Emergency Livestock Disposal Home

Project Executive Summary

Project in Detail

• Background
• Objectives
• Composting System Tested
• Research Methods
  • Construction
  • System Performance
  • Cover Material
  • Air Quality
  • Water Quality
  • Biosecurity
• Preliminary Results
• Project Sponsors & Contacts

Draft Guidelines for Emergency Cattle Mortality Composting

RESEARCH  METHODS

Air Quality

As illustrated in the figure above, the porous material covering the carcasses allows air to move into the pile, and it also allows gases produced by decomposition (some of which are odorous) to move out.  As these odors migrate through the outer aerobic layers of the pile, many are adsorbed and broken down in a process called in-situ biofiltration.  Biofiltration requires relatively slow air movement, as well as adequate moisture and biological activity in the outer layers of the pile.  Without biofiltration, odors can escape, possibly disturbing neighbors or attracting pests.  Several methods are being used to quantify the duration and intensity of downwind odors resulting from the emergency composting process.

Field Scentometry

The original research plan called for weekly odor measurements in the field during the first month following construction of composting test units.  Measurements were made at distances of 100 and 500 feet downwind from the test units using a scentometer (shown in use below), a portable device that can be used to aid the human nose in estimating odor intensities in the field. 

Experience using the scentometer during the 1st year of the project revealed several problems.

• In many cases no odor could be detected at distances of 100 and 500 feet downwind from the test piles. 

• When downwind odors could be detected, it was nearly impossible to tell which test unit(s) were the primary source of the odors.

• The cover materials (cornstalks, silage, straw) themselves each released odors of varying intensity which made it difficult to assess odors caused by the carcass degradation process. 

Olfactometry and Odor Characterization

Sampling Strategy and Methods

Weekly samples are collected from the surface of each of the composting test units during the first month following construction.  By capturing odorous air directly from the surface of the composting test units, this eliminates uncertainty regarding which cover materials are responsible for which odors. 

In addition to collecting samples from the surface of the composting test units, samples also are collected from stockpiles of cover material (silage, straw, cornstalks).  This sampling strategy facilitates identification and comparison of odors attributable solely to the cover material, and those caused by decay processes within the composting piles.

 

Samples are collected from the sides of  each test unit using an equilibrium chamber (shown below), a device that captures gases emitted from the pile surface and minimizing sample dilution caused by natural air movement over the piles. 

GGases that accumulate inside the equilibrium chamber are pulled through tubing into an odor-free Tedlar sample bag located inside an air-tight collection box (shown below).  A small battery-powered pump (setting on top of collection box) creates a vacuum inside the collection box which causes gases in the equilibrium chamber to flow into the Tedlar bag.

When the bag is filled (shown below), gas valves on the bag are closed, and the bags are transported to the olfactometry laboratory for odor intensity measurement and odor characterization.

Odor Threshold Determination (odor intensity)

Olfactometry is a scientific method of odor quantification using a panel of trained odor evaluators.  In the olfactometry laboratory, trained odor panelists sniff samples that have been drawn from the Tedlar bags and diluted with an odorless gas.  Panelists begin with samples that have been so highly diluted with odorless air that no odor is perceived.  Dilution levels are then gradually reduced until the odors become barely perceptible to the panelists.  This dilution level (ratio of the volume of odorless air to volume of sample) is known as the "odor threshold".  The more intense an odor is, the greater the amount of dilution at which odor is just barely perceptible.

Odor Characterization (odor offensiveness)

Simply because an odor is present, does not necessarily mean that it is offensive.  The pungent odor of silage, for example, is often the predominant odor near composting test units that are constructed with silage, but it is not considered to be an offensive odor by many, particularly those familiar with agriculture..  

To evaluate the type as well as the intensity of odors released from emergency cattle composting operations, an untrained group of panelists is asked to sniff and describe samples that have been diluted to just above the threshold level. Participants in the "odor characterization" sessions are given a standard list of odor descriptors and asked to select and report those that apply to each sample. 

Chemical Analysis

In addition to odor threshold  and characterization testing, samples also are subjected to chemical analysis to determine concentrations of two common odor-causing substances, hydrogen sulfide and ammonia. 

In Brief

- Downwind field scentometry observations were unsuccessful in detecting odor, identifying which test units are the odor source, and in distinguishing between odors caused released by cover materials and those caused by the composting process.

- Field scentometry has been replaced with weekly odor sampling, at the surface of each composting test unit (AND at the surface of cover material stockpiles), during the initial month following construction.

- Analysis of odor samples in the olfactometry lab permit quantification and comparison of  odors emitted by composting units, and odors from the cover materials alone.

- Samples also are evaluated for odor offensiveness, and for ammonia and hydrogen sulfide content.