Study on phosphorus recovery from digested piggery wastewater by struvite precipitation

HANOI UNIVERSITY OF SCIENCE TECHNISCHE UNIVERSITÄT DRESDEN Master Thesis STUDY ON PHOSPHORUS RECOVERY FROM DIGESTED PIGGERY WASTEWATER BY STRUVITE PRECIPITATION Vu Phuong Thuy Supervisor: Professor Dr Cao The Ha Hanoi, November 2011 ACKNOWLEDGEMENTS I would like to thank Professor Doctor Cao The Ha, my supervisor, and greatly appreciate his supervision, advice, and guidance from the early stage of this research as well as giving me experiences throughout the work During the time I was doing the research, he also gave the great opportunity, the best support and conditions in many ways for me to go to National Institute for Environment Studies, Japan to participate in the training course “Sustainable Landfill Management” Many thanks to all the staffs in the Center for Environmental Technology and Sustainable Development and the Faculty of Chemistry of Hanoi University of Science for helping me with analytical techniques I would like to thank to Dr Kazuyoshi Suzuki, Dr Anton Perera, Prof Phil Westerman for your helps with answering my questions Finally, I would like to thank to my family, my friends who are always supportive and encourage me during difficult times, especially my mom who helped me to take care of the experiment that was performed in my house ABSTRACT This research studied on struvite precipitation as a method to remove and recovery phosphorus in the real digested piggery wastewater to form a product as fertilizer There are many factors that affect to the precipitation of struvite such as pH, ion molar ratios, aeration, mixing energy, temperature… In this study, series of jar-test experiments were conducted to investigate the influence of pH, Mg:P molar ratio, Ca ions and mixing speed to the phosphorus removal efficiency and the crystallization of struvite Experiments with lab-scale reactor in batch and continuous mode were also conducted to investigate the kinetic of phosphorus removal, the controlled struvite crystallization and the quality of the generated product The results showed that, a) At pH at 9.25, the phosphorus removal efficiency was the highest b) Increasing Mg:P molar ratio (from to 2.5) and stirring speed (from 50 rpm to 100 rpm) led to enhanced phosphorus removal efficiency c) Ca ions play important role in both phosphorus removal efficiency and crystallization of struvite A presence of Ca ions at Mg:Ca of 4:1 to 2:1 will increase the phosphorus removal efficiency and affect the morphology of struvite crystals compared to Mg:Ca of 1:1, 2:1 or 1:0 d) The rate constant of phosphorus removal in the pilot-scale experiment with digested piggery wastewater when Mg ions added estimated as 0.050 -1 -1 or 3.00 hr e) It is possible to attach and grow struvite crystals on stainless steel mesh in order to recover it as fertilizer KEYWORDS Struvite, stirring speed, digested piggery wastewater, phosphorus removal, crystallization TABLE OF CONTENTS List of figures List of tables INTRODUCTION REVIEW OF LITERATURE 1.1Introduction to phosphorus and its applications 1.2Impacts of excessive phosphorus in water streams 1.3Recovery of phosphorus 1.4Phosphorus removal and recovery techniques 1.5Struvite precipitation 1.5.1Background 1.5.2Struvite chemistry 2GOAL AND OBJECTIVES 2.1Goal 2.2Objectives 3MATERIALS AND METHODS 3.1Wastewater collection and analysis 3.2Jar-test experiment procedure 3.2.1Impact of pH 3.1.2Impact of magnesi 3.1.3Impact of Calcium 3.2.4Impact of stirring s 3.3Bench-scale experiments 3.3.1Reactor design and 3.3.2Accumulation devi 3.4Analytical and assessment methods 3.4.1Analytical techniqu 3.4.2Kinetic model desi 4RESULTS AND DISCUSSIONS 4.1Characteristics of the digested piggery wastewater 4.2Jar-test experiments - Impact of factors 4.2.1pH 4.2.2Magnesium additio 4.2.3Calcium ions… 4.2.4Stirring speed 4.3Bench-scale experiments 4.3.1Batch mode experi 4.3.2Continuous mode e 5CONCLUSIONS AND RECOMMENDATIONS 5.1Conclusions… 5.2Recommendations REFERENCES LIST OF FIGURES Figure 3-1 Schematic diagram of batch mode experiment 3-2 Photo of batch mode experiment 3-3 Schematic diagram of continuous mode experiment 4-1 Effect of pH to %P-Removal 4-2 Effect of magnesium addition to %P-removal 4-3 Effect of Mg:Ca ratio to %P-removal 4-4 (a), (b), (c) Photos of struvite crystals by light microscope 4-4 (d), (e), (f) Photos of struvite crystals by light microscope 4-5 Residual P-PO4 concentration at different stirring speed versus tim 4-6 Residual P-PO4 concentration and pH value versus time 4-7 Linear of kinetic model of phosphate removal 4-8 (a), (b), (c) Photos of struvite crystal growth on stainless steel mesh 4-9 Photos of struvite crystals on inner and outer mesh 4-10 (a), (b) Photos of struvite crystals taken out of the mesh 4-11 X-RAY diffraction of recovered struvite crystals LIST OF TABLES Table 1-1 Summary of phosphorus removal technologies, Morse et al (1998) 1-2 Summary of phosphorus recovery technologies, Morse et al (1998) 4-1 Characteristic of the digested piggery wastewater (19/07/2011) 4-2 Effect of pH to %P-Removal 4-3 Effect of magnesium addition to %P-removal 4-4 Solid species examined and selected as primary precipitation 4-5 Effect of Mg:Ca ratio to %P-removal 4-6 Residual P-PO4 concentration at different stirring speed versus time 4-7 Residual P-PO4 concentration and pH value versus time 4-8 Characteristic of wastewater before and after the experiment INTRODUCTION Livestock industry is a very important sector of Vietnam which has the strong growth especially in pork production in recent years However, this can lead to many serious environmental issues as well According to Department of Livestock Husbandry, Ministry of Agriculture and Rural Development, until October 2009, the number of pigs in over Vietnam was 27.6 mil and predicted to be 36.9 mil by 2015 In 2006, there were 18,000 castle farms in Vietnam in which 6,000 were piggery farms Each year, 20-30 mil m liquid waste is discharged from pig farms and 80% of that is discharged directly into the environment without any pretreatment and caused many pollutions Livestock wastewater contains high content of nutrients In Vietnam, the most common treatment method for livestock wastewater is biogas tank and lagoon Biogas tanks can treat COD and lagoons can treat N, P but with long retention time The wastewater quality after treatment by these methods is not good enough for discharging into the environment yet Especially, there are lack of management of phosphorus and ammonium which are elements that can cause pollutions of surface water bodies by extra eutrophication Besides, phosphorus is an irreplaceable element essential for every living thing on earth which global reserve is going to run out in 60-100 years Removal of phosphorous by precipitation of struvite has been studied and used somewhere in Europe and Asia for both animal manures and municipal wastewater Struvite is a mineral formed from three specific components: magnesium, ammonium and phosphate Struvite (magnesium ammonium phosphate) precipitates as a compact crystal Therefore, a small amount of easily settleable solids is generated in a struvite precipitation process Unlike other chemical phosphorus precipitation methods (e.g using aluminum or ion salt etc.) where only phosphorus alone is removed, in struvite precipitation both phosphorus and ammonium are removed, this this important in the case of piggery wastewater containing large amount of both phosphorus and ammonium In addition, struvite is easily transported and can be used as a slow-release fertilizer (NYSERDA, 2006) This report presents the study on struvite precipitation from digested piggery wastewater The study includes discussion of the relevant background information and a literature review of struvite (Section 1), Goals and objectives of the study (Section 2); Material and methods with series of jar-test experiments and lab-scale reactor experiments (Section 3); Results and discussions (Section 4); and Conclusions and recommendation (Section 5) REVIEW OF LITERATURE 1.1 Introduction to phosphorus and its applications Together with Nitrogen and Potassium, Phosphorus is an important element for living organisms The vast majority of phosphorus sources are consumed as fertilizers in agriculture in over the world Phosphorus is necessary for the promotion of plant growth and hence, improves crop yield, seed formation and quality of fruit To balance the nutrients in soils, phosphorus can be added periodically under the form of inorganic fertilizers or manures