In general, the benefits of converting waste into methane production include having reduced GHG emissions, supplying electricity for the city, saving financial costs and building public image of the city. Moreover, having regular monitoring and experienced landfill professionals on site also contributes to the safety benefit because methane is prone to flaring.
The call with the senior engineer from the Department of Water Management, was regarding the Landfill Methane Project carried on in Durham. The project is managed by this department, but is operated by a third party called Methane Power, a private entity. The City’s primary motivations for the project were (i) offsetting closure cost for the landfill, (ii) long term monitoring and maintenance of the landfill and (iii) sustainability and good stewardship of the city assets.
The formal name of the facility is City of Durham Sanitary Landfill. The Methane Power maintains the blower, hill system, flare, and generators. After accepting the waste from 1984 to 1998, the landfill consisting of 66 wells began producing electricity commercially in 2010 and is estimated to last until 2030. The landfill itself was closed before methane production began. The useful lifetime of methane production on the landfill is estimated to be 30 years depending on the condition of the groundwater monitoring and gas migration. Recoverable quantities of methane will be present for at least a decade beyond that based on the engineer’s calculations.
The project was not paid by the City so the information on the cost of construction is not public record. The electricity is sold to Methane Power on a per kWh basis (1 cent/kWh). As the 66 wells that exist are the responsibility of the City, the engineer from the city government was able to provide us with some data on the project as well as EPA method calculations of GHG emissions. His opinion was that this method is not the most accurate one, scientifically. He also provided us with Landgem calculations related to closure but these again are rough estimates.
In 2012, the methane gas collection facility possessed the capacity of 1400 acfm (actual cubic feet per minute), and the annual operating hours were around 8766 hours. The measured value of annual collected gas volumetric flow was about 416,175,129 scf (standard cubic feet), indicating the amount of gas production in 2012 which if fact contains complex gas content besides methane (Water Department Internal Report, 2013). According to electricity generation bill provided by the senior engineer, the Durham City was paid $199,548 in FY 2012 and $205,911 in FY 2013 by utilizing methane gas to produce electricity and selling to Methane Power (Senior Engineer, 2014). With the price of $0.01/kWh, the Durham Landfill Methane project generated 19,954,800 kWh of electricity in FY 2012 and 20,591,100 kWh of electricity in FY 2013. By multiplying the emission factor, we calculated the savings of GHG emission which was otherwise emitted by regular sources of electricity generation. However, the landfill plant and power generator also emitted GHG directly, which was about 9,156.8 tons of CO2 equivalent gases in 2012 according to the data provided by the engineer (Water Department Internal Report, 2013). Hence in total, the landfill plant saved about 4,831.5 tons of GHG emissions in 2012, which was a huge environmental benefit. However, we didn’t gain other necessary data for the analysis of 2013. The specific data are shown in the table below.
Table 13 Methane Production and CO2e Emission in FY 2012
|Year||Annual Collected Methane Volumetric Flow (scf)||Electricity Generation (kWh)||CO2e Emission Saving (tons)||CO2e Direct Emission from the Landfill Plant and Generator (tons)||Net CO2e Emission (tons)|