Validation of zeolites to maximize ammonium and phosphate removal from anaerobic digestate by combination of zeolites in Ca and Na forms Page 1 Abstract Ammonium and phosphate are fundamental nutrients for human life, but their excess in water can lead to eutrophication, an uncontrolled growth of biomass with a consequent deficit of oxygen (hypoxia) that can be really dangerous for water life. This excess is principally due to human activities such as industry and agriculture (detergents, fertilizers) and the problem is expected to grow during next years. Then, it is necessary to find an efficient, simple and low cost technology able to remove the nutrients from water in order to avoid environmental damages. Moreover, the population growth, the constant improvement in agriculture and the consequent increase in fertilizers demand have made the recovery of nutrient from water a real need, as it has been estimated that a 20% of the total needs of Europe could be recovered from wastewaters. Although both ammonium and phosphate have to be recovered from wastewater, their simultaneous removal by means of one adsorbent material has rarely been reported hitherto. The merit of using one material for the simultaneous removal is obvious, even if it has not been achieved yet. In general, most of the solutions proposed for the simultaneous removal of ammonium and phosphate are based on the use of two types of reagents. A large list of removal technologies, ranging from biological to physic-chemical methods, have been widely studied: in this work, zeolites in Ca and Na forms were evaluated as sorbents for phosphate and ammonium from synthetic water and real anaerobic digestate. The sorption performance has been studied by varying zeolites dosage and initial ammonium and phosphate concentration, and the results are presented in terms of equilibrium isotherms. The evaluation of the ammonium and phosphate sorption properties of a mixture of zeolites in calcium and sodium form was carried out by batch experiments and by using a hybrid sorption filtration system in a stirred reactor tank. Finally, the stability of the phosphate and ammonium-loaded zeolite samples was evaluated by extraction experiments and by Olsen method to determine the bioavailability for their potential application as soil fertilizers. Validation of zeolites to maximize ammonium and phosphate removal from anaerobic digestate by combination of zeolites in Ca and Na forms Page 2 Validation of zeolites to maximize ammonium and phosphate removal from anaerobic digestate by combination of zeolites in Ca and Na forms Page 3 Index 1. Glossary _______________________________________________________________________ 8 2. Preface ________________________________________________________________________ 9 2.1 Origin of the project ………………………………………………………………………………………... 9 2.2 Motivation …………………………………………………………………………………………………… 9 3. Introduction _____________________________________________________________________ 10 3.1 Scope of the thesis …………………………………………………………………………………………. 10 3.2 Objectives …..……………………………………………………………………………………………….. 10 4. State of the art ___________________________________________________________________ 11 4.1 Ammonium and phosphate removal from a waste-water treatment plant ……………………………. 12 4.2 Ammonium and phosphate removal and recovery technologies ……………………………………… 12 4.2.1 Adsorption ………………………………………………………………………………………………. 12 4.2.1.1 Zeolites ……………………………………………………………………………………………… 13 4.2.2 Hybrid sorption filtration systems …………………………………………………………………….. 13 4.2.3 Electrochemical treatment …………………………………………………………………………….. 14 4.2.4 Chemical precipitation …………………………………………………………………………………. 14 5. Materials and methodology ________________________________________________________ 16 5.1 Sorbent characterization …………………………………………………………………………………… 16 5.2 Calcium zeolite preparation ……………………………………………………………………………….. 16 5.3 Equilibrium sorption study …………………………………………………………………………………. 16 5.3.1 Langmuir isotherm …………………………………………………………………………………….. 17 5.3.2 Freundlich isotherm ……………………………………………………………………………………. 18 5.4 Kinetic study ………………………………………………………………………………………………… 18 5.4.1 Pseudo first order model ……………………………………………………………………………… 19 5.4.2 Pseudo second order model …………………………………………………………………………. 19 5.4.3 Elovich model ………………………………………………………………………………………….. 20 5.5 Sorption-filtration (Ultrafiltration) stirred reactor ………………………………………………………… 20 5.5.1 Mass Balances on the hybrid sorption filtration set-up ……………………………………………. 21 5.5.2 Operational conditions ………………………………………………………………………………… 22 5.6 Speciation of loaded phosphate-ammonium zeolite samples by using a sequential extraction protocol …………………………………………………………………………………………………………….. 24 5.7 Olsen method ……………………………………………………………………………………………….. 