Livestock manure may seem like a relatively "green" form of crop fertilizer, but unfortunately it's full of phosphorous that pollutes waterways when it's carried off the land in runoff water. That's why scientists have developed a phosphorous-removal system known as MAPHEX.

An acronym for MAnure PHosphorus EXtraction, MAPHEX was created by scientists from Pennsylvania State University and the US Department of Agriculture's Agricultural Research Service. Designed to treat cow manure from storage tanks or pits on dairy farms (although it's also compatible with swine manure), it utilizes a three-step process.

First, an auger press and a centrifuge are used to separate the liquid and solid components of the manure, and the solids are removed. Next, iron sulfate is added to the remaining liquid manure, which converts the dissolved phosphorous in it to a solid form, which can be filtered out. Finally, the liquid is filtered using diatomaceous earth.

When tested on 150- and 2,700-cow dairies, MAPHEX successfully removed about 98 percent of the phosphorous from manure, plus 93 percent of the solids. Unfortunately, however, the price of diatomaceous earth makes the technology financially impractical in its current form. Running costs for the system work out to about US$750 per cow per year.

"We anticipate that refinement of the process and beneficial uses of the solids removed from the manure — such as for plant bedding, compost and fertilizer — will improve cost-efficacy considerably," says lead scientist Prof. Alex Hristov. Such refinements could include devising a method of reusing the diatomaceous earth, or simply replacing the filtration stage with another centrifuge.

Penn State and the USDA are now looking at licensing the technology, most likely to a large agricultural or waste-processing company.

Source: Penn State