IPCC Guidelines : Waste
September 11, 2023
This is part VI of a blog series - A Primer on 2006 IPCC Guidelines for Emission Inventories.
Introduction
In this post, we discuss the IPCC guidelines for the waste sector. This sector includes the three main gases - carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from the disposal, treatment and incineration of different kinds of waste. Other gases like non-methane volatile organic compounds (NMVOCs), carbon monoxide (CO), nitrogen oxides (NOx) and ammonia (NH4) are also produced by waste and wastewater treatment. However, specific methodologies to calculate the emissions of these gases are not included in the guidelines. For these calculations, it is recommended to follow guidelines developed under Convention of Long Range Transboundary Air Pollution (CLRTAP) (EMEP/CORINAIR Guidebook, EEA, 2005) and EPA's Compilation of Air Pollutant Emissions Factors (USEPA, 1995).
In order to understand the emissions from the waste sector, it is important to know the sources of waste, what is it composed of and how it is managed in a country or a region. IPCC has classified waste into four categories based on their sources of generation. It includes municipal solid waste (MSW), sludge, industrial waste and other waste. MSW consists of household waste, garden or yard waste and commercial or institutional waste. Sludge, in general, is the semi-solid slurry from domestic and industrial waste. Many countries consider all sludge in industrial waste. However, in such a case, this should be documented clearly. Industrial waste consists of all the types of waste generated through industrial processes and technologies. The fourth category - Other waste- consists of clinical waste, agricultural waste and hazardous waste like solvents, ash & cinder or even waste oil.
Data Collection
In order to document and report the waste sector emissions in an inventory, the sector is structured into five categories:
Solid waste disposal
Biological Treatment of solid waste
Incineration and open burning of waste
Wastewater Treatment and discharge
Other miscellaneous
Solid waste disposal: Waste disposal is one of the most pressing concerns around waste management techniques in many countries. Though a lot of recycling policies through waste segregation have been introduced, the amount of waste disposal continues to increase. Solid waste disposal sites generate gases like methane (CH4), carbon dioxide (CO2), NMVOCs, Nitrogen oxides (NOx) and carbon monoxide (CO). CO2, if biogenic in nature, is not calculated in this sector but is included in the Agriculture, Forestry and Other Land Use (AFOLU) sector. NMVOCs, nitrous oxides and CO emissions are calculated based on the guidelines provided in the Convention on Long-range Transboundary Air Pollution (CLRTAP). N2O is also not calculated since the amount is insignificant. Therefore, the only gas calculated in this subcategory is CH4. As per the older IPCC guidelines (Revised 1996 IPCC guidelines) CH4 emissions could be calculated based on two methodologies: Tier one - mass balance method and Tier two - First Order Decay (FOD). However, the mass balance method is highly inaccurate compared to the FOD method. The IPCC 2006 guidelines, therefore, provide a more accurate Tier 1 version of the FOD method. It is a spreadsheet model with default data based on various parameters and composition.
Box 1: Biogenic Carbon vs Fossil origin CarbonThe fundamental difference between biogenic and fossil carbon is the source. Biogenic carbon is the carbon emitted from combustion of biomass like paper, wood or food waste. On the other hand, fossil origin carbon, as the name suggests, is released when any fossil fuels, peat or mineral carbon is combusted. The idea is that fossil fuel combustion releases carbon which was locked up for a long time and will thus increase CO2 in the atmosphere in the policy relevant time scales. While, when biomass is burned, the carbon is already a part of the biogenic cycle and will most likely get absorbed in the carbon cycle. |
Biological treatment of solid waste: The organic solid waste is generally treated through either composting or anaerobic digestion. The main gases released and reported here are methane and nitrous oxide. If the gases are recovered for combustion activities, then they should be reported under the energy sector.
Incineration and open burning of waste
When waste is combusted in controlled facilities, it is defined as incinerated waste. On the other hand, when waste is either openly burned or burned in incineration chambers with no temperature control is defined as open burning. The gases produced during these processes are CO2, CH4 and N2O, the emission estimation methodologies for which are explained in the IPCC 2006 guidelines. Emissions from the other gases like NMVOCs, CO, NOx and SOx are estimated using existing inventory system guidelines like US Environmental Protection Agency (USEPA), European Monitoring and Evaluation Program (EMEP) inventory guidebook.
CO2 is an important gas in this sub-category, with only the fossil origin being accounted for in the net emissions. The biogenic carbon is not included in the net emissions (see box 1).
Wastewater Treatment and discharge
Wastewater originates from either domestic, commercial or industrial sources. Depending on the source, the wastewater is treated through different technologies. In this sub-category, the prominent gases reported are CH4 and N2O, since CO2 is biogenic in nature. CH4 is produced under anaerobic conditions and its amount depends on various factors like temperature, type of treatment system and most importantly the quality of degradable material in the wastewater. N2O, on the other hand, is generated through decomposition of nitrogen compounds especially in domestic wastewater. Additionally, emissions are also produced from the sludge formed during the treatment of wastewater. These emissions are accounted for in respective sub-categories depending on the treatment and disposal methods of sludge. For example, when sludge is composted, incinerated or disposed of on land, the emissions are accounted for under the incineration category mentioned above.
If waste is one of the key categories for a country, it is essential that Tier 3 method is used to calculate emissions. In case of lack of data, it is recommended to acquire data through surveys and determine country specific or plant specific data. However, if the sector is not a key category, then Tier 1 approach may be followed.
Cover photo from Unsplash