Phosphorus is also one of the vital elements needed for livestock as well It is consumed through the diet of animals Phosphorus has the function in preventing health problems, improve bone strength and muscle production in animal bodies Besides, phosphorus is also used in other applications such as detergent production, food processing, chemical production,… However, phosphorus can be lost from the source and discharged into the environment by different ways naturally or due to the lack of proper management For example, it can be lost from soils by some ways such as crop uptake and removal, runoff and erosion, or leaching Or it can also be lost from animal feeding source through the waste streams because not 100% of intake phosphorus will remain in animal bodies According to ICM, 2000 (http://www.ipm.iastate.edu/ipm/icm/2000/8-7- 2000/pbasics.html), 14% of phosphorus in corn and 31% of phosphorus in soybean can be digested by swine, hence, a large percentage of intake phosphorus is excreted into Figure 4-6 Residual P-PO4 concentration and pH value versus time Figure 4-7 shows the linear kinetic model of phosphate removal Rate constants were determined by fitting the experimental results with modified first-order kinetic model Reasonable fits (R = 0.975) of the data suggest that the first order kinetic model was -1 sufficient The Phosphate removal rate constants were estimated as 0.050 or 3.00 -1 hr 44 Figure 4-7 Linear of kinetic model of phosphate removal Table 4-8 Characteristic of wastewater before and after the experiment Parameter P-PO4 N-NH4 2+ Mg Ca2+ + K TSS COD Alkality 45 Results showed that struvite precipitation is easy to be achieved within maximum -1 hours With k = h , one can easy to estimate the residual phosphate concentration C after hours detention from: C C o C o ln C  kt    ln C   Co  e6  C  Co / e6  0.0025Co The total dried precipitation (M) gained from liters of wastewater in the experiment was 1940 mg The precipitated solid per liter of wastewater (m) is calculated as: m  M TSS Where ∆TSS is the reduction of TSS in wastewater after the reaction Hence: 1940 74 m    40)   381.2mg.l 1 Ammonium removal efficiency is calculated as: %P  Re moval  Ammonium removal efficiency is calculated as:  C C 141.2  45.5 %N Removal o,NNH   e,NNH 100   10067.8% C 141.2 4 o, N NH4 4.3.2 Continuous mode experiment During days of experiment, P-PO4 concentration in the effluent was measured daily and the results showed that it varied not very much The lowest P-PO4 concentration in 46 th the effluent was 8.6 mg/l in the day and the highest value measured was 14.2 mg/l in nd day Mean value of days is 8.8 mg/l P-PO4 concentration in the influent after added NH4H2PO4 was around 125 mg/l Hence, the P-removal efficiency of the reactor in continuous mode was roughly 92.8% The crystals accumulated and grew in the stainless steel device was observed and analyzed The growth of crystals was observed by the size of crystals on the device Figure 4-8 (a), (b), (c) showed the struvite crystals developed on the device after day, days and days It showed that after one day, there are many crystals on the device with the size was about – 500 µm and most of them had the “sandy-shape” size After days, most of the crystals grew longer, with common size of 500 µm And after 5days, the crystals grew very densely and filled the meshes The crystal dense was higher on the inner mesh than the outer, as shown in the Figure 4-9 47 (a) (b) (c) Figure 4-8 Photos of struvite crystal growth on stainless steel mesh 48 Figure 4-9 Photos of struvite crystals on inner and outer mesh 49 (a) (b) Figure 4-10 (a), (b) Photos of struvite crystals taken out of the mesh 50 The crystals were taken out of the meshes for XRAY analyses to determine the quality Figure 4-11 shows the X-RAY diffraction of the accumulated crystals The only compound found was struvite Hence, it can be concluded that accumulated crystals on the device are struvite crystals In order to estimate the value of recovered struvite, it is compared with diamon phosphate (DAP) by calculation phosphorus and ammonium content (%P+N) as following: DAP or (NH4)2HPO4, M = 132: %(P+N) = 28/132 + 31/132 = 44.7% Struvite or MgNH4PO4.6H2O, M = 245: %(P+N) = 14/245 + 31/245 = 18.35% Hence, kg of recovered struvite has the same