The control of mercury vapor using biotrickling filters

The feasibility of using biotrickling filters for the removal of mercury vapor from simulated flue gases was evaluated. The experiments were carried out in laboratory-scale biotrickling filters with various mixed cultures naturally attached on a polyurethane foam packing. Sulfur oxidizing bacteria, toluene degraders and denitrifiers were used and compared for their ability to remove Hg 0 vapor. In particular, the biotrickling filters with sulfur oxidizing bacteria were able to remove 100% of mercury vapor, with an inlet concentration of 300-650 microg m(-3), at a gas contact time as low as six seconds. 87-92% of the removed mercury was fixed in or onto the microbial cells while the remaining left the system with the trickling liquid. The removal of mercury vapors in a biotrickling filter with dead cells was almost equivalent to this in biotrickling filters with live cells, indicating that significant abiotic removal mechanisms existed. Sulfur oxidizing bacteria biotrickling filters were the most effective in controlling mercury vapors, suggesting that sulfur played a key role. Identification of the location of metal deposition and of the form of metal was conducted using TEM, energy dispersive X-ray analysis (EDAX) and mercury elution analyses. The results suggested that mercury removal was through a series of complex mechanisms, probably both biotic and abiotic, including sorption in and onto cellular material and possible biotransformations. Overall, the study demonstrates that biotrickling filters appear to be a promising alternative for mercury vapor removal from flue gases.     

A practical and simple method in fractional determination of ambient forms of mercury in air

A collecting method to prepare a fractional determination of ambient forms of mercury in air is proposed. Particulate mercury is collected by a glass fiber filter. Sequential trap tubes consist of four long and slender quartz tubes, in which the Chromosorb W treated with HC$\text{l}$ gas for Hg(II), the Chromosorb W treated with 0.1 M NaOH for methylmercury, the silver-wire tip for metallic mercury and the gold plate tip for dimethylmercury are packed. The collection efficiency for these trap tubes was in the range of about 85 ～ 100% at the μg or ng concentration level. With this method, the air was collected by suction at the rate of 1.5 $\text{l}$/min. for about five hours, the detection limit being 0.2 ng Hg/m³. The results indicate that the regional distribution of total mercury in air was considerably greater in the volcanic and hot spring regions. Mercury species was found to be mostly Hg(II), followed by metallic mercury, methylmercury, dimethylmercury and particulate mercury in this order.     

湿法烟气脱硫系统的脱汞性能现场实验

分析湿法烟气脱硫系统的脱汞性能,对控制燃煤电厂的汞污染具有重要意义。利用安大略水法和吸附管法分别对某600 MW电厂湿法脱硫系统的进出口的烟气进行了采样,测量了烟气中各形态汞浓度,并分析了该系统对烟气总汞、气态氧化态汞的脱除效果以及对气态单质汞的影响。研究结果表明,安大略水法和吸附管法均能较为准确地测定湿法脱硫系统进出口烟气中的汞含量,测得入口和出口的氧化汞与平均值的相对误差的绝对值分别为3.5%和1.3%;入口和出口的单质汞与平均值相对误差的绝对值分别为16.6%和3.3%。其中吸附管法操作相对简单。通过湿法烟气脱硫系统后,烟气中氧化态汞的浓度可下降87.5%,其中约67.5%的氧化态汞被湿法脱硫系统脱除,约20%的氧化态汞在脱硫浆液的还原作用下被还原为单质汞,导致脱硫系统出口的单质汞浓度高于入口。     

无汞氯耗氧比浊光度曲线法测定COD

常规的COD测定方法存在汞污染问题。氯耗氧光度曲线法,可采用比浊光度法快速测定水样氯离子浓度,并可换算出耗氧量氯COD。经过改进的回流法,可以不加硫酸汞,而采用硫酸的二次加入法,来测定表观COD,再对氯COD进行扣除,从而得到真实的COD值,该法操作简便,实现了无汞测定。恒温微沸腾消解技术的应用,又使低浓度COD分析精准度得到了保证。     

