Research and application of ammonia removal in groundwater on the treatment system using moving bed biofilm carriers

MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY ----------------------------- TRINH XUAN DUC RESEARCH AND APPLICATION OF AMMONIA REMOVAL IN GROUNDWATER ON THE TREATMENT SYSTEM USING MOVING BED BIOFILM CARRIERS MAJOR: ENVIRONMENTAL ENGINEERING CODE: 9 52 03 20 SUMMARY OF THESIS IN ENVIRONMENTAL ENGINEERING HA NOI – 2018 The work was completed at: Graduate University of Science and Technology - Vietnam Academy of Science and Technology. Facilitator 1: Assoc. Prof. Tran Duc Ha Facilitator 2: Assoc. Prof . Ngo Quoc Buu Reviewer 1: Reviewer 2: Reviewer 3: The thesis will be defended before the Examining Board at the Academy level, meeting at the Graduate University of Science and Technology - Vietnam Academy of Science and Technology at ... ............................ 2018. The thesis can be found at: - Library of the Academy of Science and Technology - National Library of Vietnam 1 INTRODUCTION 1. THE RESEARCH NECESSITY OF THE THESIS The demand for clean and hygienic water is always a top concern and has become a strategy of many countries including Vietnam. Currently, the living standard in our country is being improved gradually, awareness of health protection is increasing, especially in big cities like Hanoi. This is the second most populated area in the country with a population of about 7 million people in 2014. However, along with the development of many aspects of the capital, the issue of clean water access has not been met in both quantity and quality. The survey results of the Northern Hydrogeological - Engineering Geological Division showed that the ammonia concentration in groundwater in Hanoi has exceeded many times compared to the permitted standards, in which some places are 10-20 times higher. The biggest concern about ammonia is that the intermediates such as nitrite and nitrate compounds are formed from ammonia in the treatment process and use of water for domestic and drinking purposes under the following mechanism: During the water treatment process, there always formed naturally Nitrosomonas bacteria in the filtration tank, which converts part of the ammonia in groundwater into nitrite intermediates. With sufficient conditions, under action of a different type of bacteria that is naturally formed in the filtration tank as Nitrobacter, the nitrite intermediates will be further transformed into nitrate. While there is insufficient evidence to assess the extent and direction of the effects of ammonia-based 2 products on the human body, the harm caused by NO2-, NO3- is well known. NO2-, NO3- are the agents that cause red blood cell damage in children and may be cancer-causing agents. One of the few technologies that can meet these requirements is Moving Bed Biofilm Reactor (MBBR) which uses biofilm on the carriers moving in water when it is operating. Its treatment efficiency is only lower than the fluidized bed reactor and much higher than other techniques. Its operation is much simpler than the fluidized bed reactor that requires a high automative level. Most of the materials and equipment of the MBBR technology are easy to find and manufactured domestically. Based on the above facts, the topic "Research and application of ammonia removal in groundwater on the treatment system using moving bed biofilm carrier" was selected for this thesis. 2. OBJECTIVES AND CONTENTS OF THE THESIS 2.1. Objectives of Research - Research on ammonia removal in groundwater in Hanoi with the concentration of less than 25mg/L (20mgN/L) by simultaneous Nitrification and Denitrification process in the equipment using MBBR with porous carriers (DHY) of a high surface area of about 6,000-8,000 m2/m3, high porosity and light weight, easily moving in water without addition of substrates. - Research and design of the treatment equipment using integrated DHY carriers including MBBR tank and self-cleaning filter tank for ammonia removal in groundwater in order to ensure clean water standard for eating and drinking purposes, suitable with 3 the investment ability and operational conditions in Vietnam. 