Oxygen Stratification in Industrial Boiler Stacks

The DSS/2 software system was used to numerically simulate oxygen stratification effects in a typical industrial boiler stack. The model developed for the simulation involves turbulent mass transfer in a tube with a constant, high mass flux from the walls of the tube. The concentration profile is considered to be developing, but the velocity profile is assumed to be fully developed. The model is for a gaseous system at constant temperature and pressure; the transport properties are shown to be constant. The universal velocity profile for turbulent flow and von Karman’s expressions for the turbulent eddy diffusivity are incorporated in the model. An expression for a wall concentration profile corresponding to conditions of high mass flux at the wall is developed. The model is then expressed as a system of partial differential equations which are solved using the numerical method of lines together with the DSS/2 numerical integration system. The resulting concentration profiles are presented for various flux rates which might be encountered in a typical stack. These profiles indicate that a potential for oxygen stratification in stacks does exist; they also suggest that careful placement of the oxygen cell probe can help minimize such errors.     

A New Audit Technique for EPA Method 25

A simple, inexpensive, and accurate technique for evaluating or auditing the sampling, recovery, and analytical phases of EPA Source Reference Method 25 has been developed. The technique involves spiking a U-shaped stainless steel cartridge containing Tenax® with known quantities of selected organic compounds and thermally desorbing them at temperatures from 160°C to 180°C to generate organic vapors quantitatively. The major advantages of this technique are that no other measurement methods can be used to determine the generated organic concentrations in lieu of Method 25; and that the cartridge can easily be taken to the field for evaluation. The organic compounds generated in test runs are collected and analyzed using the Method 25 procedure. The generation of organics is quantitative and recoveries were found to be 100 ± 10%. The time required for desorption of the majority of organics is generally less than forty-five minutes at a flow rate of 100 mL/min; however, based on laboratory experience the recommended sampling time is sixty minutes. These spiked cartridges are stable at room temperature over a two-month period. Results of interlaboratory studies showed close agreement with the expected concentrations based on calculations from the mass loadings and sample volumes.     

Intermittent agitation of liquid manure: effects on methane,microbial activity,and temperature in a farm-scale study

Liquid manure storages are a significant source of methane (CH₄) emissions. Farmers commonly agitate (stir) liquid manure prior to field application to homogenize nutrients and solids. During agitation, manure undergoes mechanical stress and is exposed to the air, disrupting anaerobic conditions. This on-farm study aimed to better understand the effects of agitation on CH₄ emissions, and explore the potential for intentional agitation (three times) to disrupt the exponential increase of CH₄ emissions in spring and summer. Results showed that agitation substantially increased manure temperature in the study year compared to the previous year, particularly at upper- and mid-depths of the stored manure. The temporal pattern of CH₄ emissions was altered by reduced emissions over the subsequent week, followed by an increase during the second week. Microbial analysis indicated that the activity of archaea and methanogens increased after each agitation event, but there was little change in the populations of methanogens, archaea, and bacteria. Overall, CH₄ emissions were higher than any of the previous three years, likely due to warmer manure temperatures that were higher than the previous years (despite similar air temperatures). Therefore, intermittent manure agitation with the frequency, duration, and intensity used in this study is not recommended as a CH₄ emission mitigation practice.

Implications: The potential to mitigate methane emissions from liquid manure storages by strategically timed agitation was evaluated in a detailed farm-scale study. Agitation was conducted with readily-available farm equipment, and targeted at the early summer to disrupt methanogenic communities when CH₄ emissions increase exponentially. Methane emissions were reduced for about one week after agitation. However, agitation led to increased manure temperature, and was associated with increased activity of methanogens. Overall, agitation was associated with similar or higher methane emissions. Therefore, agitation is not recommended as a mitigation strategy.     

KAPPA-G,A Non-Gaussian Plume Dispersion Model: Description and Evaluation Against Tracer Measurements

This paper presents a mixed methodology for the simulation of atmospheric disperson phenomena in which vertical diffusion is computed using an analytical solution of the K-theory equation, while horizontal diffusion is simulated by the Gaussian formula. This new formulation, while maintaining a simple analytical form for the concentration field, incorporates the effects of power-law vertical profiles of both wind speed and eddy diffusivity. The performance of this approach, which has been implemented into a full computer package (KAPPA-G), is evaluated by comparison with data from SF₆ tracer experiments.     

