Chlor-alkali Plant Research Articles

Usage Proposal of a common urban decorative tree (Salix alba L.) to monitor the dispersion of gaseous mercury: A case study from Turda (Romania)

Closure of chloralkali plants poses a risk of abandonment of important sources of gaseous mercury. In this work, an assessment has been made of the potential for pollution from one of these plants in the proximity of a densely populated town in central Romania.The work involved a comparison between two major types of monitoring survey: biomonitoring using leaves of a tree common in urban environments; and LUMEX-based gaseous mercury analysis. For biomonitoring, 21 samples from Salix alba L. trees were taken in Turda area. Atmospheric monitoring included two mobile surveys and one at a fixed location.The results from both monitoring systems show similarities in gaseous mercury dispersion patterns, with high mercury contents clearly related to the presence of the chloralkali plant. Particularly high levels were measured in the following situations: (i) in a ‘smog’ area related with thermal inversion and (ii) during dusk. Direct monitoring suffered from limitations in acquiring information, especially in a medium-long time range, but biomonitoring provided these data and is capable of covering studies on temporary trends or comparative assessments between European cities with contrasting gaseous mercury sources.The thermal speciation of mercury contents indicates that the whole fraction of mercury in leaves corresponds to organic mercury. This finding implies a non-reversible uptake process, which in turn ensures the applicability of this technique to biomonitor long-term exposure.As a conclusion, the assessment of gaseous mercury pollution based on biomonitoring using S. alba has proven to be a useful, reliable and cost-effective methodology.

CO2 capture by carbide slag calcined under high-concentration steam and energy requirement in calcium looping conditions

In this work, calcination under high-concentration steam that can be implemented by O2/H2O combustion was proposed to replace high-concentration CO2 that usually was implemented by O2/CO2 combustion in calcium looping. CO2 capture performance of the carbide slag, an industrial solid waste from chlor-alkali plants, was investigated in a dual fixed-bed reactor under high-concentration steam calcination condition during the calcium looping cycles. Calcined under high-concentration steam (95%) atmosphere, the carbide slag can be completely and quickly decomposed at 800°C, which is 150°C lower than the calcination temperature under high-concentration CO2 (100%) atmosphere. The carbonation conversions of the carbide slag calcined under high-concentration steam condition after 1 and 10 cycles are about 42% and 36% higher than those calcined under high-concentration CO2 condition, respectively. This is because when the carbide slag is calcined under high-concentration steam, the relatively smaller CaO grains and more porous structure are generated, which are beneficial for CO2 capture by carbide slag. Due to the low calcination temperature and the high CO2 capture capacity of the carbide slag, the energy requirement in the calciner to capture per mole CO2 under high-concentration steam condition is lower than that under high-concentration CO2 condition. High-concentration steam calcination in place of high-concentration CO2 calcination improves the CO2 capture efficiency from 0.68 to 0.88 and saves a quarter of the energy consumption in the calciner for capturing per mole CO2 in the calcium looping system, when the ratio of recycled carbide slag flow rate to CO2 flow rate is 2 and the sorbent make-up ratio is 0.09. Thus, it is reasonable to consider O2/H2O combustion as an alternative energy-supply way of O2/CO2 combustion for the calcium looping of carbide slag.

Mercury in wintering American black ducks (Anas rubripes) downstream from a point-source on the lower Penobscot River, Maine, USA

Waterfowl wintering along the lower Penobscot River, Maine continue to be exposed to elevated Hg concentrations from the HoltraChem chlor-alkali plant that operated along the river between 1967 and 2000. In American black ducks (Anas rubripes) total Hg in duck breast muscle increased with residence time on contaminated marshes, reaching means of 0.82±0.21μg/g ww (wet weight) by the end of the fall hunting season, and prompting Maine to issue a human consumption advisory on duck breast muscle. Methyl Hg comprised over 99% of the total Hg in breast muscle. The ratio of Hg concentrations in blood and muscle were strongly correlated and approached 1:1 after extended residence times. Primary feather (P1) total Hg concentrations averaged 2.2±1.3μg/g fw (fresh weight), verifying low Hg exposure during feather growth on distant breeding grounds the preceding summer. Mercury concentrations in black ducks, following winter residence along the lower Penobscot exceeded levels associated with reproductive toxicity. Carry-over of Hg to summer breeding grounds may limit the subsequent reproductive success of black ducks.

