Study on the influence of additives in an industrial calcium fluoride and waterworks sludge co-melting system

This work explores the effect of additives on the pouring temperature in a waterworks and industrial calcium fluoride sludge co-melting system. Two kinds of sludge were mixed in various ratios to find a mixing ratio at which the operating temperature for subsequent additive tests was relatively low. Various proportions of either sodium carbonate (Na2CO3) or potassium carbonate (K2CO3) reagent were added to the mixed-sludge samples to elucidate the consequent changes in pouring temperature. The experimental results revealed that the pouring temperature was lowest when calcium fluoride was mixed with waterworks sludge in a ratio of 4:6 (w/w). Adding sodium carbonate or potassium carbonate reagent to the mixed-sludge samples further reduced the pouring temperature. Increasing the amount of sodium carbonate did not significantly reduce the pouring temperature beyond that observed when 2% was added, suggesting that 2% was the optimal additional percentage of sodium carbonate. In contrast, the pouring temperature was increased when over 2% potassium carbonate was added to the mixed-sludge samples, revealing that the optimal additional percentage of potassium carbonate was also 2%. These findings indicate that both sodium carbonate and potassium carbonate can be used as additives to increase the energy efficiency of the melting process, but sodium carbonate is more operationally convenient.     

Fluoride removal by a continuous flow electrocoagulation reactor

Long-term consumption of water containing excessive fluoride can lead to fluorosis of the teeth and bones. Electrocoagulation (EC) is an electrochemical technique, in which a variety of unwanted dissolved particles and suspended matter can be effectively removed from an aqueous solution by electrolysis. Continuous flow experiments with monopolar aluminium electrodes for fluoride removal were undertaken to investigate the effects of the different parameters such as: current density (12.5-50A/m(2)), flow rate (150-400 mL/min), initial pH (4-8), and initial fluoride concentration (5-25mg/L). The highest treatment efficiency was obtained for the largest current and the removal efficiency was found to be dependent on the current density, the flow rate and the initial fluoride concentration when the final pH ranged between 6 and 8. The composition of the sludge produced was analysed using the X-ray diffraction (XRD) spectrum. The strong presence of the aluminium hydroxide [Al(OH)(3)] in the above pH range, which maximizes the formation of aluminium fluoride hydroxide complex [Al(n)F(m)(OH)(3n-m)], is the main reason for defluoridation by electrocoagulation. The results obtained showed that the continuous flow electrocoagulation technology is an effective process for defluoridation of potable water supplies and could also be utilized for the defluoridation of industrial wastewater.     

电化学反应器吸附去除氟离子的研究

采用改性活性炭粉末对用纯净水加氟化钠配制而成的含氟水溶液进行动态电吸附去除实验.研究不同电压、电吸附时间,以及Cl-和SO2-4对氟离子去除的影响,并探讨吸附动力学和吸附方程.实验结果表明:活性炭对氟离子的吸附等温方程符合Freundlich方程,吸附动力学符合一级动力学方程;活性炭对氟离子去除与所施加的电位、吸附时间等因素有关,施加的电位越大,去除效果越好;随着吸附去除时间的延长,氟离子浓度下降趋缓;Cl-对氟离子去除影响很小,而SO2-4对氟离子去除有显著的不利影响.     

活性污泥法处理含砷废水初探

文章概述了含砷废水的产生及其处理方法,重点介绍了国内外研究报道较少的活性污泥法,以引起人们对这一有效除砷方法的重视。通过总结活性污泥法除砷的研究进展,探讨了活性污泥除砷的机理和影响因素,并提出今后要从活性污泥法除砷的机理、除砷工艺、及含砷废渣处理三方面开展研究,以促进该方法的应用。     

对电解铝厂周边氟污染的环境影响评价

通过测定广西某电解铝厂周边大气、土壤和农作物中氟化物含量,对该厂周边的氟化物污染进行了评价,结果表明：电解铝厂周围大气氟污染与采样点的方位成显著相关关系;农作物玉米叶片氟污染主要来自于电解铝厂无组织排放的氟化物,而土壤中总氟含量除受大气中氟化物的影响外,还与当地的地质构造、土壤类型等因素有关,与主导风向无明显的相关关系,土壤中水溶氟含量与采样点到电解铝厂距离呈负相关。     

