6.4 Incineration, Land Application and Other Processes
| Category ID | Description | EIC |
|---|---|---|
| 52 | Waste Management - Biosolids Land Application | 14099502400000 |
| 53 | Waste Management - Other | Various |
| 314 | Incineration | Various |
Introduction
This document outlines the methodology for estimating greenhouse gas (GHG) emissions from incineration, land application and ancillary processes in the San Francisco Bay Area (SFBA). These activities are waste management processes that produce carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions. Emissions are reported in specific categories based on the process:
- Category 52 (Biosolids Land Application) includes emissions generated from the application of treated wastewater sludge to agricultural or non-agricultural land as a soil amendment, providing essential nutrients that enhance soil quality and promote plant growth. During application, biosolids are typically spread on the soil surface or incorporated into the soil, where they undergo microbial processes that generate emissions. This microbial activity generates CO₂ from aerobic degradation of organic carbon, CH₄ from localized anaerobic zones in the soil where oxygen is limited, and N₂O from nitrification and denitrification processes driven by nitrogen compounds in the biosolids.
- Category 53 (Ancillary Processes) includes emissions generated from supporting activities associated with waste management and treatment systems, such as transportation of materials (e.g. transfer stations, loading terminals), on-site sorting of materials (e.g. conveyors, screeners, hoppers), and material storage (e.g. silos, stockpiles, storage ponds). These processes produce CO₂ from fossil fuel combustion associated with equipment and vehicle operation, CH₄ from anaerobic decomposition of stored organic materials (e.g., in stockpiles or storage ponds), and N₂O from stored organic nitrogen-rich material under certain microbial conditions.
- Category 314 (Incineration) includes emissions generated from thermal treatment of waste material at permitted sources. Examples of permitted sources include crematories, pathological waste incinerators, and wastewater sludge incinerators. These sources CO₂ emissions from the combustion of organic material (both fossil-derived and biogenic) and N₂O as a byproduct of high-temperature combustion processes, particularly when nitrogen-containing compounds are present in the waste stream.
Methodology
This section describes how GHG emissions are estimated for incineration, land application, and ancillary waste management categories. Categories 53 (ancillary processes) and 314 (incineration) are point source categories, which are defined as operations that emit air pollution into the atmosphere at a fixed location and for which the Bay Area Air Quality Management District (BAAQMD; also known as the Air District) has issued a permit to operate (PTO). Category 52 (land application) is an area source category since it covers emission sources that are not directly permitted by the Air District, so emissions are not systematically or annually cataloged and/or reported. Methodologies for both area source and point source categories are described separately in the subsections below.
Permitted Sources (Categories 53, 314)
As mentioned above, categories 53 and 314 are point source categories that include sources for which the Air District has issued a PTO. Point sources are operations that emit air pollution into the atmosphere at a fixed location within a facility, and for which the Bay Area Air Quality Management District (BAAQMD or the Air District) has issued a permit to operate (PTO), e.g. refinery cooling towers. These point sources could also be a collection of similar equipment and/or sources located across multiple facilities, e.g. reciprocating engines.
During the PTO issuance process, the Air District collects site-specific information from the operating facility and/or determines from published literature, e.g. United States Environmental Protection Agency’s (USEPA) AP-42 (USEPA, 2024), characteristics of a source including maximum throughput, emission factors for emitted pollutants, and control factors associated with downstream abatement devices. This data is then compared against the Air District’s Regulations to ensure compliance. Facilities that hold a PTO are required to renew their permit periodically (this period varies based on facility and source type). Upon renewal, the facilities are requested to provide any updates to source characteristics as well as the source throughput for the past twelve months. This throughput, in combination with the emission factors and controls factors stored in the Air District’s internal database, are used to programmatically estimate annual emissions at the source level. The methodology used to calculate emissions for the base year(s) of a point source category is summarized below:
Base Year(s) Emissions source,pollutant =
Activity Data source × Emission Factorpollutant × Control Factorpollutant × GWP pollutant
Base Year(s) Emissions county = ∑ Ni=1 Emissionsi
Where:
- Base Year: is a year for which activity / throughput data is available from permit records.
- Activity Data source is the throughput or activity data for applicable base year(s) at the source/equipment level. This data is usually available from the internal permit records that are provided annually to the Air District at permit renewal by the facility operator.
