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Going with the Flow
ON FARMS SUCH AS JOHN VRIEZE’S EMERALD DAIRY, every scrap of cow manure makes its way through a multi-stage process that plays out over the course of several weeks. Along the way, the foul stuff is broken down into an array of useful component parts that can be sold or reused on the farm.
The Pie
Average dairy cows produce between 85 and 120 pounds of manure a day, most of which is scraped through grates in the barn floors and swept off to a lagoon or holding tank.
Collection
Gravity carries manure through PVC pipes into a pit or a tarp-covered lagoon, where the manure is pumped into an underground anaerobic digester.
Break It Down
In the oxygen-free environment of an anaerobic digester, specialized bacteria slowly chew up manure, creating a series of byproducts.
THE BYPRODUCTS
Biogas
Methane gas from decomposing manure is captured and converted into usable forms of energy.
- Energy for farm operations
- Additional power that can be sold to utilities
Fiber & nutrient-rich biosolids
Rid of malodorous gases, these fibrous bits of partially digested manure can be turned into an array of products.
- Bedding for cows
- Fertilizers and soil additives
- Materials such as decomposable flowerpots
- Fiberboard
- Potential feedstock for cellulosic ethanol
- Potential source for bioplastics
Liquid effluent
Nutrient-rich concentrate-often called tea water- can be used to fertilize soils.
- Bioreactor fuel: Vrieze uses nutrients in water to feed a bioreactor that grows algae.
- Clean water: With additional processing, effluent can be sanitized potentially to the point of drinkability. Vrieze is awaiting a DNR permit to use the water he purifies with this technology.
Other biosolids
Clay-like solids can be made into pellets, which can be burned for heat or turned into nutrient-rich ash that is used as a fertilizer.