Current effluent/manure management
- draining that waste to a lagoon or pond to be digested by microorganisms to ‘clean’ it of organic solids, and burning off the methane that is released
- diverting the waste to a land application area
- putting solid waste to a storage pile for composting on a concrete pad or, rarely,
- using a wetland for treating the waste.
Benefits of using effluent/manure for bioenergyInstead of burning off the methane or using it as compost/fertiliser, dairy farmers can choose to capture the methane from lagoons/ponds (and turn that into electricity or heat), or use the waste to produce liquid fuel. Using dairy waste 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 economicsThe typical costs and viability of using covered anaerobic ponds for dairy waste [PDF 1.6 MB] from Australian and US experiences are described by Dairy Australia. If you are considering installing lagoons to capture and use the methane generated, refer to the detailed economic considerations/risks and recommendations outlined in Australian Pork Limited’s draft Code of practice for on-farm biogas production and use (piggeries) [PDF, 1.7 MB]. While it is written for piggeries, the following areas are relevant to dairies:
- selecting the right type of equipment
- laying a plant out
- best storage methods.
- 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.
Converting dairy waste to bioenergyDairy effluent/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 digestionDairy farmers already use anaerobic digestion to treat waste, so it is the most commonly used process 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.
- options for collecting effluent
- anaerobic, aerobic and facultative ponds
- investigating pond sites
- designing and constructing ponds
- desludging ponds
- nutrient budgeting
- occupational health and safety
- monitoring performance.
- designing and constructing a biogas plant
- being safe around biogas
- using and storing biogas
- training people
- managing risks
- managing flares, air, noise, odour and effluent
- operating and maintaining the 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 dairy 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.
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