The influence of permanently submerged macrophytes on sediment mercury distribution, mobility and methylation potential in a brackish Norwegian fjord

Macrophytes are shown to affect the microbial activity in different aqueous environments, with an altering of the sediment cycling of mercury (Hg) as a potential effect. Here, we investigated how a meadow with permanently submerged macrophytes in a contaminated brackish fjord in southern Norway influenced the conditions for sulfate reducing microbial activity, the methyl-Hg (MeHg) production and the availability of MeHg. Historically discharged Hg from a chlor-alkali plant (60–80tons, 1947–1987) was evident through high Hg concentrations (491mgTot-Hgkg−1, 268μgMeHgkg−1) in intermediate sediment depths (10–20cm) outside of the meadow, with reduced concentrations within the meadow. Natural recovery of the fjord was revealed by lower sediment surface concentrations (1.9–15.5mgTot-Hgkg−1, 1.3–3.2μgMeHgkg−1). Within the meadow, vertical gradients of sediment hydrogen sulfide (H2S) Eh and pH suggested microbial sulfate reduction in 2–5cm depths, coinciding with peak values of relative MeHg levels (0.5% MeHg). We assume that MeHg production rates was stimulated by the supply and availability of organic carbon, microbial activity and a sulfide oxidizing agent (e.g. O2) within the rhizosphere. Following this, % MeHg in sediment (0–5cm) within the meadow was approximately 10× higher compared to outside the meadow. Further, enhanced availability of MeHg within the meadow was demonstrated by significantly higher fluxes (p<0.01) from sediment to overlying water (0.1–0.6ngm−2d−1) compared to sediment without macrophytes (0.02–0.2ngm−2d−1). Considering the productivity and species richness typical for such habitats, submerged macrophyte meadows located within legacy Hg contaminated sediment sites may constitute important entry points for MeHg into food webs.

Laying Waste to Mercury: Inexpensive Sorbents Made from Sulfur and Recycled Cooking Oils.

Mercury pollution threatens the environment and human health across the globe. This neurotoxic substance is encountered in artisanal gold mining, coal combustion, oil and gas refining, waste incineration, chloralkali plant operation, metallurgy, and areas of agriculture in which mercury‐rich fungicides are used. Thousands of tonnes of mercury are emitted annually through these activities. With the Minamata Convention on Mercury entering force this year, increasing regulation of mercury pollution is imminent. It is therefore critical to provide inexpensive and scalable mercury sorbents. The research herein addresses this need by introducing low‐cost mercury sorbents made solely from sulfur and unsaturated cooking oils. A porous version of the polymer was prepared by simply synthesising the polymer in the presence of a sodium chloride porogen. The resulting material is a rubber that captures liquid mercury metal, mercury vapour, inorganic mercury bound to organic matter, and highly toxic alkylmercury compounds. Mercury removal from air, water and soil was demonstrated. Because sulfur is a by‐product of petroleum refining and spent cooking oils from the food industry are suitable starting materials, these mercury‐capturing polymers can be synthesised entirely from waste and supplied on multi‐kilogram scales. This study is therefore an advance in waste valorisation and environmental chemistry.

