Pollution, biodegradable materials

Biological processes for pollutant treatment are frequently the method of choice (see Chapter 11). However, the complexity of some wastes (e.g., refractory and/or highly toxic) necessitates other approaches such as the use of hybrid alternatives that offer the possibility for partial electrochemical degradation (e.g., the transformation of non-biodegradable material into biodegradable). This involves large savings in electricity, because—as shown in Example 10.3—in order to completely oxidize... 

Landfill has been defined (ISWA, 1992) as "The engineered deposit of waste onto and into land in such a way that pollution or harm to the environment is prevented and, through restoration, land provided which may be used for another purpose". Unfortunately, there are many examples of environmental pollution that have arisen as a result of landfill activities, and while the above may define a model landfiU, the reality has, all too often, been far from ideal. The hazards associated with different landfills will vary according to the nature of the emplaced waste, the conditions within the landfill, and the nature of the surrounding environment. An understanding of conditions such as these will help to identify potential environmental risks. For example, gas and leachate production will be very different in "old" and "new" landfills. In this context, a "modem" landfill is defined as one which has accepted a high proportion of biodegradable material and which is different to an "old" landfill which has accepted relatively inert material. 

A standard test for the presence of organic pollutants within liquids. It is, in effect, a measure of the content of biodegradable material. 

Other methods of preventing this pollution include the partial use of biodegradable materials in plastic products. Certain auxiliary elements, made of biodegradable material, are then incorporated within the container. However, the remainder of the container is substantially plastic based on petroleum. If these mixed products are included with other plastics for recycling, they can contaminate the product and render it unusable (42). 

Biomaterials have gained attractiveness in the last decades due to both ecological and economic concerns. Increased pollution, and especially visible pollution, has first driven the scientific and industrial communities to look at biofragmentable and biodegradable substitutes for traditional petroleum-based non-biodegradable materials. Then the dramatic increase of oil prices before the economic crisis of 2007 influenced the move from the biodegradable to the bio-based. Finally, the compliance of the obtained materials with thermo-mechanical constraints has turned interest to the partially bio-based materials. 

Incineration and landfill, as additional treatment techniques for residual waste, should be mentioned for completeness. The content of pollutants and harmful substances in residual waste is almost always determined by waste fractions other than biodegradable materials. Therefore, the established rnles for incineration and landfill cover biodegradable polymers in detail additional considerations of the ecotoxicological impact are not needed. 

Biodegradable polymers are likely to be increasingly important materials in the future, finding use in applications as diverse as medicine, agriculture, and pharmacy. For applications such as packaging, they remain expensive. However, with changing public attitudes towards enviromnental pollution, it is likely that objections based purely on cost will dimiiush, and that such applications will also grow in the years ahead. 

Models of chemical reactions of trace pollutants in groundwater must be based on experimental analysis of the kinetics of possible pollutant interactions with earth materials, much the same as smog chamber studies considered atmospheric photochemistry. Fundamental research could determine the surface chemistry of soil components and processes such as adsorption and desorption, pore diffusion, and biodegradation of contaminants. Hydrodynamic pollutant transport models should be upgraded to take into account chemical reactions at surfaces. 

Microbes are ubiquitous in the subsurface environment and as such may play an important role in groundwater solute behavior. Microbes in the subsurface can influence pollutants by solubility enhancement, precipitation, or transformation (biodegradation) of the pollutant species. Microbes in the groundwater can act as colloids or participate in the processes of colloid formation. Bacterial attachment to granular media can be reversible or irreversible and it has been suggested that extracellular enzymes are present in the system. Extracellular exudates (slimes) can be sloughed-off and act to transport sorbed materials [122]. The stimulation of bacterial growth in the subsurface maybe considered as in situ formation of colloids. 

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