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Phosphorus Extraction from Wastes: The Key to Phosphorus Problems?

By Nick Reckinger of FEECO International, Inc.

As one of the key nutrients in growth, phosphorus is critical to maintaining food security and life on Earth. This has scientists worried over the dwindling mineralogical reserves from which we mine this valuable nutrient source. Interestingly, the world faces a problem of too much phosphorus in other areas; excess phosphorus from nutrient runoff is contaminating waterways and causing toxic algal blooms and dead zones throughout the world.

As the world looks to feed a growing population, demand for this life-giving nutrient is not likely to waver. This has many looking at the opportunity to use this resource in a more sustainable way. Processing of organic wastes can help alleviate pressure on finite resources while diverting phosphorus from waste as runoff back into the soil where it belongs.

The Case for Recycling Phosphorus

Organic wastes are a renewable resource, so it’s easy to see why the potential to derive even a small portion of our phosphorus requirements from this growing category of wastes is so attractive. One recent study looked at three primary phosphorus waste streams (human food waste, human excreta, and animal manure) and concluded that it would take only 37% of the phosphorus available in these existing waste streams to support the yearly U.S. corn crop’s phosphorus requirements.

Recycling phosphorus from organic wastes would not only provide the world with a much needed renewable source of phosphorus, but it would also help to mitigate the environmental problems that result from phosphorus runoff. Dead zones, or hypoxic areas that kill off fish and other organisms in waterways as a result of insufficient oxygen, have largely been blamed on nutrient runoff, with agriculture being a major contributing source.

Although restoration is an option, it is costly, making the prevention of dead zones much more feasible. And while there are many contributing factors to runoff (proximity to waterways, soil type, distance to bedrock, etc.), minimizing the potential for runoff to occur through proper fertilizing techniques and nutrient management best practices will likely be a primary endeavor in protecting waterways.

Two materials in particular have seen a surge of interest for their nutrient recovery and reuse potential: biosolids and manure.

Biosolids

Biosolids, also commonly called wastewater treatment sludge, are the materials left over from the wastewater treatment process. While various methods exist for the disposal of biosolids, disposal methods such as landfilling or incineration usually disregard the valuable nutrient content that biosolids hold. Additionally, disposal is increasingly being seen as unsustainable from a long-term perspective. And with increasing regulation around land application, municipalities are in need of a workable solution.

Manure

Similarly, regulation around the land application of manure has also been increasing, putting a growing strain on farms dealing with the massive amounts of manure produced by the agricultural norm of large-scale farming operations. Farms are also limited in the distance they can haul their manure to land apply it, due to its high moisture content, which makes transportation a costly expense.

Simultaneously, farms are purchasing chemical fertilizers to provide much of their nutrient needs, while the value of the manure they land apply is not often fully realized due to runoff, resulting in an inefficient imbalance of nutrient resources for crop production.

Granulation: Key to Recycling Phosphorus?

Phosphorus recovery from organic wastes is still in its infancy as an industry, with much research under way, and still more to be done. As a fertilizer industry veteran, we have been among those on the forefront of this issue, having developed process solutions and systems around nutrient recovery from organic wastes for decades. We use our expertise in granulation to transform difficult to handle, moisture-laden materials into a dry, premium-grade granular product that exceeds the EPA’s 503 regulations for a Class A Biosolid. This, in combination with significantly reduced odor, eases many of the issues surrounding land application.

In addition to these benefits and reduced transportation costs, there is ample opportunity for customized formulations and nutrient blends through granulation. As such, granulation can serve as a means to producing a marketable product that can supplement the purchase of additional nutrients for both municipalities and large-scale farms, all while reducing waste management costs.

Reduced Runoff through Granulation

While granulation offers many benefits to the farmer and/or municipality, the granulation of organic wastes into fertilizer or soil amendment products ultimately aids in the runoff prevention effort; because granulation produces a dry product, there is less potential for runoff to occur. Unlike the moisture-rich raw materials, a dry product does not add moisture to the soil, which can increase the likelihood of runoff occurring.

Furthermore, a granular product makes following a nutrient management program much easier and more efficient. The N:P ratio is often imbalanced as a result of fertilizing to meet nitrogen demands and inadvertently over-applying phosphorus. Granular products allow the N:P ratio to be carefully controlled to suit the nutrient profile of the land where it will be applied, significantly reducing the opportunity for runoff to occur. Granules also allow for easier and more accurate dispensing; soil receives only what it needs, further reducing the chance for excess phosphorus to leach from the soil.

An Overview of the Granulation Process

The granulation process is different from one source material to the next, with necessary pre-conditioning methods also differing. However, in general, granulation works by taking the nutrient-rich cake left over from the digestion process (or the wastewater treatment sludge remaining after the water treatment process), and mixing it in a pug mill.

Additives and/or nutrients can be included here to customize the formulation. The pug mill thoroughly mixes the feed materials (along with process recycle) to form agglomerates. These granules are then dried in a rotary dryer, where the tumbling action further rounds them. A cooling step reduces the temperature of the product, yielding a product that will hold up to handling and storage, but still deliver nutrients in a timely manner upon application.

As each source material differs in how it will respond to granulation, pilot testing is required to work out process variables and scale up the process to full-scale production.

FEECO Vice President and General Manager, Lee Hoffmann, who is also a member of the Brown County Phosphorus Committee, had this to say on the matter: “The importance of utilizing our organic wastes to their fullest potential is becoming increasingly critical as the world hosts a growing population. Add to that that some of our resources are essentially being wasted as runoff, and it’s easy to see why this approach makes sense. As a fertilizer industry veteran and an expert in the transformation of wastes into value-added products, we are well positioned to provide solutions to this market.”

Conclusion

Phosphorus is an invaluable nutrient to life on Earth. Maximizing available resources, while taking the pressure off of finite phosphate reserves is essential for long-term, sustainable phosphorus management.

Considering that renewable phosphorus resources in the form of manure and biosolids are often going to waste and even contributing to environmental issues, the potential these organic wastes hold to meet sustainable phosphorus goals is an incredibly valuable opportunity.

 

Opinions expressed here do not necessarily reflect those of the Sustainable Phosphorus Alliance.

About FEECO

FEECO provides feasibility testing, process and product design, and custom processing equipment for organic waste materials, including biosolids and manure. From idea, to complete process solution and custom equipment, FEECO offers capabilities in transforming organic wastes into value-added, marketable products. FEECO is based out of Green Bay, WI. In addition to their custom process equipment and systems, they offer a unique testing facility where they can conduct both batch and continuous, pilot-scale tests to simulate commercial production conditions.