Mercury speciation and mobility in soils of industrial areas in the Baikal region, Southern Siberia, Russia

Mercury speciation and mobility in soils as a result of the chlor-alkali and metallurgy industries in Baikal region was investigated. In the period from 1973 to 1998, chlorine and alkali at the plant were produced using metallic mercury. Within the period of plant operation, the total mercury emissions release to the environment amounted to 1327 tons. The former Angarsk metallurgic plant for the production of arsenic is another technogenic source of mercury. The plant was shut down in 1949, but the technogenic dumps with high concentrations of arsenic, mercury and another heavy metals were located in the town for more than 60 years. These plants are located on the banks of the Angara River and are significant sources of technogenic mercury for the environment of the Baikal region. Mercury speciation was studied in soils near these plants. Mercury species were extracted by sequential extraction, and included water-soluble, acid-soluble, organic, tightly bound and sulfide fractions. High mercury concentrations were found in organic (41–61%) and tightly bound (38–56%) fractions in soils near the chlor-alkali plant. For the metallurgical plant soils, mercury was mainly found in the tightly bound (40–64%) and sulfide (31–51%) fractions. Mercury concentrations in mobile water and acid-soluble fractions of soils were low (0.17–2.27 and 0.04–1.06%, respectively). Such mercury distribution in the fractions was dependent on the primary mercury species that entered the soils from the two technogenic sources. The results indicate high mercury immobilization in soil and low potential bioavailability by plants.

Fluorine and metals in Polygonum arenastrum Bor. from areas influenced by various types of industry

A herbaceous plant Polygonum arenastrum Bor. (=P. aequele Lindm., Polygonum aviculare ssp. aequale (Lindman) Ascherson & Graebner) (equal-leaved knotgrass), is a widespread, good coloniser, able to survive in wastelands where other species became extinct. Therefore, the bioindication abilities of this species for F, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn were investigated. P.arenastrum was collected from 90 sites affected by six polluting factories: copper smelter, chlor-alkali plant, former ferrous-chromium smelter and active combustion smelter, power plant, cement plant and coke plant. Plant samples were collected at 0.75, 1.5, 3 and 4.5km from each of these polluters in N, S, W and E directions. For comparison, a control site with 16 sampling points was selected in an area relatively free from pollution. Concentrations of Cr, Cu, Fe, Pb and Zn in shoots and roots positively correlated with those in soil (both total and plant-available). Cu, Pb and Zn in P.arenastrum were within the values reported in literature as toxic for other plants with the highest bioaccumulation factor (BF) from soil to shoots for Cr and the highest translocation factor (TF) from roots to shoots for Co and Pb for more and less polluted and control sites. Polygonum arenastrum has a potential to accumulate Cr even in sites with low chromium concentration in soil. Polygonum arenastrum does not show any form of shoot injury at increased levels of F and metals in its tissues. Based on these characteristics we conclude that the ubiquitous P.arenastrum may be utilised as a relevant indicator of contamination in industrial zones and may function as an early warning system of increased toxicity in the environment.

Adsorption and desorption of Hg(II) by three typical soils around the chlor-alkali industry

ABSTRACTA series of batch experiments were conducted to assess the adsorption/desorption of Hg(II) within meadow soil, fluvo-aquic soil, and gray desert soil around the chlor-alkali industry in China. Results demonstrated that the descending order of the adsorptive capacity of Hg(II) to the three typical soils around a chlor-alkali plant, i.e., meadow soil (4536.24 mg/kg), fluvo-aquic soil (1598.62 mg/kg), gray desert soil (1272.51 mg/kg), and the soil organic matter, had a significant role in Hg(II) adsorption. Kinetic studies revealed that the Hg adsorption in the three soils was characterized with a fast stage and a slow stage. The Hg(II) adsorption rates are the highest for the fluvo-aquic soil, followed by the meadow soil, and then the gray desert soil. The results will play a guiding role in arid-zone soil pollution control and treatment, which will be a reference for the Northwest Oasis Environmental mercury pollution studies and integrated control in China.