有机改性蒙脱石负载巯基修复汞污染土壤

以蒙脱石作为原始材料,对其进行有机改性,将巯基基团负载在有机改性的蒙脱石上制备出重金属汞的稳定剂以稳定化修复汞污染土壤。考察稳定化时间、稳定剂添加量、浸出液pH及有机质含量对稳定化效果的影响,探究稳定化前后土壤汞形态变化。通过XRD、FTIR和SEM分析了蒙脱石、有机改性蒙脱石（Mont-OR）和负载巯基有机改性蒙脱石（Mont-OR-SH）的物理化学特征,通过原子吸收法测定汞浓度。稳定化修复结果表明,稳定化时间为30 d,稳定剂添加量为9%时,汞浸出浓度为0.066 mg·L-1,稳定率为98.3%,达到GB 5085.3-2007规定的汞限值0.10 mg·L-1。添加不同质量的小麦秸秆作为有机质的来源,均对整个稳定化有促进作用,其中添加量为6%时,促进作用最明显,改变浸出液pH,在强酸性和强碱性条件下,利用此稳定剂对汞的稳定作用降低。TESSIER五步提取法结果表明,负载巯基的有机改性蒙脱石的添加导致可交换态汞、碳酸盐结合态汞、铁锰氧化物结合态汞含量下降,而有机结合态汞、残渣态汞含量增加。实验结果证明有机改性蒙脱石负载巯基能够有效地应用于汞污染土壤修复。     

Mercury in the stomach contents of dab (Limanda limanda) from the North East Irish Sea and Mersey Estuary

A study of mercury concentrations in the stomach contents of fish from the north-east Irish Sea and Mersey Estuary has been shown to provide a means for surveillance of geographical and time-based changes in environmental exposure of fish biota to mercury in marine and estuarine ecosystems. This paper describes data for the flatfish dab (Limanda limanda), caught during the period 1986-1988. The low degree of variability in the data enables confirmation of clear trends in mercury concentration in stomach contents over time. As the inputs of mercury to the sewage sludge dumping ground in Liverpool Bay have decreased, there has been a corresponding decrease in mercury in fish food items. The mean mercury value in stomach contents around the dump site has declined to 100 microg kg(-1) (wet weight) which now predominates over the whole of Liverpool Bay. In 1986, mercury concentrations in stomach contents of fish ranged to over 750 microg kg(-1) although the majority of values were below 200 microg kg(-1). Most of the sites within the Mersey Estuary produced mean concentrations which were similar to those in the open sea, except for Garston which is the site closest to an inland, and principal alternative, source of mercury.     

Development of a regenerable system employing silica-titania composites for the recovery of mercury from end-box exhaust at a chlor-alkali facility

The release of mercury to the environment is of particular concern because of its volatility, persistence, and tendency to bioaccumulate. The recovery of mercury from end-box exhaust at chlor-alkali facilities is important to prevent release into the environment and reduce emissions as required by NESHAP (National Emission Standards for Hazardous Air Pollutants). A pilot-scale photocatalytic reactor packed with silica-titania composite (STC) pellets was tested at a chloralkali facility over a 3-month period. This pilot reactor treated up to 10 ft3/min (ACFM) of end-box exhaust and achieved 95% removal. The pilot reactor was able to maintain excellent removal efficiency even with large fluctuations in influent mercury concentration (400-1600 microg/ft3). The STC pellets were regenerated ex situ by regeneration with hydrochloric acid and performed similarly to virgin STC pellets when returned to service. On the basis of these promising results, two full-scale reactors with in situ regeneration capabilities were installed and operated. After optimization, these reactors performed similarly to the pilot reactor. A cost analysis was performed comparing the treatment costs (i.e., cost per pound of mercury removed) for sulfur-impregnated activated carbon and the STC system. The STC proved to be both technologically and economically feasible for this installation.     

Selective extraction of trace mercury and cadmium from drinking water sources.

