Current and Potential Use of Citrus Essential Oils.

Since the Middle Ages, citrus essential oils (EOs) have been widely used for their bactericidal, virucidal, fungicidal, antiparasitical, insecticidal, medicinal and cosmetic proprieties. Also nowadays, they find important applications in pharmaceutical, sanitary, cosmetic, agricultural and food industries. The best method to extract EOs from citrus plant tissue is steam distillation because of a variety of extracted volatile molecules such as terpenes and terpenoids, phenol-derived aromatic components and aliphatic components. In vitro physicochemical assays classify most of them as antioxidants

Un metodo fisico per la lisi delle cellule microbiche del suolo basato su alte pressurizzazioni con CO2

La biomassa microbica del suolo (BMS), una piccola ma altamente dinamica frazione della sostanza organica del suolo, svolge un ruolo chiave nell’ecosistema suolo e pertanto le sue dimensioni e la sua attività sono determinanti per la fertilità e la qualità del suolo[1]. Perciò, lo studio e la caratterizzazione della MBS sono essenziali per la valutazione della qualità del suolo. I due metodi ancora ampiamente utilizzati per la determinazione della MBS sono la fumigazione-incubazione (FI) e la fumigazione-estrazione (FE)[2][3]. Entrambi i metodi si basano sulla fumigazione dei campioni di suolo con cloroformio (CHCl3) per lisare le cellule microbiche e determinarne il materiale citoplasmatico. L'uso del CHCl3, tuttavia, solleva diverse criticità, prima fra tutte la sua tossicità per l'uomo e per l'ambiente[4] e inoltre, diversi autori hanno dimostrato che il CHCl3 non è completamente efficiente nel lisare le cellule microbiche[5][6][7]. Pertanto, lo scopo di questo studio è stato quello di sviluppare un nuovo approccio per lisare le cellule microbiche, che possa essere più affidabile e sicuro per l'ambiente rispetto alla fumigazione. Il metodo proposto, chiamato CO2HP (CO2 - High Pressure), si basa su un'elevata pressurizzazione del suolo con CO2, seguita da una rapida depressurizzazione. Per mettere a punto il metodo CO2HP, sono state testate diverse combinazioni di pressione e durata di pressurizzazione e, per valutare la capacità del metodo CO2HP di lisare le cellule microbiche del suolo, è stato effettuato un confronto con i metodi classici FI e FE. I risultati dimostrano che il nuovo metodo CO2HP è più efficiente del CHCl3 nel lisare le cellule microbiche del suolo. La combinazione più efficiente è risultata essere 600 psi per la pressurizzazione della CO2 e 32 ore di durata.Soil microbial biomass (SMB), a small but highly dynamic pool of living organic matter, plays a key role in nutrient cycling, and therefore its size and activity are crucial determinants of soil fertility and quality[1]. For these reasons, the study and characterization of soil microbial biomass (SMB) are essential for soil quality assessment. The two methods still widely used for SMB determination are chloroform incubation (FI) and chloroform extraction (FE)[2][3]. Both methods rely on the ability of chloroform (CHCl3) to lyse soil microbial cells so as to determine the cytoplasmic material. The use of CHCl3, however, raises several critical issues, chief among them that it is toxic to humans and the environment[4]. In addition, several authors have shown that CHCl3 is not completely efficient in lysing microbial cells[5][6][7]. Therefore, the aim of this study was to develop a new approach, possibly more reliable and environmentally safe than the CHCl3-based method, for lysing soil microbial cells. The proposed method is based on high pressurization of the soil with CO2, through the use of a steel reactor, followed by rapid depressurization through gas release. Hereafter, we will call this approach CO2HP (CO2-High Pressure). To set up CO2HP method, different combinations of pressure and duration of pressurization were tested, and to evaluate the ability of the CO2HP method to lyse soil microbial cells, a comparison was made with the classical FI and FE methods. The results indicate that the new CO2HP method is more efficient than CHCl3 in lysing soil microbial cells. The most efficient combination was found to be 600 psi for CO2 pressurization and 32 hours duration

