Soil attenuation of As(III,V) and Se(IV,VI) seepage potential at ash disposal facilities

Leachate from ash landfills is frequently enriched with As and Se but their off-site movement is not well understood. The attenuation potential of As and Se by soils surrounding selected landfills during leachate seepage was investigated in laboratory column studies using simulated ash leachate. As(III, V) and Se(IV, VI) concentrations as well as pH, flow rate, and a tracer were monitored in influent and effluent for up to 800 pore volumes followed by sequential desorption, extraction, and digestion of column segments. Column breakthrough curves (BTCs) were compared to predictions based on previously measured sorption isotherms. Early As(V) breakthrough and retarded As(III) breakthrough relative to predicted BTCs are indicative of oxidative transformation during seepage. For Se(VI), which exhibits linear sorption and the lowest sorption propensity, measured BTCs were predicted fairly well by equilibrium sorption isotherms, except for the early arrival of Se(IV) in one site soil, which in part, may be due to higher column pH values compared to batch isotherms. Most of the As and Se retained by soils during leaching was found to be strongly sorbed (60–90%) or irreversibly bound (10–40%) with <5% readily desorbable. Redox potential favoring transformation to the more sorptive valence states of As(V) and Se(IV) will invoke additional attenuation beyond equilibrium sorption-based predictions. With the exception of Se(IV) on one site soil, results indicate that attenuation by down-gradient soils of As and Se in ash landfill seepage will often be no less than what is predicted by equilibrium sorption capacity with further attenuation expected due to favorable redox transformation processes, thus mitigating contaminant plumes and associated risks.     

Sulfur recirculation for increased electricity production in Waste-to-Energy plants

Sulfur recirculation is a new technology for reducing boiler corrosion and dioxin formation. It was demonstrated in full-scale tests at a Waste to Energy plant in Göteborg (Sweden) during nearly two months of operation. Sulfur was recirculated as sulfuric acid from the flue gas cleaning back to the boiler, thus creating a sulfur loop.The new technology was evaluated by extensive measurement campaigns during operation under normal conditions (reference case) and operation with sulfur recirculation. The chlorine content of both fly ash and boiler ash decreased and the sulfur content increased during the sulfur recirculation tests. The deposit growth and the particle concentration decreased with sulfur recirculation and the dioxin concentration (I-TEQ) of the flue gas was reduced by approximately 25%. Sulfuric acid dew point measurements showed that the sulfuric acid dosage did not lead to elevated SO₃ concentrations, which may otherwise induce low temperature corrosion.In the sulfur recirculation corrosion probe exposures, the corrosion rate decreased for all tested materials (16Mo3, Sanicro 28 and Inconel 625) and material temperatures (450 °C and 525 °C) compared to the reference exposure. The corrosion rates were reduced by 60–90%. Sulfur recirculation prevented the formation of transition metal chlorides at the metal/oxide interface, formation of chromate and reduced the presence of zinc in the corrosion products. Furthermore, measured corrosion rates at 525 °C with sulfur recirculation in operation were similar or lower compared to those measured at 450 °C material temperature in reference conditions, which corresponds to normal operation at normal steam temperatures. This implies that sulfur recirculation allows for higher steam data and electricity production without increasing corrosion.     

Note: steps taken to optimise probe specificity and signal intensity prior to field validation of the MIDTAL (Microarray for the Detection of Toxic Algae)

A microarray for the detection of toxic algal species was developed in the European Union 7th Framework project MIDTAL. We initially tested all available fluorescence in situ hybridisation probes for toxic algae, which are normally designed to a length of 18 nt, and found that in most cases the signal was rather weak or all probes designed from the second half of the molecule were inaccessible in a microarray format because of secondary structure of the ribosomal RNA molecule We modified the length of the probes, the fragmentation of the rRNA, the stringency of the washing buffers and the length of the spacer molecules linking the probes to the glass surface of the microarray. Because of the secondary structure of the rRNA molecule, regions of the molecule can be difficult to access by the probes. Each of these modifications has improved probe accessibility and probe specificity to reduce false positives.     

Review: advances in electrochemical genosensors-based methods for monitoring blooms of toxic algae

Harmful algal blooms (HABs), which have expanded worldwide in their occurrence and frequency, are a serious menace to aquatic ecosystems and humans. The development of rapid, accurate and cost-effective detection systems for toxic algal monitoring in aquatic environments is urgently required. Although many efforts have been devoted to develop reliable tools to monitor the entire spectrum of existing toxic algae, a portable semi-automated system that enables HAB monitoring at a low cost is still not available for general purchase. This work reviews the challenges and opportunities in translating the remarkable progress of electrochemical genosensors-based methods towards practical in situ HAB monitoring applications. It is specifically focused on reviewing the optimised methods for a detection system based on a sandwich hybridisation assay (SHA) performed over transducer platforms of different materials, geometries and dimensions and presenting the diverse advantages and disadvantages among them. Probe design and specificity and optimisation of the genosensor in terms of hybridisation conditions and electrochemical signal are discussed as well as their long-term stability and storage and semi-automation attempts. With continuous innovation and attention to key challenges, we expect semi-automatic devices containing DNA-based electrochemical biosensors to have an important impact upon monitoring of serious HAB events.     

