Preparation of Calcium Silicate Reagent from Fly Ash and Lime in a Flow Reactor

Abstract

The batch reaction between fly ash and hydrated lime in water to produce high surface area calcium silicates for flue gas desulfurization has been examined extensively. This paper examines the reaction in a flow reactor using two low-calcium fly ashes and introducing gypsum, calcium sulf ite hemihydrate, and calcium chloride as additives to the reaction. The flow system is compared to the batch reaction at similar operating conditions and a segregated flow model is used to approximate flow reactor behavior.

Experiments with calcium chloride and gypsum additives were modeled fairly well by the segregated flow approximation at residence times less than 12 hours. The flow reactor produced low surface area material at longer residence times when gypsum was present. Because the changing solution chemistry affected the batch reaction rate the fly ash and hydrated lime system without gypsum or calcium chloride could not be approximated using batch reaction data. In this case, the flow reactor produced higher surface area product than the batch reactor for a given residence time due to the increased calcium hydroxide availability.     

Methane emissions from 20 landfills across the United States using vertical radial plume mapping

Landfill fugitive methane emissions were quantified as a function of climate type and cover type at 20 landfills using U.S. Environmental Protection Agency (EPA) Other Test Method (OTM)-10 vertical radial plume mapping (VRPM) with tunable diode lasers (TDLs). The VRPM data were initially collected as g CH₄/sec emission rates and subsequently converted to g CH₄/m²/day rates using two recently published approaches. The first was based upon field tracer releases of methane or acetylene and multiple linear regression analysis (MLRM). The second was a virtual computer model that was based upon the Industrial Source Complex (ISC3) and Pasquill plume stability class models (PSCMs). Calculated emission results in g CH₄/m²/day for each measured VRPM with the two approaches agreed well (r ² = 0.93). The VRPM data were obtained from the working face, temporary soil, intermediate soil, and final soil or synthetic covers. The data show that methane emissions to the atmosphere are a function of climate and cover type. Humid subtropical climates exhibited the highest emissions for all cover types at 207, 127, 102, and 32 g CH₄/m²/day, for working face (no cover), temporary, intermediate, and final cover, respectively. Humid continental warm summers showed 67, 51, and 27 g CH₄/m²/day for temporary, intermediate, and final covers. Humid continental cool summers were 135, 40, and 26 g CH₄/m²/day for the working face, intermediate, and final covers. Mediterranean climates were examined for intermediate and final covers only and found to be 11 and 6 g CH₄/m²/day, respectively, whereas semiarid climates showed 85, 11, 3.7, and 2.7 g CH₄/m²/day for working face, temporary, intermediate, and final covers. A closed, synthetically capped landfill covered with soil and vegetation with a gas collection system in a humid continental warm summer climate gave mostly background methane readings and average emission rates of only 0.09 g CH₄/m²/day flux when measurable.

Implications The OTM-10 method is being proposed by EPA to quantify surface methane emissions from landfill covers. This study of 20 landfills across the United States was done to determine the efficacy of using OTM-10 for this purpose. Two recently published models were used to evaluate the methane flux results found with VRPM optical remote sensing. The results should provide a sense of the practicality of the method, its limitations at landfills, and the impact of climate upon the cover's methane flux. Measured field data may assist landfill owners in refining previously modeled methane emission factor default values.     

Comparative embryotoxicity of a pentabrominated diphenyl ether mixture to common terns (Sterna hirundo) and American kestrels (Falco sparverius)

Concentrations of polybrominated diphenyl ethers (PBDEs) in Forster’s tern (Sterna forsteri) eggs from San Francisco Bay have been reported to range up to 63 μg g⁻¹ lipid weight. This value exceeds the lowest-observed-adverse-effect level (1.8 μg g⁻¹ egg wet weight; ∼32 μg⁻¹ lipid weight) reported in an embryotoxicity study with American kestrels (Falco sparverius). As a surrogate for Forster’s terns, common tern (Sterna hirundo) eggs were treated by air cell injection with corn oil vehicle (control) or a commercial penta-BDE formulation (DE-71) at nominal concentrations of 0.2, 2, and 20 μg g⁻¹ egg. As a positive control, kestrel eggs received vehicle or 20 μg DE-71 g⁻¹ egg. In terns, there were no effects of DE-71 on embryonic survival, and pipping or hatching success; however, treated eggs hatched later (0.44 d) than controls. Organ weights, organ-to-body weight ratios, and bone lengths did not differ, and histopathological observations were unremarkable. Several measures of hepatic oxidative stress in hatchling terns were not affected by DE-71, although there was some evidence of oxidative DNA damage (8-hydroxy-deoxyguanosine; 8-OH-dG). Although DE-71 did not impair pipping and hatching of kestrels, it did result in a delay in hatch, shorter humerus length, and reduced total thyroid weight. Concentrations of oxidized glutathione, reduced glutathione, thiobarbituric acid reactive substances, and 8-OH-dG in liver were greater in DE-71-treated kestrels compared to controls. Our findings suggest common tern embryos, and perhaps other tern species, are less sensitive to PBDEs than kestrel embryos.     