2.2. Contents of Research (1) Collect data and survey the current status of exploitation and technological line of water plants in Hanoi area in order to evaluate groundwater quality, ammonia pollution and influential factors such as pH, temperature, alkalinity, organic matters, phosphorus and ammonia treatment efficiency of existing production lines. (2) An overview of ammonia treatment methods in the country and the world, analyze advantages and disadvantages and raise the existing problems. (3) An overview of ammonia treatment by microbiological method to understand the treatment mechanism, various types of microorganisms, influential factors and kinematic reaction models as the basis for selecting the pilot models, analyzing and evaluating the results obtained on the experimental model and field pilot model. (4) An overview of biofilm and the works using this technology, evaluating the advantages and disadvantages of each type of biofilm, each type of work for which to propose moving bed biofilm carriers to use for design of ammonia removal system in ground water in Hanoi. (5) Experimental research on laboratory model: Batch and continuous experiments are made to determine kinematic parameters such endogenous degradation factor kp (d-1), biomass efficiency Y (g SK/g N-NH4+), ammonia semi-saturation indicator Ks (mgN/L), substrate consumption coefficient k (μ/Y). Assessing the factors that affect the nitrification process: ammonia input, dissolved oxygen 4 concentration (DO), carrier density, number of reactor compartments. Assessing the factors that affect the simultaneous denitrification process in aerobic medium, effect of substrate concentration and establishing experimental equation for specific denitrification rate (U). (6) Designing and constructing an integrated module for the MBBR system using porous DHY carriers at the field, pilot run to test kinematic parameters and building a data set for design calculations. 2.3. Scope Groundwater in Hanoi area where the ammonia concentration (NH4+) is less than 25 mg/L (20 mgN/L), including urban and rural areas. It can also be applied to water plants in other areas where water is contaminated with ammonia including surface water. 2.4. Subject - DHY carrier has a large surface area of 6000-8000 m2/m3 with simultaneous nitrification and denitrification process under aerobic condition. - The system uses MBBR integrated with self-cleaning filter (DHK). 2.5. Experimental research - Conducting two types of experimental model: batch and continuous experiment for ammonia nitrogen treatment with water samples simulated from actual groundwater quality, in which the limitations of research and fluacutation are as follows: NH4+ < 50mgN/L, temperature ranges from 25-30oC, organic matters are negligible, phosphorus concentration ranges from 0,5-1,5 mg/L, pH: 5 7,2-8,0, alkalinity ranges from 200-300 mg(CaCO3)/L. - Batch experiment: Assessing the effects of retention time, density of the carriers, oxygen concentration, substrate and the number of reaction compartments, from which the optimal parameters could be given for nitrification and dennitrification process. - Continuous experiment: The model is designed based on the parameters obtained from batch experiment to determine the kinematic parameters for nitrification and denitrification for DHY carrier. - Designing an integrated MBBR and DHK tank with capacity of 5m3/h for ammonia removal in order to verify the kinematic parameters obtained in the laboratory in Yen Xa water plant, Thanh Tri district. 6 CHAPTER 1. OVERVIEW OF AMMONIA REMOVAL IN GROUNDWATER BY APPLICATION OF MBBR TECHNOLOGY 1.1. Overview of ammonia pollution situation in Hanoi Most of groundwater in Hanoi has an iron concentration of 3-20 mg/L which is much higher than the clean water standard of 0.3 mg/L. In addition, the concentration of manganese and organic matters in some areas is about 1 - 5 times higher than the clean water standard of maganese as 0.3 mg/L and organic matter as 2mg/L. Particularly, the south and southwest of Hanoi is polluted with ammonia (NH4 +) with a very high ammonia concentration of 5-25 mg/l (3.8-20 mgN/L) compared to the clean water standard of 3 mg/L (2.3 mgN/L). Currently, the water treatment technology in Hanoi is mainly to remove iron, manganese in the groundwater using the processes of aeration, sedimentation, contact and rapid filtration. The effluent quality complies with the national standard QCVN 01: 2009/BYT except the ammonia that is almost untreated. According to the survey results, the ammonia concentration is about 10-20% lower than the input level. As a result, the ammonimum concentration remains 5-20 mg/L (4-18 mgN/L) in the water supplied for the city, which is higher than the standard of 3 mg/L (2.3 mgN/L). 