Current practices for nutrient removal or recovery of phosphorus focus on chemical precipitation technologies, where the recovered products are low-grade, slow-release, low-value land applied fertilizers. Three significant deficiencies re this process - the cost of recovery is greater than the market value as commercial P fertilizer; the land application of such materials perpetuates the current cycle of pollutant nutrient "leakage" into surface waters; and the approach is not viable to address non-point source pollution or the legacy P present in impaired water bodies. Hence, research was initiated based on commercially available Hybrid Ion Exchange Nanomaterials (HIX-Nano), which remove naturally occurring arsenic from drinking water, and apply it to remove, recover, reconcentrate, reuse and recycle soluble reactive phosphorus from diverse organic waste and wastewaters.
The infusion of high surface area nano iron oxide into conventional ion exchange resins, HIX-(Fe) Nano makes it possible to remove phosphates from wastewater and this has been proven by Lehigh U., ESSRE Consulting and others. Thus, residual dissolved phosphorus not chemically precipitated is captured and removed to supplement and complement the current P recovery processes or capture all of the dissolved P where nutrient recovery does not occur. The key to nutrient recovery is regeneration of the spent media and the conventional chemistry to achieve this is with a weak alkaline (caustic soda) rinse to desorb captured phosphate. The end product is a phosphate solution with a peak concentration of about 1600 mg/L. However, Na does not add any nutrient value whereas potassium hydroxide or ammonium hydroxide or both will add N and K to desorbed P and allow the custom formulation of N-P-K liquid products for hydroponic growers and greenhouse horticulturists. Moreover, when the source of concentrated N and P is livestock manures, there is a way to impart the micronutrients, Ca, Mg, Fe, etc. into the liquid formulations that will result in an N-P-K Plus product.
We know that making liquid fertilizer products from manures will help valorize manure treatment because hydroponic growers will pay a premium for a premixed N-P-K product and such an approach will limit the recycled nutrients "leakage" when direct land application is avoided. We also know that commercial synthetic fertilizer production is energy intensive and that any form of pollutant nutrient recovery/reuse will reduce GHG emissions via avoided fertilizer production.
We have also learned that we can do better in terms of manure valorization, if we take the view that even small amounts of soluble reactive phosphorus serve as a "biocatalyst" for intense and frequent harmful algae blooms in fresh and coastal waters. Hence, why not convert recovered nutrients into non-fertilizer products that are more highly valued in the marketplace. In mind are inorganic chemical catalysts that contain P and happen to be widely used in the Oil & Gas sector and Energy Storage sector, as follows:
1) Fluidized Catalytic Catalysts (FCC) - Phosphate-Zeolites (Oil Refineries)
2) Li-ion Battery Cathode Materials - LiFePO4 (Energy Storage)
Finally, we have also learned of recent advances in HIX-Nano technology, where the oxide of Nano Fe particles are replaced with that of Zirconium (Zr) particles. The HIX-(Zr) Nano resin exhibits enhanced P removal/regeneration potential and concurrent removal/recovery of pollutant nutrient N-Nitrate.
The attributes of the HIX-nanomaterial capabilities in manure treatment manifest in the advancement of 4Rs Nutrient Stewardship for fertilizers including land application of manure - Right type, Right place, Right rate and Right time - into “5Rs” of livestock manure management of the dissolved nutrient losses: Remove, Recover, Reconcentrate, Reuse and Recycle.
The HIX-Nano can be configured and operated with equal efficiency for wastewater streams with high concentrations of nutrients (direct manure treatment after liquid/solids separation) or dilute runoff concentrations or very dilute legacy concentrations in surface or groundwater sources. A commercial business model of HIX 5Rs treatment is established as a “hub” and “spoke” system. The spokes are all of the pollutant nutrient pathways to surface waters shown in Figure 1, adapted from Wind’s version (2007).
Thus, the application of HIX-Nano technology serves as a barrier to pollutant nutrient leakage from all sources. Hence, each farm, wastewater treatment plant, each urban stormwater runoff source within the watershed is a “spoke”. Spent HIX-Nano is transported to a nearby Regeneration Center (Hub) and “refreshed” media is sent (i.e., recycled) back to the source (Spoke) for continued removal of nutrients. At the Regeneration Center, the further processing of recovery via regeneration and reconcentration generates custom liquid fertilizer products and the aforementioned inorganic chemical catalysts and materials. Hence, the Regeneration Center also serves as a Product Distribution Center - an all-purpose Hub. Moreover, regardless of the location of the Hub within or outside the watershed, the recycling of nutrients in products that are not land applied fertilizer in essence “export” pollutant nutrients out of the watershed irrespective of the location of use. Add the quantification of recycled nutrients to manufacture specific formulations, the HIX-Nano Hub-Spoke model becomes an additional revenue stream to producers for nutrient trading credits, where these programs exist, and a useful tool to develop trading credit programs where they do not exist.
The potential to simultaneously Remove, Recover, Reconcentrate, Reuse and Recycle pollutant nutrients N and P from manures doubles the work ahead. For the reuse/recycle of fertilizer products confirmation is needed that N-P-K products will be free of impurities and commercially accepted after fertilization testing; similar confirmation path for N (NH4+ and N-NO3)-P-K products. Once established for reuse, HIX-Nano filters can be applied to the flushing discharge of spent fertilizer/nutrient solution for capture of N or P, thus closing the pollutant overload loop and recycling recycled pollutant nutrients.
For the reuse/recycle of treated water deficient in P when removing soluble P only, this needs to be tested for spray application onto soils oversaturated with P to assure compliance with the Nutrient Management Plans for N and P and thus safe reuse and reclamation of this water.
For the catalytic products thorough testing of composition (impurities), stability and performance testing needs to be carried out to gain acceptance as "green" catalysts or solution precursors for "green" catalysts. In either case, reconcentration must be carried out (thermal or mechanical) in a cost-effective way and in a way that carries out manure pathogen total destruction when the source of removed nutrients is from livestock manures .Similar research efforts are needed for battery cathode material manufactured from recycled pollutant P. Moreover for both catalysts and battery materials, if the final disposition of these materials is landfilling, the application of HIX-Nano on landfill leachate containing P will close the nutrient pollution loop by applying 5Rs treatment principles.
Lastly, to address the Food-Energy-Water nexus challenge the future plans will favor HIX-Nano application on manure digestate after liquid/solids separations. Nutrient recycling using HIX-Nano will also come into play with biomass to energy technologies such as Anaerboic Digestion and Hydrothermal Liquefaction, where the output is biofuels or biofuels and biochemical.
Ed Weinberg, PE, President, ESSRE Consulting, Inc.
Ed Weinberg can be reached at (215) 630-0546. Additional key people:
Dr. Mark Snyder, Lehigh U.; Dr. Raul Lobo, U of Delaware.
Dr. Arup K. SenGupta, Lehigh U.
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