Fate of bulk and trace organics during a simulated aquifer recharge and recovery (ARR)-ozone hybrid process

The attenuation of bulk organic matter and trace organic contaminants (TOrCs) was evaluated for various aquifer recharge and recovery (ARR)-ozone (O₃) hybrid treatment process combinations using soil-batch reactor and bench-scale ozonation experiments as a proof of concept prior to pilot and/or field studies. In water reclamation and especially potable reuse, refractory bulk organic matter and TOrCs are of potential health concern in recycled waters. In this study, the role of biotransformation of bulk organic matter and TOrCs was investigated considering different simulated treatment combinations, including soil passage (ARR) alone, ARR after ozonation (O₃-ARR), and ARR prior to ozonation (ARR-O₃). During oxic (aerobic) ARR simulations, soluble microbial-like substances (e.g., higher molecular weight polysaccharides and proteins) were easily removed while (lower molecular weight) humic substances and aromatic organic matter were not efficiently removed. During ARR-ozone treatment simulations, removals of bulk organic matter and TOrCs were rapid and effective compared to ARR alone. A higher reduction of effluent-derived organic matter, including aromatic organic matter and humic substances, was observed in the ARR-O₃ hybrid followed by the O₃-ARR hybrid. An enhanced attenuation of recalcitrant TOrCs was observed while increasing the ozone dose slightly (O₃: DOC = 1). TOrC removal efficiency also increased during the post-ozone treatment combination (i.e., ARR-O₃). In addition, the carcinogenic wastewater disinfection byproduct N-nitrosodimethylamine (NDMA) was eliminated below the method reporting limit (<5 ng L⁻¹) both during ARR treatment alone and the ARR-ozone hybrid.     

An evaluation of the applicability of microarrays for monitoring toxic algae in Irish coastal waters

The applicability of microarrays to monitor harmful algae across a broad range of ecological niches and toxic species responsible for harmful algal events has been one of the key tasks in the EU Seventh Framework Programme (FP7)-funded Microarrays for the Detection of Toxic Algae project. The technique has a strong potential for improving speed and accuracy of the identification of harmful algae and their toxins to assist monitoring programmes. Water samples were collected from a number of coastal sites around Ireland, including several that are used in the Irish National Phytoplankton and Biotoxin Monitoring Programme. Ribosomal RNA was extracted from filtered field samples, labelled with a fluorescent dye, and hybridised to probes spotted in a microarray format on a glass slide. The fluorescent signal intensity of the hybridisation to >120 probes on the chip was analysed and compared with actual field counts. There was a general agreement between cell counts and microarray signal. Results are presented for field samples taken from a range of stations along the Irish coastline known for harmful algal events during the first field trial (July 2009–April 2010).     

Cadmium adsorption by willow root: the role of cell walls and their subfractions

Plant cell walls may play an important role in the uptake and accumulation of heavy metals. This study was undertaken to obtain a better understanding of the role of the root cell walls (RCW) and their subfractions on adsorption of cadmium (Cd) in a promising woody phytoremediation species, Salix jiangsuensis J172. In order to examine how Cd binding was affected by pectin and hemicellulose, RCW were isolated and sequentially fractioned by removing pectin (RCW1), partial removal of hemicellulose (RCW2), and complete removal of hemicellulose (RCW3). The RCW and fractions were characterized by Fourier transform infrared spectroscopy, which suggested decomposition of hemicellulose and a decline in nitrogen content following cell wall isolation and fractionation. The adsorption affinity of Cd increased gradually following the sequential extraction of root cells, suggesting that hemicellulose negatively impacted Cd adsorption, while pectin and cellulose enhanced Cd adsorption. Cd adsorption dynamics and isotherms could be best described by the pseudo-second-order (R?>?0.99) and Freundlich (R?>?0.97) models, respectively. Thermodynamic properties (?G, ?H, and ?S), determined using the van’t Hoff equation, indicated that while Cd adsorption was endothermic, and spontaneous for RCW2 and RCW3, adsorption was not spontaneous for the root, RCW, and RCW1. The results provide evidence for the importance of the root cell walls in the adsorption of Cd by willow roots.     