- Emission Factorpollutant is a factor that allocates an amount of emissions, in mass, of a particular pollutant by unit of activity data. For example, tons CO2 per gallons of gasoline burned or pounds of N2O per million standard cubic feet of natural gas combusted. GHG emissions are calculated by using specific emission factors for every source/operation for which information has been supplied by the facility (and verified/validated through source tests). If no specific emission factors are available, generalized factors developed by Air District staff are used to determine emissions. These default factors typically come from published literature such as USEPA’s AP-42 (USEPA, 2024) or California Air Resource Board’s (CARB) Mandatory Reporting Requirement (CARB, 2019) for Greenhouse Gases.
- Control Factorpollutant is a fractional ratio (between 0 and 1) that captures the estimated reduction in emissions as a result of District rules and regulations.
- GWP pollutant is the Global Warming Potential. The current version of the GHG emissions inventory incorporates the global warming potential (GWP) reported in the Fifth Assessment report of the Intergovernmental Panel for Climate Change (IPCC, 2014). The GWPs for the three principal GHGs are 1 for carbon dioxide (CO2), 34 for methane (CH4), and 298 for nitrous oxide (N2O), when calculated on a 100-year basis with climate-carbon feedback included.
- N is the number of permitted and similar sources in a county.
If available, a facility can provide emission factors specific to the source that are verified and validated through source tests to estimate GHG emissions. If no specific emission factors are available, general factors developed by Air District staff are used to estimate emissions. These source level emissions are then sorted and aggregated by year, county, and category.
Further speciation and quality assurance of emissions, including those of GHGs, are performed as a part of the inventory refinement process. A systematic crosswalk has been developed between CARB’s California Emissions Projection Analysis Model (CEPAM) source category classification using the primary sector emission inventory codes (EICs) and the Air District’s source category classification (category identification number - cat_ids), which ensures consistency when reporting annual emissions under the California Emissions Inventory Data Analysis and Reporting Systems (CEIDARS) to CARB (CARB, 2022a). This emissions data represents the reported base years emissions for a point source category.
Once base year emissions are determined, historical backcasting and forecasting of emissions relative to the base year emissions are estimated using growth profiles as follows:
Current Year Emissionscounty = Base Year(s) Emissioncounty x Growth Factor
Where:
- Growth Factor: is a scaling factor that is used to derive historical emissions estimates for years for which activity data and/or emissions are not available, and to forecast emissions for future years, using surrogates that are assumed to be representative of activity and/or emissions trends.
Categories 53 and 314 use the methodology outlined above with the following base years, backcast, and projections. For those years where no data is available, emissions data are backcast to year 1990, as well as forecasted to year 2050 using either interpolation or another mathematical approach (see Trends section), or by applying a growth profile based on socioeconomic indicators. GHG emissions data from the years 1990 to 2050, including the projections outlined below, are analyzed for each source category and pollutant, with the trends evaluated and corrected for any observed anomalies and addressed accordingly:
- Historical backcast (1990-2006): Extrapolated to 1990 using historical throughput trends from internal database
- Reported throughputs by permitted facilities to the Air District for years 2007-2022
- Future projection (2023-2050)
- California Department of Finance Population Projections (CADOF, 2024) for category 314,
- A custom profile developed to estimate future activity and emissions at SFBA’s composting facilities using the CalRecycle database and capacity utilization rates (CALSWIS, 2024) for category 53.
Emissions data is finally aggregated under sub-sectors and sectors for tracking trends and documentation purposes.
Local Controls
Relevant Air District rules and regulations have been reviewed, and the effect of regulatory controls is confirmed to be included in the estimation of permitted source emissions. Rules that apply to ancillary processes or incineration permitted sources are summarized below:
- Regulation 8, Rule 34 (Solid Waste Disposal Sites; BAAQMD, 2005) limits the emission of non-methane organic compounds (NMOC) and methane from the waste decomposition process at solid waste disposal sites. Landfill operators are required to submit reports containing the design capacity of the landfill and estimated NMOC emission rates. Although there are no formal requirements to control GHG emissions from ancillary processes, throughput and emissions for these processes are impacted if a landfill operation is required to scale down operations due to throughput or NMOC emission rates exceeding thresholds as defined in the rule.
- Regulation 11, Rule 13 (Medical Waste Incinerators; BAAQMD, 1991) controls emissions of dioxins from medical waste incinerators. Although there are no formal requirements to control GHG emissions from medical waste incinerators, the rule requires a minimum temperature and residence time for operation, which in turn affects the combustion process and GHG emission factors from medical waste incinerators.
