Physicochemical mechanisms controlling the periodic release of flammable gases from hanford tanks

Hanford tanks contain more than 60 million gallons of high-level wastes produced by decades of extracting plutonium from irradiated uranium fuel. The wastes were concentrated to a thick slurry consistency by evaporation prior to storage to minimize space. The resulting concentrated waste properties introduced unanticipated, detrimental conditions affecting workers' and the public's health and safety and involving the release of potentially flammable gases. The released gases consist primarily of hydrogen, nitrous oxide, and ammonia. Dilution and sluicing were initially proposed to mitigate the flammable gas safety conditions. As a result of evaluations, the mechanisms and conditions that are thought to control the accumulation and spontaneous release of flammable gases were identified and confirmed. The technical rationale was established for developing operational approaches to mitigate the periodic generation of flammable gases in existing tanks and to avoid any reoccurrence of this serious safety problem during future waste management activities. The chemistry of the two highest risk tanks was examined to test the potential for reversing the conditions causing gas buildup and the consequences of sluicing without appropriate chemical conditioning. The identified mechanisms apply equally to the remaining flammable gas tanks at Hanford as well as to other waste tanks in the DOE complex, particularly those at Savannah River. Passive means of mitigating the flammable gas condition require less than 1:1 dilution, and sluicing wastes from tank 106-C can be accomplished without creating a flammable gas condition. Carbonate equilibria reactions and their effect on aluminum speciation are largely overlooked and provided the key for explaining the episodic release of flammable gases from tank wastes. The reaction of atmospheric carbon dioxide with a sodium hydroxide-rich waste solution produces carbonate precipitates. More importantly, this reaction lowers the pH of the waste and precipitates aluminum hydroxide as a gel. The wastes contain substantial amounts of complexing agents such as ethylene diamine tetraacidicacid (EDTA), hydroxy ethylene diamine triacidic acid (HEDTA), and their degradation products. These complexing agents stabilize the aluminum hydroxide gel together with chromium, manganese and iron hydroxides, and oxybydroxides under the resulting pH conditions. These complex species may coprecipitate and accumulate as a metastable layer in the middle and lower levels of th tank. The complexed aluminum hydroxide acts as a binding agent trapping other particulates in a microcrystalline mat. Microcrystalline particles such as sodium nitrite provide the structural strength for the mat. Once the gas accumulation below the gel layer achieves a critical buoyancy sufficient to rupture the microcrystalline mat, a gas release event occurs. The cycle of gas buildup and release continues each time the buoyancy of the trapped gas exceeds the hydrostatic pressure and the gels' plasticity modulus. Stokes Law predicts a particle settling rate in the tank of less than 50 days, well within the bistorical periodicity of GREs. Laboratory tests, forming the basis of a recent patent application, verify that large quantities of complexed aluminum hydroxide gel are produced by passing carbon dioxide through simulated waste solutions (Hobl, 1993) equivalent to those found in tank 101-SY. It was confirmed that a simple adjustment of pH witll redissolve the gel, thereby reducing viscosity and safely facilitating continuous flammable gas release. Additional experiments were undertaken to provide a basis for understanding the role of complexed aluminum hydroxides in the CO₂/NaOH/Al(OH)₃ (complexing agents)/NaAlO₂ system. This article examines a plausible mechanism for the periodic release of flammable gas and considerations for: (1) remediating existing flammable gas tanks through a combination of chemical treatment and mixer pumps; (2) diluting, combining, retrieving, and storing wastes; (3) preventing clogging of transfer lines; (4) sludge and soil washing; and (5) cribs, ponds, basins, and ground-water cleanup. This study provides a singificant breakthrough for tank waste management by explaining key mechanisms controlling episodic release of flammable gases. The breakthrough provides the bases for removing the tanks classified as flammable gas from the wathclist and has broad operational applications with a potential for billions of dollars in cost savings.     

Goal setting and competition as determinants of task performance

Although research has demonstrated that difficult, specific goals produce higher performance than easy or non-specific goals, little research has examined goal setting in relation to competition. In such circumstances, at least four potential outcomes are logically possible (i.e. complete or partial performance enhancement with competition versus complete or partial performance reduction). Thus, this investigation manipulated goal level and competition in a 3 × 2 factorial design. Participants (N = 109) solved routine arithmetic problems. Results demonstrated that competition had a significant dysfunctional effect on task performance within goal setting conditions.     

