Climate change arising from mindless release of greenhouse gases poses an existential risk to human welfare globally, but in the wringing of hands over what to do, save some attention to the mindless release of the element phosphorus, as it is forever lost as a macronutrient and as it damages aquatic ecosystems. As a carbon tax may be necessary to compel corrective human behavior, so too may a phosphorus tax be necessary, which could transform wastewater treatment.
Phosphorus has been in the news lately, perhaps because I watch for all things “P.” I learned from one news report that yet another hypothesis has been explored to explain the high concentration of phosphorus on the Earth’s crust, one that points to the solubilization of P during a period of intense electrical storm activity at Earth’s creation (Lightning Might Have Sparked Early Life on Earth). The Atlantic story from February, “Humanity is Flushing Away One of Life’s Essential Elements: we broke phosphorus,” reminds us that the explosive rise of humanity on Earth over the past 200 years arose not exclusively with discovery of how fossil carbon could be deployed for mechanical energy, but also from the discovery of fossil sources of phosphorus that could boost agricultural production and, hence, sustain the era of industrialization. I have also keyed in on the role of phosphorus in fresh and brackish waters in promoting excess growth of cyanobacteria, the source of HABs, or harmful algae blooms, which can kill fish, birds, pets and, not incidentally, people (Time for bold action to protect Lake Erie from toxic algal blooms: George A. Elmaraghy). It is this last news commentary that holds the most importance to us biosolids professionals. The article points to the growing consensus that excess total soil phosphorus from organic amendments is responsible for dangerous HABs. This issue with phosphorus, with no clear solution, is just plain taxing to read.
Compared to carbon in the political and social marketplace of environmental ideas, phosphorus management is woefully undervalued. Yet, it shares some interesting parallels. The unrestrained release of carbon dioxide from fossil fuel use is akin to the unrestrained release of phosphorus from our agricultural and wastewater management systems. Both releases pose major environmental consequences.
Scientists and economists have spent decades delving deeply into ways of reducing the unrestrained release of carbon. They look to internalize the external costs of carbon emissions and to compel conversion to a non-fossil fuel global economy using incentives consistent with our global economic system. Broad agreement has formed around the idea that the most promising control measure is a carbon tax. Even with this agreement, carbon taxation can barely get out of the starting gate (see Carbon Tax, Its Purpose, and How It Works). Its simpler cousin, carbon emission trading, is a voluntary marketplace for carbon emission trading. In that system, a ton of carbon equivalent is valued at about $20 (Value of Carbon Market Update 2020), but this is hardly a value that would sustain major innovation in the energy sector, hence the need for a tax. A recent economic study suggested a tax of $50 per ton of carbon dioxide equivalent (Harnessing the Power of Markets to Solve Climate Problems). NOAA estimates that the global emission of carbon in 2019 was 10 gigatons, which corresponds to a HUGE potential tax needed for economic leverage to solve a HUGE environmental challenge.
Phosphorus is also a huge environmental challenge. Phosphorus flows from its source in mines, to farms, to soil, to food, and then to its ultimate release to sinks in river sediment and oceans, where it is lost to any possibility of beneficial recovery, even though phosphorus reserves essential for agricultural production may ultimately prove finite. The flow of P is almost entirely uni-directional, in the same manner as the carbon in fossil fuels goes from mines eventually to the atmosphere where it is irrecoverable. What is the voluntary marketplace for phosphorus emissions? What does the research on a phosphorus tax say about pricing? There is no market and there is no economic research. Agronomists, farmers, and environmental regulators have been struggling to understand and to manage the flow of phosphorus onto and off of farmlands without the benefit of such marketplace or research.
Persons smart in the study of sustainability have called attention this gap in the phosphorus issue. The authors of Reconsideration of the Planetary Boundary for Phosphorus write of “the contrast between large amounts of P needed for food production and the high sensitivity of freshwaters to pollution by P runoff. At the same time, some regions of the world are P-deficient, and there are some indications that a global P shortage is possible in coming decades. More efficient recycling and retention of P within agricultural ecosystems could maintain or increase food production while reducing P pollution and improving water quality.” This observation would clearly include recycling the phosphorus that is captured in biosolids. Similarly, in the article Phosphorus use-efficiency of agriculture and food system in the US, the researchers observe “Improving yields of livestock and crop cultivation without additional phosphorus input and reducing household food waste are shown to be effective measures to improve life-cycle phosphorus use-efficiency.” They call for “a concerted effort by all entities along the life-cycle for efficient use of phosphorus.” That effort would naturally include us biosolids practitioners.
If a program in the wastewater profession exists for a “life-cycle for efficient use of phosphorus” I am having problems finding it. The “big-thinkers” in the study of P know this, too. In Our Losing Phosphate Wager, the writer concludes: “most of that phosphate-containing organic sludge is treated and sterilized … But it is not recycled for use in chemical fertilizers… Let’s invest in methods of recycling this massive amount of phosphate waste.”