Mercury levels in parturient and newborns from Aveiro region, Portugal

ABSTRACTSince the outbreak of methylmercury (MeHg) poisoning in Japan and Iraq, mercury (Hg) is classified as well-established teratogen. The Portuguese region of Aveiro faced some decades ago an environmental Hg contamination due to activities from a chlor-alkali plant. Until now, no apparent evaluation was conducted regarding prenatal exposure to Hg in this area. The main objectives of this study were to: i) assess maternal and fetal exposure to Hg in the Aveiro region using noninvasive biological matrices; ii) examine the influence of variables that may contribute to Hg exposure during pregnancy; and iii) improve knowledge regarding metal accumulation and distribution over the maternal–fetal–placental unit. This study was performed in 50 mother–newborn pairs from the Aveiro district. Total Hg (THg) was quantified in maternal scalp hair, placenta, amniotic membrane, and umbilical cord. Maternal hair presented THg levels with a mean value of 900 ng/g, which is lower than the USEPA and WHO acceptable threshold. Regarding THg levels in placenta and umbilical cord, mean values were similar (decidua basalis: 32.84 ng/g; chorionic plate: 30.18 ng/g; umbilical cord: 30.67 ng/g). The amniotic membrane presented the highest THg levels with a mean concentration of 42.35 ng/g, reaching a maximum of 134.1 ng/g. Further, a significant positive correlation was noted between THg levels found in hair, and all matrices analyzed reinforcing the use of hair in biomonitoring studies with respect to maternal exposure to Hg. In general, levels of THg found in our study were lower than those in previous studies performed in Europe. Consumption of fish rich in selenium and bottled water was negatively correlated with THg levels. Finally, data demonstrated that Hg is capable of crossing the placental barrier and accumulate in placental tissues. Amniotic membrane seemed to play a role in metal detoxification, but further investigations are necessary to examine whether this catabolic process affects Hg accumulation.

Transcriptomic approach for assessment of the impact on microalga and macrophyte of in-situ exposure in river sites contaminated by chlor-alkali plant effluents

Water quality degradation is a worldwide problem, but risk evaluation of chronic pollution in-situ is still a challenge. The present study aimed to evaluate the potential of transcriptomic analyses in representative aquatic primary producers to assess the impact of environmental pollution in-situ: the microalga Chlamydomonas reinhardtii and the macrophyte Elodea nuttallii were exposed 2 h in the Babeni Reservoir of the Olt River impacted by chlor-alkali plant effluent release resulting in increased concentrations of Hg and NaCl in receiving water.The response at the transcriptomic level was strong, resulting in up to 5485, and 8700 dysregulated genes (DG) for the microalga and for the macrophyte exposed in the most contaminated site, respectively. Transcriptomic response was congruent with the concentrations of Hg and NaCl in the water of the impacted reservoir. Genes involved in development, energy metabolism, lipid metabolism, nutrition, and RedOx homeostasis were dysregulated during in-situ exposure of both organisms. In addition, genes involved in the cell motility of C. reinhardtii and development of the cell wall of E. nuttallii were affected. DG were in line with adverse outcome pathways and transcriptomic studies reported after exposure to high concentrations of Hg and NaCl under controlled conditions in the laboratory.Transcriptomic response provided a sensitive measurement of the exposure as well as hints on the tolerance mechanisms of environmental pollution, and is thus promising as an early-warning tool to assess water quality degradation.

Erratum to: Gaseous Elemental Mercury Level and Distribution in a Heavily Contaminated Site: the Ex-chlor Alkali Plant in Torviscosa (Northern Italy)

