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.
Benefits of using manure for bioenergyInstead 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.
Evaluating the economicsAn assessment of methane capture and use from the intensive livestock industry [PDF 1.9 MB] published by AgriFutures Australia:
- 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.
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 bioenergyFeedlot 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.
Anaerobic digestionAnaerobic 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.
- 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.
- Suitable types of anaerobic digesters, yields of biogas, and costs/benefits [PDF 215 KB], compared to conventional alternatives, are detailed in Chapter 8.1 of Dairy Australia report from 2008.
- Instructions about how to use a pond for anaerobic digestion of effluent [PDF 540 KB] are given in a fact sheet from Dairying for Tomorrow program fact sheet.
- Read about supply, infrastructure requirements, costs, incentives and managing risks of anaerobic digestion ponds [PDF 1.4 MB] in a Dairy Australia fact sheet.
- Australian Pork Limited’s draft Code of practice for on-farm biogas production and use [PDF, 1.7 MB] focuses on on-farm, covered anaerobic digestion in Australia, based on international best practice, and is very detailed about logistics of setting up and running a plant.
MicroorganismsPutting 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 methodsHeat 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.
ADI Systems Asia Pacific Ltd
83 Castle Street, Dunedin, New Zealand, 9058
83 Castle Street, Dunedin, New Zealand, 9058
Phone: 1 800 751 806