The removal of lignin and phenol from paper mill effluents by electrocoagulation

This study aims to investigate the treatment of paper mill effluents using electrocoagulation. Removal of lignin, phenol, chemical oxygen demand (COD) and biological oxygen demand (BOD) from paper mill effluents was investigated at various current intensities by using different electrodes (Al and Fe) and at various electrolysis times (1.0, 2.5, 5.0 and 7.5min). It was observed that the experiments carried out at 12V, an electrolysis time of 2min and a current intensity of 77.13mA were sufficient for the removal of these pollutants with each electrode. The removal capacities of the process using an Al electrode were 80% of lignin, 98% of phenol, 70% of BOD, and 75% of COD after 7.5min. Using an Fe electrode the removal capacities were 92%, 93%, 80% and 55%, respectively. In addition, it was found that removal of lignin, phenol, BOD and COD increased with increasing current intensity. In the experiments carried out at different current intensities, higher removal can be explained through a decrease in intra-resistance of solution and consequently an increase at the transfer speed of organic species to electrodes. It was also found that Al electrode performs higher efficiency than Fe electrode except for COD removal. However, the time required for removal of BOD was more than that of COD. The results suggest that electrocoagulation could be considered as an effective alternative to paper mill effluents treatment.     

Solar oxidation and removal of arsenic from water: An experimental study

Arsenic poses a significant threat to both human health and the environment. Arsenic removal through solar oxidation has been investigated in a batch process. Arsenic was artificially added to both deionized and tap water to conduct the experiments. Clean, colorless, transparent, Polyethylene Terephthalate (PET) bottles were used for Solar Oxidation and Removal of Arsenic (SORAS) experiments. Various parameters including concentration of arsenic, iron, and photo-catalyst were varied during the experiments. The maximum arsenic removal efficiency obtained was 94% and 88% for deionized water and tap water respectively when ferrous ammonium sulphate and lemon juice were used. Maximum efficiency of 88% and 82% was obtained for deionized and tap water respectively when locally available ferrous alum and glacial acetic acid were used. The change in volume of the photo-catalyst (lemon juice and glacial acetic acid) also did not affect the SORAS process significantly. Therefore, the recommended volume for the photo-catalyst was 1–2 ml/L. SORAS can very well be used for areas contaminated with arsenic having concentrations less than 100 μg/L.     

不同操作条件对纳滤膜去除水中五价砷的研究

采用纳滤膜（NF90）过滤自配含砷水,研究在不同操作条件下纳滤膜对水中砷去除效果的影响。本实验探讨膜进水浓度、水的pH值、膜进水温度、操作压力、水中天然有机物浓度等对膜除砷效率的影响。结果表明：纳滤膜对水中五价砷（As（Ⅴ））的去除率很高,最高去除率能达到99%,在实验的前2.5个小时内,砷的去除率均在90%以上。但是,纳滤膜除砷效率随着时间变化,去除率会降低。不同的操作条件对纳滤膜除砷的影响很大,研究不同条件的影响对应用很有意义。     

Effects of arsenic concentrations and forms on arsenic uptake by the hyperaccumulator ladder brake

Ladder brake (Pteris vittata L.) is a newly discovered arsenic hyperaccumulator. No information is available about arsenic effects on ladder brake. This study determined the effects of different arsenic concentrations (50 to 1000 mg kg(-1)) or forms (organic vs. inorganic and arsenite vs. arsenate) applied to soils on growth and arsenic uptake by ladder brake. Young plants were grown in a greenhouse for 12 or 18 wk. Ladder brake was highly tolerant of arsenic and survived in soil containing up to 500 mg As kg(-1). The fact that addition of arsenate up to 100 mg As kg(-1) increased fern biomass by 64 to 107%, coupled with higher arsenic concentration in younger fronds at low soil arsenic concentrations and older fronds at high soil arsenic concentrations, implies that arsenic may be beneficial for fern growth. Addition of 50 mg As kg(-1) was best for fern growth and arsenic accumulation, resulting in the highest fern biomass (3.9 g plant(-1)), bioconcentration factor (up to 63), and translocation factor (up to 25). With an exception of FeAsO4 and AlAsO4, which had the lowest effects due to their low solubility, little difference was observed among other arsenic forms mainly because of arsenic conversion in soil. Aboveground biomass was mostly responsible for accumulation of arsenic by plant (75-99%). Up to 26% of the added arsenic was removed by ladder brake, showing the high efficiency of ladder brake in arsenic removal. The results suggest that ladder brake may be a good candidate to remediate arsenic-contaminated soils.     