In this paper, a new alternative method, i.e., selective extraction by weakly basic anion exchange resin, has been developed for the removal of trace cadmium and mercury ions from drinking water sources. The mechanism of heavy metal removal is based on selective extraction as the results of LEWIS-base-acid interactions. Transfer of trace mercury species from liquid to resin phase coincides well with the performance of film diffusion. The results demonstrated that the presence of chlorine has a negligible influence on the removal of mercury. However, humic acids can strongly bind mercury by the formation of complex compounds and therefore become the obstacle in the diffusion progress. At neutral or base pH, the resin material exhibits the favorable uptake of heavy metals. In filter experiments, the studied resin material offers favorable properties in the selective extraction of trace mercury and cadmium.     

Measurements of atmospheric mercury species during an international study of mercury depletion events at Ny-Ålesund,Svalbard, spring 2003. How reproducible are our present methods?

Six groups participated in an international study of springtime atmospheric mercury depletion events (AMDEs) at Ny-Ålesund in the Norwegian Arctic during April and May 2003 with the aim to compare analytical methods for measurements of atmospheric mercury species and study the physical and chemical processes leading to AMDEs. Five groups participated in the method comparison that was conducted at three different locations within Ny-Ålesund. Various automated and manual instrumentation were used to sample, measure and compare gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and mercury associated with particles (Hg-P). The concentration of GEM was reproducible during background conditions. For the first time using ambient air, the statistics associated with round robin test procedures were applied. This was found to be an appropriate tool to investigate the reproducibility of GEM measurements in ambient air. The precision for each group measuring GEM concentrations was found to be consistently good (within 5%). Five AMDEs were recorded during the study. Using four different methods, including single and replicate samples, all groups recorded higher values of RGM and Hg-P during AMDEs. The results show that measuring comparable atmospheric mercury species at both the same and different locations (within the Ny-Ålesund area) is difficult. Not only do site location and site characteristics create challenges when trying to intercompare results but there are difficulties, as well, in obtaining comparable results with similar sampling and analysis methods. Nevertheless, with our current procedures for atmospheric mercury identification we can differentiate with certainty between “high” and “low” concentration values of RGM and Hg-P.     

Evaluation of an offline method for the analysis of atmospheric reactive gaseous mercury and particulate mercury

Reactive gaseous mercury (RGM) and particulate mercury (PHg) were collected in Milwaukee, WI, between April 2004 and May 2005, and in Riverside, CA, between July 25 and August 7, 2005 using sorbent and filter substrates. The substrates were analyzed for mercury by thermal desorption analysis (TDA) using a purpose-built instrument. Results from this offline-TDA method were compared with measurements using a real-time atmospheric mercury analyzer. RGM measurements made with the offline-TDA agreed well with a commercial real-time method. However, the offline TDA reported PHg concentrations 2.7 times higher than the real-time method, indicating evaporative losses might be occurring from the real-time instrument during sample collection. TDA combined with reactive mercury collection on filter and absorbent substrates was cheap, relatively easy to use, did not introduce biases due to a semicontinuous sample collection strategy, and had a dynamic range appropriate for use in rural and urban locations. The results of this study demonstrate that offline-TDA is a feasible method for collecting reactive mercury concentrations in a large network of filter-based samplers.     

Relative accuracy testing of an X-ray fluorescence-based mercury monitor at coal-fired boilers

The relative accuracy (RA) of a newly developed mercury continuous emissions monitor, based on X-ray fluorescence, was determined by comparing analysis results at coal-fired plants with two certified reference methods (American Society for Testing and Materials [ASTM] Method D6784-02 and U.S. Environment Protection Agency [EPA] Method 29). During the first determination, the monitor had an RA of 25% compared with ASTM Method D6784-02 (Ontario Hydro Method). However, the Ontario Hydro Method performed poorly, because the mercury concentrations were near the detection limit of the reference method. The mercury in this exhaust stream was primarily elemental. The second test was performed at a U.S. Army boiler against EPA Reference Method 29. Mercury and arsenic were spiked because of expected low mercury concentrations. The monitor had an RA of 16% for arsenic and 17% for mercury, meeting RA requirements of EPA Performance Specification 12a. The results suggest that the sampling stream contained significant percentages of both elemental and oxidized mercury. The monitor was successful at measuring total mercury in particulate and vapor forms.     