Identification of fungal proteases potentially suitable for environmentally friendly cleaning-in-place in the dairy industry

Fourteen fungi were screened for ability to produce proteases with activity on milk protein. The proteases produced were assessed on a lab-scale in terms of their potential suitability for cleaning-in-place (CIP) in the dairy industry. Cleaning performance was assessed by determining the ability of the enzymes to remove an industrial-like milk fouling deposit from stainless steel. Based on the results observed, the extracellular protease activity produced by Schizophyllum commune was selected as most suitable for potential CIP application. A CIP procedure involving a sodium carbonate rinse followed by enzymatic cleaning with this fungal enzyme activity was developed. Satisfactory cleaning, judged by quantification of residual organic matter and protein on the stainless steel surface after cleaning, was achieved using the developed CIP procedure at 40 °C. This CIP procedure, based on biodegradable enzymes working at low temperature is more environmentally favourable than conventional CIP methods using caustic based cleaning solutions at 70-80 °C. Potential environmental benefits of the developed enzymatic CIP procedure include reduced energy consumption, decreased chemical usage and a reduced requirement for pH neutralisation of the resultant waste prior to release.     

EMAP Design and River Reach File 3 (RF3) as a Sample Frame in the Central Valley, California

The Central Valley, California, R-EMAP project assessed the effects of highly modified, agriculturally dominated landuse on the aquatic resources of the lower portion of the Central Valley watersheds. The focus of this paper is to assess the utility of the EMAP design and the River Reach File version 3 (RF3) 1:100,000 scale Digital Line Graph (DLG) as a sampling frame. The study area is 34,099 mi²(88,316 km²) and comprises the lower reaches of the Sacramento River and San Joaquin River watersheds to the 1000 ft. (305 m) elevation. Sampling sites are selected using a tessellation stratified design to represent the two main populations of interest: natural streams and man-made waterways. Sites are selected to represent 13,226 miles of streams and sloughs, and 14,648 miles of irrigation canals, ditches and drains. To achieve an approximately equal sample size across stream orders and basins, the sample design was weighted by Strahler order categories to ensure sampling occurred in the higher order streams. Based on office and field reconnaissance, the study provided information on the quality of RF3 as a sampling frame. Site selection using RF3 had a success rate of approximately 44%. The RF3 database has an error rate of approximately 7%. When human influence factors were included, the error rate increased to 16%. There was an 11% error rate when selecting sites for natural streams, and approximately a 14% error rate for man-made waterways. The reconnaissance information indicated that presence or absence of irrigation ditches and return drains depends on changing agricultural uses. Some of the error in the RF3 for natural streams and man-made waterways can be attributed to rapid urban expansion, especially in the San Joaquin basin.     

Constructing “not Implausible” Climate and Economic Scenarios for Egypt

A space of “not-implausible” scenarios for Egypt's future under climate change is defined along two dimensions. One depicts representative climate change and climate variability scenarios that span the realm of possibility. Some would not be very threatening. Others portend dramatic reductions in average flows into Lake Nassar and associated increases in the likelihood of year to year shortfalls below critical coping thresholds; these would be extremely troublesome, especially if they were cast in the context of increased political instability across the entire Nile Basin. Still others depict futures along which relatively routine and relatively inexpensive adaptation might be anticipated. The ability to adapt to change and to cope with more severe extremes would, however, be linked inexorably to the second set of social–political–economic scenarios. The second dimension, defined as “anthropogenic” social/economic/political scenarios describe the holistic environment within which the determinants of adaptive capacity for water management, agriculture, and coastal zone management must be assessed. This revised version was published online in July 2006 with corrections to the Cover Date.