嘉陵江下游饮用水氟化物时空变异特征研究

饮用水中可溶性氟化物是公众摄入氟的主要途径,其含量水平影响人体健康.分别于2015～2017年的丰水期和枯水期6次随机采集监测了嘉陵江下游52个饮用水样中氟化物含量,并基于地理信息系统平台和健康风险指数法进行了评价.结果表明,该区域饮用水中氟化物浓度平均为0.20～0.25 mg/L.除2015年部分样点外,其余样点的...     

Characteristics of a bioxalate chelating extraction process for removal of chromium,copper and arsenic from treated wood

The disposal of wood waste treated with chromated copper arsenate (CCA) is a problem in many countries. We have proposed a novel chelating extraction technique for CCA-treated wood using bioxalate, a solution of oxalic acid containing sufficient sodium hydroxide to adjust the pH to 3.2, which is an effective way to obtain an extraction efficiency of 90% for chromium, copper, and arsenic. The purpose of the present study was to investigate the characteristics of bioxalate extraction of CCA-treated wood. Extractions of CCA-treated western hemlock chips with solutions of bioxalate, oxalic acid, and sodium hydroxide were carried out. The use of bioxalate was confirmed as the most effective extraction technique for chromium, copper and arsenic, with an efficiency of 90%. Extraction with simple oxalic acid was ineffective for copper (less than 40% extraction efficiency), but effective for chromium and arsenic, with 90% efficiency. Sodium hydroxide showed a similar tendency, being ineffective for chromium and copper (less than 20% extraction efficiency), but relatively effective for arsenic (around 70–80% efficiency). We also discovered an interesting phenomenon whereby the addition of sodium hydroxide to a simple oxalic acid solution during the oxalic acid extraction progress resulted in dramatically increased extraction efficiency for copper, chromium and arsenic, up to 90%. Although oxalic acid was ineffective for copper extraction, the addition of sodium hydroxide during the oxalic acid extraction process rendered it effective.     

高氟温泉水中氟在周边水环境中的分布特征与评价

针对温泉水中高氟现象,本实验利用离子选择性电极法,分析测定高氟温泉水周边河水中氟含量及河水底泥中氟含量。通过对高氟温泉水分布特征的研究可初步得知,温泉中高氟在周边水环境中分布因其氟含量大、不易被重视,对环境的影响相对较大。     

Arsenic and chromium removal by mixed magnetite–maghemite nanoparticles and the effect of phosphate on removal

Adsorption of arsenic and chromium by mixed magnetite and maghemite nanoparticles from aqueous solution is a promising technology. In the present batch experimental study, a commercially grade nano-size ‘magnetite’, later identified in laboratory characterization to be mixed magnetite–maghemite nanoparticles, was used in the uptake of arsenic and chromium from different water samples. The intent was to identify or develop a practical method for future groundwater remediation. The results of the study showed 96–99% arsenic and chromium uptake under controlled pH conditions. The maximum arsenic adsorption occurred at pH 2 with values of 3.69 mg/g for arsenic(III) and 3.71 mg/g for arsenic(V) when the initial concentration was kept at 1.5 mg/L for both arsenic species, while chromium(VI) concentration was 2.4 mg/g at pH 2 with an initial chromium(VI) concentration of 1 mg/L. Thus magnetite–maghemite nanoparticles can readily adsorb arsenic and chromium in an acidic pH range. Redox potential and pH data helped to infer possible dominating species and oxidation states of arsenic and chromium in solution. The results also showed the limitation of arsenic and chromium uptake by the nano-size magnetite–maghemite mixture in the presence of a competing anion such as phosphate. At a fixed adsorbent concentration of 0.4 g/L, arsenic and chromium uptake decreased with increasing phosphate concentration. Nano-size magnetite–maghemite mixed particles adsorbed less than 50% arsenic from synthetic water containing more than 3 mg/L phosphate and 1.2 mg/L of initial arsenic concentration, and less than 50% chromium from synthetic water containing more than 5 mg/L phosphate and 1.0 mg/L of chromium(VI). In natural groundwater containing more than 5 mg/L phosphate and 1.13 mg/L of arsenic, less than 60% arsenic uptake was achieved. In this case, it is anticipated that an optimum design with magnetite–maghemite nanoparticles may achieve high arsenic uptake in field applications.     