nutrient content as 0.41 kg DAP 51 d=2.701 4000 Faculty of Chemistry, HUS, VNU, D8 ADVANCE-Bruker Mau +18 Lin (Cps) 3000 d=3.297 d=3.567 d=4.283 1000 d=4.154 d=3.021 2000 20 30 60 40 50 70 2-Theta - Scale File: Thuy Cetas mau +18.raw - Type: Locked Coupled - Start: 20.000 ° - End: 70.010 ° - Step: 0.030 ° - Step time: s - Temp.: 25 °C (Room) - Time Started: 10 s - 2-Theta: 20.000 ° - Theta: 10.000 ° - Chi: 01-077-2303 (C) - Struvite - MgNH4PO4(H2O)6 - Y: 11.71 % - d x by: - WL: 1.5406 - Orthorhombic - a 6.95500 - b 6.14200 - c 11.21800 - alpha 90.000 - beta 90.000 - gamma 90.000 - Primitive - Pmn21 ( Figure 4-11 X-RAY diffraction of recovered struvite crystals 52 CONCLUSIONS AND RECOMMENDATIONS 5.1 Conclusions The series of jar-test experiments gave a comprehension of which factors affect the most to the process of phosphate removal and struvite crystallization in wastewater In considered factors, pH and Ca ions are found to be ones that play important roles in phosphate removal and struvite crystallization a) pH at 9.25, the phosphorus removal efficiency was highest but it is supposed to be 8.80 when considering to apply the method in reality because of the reasonableness for economy (i.e., cost for chemical addition) and environmental protection (i.e., pH value in water effluent should not be too high when discharged into the environment) b) Increasing Mg:P molar ratio (from 1:1 to 2.5:1) and stirring speed (from 50 rpm to 100 rpm) enhances but not change much in phosphorus removal efficiency c) Ca ions play important role in both phosphorus removal efficiency and crystallization of struvite A presence of Ca ions at Mg:Ca of 4:1 to 2:1 will increase the phosphorus removal efficiency and affect the morphology of struvite crystals compared to Mg:Ca of 1:1 or 2:1 or without any Ca ions The Mg:Ca of 3:1 is found to be the most suitable for struvite crystallization as well as phosphate removal efficiency in wastewater For digested piggery wastewater, there are always the presence of both Mg and Ca ions at certain concentration It is necessary to supplement Mg salts to control the process of struvite precipitation Bench-scale experiments at batch mode, fluidized bed reactor with aeration for increasing pH and stirring is a very good and effective design for phosphate removal NaOH solution and magnesium salts must be added into wastewater as control the pH 53 and balance the Mg:Ca molar ratio as explained in previous jar-test experiments The rate constant of phosphorus removal in digested piggery wastewater when Mg ions -1 -1 added estimated as 0.050 or 3.00 hr The bench-scale experiment in continuous mode with accumulation device for struvite crystals showed that it is possible to attach and grow struvite crystals on stainless steel mesh in order to recover struvite as a pure product can be used as good quality slow release fertilizer 5.2 Recommendations Further studies should be done on: - Investigating the best material and best design for the mesh in order to attach struvite crystals to accumulate; - Investigating which source of Mg is best for the process of struvite precipitation in terms of technical and economical aspect It is necessary to find out possible solutions to cut/reduce the chemical costs For example, use natural calcined magnesite (MgCO3), dolomite (CaMg(CO3)2), serpentinite, talc, etc… to increase Mg content as well as for pH regulation; - Larger and longer pilot-scale as well as integrating into whole wastewater treatment system in order to find out the feasibility of the technique in livestock facilities 54 REFERENCES Battistoni, P Pavan, F Cecchi, J Mata-Alvares, (1998), “Phosphate removal in real anaerobic supernatants: modelling and performance of a fluidized bed reactor”, Water Science and Technology, Vol 38, No 1, 275-283 Beal, L.J., R.T Burns, K.J Stalder, 1999, “Effect of anaerobic digestion on struvite production for nutrient removal from swine waste prior to land application”, presented at the 1999 ASAE Annual International Meeting, Toronto, Ontario, Canada, 18-21 th Bishop, P L., 2006, “Control of struvite deposition in wastewater treatment plants”, 11 Annual Central States Water Environment Association Education Conference, Minnesota: Central States Water Environment Association