A high CO2 pressure-based method for soil microbial cells disruption

Soil microbial biomass (SMB), a small but highly dynamic living organic matter pool, plays a pivotal role in nutrient cycling and thus its size and activity are major determinants for soil fertility and quality. Indeed, SMB performs more than 90% of the key functions in the degradation and recirculation of organic matter and nutrients[1]. Moreover, due to its nature, SMB quickly responds to biotic and abiotic factors, thus becoming a sensitive indicator of most disturbances and changes occurring in the soil ecosystem[2]. For all these reasons, the study and characterization of soil microbial biomass (SMB) is essential for the assessment of soil quality. The two methods still widely used for determining microbial biomass are the chloroform-fumigation incubation (FI) and chloroform-fumigation extraction (FE) methods[3][4]. Both methods are based on the ability of chloroform (CHCl3) in lysing soil microbial cells, so that nutrients held by them can be then determined by different techniques. The use of CHCl3, however, rises several critical issues. Not to be forgotten, it is an alkyl halide toxic to humans and the environment[5]. Furthermore, CHCl3 has been shown not to be very efficient in lysing the microbial cells. Badalucco et al. [6][7] demonstrated that amounts of phenol-reactive C and anthrone-reactive C represented higher proportions of total extractable C after CHCl3 fumigation than before, thus arguing that some non-biomass sugars were solubilized during the 24 h fumigation. Later, Badalucco et al.[8], showed that the efficiency of CHCl3 in lysing microbial cells appeared to be inversely related to the stability of soil aggregates, due to its lower diffusion in more clayey soils. Also, Toyota et al.[9] by using a sandy loam soil showed that approximately 10% of bacterial colony forming units survived a 5-day CHCl3 fumigation. This percentage could have been much higher when fumigating a clayey soils. Finally, Alessi et al.[10] demonstrated that significant concentrations of CHCl3 were adsorbed, and thus retained, by the clay fraction of soils. Therefore, the major problem in the indirect assessment of the microbial biomass inhabiting soil still persists and consists in that there is not yet a highly efficient, and possibly environmentally safe, disruption technique of microbial cells for subsequent extraction and quantification of intracellular matter. Thus, the purpose of this study was to set up a new method, possibly more reliable and environmentally safe compared to the CHCl3 based one, for lysing soil microbial cells. The method proposed here is based on a remarkable pressurization of the soil with gaseous CO2, through the use of a steel reactor, followed by rapid depressurization via the gas release. Hereafter, we call this approach CO2HP (CO2 – High Pressure). With increasing pressurization, it is expected that the microbial cells are gradually penetrated and filled with the gas. After being saturated by the gas, the applied pressure is suddenly released so that the absorbed gas will rapidly expand inside the cells; therefore, the cells are mechanically ruptured like a popped balloon. This technique, which was first reported by Fraser in 1951[11], has been implemented by several workers, applying it on pure microbial cultures as a novel sterilization/inactivation method for heat-sensitive materials like foods[12][13] but never in soil. One agricultural and one forest soil were used to set up the CO2HP method. The ability of the new method in lysing the soil microbial cells was assessed by determining, in soils pressurized or fumigated by chloroform, either the CO2-C released during 10-d incubation at controlled conditions or the KCl extractable C. In order to evaluate the most efficient pressure and time of pressurization, soils were pressurized with CO2 at pressures ranging from 400 to 800 psi and from 2 to 32 hours as duration. Results indicate that the new CO2HP method is more efficient than CHCl3 in lysing soil microbial cells. The most efficient combination was found to be 600 psi for CO2 pressurization and at 32 hours as duration. Bibliography [1] Singh, J. S., & Gupta, V. K. (2018). Soil microbial biomass: a key soil driver in management of ecosystem functioning. Science of the Total Environment, 634, 497-500. [2] Laudicina, V. A., Dennis, P. G., Palazzolo, E., & Badalucco, L. (2012). Key biochemical attributes to assess soil ecosystem sustainability. Environmental protection strategies for sustainable development, 193-227. Springer, Dordrecht. [3] Jenkinson, D. S., Powlson, D. S., 1976. The effects of biocidal treatments on metabolism in soil, a method for measuring soil biomass. Soil Biology and Biochemistry, 8, 209- 2013 [4] Vance, E. D., Brookes, P. C., Jenkinson, D. S., 1987. An extraction method for measuring soil microbial biomass C. Soil Biology and Biochemistry, 19, 703-707 [5] Lionte, C., 2010. Lethal complications after poisoning with chloroform—case report and literature review. Human & Experimental Toxicology, 29(7), 615-622. [6] Badalucco, L., Nannipieri, P., Grego, S., Ciardi, C., 1990. Microbial biomass and anthrone-reactive carbon in soils with different organic matter contents. Soil Biology and Biochemistry 22, 899-904 [7] Badalucco, L., Gelsomino, A., Dell'Orco, S., Grego, S., Nannipieri, P., 1992. Biochemical characterization of soil organic compounds extracted by 0.5 M K2SO4 before and after chloroform fumigation. Soil Biology and Biochemistry 24, 569-578. [8] Badalucco, L., De Cesare, F., Grego, S., Landi, L., Nannipieri, P., 1997. Do physical properties of soil affect chloroform efficiency in lysing microbial biomass? Soil Biology and Biochemistry, 29 (7), 1135–1142 [9] Toyota, K., Ritz, K., Young, I.M., 1996. Survival of bacterial and fungal populations following chloroform-fumigation: effects of soil matric potential and bulk density. Soil Biology and Biochemistry 28, 1545-1547. [10] Alessi, D.S., Walsh, D.M., Fein, J.B., 2011. Uncertainties in determining microbial biomass C using the chloroform fumigation–extraction method. Chemical Geology, 280 (1-2), 58-64 [11] Fraser, D., 1951. Bursting bacteria by release of gas pressure. Nature, 167 (4236), 33-34. [12] Nakamura, K., Enomoto, A., Fukushima, H., Nagai, K., Hakoda, M., 1994. Disruption of Microbial Cells by the Flash Discharge of High-pressure Carbon Dioxide. Bioscience, Biotechnology, and Biochemistry, 58 (7), 1297–1301 [13] Garcia-Gonzalez, L., Geeraerd, A.H., Spilimbergo, S., Elst, K., Van Ginneken, L., Debevere, J., Van Impe, J.F., Devlieghere, F., 2007. High pressure carbon dioxide inactivation of microorganisms in foods: The past, the present and the future. International Journal of Food Microbiology, 117, 1-2

