The search for safer and sustainable management of animal manure is a global and topical challenge, in particular for the reduction of nitrogen (N) content. The use of natural adsorbents as zeolite-rich tuffs is recognized as a valid method to recover N, in the form of ammonium (NH₄⁺), from animal manure. While the scientific literature is rich in studies performed on synthetic solutions and using clinoptilolite zeolites as adsorbent, it lacks information concerning adsorption in real liquid manure and using other types of zeolite-rich tuffs (e.g., chabazite). This work aims at exploring the NH₄⁺ adsorption process from raw liquid swine manure, using a chabazite-rich zeolite tuff as adsorbent. The effects of temperature, contact time, and grain size have been assessed. Isotherms, kinetic models, and thermodynamic parameters have been investigated. Harkins-Jura isotherm correlates well with the observed data, in accordance with the formation of an adsorption multilayer. Kinetic data have been explained by intraparticle diffusion and pseudo-second-order models. In conclusion, the natural chabazite tuff has proven to be a valid material for NH₄⁺ adsorption from raw liquid swine manure. In particular, to reach the highest adsorption capacities and adsorption rates, it is recommended to use it at a fine particle size and with dosages < 6 %.

Using zeolite-rich tuffs for improving soil properties and crop N-use efficiency is becoming popular. However, the mechanistic understanding of their influence on soil N-processes is still poor. This paper aims to shed new light on how natural and NH₄⁺-enriched chabazite zeolites alter short-term N-ammonification and nitrification rates with and without the use of nitrification inhibitor (DMPP). We employed the ¹⁵N pool dilution technique to determine short-term gross rates of ammonification and nitrification in a silty-clay soil amended with two typologies of chabazite-rich tuff: (1) at natural state and (2) enriched with NH₄⁺-N from an animal slurry. Archaeal and bacterial amoA, nirS and nosZ genes, N₂O-N and CO₂-C emissions were also evaluated. The results showed modest short-term effects of chabazite at natural state only on nitrate production rates, which was slightly delayed compared to the unamended soil. On the other hand, the addition of NH₄⁺-enriched chabazite stimulated NH₄⁺-N production, N₂O-N emissions, but reduced NO₃⁻-N production and abundance of nirS-nosZ genes. DMPP efficiency in reducing nitrification rates was dependent on N addition but not affected by the two typologies of zeolites tested. The outcomes of this study indicated the good compatibility of both natural and NH₄⁺-enriched chabazite zeolite with DMPP. In particular, the application of NH₄⁺-enriched zeolites with DMPP is recommended to mitigate short-term N losses.

Notwithstanding the widespread use of natural and pre-exchanged zeolites for zootechnical effluent treatment, little attention has been dedicated to the variation in the chemical composition of the treated slurries, besides the effects on their NH₄⁺ content. This paper aimed at elucidating the compositional variations in terms of major and trace elements of a raw pig-slurry (PS) after three sequential treatment cycles (TC) with three different grain sizes of natural and Na-exchanged zeolite-rich volcanic tuffs (natural ZTs and NaZTs). A series of laboratory batch experiments revealed that all ZTs had profoundly influenced the final PS chemical composition. As expected, the NaZTs were more efficient in terms of NH₄⁺ removal than the natural ZTs, reaching almost 60% reduction of the initial content after three TCs. A parallel effect of this efficient removal was the remarkable increase in Na⁺. The Na-forms of ZTs led also to stronger competition with K⁺ ions, resulting in adsorption of this macronutrient and hence in a reduction of the fertilization value of the PS. In terms of heavy metals and other trace elements, all the treatments with ZTs had significantly increased the Li, Ba, Rb, Sr, Ga, and U content in the PS.

