BIOLOGICAL DENITRIFICATION OF WASTEWATER USING A HYBRID REACTOR
S.BHUVANESH
DEPARTMENT OF BIOCHEMICAL ENGINEERING AND BIOTECHNOLOGY INDIAN INSTITUTE OF TECHNOLOGY DELHI
FEBRUARY 2015
© Indian Institute of Technology Delhi (IITD), New Delhi, 2015
BIOLOGICAL DENITRIFICATION OF WASTEWATER USING A HYBRID REACTOR
by
S.BHUVANESH
DEPARTMENT OF BIOCHEMICAL ENGINEERING AND BIOTECHNOLOGY
Submitted
In fulfillment of the requirements of the degree of DOCTOR OF PHILOSOPHY
to the
INDIAN INSTITUTE OF TECHNOLOGY DELHI
FEBRUARY 2015
i
Certificate
This is to certify that the thesis entitled “Biological Denitrification of Wastewater Using a Hybrid Reactor” being submitted by Mr. S.Bhuvanesh is worthy of consideration for the award of the degree of Doctor of Philosophy. The thesis has been prepared under my supervision and guidance in conformity with the rules and regulations of Indian Institute of Technology Delhi and is a record of the original bonafide research work. The results presented in this thesis have not been submitted in part or full to any other universities or institutes for the award of any other degree or diploma.
Dr. T.R.Sreekrishnan
Date: Professor
New Delhi Department of Biochemical Engineering and
Biotechnology
Indian Institute of Technology Delhi
ii
Acknowledgements
I am deeply indebted to my supervisor Prof. T.R.Sreekrishnan whose guidance, stimulating suggestions and encouragement helped me in all the time of research and writing of this thesis. I have learnt from him not only science but life as well.
I am so grateful to Dr. V.Saravanan and Dr. Ziauddin Shaikh for their valuable inputs for my thesis.
The members of the Waste Treatment Lab and Downstream Processing Lab have contributed immensely to my personal and professional time at IIT Delhi. I want to thank them for all their help, support, interest and valuable hints. Especially I am obliged to Mr.
Muthumareeswaran, Mr. Satyendra Singh, Dr. Surajbhan Sevda, Dr. Kanakana Kundu, Ms.
V.P.Ranjusha, Mr. S.Premnath, Dr. Rashi Vashist, Ms. Akanksha Mehrotra, Mr.Sunil Kumar and Mrs. Pragya. I want to give my special thanks to Mr. N.Maneesh for all his mental support and assistance with my work. My gratitude is always there to all the good souls whose names I have failed to mention that have helped me either directly or indirectly.
Lastly, I would like to thank my family for all their love and encouragement. For my parents who raised me with a love of science and supported me in all my pursuits. And my brother Mr. S.Pravin whose constant encouragement pushed me so far. This thesis would not have been complete without the support of my wife and neither would be this acknowledgement without thanking her.
(S.BHUVANESH)
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Abstract
In this work, denitrification of wastewater using a hybrid anaerobic reactor, developed at the Waste Treatment Laboratory in the Department of Biochemical Engineering and Biotechnology, IIT Delhi, under anoxic conditions has been studied.
The effect of wastewater characteristics, reactor operating conditions and reactor geometry on granulation and denitrification has been studied. The long start-up period, observed in several other systems using granular biomass, was not observed in the hybrid reactor. The reactor was able to handle a nitrate loading rate of 50 g NO3-N/m3.day at the end of 3 days start-up. At the end of 15 days, almost spherical granules with a settling velocity of 1.5 cm/s and a mean diameter of 0.5 mm were produced. By stepwise increment of the influent nitrate concentration, the removal rate reached 740 g NO3–N/m3.day with a removal efficiency of almost 100% at a hydraulic retention time of 6 h or higher. For complete denitrification, the ratio of the organic substrate required to the amount of nitrate nitrogen removed was as low as 2.2 g COD/g NO3–N. The study was extended to a nitrified toxic industrial effluent.