Relief and calcium from gypsum as key factors for net inorganic carbon accumulation in soils of a semiarid Mediterranean environment

In semiarid environments, the total inorganic carbon (TIC) in soil may contribute to the total carbon (C) pool more than the total organic C pool (TOC), thus playing a key role in storing atmospheric CO2. However, due to the different origin pathways of soil carbonates, not all of the TIC pool can be accounted for CO2 sequestration. Indeed, the inorganic C can be accounted for a net sink of CO2 only when calcium (Ca2+) forming carbonates originate from non-carbonate minerals (atmogenic inorganic C, AIC). The aim of this study carried out in a gypsiferous area is to investigate the dissolution of Ca2+ that comes from gypsum (CaSO4⋅2H2O) in the formation of soil atmogenic carbonates and to quantify the different forms of inorganic C pools to understand their role in storing CO2 in comparison to the TOC pool. To this end, five soil profiles were studied along a hillslope in a gypsiferous afforested area. Soil samples were analysed to determine their main chemical properties, as well as Ca2+, Sr2+, and the 87/86Sr isotopes ratios in different soil fractions. Ca2+ that comes from gypsum, which contributes to the formation of atmogenic carbonates, ranged from 0% to 63%; the remaining percentage resulted from the parent material or other sources (e.g., aeolian dust). The distribution of Ca2+ in soils depended on the relief and the distance of the soils from gypsum outcrops. The accumulation of AIC in soil developed on Holocene deposits reached a maximum accumulation of 16 kg m− 3 in the first meter of depth. The average Sr2+/ Ca2+ ratio in primary carbonates was 0.333, whereas it was 0.192 in secondary carbonates, thus suggesting that different sources contribute to Ca2+ in both carbonate types. Consequently, the Sr2+/Ca2+ ratio of soil carbonates could be a useful indicator of the presence of secondary carbonates. Overall, results suggest that gypsum plays a key role in the net accumulation of inorganic C in the soil, contributing to store atmospheric CO2. Finally, considering that the AIC pool was lower than the organic C pool, the latter was by far the most important element in fixing atmospheric CO2 in the soils of the semiarid Mediterranean environment that were surveyed