Mercury (Hg) poses environmental and health risks due to its global distribution and high toxicity exhibited in some of its chemical forms. Although Hg is naturally present in the environment, human activities have increased its cycling among the land, atmosphere and ocean by a factor of three to five comparing the pre-industrial period to the present day. The Torviscosa chlor-alkali plant (CAP), which operated since the beginning of twentieth century, was one of the most important Cl2 production capacity in the Northern Italy and was responsible for an uncontrolled discharge of Hg in the surrounding area. Previous studies reported the high degree of Hg pollution in soils, river sediments and surface waters of the area, but the Hg level in the atmospheric media was never taken into consideration. In this work, an integrated approach was applied with the aim to assess the level, distribution and dispersion of gaseous elemental mercury (GEM) close to the CAP area. GEM levels were monitored by means of four surveys conducted from September 2014 to July 2015, at fixed locations and covering an area of about 10 km2 (including CAP area, Torviscosa village and reclaimed land), accomplished to Hg bioaccumulation measurements in selected lichens. The results indicate that the CAP area currently represents the main source of GEM in the Friuli Venezia Giulia region. The highest levels were found close to the old factory’s buildings (more than 5000 ng m−3), whereas other sites are less impacted. The emission of GEM is not clearly related to the intensity of solar radiation (temperature) at the soil level; however, this latter influences the release from the old buildings employed in the past for the production activities. The most important factor driving the GEM dispersion is the wind, as confirmed by the map of lichens bioaccumulation. In this context, the GEM plume partially affects the nearby village of Torviscosa (about 1 km), but the values found were always well below the international thresholds for residential areas, thus excluding the risk of inhalation for local inhabitants.

Characterization of Mercury Contamination Surrounding a Chloralkali Production Facility in Tuzla, Bosnia and Herzegovina

ABSTRACTTuzla is among the most polluted cities of Bosnia and Herzegovina. The main source of pollution in the area is soil heavily contaminated by mercury released from a former chloralkali plant. This paper is focused on the characterization of mercury contaminated soil and air surrounding the chloralkali plant. In soil, the mobility and transformation of mercury were investigated by sequential extraction, while the methylation and reduction potentials were determined by the use of a radioactive tracer. Mercury emission from soil was determined by laboratory and by flux chamber measurements in the field. In addition, mercury concentrations in air were estimated by the analysis of air and the transplanted lichen Hypogymnia physodes. Mercury in soils in the vicinity of the chloralkali plant exceeded the background value by a factor of more than 3000. The fractionation of mercury in surface soil by sequential extraction showed that the mercury in soil was primarily bound to organic matter and a fraction containing elemental mercury and mercury (I) chloride is also significant. The obtained methylation and reduction potentials are low. The mercury flux from soil was estimated by two approaches. Fluxes of up to 8000 ng/m2/day were measured at the most polluted site; evaporation from soil was shown to be the primary source of elevated mercury in air. Air concentration mapping also revealed other sources of mercury; the most likely is the 715 MW coal power plant in the vicinity of former chloralkali facility.

Sensitivity analysis for optimisation of brine purification process

A two-stage brine purification process involving an ion exchange column and a secondary filter is an important process unit in a chlor-Alkali plant. As part of the effort to increase the plant capacity, the throughput of this process has been increased, which has subsequently caused non-conformance to the production specifications unless the filter is changed more frequently. Investigations are then carried out to study the sensitivity of potential variables to be manipulated in order to optimise the process, and increase the filter life. The results obtained from plant tests show that by increasing Calcium to Magnesium ratio, and maintaining lower excess sulphate the filter life can be increased. Based on these findings, a recycle stream is introduced and better performance is obtained. Following this modification, better performance is obtained, however, due to some production issues, the target desired improvement level is not achieved.

The history of mercury pollution near the Spolana chlor-alkali plant (Neratovice, Czech Republic) as recorded by Scots pine tree rings and other bioindicators

We assessed >100years of mercury (Hg) pollution recorded in the tree rings of Scots Pine near a Czech chlor-alkali plant operating since 1941. Hg concentrations in tree rings increased with the launching of plant operations and decreased when Hg emissions decreased in 1975 due to an upgrade in production technology. Similar to traditional bioindicators of pollution such as pine needles, bark and forest floor humus, Hg concentrations in Scots Pine boles decreased with distance from the plant. Mean Hg in pine bole in the 1940s ranged from 32.5μg/kg Hg at a distance of 0.5km from the plant to 5.4μg/kg at a distance of >4.7km, where tree ring Hg was the same as at a reference site, and other bioindicators also suggest that the effect of the plant was no longer discernible. Tree ring Hg concentrations decreased by 8–29μg/kg since the 1940s at all study sites including the reference site. The lack of exact correspondence between changes at the plant and tree ring Hg indicated some smearing of the signal due to lateral translocation of Hg from sapwood to heartwood. Bole Hg concentrations reflected local and regional atmospheric Hg concentrations, and not Hg wet deposition.

