Optical gas imaging (OGI) is an effective tool for detecting gas leaks from process equipment. Despite the fact that OGI has been used for leak detection for over a decade, its detection limit is an elusive performance metric and has not been systematically characterized and quantified like other detection instruments. A substantial body of research has been performed that has shed some light on the OGI detection limits and the factors that dictate the detection limits. The OGI detection limit expressed as ppm-m and ppm now can be quantified as a function of ΔT (differential temperature between the gas plume and the background), the OGI camera type, and the specific gas in question. Furthermore, the OGI detection limit expressed as grams per hour can be calculated based on the ΔT and the distance from the OGI camera to the leak location under common leak survey conditions. For the same OGI camera, the detection limit can vary by several orders of magnitude due to ΔT and distance. The present work has demonstrated how different OGI detection limits can be. More importantly, this work has, for the first time, formulated equations that can be used to determine OGI detection limits with a given set of leak detection conditions. Being able to quantify OGI detection limit and understand the variables that dictate the detection limit is a significant advancement. It will help OGI to become accepted as a mature field instrument. The variables characterized in this work should have an impact on the development of OGI leak survey protocols, such as Appendix K to Code of Federal Regulations 40 CFR Part 60 in the United States. Established detection limits will also help emission inventory for fugitive emissions when OGI is used as the sole leak detection method.
Implications: Optical gas imaging (OGI) has been used for leak detection and control of fugitive volatile organic compound (VOC) emissions and methane emissions due to equipment leaks. However, detection limits of OGI have not been characterized and quantified like other detection instruments. The lack of well-understood detection limits has hindered broader applications of OGI. The work presented in this paper represents important steps that will enable OGI users and policymakers to establish (1) OGI detection limits under various conditions, (2) OGI leak survey criteria for a desired minimum detectable leak size, and (3) maximum potential emissions from the nondetect sources in emission inventory studies. 相似文献
The effect of riboflavin (1 microM) on the fate of TNT (20 mg/l) in a natural water environment was studied. The relative contribution of photolysis, microbial assemblages and freshwater matrix to TNT degradation was examined. The rates, extent and products of TNT and riboflavin transformation were compared under different experimental conditions. It was found that riboflavin significantly enhanced the degradation of TNT in natural water environment. Thus it is a potentially useful photosensitizing agent for the treatment of TNT-contaminated surface water. Furthermore, in the presence of riboflavin, two new intermediates with max. absorption wavelength of 230 nm were found, demonstrating that transformation of TNT in the presence of riboflavin undergoes different pathways. 相似文献
Polycyclic aromatic hydrocarbons (PAHs) are a group of toxic, persistent, bioaccumulating organic compounds containing two or more fused aromatic rings. They are listed by the U.S. Environmental Protection Agency as priority pollutants because of their carcinogenicity and toxicity. Employing ozonation as a remediation technique, this work investigated the treatability of a sediment sample from a freshwater boat slip subjected to coal tar contamination over a long period. The contaminated sediment sample contained high levels of PAHs in the forms of naphthalene, phenanthrene, pyrene, and benzo[a]pyrene, among other byproducts present in the humic and solid phases of the sediment. The objectives of this work were to examine (1) the degradation of PAHs in the contaminated sediment as treated by ozonation in the slurry form, (2) the effects of ozonation upon the soil matrix and the biodegradability of the resultant PAH intermediates, and (3) the feasibility of a combined technique using O3 as a pretreatment followed by biological degradation. The sediment was made into 3% w/w soil slurries and ozonated in a 1.7-L semi-batch, well-stirred reactor equipped with pH control and a cold trap for the gaseous effluent. Samples were collected after different ozonation durations and tested for biochemical oxygen demand (BOD), chemical oxygen demand (COD), UV absorbance, and toxicity, along with quantitative and qualitative determinations of the parent and daughter intermediates using gas chromatography/flame ionization detection (GC/FID), GC/mass spectrometry (MS), and ion chromatography (IC) techniques. The GC/MS technique identified 16 compounds associated with the humic and solid phases of the sediment. Intermediates identified at different ozonation times suggested that the degradation of PAHs was initiated by an O3 attack resulting in ring cleavage, followed by the intermediates' oxidation reactions with O3 and the concomitant OH radical toward their mineralization. Results suggested that ozonation for 2 hr removed 50-100% of various PAHs in the solid and liquid phases (as well as the aqueous and gaseous media resulting from the treatment process) of the sediment sample and that organic and inorganic constituents of the sediment were also altered by ozonation. Measurements and comparisons of BOD, COD, UV absorbance, and toxicity of the samples further suggested that ozonation improved the bioavailability and biodegradability of the contaminants, despite the increased toxicity of the treatment effluent. An integrated chemical-biological system appeared to be feasible for treating recalcitrant compounds. 相似文献
In enhanced biological phosphorus removal (EBPR) systems, polyphosphate-accumulating organisms (PAOs) are primarily responsible for removing phosphate from wastewater. Propionate is an abundant carbon substrate in many EBPR plants and has been suggested to provide PAOs an advantage over their carbon competitors--the glycogen-accumulating organisms (GAOs). The aerobic metabolism of PAOs enriched with a propionate carbon source is studied in this paper. A metabolic model is proposed and experimentally validated to characterize the aerobic biochemical transformations by PAOs. The model predicts very well the experimental data obtained from the enriched PAO culture through solid-, liquid-, and gas-phase analyses. This model may be combined with previously formulated metabolic models to better describe the biochemical activity of PAOs with acetate and propionate as the primary carbon sources. Furthermore, it can also facilitate the study of the effect of different carbon sources on PAO-GAO competition. 相似文献