Zeolites for the nutrient recovery from wastewater

To meet the growing food demand of the world population, excessive use of chemical fertilizers is occurring to improve soil fertility and crop production. The excessive use of chemical fertilizers is not economically and environmentally sustainable. Indeed, from one hand, due to the increasing demand of fertilizers is rising their costs whereas, on the other hand, the accumulation of fertilizers in wastewaters is altering the homeostasis of the ecosystems thus causing serious damages to human health [1,2]. The recovery of nutrients, such as nitrogen (N) and phosphorus (P), from wastewaters is a good option to counteract both economic and environmental issues raised by the excessive use of fertilizers [3]. Adsorption is among the most widely used methods for nutrient recovery from wastewaters due to its efficiency and simplicity. The choice of appropriate adsorbent materials is a key issue for ensuring high performance and low costs of the process [4]. Over the years, several materials have been studied to absorb nutrients from wastewaters. Zeolites, both natural and modified, have attracted great attention due to their relevant specific capacity, selectivity, safety, and stability [5]. However, considering that in municipal effluents the inorganic P exists as the anionic forms of dihydrogen or monohydrogen phosphates (H2PO4 − and HPO42−, respectively) and N in both cationic (ammonium, NH4+) and anionic (nitrate, NO3−) form [6], natural zeolites can be only used for the direct recovery of NH4+

Soil bioindicators and weed emergence as affected by essential oils extracted from leaves of three different Eucalyptus species

The widespread use of synthetic herbicides has resulted in herbicide-resistant weeds, altered ecological balance and negative effects on human health. To overcome these problems, efforts are being made to reduce the reliance on synthetic herbicides and shift to natural products. Essential oils (EOs) extracted from plants have been demonstrated to have potential herbicide activity. EOs, composed by volatile organic compounds and characterized by a strong odor, are used in the cosmetic, pharmaceutical and food industries as they are thought to be safe compounds for humans, animals, and the environment. EOs extracted from Eucalyptus leaves have antimicrobial, antiviral, fungicidal, insecticidal, anti-inflammatory, anti-nociceptive and anti-oxidant effects. Moreover, in vitro studies have demonstrated that they have inhibitory effects on germination of seeds of many crops and weeds. The aim of this work was to evaluate the in vivo effects of EOs extracted from Eucalyptus leaves on both weed emergence and biochemical soil properties. Furthermore, since the diverse species of Eucalyptus have shown to have different biological activities, EOs were extracted from three Eucalyptus species (E. camaldulensis, E. globulus, E. occidentalis). Fresh leaves were collected from an afforested area near Piazza Armerina (province of Enna, Italy) and their EOs extracted by hydrodistillation. Soil samples were collected from the topsoil (<5 cm) of an Inceptisol within the experimental farm of the University of Palermo, air-dried and sieved at 1 cm. Five hundred grams of this soil were filled in each of 20 aluminum pots (10×20 cm). The soil samples were brought up to 100% of the water holding capacity (WHC) by adding 150 mL of tap water, followed by 70 mL of tap water containing 8 mL L-1 of one of the three extracted EOs. This experimental test was repeated for remaining two EOs. Fitoil was used as emulsifier at a concentration of 0.1% (v/v). The control consisted of the soil treated as the EO treatment but with Fitoil only. The soils were incubated in greenhouse conditions. After 2 days, the 100% WHC halved and then it was kept to this level (50% WHC) by watering soil daily. The experiment was carried out in quadruplicate. After one month the soil were brought up to 100% of WHC, plant biomass and height of germinated weeds and soil biochemical properties were evaluated. This work reports the results and discuss them

