Uncertainty assessment

EMISSION FACTORS

There are large uncertainties associated with the default emission factors for Tier 1 (see Tables 10.14 to 10.16). The uncertainty range for the default factors is estimated to be +30%. Improvements achieved by Tier 2 methodologies are estimated to reduce uncertainty ranges in the emission factors to +20%. Accurate and well-designed emission measurements from well characterised types of manure and manure management systems can help reduce these uncertainties further. These measurements must account for temperature, moisture conditions, aeration, VS content, duration of storage, and other aspects of treatment.

The default values may have a large uncertainty for an individual country because they may not reflect the specific manure management conditions present within the country. Uncertainties can be reduced by developing and using MCF, Bo, and VS values that reflect country/region specific conditions.

Table 1G.18 Definitions of manure management systems

System

Definition

Pasture/Range/Paddock

The manure from pasture and range grazing animals is allowed to lie as deposited, and is not managed.

Daily spread

Manure is routinely removed from a confinement facility and is applied to cropland or pasture within 24 hours of excretion.

Solid storage

The storage of manure, typically for a period of several months, in unconfined piles or stacks. Manure is able to be stacked due to the presence of a sufficient amount of bedding material or loss of moisture by evaporation.

Dry lot

A paved or unpaved open confinement area without any significant vegetative cover where accumulating manure may be removed periodically.

Liquid/Slurry

Manure is stored as excreted or with some minimal addition of water in either tanks or earthen ponds outside the animal housing, usually for periods less than one year.

Uncovered anaerobic lagoon

A type of liquid storage system designed and operated to combine waste stabilization and storage. Lagoon supernatant is usually used to remove manure from the associated confinement facilities to the lagoon. Anaerobic lagoons are designed with varying lengths of storage (up to a year or greater), depending on the climate region, the volatile solids loading rate, and other operational factors. The water from the lagoon may be recycled as flush water or used to irrigate and fertilise fields.

Pit storage below animal confinements

Collection and storage of manure usually with little or no added water typically below a slatted floor in an enclosed animal confinement facility, usually for periods less than one year.

Anaerobic digester

Animal excreta with or without straw are collected and anaerobically digested in a large containment vessel or covered lagoon. Digesters are designed and operated for waste stabilization by the microbial reduction of complex organic compounds to CO2 and CH4, which is captured and flared or used as a fuel.

Burned for fuel

The dung and urine are excreted on fields. The sun dried dung cakes are burned for fuel.

Cattle and Swine deep bedding

As manure accumulates, bedding is continually added to absorb moisture over a production cycle and possibly for as long as 6 to 12 months. This manure management system also is known as a bedded pack manure management system and may be combined with a dry lot or pasture.

Composting - in-vessela

Composting, typically in an enclosed channel, with forced aeration and continuous mixing.

Composting - Static pilea

Composting in piles with forced aeration but no mixing.

Composting - Intensive windrow3

Composting in windrows with regular (at least daily) turning for mixing and aeration.

Composting - Passive windrowa

Composting in windrows with infrequent turning for mixing and aeration.

Poultry manure with litter

Similar to cattle and swine deep bedding except usually not combined with a dry lot or pasture. Typically used for all poultry breeder flocks and for the production of meat type chickens (broilers) and other fowl.

Poultry manure without litter

May be similar to open pits in enclosed animal confinement facilities or may be designed and operated to dry the manure as it accumulates. The latter is known as a high-rise manure management system and is a form of passive windrow composting when designed and operated properly.

Aerobic treatment

The biological oxidation of manure collected as a liquid with either forced or natural aeration. Natural aeration is limited to aerobic and facultative ponds and wetland systems and is due primarily to photosynthesis. Hence, these systems typically become anoxic during periods without sunlight.

a Composting is the biological oxidation of a solid waste including manure usually with bedding or another organic carbon source typically at thermophilic temperatures produced by microbial heat production.

ACTIVITY DATA - LIVESTOCK POPULATIONS

See Section 10.2 Livestock and Feed Characterisation for discussion on uncertainty of animal population and characterisation data.

ACTIVITY DATA - MANURE MANAGEMENT SYSTEM USAGE

The uncertainty of the manure management system usage data will depend on the characteristics of each country's livestock industry and how information on manure management is collected. For example, for countries that rely almost exclusively on one type of management system, such as pasture and range, the uncertainty associated with management system usage data can be 10% or less. However, for countries where there is a wide variety of management systems used with locally different operating practices, the uncertainty range in management system usage data can be much higher, in the range of 25% to 50%, depending on the availability of reliable and representative survey data that differentiates animal populations by system usage. Preferably, each country should estimate the uncertainty associated with their management system usage data by using the methods described in Volume 1, Chapter 3.

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