliform and heterotrophic plate count (HPC) bacteria for a maximum of 21 days residence time of water in pipes. Our results show that, besides the nutrient added and the absence of any additional source of contamination and additional supply of nutrient, there was significant growth of the above mentioned bacteria in the pipes and bottles for a couple of days, after which the bacterial population began to decrease. The results indicate that the bacteria used the nutrient to grow and multiply until the nutrient was totally consumed and became depleted in the bulk water phase, after which the bacterial population reached a near stationary level and subsequently declined. This suggests the death of some of the bacteria and their dead cells were used by other bacteria for growth and survival. Using a detection limit of 3.3 CFU/100 mL for the coliforms, the study shows that after sometime, no bacteria were found in the water phase of the pipe, however, the biofilm in the pipes still harbored some of the bacteria. The results have revealed that the bacteria also have the tendency to move from the water phase to the biofilm since the latter provides a more suitable environment for bacteria to thrive on and grow, thus prolonging their survival in the system.

Fish Swim Bladder-Derived Porous Carbon for Defluoridation at Potable Water pH

The levels of fluoride in various ground water sources in East Africa are above the World Health Organization upper limit of 1.5 mg/L. Research on diverse defluoridation technologies has proven that adsorption stands out as an affordable, efficient, and facile technology. Fish swim bladder-derived porous carbon (FBPC) activated by KOH and surface oxidized by nitric acid was successfully investigated as an adsorbent for defluoridation at portable water pH. The FBPC was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Batch methods were used to study physiochemical parameters viz., initial fluoride concentration, temperature, adsorbate dosage, contact time and pH. Freundlich, Temkin, Langmuir and Dubinin-Radushkevich isotherms were plotted and analyzed to understand the adsorption process. Bangham, Weber Morris, pseudo first and second-order models were used to elucidate the kinetics of adsorption. Optimal conditions for fluoride removal were found to be: pH of 6, FBPC adsorbent dose of 5.0 g/L and contact time of 50 min. Flouride adsorption followed pseudo second-order kinetic model and Langmuir isotherm best describes the adsorption process.

磁性Ce-La-MOFs@Fe_(3)O_(4)的除氟性能

通过水热法制备了Ce-La-MOFs@Fe_(3)O_(4)复合材料,研究了Ce-La-MOFs@Fe_(3)O_(4)对水溶液中F^(-)的吸附性能,并通过响应曲面法优化了吸附条件。实验结果表明:在pH=3.6、实验温度为40℃、初始氟离子浓度为17.4 mg/L的条件下,Ce-La-MOFs@Fe_(3)O_(4)的吸附效果最佳,F^(-)去除率可达94.5%。除氟特性实验数据更适合用Langmuir模型进行描述,拟合得到最大吸附容量(q_(max))为147.23 mg/g,热力学参数ΔG^(o)、ΔH^(o)和ΔS^(o)表明该吸附反应是一个自发吸热的熵增过程。动力学研究表明Ce-La-MOFs@Fe_(3)O_(4)对F^(-)的吸附符合准二级反应动力学过程。对复合材料的形貌和结构进行了表征分析,并结合吸附热力学和动力学研究探讨了吸附机理,该吸附过程主要是离子交换和静电吸附共同作用。共存离子实验、循环再生实验结果显示,Ce-La-MOFs@Fe_(3)O_(4)对F^(-)具有较好的选择性,该复合材料的再生性能较好,回收率可达96%,两次循环后对F^(-)的去除率仍达81.74%。

高比表面积羟基磷灰石的制备及其在磷酸铁废水除氟中的应用

为提高羟基磷灰石(Hydroxyapatite,HAP)对氟离子的吸附效率,采用化学沉淀法,通过优化反应温度、Ca/P摩尔比、陈化时间等合成条件制备高比表面积HAP,通过FTIR、XRD、XPS、SEM和BET等对合成的HAP进行表征,并评价HAP对模拟废水中氟离子的吸附性能。结果表明:HAP的最优制备条件为反应温度20℃、Ca/P摩尔比1.6、陈化时间24 h,所制备的HAP比表面积达108.0 m^(2)/g;HAP对氟离子的吸附为自发和吸热过程,符合Langmuir吸附模型,在303 K下氟离子的最大吸附容量为13.53 mg/g,吸附过程符合准二级反应动力学模型;在酸性条件下,HAP的除氟机理为离子交换。磷酸铁废水HAP吸附除氟实验表明,出水氟离子浓度可连续32 h低于1.0 mg/L,体现了较好的除氟效果。研究结果可为高效除氟吸附剂的制备以及磷酸铁废水深度除氟提供一定的指导。

