Producing biomass: Biomass types: Animal waste: Feedlot waste
Manure from feedlot cattle or pigs can be converted into biogas (a renewable energy source consisting mostly of methane and carbon dioxide), liquid fuel and/or nutrient-rich solids. Biogas can be burnt to generate electricity and heat, upgraded into a transport fuel (biomethane) and can yield other useful products.

Current feedlot manure management

Dung that dries before being collected is handled as a semi-solid or solid, and called manure. Most feedlot owners collect waste from feed and pen areas regularly and then it is:
  • spread on pasture or cropping country as a natural fertiliser
  • stockpiled for spreading (as quickly as possible)
  • composted on concrete pads by adding straw to the manure.
What Australia does with its animal waste is described in the 2008 report: Animal waste management country specific profile: Australia [PDF 60 KB].

Benefits of using manure for bioenergy

Instead of using the manure for compost, feedlot owners can capture methane from the decomposing manure (and turn that into electricity or heat), or use the waste to produce liquid fuel.

Using feedlot manure to create bioenergy has many benefits, such as:
  • reducing the amount of waste that needs to be disposed of
  • recovering energy from waste
  • reducing odour problems
  • reducing potential for groundwater contamination
  • giving a use to waste that previously had little or no market or environmental value
  • reducing water use by reusing washing water for the plant/lagoon
  • generating income from waste/diversifying income sources
  • moderating the impacts of commodity prices
  • killing harmful bacteria, flies and weed seeds normally in and around manure
  • converting organic nitrogen into a form available to be used by plants.
Some of these benefits are described in the paper Livestock waste-to-bioenergy generation opportunities [PDF 322 KB, page 7941–2].

Evaluating the economics

An assessment of methane capture and use from the intensive livestock industry [PDF 1.9 MB] published by RIRDC:
  • explores the viability of methane capture and use systems for the Australian intensive livestock industry
  • reviews existing manure methane systems from intensive livestock industries operating within Australia and overseas
  • presents technologies that are best suited for capturing methane in the Australian context.
Some projects will only be viable if they also sell the dewatered, digested solids produced as a by-product.

Large, intensive livestock operations may be able to partner with nearby coal-fired power stations or cement works for co-combustion (where the waste would be burned with coal).

Using animal waste for biogas is the subject of 14 international case studies described in: The generation of biogas on-farm using animal and dairy waste [PDF 752 KB]. Cost-benefit analyses and technical specifications are covered.

There are many options to dispose of or treat effluent from intensive livestock industries, with different costs [pages 22–29], which are described in this RIRDC report published in 2008.

How much manure is produced?

Detailed data about how much manure feedlot cattle produce (based on live weight and stocking density) is available from this report from the Department of Agriculture, Forestry and Fisheries.

Feedlots generated over 10 million tonnes of manure a year (at 2008), and effluent from feedlots may offer immediate potential to harvest methane to produce biogas for electricity [PDF 60 KB, page 5–6]. There are over 120,000 rural enterprises in Australia with production systems that provide greenhouse gas sources, such as manure.

Converting feedlot manure to bioenergy

Feedlot manure can be turned into bioenergy through two processes.
  • Biological processes
    • uses anaerobic processes or microorganisms
    • produces biogas, liquid fuel and nutrient-rich solids
  • Thermochemical processes
    • uses heat or chemicals
    • produces biogas, hydrocarbon fuel (bio-oil) and charcoal.
These processes are described in more detail on a Victorian Department of Primary Industries webpage, and in much more detail in a paper about bioenergy opportunities from livestock waste [PDF 322 KB].

Anaerobic digestion


Anaerobic digestion is one of the most common processes for producing bioenergy. It uses simple bacteria to break down waste in oxygen-free conditions (anaerobic) to produce biogas and nutrient-rich solids.

You can use biogas, solids and cleaner waste water for:
  • heating or electricity, by burning biogas in a boiler, heater or engine
  • natural gas, by further processing the biogas
  • fertiliser, by using the ‘undigested’ solid remains
  • irrigation, by using the water separated from the solids.
Anaerobic digestion is possible using:
  • a ‘lagoon’ or pond that holds effluent, covered with an airtight cover that collects biogas
  • ‘complete mixed’ digestion in heated above- or below-ground tanks full of effluent
  • ‘fixed film’ digestion in a tank packed with materials that the microorganisms grow on
  • ‘plug-flow’ digestion in heated underground tanks, where effluent is put through semi-regularly.
Effluent quality and volume, temperature, pH, and time all affect how much biogas is produced by anaerobic digestion, and can be carefully controlled to increase production.

Although the following resources are for dairy and piggery operations, they offer useful advice:

Microorganisms


Putting waste in specialised tanks/containers with microorganisms produces hydrogen [PDF 183 KB], which can be burnt for heat/electricity.

The microorganisms include:
  • algae, using photosynthesis
  • bacteria, using fermentation in lit conditions
  • bacteria, using fermentation in the dark.

Thermochemical methods


Heat or chemical processes also exist for converting waste to energy: pyrolysis, gasification and direct liquefaction. Two of these may be suitable for your feedlot waste:
  • Pyrolysis: heating waste to very high temperatures without oxygen to form solid (biochar), liquid (bio-oil) and/or gases (syngas) depending on the speed and temperature of the process. The gases and compounds in the liquids can be used to generate bioenergy.
  • Gasification: heating waste to high temperatures with a limited supply of oxygen so it is only partly burnt and produces syngas and a small amount of biochar.

Contacts

ADI Systems Ltd

ADI Systems

ADI Systems (Asia Pacific), 50 Yeo Street, Neutral Bay, NSW 2089
Phone: 1.800.751.806 (toll free)

asiapacific@adi.ca
Duncan Veal

Meat & Livestock Australia

North Sydney NSW 2060,
Phone: 02 9463 9366

dveal@mla.com.au
Liz Hamilton

Victorian Bioenergy Network

Geelong Victoria 3220,
Phone: 03 5235 8324

bioenergyinvictoria@gmail.com