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. Cao The Ha Hanoi, November 2011 TIEU LUAN MOI download : skknchat@gmail.com 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. TIEU LUAN MOI download : skknchat@gmail.com 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 1 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. 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. TIEU LUAN MOI download : skknchat@gmail.com TABLE OF CONTENTS Page List of figures.3 List of tables.5 1 REVIEW OF LITERATURE .1 Introduction to phosphorus and its applications.2 Impacts of excessive phosphorus in water streams.3 Recovery of phosphorus.4 Phosphorus removal and recovery techniques.2 Struvite chemistry in wastewater.14 2 GOAL AND OBJECTIVES.17 3 MATERIALS AND METHODS.1 Wastewater collection and analysis.2 Jar-test experiment procedure.1 Impact of pH.2 Impact of magnesium addition.3 Impact of Calcium ions.21 1 TIEU LUAN MOI download : skknchat@gmail.4 Impact of stirring speed.3 Bench-scale experiments.1 Reactor design and batch mode experiment.2 Accumulation device design and continuous mode experiment.4 Analytical and assessment methods.2 Kinetic model design for phosphorus removal.28 4 RESULTS AND DISCUSSIONS.1 Characteristics of the digested piggery wastewater.2 Jar-test experiments - Impact of factors.3 Bench-scale experiments.1 Batch mode experiment.2 Continuous mode experiment.46 5 CONCLUSIONS AND RECOMMENDATIONS.55 2 TIEU LUAN MOI download : skknchat@gmail.com LIST OF FIGURES Figure 3-1 Schematic diagram of batch mode experiment.23 3-2 Photo of batch mode experiment.24 3-3 Schematic diagram of continuous mode experiment.26 4-1 Effect of pH to %P-Removal.32 4-2 Effect of magnesium addition to %P-removal.33 4-3 Effect of Mg:Ca ratio to %P-removal.36 4-4 (a), (b), (c) Photos of struvite crystals by light microscope.
Photos of struvite crystals by light microscope.40 4-5 Residual P-PO4 concentration at different stirring speed versus time.42 4-6 Residual P-PO4 concentration and pH value versus time.44 4-7 Linear of kinetic model of phosphate removal.45 4-8 (a), (b), (c) Photos of struvite crystal growth on stainless steel mesh.48 4-9 Photos of struvite crystals on inner and outer mesh.49 4-10 (a), (b) Photos of struvite crystals taken out of the mesh.50 4-11 X-RAY diffraction of recovered struvite crystals.52 3 TIEU LUAN MOI download : skknchat@gmail.com LIST OF TABLES Table 1-1 Summary of phosphorus removal technologies, Morse et al.10 1-2 Summary of phosphorus recovery technologies, Morse et al.11 4-1 Characteristic of the digested piggery wastewater (19/07/2011).30 4-2 Effect of pH to %P-Removal.31 4-3 Effect of magnesium addition to %P-removal.33 4-4 Solid species examined and selected as primary precipitation.34 4-5 Effect of Mg:Ca ratio to %P-removal.35 4-6 Residual P-PO4 concentration at different stirring speed versus time.42 4-7 Residual P-PO4 concentration and pH value versus time.43 4-8 Characteristic of wastewater before and after the experiment.45 4 TIEU LUAN MOI download : skknchat@gmail.com 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. In 2006, there were 18,000 castle farms in Vietnam in which 6,000 were piggery farms.
Each year, 20-30 mil m3 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.
using aluminum or ion salt etc.) where only phosphorus alone is removed, in struvite 5 TIEU LUAN MOI download : skknchat@gmail.com 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).
6 TIEU LUAN MOI download : skknchat@gmail.com 1 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.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 7 TIEU LUAN MOI download : skknchat@gmail.com waste streams. Due to the mismanagement of this mineral element, there are many issues related to environmental problems, especially water environment.2 Impacts of excessive phosphorus in water bodies Phosphorus is not toxic, but it can affect the biological activity in clean water bodies.
Once phosphorus level in surface water exceeds the critical value for aquatic plant growth, it can cause eutrophication to happen and degrade the water quality. Advanced eutrophication can also lower dissolved oxygen and increasing the BOD (biological oxygen demand) and hence, reduce the aquatic wildlife populations and species diversity in the water body. The USEPA (United States Environmental Protection Agency) recommends that total phosphorus should not exceed 0.1 mg/L in streams and that should not exceed 0.05 mg/L in streams where they enter a lake or reservoir.3 Recovery of phosphorus Phosphorus in phosphate rocks is an irreplaceable resource. In order to meet the increasing demand of fertilizers for agriculture and other purposes, phosphate resources are mined with an increasing rate.
In order to contribute to the security of phosphate resource on earth as well as to prevent the potential environmental issues, phosphate should be removed and recovered from waste streams before discharged into the surface water. This includes extracting phosphates from the sources in the forms that can be used in industry as a renewable resource or as fertilizers in agriculture. 8 TIEU LUAN MOI download : skknchat@gmail.com Numerous of studies and applications of phosphorus recovery have been conducted with effort of recovery this resource from waste streams of which precipitation is the most common concerned method. Phosphorus can be extracted from the waste streams (i., sewage treatment plant, livestock waste…) in the forms of precipitated compounds such as calcium phosphate, magnesium phosphate, magnesium ammonium phosphate or struvite.
Recovery of phosphorus in waste streams will help to minimize environmental damages, contribute to balance phosphate rock resource on earth and offer economic returns of the recovered products. Phosphorus removal and recovery has been the concerned topic all over the world for several decades. Many methods and technologies have been researched and introduced until now, however its applications in reality are still limited. In the world, the industrial use of recovered phosphorus from waste streams has been successfully implied in several plants in developed countries (Japan, Netherland).
Phosphorus removal and recovery techniques still continue to be an attractive subject all over the world for national and international authorities, scientific institutions, industry and other interested parties… In the next part of this report, an overview of existing techniques on phosphorus removal and recovery will be described in details.4 Phosphorus removal and recovery techniques According to Morse et al. 1998, a wide range of technologies for phosphorus removal and recovery were developed including chemical precipitation, biological phosphorus removal, crystallization, novel chemical precipitation approaches and a number of wastewater and sludge-based methods. 9 TIEU LUAN MOI download : skknchat@gmail.