Effect of salt solution treatment on impurity removal: A case study on phosphogypsum

This study gives a brief demonstration of impurity removal efficiency upon salt solution treatment of phosphogypsum (PG). The experimental set up has been designed according to a multi-variable Box–Behnken Design (BBD) with stirring time, solid: liquid (PG:salt solution) ratio and temperature as the conducted in various salt solutions. PG sample has been treated with sea water, 5% NaCl and 10% NaCl solutions according to the BBD matrix. Fluoride (F), copper (Cu), manganese (Mn), and nickel (Ni) amounts in the PG sample have been measured upon pre- and post-treatment with salt solutions. Among other operating conditions, temperature has been the dominant factor on fluoride removal efficiency, and responses for the factors determined in the experiment runs indicated that a significant correlation could be established between temperature and fluoride removal, sea water being the most efficient salt solution. Higher copper, manganese, and nickel removal efficiencies have been observed in single salt NaCl solution systems however no significant correlation could be established between factors. Results indicate that pre-treatment of PG located near coastal regions with sea water can be a cost-effective approach and applicable on industrial scale when fluoride removal is of importance.     

Groundwater purification by membrane technology

Hyperfiltration and nanofiltration membranes were tested with different water matrices for the removal of excess fluoride from underground water. Initially, the experiments were done with synthetic samples prepared by adding known amounts of sodium fluoride and calcium chloride in distilled water. The effect of feed water composition, pH, temperature of feed water, operating pressure, and feed water flow rate on separation efficiency of both types of membrane was studied by varying one parameter at a time and keeping all other parameters constant. Thus, the optimum operating conditions for the process were determined and after that ground water samples collected from three villages of district Gurgaon, Haryana, India (Farukhnagar, Wazirpur, and Mevka) were treated under optimum operational conditions. The mass transfer coefficient and membrane parameters were estimated for each data point using two-parameter model (Film theory and Solution-diffusion model) to study the concentration polarization on membrane surface. The nanofiltration membrane showed high percentage rejection of bivalent ions when compared to monovalent ions in a binary system. But in multicomponent system, when fluoride and calcium coexisted, the removal of fluoride was comparable to calcium removal because of the low solubility product of calcium fluoride. The results with RO membrane revealed that it removes practically all the ions present in water at high pressure, which need to be passed through a lime column to remineralize the water, to make it suitable for drinking purposes, whereas by running the system at low pressure which will further reduce the cost of operation, rejection percentage goes down to get permeate of required quality.     

Review of fluoride removal from drinking water

Fluoride in drinking water has a profound effect on teeth and bones. Up to a small level (1–1.5 mg/L) this strengthens the enamel. Concentrations in the range of 1.5–4 mg/L result in dental fluorosis whereas with prolonged exposure at still higher fluoride concentrations (4–10 mg/L) dental fluorosis progresses to skeletal fluorosis. High fluoride concentrations in groundwater, up to more than 30 mg/L, occur widely, in many parts of the world. This review article is aimed at providing precise information on efforts made by various researchers in the field of fluoride removal for drinking water. The fluoride removal has been broadly divided in two sections dealing with membrane and adsorption techniques. Under the membrane techniques reverse osmosis, nanofiltration, dialysis and electro-dialysis have been discussed. Adsorption, which is a conventional technique, deals with adsorbents such as: alumina/aluminium based materials, clays and soils, calcium based minerals, synthetic compounds and carbon based materials. Studies on fluoride removal from aqueous solutions using various reversed zeolites, modified zeolites and ion exchange resins based on cross-linked polystyrene are reviewed. During the last few years, layered double oxides have been of interest as adsorbents for fluoride removal. Such recent developments have been briefly discussed.     