Why is it the case that so much phosphorus in wasted? Current regulatory requirements and economic equations would have such “concerted efforts” and investments seem nonsense. The paper Cost effectiveness of phosphorus removal processes in municipal wastewater treatment pegs the cost of phosphorus removal from wastewater at $42 to $61` per pound of phosphorus, in comparison to the commodity value of phosphorus at about 12 cents per pound. P removal is evaluated at treatment plants for value other than fertilizer value. The 2019 WEFTEC paper “A Review for Practitioners of 10 years Industry Experience with P Recovery Technologies” frames the primary drivers as operational and maintenance savings, such as reduced polymer usage, improved cake solids, dependable permit compliance, and reduced struvite deposits in tanks and pumps. The imperative for phosphorus extraction technology has a noble aspect as resource recovery, but not a monetary or regulatory imperative. A Wikipedia article on “peak phosphorus” duly notes “research on phosphorus recovery methods from sewage sludge has been carried out in Sweden and Germany since around 2003, but the technologies currently under development are not yet cost effective, given the current price of phosphorus on the world market.”
Yet in the Mid Atlantic region, high phosphorus concentrations in biosolids may well pose a threat to the goal of biosolids recycling. Environmental consequences of phosphorus releases have grown in this region, particularly in the harm to the Chesapeake Bay and Great Lakes “sinks.” The Great Lakes Restoration Initiative (GLRI) confers “a priority to reduce phosphorus runoff” for reducing HABs, harmful algae blooms (Preventing HABs) Approaches for reducing phosphorus releases to the Chesapeake Bay are extraordinarily rife with economic, technical and political complexity, as implicit in the Chesapeake Bay Foundation’s Phosphorus Management description of Maryland’s Phosphorus Management Tool, and by the Pennsylvania DEP’s proposal to introduce within its biosolids general permit aspects of phosphorus control.
These regulatory initiatives stem from work by soil and nutrient scientists that connect the dots between total soil phosphorus and phosphorus loadings in streams. Recent journal articles discuss these complex connections. Many agricultural regions have soils with excess phosphorus. In the report A statewide assessment of the impacts of phosphorus-index implementation in Pennsylvania we learn that “The soils data indicated that statewide about 50% of samples had P levels in excess of those required for optimal crop production.” These soils pose a risk for watersheds: The report The Challenges of Managing Legacy Phosphorus Losses from Manure-Impacted Agricultural Soils explains that “soil test phosphorus (STP) concentrations that far exceed agronomic optimum… from long-term manure applications often serve as a source of P via a gradual release of dissolved P in runoff or leaching events. These losses of “legacy P” from manure-impacted soils are difficult to control and are linked to water-quality degradation in sensitive water bodies, like the Chesapeake Bay.” Scientists have studied the option of stopping additional P additions, as might occur from ceasing use of manure and biosolids. The report Agronomic and environmental phosphorus decline in coastal plain soils after cessation of manure application found that “over the 15 years, the M3-P across manure treatments declined steadily at 7.7–15.3 mg kg-1 yr-1. ….sufficient P will persist for decades as indicated by the abundance of agronomic and environmental P pools.”
If organic residual sources of carbon, nitrogen, and micronutrients from manures and biosolids are to be used in agricultural systems, the sources will by necessity also contain phosphorus. Are there ways to reduce the potential for phosphorus impacts? One major way to reduce potential P release from biosolids is to precipitate the biosolids-borne phosphorus as an iron or aluminum mineral, as can be verified by the Water Extractable Phosphorus test (see Assessment of plant availability and environmental risk of biosolids-phosphorus in a U.S. Midwest Corn-Belt Soil). But for other technologies able to control P release from organic residuals, their deployment is spotty and their demonstrated cost-effectiveness at the farm level have not yet shown. Nutrient management planners surveyed in Pennsylvania recommended “PA-PI [Pennsylvania Phosphorus Index] should more strongly discourage manure application to fields with insufficient ground cover, near subsurface drainage and surface inlets, and during winter. In addition, the PA planners said the PA-PI should more strongly encourage soil conservation practices such as no-till, use of cover crops, and vegetated buffers” (Nutrient management planners’ feedback on New York and Pennsylvania phosphorus indices). Since much manure and biosolids are surface applied as part of a no-till conservation plan, one study (Best management practices to minimize agricultural phosphorus impacts on water quality) suggested: “ … the one-time plowing of P-stratified soils may reduce the long term loss of P in surface runoff as long as plowing induced erosion is minimized, providing landowners an additional option in keeping these soils in production under P-based nutrient management strategies.” Yet, but this approach is not regularly used, nor is it officially sanctioned. The report One size does not fit all: towards regional conservation practice guidance to reduce phosphorus loss risk in the lake erie watershed concludes “however, the application of specific conservation practices in certain environments (e.g. no‐till with surface application, cover crops) may not be effective and can even lead to unintended consequences.”
We biosolids managers have a conundrum in our approach to phosphorus. In the mid-Atlantic region, many of the farmlands to which biosolids might beneficially and economically be delivered have soils with phosphorus levels already adequate for crop growth. We also have technologies available that can capture a significant proportion of the phosphorus, removals of 40 percent or better of total loads of phosphorus received in the effluent, and in a form that can be delivered to farms and soils in need of phosphorus. But we do not have a driver in place that can match the cost of phosphorus extraction at our treatment facilities to the benefits of reducing phosphorus release to the environment or of returning phosphorus to agricultural regions that need it. Purely hypothetically now, and for the sake of argument, what if a phosphorus tax were applied to the discharge of phosphorus to our publicly owned sewers, the proceeds of which would be directed to farmers or to wastewater operations or to both? Phosphorus is an issue which, like climate change, resists a compartmentalized, “one-size-fits-all” solution. We need innovative approaches and we need financial resources. Indeed, the situation with biosolids phosphorus is taxing.