Development of a Regenerable System Employing Silica-Titania Composites for the Recovery of Mercury from End-Box Exhaust at a Chlor-Alkali Facility

Abstract

The release of mercury to the environment is of particular concern because of its volatility, persistence, and tendency to bioaccumulate. The recovery of mercury from end-box exhaust at chlor-alkali facilities is important to prevent release into the environment and reduce emissions as required by NESHAP (National Emission Standards for Hazardous Air Pollutants). A pilot-scale photocatalytic reactor packed with silica-titania composite (STC) pellets was tested at a chlor-alkali facility over a 3-month period. This pilot reactor treated up to 10 ft³/min (ACFM) of end-box exhaust and achieved 95% removal. The pilot reactor was able to maintain excellent removal efficiency even with large fluctuations in influent mercury concentration (400–1600 μg/ft³).The STC pellets were regenerated ex situ by regeneration with hydrochloric acid and performed similarly to virgin STC pellets when returned to service. On the basis of these promising results, two full-scale reactors with in situ regeneration capabilities were installed and operated. After optimization, these reactors performed similarly to the pilot reactor. A cost analysis was performed comparing the treatment costs (i.e., cost per pound of mercury removed) for sulfur-impregnated activated carbon and the STC system. The STC proved to be both technologically and economically feasible for this installation.     

Evaluation of an Offline Method for the Analysis of Atmospheric Reactive Gaseous Mercury and Particulate Mercury

Abstract

Reactive gaseous mercury (RGM) and particulate mercury (PHg) were collected in Milwaukee, WI, between April 2004 and May 2005, and in Riverside, CA, between July 25 and August 7, 2005 using sorbent and filter substrates. The substrates were analyzed for mercury by thermal desorption analysis (TDA) using a purpose-built instrument. Results from this offline-TDA method were compared with measurements using a real-time atmospheric mercury analyzer. RGM measurements made with the offline-TDA agreed well with a commercial real-time method. However, the offline TDA reported PHg concentrations 2.7 times higher than the real-time method, indicating evaporative losses might be occurring from the real-time instrument during sample collection. TDA combined with reactive mercury collection on filter and absorbent substrates was cheap, relatively easy to use, did not introduce biases due to a semicontinuous sample collection strategy, and had a dynamic range appropriate for use in rural and urban locations. The results of this study demonstrate that offline-TDA is a feasible method for collecting reactive mercury concentrations in a large network of filter-based samplers.     

Studies on thio-substituted polyurethane foam (T-PUF) as a new efficient separation medium for the removal of inorganic/organic mercury from industrial effluents and solid wastes

Novel thio-substituted flexible polyurethane foam (T-PUF) was synthesised by addition polymerisation of mercaptan with the precursors of an open-cell polyurethane foam, which can be used as a highly selective sorbent for inorganic and organic mercury from complex matrices. The percentage extraction of inorganic mercury was studied at different flow-rates, over a wide pH range at different concentrations ranging from 1 ppm, to 100 ppm. The break-through capacity and total capacity of unmodified and thio-foams were determined for inorganic and organic mercurials. The absorption efficiency of thio-foam was far superior to other sorbent media, such as activated carbon, polymeric ion-exchange resins and reagent-loaded polyurethane foams. It was observed that even at the 1000 ppm level, divalent ions like Cu, Mg, Ca, Zn do not appreciably influence the per cent extraction of inorganic mercury at the 10 ppm level. These matrix levels are the most concentrated ones which are likely to occur, both in local sewage and effluent waters. Further, the efficiency of this foam was sufficiently high at 10-100 ppm levels of Hg, even from 5-10 litres of effluent volumes using 50 g of thio-foam packed into different columns in series. Thio-foams were found to possess excellent abilities to remove and recover mercury even at low levels from industrial effluents and brine mud of chlor-alkali industry after pre-acid extraction. This makes it a highly efficient sorbent for possible application in effluent treatment. Model schemes for the removal and recovery of mercury from industrial effluents and municipal sewage (100-1000 litre) by a dynamic method are proposed and the costs incurred in a full-scale application method are indicated to show that the use of thio-foam could be commercially attractive.     