Toward an Assessment of the Global Inventory of Present-Day Mercury Releases to Freshwater Environments.

Aquatic ecosystems are an essential component of the biogeochemical cycle of mercury (Hg), as inorganic Hg can be converted to toxic methylmercury (MeHg) in these environments and reemissions of elemental Hg rival anthropogenic Hg releases on a global scale. Quantification of effluent Hg releases to aquatic systems globally has focused on discharges to the global oceans, rather than contributions to freshwater systems that affect local exposures and risks associated with MeHg. Here we produce a first-estimate of sector-specific, spatially resolved global aquatic Hg discharges to freshwater systems. We compare our release estimates to atmospheric sources that have been quantified elsewhere. By analyzing available quantitative and qualitative information, we estimate that present-day global Hg releases to freshwater environments (rivers and lakes) associated with anthropogenic activities have a lower bound of ~1000 Mg·a−1. Artisanal and small-scale gold mining (ASGM) represents the single largest source, followed by disposal of mercury-containing products and domestic waste water, metal production, and releases from industrial installations such as chlor-alkali plants and oil refineries. In addition to these direct anthropogenic inputs, diffuse inputs from land management activities and remobilization of Hg previously accumulated in terrestrial ecosystems are likely comparable in magnitude. Aquatic discharges of Hg are greatly understudied and further constraining associated data gaps is crucial for reducing the uncertainties in the global biogeochemical Hg budget.

Biofilm composition in the Olt River (Romania) reservoirs impacted by a chlor-alkali production plant

Freshwater biofilms can be useful indicators of water quality and offer the possibility to assess contaminant effects at the community level. The present field study examines the effects of chlor-alkali plant effluents on the community composition of biofilms grown in the Olt River (Romania) reservoirs. The relationship between ambient water quality variables and community composition alterations was explored. Amplicon sequencing revealed a significant modification of the composition of microalgal, bacterial and fungal communities in the biofilms collected in the impacted reservoirs in comparison with those living in the uncontaminated control reservoir. The abundance corrected Simpson index showed lower richness and diversity in biofilms collected in the impacted reservoirs than in the control reservoir. The biofilm bacterial communities of the impacted reservoirs were characterized by the contaminant-tolerant Cyanobacteria and Bacteroidetes, whereas microalgal communities were predominantly composed of Bacillariophyta and fungal communities of Lecanoromycetes and Paraglomycetes. A principal component analysis revealed that major contaminants present in the waste water of the chlor-alkali production plant, i.e. Na+, Ca2+, Cl- and Hg, were correlated with the alteration of biofilm community composition in the impacted reservoirs. However, the biofilm composition was also influenced by water quality variables such as NO3-, SO42-, DOC and Zn from unknown sources. The results of the present study imply that, even when below the environmental quality standards, typical contaminants of chlor-alkali plant releases may affect biofilm composition and that their impacts on the microbial biodiversity might be currently overlooked.

