Growing Interest in Low-Cost Phosphorus Removal

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Friday, March 05, 2010

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Growing Interest in Low-Cost Phosphorus Removal

CANADA - Phosphorus-based livestock manure application limits are fuelling interest in low-cost phosphorus removal technology, writes Bruce Cochrane.

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A new low-cost technology for recovering phosphorus from liquid swine manure is expected to interest Manitoba farmers facing new phosphorus-based limits on the application of livestock manure fertilizer.

The University of Manitoba's Faculty of Agricultural and Food Sciences is participating in a project in which two 500-litre settling tanks are being used to recover magnesium ammonium phosphate, or struvite, from liquid hog manure for use as phosphorus fertilizer.

PhD candidate, Joe Ackerman, explains phosphorus in its soluble form can combine with magnesium and ammonium to form a crystal that can be used as a slow release fertiliser.

Joe Ackerman – University of Manitoba:

This crystal dissolves slowly.

It's got ammonia in it as well as phosphate in it and magnesium is not a problem with most soils.

We set up a pilot scale reactor which was basically two 500 litre tanks and that was operated this summer pumping supernatant into it and dosing it and then collecting this precipitate that came out.

That was quite successful.

We were able to remove about 70 per cent of total phosphate from the liquid that we ran through. That's with the overnight settling. We'd like to bring that time down.

The product, once it was dried down and analysed, it came out as about six per cent total phosphorus and a little more than six per cent total nitrogen and about four per cent potassium. It's a reasonable fertiliser.

There are areas we'd like to perfect and develop though and that will be this coming summer.

Mr Ackerman notes only a small portion of the phosphorus in liquid swine manure is in the soluble form but during anaerobic digestion the acidity increases, causing more phosphorus to become soluble and available.

He says bench-scale studies will evaluate the proportion of phosphorus that can be made soluble under anaerobic digestion.