The use of natural sorbent geomaterials, like zeolitites (rocks containing > 50% of zeolites) is recognized as a valid method to recover N in the form of ammonium ions (NH4+) from Zootechnical Wastewaters (ZoWs).Using zeolite-rich tuff as N sorbent from ZoWs lead to varius advantages like the decrease in environmental impact of ZoWs (decreased N content) and the subsequent creation of a high-value soil amendment employable also in organic agriculture (NH4-charged zeolite-tuff).In order to understand the characteristics of NH4-charged zeolites (CZ) as sorbent, it is mandatory a deep investigation on their sorption dynamics when they react with ZoWs. Scientific literature is rich of studies about sorption in sintetic solutions (especially NH4CL) while it lacks studies about sorption in real ZoWs.The aim of this work was therefore to characterize the NH4 sorption dynamics of a chabazite zeolite tuff from swine manure. In particular, two grain sizes were selected, a micronized (< 125 µm, CHAµ) and a granular one (0.7-2.0 mm, CHAg). A series of batch experiments were performed to investigate the effects of temperature, contact time and grain size on sorption of NH4. Equilibrium data were fitted with appropriate isothermal models; kinetic models were also investigated to characterize the kinetik sorption reactions and the thermodinamic parameters like change in free energy (ΔG), enthalpy (ΔH) and entropy (ΔS).Results have shown a significant grain size effect with respect to the equilibrium loading (qe), with better performances for CHAµ in all the temperatures investigated; the isothermal data showed that the influence of temperature is less for CHAµ with respect to CHAg.The kinetic data differs from the two grain size investigated, in particular CHAg showed an initial external surface adsorption and macropore diffusion during the first 60 minutes of contact, then the diffusion occurs also inside the micropores. The Intraparticle Diffusion model (ID) for CHAµ showed that the diffusion in the macropores are much more fast than CHAg and the intercept indicates the formation of a boundary layer thicker than CHAg. Pseudo-second-order kinetic model well explained CHAg behavior but not that of CHAµ. Both grain sizes were well explained by Elovich equation wich is a model used to explain the sorption kinetics for energetically heterogeneous solids surfaces (as likely the surface of the zeolite-tuff employed).Thermodinamic data showed that the energy in the liquid-solid adsorption surfaces increased during adsorption (ΔH ˃ 0), thus the cation exchange reaction needs energy from the liquid phase.The free standard entropy change (ΔS) is also positive, indicating that the NH4 sorption is a directional process with no significant differences with respect to the tested temperatures and that the randomness at the solid-solution interface increased during adsorption.The negative values of Gibbs free energy (ΔG) indicates that the NH4 sorption is an exergonic process (spontaneous reaction).

The use of zeolite-rich tuffs is a valid method for recovering nitrogen from wastewaters. This paper aims at describing the NH₄⁺ adsorption processes of an Italian chabazite zeolite tuff used for the treatment of raw liquid swine manure. The effects of temperature, grain size and contact time were investigated. The isothermal analysis showed a multilayer adsorption behavior, well explained by the Harkins–Jura model, while kinetics was explained by pseudo-second-order, Elovich and intraparticle diffusion models. This study highlighted the complexity of the adsorption process from raw liquid manure, as well as the significant differences between tested particle sizes of the same zeolite tuff.

Both nitrogen (N) and phosphorous (P) are essential for life and their supply sustain the global population growth, thus, the question about “how correctly manage nutrient-rich wastewaters?” is a primary issue for many countries. The storage and the subsequent thoughtless use of these materials, as breeding farm and biogas plants wastewaters, has enormous impacts on the environment, causing eutrophication of water bodies and greenhouse gas emissions. The development of low-cost, low environmental impact and high yield treatment technologies is thus necessary to incentivize the circularity of resources, promoting their reuse and encouraging recycling in agri-food systems.The recovery of N and P by struvite precipitation (MgNH4PO4·6H2O) is a promising strategy, but these technologies are in general too expensive, energy-demanding, or they alter the treated wastewaters, making them not suitable for agricultural purposes unless additional treatments are carried out.This work investigates an innovative wastewater treatment processes that foresee the use of a natural chabazite-rich zeolitite (rock containing more than 50 % of zeolite minerals) in combination with struvite chemical precipitation. The adsorption batch (phase 1) is intended to improve the NH4+/Mg2+ and NH4+/PO43- molar ratios, to enhance struvite yield (phase 2) with fewer amounts of reagents required, thus to improve both the efficiency and the cost-effectiveness of struvite production. For the 1st phase, both natural zeolitite (NZT) and the K+-enriched (KZT) zeolitite were tested. KZT was intended to counteract any possible interference for struvite precipitation, which could instead happen with NZT due to the input of Ca2+ ions in solution.In the 2nd phase (struvite precipitation), 2 different Mg:NH4:PO4 molar ratios were tested, in particular a condition of NH4+ excess (MR1) and a condition with Mg2+ in excess (MR2).Treatments in which NZT (NZT-S) and KZT (KZT-S) were added prior to struvite precipitation were compared to a conventional struvite precipitation method without the use of zeolitites (CNTR).NZT-S_MR1 was found to be the most feasible strategy because of the highest NH4+-N removal efficiency, highest struvite precipitation efficiency (less waste of reagents), and less unwanted alterations of the treated wastewater. The precipitate obtained was 89.9 mass % composed of struvite with 3.5 % N, poor in hazardous heavy metals.The NH4+-N removal efficiency was in order: NZT-S > KZT-S > CNTR, with the highest reduction of 84.8 % recorded by NZT-S_MR1 and the lowest recorded by the CNTR (67.2 and 75.0 % for MR1 and MR2 respectively).The addition of a “zeolite phase” in struvite precipitation process thus represents i) a valuable method for improving the efficiency of struvite production ii) a method for saving chemical reagents in struvite production and iii) an efficient way to recover and recycling N in agriculture.