Historical sedimentary trends of mercury and other trace elements from two saltmarshes of the Marano and Grado lagoon (northern Adriatic Sea)

Previous research conducted in the Marano and Grado lagoon (northern Adriatic Sea) has shown that this environment has been affected by trace metal contamination, especially by mercury (Hg), from both industrial (the chlor-alkali plant) and mining activities (Idrija mine, Slovenia). Sediment cores were collected from two different saltmarshes of this lagoon environment to evaluate the degree of the anthropogenic enrichments and the geochronology of Hg accumulation. Core subsampling was performed by cutting 1-cm thick slices at discrete intervals. Mercury determination was done differently from the other parameters in that the two long cores were subsampled at 1-cm intervals to obtain continuous concentration profiles. Samples were completely decomposed, using a mixture of mineral acids in a closed microwave system before being analysed for trace metal content using ICP-OES. Total Hg content in the solid phase was determined by DMA-80. 137Cs was measured via gamma spectrometry. 210Pb activity was measured via alpha-counting of its daughter, 210Po, assuming secular equilibrium between the two isotopes. In saltmarsh sediments, Fe, Co, Li, Sc and V show no enrichment at both sites thus suggesting that they are essentially lithogenic elements. Conversely, enrichments are minimal (EF = <2) for As, Cd, Cr, Ni, Pb and Zn and moderate (EF = 2–5) for Cu and Mn and also for Pb and Zn but only in some levels of the sedimentary sequences. An exception is Hg, as expected due to the long-term input proceeding from the historical mining activity which has especially affected the eastern sector of the lagoon. The core collected from the saltmarsh in the eastern lagoon (Grado) displays a better time resolution during the last century although the Hg background level has not been reached. Conversely, the core collected in the western sector (Marano) has recorded a longer and more complete history of Hg contamination, from the beginning of the peak of Hg extraction activity at the Idrija mine (1850). Both saltmarshes still receive Hg inputs and the sediment accumulation rates in the upper section appear to have increased over the last 10–20 years (from 0.30 to 0.45 cm year−1 at Marano and from 0.30 to 0.74 cm year−1 at Grado). Many of these morphological structures suffer erosive processes thus representing a potential source of contaminants associated with sediments, in particular Hg. Conservation and monitoring of saltmarshes should be taken into consideration also from this environmental point of view.

Freshwater Mussel (Unionidae) Abundance and Diversity Upstream and Downstream of a Superfund Site on the North Fork Holston River, Saltville, Virginia

ABSTRACT The North Fork Holston River (NFHR) historically supported 33 unionid mussel species downstream of Saltville, VA. Because of industrial contamination over decades from a chlor-alkali plant, a U.S. Environmental Protection Agency Superfund Site (SITE) was created with Hg and MeHg designated as contaminants of concern. Mussel surveys were conducted at 18 NFHR locations to determine abundance, species richness, and recruitment upstream and downstream of the SITE. Seventeen unionid species were collected, and mean species richness of upstream sites (8.8 species, n = 6 sites) was greater than the mean of downstream locations (3.8 species, n = 12). The catch-per-unit-effort mean from upstream sites (10.4 mussels/h, n = 3 sites) was greater than the mean of downstream sites (3.5 mussels/h, n = 12). Mean density of upstream (1.8 mussels/m2, n = 6 sites) sites was higher than observed at downstream (1.0 mussels/m2, n = 8) locations. Results show that species richness in the entire lower NFHR is less than ...

Adsorption performance of coconut shell activated carbon for the removal of chlorate from chlor-alkali brine stream.

Activated carbon from coconut shell was used to investigate the adsorption of chlorate from a chlor-alkali plant's brine stream. The effect of pH, flowrate, chlorate and chloride concentration on the breakthrough curves were studied in small-scale column trials. The results obtained show enhanced adsorption at low flowrates, higher chlorate concentrations, and at a pH of 10. These studies show that introducing an activated carbon adsorption column just before the saturator would remove sufficient quantities of chlorate to allow more of the chlor-alkali plant's brine stream to be reused. From column dynamic studies, the Thomas model showed close approximation when the chlorate in the effluent was higher than breakthrough concentrations and there was close correlation at high influent concentration. The qo (maximum adsorption capacity) values were close to those obtained experimentally, indicating close representation of the breakthrough curve by the Thomas model.

