Metal Contaminants in Leachate from Sanitary Landfills

The uncontrolled disposal of solid wastes poses an immediate threat to public health and a long term threat to the environmental well being of future generations. Solid waste is waste resulting from human activities that is solid and unwanted (Peavy et al., 1985). If unmanaged, dumped solid wastes generate liquid and gaseous emissions that are detrimental to the environment. This can lead to a serious form of contamination known as metal contamination, which poses a risk to human health and ecosystems. For example, some heavy metals (cadmium, chromium compounds, and nickel tetracarbonyl) are known to be highly toxic, and are aggressive at elevated concentrations. Iron, copper, and manganese can cause staining, and aluminium causes depositions and discolorations. In addition, calcium and magnesium cause hardness in water causing scale deposition and scum formation. Though not a metal but a metalloid, arsenic is poisonous at relatively high concentrations and when diluted at low concentrations causes skin cancer. Normally, metal contaminants are found in a dissolved form in the liquid percolating through landfills. Because average metal concentrations from full-scale landfills, test cells, and laboratory studies have tended to be generally low, metal contamination originating from landfills is not generally considered a major concern (Kjeldsen et al., 2002; Christensen et al., 1999). However, a number of factors make it necessary to take a closer look at metal contaminants from landfills. One of these factors relates to variability. Landfill leachate can have different qualities depending on the weather and operating conditions. Therefore, at one moment in time, metal contaminant concentrations may be quite low, but at a later time these concentrations could be quite high. Also, these conditions relate to the amount of leachate that is being generated. Another factor is biodiversity. It cannot be assumed that a particular metal contaminant is harmless to flora and fauna (including micro organisms) just because it is harmless to human health. This has significant implications for ecosystems and the environment. Finally, there is the moral factor. Because uncertainty surrounds the potential effects of metal contamination, it is appropriate to take precautions to prevent it from taking place. Consequently, it is necessary to have good scientific knowledge (empirically supported) to adequately understand the extent of the problem and improve the way waste is being disposed of

The synthesis and application of novel profluorescent nitroxides as probes for polymer degradation

This PhD project has expanded the knowledge in the area of profluorescent nitroxides with regard to the synthesis and characterisations of novel profluorescent nitroxide probes as well as physical characterisation of the probe molecules in various polymer/physical environments. The synthesis of the first example of an azaphenalene-based fused aromatic nitroxide TMAO, [1,1,3,3-tetramethyl-2,3-dihydro-2-azaphenalen-2-yloxyl, was described. This novel nitroxide possesses some of the structural rigidity of the isoindoline class of nitroxides, as well as some properties akin to TEMPO nitroxides. Additionally, the integral aromatic ring imparts fluorescence that is switched on by radical scavenging reactions of the nitroxide, which makes it a sensitive probe for polymer degradation. In addition to the parent TMAO, 5 other azaphenalene derivatives were successfully synthesised. This new class of nitroxide was expected to have interesting redox properties when the structure was investigated by high-level ab initio molecular orbitals theory. This was expected to have implications with biological relevance as the calculated redox potentials for the azaphenalene ring class would make them potent antioxidant compounds. The redox potentials of 25 cyclic nitroxides from four different structural classes (pyrroline, piperidine, isoindoline and azaphenalene) were determined by cyclic voltammetry in acetonitrile. It was shown that potentials related to the one electron processes of the nitroxide were influenced by the type of ring system, ring substituents or groups surrounding the moiety. Favourable comparisons were found between theoretical and experimental potentials for pyrroline, piperidine and isoindoline ring classes. Substitution of these ring classes, were correctly calculated to have a small yet predictable effect on the potentials. The redox potentials of the azaphenalene ring class were underestimated by the calculations in all cases by at least a factor of two. This is believed to be due to another process influencing the redox potentials of the azaphenalene ring class which is not taken into account by the theoretical model. It was also possible to demonstrate the use of both azaphenalene and isoindoline nitroxides as additives for monitoring radical mediated damage that occurs in polypropylene as well as in more commercially relevant polyester resins. Polymer sample doped with nitroxide were exposed to both thermo-and photo-oxidative conditions with all nitroxides showing a protective effect. It was found that isoindoline nitroxides were able to indicate radical formation in polypropylene aged at elevated temperatures via fluorescence build-up. The azaphenalene nitroxide TMAO showed no such build-up of fluorescence. This was believed to be due to the more labile bond between the nitroxide and macromolecule and the protection may occur through a classical Denisov cycle, as is expected for commercially available HAS units. Finally, A new profluorescent dinitroxide, BTMIOA (9,10-bis(1,1,3,3- tetramethylisoindolin-2-yloxyl-5-yl)anthracene), was synthesised and shown to be a powerful probe for detecting changes during the initial stages of thermo-oxidative degradation of polypropylene. This probe, which contains a 9,10-diphenylanthracene core linked to two nitroxides, possesses strongly suppressed fluorescence due to quenching by the two nitroxide groups. This molecule also showed the greatest protective effect on thermo-oxidativly aged polypropylene. Most importantly, BTMIOA was found to be a valuable tool for imaging and mapping free-radical generation in polypropylene using fluorescence microscopy.