Dental fluorosis—a case study from Nawa tehsil in Nagaur district,Rajasthan (India)

A study was carried out in Nawa tehsil of Nagaur district to assess the prevalence of dental fluorosis and its crippling effect due to ingestion and prolonged exposure of fluoride over a long period of time. During the survey of the study area, high concentration of fluoride (14.62 ppm) has been recorded. The presence of fluoride in quantities in excess of limits is a serious matter of concern from a public health point of view. Due to higher fluoride level in groundwater, several cases of dental fluorosis have appeared at alarming rate in the study area. The children’s teeth are damaged and are characterized by black and brown stains as well as cracking and pitting of the teeth have been observed. In the study area, 93.12% population suffered from dental fluorosis, and it was more prevalent in men (94.90%) than in women (90.00%). Dental fluorosis was also examined according to different grades. Out of the total 72 afflicted, in the 4–16-year age group, 41.46% were suffering from Grade I, Grade II was more prevalent in 33.85% of the 17–28-year age group and similarly Grade II was more prevalent in 39.13% of the 29–40-year age group. In the age group of above 40 years, grade III and grade IV were more prevalent. Thus, in the higher age group, the prevalence and severity of fluorosis is almost certainly due to longer exposure to fluoride. The major risk factor consistently identified for dental fluorosis was the consumption of fluoridated drinks and fluoride supplements. Ingestion of calcium, vitamin D and vitamin C is effective in protection from fluoride toxicity to certain extent.     

北京市垃圾填埋场地下水中砷、汞含量分析

生活垃圾的处置一直以填埋为主,垃圾填埋承载着巨大的环境压力,尤其是垃圾填埋产生的渗滤液会对地下水造成砷、汞污染。为了解北京市生活垃圾填埋场地下水砷、汞污染水平,在北京市5座生活垃圾填埋场布设采样点,采集36个地下水样品,采用氢化物发生-原子荧光法,分析了地下水砷、汞含量特征。结果表明,36个地下水样品砷浓度范围0.41~4.82μg/L,汞浓度范围0.024~0.121μg/L,北京市典型垃圾填埋场地下水样品不存在砷、汞污染问题。     

Forecast optimal fluoride concentration data in drinking water according to the ambient temperature in Golestan,Iran

Controlling fluoride concentrations in drinking water at optimal levels could be effective in preventing certain negative health effects in humans. This study investigated optimal fluoride concentrations in potable water in Golestan province, according the ambient temperatures in the province. The study used data on fluoride concentrations in drinking water supplied by the Water and Wastewater Company of Golestan Province. The annual mean maximum temperatures were extracted from a website that recorded daily ambient temperature. The optimal value of fluoride in drinking water for each county of Golestan province was calculated by the Galgan and Vermillion formula. The results show that all of the counties should contain fluoride concentrations ranging from 0.73 to 0.766 milligrams per liter (mg/L) according to the calculation formula, while fluoride concentrations were instead reported to range between 0.23 and 0.53 mg/L by the Water and Wastewater company. In addition, according to World Health Organization (WHO) recommendations, the concentrations of fluoride in potable in all of the cities in Golestan province fall below the WHO standard. In conclusion, we suggest that the fluoride concentrations in Golestan province's drinking water should be taken into account by the appropriate authorities and that optimal fluoride concentrations in drinking water according to ambient temperatures be set to avoiding negative health impacts.     

Cellulose-based anion exchanger with tertiary amine functionality for the extraction of arsenic(V) from aqueous media

A novel cellulose-based anion exchanger (Cell-AE) with tertiary amine functionality was synthesized by graft polymerization reaction of cellulose and glycidyl methacrylate using N,N′-methylene-bis-acrylamide as a crosslinker and benzoyl peroxide as an initiator, followed by dimethylamine (amination) and acid (HCl) treatment. The chemical modification was confirmed by infrared spectroscopy and CHN analysis. The anion exchanger was used in batch processes to study AS(V) adsorption in solutions. The operating variables studied were pH, contact time, initial As(V) concentration, sorbent mass, and ionic strength. The process was affected by solution pH with an optimum adsorption occurring at pH 6.0. Adsorption equilibrium was achieved within 1 h. Increasing ionic strength of solution negatively affected the arsenic uptake. The adsorption process performed more than 99.0% of As(V) removal from an initial concentration of 25.0 mg/L. The process of adsorption followed pseudo-second-order kinetics. The adsorption equilibrium isotherm data were analyzed using the Langmuir, Freundlich, Redlich–Peterson and Langmuir–Freundlich equations. The Langmuir–Freundlich isotherm described the adsorption data over the concentration range 25–400 mg/L. The adsorption mechanism appears to be a ligand-exchange process. A simulated groundwater sample was treated with Cell-AE to demonstrate its efficiency in removing As(V). The adsorbed As(V) ions were desorbed effectively by a 0.1 M NaOH solution.