Assessment of Uncertainty in Long-Term Mass Balances for Acidification Assessments: A MAGIC Model Exercise

Long-term (1860–2010) catchment mass balance calculations rely on models and assumptions which are sources of uncertainty in acidification assessments. In this article, we report on an application of MAGIC to model acidification at the four Swedish IM forested catchments that have been subject to differing degrees of acidification stress. Uncertainties in the modeled mass balances were mainly associated with the deposition scenario and assumptions about sulfate adsorption and soil mass. Estimated base cation (BC) release rates (weathering) varied in a relatively narrow range of 47–62 or 42–47 meq m⁻² year⁻¹, depending on assumptions made about soil cation exchange capacity and base saturation. By varying aluminum solubility or introducing a dynamic weathering feedback that allowed BC release to increase at more acidic pHs, a systematic effect on predicted changes in acid neutralizing capacity (ΔANC ca. 10–41 μeq l⁻¹) and pH (ca. ΔpH = 0.1–0.6) at all sites was observed. More robust projections of future changes in pH and ANC are dependent on reducing uncertainties in BC release rates, the timing, and extent of natural acidification through BC uptake by plants, temporal changes in soil element pools, and fluxes of Al between compartments.     

Speciation and transport of arsenic in an acid sulfate soil-dominated catchment, eastern Australia

Factors controlling the transport of geogenically-derived arsenic from a coastal acid sulfate soil into downstream sediments are identified in this study with both solid-phase associations and aqueous speciation clearly critical to the mobility and toxicity of arsenic. The data from both sequential extractions and X-ray adsorption spectroscopy indicate that arsenic in the unoxidised Holocene acid sulfate soils is essentially non-labile in the absence of prolonged oxidation, existing primarily as arsenopyrite or as an arsenopyrite-like species, likely arsenian pyrite. Anthropogenically-accelerated pedogenic processes, which have oxidised this material over time, have greatly enhanced the potential bioavailability of arsenic, with solid-phase arsenic almost solely present as As(V) associated with secondary Fe(III) minerals present. Analyses of downstream sediments reveal that a portion of the arsenic is retained as a mixed As(III)/As(V) solid-phase, though not at levels considered to be environmentally deleterious. Determination of arsenic speciation in pore waters using high performance liquid chromatography/Inductively Coupled Plasma-Mass Spectrometry shows a dominance of As(III) in upstream pore waters whilst an unidentified As species reaches comparative levels within the downstream, estuarine locations. Pore water As(V) was detected at trace concentrations only. The results demonstrate the importance of landscape processes to arsenic transport and availability within acid sulfate soil environments.     

Nitrous oxide and methane emission from a flooded rice field as influenced by separate and combined application of herbicides bensulfuron methyl and pretilachlor

Combination of divergent active principles to achieve broad-spectrum control is gaining popularity to manage the weed menace in intensive agriculture. However, such application could have non-target impacts on the soil processes affecting soil ecology and environmental interactions. A field experiment was conducted to investigate the impact of separate and combined applications of herbicides bensulfuron methyl and pretilachlor on the emission of N₂O and CH₄, and related soil and microbial parameters in a flooded alluvial field planted to rice cv Lalat. Single application of the herbicide bensulfuron methyl or pretilachlor resulted in a significant reduction of N₂O and CH₄ emissions while the combination of these two herbicides distinctly increased N₂O and CH₄ emissions. Cumulative N₂O emissions (kg N₂O-N) followed the order of bensulfuron methyl (0.35 kg ha⁻¹) < pretilachlor (0.36 kg ha⁻¹) < control (0.45 kg ha⁻¹) < bensulfuron methyl 0.6% + pretilachlor 6.0% single dose (0.49 kg ha⁻¹) < bensulfuron methyl 0.6% + pretilachlor 6.0% double dose (0.54 kg ha⁻¹). Cumulative CH₄ emissions (kg CH₄), on the other hand, followed the order of bensulfuron methyl (47.89 kg ha⁻¹) < pretilachlor (73.17 kg ha⁻¹) < bensulfuron methyl 0.6% + pretilachlor 6.0% single dose (93.50 kg ha⁻¹) < control (106.54 kg ha⁻¹) < bensulfuron methyl 0.6% + pretilachlor 6.0% double dose (124.67 kg ha⁻¹). The inhibitory effect of separate application of herbicides bensulfuron methyl 0.6% and pretilachlor 6.0% on N₂O emission was linked to lower mineral N, lower denitrifying and nitrifying activity and low denitrifier and nitrifier populations. Inhibitory effect on CH₄ emission, on the contrary, was linked to prevention in the drop of redox potential, lower readily mineralizable carbon (RMC) and microbial biomass carbon (MBC) contents as well as lower methanogenic and higher methanotrophic bacterial population. Admittedly, stimulatory effect of combined application of herbicides bensulfuron methyl 0.6% and pretilachlor 6.0% at double dose on N₂O and CH₄ emission was related to reversal of the identified indicators of inhibition. Results indicate that while individual application of herbicides bensulfuron methyl 0.6% or pretilachlor 6.0% can reduce N₂O and CH₄ emission from flooded soil planted to rice, their combined application at normal dose can keep the emission at a comparatively lower level with significantly higher grain yield as compared to the herbicides applied alone.     