Evaluation of polycaprolactone scaffold degradation for 6 months in vitro and in vivo

The use of polycaprolactone (PCL) as a biomaterial, especially in the fields of drug delivery and tissue engineering, has enjoyed significant growth. Understanding how such a device or scaffold eventually degrades in vivo is paramount as the defect site regenerates and remodels. Degradation studies of three-dimensional PCL and PCL-based composite scaffolds were conducted in vitro (in phosphate buffered saline) and in vivo (rabbit model). Results up to 6 months are reported. All samples recorded virtually no molecular weight changes after 6 months, with a maximum mass loss of only about 7% from the PCL-composite scaffolds degraded in vivo, and a minimum of 1% from PCL scaffolds. Overall, crystallinity increased slightly because of the effects of polymer recrystallization. This was also a contributory factor for the observed stiffness increment in some of the samples, while only the PCL-composite scaffold registered a decrease. Histological examination of the in vivo samples revealed good biocompatibility, with no adverse host tissue reactions up to 6 months. Preliminary results of medical-grade PCL scaffolds, which were implanted for 2 years in a critical-sized rabbit calvarial defect site, are also reported here and support our scaffold design goal for gradual and late molecular weight decreases combined with excellent long-term biocompatibility and bone regeneration. (C) 2008 Wiley Periodicals, Inc. J Biomed Mater Res 90A: 906-919, 2009

Report : colorbond degradation model

This report documents work carried out in order to develop and prove a model for predicting the lifetime of painted metal components, with a particular emphasis on Colorbond® due to its prominent use throughout Australia. This work continues on from previous developments reported in 2002-059-B No. 12 [1]. Extensions of work included the following research: (1) Experimental proving of the leaching of chromate inhibitors from Colorbond® materials. (2) Updated models for the accumulation of salts and the time of wetness for gutters, based upon field observations. (3) Electrochemical Impedance Spectroscopy investigations aimed at correlating the corrosion rates of weathered Colorbond® with those predicted by modeling.

A review on degradation models in reliability analysis

With increasingly complex engineering assets and tight economic requirements, asset reliability becomes more crucial in Engineering Asset Management (EAM). Improving the reliability of systems has always been a major aim of EAM. Reliability assessment using degradation data has become a significant approach to evaluate the reliability and safety of critical systems. Degradation data often provide more information than failure time data for assessing reliability and predicting the remnant life of systems. In general, degradation is the reduction in performance, reliability, and life span of assets. Many failure mechanisms can be traced to an underlying degradation process. Degradation phenomenon is a kind of stochastic process; therefore, it could be modelled in several approaches. Degradation modelling techniques have generated a great amount of research in reliability field. While degradation models play a significant role in reliability analysis, there are few review papers on that. This paper presents a review of the existing literature on commonly used degradation models in reliability analysis. The current research and developments in degradation models are reviewed and summarised in this paper. This study synthesises these models and classifies them in certain groups. Additionally, it attempts to identify the merits, limitations, and applications of each model. It provides potential applications of these degradation models in asset health and reliability prediction.

Retention and degradation of organics in Rundle waste shale/retort water mixtures

Batch, column and field lysimeter studies have been conducted to evaluate the concept of codisposal of retort water with Rundle (Queensland, Australia) waste shales. The batch studies indicated that degradation of a significant proportion of the total organic load occurs if the mixture is seeded with soil or compost. These results are compared with those from laboratory column studies and from the field lysimeter at the Rundle site. G.c.-m.s. analysis of some of the eluants indicated that significant degradation of the base-neutral fraction occurs even if no soil seed is added, and that degradation of this fraction was higher under anaerobic conditions.