24 5.8 Sample analysis …………………………………………………………………………………………….. 24 5.8.1 Spectrophotometry …………………………………………………………………………………….. 24 5.8.2 Chromatographic analysis …………………………………………………………………………….. 25 5.9 Cleaning ……………………………………………………………………………………………………... 25 6. Results and discussion ___________________________________________________________ 26 6.1 Chemical and mineralogical characterization of the adsorbents ……………………………………… 26 6.2 Characterization of the model ammonium and phosphate containing effluents …………………….. 27 6.3 Mechanism of adsorption ………………………………………………………………………………….. 28 Validation of zeolites to maximize ammonium and phosphate removal from anaerobic digestate by combination of zeolites in Ca and Na forms Page 4 6.3.1 Ammonium ……………………………………………………………………………………………… 28 6.3.2 Phosphate ………………………………………………………………………………………………. 28 6.4 Removal of ammonium and phosphate from synthetic solutions by synthetic zeolites……………… 29 6.4.1 Influence of the solid to liquid phase ratios …………………………………………………………. 29 6.4.2 Effect of the initial ammonium and phosphate concentrations on zeolites sorption capacities .. 31 6.4.3 Sorption Equilibrium data for the binary system ……………………………………………………. 34 6.5 Removal of ammonium and phosphate from anaerobic digestates …………………………………... 35 6.5.1 Influence of the solid to liquid phase ratios …………………………………………………………. 35 6.5.2 Ammonium and phosphate sorption kinetics ……………………………………………………….. 37 6.5.2.1 Effect of zeolite mixtures on ammonium and phosphate removal …………………………… 37 6.5.2.2 Removal of ammonium and phosphate from anaerobic digestates …………………………. 39 6.5.3 Ammonium and phosphate sorption modelling …………………………………………………….. 41 6.6 Integration of zeolite sorption and ultrafiltration for ammonium and phosphate removal ………….. 43 6.6.1 Effect of MgO on ammonium and phosphate removal from synthetic water ……………………. 43 6.6.2 Phosphate and ammonium removal in hybrid system using real digestate water ……………… 48 6.7 Regeneration of loaded zeolites ………………………………………………………………………….. 51 6.7.1 Elution with KCl, HCl and NaOH ……………………………………………………………………… 51 6.7.2 Evaluation of the phosphate availability by using the Olsen method ……………………………. 53 6.8 Loaded zeolites characterization …………………………………………………………………………. 54 7. Conclusion _____________________________________________________________________ 58 8. Acknowledgments _______________________________________________________________ 59 9. Bibliography ____________________________________________________________________ 60 Validation of zeolites to maximize ammonium and phosphate removal from anaerobic digestate by combination of zeolites in Ca and Na forms Page 5 Index of figures Figure 1: Ammonium and phosphate fertilizer demand from 2013 to 2017…………………………………. 11 Figure 2: Scheme of the sorption-filtration pilot plant………………………………………………………….. 20 Figure 3: Vacuum filter for anaerobic digestate water…………………………………………………………. 23 Figure 4: Thermo Scientific Dionex ICS-1100 for anions and the Thermo Scientific Dionex ICS-1000….. 25 Figure 5: NaZe XRD difractogram……………………………………………………………………………….. 26 Figure 6: CaZe XRD difractogram……………………………………………………………………………….. 27 Figure 7: Effect of zeolites amount on adsorption capacity of ammonium ions (C0 720 mg/l) and phosphate ions (C0 120 mg/l) ………………………………….………………………………………………… 29 Figure 8: Effect of zeolites amount on adsorption capacity of ammonium ions (C0 720 mg/l) and phosphate ions (C0 120 mg/l) ………………………………….………………………………………………… 30 Figure 9: Effect of zeolites amount on removal efficiency of ammonium ions (C0 720 mg/l) and phosphate ions (C0 120 mg/l) ………………………………….………………………………………………… 31 Figure 10: Effect of ammonium and phosphate initial concentration C0 on their adsorbed amount by 8 g/l of calcium zeolite ………………………………….…………………………………………………………… 32 Figure 11: Comparison between effect of ammonium and phosphate initial concentration C0 on their ammonium adsorbed amount by 8 g/l of calcium zeolite and on ammonium removal efficiency ………… 33 Figure 12: Comparison between effect of ammonium and phosphate initial concentration C0 on their phosphate adsorbed amount by 8 g/l of calcium zeolite and on phosphate removal efficiency ………….. 33 Figure 13: Isotherm models at for ammonium adsorption on synthetic calcium zeolite and experimental data………………………………….………………………………….…………………………………………… 34 Figure 14: Isotherm models at for phosphate adsorption on synthetic calcium zeolite and experimental data………………………………….………………………………….…………………………………………… 35 Figure 15: Effect of zeolites amount on adsorption capacity of ammonium ions (C0 860 mg/l) and phosphate ions (C0 50 mg/l) ………………………………….………………………………………………….. 36 Figure 16: Effect of zeolites amount on removal efficiency of ammonium ions (C0 860 mg/l) and phosphate ions (C0 50 mg/l) ………………………………….………………………………………………….