Probability of intellectual disability is associated with soil concentrations of arsenic and lead

Background

The association between metals in water and soil and adverse child neurologic outcomes has focused on the singular effect of lead (Pb), mercury (Hg), and arsenic (As). This study describes the complex association between soil concentrations of As combined with Pb and the probability of intellectual disability (ID) in children.

Methods

We used a retrospective cohort design with 3988 mother child pairs who were insured by Medicaid and lived during pregnancy and early childhood in South Carolina between 1/1/97 and 12/31/02. The children were followed until 6/1/08, using computerized service files, to identify the diagnosis of ID in medical records and verified by either school placement or disability service records. The soil was sampled using a uniform grid and analyzed for eight metals. The metal concentrations were interpolated using Bayesian Kriging to estimate concentration at individual residences.

Results

The probability of ID increased for increasing concentrations of As and Pb in the soil. The Odds Ratio for ID, for one unit change in As was 1.130 (95% confidence interval 1.048-1.218) for Pb was 1.002 (95% confidence interval 1.000-1.004). We identified effect modification for the infants based on their birth weight for gestational age status and only infants who were normal size for their gestational age had increased probability of ID based on the As and Pb soil concentrations (OR for As at normal weight for gestational age = 1.151 (95% CI: 1.061-1.249) and OR for Pb at normal for gestational age = 1.002 (95% CI: 1.002-1.004)). For normal weight for gestational age children when As = 22 mg kg⁻¹ and Pb = 200 mg kg⁻¹ the risk for ID was 11% and when As = 22 mg kg⁻¹and Pb = 400 mg kg⁻¹ the probability of ID was 65%.

Conclusion

The probability of ID is significantly associated with the interaction between Pb and As for normal weight for gestational age infants.     

Estrogen receptor mediated activity in bankside groundwater, with flood suspended particulate matter and floodplain soil - an approach combining tracer substance, bioassay and target analysis

Bankside groundwater is widely used as drinking water resource and, therefore, contamination has to be avoided. In the European Union groundwater protection is explicit subject to Water Framework Directive. While groundwater pollution may originate from different sources, this study investigated on impacts via flood events.Groundwater was sampled with increasing distance to the river Rhine near Karlsruhe, Germany. Samples were HPLC-MS-MS analyzed for the river contaminant carbamazepine to indicate river water infiltration, giving permanent presence in 250 m distance to the river (14-47 μg L⁻¹). Following a flood event, concentrations of about 16-20 μg L⁻¹ could also be detected in a distance of 750 m to the river. Furthermore, estrogenic activity as determined with the Yeast Estrogen Screen assay was determined to increase up to a 17β-ethinylestradiol equivalent concentration (E-EQ) = 2.9 ng L⁻¹ near the river, while activity was initially measured following the flood with up to E-EQ = 2.6 ng L⁻¹ in 750 m distance. Detections were delayed with increasing distance to the river indicating river water expansion into the aquifer.Flood suspended matter and floodplain soil were fractionated and analyzed for estrogenic activity in parallel giving up to 1.4 ng g⁻¹ and up to 0.7 ng g⁻¹, respectively. Target analysis focusing on known estrogenic active substances only explained <1% of measured activities.Nevertheless, river water infiltration was shown deep into bankside groundwater, thus, impacting groundwater quality. Therefore, flood events have to be in the focus when aiming for groundwater and drinking water protection as well as for implementation of Water Framework Directive.