除氟剂在矿井水除氟实验中的应用研究

通过对比4种药剂的除氟性能,挑选出最佳除氟剂并探究了不同因素对其除氟效果的影响。结果显示:4种药剂氟化物去除效果为:ZMCF>CF-B>CF-A>PAC。最佳实验条件ZMCF除氟剂投加量为100 mg/L,PAC投加量为160 mg/L,PAM投加量为1.2 mg/L,pH为6~7,反应沉淀30 min后,出水氟化物浓度为0.52 mg/L。共存阴离子Cl-和SO_(4)_(2-)对除氟效果影响较小。现场实验结果显示,最佳实验条件下处理后出水氟化物含量为0.75~0.93 mg/L,平均值为0.83 mg/L,氟化物浓度可稳定在1.0 mg/L以下,符合煤矿矿井水排放要求。出水浊度为8.9~14.6 NTU,经后续系统过滤后进一步降低出水浊度,从而排放利用。

一种高效复合除氟剂及其在高盐废水中除氟的研究

一种高效复合除氟剂包含聚合氯化铝、六水氯化铝、硫酸铝以及硫酸锌等有效成分,按质量百分比计含聚合氯化铝70%~80%,六水氯化铝5%~10%,硫酸铝5%~10%,硫酸锌0.1%~1.0%。使用方法为将高效复合除氟剂配置成500 g/L的溶液,加入氟离子初始浓度为10.6 mg/L的高盐废水中,经过搅拌后沉淀,调节终点pH在7.0左右,氟化物去除率高达95%以上,可达到出水指标1.0 mg/L以下。

新型饮水除氟剂蛇纹石降氟效果研究

目的 研究确定蛇纹石降氟效果和最佳降氟条件 ,为广大地氟病病区提供新的防病措施。方法 通过实验室检测和现场观察 ,利用单因素分析和正交实验方法确定水温、p H、粒度、接触时间、再生剂浓度对蛇纹石降氟容量的影响。结果 对蛇纹石降氟效果影响较大的因素依次为 :接触时间、粒度、再生剂浓度。降氟最佳操作条件为 :粒度 6 0～ 80目 ,明矾液浓度 0 .0 739mol/L ,接触时间 30 min。水温对降氟效果无显著影响 ;p H在 7.16～ 8.18之间 ,蛇纹石降氟容量没有差异 (P >0 .0 5 )。结论 利用蛇纹石降氟 ,效果明显 ,简便易行 。

活化蛇纹石降砖茶水氟含量可行性研究

目的 观察蛇纹石活化后降砖茶水氟效果及降氟前、后砖茶水化学成分的改变。方法 按少数民族饮砖茶习惯熬制的砖茶水 (含茶 5 g/ L,砖茶水含氟量约 3.5 2 m g/ L)经活化蛇纹石处理后 ,观察其氟含量及砖茶水水质变化。用电极法测砖茶水氟含量。用原子吸收分光光度法测砖茶水中 Mg、Ca、Zn、Fe、Cu等元素含量。结果 活化蛇纹石对砖茶水有降氟作用 ,在最佳条件下蛇纹石降氟容量可达 0 .31m g/ g;降氟后砖茶水中镁、钙、锌、铁、铜含量均有不同程度升高。结论 蛇纹石作为一种降氟剂是安全、价廉、有效 ,并能释放有益人体健康的元素。

除氟剂筛选及其与茶汤相互影响的研究

目的筛选一种砖茶除氟剂,研究除氟剂与茶汤的相互影响。方法感官品评与理化成分分析相结合。结果DFR能将茶汤中的氟含量降至卫生标准以下,且茶汤环境对DFR性能影响均较理想,茶汤氟浓度越高,DFR除氟量越大。茶汤的pH值与DFR的最佳使用pH值范围相符。接触时间超过15min,除氟量趋于稳定。DFR对茶汤感官、有害成分、有益成分影响均较小。结论DFR能用于砖茶除氟。