- Regulation 5 (Open Burning; BAAQMD, 2019) strictly prohibits the open burning of waste. It is assumed that there is no household burning of waste within the Air District and incineration of waste only occurs in permitted point sources covered in category 314.
Historical Emissions
Historical emissions for point sources are derived from source-specific data provided by the facility on throughputs, compiled or reported emission factors, and regulation-based control factors. This information is archived in the Air District’s internal database and is queried to retrieve the data for historical and current years. Interpolation techniques to account for missing data are used when necessary.
In the case of GHGs, up until the year 2006, the Air District was not engaged in systematic information collection during permit renewal process. This changed when AB32 bill was passed into a statewide law in 2006, and a statewide Cap and Trade system was introduced to reduce GHG emissions from specific facilities. Hence, GHG emissions data for years 1990-2006 are derived from the historical emissions data reported in the base year 2011 GHG inventory (released in year 2012). The historic emissions dataset is scaled to sync with the data in the permit database (which started systematic GHG data accounting from year 2006 onwards), to generate a complete GHG emissions time series for each point source category from 1990 to 2050.
Future Projections
Forecasting of point source emissions is done based on calculations as shown in the equation below using recently updated growth profiles and a base year of 2022. The growth profiles for the current base year inventory have been verified and updated to represent the most likely surrogate for forecasting emissions for a given category up to the year 2050. Forecasting for point source emissions includes impact of in-place regulations but does not include estimation of controls that will theoretically be implemented as part of future policy emission targets or proposed regulation and legislation.
PE = Gr × Ci × Ei
PE = projected emissions of pollutant i in a future year
Gr = growth rate by economic profile of industry or population
Ci = control factor of pollutant i based on adopted rules and regulations
Ei = base year emissions of pollutant i
For category 314, California Department of Finance Population Projections (CADOF, 2024) is used to project activity and derive emissions for the future years. This activity is projected to track steadily but gradually upwards, consistent with SFBA’s population growth. A custom profile developed to estimate future activity and emissions at SFBA’s composting facilities (category 1936), using the CalRecycle database and capacity utilization rates (CALSWIS, 2024), is used to project emissions for category 53. This activity is expected to gradually increase as more organic waste is diverted from landfills towards sustainable and alternate end-uses including composting, biogas production, land application of sludge etc., as part of the statewide law SB1383 to curb methane emissions (SB1383, 2016).
Area Sources (Category 52)
Category 52 is considered an area source category as it accounts for emissions from land application processes that are not directly permitted by the Air District, and thus not routinely or annually catalogued. The methodology used to calculate emissions for the reported base year(s) of these area source categories is as follows:
Base Year(s) Emissionscounty,pollutant =
Activity Data × Emission Factorpollutant × Control Factorpollutant × Fractioncounty × GWPpollutant × Fractionin District
Where:
- Base Year: is a year for which activity / throughput data is available (or can be derived or estimated)
- Activity Data: is the throughput or activity data for applicable base year(s).
- Emission Factorpollutant: is a factor that expresses how the amount, in mass, of a particular pollutant is emitted per unit of activity data. Examples include tons of CO2 per gallon of gasoline burned and pounds of N2O per million standard cubic feet of natural gas combusted. This factor generally comes from a published literature source such as EPA’s AP-42 or CARB’s Mandatory Reporting Requirement (MRR) for Greenhouse Gases.
- Control Factorpollutant: is a fractional ratio (between 0 and 1) that captures the estimated reduction in emissions due to Air District rules and regulations.
- Fractioncounty: is the fraction of total regional emissions (between 0 and 1) estimated to be allocated to a particular county. It is typically derived from regional socioeconomic metrics and/or actual county-level throughput data.
- GWP is the Global Warming Potential. The current version of the GHG emissions inventory incorporates the global warming potential (GWP) reported in the Fifth Assessment report of the Intergovernmental Panel for Climate Change (IPCC, 2014). The GWPs for the three principal GHGs are 1 for carbon dioxide (CO2), 34 for methane (CH4), and 298 for nitrous oxide (N2O), when calculated on a 100-year basis with climate-carbon feedback included.
- Fractionin District: The BAAQMD jurisdiction covers only a portion of Solano and Sonoma County. For this reason, additional allocation must be done for these counties to determine the proportion of the county’s emissions occurring within BAAQMD’s jurisdiction.