1.2. Ammonia removal by biological method The bio-based ammonia treatment can be carried out in three main processes: (1) conventionally nitrification and denitrification; (2) Anammox is an anaerobic ammonia oxidation process in which 7 ammonia and nitrite are directly reduced into nitrogen gas; (3) Sharon is the partial nitrification process, its product is also nitrite and then denitrified into nitrogen gas as the principle of "hopping" treatment of the process. The Anammox and Sharon processes can save about 25% of the oxygen and 40% of the organic matters, but require rigorous and relatively complicated control during operation. Therefore, this thesis focuses on the conventional ammonia treatment method, that is nitrification and denitrification into nitrogen gas. 1.3. Biofilm technique 1.3.1. Biofilm carrier The DHY carriers are made of polyurethane by the Vietnam Construction and Environment Joint Stock Company (VINSE). Its surface area is calculated based on the geometrical dimension of the substrate and its porous structure. The very small holes inside the substrate creates surfaces for the growth and development of microorganisms; The diffusion and metabolism mechanism is similar to the fixed biofilm. Thus, the biomass transfer process in the moving carrier system is higher than that of the fixed carrier system. The DHY carrier is made of polyurethane (PU) with high porosity of 92-96%, large surface area which can be up to 15,000 m2/m3 (normally from 6,000 to 8,000 m2/m3). Due to the porous structure of the carrier, it has a very low specific gravity of about 33 kg/m3, the substrate is highly flexible, limits the movement of oxygen out of the tank by which the pressure and volume of gas 8 required for the tank is reduced, save energy and reduce operating costs. The carriers in the tank accounts for about 20-30%. 1.3.2. Moving Bed BioFilm Reactor (MBBR) The biofilm technology is a common solution in many water treatment plants, such as BF, Rotating Biological Contactors (RBC), submerged biofilm with various types of filtration materials. The carriers in the tank accounts for a very high percentage (usually from 40-100%), but their ammonia treatment efficiency is not high (only about 60-70%), the structure is large and easily clogged. The Moving Bed Biofilm Reactor (MBBR) solves the remaining problems in the reactors using fixed biofilms such as reducing the volume of structure, reducing energy costs, and significantly increasing the efficiency of ammonia treatment to about 90-95%. 1.4. Research situation in Vietnam and the world Currently, the ammonia treatment technology requires to build many tanks to separate the treatment processes, the carriers used have small surface area, high density, and requires to supplement the substrate for denitrification or water circulation, strict control of oxygen concentration, much energy consumption and complicated operational management. The biofiltration method using MBBR allows an increase in microbial density per unit volume to ten times higher than the activated sludge technique and thus, it significantly increases the treatment efficiency. On the other hand, there is an occurence of self-selection and enhancement of the density of slow-growing microorganisms in the biofilm. The operation of the treatment 9 system faces the difficulty in the biomass transfer (providing food for microorganisms in biofilm of thickness up to mm) for high- density microorganisms. The Fluidized Bed and Moving Bed Biofilm Reactor (MBBR) are developed to promote the biomass transfer in the treatment system, overcome the constraints of other biofilm techniques such as Trickling Filter, Biological Rotating Reactor, subermerged filter. The MBBR is less efficient than the Fluidized Bed because of its lower carrier area but it has the advantage of simple operation, suitable for medium and small-sized treatment scale in Vietnam. The operation of the Fluidized Bed system requires a very high automation. Therefore, the next step is to integrate the biological processes on appropriate bio-carriers and integrate the tanks in modular form. 10 CHAPTER 2. SUBJECT AND RESEARCH METHODOLOGY 2.1. Scope and subject of the research The scope of the reasearch is Hanoi groundwater. The research subject is ammonia treatment system using DHY carriers, integrated with self-cleaning filter. This equipment is installed behind the existing rapid filter of Yen Xa water plant (filtered water and undisinfected with activated chlorine). The capacity of the field pilot is 5m3/h. The nitrification and denitrification processes inside the carrier in aerobic conditions, the determination of kinematic parameters, the calculated parameters through the batch and continuous experimental system in laboratory. Implementing design and field pilot run in order to inspect the results and propose a set of parameters for calculation and design of the ammonia treatment system for ground water. Pilot run is to verify the results and propose calculation parameters, design MBBR module. 