Denitrification was on par with the synthetic wastewater and efficiency of more than 95% was achieved.
To understand the cause of rapid start-up in the hybrid reactor, present knowledge of the granulation process has been reviewed and based on the experimental observation during the study, a hypothesis for the mechanism of granulation has been presented.
Finally, based on the data obtained with the laboratory-scale hybrid reactor, a mathematical model has been developed for the reactor. The model combines the biofilm flux and the bed fluidization to predict the reactor dimensions, substrate concentration along the reactor height and the fluidized bed height required for complete denitrification.
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Contents
Certificate ... i
Acknowledgements ... ii
Abstract ... iii
Contents...iv
List of Figures ... viii
List of Tables ... x
Nomenclature ... xi
1 Introduction and Objectives ... 1
1.1 Background ... 1
1.2 Objectives ... 4
2 Literature Review... 7
2.1 Nitrogen Cycle ... 7
2.2 Biological Nitrogen Removal from Wastewaters ... 8
2.3 Biological Denitrification ... 10
2.4 Simultaneous Nitrification and Denitrification ... 11
2.5 Microbial Granulation ... 12
2.5.1 Anaerobic Granules ... 13
2.5.2 Aerobic Granules ... 13
2.6 Hybrid Anaerobic Reactor ... 13
2.7 Model for Hybrid Anaerobic Reactor ... 16
v
2.7.1 Bed Fluidization Model ... 17
2.7.1.1 Terminal Settling Velocity ... 18
2.7.1.2 Fluidization Mechanics... 20
2.7.1.3 Biogranule Terminal Settling Velocity ... 22
2.7.1.4 Bed Expansion Characteristics ... 22
2.8 Microbial Granulation Models ... 23
2.8.1 Inert Nuclei Model ... 24
2.8.2 Selection Pressure Model ... 24
2.8.3 Multi-Valence Positive Ion-Bonding Model ... 25
2.8.4 ECP Bonding Model ... 26
2.8.5 Synthetic and Natural Polymer-Bonding Model... 26
2.8.6 Local Dehydration and Hydrophobic Interaction Model ... 26
2.8.7 Surface tension model ... 27
3 Materials and Methods ... 29
3.1 Reactors and Experimental Set-up ... 29
3.2 Wastewater and Feed ... 31
3.3 Start-up and Operating Conditions ... 33
3.3.1 Lab-scale HAR... 33
3.3.1.1 Granulation Studies ... 34
3.3.1.2 Reactor Performance Studies ... 36
3.3.2 Pilot-scale HAR ... 37
vi
3.4 Hybrid Aerobic Reactor ... 37
3.5 Analytical Methods ... 39
4 Results and Discussion ... 40
4.1 Microbial Granulation ... 40
4.1.1 Seed sludge ... 41
4.1.2 Cation binding and pH ... 42
4.1.3 Carbon source ... 48
4.1.4 Superficial up-flow velocity and reactor geometry ... 51
4.1.5 Nitrate load and Hydraulic Retention Time ... 54
4.1.6 Temperature ... 56
4.2 Properties of the Granules ... 57
4.3 Mechanism of Microbial Granulation in the HAR... 68
4.4 Granule Stability ... 71
4.5 Nitrate Removal and Reactor Performance ... 71
4.6 Denitrification of Actual Wastewater ... 82
4.7 Aerobic Granulation in the Hybrid Reactor ... 85
4.7.1 Granulation ... 86
4.7.2 Reactor Performance ... 88
4.8 Model Development ... 90
4.8.1 Denitrification Stoichiometry ... 90
4.8.2 Biofilm Model ... 92
vii
4.8.2.1 Nitrate Flux ... 93
4.8.2.2 Carbon Flux ... 96
4.8.3 Bed Fluidization Model ... 100
4.8.4 Reactor Model ... 102
4.8.5 Model Parameters ... 103
4.8.5.1 Reactor Constants ... 103
4.8.5.2 Kinetic Constants ... 104
4.8.6 Model Validation with Experimental Data ... 104
5 Summary and Conclusion ... 107
6 Future Scope ... 110
References ... 111
Appendices ... 123
Appendix A ... 123
Appendix B ... 134
Appendix C ... 137
viii
List of Figures
Figure 1: Nitrogen cycle in the environment ... 8
Figure 2: Biological nitrogen removal from wastewater ... 9
