No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

The criteria involved in the degradation of polyethylene-based degradable polymer samples have been investigated, with a view to obtaining a clearer mechanism of photo-biodegradation. The compatibility of degradable polymer samples during materials recycling was also studied. Commercial and laboratory prepared degradable polymer samples were oxidised in different environments and the oxidation products formed were studied using various analytical chromatographic and spectroscopic techniques such as HPLC, FT-IR and NMR. It was found that commercial degradable polymer samples which are based on the ECO systems, degrade predominantly via the Norrish II process, whereas the other degradable systems studied (starch-filled polyethylene systems, transition metal systems, including metal carboxylate based polyethylene systems and the photoantioxidant-activator systems) photodegrade essentially via the Norrish I process. In all cases, the major photoxidation products extracted from the degradable polymer samples were found to be carboxylic acids, although, in the polymer itself a mixture of carbonyl containing products such as esters, lactones, ketones and aldehydes was observed. The study also found that the formation of these hydrophilic carbonyl products causes surface swelling of the polymer, thus making bioerosion possible. It was thus concluded that environmental degradation of LDPE is a two step process, the initiation stage being oxidation of the polymer which gives rise to bioassimilable products, which are consequently bioeroded in the second stage, (the biodegradation step). Recycling of the degradable polymer samples as 10% homogeneous and heterogeneous blends was carried out using a single screw extruder (180°C and 210°C) and an internal mixer (190°C). The study showed that commercial degradable polymer samples may be recycled with a minimal loss in their properties.

Concerns regarding climate change are becoming a driver behind legislation at both UK and EU levels, and also on the wider, planetary scale. This is the case with emissions from landfills where the release of methane is being targeted for reduction. This thesis uses an integrative approach, incorporating concepts of hierarchy from systems theory, to model landfill as a complex biophysical technology. It assesses the contribution to carbon deposition and global warming of landfill through changes to that technology itself and through changes in the waste stream caused by potential waste policies. The thesis develops an holistic, conceptual model of the landfill system, mapping flows and transformations of carbon within that system. It further develops this conceptual model into a calculating model of landfill as a waste management technology incorporating measurements taken to provide new data and validate published data to calibrate the model. It thus applies modelling techniques to a biophysical technology, producing an integrated model of the landfill that allows the knowledge gained from other research to be used to explore engineering and operational decisions on landfills. The thesis includes results from measurements of the composition of household waste, and of the biochemical methane potential (BMP) of fractions of that waste. It includes measurements of the residual BMP in samples of excavated waste and measurements of gas flows. The main results suggest the following: • Early capping of landfilled waste is important in reducing the global warming impact; • If the rate of degradation of the waste is accelerated in the drive towards sustainability, capping should be carried out even earlier if the global impact is not to be increased; • Although recycling parts of the degradable elements of the waste stream has the effect of reducing the global impact, extensive recycling has implications for landfill engineering.

Due to the pressure of recent legislative changes (eg: the EU Landfill Directive and the imposition of a Landfill Tax), composting as a waste disposal technique is now being viewed as the preferred alternative to the landfilling of organic waste. However, while composting has been practised in one form or another for 2500 years, the underlying principles behind the microbial ecology of composting, is poorly understood. In order to obtain an insight into the ecology and hence, the critical nature of the composting process, a number of low cost open-windrows containing urban botanical wastes were established. These windrows were subjected to microbial and physico-chemical analysis over the initial period of exothermically active composting (25 days). This study demonstrated that, whilst average temperatures within open windrows can reach in excess of 65 °C, the sustainability and range of these temperatures depended upon the windrow bulk density. Windrows with bulk densities of 600kgm*3 had a larger insulation factor and thus, were able to sustain high temperatures for longer periods. However, these windrows were more susceptible to the development of areas of low temperature (cold spots) at depths below 20cm. Windrows with bulk densities of 400kgm'3 had smaller insulation factors and therefore, lost heat at a faster rate than windrows with higher bulk densities. This loss of heat was observed to be the case with the windrow surface layers, but they exhibited fewer cool spots at lower levels. This study found that the average microbial population of windrow material was 2.29x1013 CFU kg*1 and that each microbial cell could generate between 6.33 and 8.56xl0*13 Mjkg*1. This resulted in the generation of between 1.13 and 1.70 Mjkg*1 °C*1 of heat energy. Contrary to the published literature, this study observed that temperatures above 65 °C did not result in the significant loss of ammonia from the windrow. However, high levels of ammonia did suppress the formation of nitrate within the windrows. Experiments investigating microbial population kinetics within the windrows indicated that observed changes were proportional to temperature up to 60 °C, when a reduction in population numbers was observed between 60 °C and 65 °C. However, between 60 °C and 70 °C population levels increased once again. It was also noted that at the start of the composting process, 13 different microbial species or genera could be identified. However, after 17 days of exothermic composting, this had been reduced to 2 genera, including a novel large bacterial species belonging to the genus Bacillus. This study also showed that samples of windrows exposed to temperatures above 55 °C for 48 hours did not eliminate mesophilic or psycrotrophic microbial populations as previously assumed by other workers, but only suppressed their metabolism during the high temperature period.

No description available.