The reverse osmosis system used for processing liquid manure is considerably bigger than the drinking water filter many people install under their kitchen sinks.
The two common products exiting all manure separation systems are solids and liquids. In most cases, both can be used as fertilizer without further processing. However, both can also be refined further to concentrate the nutrients or make them more environmentally friendly.
At a cost of $2 million, the Verkooyen manure brokerage company in Holland developed a large scale reverse osmosis plant capable of processing 22 million gallons per year. The facility includes two 440,000 gallon tanks and costs about $200,000 annually to operate, most of which goes to filters and a polymer additive.
Liquid is pumped from a separation plant to the reverse osmosis plant, where it runs through a paper filtration and a conventional reverse osmosis system. The reverse osmosis system is basically the same as that used by custom spray applicators to clean water in their sprayers.
The concentrate that doesn’t make it through the filters contains all the nutrients that aren’t in the pile of solids, mainly inorganic nitrogen and potassium.
The product contains 80 pounds of inorganic nitrogen (ammonia) per 1,000 gallons of liquid, which is valued at the going rate for a pound of nitrogen. It’s typically applied to potatoes at a rate of 2,000 gallons per acre, which equates to 160 pounds total nitrogen per acre.
The concentrate also contains 90 pounds of potassium (K2O) per 1,000 gallons of liquid. One important characteristic, however, is that it contains no phosphorus pentoxide (P2O5) at all.
The significance is that university research in Holland is convincing the government that the concentrate should no longer be classified as a manure product. Because of the reverse osmosis processing, it is far enough removed from manure that it should be classified simply as a fertilizer. If the change comes about, it will expand the possible uses of the concentrate and open up a lot of farm acres. This in turn will open up a lot of processing opportunities for livestock manure.
The other product coming out of the reverse osmosis facility is the one we normally think of as the main product of reverse osmosis, that being clean drinkable water. Water coming out of the Verkooyen plant runs through an ion exchange to remove any final bit of ammonia. It’s then released back into nature as pure, clean H2O.