Scientific uncertainties in atmospheric mercury models II: Sensitivity analysis in the CONUS domain

In this study, we present the response of model results to different scientific treatments in an effort to quantify the uncertainties caused by the incomplete understanding of mercury science and by model assumptions in atmospheric mercury models. Two sets of sensitivity simulations were performed to assess the uncertainties using modified versions of CMAQ-Hg in a 36-km Continental United States domain. From Set 1 Experiments, it is found that the simulated mercury dry deposition is most sensitive to the gaseous elemental mercury (GEM) oxidation product assignment, and to the implemented dry deposition scheme for GEM and reactive gaseous mercury (RGM). The simulated wet deposition is sensitive to the aqueous Hg(II) sorption scheme, and to the GEM oxidation product assignment. The inclusion of natural mercury emission causes a small increase in GEM concentration but has little impact on deposition. From Set 2 Experiments, it is found that both dry and wet depositions are sensitive to mercury chemistry. Change in model mercury chemistry has a greater impact on simulated wet deposition than on dry deposition. The kinetic uncertainty of GEM oxidation by O₃ and mechanistic uncertainty of Hg(II) reduction by aqueous HO₂ pose the greatest impact. Using the upper-limit kinetics of GEM–O₃ reaction or eliminating aqueous Hg(II)–HO₂ reaction results in unreasonably high deposition and depletion of gaseous mercury in the domain. Removing GEM–OH reaction is not sufficient to balance the excessive mercury removal caused by eliminating the HO₂ mechanism. Field measurements of mercury dry deposition, better quantification of mercury air-surface exchange and further investigation of mercury redox chemistry are needed for reducing model uncertainties and for improving the performance of atmospheric mercury models.     

Mercury in salt marshes ecosystems: Halimione portulacoides as biomonitor

Mercury concentrations were quantified in Halimione portulacoides (roots, stems and leaves) as well as in sediments from eight Portuguese estuarine systems, covering seventeen salt marshes with distinct degrees of mercury contamination. The concentration of mercury in the sediments ranged from 0.03 to 17.0 microg g(-1). The results show that the accumulation of mercury differed according to the organ of the plant examined and the concentration of mercury in the sediments. Higher mercury concentrations were found in the roots (up to 12.9 microg g(-1)) followed by the leaves (up to 0.12 microg g(-1)), while the stems had the lowest concentrations (up to 0.056 microg g(-1)). A linear model explained the relation between the concentrations of mercury in the different plant organs: roots and stems (R(adj)(2)=0.75), stems and leaves (R(adj)(2)=0.85) and roots and leaves (R(adj)(2)=0.78). However, the results show that the variation of mercury concentration in the roots versus mercury concentration in the sediments was best fitted by a sigmoidal model (R(adj)(2)=0.89). Mercury accumulation in the roots can be described in three steps: at a low range of mercury concentrations in the sediments (from 0.03 up to 2 microg g(-1)), the accumulation of mercury in roots is also low reaching a maximum concentration of 1.3 microg g(-1); the highest rates of mercury accumulation in the roots occur in a second step, until the concentrations of mercury in the sediments reach approximately 4.5 microg g(-1); after reaching this maximum value, the rate of mercury accumulation in the roots slows down leading to a plateau in the concentration of mercury in the roots of about 9.4 microg g(-1), which corresponds to a mercury concentration in the sediments of about 11 microg g(-1). A linear model explained also the accumulation of mercury in leaves versus the mercury concentration in the sediments (R(adj)(2)=0.88). Differences in responses of roots and leaves are explained by the dynamics of the plant organs: old roots are mineralised in situ close to new roots, while leaves are renewed. Previous studies have already shown that H. portulacoides is a bioindicator for mercury and the results from this work sustain that H. portulacoides may also be used as a biomonitor for mercury contamination in salt marshes. Nevertheless, caution should be taken in the application of the models, concerning the life cycle of the species and the spatial variability of the systems.     