Once base year emissions are determined, historical backcasting and forecasting of emissions relative to the base year emissions are estimated using growth profiles as follows:
Current Year Emissionscounty = Base Year(s) Emissioncounty x Growth Factor
Where:
- Growth Factor: is a scaling factor that is used to derive historical emissions estimates for years for which activity data and/or emissions are not available, and to forecast emissions for future years, using surrogates that are assumed to be representative of activity and/or emissions trends.
More details on throughput, county distribution, emission factors and controls are provided in the following subsections:
Activity Data / Throughput
Activity data for biosolids land application are reported annually by the Bay Area Clean Water Agencies (BACWA) to Solano County and are available through BACWA’s online biosolids library (BACWA, 2024). Each annual report includes the dry mass of biosolids (in metric tons) applied to land in Solano County, as well as the percentage of total San Francisco Bay Area (SFBA)-generated biosolids that are applied to land in each county. Reports are available for each year from 2011 through 2023.
In 2022, 7,900 metric tons of biosolids were reported as applied to land in Solano County. According to BACWA data, this represents approximately 25% of all biosolids generated by SFBA wastewater agencies that were applied to land. Smaller portions of SFBA-generated biosolids were applied to lands in Napa County (2%) and Sonoma County (8%). However, dry mass values are not directly reported for these counties.
To estimate the dry mass of biosolids land-applied in other SFBA counties, the Solano County dry mass is scaled using the relative county fractions provided in the BACWA reports. This approach assumes the Solano throughput is representative and can be ratioed using the formula:
Dry MassCounty = Dry MassSolano × (%County ÷ %Solano)
Where:
- Dry MassCounty = Estimated dry mass of biosolids applied in other SFBA County
- Dry MassSolano = Reported dry mass of biosolids applied in Solano County (7,900 metric tons in 2022)
- %County = Percentage of SFBA-generated biosolids applied in other SFBA County
- %Solano = Percentage of SFBA-generated biosolids applied in Solano County (25% in 2022)
The table below shows the estimated dry mass of biosolids applied to land in each SFBA county based on 2022 data. The remaining 65% of biosolids generated in the SFBA were applied to counties outside the Air District’s jurisdiction and are not included in this inventory.
County | Reported Dry Mass Applied in 2022 | % of SFBA Generated Biosolids Applied in County | Calculated Dry Mass Applied in 2022 |
Solano | 7,900 | 25% | 7,900 |
Napa | NA | 2% | 7,900*(0.02/0.25) = 632 |
Sonoma | NA | 8% | 7,900*(0.08/0.25) = 2,528 |
County Distribution / Fractions
As mentioned in the previous subsection, county fractions are presented in BACWA’s annual reports to Solano County. The county distribution is derived from the total dry mass of biosolids delivered to and applied in each county and only includes throughput for counties within the Air District’s jurisdiction. Since the amount of material applied in each county varies annually, the county distribution will also change from year to year. The table below shows the county distribution for biosolids land application for base year 2022.
| ID | Description | ALA | CC | MAR | NAP | SF | SM | SNC | SOL | SON |
|---|---|---|---|---|---|---|---|---|---|---|
| 314 | Incineration | 0.0 | 1.0 | 0.0 | 0.00 | 0.0 | 0.0 | 0.0 | 0.00 | 0.00 |
| 52 | Waste Management - Biosolids Land Application | 0.0 | 0.0 | 0.0 | 0.13 | 0.0 | 0.0 | 0.0 | 0.55 | 0.33 |
| 53 | Waste Management - Other | 0.0 | 1.0 | 0.0 | 0.00 | 0.0 | 0.0 | 0.0 | 0.00 | 0.00 |
BAAQMD Jurisdiction Fraction
The BAAQMD jurisdiction only accounts for a part of Solano and Sonoma counties. The remaining area is covered by other Air Districts. For category 52, the percentage of Solano and Sonoma County agricultural employment within the Air District boundary (or jurisdiction) is estimated using the Association of Bay Area Government’s (ABAG) Plan Bay Area 2050 dataset (ABAG, 2021). The dataset summarizes agricultural employment by Travel Analysis Zone (TAZ). Agricultural employment is assumed to be a reasonable approximation for agricultural activity and land application rates within each county. The agricultural employment for each TAZ within BAAQMD’s jurisdictional boundaries is summed and divided by the total county-wide agricultural employment to estimate the percentage of population within the Bay Area for Solano and Sonoma counties. These proportions are shown below:
County | % of Agricultural Employment within the District’s jurisdiction |
Solano | 0.34 |
Sonoma | 0.63 |
Emission Factors
CO2, CH4, and N2O emission factors for biosolids land application are derived from Nordahl et al. (2023), specifically the mean values reported in Table 1 for sludge feedstock. These values originally represent emissions in kilograms per kilogram of wet biosolids. However, to align with how biosolids quantities are reported in this inventory (measured in dry metric tons), the emission factors are converted accordingly.
