8.1 Methodology and Trends

8.2 Key Sources

8.3 Non-key Sources

8.1 Methodology and Trends

The GHG emissions from the Waste sector result from the processes of accumulation, disposal and management of solid wastes from the households and industry, as well as from domestic and industrial wastewater handling.

Solid waste can be managed by disposal on landfills, recycling and incineration for energy or destruction. This sector accounts only for the GHG emissions from disposed solid waste and waste incineration for non-energy use.

According to some definite criteria, such as mechanical cover materials, leveling of the waste etc., landfills are classified as managed and unmanaged.

The disposed solid wastes emit CH₄ as a result of the processes of anaerobic and aerobic decomposition of organic mater contained in it. For estimating the volumes of CH₄ emitted in Bulgaria is used the default methodology recommended in the IPCC Guidelines. This methodology uses indices and parameters that account for:

• the category of waste site and composition of waste;
• the fraction of degradable organic matter and the amount which actually degrades;
• the amount of organic matter converted to methane;
• the amount of methane flared;
• the amount of oxidized methane in the upper layers of landfills.

The second most important CH₄ emissions source is the wastewater handling. The Industrial Wastewater handling on one hand and the Municipal Sewage treatment on the other hand form two separate categories in this sector. Wastewater handling is a CH₄ source only when carried out under anaerobic conditions. Usually the anaerobic and aerobic treatments combine which imposes the use of correction coefficient. The treatment of wastewater sludge is referred to this source, too. As during the amount of sludge hasn't been under statistical examination during the last two years, it is assumed that 5 % of the overall wastewater steam is removed as sludge.

The CH₄ emissions are estimated after the default method recommended in the IPCC Guidelines. This method comprises of the following steps:

1. Determine the total amount of organic material in the wastewater and sludge produced for each wastewater handling system;
2. Estimate emissions factors for each wastewater handling system;
3. Multiply the emissions factors for each wastewater handling system by the total amount of organic material in the wastewater produced for each system

The input data for industrial wastewater and sludge and for domestic wastewater and sludge have different levels of aggregation and punctuality. Data for the domestic wastewater and sludge are vaguer because are estimated after average parameters per capita of the population. In Bulgaria the industrial wastewater and sludge are reviewed by industrial branches which allow specifying the different organic matter contents. Thus the punctuality of the methane emissions estimated is improved.

The Waste sector also includes the N₂O emissions resulting from protein consumption by humans.

Figure 8.1 presents the CH₄ emission trends from Waste.

As seen in trend analysis CH₄ emissions from solid waste disposal decreased from 300 to 200 Gg annually during the period 1997 - 1999 and remained relatively stable during the last two years. The CH₄ emissions from wastewater and sludge are significantly smaller and have emission trend which, unlike that of solid wastes, doesn't vary to such a degree. The sudden drop of the CH₄ emissions after 1994 is due to change in methodology applied by NSI for assessment of the amounts of solid waste disposed.