ALTERNATIVE METHODS FOR DETERMINING THE BIOCHEMICAL METHANE POTENTIAL OF MUNICIPAL SOLID WASTES
The biochemical methane potential (BMP) of a substance is a measure of the volume of methane gas produced per unit mass of that substance, through the process of anaerobic biodegradation. As the socio-economic consequences of climate change have become more apparent, the ability to predict the long-term cumulative environmental impact of various human activities has become more necessary. Landfills can be a substantial source of methane (a greenhouse gas) to the atmosphere, and consequently BMP is an important tool for predicting the potential cumulative long-term impacts of a landfill to the environment. From a strictly economic perspective, the practice of landfill methane extraction for industrial uses is becoming much more common. In this case, BMP is an important tool for predicting the economic feasibility of such a project. Current methods for determining the BMP of municipal solid wastes (MSW) are both time-consuming and inconsistent. A review of literature on the topic yields many different descriptions of the test, with large variations in sample sizes, incubation times, procedures, etc. Most of these methods also require expensive, and specialized equipment. This thesis describes a simple approach to the BMP test that might be carried out in a variety of laboratory settings, such as an on-site lab equipped with basic, simple, and inexpensive equipment. The method relies on a much larger than typical sample mass to produce large volumes of gas that are measured for composition multiple times over the course of the test. The volume and composition data is then used to produce a cumulative methane potential curve which can be fitted to a first-order decay model in order to predict an ultimate BMP value. The taking of multiple measurements on large volumes of gas, allows for the use of a portable field instrument called the GEMTM2000 to measure gas composition. By fitting the data to a curve in order to determine ultimate methane potential, individual measurement errors are averaged out and the final result has a precision similar to more traditional BMP methods, which rely on bulky and expensive gas chromatographs. Testing has been conducted on MSW samples from 3 separate sites. The method used involved comparatively large samples of waste (~200 g) and no limit was set on incubation time. The use of large waste samples produces large quantities of gas that must be collected and analyzed often. The method provided favourable results, consistent within acceptable limits of variability when compared with other BMP methods. There is even some evidence suggesting that the use of large waste samples improves the accuracy of the test, despite the use of equipment which provides less precise measurements of gas concentration. Given the long duration required for testing, the results were also evaluated for possible correlations between loss on ignition data and specific gravity measurements; two simple tests that can be conducted rapidly. Both data sets show a rough correlation with BMP, and may be used to quickly estimate ultimate BMP values, but the loss on ignition relationship provides the better correlation. Lastly, initial steps were taken in the development of what has been dubbed the Biochemical CO2 Potential (BCP) test, taking advantage of the relatively quicker rate of aerobic degradation. There are preliminary indications that the BCP method may be a viable alternative to the BMP, but the data set so far is small and further research is required to confirm that hypothesis.
DegreeMaster of Science (M.Sc.)
DepartmentCivil and Geological Engineering
CommitteeFonstad, Terry; Helgason, Warren; Soltan, Jafar
Copyright DateOctober 2015
Biochemical Methane Potential
Municipal Solid Waste