Phytotoxic potential of Citrus essential oils on weed species

Environmental constraints of crop production systems have stimulated interest in alternative weed management strategies. In fact, the continued use of synthetic herbicides may threaten sustainable agricultural production and result in serious ecological and environmental problems, such as the increased incidence of resistance in weeds to important herbicides and increased environmental pollution and health hazards. Public awareness and demand for environmentally safer herbicides with less persistence and less contaminating potential make searches for new weed control strategies. Citrus Essential oils are generally used in the cosmetic, medicinal, and food industries, and are thought to be safe compounds for humans, animals, and the environment. EOs can be extracted by hydro distillation and cold pressing. The two methods are based on different procedures. Hydro distillation is carried out with a Clevenger-apparatus that conducts the distillation process by boiling, condensing and decantation to separate the EOs. The cold pressing consist of crushing and pressing the peels thus leading to the formation of a watery emulsion. Then, the emulsion is centrifuged to separate out the EOs. Since no external substance are needed, this process ensures that the resulting EOs retains all their properties. The allelopathic and phytotoxic effects of EOs obtained from other species and their potential use for weed management has been well documented. The objectives of this study were to evaluate in vitro the phytotoxic effects of Citrus EOs (Citrus sinensis, Citrus limon and Citrus reticulata) extracted by hydro distillation and cold pressing on main weed species (Amaranthus retroflexus, Portulaca oleracea., Echinochloa crus-galli, Avena sativa). For all EOs six concentrations were tested (0.5, 1, 2, 4, 8, 12) μl/ml and 5 repetitions with 20 seeds each (for dicotyledons) or 10 repetitions with 10 seeds each (for monocotyledons) were performed. They were applied for one hundred seeds for concentration. Twenty seeds were placed into 9 cm diameter Petri dishes for Amarantus and Portulaca. In each Petri dish, 5 ml of distilled water were added. This volume kept the filter papers uniformly soaked-wet without flooding. For Avena and Echinocloa ten seeds were placed into petri dishes and 6 ml of distilled water was added. The essential oil was placed in a sheet of filter papers in contact with the seeds. The controls were prepared with the same quantities of distilled water. Petri dishes were incubated in the room germination (EQUITEC) at 20/30 °C (±1 °C), alternating temperature (6/18 h dark and light (cool white Radium NL 36W/840; 3100 lm)). Dishes were sealed to reduce evaporation, and no more additional water was supplied during the tests. To evaluate the possible phytotoxic effects of the essential oils and their main compounds on seed germination and seedling growth data were registered by taking photos after 3,5, 7, 10 and 14 days after incubation and will be processed using Digimizer. Then data will be analysed and discussed

Nutrient recovery from treated wastewaters by biochar and zeolite: implications for soil fertility

The increasing demand for food due to the mounting world population, coupled with the exhaustion of phosphorus (P) mines and the rising use of more and more expensive nitrogen (N) fertilizers, impose to find alternative sources of such nutrients. The recovery of N and P from treated urban wastewaters through the use of adsorbent materials and their reuse as enriched nutrient amendments to improve soil fertility may be a valid alternative. Zeolites and biochar are suitable materials for the adsorption of nutrients from treated urban wastewaters. Zeolites are crystalline microporous tectosilicates with a negatively charged structure, due to Al replacing Si, compensated by weakly bonded exchangeable cations. They are commonly used for ammonium recovery, showing an absorption capacity higher than 93% within the first 10 minutes of contact with the liquid phase. Once the zeolites are exhausted, they can be either regenerated by washing with NaCl, allowing also the recovery of ammonium, or directly applied to soil as slow-release fertilizers. Several studies have analysed the absorption capacity of zeolites at laboratory and pilot scale, but only few at plant full-scale. On the other hand, biochar is obtained by pyrolysis of plant biomass at 300-800°C and in the absence of oxygen. Studies carried out to investigate the potential of biochar to act as absorbent for the removal of P from aqueous solutions are few and, often, contrasting each other. This is probably due to the performance and properties of biochar that are highly influenced by many factors such as temperature, heating rate and residence time during pyrolysis, the feedstock used as raw material and its particle size. For this reason, the research on the adsorption and desorption properties of biochar is in its early stages, being several questions still unanswered. Even few are studies about the role of P-enriched biochar to improve the availability of P for plants in agricultural soils. Based on the above considerations, the objectives of the PhD project, carried out within the Wider Uptake project (Horizon2020 EU project), are: (i) to identify the most suitable zeolite and biochar for the recovery of inorganic N and P from treated urban wastewaters at plant full-scale, (ii) to study the mechanisms of P absorption on biochar, iii) to evaluate the impact of P-enriched biochar and of ammonium recovered from zeolite on soil chemical and biochemical properties

