Mining Biosolids: A Case for Extracting Phosphorus

Phosphorus has been front and center in my attention this week, though not for the first time. Fifteen years ago I provided samples of Philadelphia’s product for seminal research sponsored by WERF (Project 99-PUM-2T) resulting in the Water Extractable Phosphorus test protocol, a linchpin to sustaining land application in some of our East Coast states. I was quickly reminded that phosphorus in water and soil is a very complicated topic. If you have any doubt, wrap your mind around the U. of Minnesota publication “Understanding Phosphorus Fertilizers.” Phosphorus management and regulation are looming large in the coming years: new regulations, new wastewater removal and extraction technologies, new soil management techniques, and new nutrient trading opportunities. These issues are captured in the WEF R&BC subcommittee “Phosphorus in Biosolids” fact sheet.

But it was the nexus of Phosphorus and Morocco that sparked my attention this week. I learned that Charlie Alcorn, my colleague who helps to assemble this weekly news, will be returning to the US soon from his nearly half year in Marrakech, Morocco, where he has been adding to his arsenal of world experiences, while also preparing Biosolids in the News. Perhaps you share my fascination with the factoid that Morocco is the locus of 80% of proven rock phosphate reserves in the world. This country may exert serious economic control over future food production; not in my lifetime, or perhaps even in yours. But someday.

The Morocco issue got me thinking. Just how big a deal could it be for US agriculture if all of the phosphorus in wastewater were recovered and deployed back to farming so that we could avoid becoming dependent on imports? To answer this question required a lot of time-consuming internet snooping.

According to the Fertilizer Institute, US farmers used 5 million tons of phosphate to grow crops, half of this use going to field corn. Importantly, over the last decade P demand has not grown, even though crop production has, because P utilization has become more efficient. US phosphate production is double the 5M ton amount, so the US is serious exporter to the world. But the P reserves in US mines (mostly Florida) are apparently not large, so this P demand needs to be watched. If this is the first time you are hearing of this coming crisis in phosphorus, check out Phosphate: A Critical Resource Misused and Now Running Low.

Wastewater from domestic and agriculture sources may be the key to what may someday be called “phosphorus security.”

Just how significant might wastewater plants be as a source of phosphorus? As elemental P, our biosolids typically has about 3.5% P on a dry weight basis (I used the Global Atlas of Excreta for this), and treatment plant effluent has a concentration of about 7 mg/L (I used an Idaho DEC publication for this estimate). From the NEBRA report of 2007, we have an inventory of 7,180,000 dry metric tons of biosolids annually from POTWs, and from a US EPA publication I learn that POTWs serve 75% of the US population and have a flow of 32 billion gallons daily.

Cranking through a buffluent. The total loading through POTWs of 5.1 pounds annually per capita jibes reasonably well with the estimate in dietary research ( a National Institutes of Health publication) of a human food input of about 1.5 pounds P coming annually from food, and double that coming from soaps, detergents and water (see a Wiki article on phosphoric acid). At least it is in a ballpark. (Please, anyone, feel free to double check me on this.)

When you use the factor of 5 pound per capita P (which is 12 pounds expressed as phosphate) through domestic sewage multiplied by the 300 million people, you have very nearly 2 million tons of phosphate. That is 40% of P fertilizer needs in US agriculture. And this is entirely without considering the potential for recovering phosphorus from all animal manure, which is a much larger number. With some imagination, manure and biosolids management could provide a sustaining cycle of P for US agriculture.

That is, if we should choose to commit to deploying technology to accomplish this feat at our nation’s POTWs. What is more, by extracting Phosphorus in this way, you will avoid all those nasty pathways that cause P release to lakes and estuaries, either from effluent or from land-applied biosolids. Can we afford to deploy such technology?

Phosphorus commands a good price, and, if its supply is limited in the future, the price should rise. Companies such as Ostara Nutrient Recovery Technologies, Inc., are counting on it, I am guessing. If you haven’t checked out Alibaba for all things weirdly for sale on the internet, do so now. You can buy anything, e.g. phosphorus fertilizer commodities. On the world market, phosphorus has a value today of about $0.25 to $0.75 per pound of available P. This may not sound like a lot on the individual person level (we each put out say $2 of P annually), but on a metropolitan scale it may be enough to help drive important changes to the way we design and operate our treatment plants.

Anticipating this evolution in municipal treatment, WEF prepared the document Moving toward Water Resource Recovery Facilitiesreleased just last October.

Buy it. This book is food for thought, and you need phosphorus to grow food.