碳纳米管负载氧化铝材料的制备及其吸附水中氟离子的研究

采用碳纳米管和硝酸铝制备了碳纳米管负载氧化铝新型除氟材料 .X射线衍射检测发现 ,当焙烧温度低于 85 0℃时 ,氧化铝为无定形态 ,当焙烧温度为 1 0 5 0℃时 ,氧化铝为α形态 ,扫描电子显微镜观察到碳纳米管与氧化铝均匀掺杂 .同时用碳纳米管负载氧化铝复合材料进行水中氟离子的吸附研究 ,结果表明 ,该复合材料具有优良的除氟效能 .氧化铝负载量为 30 %、焙烧温度为 4 5 0℃条件下制备的碳纳米管负载氧化铝复合材料的吸附除氟能力是 γ-氧化铝的 2 .0～ 3.5倍 ,与 IRA-4 1 0聚合树脂的吸附除氟能力相当 ,适宜p H范围为 5 .0～ 9.0 ,吸附等温线符合 Freundlich方程 .

负载金属镧的壳聚糖对含氟水的处理

采用负载镧的壳聚糖作为含氟水的吸附剂,最佳制备工艺条件为:壳聚糖用量为1g·L-1,La3+浓度为0.15mol·L-1,反应时间为6h,吸附剂粒径为0.1mm;除氟剂的最优工作条件为:pH为7,温度50℃,搅拌速度400r·min-1,吸附时间60min。当吸附剂用量为1.6g·L-1时,对水中浓度为20mg·L-1的F-去除率达到98.4%。用0.1mol·L-1的NaOH对吸附饱和后的吸附剂进行解吸处理24h,可以有效地恢复其吸附性能。吸附剂对F-的吸附过程符合Langmuir吸附等温线方程;对F-的饱和吸附容量为476.190mg·g-1。

羟基磷灰石降氟剂合成方法降氟机理研究进展

合成羟基磷灰石用作饮水降氟剂具有降氟容量大、操作简便 ,处理后水质基本不变化 ,滤料容易再生 ,且不产生二次污染的特点。羟基磷灰石的降氟方法优于目前较普及的活性氧化铝、骨碳和电渗析除氟法。

吸附法除氟技术的原理与方法

在水处理中应用的除氟的方法主要有:沉淀法、吸附法、电凝聚法、电渗析法、反渗透法和离子交换法等,其中吸附法是处理高含氟水的重要方法。本文重点介绍了几种常用的及新型的氟吸附剂的特点及应用概况,其中包括:铝盐吸附剂、铁盐吸附剂、稀土类吸附剂、生物类吸附剂以及其他类型的吸附剂;介绍了几种常用的及新型的氟吸附剂的除氟作用机理,并对今后的除氟研究进行了展望。

磁性羟基磷灰石的制备及其除氟性能研究

氟离子在饮用水中浓度超过1.0 mg/L,将对人体健康造成极大危害。通过原位共沉淀法将具有磁性的四氧化三铁掺入羟基磷灰石(HAP)中制备磁性HAP。磁性HAP可通过普通磁体将其吸附并分离回收。实验结果表明,最佳的制备条件为反应温度和时间为60℃和1 h,陈化温度和陈化时间为25℃和12 h,四氧化三铁用量为0.08g。比较了HAP和磁性HAP对水溶液中氟离子的去除效果。Langmuir模型更适合于该体系,拟合得到最大吸附容量为13.70 mg/g,说明磁性HAP对氟离子的吸附属于单层吸附。ΔG^0<0和ΔH^0>0表明该吸附过程为自发的吸热过程。吸附过程符合拟二级动力学。磁性HAP循环再生使用4次以上,仍能保持85%以上的除氟效率。高吸附容量和优异的循环使用性能表明磁性HAP是一种有效的、可重复使用的除氟吸附剂。

改性粘土除氟剂处理高氟地下水研究

利用自行制备的改性粘土除氟剂处理含氟量较高的配水,研究了改性粘土的优化制备条件和不同因素对其除氟效果的影响,并进行地下水原水除氟验证,最后考察了改性粘土除氟剂的再生性能。结果表明,将0.3mol/L的Al2(SO4)3和2%(质量分数)的NaOH按1∶3(质量比)混合制成改性溶液,再将改性溶液与粘土按1.0∶3.0(质量比)混合后,在400℃下煅烧2h所制得的除氟剂除氟效果最好,最高氟吸附容量可达0.2168mg/g;地下水出水氟质量浓度为0.807mg/L,低于《生活饮用水卫生标准》(GB5749—2006)限值(1mg/L);制得的改性粘土除氟剂对氟具有较好的吸附重复性,可实现多次再生。