Is Levoglucosan a Suitable Quantitative Tracer for Wood Burning? Comparison with Receptor Modeling on Trace Elements in Lycksele,Sweden

Abstract

Particle emissions from residential wood combustion in small communities in Northern Sweden can sometimes increase the ambient particle concentrations to levels comparable to densely trafficked streets in the center of large cities. The reason for this is the combination of increased need for domestic heating during periods of low temperatures, leading to higher emission rates, and stable meteorological conditions. In this work, the authors compare two different approaches to quantify the wood combustion contribution to fine particles in Northern Sweden: a multivariate source-receptor analysis on inorganic compounds followed by multiple linear regression (MLR) of fine particle concentrations and levoglucosan used as a tracer. From the receptor model, it can be seen that residential wood combustion corresponds with 70% of modeled particle mass. Smaller contributions are also seen from local nonexhaust traffic particles, road dust, and brake wear (each contributing 14%). Of the mass, 1.5% is explained by long-distance transported particles, and 2% derives from a regional source deriving from either oil combustion or smelter activities.

In samples collected in ambient air, a significant linear correlation was found between wood burning particles and levoglucosan. The levoglucosan fraction in the ambient fine particulate matter attributed to wood burning according to the multivariate analysis ranged from <2% to 50%. This is much higher than the fraction found in the emission from the boilers expected to be responsible for most emissions at this site (between 3% and 6%). A laboratory emission study of wood and pellet boilers gave 0.3%_wt to 22%_wt levoglucosan to particle mass, indicating that the levoglucosan fraction may be highly dependent on combustion conditions, making it uncertain to use it as a quantitative tracer under real-world burning conditions. Thus, quantitative estimates of wood burning contributions will be very uncertain using solely levoglucosan as a tracer.     

Air pollution and climate gradients in western Oregon and Washington indicated by epiphytic macrolichens

Human activity is changing air quality and climate in the US Pacific Northwest. In a first application of non-metric multidimensional scaling to a large-scale, framework dataset, we modeled lichen community response to air quality and climate gradients at 1416 forested 0.4 ha plots. Model development balanced polluted plots across elevation, forest type and precipitation ranges to isolate pollution response. Air and climate scores were fitted for remaining plots, classed by lichen bioeffects, and mapped. Projected 2040 temperatures would create climate zones with no current analogue. Worst air scores occurred in urban-industrial and agricultural valleys and represented 24% of the landscape. They were correlated with: absence of sensitive lichens, enhancement of nitrophilous lichens, mean wet deposition of ammonium >0.06 mg l(-1), lichen nitrogen and sulfur concentrations >0.6% and 0.07%, and SO(2) levels harmful to sensitive lichens. The model can detect changes in air quality and climate by scoring re-measurements.     

The ecological condition of Gulf of Mexico resources from Perdido Key to Port St. Joe, Florida: Part II near-shelf coastal resources

In 1999, the United States Environmental Protection Agency Gulf Ecology Division initiated a pilot study to assess the condition of nearshore coastal resources. Near-shelf areas associated with coastal beaches are susceptible to land based activities, but are not consistently monitored. Additionally, few or no marine water quality criteria exist for evaluating these waters. The goal of this pilot study was to assess the ecological condition of Gulf of Mexico near-shelf resources using a probability-based survey design. Data are used to generate a baseline assessment of condition in coastal nearshore areas and provide a comparative tool for evaluating future trends in condition. Water quality, sediment quality and benthic diversity data can provide a baseline assessment for managers to evaluate the potential for future problems such as nutrient over-enrichment, sediment contamination and degraded biological condition. We present results from a probability-based survey demonstration assessing near-shelf resources along the Florida panhandle.     

Mini Review: Probes for Detecting Prymnesium parvum and Preliminary Results From Gene Expression Studies1

Medlin, Linda K., Sonja Diercks, and Sara Beszteri, 2010. Mini Review: Probes for Detecting Prymnesium parvum and Preliminary Results From Gene Expression Studies. Journal of the American Water Resources Association (JAWRA) 46(1):144-152. DOI: 10.1111/j.1752-1688.2009.00398.x Abstract: Prymnesium parvum is common in brackish and marine coastal waters within temperate zones, world-wide. P. parvum forms recurrent blooms causing fish kills in many parts of the world. Harmful blooms are formed in nutrient rich, low salinity lakes, ponds, river systems, or estuaries. Probes made to this species and to the genus Prymnesium have been tested in dot blot and fluorescent in situ hybridization (FISH) and used with a solid-phase cytometer using a tyramide signal amplification (TSA) enhanced FISH hybridization to provide a means to identify the cells before blooms develop with automated counting. Field counts from light microscopy have been compared with solid-phase cytometer counts. Additional detection systems, such as biosensors and microarrays, have also been developed to identify rapidly this species without resorting to electron microscopy. Advantages and disadvantages of each detection system are discussed. A study of the genes expressed by P. parvum under environmental conditions that can induce blooms or stress was undertaken to try to understand the ecology behind toxic blooms.     

Effect of land cover data on nitrous oxide inventory in fen meadows

Landscape representations based on land cover databases differ significantly from the real landscape. Using a land cover database with high uncertainty as input for emission inventory analyses can cause propagation of systematic and random errors. The objective of this study was to analyze how different land cover representations introduce systematic errors into the results of regional N2O emission inventories. Surface areas of grassland, ditches, and ditch banks were estimated for two polders in the Dutch fen meadow landscape using five land cover representations: four commonly used databases and a detailed field map, which most closely resembles the real landscape. These estimated surface areas were scaled up to the Dutch western fen meadow landscape. Based on the estimated surface areas agricultural N2O emissions were estimated using different inventory techniques. All four common databases overestimated the grassland area when compared to the field map. This caused a considerable overestimation of agricultural N2O emissions, ranging from 9% for more detailed databases to 11% for the coarsest database. The effect of poor land cover representation was larger for an inventory method based on a process model than for inventory methods based on simple emission factors. Although the effect of errors in land cover representations may be small compared to the effect of uncertainties in emission factors, these effects are systematic (i.e., cause bias) and do not cancel out by spatial upscaling. Moreover, bias in land cover representations can be quantified or reduced by careful selection of the land cover database.