An intergrated waste survey and environmental effects of COGIDO, a bleached pulp and paper mill in Vietnam, on the receiving waterbody

An integrated investigation on wastewater characterization and the environmental effects from the COGIDO pulp and paper mill in Bien Hoa Industrial Estate, Vietnam, a chlorine bleached soda integrated pulp and paper mill operating without a chemical recovery system, on the receiving water body was conducted during the rainy and dry seasons in 1993 and 1995. The pollution load from the mill was very high in terms of BOD, COD and SS (COD_m: 58.7 t/d; BOD: 33.3 t/d and SS: 25.1 t/d). The effluent toxicity was determined using four toxicity tests: the green micro-alga, Selenastrum capricornutum, Microtox (marine bacteria: Photobacterium phosphoreum), the duckweed, Lemna aequinoctialis, and fish (silver barb: Puntius gonionotus, and Tilapia: Tilapia nilotica). Selenastrum capricornutum was the most sensitive among the tested organisms. The mill toxicity emission rate (TER) was as high as 338 610 (Selenastrum test). The bleaching-pulp and semi-chemical pulp plants which contributed the largest pollution load to the total COGIDO effluent, therefore, were targeted for abatement measures. Physico-chemical parameters as well as qualitative and quantitative aquatic organism composition for the river water were established. The BOD₅ and COD values exceeded the potable surface water standard by a factor of 2 to 4. The species diversity and abundance of the phytoplankton, zooplankton and zoobenthos were found to be lower (20–40%) than that of unpolluted rivers in Vietnam, whereas pollution-indicator species increased up to four times during the dry season 1995.     

Combating drought through preparedness

Drought is a complex, slow–onset phenomenon that affects more people than any other natural hazard and results in serious economic, social, and environmental impacts. Although drought affects virtually all climatic regimes and has significant consequences in both developed and developing countries, its impacts are especially serious in developing countries where dryland agriculture predominates. The impacts of drought are often an indicator of unsustainable land and water management practices, and drought assistance or relief provided by governments and donors encourages land managers and others to continue these practices. This often results in a greater dependence on government and a decline in self–reliance. Moving from crisis to risk management will require the adoption of a new paradigm for land managers, governments, international and regional development organizations, and non–governmental organizations. This approach emphasizes preparedness, mitigation, and improved early warning systems (EWS) over emergency response and assistance measures. Article 10 of the Convention to Combat Desertification states that national action programmes should be established to identify the factors contributing to desertification and practical measures necessary to combat desertification and mitigate the effects of drought. In the past 10 years, there has been considerable recognition by governments of the need to develop drought preparedness plans and policies to reduce the impacts of drought. Unfortunately, progress in drought preparedness during the last decade has been slow because most nations lack the institutional capacity and human and financial resources necessary to develop comprehensive drought plans and policies. Recent commitments by governments and international organizations and new drought monitoring technologies and planning and mitigation methodologies are cause for optimism. The challenge is the implementation of these new technologies and methodologies. It is critical for governments that possess this experience to share it with others through regional and global networks. One way to accomplish this goal is to create a network of regional networks on drought preparedness to expedite the adoption of drought preparedness tools to lessen the hardships associated with severe and extended drought episodes.     

Fate of atrazine and chlorpyrifos during solid state fermentation—examination of processes

Abstract

Solid state fermentation (SSF) was investigated as a means to dispose of two commonly used pesticides, chlorpyrifos (O, O‐diethyl O‐(3,5,6‐trichloro‐2‐pyridyl) phosphorothioate) and atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine). SSF experiments were carried out in bench‐scale bioreaetors (equipped with CO₂ and volatile organic traps) containing a mixture of lignocellulosic materials and a radiolabeled pesticide. Ethyl acetate‐extractable, alkali soluble, and alkali insoluble fractions were evaluated for radioactivity following a 60‐d incubation period at 40°C. The majority of the [2, 6‐pyridyl‐¹⁴C]chlorpyrifos was associated with the ethyl acetate extract (about 74%), 17% was trapped as organic volatiles by polyurethane foam traps and < 0.5% of the chlorpyrifos was mineralized to CO². Only small amounts of the radioactivity were associated with alkali soluble (0.0003%) and alkali insoluble (0.3%) fractions. In the [¹⁴C‐U‐ring] atrazine bioreactors, very little of the radioactivity volatilized (<0.5%) and less than 0.5% was mineralized to CO₂. Approximately 57% of the applied radioactivity was associated with the ethyl acetate extract while 9% and 24% of the radioactivity was associated with the alkali soluble (humic and fulvic acids) and alkali insoluble fractions, respectively. Possible reaction mechanisms by which covalent bonds could be formed between atrazine (or metabolites) and humic substances were investigated. The issue of bound atrazine residue (alkali soluble fraction) was at least partially resolved. Oxidative coupling experiments revealed that formation of covalent bond linkages between amino substituent groups of atrazine residue and humic substances is highly unlikely.     