Monitoring of Diaphragm Cell Chlor-Alkali Plants for Improved Safety and Performance

IntroductionSenSevere LLC (Pittsburgh, PA) has recently introduced new technologies for the monitoring critical diaphragm cell chlor-alkali plant metrics. We have developed a semiconductor-based sensor for the monitoring of hydrogen in chlorine and an RF-based sensor for the monitoring of brine level. These sensors, along with reporting temperature and voltage, have been engineered in conjunction with wireless data transmission such that a cell-by-cell graphical display of cell room parameters facilitates level adjustment, scheduling of maintenance, and the avoidance of unsafe operating conditions. Lessons learned during plant trials and commercialization are reviewed. Technology SenSevere’s chlor-alkali developments began with adapting an academic semiconductor-based H2 sensing technology to the problem of detecting H2 in wet Cl2 over the range 0 - 5 vol.%. Circumstances such tears in diaphragms from pressure fluctuations can lead to levels of hydrogen approaching the lower explosion limit. Lower levels can also result in dangerous conditions downstream in liquefaction. The monitoring of brine level is important for several reasons. If level is too high, brine flow will be too high resulting in low caustic strength. The steam requirements in the evaporator train will then be too high. If level is too low, high current density and low brine flow may result in cell overheating, additional loss of current to oxygen production, and, dangerously, the possibility of hydrogen crossover through unflooded portions of the diaphragm. “Seeing” through foam to establish a valid brine level has traditionally required guesswork. With the development of the hydrogen and brine monitors, and powering them from the voltage across each individual cell, simultaneous monitoring cell voltage and temperature became straightforward. The feasibility of 2.4 GHz wireless was demonstrated for cell room service and a customized intelligence system was developed that stores, processes, and presents the data in a simple actionable format. The solution offered displays simple green/yellow/red color-coded data in order to aid in scheduling cell cut-outs and maintenance. Lessons learnedOne of the core technologies arose during the course of Ph.D. research at Carnegie-Mellon University. As such, a license was required in order to secure freedom to operate. As is common, university research is more an indicator of feasibility than a ready-made solution set to go to market. It is important in licensing to recognize specific applications and a full understanding of plant conditions will dictate additional invention and adaptation. As such, licensing discussions must be clear as to what technologies are components, rather than complete systems, and value them as such. Royalty streams should decline, if not end prior to patent expiry, as academic patents are generally starting points soon superseded. It is important to find a plant location willing to host R&D and tolerate a flexible time line due to the number of iterations likely required. Numerous surprise practicalities will surface. Such a host plant should have a reasonably common cell room technology and be willing to share non-commercial data with other operators. Purposes must also be understood: most monitoring systems are meant to be strictly advisory. Liability issues need to be addressed. Straightforward visualization and reduction of data to actionable conclusions has been our goal. It is important not to overwhelm the client with unneeded data simply because it is possible. Agreeing a set of averaging algorithms and thresholds is critical so as to avoid alarming of the type that might undermine system credibility. Though in certain industries uncertainty remains over the security of wireless control systems, monitoring is often treated differently. Obtaining approval for wireless rather than 4-20 mA has proven key to minimizing disruption and moving forward. Every diaphragm cell plant is unique. Differences in cell technology can require modifications to sensing positions and fixturing. The result is that relationships are central to working sufficiently closely to tie the data obtained to known plant events. An engineer must be assigned to solve problems and help navigate plant culture. For small/unknown entities, it is important to form a win/win relationship with an established distributor who would benefit from new reasons to call on their customers. To this end, SenSevere formed a relationship with Industrie DeNora (Milan, Italy), a long-established supplier to the chlor-alkali industry. It is also important to gain an understanding of how plants purchase and who makes decisions. Is it easier to access an operating budget than a capital budget? Would the plant prefer a service? Is certification necessary prior to advance testing? StatusKey elements of the SenSevere monitoring system are now on test within four North American diaphragm cell chlor-alkali plants. Additional installations are being sought.