To reflect emissions on a dry mass basis, the emission factors are adjusted to account for the moisture content of biosolids applied to land in the SFBA. Based on the most recent data from the BACWA Biosolids Trends Survey Report (BACWA, 2024), the average moisture content of biosolids utilized for land application is approximately 76%. This value represents the proportion of water by mass in the total wet biosolids. It is noted that CO₂ emissions from biosolids land application are considered biogenic and, consistent with standard inventory guidance, are excluded from the total anthropogenic GHG emissions reported in the regional inventory.
Because only the dry fraction of the biosolids contributes to greenhouse gas emissions during land application, the original emission factors are divided by the dry solids fraction (1 – 0.76 = 0.24). This conversion yields emission factors in units of kilograms per metric ton of dry biosolids. The original emission factors from Nordahl et al. (2023) and adjusted emission factors per weight of dry mass are shown in the table below.
Emission Factor | Adjusted Emission Factor (kg/metric ton dry feedstock) | |
CH4 | 0.23 | 0.23 ÷ (1-0.76) = 0.98 |
N2O | 0.084 | 0.084 ÷ (1-0.76) = 0.35 |
CO2 | 17.5 | 17.5 ÷ (1-0.76) = 72.9 |
Control Factors / Emission Controls
Since there are no current Air District rules that directly regulate emissions or activity associated with biosolids land application, no control factors are formally applied in the emissions calculations at this time. However, three proposed rules under Regulation 13 are in various stages of development and may influence future land application practices and associated emissions if adopted:
- Regulation 13, Rule 2: Organic Material Handling Operations (BAAQMD, 2024a; development currently suspended)
This rule was initially proposed to address CH₄, ROG, and TOG fugitive emissions from the handling, transfer, and temporary storage of organic materials, such as food waste, green waste, and biosolids. If revived and adopted, this rule could affect facilities that temporarily store biosolids prior to land application by requiring improved handling practices (e.g., enclosed transfer areas or time limits on storage) to minimize emissions. Although the rule’s development is currently suspended, its potential implementation could lead to changes in how biosolids are managed before being transported for land application. - Regulation 13, Rule 3: Composting Operations (BAAQMD, 2024b; development currently suspended)
Rule 13-3 was intended to reduce CH4 and ROG emissions from composting facilities by requiring best management practices such as aeration controls, moisture management, and pile covering. While biosolids land application is distinct from composting, any expansion of the rule’s scope in the future—particularly if biosolids composting or co-composting with green waste is included—could indirectly impact the volume of biosolids being diverted to land application versus composting, thereby affecting the overall activity level in this inventory category. - Regulation 13, Rule 4: Sewage Treatment and Anaerobic Digestion (BAAQMD, 2024c; currently in development)
This rule focuses on controlling CH4, N₂O, and ROG emissions from wastewater treatment and anaerobic digestion operations. Although its primary scope is within treatment plant boundaries, implementation of this rule could impact biosolids characteristics and quantities. For example, if the rule leads to increased use of advanced digestion or biosolids drying technologies to reduce on-site emissions, it may reduce the volume or alter the composition of biosolids available for land application. These changes could, in turn, affect land application activity levels and the associated emissions profile in future inventories.
Until any of these rules are finalized and adopted, emissions from biosolids land application continue to be estimated without applying control factors.
Historical Emissions
Since wastewater operations typically scale with population, emissions from biosolids generation and land application sources are assumed to follow the same trend. For years 1990-2010, total population by county, obtained from the California Department of Finance (CADOF, 2024), is used to develop the backcast profile for category 52. As mentioned previously, annual BACWA reports contain actual land application data for 2011-2021 and are used to develop the backcast profile for these years.