Burns, R.T., Moody, L.B., Celen, I., Buchanan, J.R., 2003, “Optimization of phosphorus precipitation from swine manure slurries to enhance recovery” Water Science and Technology 48 (1), 139-146 Daisuke et al., (2011), “A Novel Approach to Estimate Precipitable Inorganic Species in the Anaerobic Digestion Tank” El Diwani, G., El Rafie, S., El Ibiari, N N., El-Aila, H I., 2006, “Recovery of ammonia nitrogen from industrial wastewater treatment as struvite slow releasing fertilizer”, Desalination, 214, 200-214 Etter, B., Tilley, E., Khadka, R., Udert, K M., 2010, “Low-cost struvite production using source-separated urine in Nepal”, Water Research, 45, 852-862 Hong-Duck, R., Sang-Ill, L., 2010, “Application of struvite precipitation as a pretreatment in treating swine wastewater”, Process Biochemistry, 45, 563-572 55 ICM (Intergrated Crop Management), 2000 (http://www.ipm.iastate.edu/ipm/icm/2000/8-72000/pbasics.html); Kristell S Le Corre, Eugenia V., Phil H., Simon A P., 2004, “Impact of calcium on struvite crystal size, shape and purity”, Journal of Crystal Growth 283, 514–522 Kumashiro, H.Ishiwatari, Y.Nawamura, 2001, “A pilot plant study on using seawater as a magnesium source for struvite precipitation”, Second international conference on recovery of phosphate from sewage and animal wastes, Holland LAGEP, 2002, CEEP, “Phosphate recovery by struvite precipitation in a stirred reactor” Mitani, Y Sakai, F Mishina, S Ishiduka, 2001, “Struvite recovery from wastewater having low phosphate concentration”, Second international conference on recovery of phosphate from sewage and animal wastes, Holland Morse G K., Brett S W., Guy J A., and Lester J N, 1998, “Review: Phosphorus removal and recovery technologies”, The Science of Total Environment, 69-81 Münch and K Barr, 2001, “Controlled struvite crystallization for removing phosphorus from anaerobic digester sidestreams”, Water Research, Vol 35, No 1,151-159 NYSERDA (Newyork state Energy Research and Development Authority), 2006, “Struvite recovery from digested daily manure and regional manure anaerobic digested study” Ohlinger, K., T Young, E Schroeder, 1998, “Predicting struvite formation in digestion”, Water Research, Vol 32, No 12, 3607-3614 Ohlinger, K., T Young, E Schroeder, 1999, “Kinetics effects on preferential struvite accumulation in wastewater”, Journal of Environmental Engineering, 125, 730-737 56 Piekema, A Giesen, 2001, “Phosphate recovery by the crystallization process: experience and developments”, Second international conference on recovery of phosphate from sewage and animal wastes, Holland Quintana, M., Sánchez, E., Colmenarejo, M F., Barrera, J., García, G., Borja, R, 2005, “Kinetics of phosphorus removal and struvite formation by the utilization of by-product of magnesium oxide production”, Chemical Engineering Journal , 111, 45-52 Y Ueno, M Fujii, 2001,“3 years operating experience selling recovered struvite from fullscale plant”, Second international conference on recovery of phosphate from sewage and animal waste, Holland Uysal, A., Yilmazel, Y D., Demirer, G N., 2010, “The determination of fertilizer quality of the formed struvite from effluent of a sewage sludge anaerobic digester”, Journal of Hazardous Materials, 181, 248-254 Ye, Z.-L., Chen, S.-H., Wang, S.-M., Lin, L.-F., Yan, Y.-J., Zhang, Z.-J., et al., 2009, “Phosphorus recovery from synthetic swine wastewater by chemical precipitation using response surface methodology”, Journal of Hazardous Materials, 176, 1083–1088 57 STATEMENT UNDER OATH I hereby confirm that I have written this thesis on my own and that I have not used other media or materials than the ones I referred to in this thesis th Hanoi, 25 November, 2011 _ Vu Phuong Thuy ... presents the study on struvite precipitation from digested piggery wastewater The study includes discussion of the relevant background information and a literature review of struvite (Section 1), Goals... a struvite precipitation process Unlike other chemical phosphorus precipitation methods (e.g using aluminum or ion salt etc.) where only phosphorus alone is removed, in struvite precipitation. .. Formation of struvite can occur when certain conditions are met At elevated pH condition and when the concentrations of magnesium, ammonium, phosphate ions exceed the solubility product for struvite,