Assessment of struvite and k-struvite recovery from digested manure
- Autores: Elena Tarragó Abella
- Directores de la Tesis: Maria Dolors Balaguer Condom (dir. tes.), Sebastià Puig Broch (codir. tes.), Maël Ruscalleda Beylier (codir. tes.)
- Lectura: En la Universitat de Girona ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Fabrizio Adani (presid.), Marta Coma Bech (secret.), Jesús Colprim Galcerán (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia y Tecnología del Agua por la Universidad de Girona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
During the last few centuries, humans have had an impact on the natural phosphate cycle due to the exponential increase of population, with its consequent increase in food demand, and its demand as a fertilizer. Phosphorus is obtained from guano (bird droppings) and phosphate rock (apatite), being a non-renewable resource. Many predictions stablish that the resource could be exhausted in 100-250 years, increasing its price every year. Therefore, the actions for the coming 10–25 years must focus on the recovery of phosphorus rather than its removal, reinforced by European policies. Thus, phosphorus could be recovered from renewable sources, such as manure.
In relation, manure has been applied directly to the soil as a fertilizer for many years, but its impact on the environment, especially on water quality, has forced to treat manure before its application, usually by removing the organics and nutrient content. However, manure has a high content of nutrients, which can be recovered, obtaining nutrients from renewable sources. In this PhD thesis, the recovery of phosphorus as struvite (MgNH4PO4·6H2O) and/or K-struvite (MgKPO4·6H2O) from manure are proposed. The recovery of nutrients (nitrogen, N; phosphorus, P; and potassium, K) from waste streams is considered to be an essential and significant breakthrough for assuring long-term and economical phosphorus supply, while recovering a valuable slow-release fertilizer.
The first two chapters of this PhD thesis are related to the properties of the product recovered from manure, as well as the size of the crystals recovered. First, a methodology is developed to control the particle size of struvite, based on the control of the up-flow velocity. The designed crystallizer (a combined air-lift reactor with a settler) allows to assess the viability of using the up-flow velocity as a control parameter for the growth of struvite particles, first in batch tests and following, in continuous mode to enhance the growth phase. Moreover, it is demonstrated that the up-flow velocity determines the minimum theoretical equivalent diameter that can be recovered. Thus, the up-flow velocity is proven a successful controlling parameter of particle size to the customers’ requirements for fertilizer application.
Following, struvite recovery from digested manure is studied, as well as the properties of the product recovered. It was demonstrated that struvite could be recovered at the optimal pH of 8.5, although co-precipitation of other products (i.e. Mg3(PO4)2) was observed, without affecting the fertilizer properties. However, manure is a complex stream for struvite recovery, and a challenging technology due to the high content of solids, which many authors identify as one of the main limitations. Therefore, a study to determine the role of solids in struvite nucleation and growth, as well as the effect of suspended solids in the properties of the product recovered, was developed. It was demonstrated that solid particles not only did not inhibit struvite formation, but they acted as nuclei enhancing heterogeneous nucleation, and favored the aggregation and/or agglomeration of struvite crystals.
Finally, the last chapter of this PhD thesis aims to provide a methodology to recover the most limited macronutrient in soils (potassium) as K-struvite from swine manure. At present, the recovery of potassium struvite is nascent, and its crystallization from waste streams is at the proof of concept stage. Therefore, a theoretical approach was first conducted with Minteq software, and later modelled and experimentally adjusted in batch tests, while determining the effect of pH and temperature. Thus, the viability of the process was proven recovering K-struvite directly from digested manure after a solid/liquid separation and a nitrogen removal through Anammox.
This PhD thesis aims to bring innovation and insights on the recovery of essential macronutrients (potassium, phosphorus and nitrogen) for plants’ growth from waste streams. Specifically, the sustainable recovery of fertilizers (i.e. ammonium and/or potassium struvite) from swine manure.
