Repository logo

Theses and Dissertations

Permanent URI for this collection

https://hdl.handle.net/10217/100514

Browse

Browsing Theses and Dissertations by Author "Archibeque, Shawn L., advisor"

Now showing 1 - 1 of 1
  • Thumbnail Image
    ItemOpen Access
    Dairy farm phosphorus recovery and re-use to reduce water quality risk and improve phosphorus cycling in agriculture
    (Colorado State University. Libraries, 2008) Massey, Michael Stanley, author; Archibeque, Shawn L., advisor; Ippolito, James A., committee member; Sheffield, Ron E., committee member; Davis, Jessica G., committee member; Peterson, Gary A., 1940-, committee member
    Phosphorus (P) is a limited natural resource, and its efficient use and cycling are important for the long-term sustainability of agricultural and industrial production. The over-application of P in dairy wastewater to fields, in addition to being inefficient, can lead to the degradation of water quality through P-induced eutrophication from agricultural runoff. This is especially true in areas where dairies and other livestock operations are increasingly concentrated around sources of fresh water such as rivers. Phosphorus recovery and re-use has the potential to reduce the amount of P applied to fields near the dairy while providing a useful, marketable, and easily transportable P fertilizer. This study evaluated the efficiency of magnesium (Mg) phosphate recovery on dairy farms using actual wastewater under field conditions, the nature of various recovered products including magnesium ammonium phosphate hexahydrate (struvite) and magnesium ammonium phosphate hydrate (dittmarite), and the feasibility of using Mg phosphates as fertilizers in slightly acidic and alkaline soil conditions. Dairy wastewater was treated using a cone-shaped fluidized bed reactor and two treatment processes which differed in the chemicals used for pH manipulation. The "conventional" process made use of hydrochloric acid and anhydrous ammonia for pH adjustment, while the "new" process used acetic acid and potassium hydroxide. The "new" process has the potential to produce a certified organic soil amendment with minimal modification to current organic production standards. After wastewater treatment, the recovered P products, along with other samples of recovered Mg phosphates including crystalline struvite and dittmarite, were examined with powder x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy. Finally, struvite, dittmarite, and a heterogeneous recovered product were applied in greenhouse fertilizer trials alongside commercial triple superphosphate (TSP) and certified organic rock phosphate (RP). The fertilizers' performance was tested at two application rates (45 kg ha- 1 and 90 kg ha-1 ) and two soil pH levels (6.5 and 7.6). The "conventional" treatment method removed 14% of the total phosphorus (TP) in the dairy wastewater, while the "new" method removed 9% of TP, along with 12% and 9% of the Mg for the conventional and new methods, respectively. Detailed analysis and characterization of the products, as well as recovered struvite and dittmarite, showed great variation among the chemical, microscopic, and macroscopic characteristics of the different types of recovered Mg phosphates. Fertilizer trials found that TSP and recovered struvite and dittmarite crystals increased plant P concentration in spring wheat (Triticum aestivum L.) grown in slightly acidic soil. At high soil pH, the recovered Mg phosphates increased plant dry matter production over the control and also performed similarly to TSP. The results of the current study indicate that P recovery through Mg phosphate precipitation is possible on dairy farms, but improvements must be made in removal efficiency and consistency of product characteristics. Furthermore, the resulting recovered phosphates may be useful as fertilizers in both acidic and alkaline soils.