Future Projections
Similar to the development of the backcast profile, the forecast profile is developed using the California Department of Finance population projections for each county for future years (2023-2050).
Sample Calculations
The table below shows an example calculation for calculating base year 2022 GHG emissions from biosolids land application in Sonoma County. Emissions are reported in metric tons of CO2 equivalents (MTCO2eq) per year.
Step 1 | Obtain dry mass applied in Solano county (metric tons) | 7,900 | ||
Step 2 | Obtain SFBA percent of BACWA biosolids applied in Solano county | 25% | ||
Step 3 | Calculate total dry mass of BACWA biosolids applied in SFBA (metric tons) | 7,900 ÷ 0.25 = 31,600 | ||
Step 4 | Obtain percent of BACWA biosolids applied in Sonoma county | = 8% | ||
Step 5 | Calculate dry mass applied in Sonoma county (metric tons) | 31,600 × 0.08 = 2,528 | ||
Step 6 | Obtain percent of agricultural employment in Sonoma county within BAAQMD jurisdiction (ABAG, 2021) | 62.7% | ||
Step 7 | Estimate total dry mass applied in Sonoma county within BAAQMD Jurisdiction (metric tons) | 2,528 × 0.627 = 1,585 | ||
Step 8 | Calculate dry fraction of biosolids (BACWA, 2024) | 36,992 (total dry MT biosolids applied) ÷ 155,589 (total wet MT biosolids applied) = 24% (dry fraction of biosolids) 🡪 76% (wet fraction or moisture content of biosolids) | ||
CO2_bio | CH4 | N2O | ||
Step 9 | Gather emission factors from Nordahl et al., 2023 (kg/kg wet mass) | 0.0175 | 2.34 × 10-4 | 8.36 × 10-5 |
Step 10 | Convert emission factors to use dry mass as Basis (kg/kg dry mass) | 0.0175 ÷ (1-0.76) = 0.073 | 2.34 × 10-4 ÷ (1-0.76) = 9.75 × 10-4 | 8.36 × 10-5 ÷ (1-0.76) = 3.48 × 10-4 |
Step 11 | Calculate emissions (metric tons/year) | 0.073 × 1585 = 115.6 | 9.75 × 10-4 × 1585 = 1.55 | 3.48 × 10-4 × 1585 = 0.56 |
Step 12 | Global Warming Potential | 1 | 34 | 298 |
Step 13 | Calculate emissions using GWP not including CO2_bio (MTCO2eq/year) | 115.6 × 1 = 115.6 | 1.55 × 34 = 52.7 | 0.56 × 298 = 166.9 |
52.7 + 166.9 = 220 MTCO2eq/year | ||||
Assessment of Methodology
Routine updates to the biosolids land application GHG inventory include incorporating the most recent annual BACWA land application reports to Solano County for each year not covered in the previous iteration and updating GWPs for each greenhouse gas to match the most recently published IPCC assessment report. Additional updates to the inventory for base year 2022 include updating emission factors based on recent studies and using the material moisture content to convert from wet to dry mass to ensure consistent units between activity data and emission factors.
Base Year | Revision | Reference |
2022 |
|
|
2015 |
|
|
Emissions
The table below shows the total GHG emissions by pollutant in MTCO2eq for incineration, land application, and ancillary processes categories.
| ID | Description | CH2Cl2 | CH4 | CO2 | CO2_bio | N2O | Total |
|---|---|---|---|---|---|---|---|
| 53 | Waste Management - Other | 0.0 | 6822.4 | 7.5 | 0.0 | 0.0 | 6829.9 |
| 52 | Waste Management - Biosolids Land Application | 0.0 | 161.1 | 0.0 | 354.3 | 504.4 | 1019.8 |
| 314 | Incineration | 0.0 | 0.2 | 793.1 | 0.1 | 0.2 | 793.6 |
Summary of Base Year 2022 Emissions
Incineration, land application, and ancillary processes produce CO2, CH4, and N2O emissions based on the type of process and materials processed. Emissions are initially calculated in pounds and then converted to MTCO2eq.
The tables below show the contribution of incineration, land application, and ancillary processes GHG emissions to the overall regional total and to the Waste Management sector.