2.2. Determination of kinematic parameters 2.2.1. Nitrification In order to design a water treatment system based on a kinematic model, the kinematic constants must be known. Characteristic values for kinematic process including the substrate consumption coefficient k (μ/Y), the semi-saturation indicator Ks, endogenous degradation constant kp, can only be determined from experiments with respect to a specific experimental system. The experimental system is a reactor containing the concentration of microorganism X which agitates and operates 11 continuously (where the inflow rate is equal to the outflow rate, the substrate concentration in the inflow is S0, the outflow is S. The concentration of microorganisms in the inflow is X0 (g/l), the outflow is Xe (g/l). The substrates are used by microorganisms to synthesize cells, a part enters in biochemical reaction in order to generate energy, the number of microbiological cells formed correspond to the loss of substrate in the system. Then, the cell growth rate Vg(g/l.d) is defined by the formula: g dX V .X dt    (2-16) (2-16) Where μ (1/d) is the specific correlation coefficient for each microbial species or specific growth constant. vsu is the substrate decrease rate, accordingly: vg = -Y.vsu (2-17) (2-17) Where Y is the biomass efficiency, which means that when an amount of substrate is consumed, a certain amount of biomass (g/g) is produced, the sign (-) indicates two opposite processes. However, the need for materials to grow microorganisms in accordance with the expression (2-17) is rarely satisfied. When it does not meet the major demand, the growth rate will decrease, which is attributable to the change in specific growth constant value, so according to Monod kinematics, μ is calculated as follows: max S S . K S     (2-18) (2-18) Combining equations (2-16), (2-17) and (2-18), we have: 12   m su S .X.S V Y K S     (2-19) (2-19) Or the rate of substrate decline is also defined:   osu o S SQ V S S V        (2-20) Using a continuous agitation experimental system, then, the cell retention time is defined: c w r e e V.X Q .X Q .X    (2-21) (2-21) In which: Qw: Flow rate of water-sludge mixture entering the sludge tank Qe: Flow rate getting out of the reactor V: Reactor volume X, Xe, Xr: Density of microorganism in the reactor in the inffluent and effluent. Accordingly, the equilibrium equation describing the variation in biomass density and the substrate concentration is expressed as follows:   'o w r e e g dX Q.X Q .X Q .X V.v dt     (2-22) In which: Q: Influent rate equal to Qe X0: Microbiological concentration in the influent v,g: Real biomass growth rate v,g = vg + vp = -Yvsu – kp.X (2-23) (2-23) V: Volume of reaction block 13 In a stable operating state with microbial density X, the microbial density does not change over time dX/dt = 0. The concentration X0 in the influent is usually very small so X0=0. From the equation (2-22) and (2-23): w r e e su p Q .X Q .X Yv k .X V     (2-24) Divide 2 sides by X: w r e e su p Q .X Q .X Yv k V.X X     (2-25) The left side of the equation is the inverse of the sludge age, then (2-24) is rewritten: su p c Yv1 k X     (2-26) Combining the equation (2-18) and (2-19) we have:   Om su S S S.X.S V Y K S        (2-27) Where the specific substrate consumption coefficient k means the ability to consume substrate per unit of formed biomass. mk Y   (2-28) Combining 2-27 and 2-28 we have: 0 su S S Sk.X.S V K S        (2-29) Divide two sides by X, o S S Sk.S K S .X     (2-30) Linearization of (2-30) by inversion: 14 S o K.X 1 S S k.S k     (2-31) If we consider the left-hand side (2-31) as a function, 1/S is a variable, we obtain the linear equation with the slope (Ks/S and the vertical cutoff is 1/k), accordingly k, Ks could be calculated. The values kp and Y are defined as follows: Using the relation of the expression (2-26) and taking 1/ as a function, vsu/X is a variable, from which Y and kp could be determined. 2.2.2. Denitrification As the denitrification is heterotrophic aeration process, so experiment made to calculate the kinematic parameters is using for the organic matter consumption process, as it is the control element of denitrification process. The kinematic model established to describe denitrification include Monod and empirical models. The denitrification rate can be expressed as: U = k (2-32) U = k.X (2-33) Where k is the constant of reaction rate, X is the concentration of microorganisms. With the continuous-flow reaction technique, the denitrification efficiency and reaction rate are calculated from experiments by the formula: O O S S H S   (2-34) O OS S S .H.Qr V     (2-35) n rar k.S (2-36) 15 Accordingly, the rate of specific substrate consumption for nitrate is calculated by the formula: r U X  (2-37) r/X means the rate of substrate consumption per unit of mass (concentration) of microorganisms, which is called the specific denitrification rate U. Then, the equation (2-37) is written as follows: o oS S S Sr QU . X .X V X    