Chief executive Gary Corbett told the Australian Dairy Conference in Geelong in late February that when it drew up a list of requirements such as efficient odour, pathogenic bacteria, fly, nitrogen and phosphorous control, reduced air emissions, ease and operation and return on capital through byproducts such as fertiliser, electricity, heat and emission credits, anaerobic digesters best fitted the bill.
Sand is removed, solids sized, flow equalised and other organic wastes mixed in before the barn scrapings are added to the digesters which can process two million gallons at a time. They provide the perfect environment through heating and mixing for bacteria to convert organic waste into methane-rich biogas.
Biogas scrubbers can then produce renewable energy in the form of electricity, natural gas and fuel but Corbett said all these options had their own challenges.
All electrical needs on the farms are supplied as well as selling electricity to the grid, with plans now underway to look at drying off carbon dioxide so 100% methane could be produced instead of the 60% level reached at present, which the farms could use themselves.
Last year Fair Oaks Farms’ 42 tractor-trailers started using gas to run on to deliver milk to processors, which he said took the equivalent of 2.5 million gallons of diesel off the road. They’re powered by 9 litre, 12l or 15l engines depending on loads carried and can travel 600 miles on one refill from the farms’ own fuel stations.
“But there’s no alternative if they run out of gas.”
The next step is for tractors used onfarm to be converted.
Nutrient recovery has moved from production of a low nutrient loam to a high nutrient liquid by use of sulphuric acid towers. This can be applied by pivot or injected into the soil. No nitrogen fertiliser is bought and a decanting and centrifuging process takes out phosphorous which can be directly applied through GPS technology so there’s no risk of overdoing applications.
Corbett said Fair Oaks Farms was now investigating removing ammonia from the digested manure to create ammonium sulfate. The potassium which remained in the water drawn off was valuable for growing algae. Duckweed, with a higher protein content than soy bean meal which cost US$450/tonne to buy, could also be grown and was more palatable to cows then algae.
Digested dairy manure solids could replace peat moss, a form of sequestered carbon long used to improve soils’ water retention. Reverse osmosis technology could mean drinking water could also be produced once algae had been grown.
While Fair Oaks Farms was looking at teaming up with others to increase natural gas production Corbett said it would keep the nutrient recovery part of the business for itself.
“It will pay terrific dividends in the future."
