Plants need nutrients, especially nitrogen and phosphorus. Phosphorus, taken from the Earth, could be facing a shortage unless scientists can find ways to recycle it.
Scientists at Tel Hai College and MIGAL Institute in Israel are working on a way to make phosphorus fertilizer from dairy wastewater, and they are taking the element from the wastewater using aluminum water treatment residue -- the leftovers that come from making clean drinking water, according to an announcement from the Soil Science Society of America.
"The material left after purification, called aluminum water treatment residue, is normally taken to a landfill to be buried," said Michael "Iggy" Litaor, who led this work. "We changed this material by mixing it with dairy wastewater rich with phosphorus and organic matter. We then found it can be just as good as common fertilizers."
The benefits of the practice could go beyond recycling phosphorus. Putting too much of the commercially available fertilizers on fields can hurt the quality of nearby water resources.
"Phosphorus is an important nutrient needed by most crops. However, it is a non-renewable resource," Litaor explained. "If we continue with the current rate of use, what we have may be depleted in 100-250 years. There are also side effects of too much fertilizer. Hence, scientists around the world are searching for simple and affordable ways to recycle the element without lowering crop yield."
In their study, Litaor and his team mixed the aluminum water treatment residue with dairy wastewater. Dairy wastewater comes from washing cow udders before milking and from cooling cows during hot days. It is high in phosphorus because of detergents used while cleaning the sheds that house the cows as well as due to runoff from cows' urine.
Chemical reactions between the phosphorus, aluminum and organic matter allow the mixture to become a possible fertilizer.
Litaor and his team then put the potential fertilizer on lettuce to see how well it worked. They found that it did just as well as common fertilizers.
"This experiment clearly showed that we can use aluminum refuse to recapture phosphorus from dairy wastewater and use it as fertilizer," he said. "We showed that the water treatment residue can take phosphorus from the wastewater and put it in soil that doesn't have much phosphorus. This may offset somewhat the mining of this non-renewable resource."
If this method of making fertilizer were to become widely practiced, Litaor sees the possibility of building plants next to dairies with lots of cattle, which would provide a large supply of phosphorus. A company could bring in the leftovers from water treatment systems to produce fertilizer. It could be used by large farms or sold to others.
He said the next step in this research is to look at the use of water treatment leftovers that contain iron, because many soils also lack this element. The scientists must further show that no unwanted materials such as hormones and antibiotics are in the fertilizer.
"I also want to find an investor who will support us taking this idea to the marketplace," Litaor added. "After many years of research on phosphorus in wetlands, streams and rivers, I decided to look for an efficient means to recycle the element using wastes we were already producing."
Read more about this research in the Soil Science Society of America Journal. This research was supported by the U.S.-Israel Binational Agricultural Research & Development Fund and the Israel Department of Agriculture.