Parental investment, adult sex ratios, and sexual selection in a socially monogamous seabird

Although most birds are monogamous, theory predicts that greater female parental investment and female-biased adult sex ratios will lower the polygyny threshold. This should result in polygynous mating, unless obligate biparental care or the spatial and temporal distribution of fertilizable females constrains a male’s ability to take advantage of a lowered polygyny threshold. Here we present data on the extent of male sexually dimorphic plumage, adult sex ratios and breeding season synchrony in three populations of a socially monogamous seabird, the brown booby Sula leucogaster. For one of these populations, San Pedro Mártir Island, we also present data on differences in male and female parental investment, mortality and probability of pairing. The extent of plumage dimorphism varied among populations. Sex ratios were female biased in all populations. On San Pedro Mártir Island, parental investment was female biased, females failed more often than males to find a mate, but there was no polygyny. We suggest that on San Pedro Mártir: (1) a period of obligate biparental care coupled with a relatively synchronous breeding season constrained the ability of males to take advantage of a high environmental polygamy potential and (2) the resulting socially monogamous mating system, in combination with the female-biased adult sex ratio, caused females to be limited by the availability of males despite their greater parental investment. Received: 18 November 1999 / Accepted: 24 January 2000     

Begging behavior and food acquisition by brown-headed cowbird nestlings

Understanding the selective forces that limit the exaggeration of begging signals is a critical issue in understanding the evolution of begging behavior. I studied the begging behavior of nestlings of the brown-headed cowbird (Molothrus ater), a brood parasite. In the nests of indigo buntings (Passerina cyanea), brown-headed cowbird nestlings received approximately twice as much food per hour than their host nestmates. I tested three hypotheses for the mechanism by which cowbirds acquired more food than their bunting nestmates: the size advantage hypothesis, the signal exaggeration hypothesis, and the novel begging behavior hypothesis. I found support for the hypotheses that cowbirds acquire more food as a result of their larger body size, and due to the exaggeration of begging signals that are not dependent on body size. I did not find support for the role of novel begging behaviors in cowbird food acquisition. These results suggest that food acquisition by host chicks in unparasitized nests could be increased by the exaggeration of begging signals. Recent work suggests that such exaggeration may be limited by the risk of nest predation, but further studies are needed. Received: 12 December 1997 / Accepted after revision: 29 December 1997     

Thermally induced filter bias in TEOM mass measurement

Researchers at the National Institute for Occupational Safety and Health (NIOSH) have long used stationary tapered element oscillating microbalances (TEOMs) in laboratory settings. They have served to assess the mass concentration of laboratory-generated particulates in experimental dust chambers and they provide a reference method for comparison with other particulate-measuring instruments. Current NIOSH research is focused on further adapting TEOM technology as a wearable personal dust monitor (PDM) for coal mining occupations. This investigation's goal is to help identify, quantify, and provide means for resolving certain TEOM-related error. The present research investigated bias caused by thermal effects on filter assemblies. New filters used in the PDM for 8 h tests show an average positive bias of 25.5 microg, while similar tests of equivalent filters used in two 1400A model TEOMs show an average positive bias of 34.3 microg. The derived bias values allow correction of previously collected biased data. Also, pre-heating the filters for 24 h at 46 degrees C shows significant bias reduction, with PDM pre-heated filters subsequently averaging -3.3 microg and 1400A TEOM filters averaging 5.9 microg. On a single-point comparison to gravimetric sampling, a 25.5 microg bias is only significant at low mass loadings. At 2.5 mg, this bias represents a negligible 1% of the mass measurement. If ordinary linear regression is used, the bias is still insignificant. However, if the more valid weighted linear regression is used, it gives more weight to the smaller dependent variable values, which are more impacted by the bias. Consequently, what is 1% bias on a single high-mass value can translate into a larger bias percentage at high-mass values when performing a weighted regression on data that include a large number of low-mass values.     

Emissions and distribution of methyl bromide in field beds applied at two rates and covered with two types of plastic mulches

A field experiment was conducted to compare two plastic mulches and two application rates on surface emissions and subsurface distribution of methyl bromide (MBr) in field beds in Florida. Within 30 minutes after injection of MBr to 30 cm depth, MBr had diffused upward to soil surface in all beds covered with polyethylene film (PE) or virtually impermeable film (VIF) and applied at a high rate (392 kg/ha) and a low rate (196 kg/ha). Due to the highly permeable nature of PE, within 30 minutes after injection, MBr volatilized from the bed surfaces of the two PE-covered beds into the atmosphere. The amount of volatilization was greater for the high rate-treatment bed. On the other hand, volatilization of MBr from the bed surfaces of the two VIF-covered beds were negligible. Volatilization losses occurred from the edges of all the beds covered with PE or VIF and were greater from the high rate-treatment beds. Initial vertical diffusion of MBr in the subsurface of the beds covered with PE or VIF was mainly upward, as large concentrations of MBr were detected from near bed surfaces to 20 cm depth in these beds 30 minutes after injection and little or no MBr was found at 40 cm depth. The two VIF-covered beds exhibited greater MBr concentrations and longer resident times in the root zone (0.5-40 cm depth) than corresponding PE-covered beds. Concentrations of MBr in the root zone of the high rate-treatment beds were 3.6-6.1 times larger than the low rate-treatment beds during the first days after application. In conclusion, VIF promoted retention of MBr in the root zone and, if volatilization loss from bed edges can be blocked, volatilization loss from VIF-covered beds should be negligible.