EPA releases Inventory of U.S. Greenhouse Gas Emissions and Sinks

The U.S. EPA released the annual “Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012” on 15-APR-2014.

Excerpts from the report include:

In 2012, CH4 emissions from domestic wastewater treatment were 7.8 Tg CO2 Eq. (373 Gg CH4). Emissions remained fairly steady from 1990 through 1997, but have decreased since that time due to decreasing percentages of wastewater being treated in anaerobic systems, including reduced use of on-site septic systems and central anaerobic treatment systems (EPA 1992, 1996, 2000, and 2004, U.S. Census 2011). In 2012, CH4 emissions from industrial wastewater treatment were estimated to be 4.9 Tg CO2 Eq. (234 Gg CH4).  The 2012 emissions of N2O from centralized wastewater treatment processes and from effluent were estimated to be 0.3 Tg CO2 Eq. (1 Gg N2O) and 4.7 Tg CO2 Eq. (15.2 Gg N2O), respectively. Total N2O emissions from domestic wastewater were estimated to be 5.0 Tg CO2 Eq. (16.2 Gg N2O). N2O emissions from wastewater treatment processes gradually increased across the time series as a result of increasing U.S. population and protein consumption.

The methodology for domestic wastewater CH4 emissions from septic systems were estimated by multiplying the United States population by the percent of wastewater treated in septic systems (about 20 percent) and an emission factor (10.7 g CH4/capita/day), and then converting the result to Gg/year.  Methane emissions from POTWs were estimated by multiplying the total BOD5 produced in the United States by the percent of wastewater treated centrally (about 80 percent), the relative percentage of wastewater treated by aerobic and anaerobic systems, the relative percentage of wastewater facilities with primary treatment, the percentage of BOD5 treated after primary treatment (67.5 percent), the maximum CH4-producing capacity of domestic wastewater (0.6), and the relative MCFs for well-managed aerobic (zero), not well managed aerobic (0.3), and anaerobic (0.8) systems with all aerobic systems assumed to be well-managed.

Methane emissions from anaerobic digesters were estimated by multiplying the amount of biogas generated by wastewater sludge treated in anaerobic digesters by the proportion of CH4 in digester biogas (0.65), the density of CH4 (662 g CH4/m3 CH4), and the destruction efficiency associated with burning the biogas in an energy/thermal device (0.99).

With regard to N2O emission estimates, an estimate for the N removed as sludge (NSLUDGE) was obtained by determining the amount of sludge disposed by incineration, by land application (agriculture or other), through surface disposal, in landfills, or through ocean dumping. In 2012, 280 Gg N was removed with sludge.

From 1990 to 2012, the amount of material composted in the United States has increased from 3,810 Gg to 18,919 Gg, an increase of approximately 397 percent. From 2000 to 2012, the amount of material composted in the United States has increased by approximately 27 percent. Emissions of CH4 and N2O from composting have increased by the same percentage.

See, attached

US-GHG-Inventory-2014-Chapter-8-2