Canadian research examines removal of phosphorus from manure
November 30, 1999 by David Schmidt
Since nutrients are brought onto a dairy farm in the form of feed and fertilizer, an equivalent amount of nutrients needs to be removed from the farm to make it sustainable.
Since nutrients are brought onto a dairy farm in the form of feed and fertilizer, an equivalent amount of nutrients needs to be removed from the farm to make it sustainable. Milk, the main product leaving a farm, does not take enough of those nutrients to balance the equation. That is particularly true in British Columbia’s Fraser Valley, where farms as large as 3,000 cows are packed onto small acreages and fed a diet rich in imported hay and grain. The manure is then spread onto the limited farmland, increasing, even overloading, nutrients in the fields and leading to a vicious cycle. Homegrown corn and other forages become increasingly rich in phosphorus, leading to cow health issues. Excess phosphorus also leaches out of the field, causing eutrophication of nearby watercourses. At the same time, the world is running out of raw phosphorus, an essential ingredient in fertilizer.
The answer seems all too obvious – remove phosphorus before the manure is applied to the land and use it to create fertilizer for areas not rich in cow manure, such as the fields that originally supplied the imported hay and grain.
That, in a nutshell, is the premise behind some leading research and development being conducted at the University of British Columbia (UBC). After several years of testing in the UBC engineering labs, UBC civil engineering professors Victor Lo and Don Mavinic and their associates are about to build a pilot-scale recovery system at the UBC Dairy Education and Research Centre in Agassiz, B.C. The system would remove phosphorus from the manure and convert it into struvite (ammonium magnesium phosphate) crystals.
Lo, Mavinic and DERC director Jim Thompson call their system a “logical, integrated approach” to manure management that would prevent pollution and include efficient solids destruction. The latter would produce both salable nutrients and bioenergy.
“Our dream is to have a system on the farm which removes some of the energy and nutrients,” says DERC director Jim Thompson.
Mavinic says they are already using the patented system to produce struvite from sewage waste at a plant in Edmonton and are building plants at seven plants in the U.S. and one in England.
“Now we intend to produce it from dairy and hog manure,” he says, noting there is far more potential to produce struvite from animal waste than from human waste.
Lo notes a herd of only 50 cows produces 2.75 tonnes of manure per day at 15 percent total solids. Given its nutrient content, that’s an annual total of 5.3 tonnes of nitrogen, 1.1 tonnes of potash, 3.4 tonnes of phosphorus plus lesser amounts of calcium and other minerals.
“Humans excrete three to four grams of phosphorus/day but cows and pigs excrete 50 to 100 grams/day. The herd at DERC (about 300 milking cows plus young stock and replacements) excretes as much phosphorus as all the people in Whistler,” Mavinic states, pointing out that while there are six to seven billion people in the world, there are 10 times as many cows.
Under the UBC system, manure first goes through a liquid/solids separator. The liquid goes through an anaerobic digester to create bioenergy, then through an advanced oxidation process in a type of microwave oven to stabilize the nutrients and organic particles. Finally, those particles go through a crystallization process to produce struvite.
Using this process, Lo projects the waste from 50 cows would generate over $12,000 a year – $6,400 from the methane/biogas and $6,000 from the struvite.
He claims the treated effluent will meet standard discharge criteria, whereas the solids can be composted to generate additional revenue.
“Our pilot plant will be a first in the world,” Mavinic says.
Both NSERC (Natural Sciences and Research Council of Canada) and Agriculture and Agri-Food Canada (AAFC) have provided funding support for the project. Mavinic has also received an NSERC Synergy Award for Innovation for his groundbreaking research.