Can the presence of Biochar negatively affect the ability of chloroform to lyse soil microbial cells?

Biochar is the solid product of the thermochemical decomposition of biomass at moderate temperatures (350–700 °C)[1] under oxygen-limiting conditions. It is nowadays utilized in various applications, for example, in the synthesis of new materials for environmental remediation, catalysis, animal feeds, adsorbent for odours, etc.[2]. In recent decades, interest has grown in the application of biochar as a soil amendment due to its beneficial effects on soil fertility and crop productivity. Biochar amendment is known to alter soil porosity, improve soil structure, increase soil surface area[3], cation exchange capacity, soil organic carbon content and soil microbial biomass[1]. The latter variable is one of the most widely adopted biological indicator for the evaluation of soil fertility status. In fact, the microbial component is the engine that governs energy transfers and nutrient transformations in the soil, thus playing a key role in its fertility. The most widely used methods for determining soil microbial biomass are the chloroform-incubation (FI) and chloroform-extraction (FE) methods[4][5], both relying on the ability of chloroform (CHCl3) fumigation to lyse soil microbial cells and release their contents. Over the years, several critical issues related to the use of CHCl3 have risen due to its toxicity to humans and the environment, as well as due to its not fully proved ability to lyse soil microbial cells. Toyota et al.[6] showed that approximately 10% of bacterial colony forming units in a sandy loam soil survived a 5-day CHCl3 fumigation. This percentage was much higher when fumigating a clayey soils. Alessi et al.[7] demonstrated that significant concentrations of CHCl3 were adsorbed, and thus retained by the clay fraction of soils thus negatively affecting the extractability of microbial-derived constituents. Such a controversial ability of CHCl3 to lyse microbial cells may be even more critical when applied to soils amended with biochar. Indeed, biochar, due to its porous structure and high specific surface area can adsorb several volatile organic compounds, including CHCl3[8]. Therefore, the aim of this study was to assess the ability of CHCl3 to lyse microbial cells in soils amended with two different biochars (EG) and (NB). Treatments were: soil without biochar (control), soil amended with 16 g of EG or NB biochar per kg of air dry soil (corresponding to 20 t ha-1) and soil amended with double amount of EG or NB biochar (corresponding to 40 t ha-1). The ability of the CHCl3 to lyse soil microbial cells in soils with or without biochar was assessed by quantifying either the amount of CO2-C released during incubation or the extractable C and N in fumigated soils, and comparing with the corresponding amount of C obtained from soil pressurized with CO2 (CO2HP). The latter is a new method, under evaluation, that causes lysis of soil microbial cells by high CO2 pressurization and subsequent rapid decompression. Since the CO2HP method is based on a physical approach, it should not be influenced by the presence of biochar in the soil samples being analyzed. Results showed that the amount of CO2-C emitted during the incubation of pressurized soils amended with biochar is higher than that of the same soils but fumigated, thus suggesting higher cell lysis efficiency of the CO2HP method than the CHCl3 in soil amended with biochar. Moreover, extractable C and N results suggested that the ability of CHCl3 depends on the type and concentration of biochar used. CHCl3 could be partly adsorbed and thus retained in the soil after fumigation and risks overestimating the C of the microbial biomass or does not allow for complete lysis of soil microbial cells. Bibliography [1] Brassard, P., Godbout, S., Lévesque, V., Palacios, J. H., Raghavan, V., Ahmed, A., Houge R., Jeanne T. &amp; Verma, M., 2019. Char and Carbon Materials Derived from Biomass,109-146. Elsevier. [2] Conte, P., Bertani, R., Sgarbossa, P., Bambina, P., Schmidt, H.P., Raga, R., Lo Papa, G., Chillura Martino, D.F. &amp; Lo Meo, P., 2021. Agronomy, 11(4), 615. [3] Hardie, M., Clothier, B., Bound, S., Oliver, G., &amp; Close, D., 2014. Plant and Soil, 376(1), 347-361. [4] Jenkinson, D. S., Powlson, D. S., 1976. Soil Biology and Biochemistry, 8, 209- 2013 [5] Vance, E. D., Brookes, P. C., Jenkinson, D. S., 1987. Soil Biology and Biochemistry, 19, 703-707 [6] Toyota, K., Ritz, K., Young, I.M., 1996. Soil Biology and Biochemistry 28, 1545-1547. [7] Alessi, D.S., Walsh, D.M., Fein, J.B., 2011. Chemical Geology, 280 (1-2), 58-64 [8] Kumar, A., Singh, E., Khapre, A., Bordoloi, N., &amp; Kumar, S., 2020. Sorption of volatile organic compounds on non-activated biochar. Bioresource Technology, 297, 122469