Bioaccumulation of mercury in a vestimentiferan worm living in Kagoshima Bay,Japan

The present study reports on the mercury concentrations of the vestimentiferan worm, Lamellibrachia satsuma, (Annelida: Pogonophora) found near hydrothermal vents at a depth of 80-100 m in the northern parts of Kagoshima Bay. The vestimentiferan worms had total mercury concentrations of 238 ng/g in the anterior muscle of the body and 164 ng/g in the posterior trophosome. Methylmercury constituted only 7.6% of total mercury detected anteriorly and 16.3% posteriorly. The mean total mercury concentration in filtrated ambient seawater of the worm habitat was 1.1 ng/l. The worm should accumulate mercury in seawater by a one-step into the anterior and posterior parts as 2.2 x 10(%) and 1.5 x 10(5) times those of the filtered ambient seawater, respectively. The bioaccumulation factor of mercury by the worms with only their respiration would be actually larger than that by other marine animals through food webs. The high bioaccumulation factor of mercury in the worms suggest the following two possibilities: (i) the biological half-life of organomercury in the worm could be exceptionally long; or (ii) the lifetime of vestimentiferan worms examined in the present study could be extremely long. Various metals in one specimen of the worm were analyzed by using ICP-MS, and then gold as well as silver were detected in the worm. Gold was detected for the first time from marine animals.     

Biosensors for detection of mercury in contaminated soils

Biosensors based on whole bacterial cells and on bacterial heavy metal binding protein were used to determine the mercury concentration in soil. The soil samples were collected in a vegetable garden accidentally contaminated with elemental mercury 25 years earlier. Bioavailable mercury was measured using different sensors: a protein-based biosensor, a whole bacterial cell based biosensor, and a plant sensor, i.e. morphological and biochemical responses in primary leaves and roots of bean seedlings grown in the mercury-contaminated soil. For comparison the total mercury concentration of the soil samples was determined by AAS. Whole bacterial cell and protein-based biosensors gave accurate responses proportional to the total amount of mercury in the soil samples. On the contrary, plant sensors were found to be less useful indicators of soil mercury contamination, as determined by plant biomass, mercury content of primary leaves and enzyme activities.     

Development of the DGT technique for Hg measurement in water: comparison of three different types of samplers in laboratory assays

The Diffusive Gradients in Thin films (DGT) technique is an operationally defined method to determine the dissolved fraction of trace elements in water. The aim of this study was to develop this technique for the measurement of the bioavailable mercury species in natural waters. For that purpose, three types of DGT units (commercial, manufactured with agarose diffusive gel (DG) and manufactured with polyacrylamide DG) were tested under controlled conditions using an Hg(II) solution both with and without dissolved organic matter (DOM). An acid digestion method using aqua regia was optimised to efficiently digest the resin gel discs prior to analysis. A good performance was obtained for the three DGT types when deployed in a DOM-free mercury solution in the laboratory, and it was demonstrated that polyacrylamide gel can be used as diffusive layer for mercury sampling. However, when the DGT units were deployed in a mercury solution containing DOM, performance differences were observed. Furthermore, the mass of background mercury (blanks) varied among the different DGT types. In the light of the results, the devices manufactured with polyacrylamide DG seemed to be the best choice for dissolved mercury determination.     

Spectrophotometric determination of sulphur dioxide

Sulphur dioxide, an important industrial gas and air pollutant, is usually estimated using mercury salts. The authors have developed a method in which hazardous mercury salts are avoided. Sulphur dioxide is trapped in aqueous morpholine and mixed with the excess of dichromate solution in acidic medium. The hexavalent chromium in dichromate is reduced to trivalent chromium by sulphur dioxide and the excess of hexavalent chromium is determined with diphenylcarbazide which yields a soluble red-violet complex with an absorption maximum at 540 nm. The decrease in the absorbance values of the red-violet complex formed after reduction, when compared to that of a reagent control, is proportional to the concentration of sulphur dioxide used for reduction. Beer's law operates between 0.4 and 4 microg ml(-1) concentration of sulphur dioxide in solution.