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The application of thermography technology in determination of sampling locations on composting windrows
Abolghasemi Riseh, Saeideh
Composting is the process of the degradation and recycling of organic solid waste under an aerobic condition. The application of composting has been grown due to different benefits that composting process has over other solid waste management practices such as depositing wastes in landfills. Based on EPA 2009 report, the amount of municipal solid waste (MSW) recovery by composting in 1990 from 4.2 million tons increased to 20.8 million tons in 2009. However, composting process has some environmental impacts. One of the most important problems that composting is known to have is the emission of harmful gases during the composting process. The most common pollutant emitted from different types of compost substrates are CO2, CH4, NH3, NO2, NO, N2O, N2, H2S, and wide array of VOC's. Air pollution control agencies have tried to regulate some of these emissions and there were several studies conducted on measuring the emissions. However, during recent studies, researchers have found that different sampling locations on the pile would result in great difference in measured emissions. Therefore, random sampling could not represent the average emission rate and a more accurate sampling location would be needed for emission rate studies. It has found that the highest temperature is generated in the center of the pile due to the high rate of microorganism activities as well as being insulated by surrounding mass. Due to the high temperatures in the center, a chimney effect is proposed by which air is drawn through the lower sections into a pile and warm air is moved upwards and tends to escape from available cracks in the windrow. As the result, different emission rates along the surface of windrow could be observed. This study investigated the relationship between the surface temperature and the level of emission. Considering the fact that the escaping emissions have higher temperature, we particularly tested the hypothesis of that the locations with highest temperature would result in higher emissions and the locations with coldest temperature would result in less emissions. The study was conducted for ninety days on four different windrows of greenwaste composting including control, pesudo-biofilter, interactive, and reduced size pile. A Thermal camera was used to determine the temperature profile and to show the hottest and coldest locations of each pile. At the same time, samples were taken from the determined hot and cold locations. Four different emissions of CO2, CH4, VOC, and N2O were analyzed from the samples. It was found that 93 percent of time, control, pseudo-biofilter, and interactive piles had the highest CH4 emission from the hottest locations and lowest CH4 emission from the coldest spots. The reduced size pile followed this hypothesis only 50 percent of the time for CH4 emission. Control pile also followed the hypothesis 100, 71, and 79 percents for CO2, VOC, and N2O emissions respectively. Pseudo-biofilter had the result of 93, 71, and 92 percents for CO2, VOC, and N2O emissions respectively. Interactive Pile followed the hypothesis 79 percent for CO2 emissions, 71 percent for VOC emissions, and 79 percent for N2O emissions. Among all the studied composting piles, reduced size pile had the least compatibility to the hypothesis with 64, 50, and 36 percent for CO2, VOC, and N2O emissions respectively. One acceptable explanation was that the pile never became microbial activated due to its small size. At the end, the usage of the Thermal camera in determination of sampling places for emission measurement from composting piles is suggested based on the results. Although there was not any qualitative relationship between the temperature and gas emission rates, a quantitative relationship could be found between temperature frequency and gas emission rates in each pile. Therefore, based on this relationship, an equation for calculating the average emission rate was proposed.
Thesis (M.S.) Civil Engineering
(M.S.) -- San Diego State University, 2011
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