Contribution of Incineration, Land Application and Other Processes Emissions by Sector| Subsector | Sector | Subsector GHG Emissions (MMTCO2eq) | Sector GHG Emissions (MMTCO2eq) | % of Sector |
|---|---|---|---|---|
| Incineration, Land Application and Other Processes | Waste Management | 0.008 | 2.61 | 0.32% |
Contribution of Incineration, Land Application and Other Processes Emissions to Regional Total
| Subsector | Subsector GHG Emissions (MMTCO2eq) | Regional Total GHG Emissions (MMTCO2eq) | % of Regional Total |
|---|---|---|---|
| Incineration, Land Application and Other Processes | 0.008 | 65.68 | 0.01% |
Trends
The time series chart below shows the emission trends for incineration, land application, and ancillary processes categories.
Summary of Trends
GHG emissions from incineration point sources have decreased over time since year 2000 and are projected to remain low in future years. The prevalence of incineration as a waste management strategy has declined due to the increasing adoption of alternative methods, such as composting. For example, BACWA reports show that incineration of biosolids has decreased by nearly 40% since 2015, while composting of biosolids has increased more than threefold (BACWA, 2024).
Conversely, GHG emissions from ancillary processes have increased in recent years and are projected to maintain emissions similar to base year 2022 levels. As alternative waste management strategies such as composting have been more frequently adopted, ancillary processes involved in the transportation, sorting, and storage of waste materials have increased due to the additional processing of waste that is required compared to traditional methods such as landfilling or incineration.
Although the total amount of biosolids generated by SFBA wastewater agencies does not vary significantly from year to year, the amount used for land application within the Air District depends on factors such as supply, demand, and tipping fees from operations both within and outside of BAAQMD jurisdiction. Therefore, the throughput and emissions for biosolids land application is difficult to predict, which is seen in the emissions trend calculated from actual throughput data from years 2011-2023. The projected future year emissions are assumed to scale with biosolids generation rates (i.e. population growth) as a best estimate.
Uncertainties
Uncertainty in the activity data for biosolids land application arises primarily from limitations in data coverage and the use of proportional scaling to estimate regional throughput. BACWA annually reports the dry mass of biosolids applied to land in Solano County and provides the percentage distribution of SFBA-generated biosolids applied in other counties. However, dry mass data are only directly reported for Solano County; values for other SFBA counties where land application occurs are estimated by scaling the Solano County throughput using county-specific allocation percentages. This introduces uncertainty due to potential variability in application rates, treatment methods, and moisture content across counties. Additionally, the BACWA allocation percentages represent the share of biosolids delivered to each county, which may not fully align with the actual amount applied to land within each county in a given year. Lastly, biosolids that are transported to and applied in counties outside the jurisdiction of the Air District are excluded from the inventory, which may result in an underestimation of total land application activity originating from SFBA sources.
Emission factors in Nordahl et al., (2023) are based on a limited number of sludge samples and are conducted in controlled laboratory environments that are not representative of real-world field conditions. The feedstocks sampled from in the study are also sourced from a single facility, which may have a composition that varies significantly from other waste management sites.
The fraction of agricultural employment within Air District boundaries is used to estimate the fraction of biosolids applied to land within the Air District, assuming that agricultural employment is a suitable estimate for agricultural land acreage. The actual fraction of agricultural land within the Air District may differ slightly. Future inventories will explore the use of county zoning maps and wilderness masks to refine this estimate.
Contact
Author: Tan Dinh
Reviewer: Abhinav Guha
Last Update: 08/29/2025
References
ABAG. 2021. Plan Bay Area 2050, Association of Bay Area Governments. https://planbayarea.org/finalplan2050
BAAQMD. 1991. Regulation 11 Rule 13: Medical Waste Incinerators, Bay Area Air Quality Management District. https://www.baaqmd.gov/en/rules-and-compliance/rules/reg-11-rule-13-medical-waste-incinerators
BAAQMD. 2005. Regulation 8 Rule 34: Solid Waste Disposal Sites, Bay Area Air Quality Management District. https://www.baaqmd.gov/en/rules-and-compliance/rules/reg-8-rule-34-solid-waste-disposal-sites?rule_version=Adopted
BAAQMD. 2019. Regulation 5: Open Burning, Bay Area Air Quality Management District. https://www.baaqmd.gov/en/rules-and-compliance/rules/reg-5-open-burning
BAAQMD. 2024a. Regulation 13 Rule 2: Organic Material Handling Operations, Bay Area Air Quality Management District. https://www.baaqmd.gov/en/rules-and-compliance/rules/regulation-13-rule-2-organic-material-handling-operations
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