There are people out there studying global cycling and reserves of elements. Carbon cycling is well known, from climate research, but there are headlines now and again about trace elements that we might run out of — tantalum, neodymium, germanium, gallium — that play a role in industrial products or processes. But the really scary numbers are for phosphorus, if you believe the USGS estimate of current reserves: peak production by 2030 and exhaustion of the global reserves by 2100. Remember, phosphorus (along with nitrogen) is responsible for revolutionizing our agricultural yields in the mid-1900s, and farmers throughout the developed world use it heavily.
The reason why I think phosphorus scarcity is a good thing, is that there’s another obvious source of phosphorus in the world: human and animal wastes. When the price of newly mined phosphorus gets high enough, projects to recover phosphorus from wastewater treatment plants or feedlot manure piles will be economical. This type of “recycling” phosphorus is, in my humble opinion, more sustainable in the long term than the typical “use it and throw it away” thinking we have about, well, everything we use.
It’s refreshing to see that my line of thinking is shared by those in the Encina Wastewater Treatment Plant in Carlsbad, California. They performed a pilot study last year and have begun evaluating the cost-effectiveness of implementing a full-scale system to recover phosphorus in little pellets to be used as fertilizer. The pellets are composed of phosphorus, nitrogen, and magnesium in a mineral called “struvite”. Researchers at Eawag have found that struvite precipitates more readily from urine than mixed wastes, and they have therefore pushed for “source separation”. (Side note: It wasn’t the best thing to be the subject of their urine collection system while I worked there.)
Think about some of these trends, though. Wastewater treatment has historically been about meeting some minimum level of treatment so that wastes could be dumped into our waterways. Between the biogas recovery and fertilizer production, there is a shift towards viewing wastewater as a potential resource instead of a waste stream. Any way to recycle these “wastes” back into productive use will lead to not only greater sustainability for wastewater treatment, but also larger profits for the treatment plants. I will post more about this when it comes to the Los Angeles water balance, but it is worth noting that most of what exits a wastewater treatment plant is water. If we could recycle this, too, wastewater treatment could be a huge boon to the energy, agricultural, and water needs of our society. Now that’s impressive.