Natural zeolitites in combination with struvite precipitation technology for the recovery of nutrients from agricultural wastewaters

  1. Galamini, Giulio
Dirigida por:
  1. Massimo Coltorti Director/a
  2. Giacomo Ferretti Director/a

Universidad de defensa: Universidad de Cádiz

Fecha de defensa: 13 de mayo de 2022

Tribunal:
  1. Costanza Bonadiman Presidente/a
  2. Jesús Gómez Enri Secretario
  3. Sergio Calabrese Vocal
  4. Katharina Maria Keiblinger Vocal

Tipo: Tesis

Teseo: 745934 DIALNET lock_openTESEO editor

Resumen

The World Health Organization has emphasized the importance to start turning the perception of “nutrient-rich wastewaters”, from “wastes” to dispose of, to “resources”, useful for plant nutrition, but, despite this, 80% of municipal wastewaters globally produced are still discarded in the environment, without having been subjected to any treatment. On the other hand, the thoughtless use of excreta and derived materials for fertilization practices threatens the environmental systems, leading to pollution, soil degradation, and water contamination. The question of “how to efficiently dispose of nutrient-rich wastewaters” or, in other words, “how to improve the recycling of nutrients in agro-ecosystems”, remains thus a crucial topic for the sustainability of human activities. A promising technology consists in the precipitation of struvite crystals for the recovery of both nitrogen (N) and phosphorous (P). But, even if these processes are starting to scale up at industrial levels, the unbalance between the struvite components in wastewaters, as Mg2+, NH4+ and PO43-, remains one of the main issues for its implementation. The possibility to recover the excess of NH4+ before struvite precipitation may potentially increase the efficiency of struvite technologies. Within this thesis work, it was investigated a wastewater treatment process that uses natural zeolitites (rocks containing more than 50% in zeolite minerals) in combination with struvite precipitation, for the removal and recovery of N and P, in the form of struvite crystals and NH4+-N-enriched zeolitites. Before the wastewater treatment experiment, the NH4+-N adsorption properties of the applied zeolitite were characterized (experiment A) in terms of isotherms, kinetic models, and thermodynamic parameters, from livestock wastewater (pig manure), and two different grain sizes have been investigated: a granular zeolitite and a micronized one. Even if both showed interesting features, the micronized zeolitite demonstrated to reach higher adsorption capacities, with better temperature stability. This material was thus chosen for experiment B, where different treatment strategies have been investigated for the recovery of struvite from anaerobically digested wastewater. The investigated treatments were composed of two distinct steps: the 1st phase (zeolitite adsorption batch) tested the natural micronized zeolitite and a modified one (K+-enriched) for the reduction of NH4+-N loads. In the 2nd phase (struvite precipitation), 2 different Mg:NH4:PO4 molar ratios were tested, in particular, a condition of NH4+ excess (MR1) and another with Mg2+ in excess (MR2). Both these conditions were described in the literature as the best for struvite precipitation. The outcomes of experiment B suggested that the most feasible practice consists in the use of the natural zeolitites, in combination with the MR1 condition. This treatment showed indeed the highest nutrient removal efficiency, highest efficiency in struvite precipitation, and less alteration of the treated wastewater. The precipitate obtained was 89.9 mass % composed of struvite, poor in hazardous heavy metals, with 3.5% of nitrogen. The materials obtained, as the N-charged zeolitites, the struvite precipitates and the nutrient-depleted wastewater may potentially be used in agriculture, for crop nutrition, and/or as soil amendment. Even if the treatment described within this thesis work used livestock wastewaters and a derivate one, the methodology proposed may be appliable to any other nutrient-rich wastewater, as municipal ones.