Zeolite – Ammonium interaction: physical-chemistry of adsorption process

Zeolites are crystalline microporous tectosilicates, either natural or synthetic. Natural zeolites were formed as a result of the interaction of volcanic rocks and volcanic ash with alkaline groundwater. Due to the formation process, there are more than 50 types of natural zeolites, the most common being clinoptilolite, which belongs to the heulandite family and has the simplified ideal formula of (Na,K,Ca)2-3Al3(Al,Si)2Si13O36·12(H2O). Geological settings and conditions during zeolite formation and geological weathering influence several parameters such as mineralogy, rock porosity/permeability and reaction rate, all of which affect their operational capabilities, hence their use in technical applications. Indeed, zeolites, due to their properties, can be used in several operations, including gas separation, adsorption, ion exchange and catalysis. In recent years, they have been playing an important role in the recovery and removal of nutrients from treated wastewater due to their ion exchange property. Their ability to adsorb cations (such as ammonium ions) comes from the substitution of Si4+ by Al3+, which increases the negative charge of the mineral lattice. The resulting negative charge is balanced by exchangeable cations such as Na+, K+ and Ca2+. The recovery of nutrients (nitrogen and phosphorus) from wastewater is necessary, as their presence in wastewater accelerates the eutrophication of receiving water bodies, creating a potentially toxic environment for fish and other aquatic life. In addition, nutrient recovery from wastewater allows solving problems i.e. the poor access to fertilizers in developing countries and the looming high cost of fertilizers; in fact, the recovered fraction of nutrients can be reused as fertilizer in agriculture promoting a circular economy approach. Furthermore, the use of natural adsorbent materials, such as zeolites, to recover nutrients from wastewater overcomes the problem associated with existing technologies. Which are often expensive and difficult to apply, limiting their use in economically poor countries due to lack of infrastructure and maintenance costs. However, the removal of ammonium by ion exchange on zeolites is influenced by the origin of the zeolites used. Previous studies on clinoptilolites with different lithological matrix have shown how the ability to adsorb NH4+ varies in clinoptilolites of different origin. For example, a Canadian clinoptilolite was capable of adsorbing about 20 mg NH4+ g-1, while a Chinese clinoptilolite did not exceed 5 mg NH4+ g-1. The original matrix may also have an influence on the treatment when natural zeolites are treated to increase the adsorption capacity. Based on the above considerations, the objectives of the PhD project, carried out within the Wider Uptake project (Horizon2020 EU project), are: i) to compare the ammonium adsorption rate on two clinoptilolites of different origin (Slovakia and Cuba), ii) to evaluate the effect that the matrix had on the treatment carried out to improve the adsorption capacit