Moisture biodegradation

R. N. Miller, "A Field-Scale Investigation of Enhanced Petroleum Hydrocarbon Biodegradation ia the Vadose Zone Combining Soil Venting as an Oxygen Source with Moisture and Nutrient Addition," doctoral dissertation submitted to the Civil and Environmental Engineering Department,... 

Although very good rates of biodegradation have been claimed in composting tests it is stated that biodegradation will only occur where there is sufficient moisture and concentration of soil bacteria and fungi and somewhat elevated temperatures. 

As previously mentioned, some urethanes can biodegrade easily by hydrolysis, while others are very resistant to hydrolysis. The purpose of this section is to provide some guidelines to aid the scientist in designing the desired hydrolytic stability of the urethane adhesive. For hydrolysis of a urethane to occur, water must diffuse into the bulk polymer, followed by hydrolysis of the weak link within the urethane adhesive. The two most common sites of attack are the urethane soft segment (polyol) and/or the urethane linkages. Urethanes made from PPG polyols, PTMEG, and poly(butadiene) polyols all have a backbone inherently resistant to hydrolysis. They are usually the first choice for adhesives that will be exposed to moisture. Polyester polyols and polycarbonates may be prone to hydrolytic attack, but this problem can be controlled to some degree by the proper choice of polyol. 

As previously mentioned, a minimum level of soil moisture is necessary for successful biodegradation. The continuous circulation of air during bioventing results in the evaporation of soil moisture. For this reason, the design of these systems must include an appropriate installation for adding water to the contaminated zone. Care must be taken to avoid the addition of excess water. If soil moisture is significantly increased, e.g., above the limit of 85%, air circulation is no longer effective due to the decrease in free soil porosity. 

Anaerobic. Moisture is added to the waste mass in the form of recirculated leachate and from other sources to obtain optimal moisture levels. Biodegradation occurs in the absence of oxygen (anaerobically) and produces landfill gas. Landfill gas, primarily methane, can be captured to minimize greenhouse gas emissions and for energy projects. 

In addition to the bio degradability of PHAs, they have another important feature, which is their hydrophobicity. This makes PHAs superior to their biodegradable competitors like starch and proteins in moisture resistance, despite the higher price of PHAs [18]. Apart from the unique combination of biodegradability and hydrophobicity, PHAs have other interesting and useful material characteristics. The combination of the various special material properties should be kept in mind for application development. 

An almost infinite variety of chemical reactions is possible among soil, additives, and organic contaminate. However, at the moisture, temperature, and pressure conditions present at most sites, only a few reactions are responsible for most stabilization processes. Aside from such processes as absorption, volatilization, and biodegradation, chemical reactions include processes such as hydrolysis, oxidation, reduction, compound formation, and fixation on an insoluble substrate. 

The interfacial microenvironment around a microbial community, that is the sum of the physical, chemical, and biological parameters which affect a microorganism, determines whether a particular microorganism will survive and/or metabolize. The occurrence and abundance of microorganisms in an environment are determined by nutrient availability, and various physicochemical factors such as pH, redox potential, temperature, and solid phase texture and moisture. Because a limitation imposed by any one of these factors can inhibit biodegradation, the cause of the persistence of a pollutant is sometimes difficult to pinpoint. The summary follows [39,92,94,97,109,110,172,173,176,189,190, 195,248-252,256-300]. 

Cardias Williams, F. and Hale, M.D. (2003). The resistance of wood chemically modified with isocyanates the role of moisture content in decay suppression. International Biodeterioration and Biodegradation, 52(4), 215-221. 

Eilm products with good mechanical characteristics are only obtained if thermoplastic, plasticized starch has been used. If no plasticizer is used, biodegradable polymers with limited mechanical properties will be obtained. In this case, coextmsion with the base polyester or another polymer is the way to upgrade the mechanical and/or moisture barrier properties (for comparison see Table 6). 

Because of their sensitivity to moisture biodegradable polymers need to be processed either in a predryed form or on extruders, which extract volatile components [27]. 

The GT-1000 microbes cannot degrade inorganic compounds and the biodegradation rates are dependent on temperature, moisture, and slurry and chemical characteristics. 

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