Figure 3: Schematic representation of the hybrid reactor ... 16
Figure 4: The hybrid reactor ... 30
Figure 5: Effect of CaCl2 on sludge settling in a column ... 45
Figure 6: Effect of high superficial velocity ... 52
Figure 7: Close-up image of the dried granules ... 58
Figure 8: Image of the final granule taken using a 4X objective lens ... 60
Figure 9: SEM image of the final granule ... 62
Figure 10: SEM image the initial granules ... 63
Figure 11: SEM images of the initial granules ... 64
Figure 12: EDX Spectrograph of the elements in the initial granules ... 65
Figure 13: EDX Spectrograph of the elements in the final granules ... 67
Figure 14: Denitrification in the HAR ... 73
Figure 15: Plot showing the effect of pH on nitrate removal ... 74
Figure 16: Denitrification in the HAR at COD/NO3-N ratio of 15... 75
Figure 17: Denitrification in the HAR at COD/NO3-N ratio of 9... 76
Figure 18: Denitrification in the HAR at COD/NO3-N ratio of 3.6... 77
Figure 19: Denitrification in the HAR at COD/NO3-N ratio of 2.2... 78
Figure 20: Denitrification in the HAR at maximum nitrate loading ... 80
Figure 21: Performance of the reactor at different HRT ... 81
Figure 22: Denitrification of the actual wastewater ... 83
Figure 23: Plot showing the effect of pH on denitrification of industrial effluent ... 85
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Figure 24: Image of the granules obtained in reactor R4 ... 88
Figure 25: Performance of the aerobic hybrid reactor for SND ... 89
Figure 26: Plot showing the order of the reaction for denitrification in the HAR ... 93
Figure 27: Flow chart outlining the algorithm to solve the biofilm model. ... 99
Figure 28: Flow chart outlining the algorithm to calculate bed voidage of the HAR ... 101
Figure 29: Schematic representation of compartments within the reactor ... 102
x
List of Tables
Table 1: Dimensions of the different reactors ... 31
Table 2: Composition of synthetic wastewater for denitrification ... 32
Table 3: Composition of nitrified industrial wastewater ... 33
Table 4: Properties of the seed sludge ... 34
Table 5: Different experimental conditions used for the granulation study ... 36
Table 6: Composition of synthetic wastewater for SND ... 38
Table 7: The sludge volume index after three days of reactor operation... 43
Table 8: Effect of COD/NO3-N ratio and the sludge loading rate on sludge granulation ... 50
Table 9: Effect of reactor configuration on granulation start-up and maintenance ... 54
Table 10: Effect of initial nitrate load on sludge granulation ... 55
Table 11: Effect of temperature on sludge granulation ... 56
Table 12: Properties of the granules in the hybrid reactor. ... 59
Table 13: Settling velocity of the granules ... 61
Table 14: Concentration of elements obtained from EDX analysis of initial granules ... 65
Table 15: Concentration of elements obtained from EDX analysis of final granules ... 68
Table 16: Comparison of the performance of the hybrid reactor with other systems... 82
Table 17: Effect of reactor configuration on granulation start-up and maintenance ... 87
Table 18: Estimation of the stoichiometric parameters for the HAR ... 92
Table 19: List of differential equations with their boundary conditions ... 99
Table 20: Reactor parameters for reactor dimensions ... 103
Table 21: Kinetics and physical parameters for denitrification ... 104
Table 22: Comparison of model predicted values and experimental values ... 105
xi
Nomenclature
A - Cross sectional area of the column in cm2
ANAMMOX - Anaerobic Ammonium Oxdiation
B - Diameter of the inlet tube in HAR in cm
C - Height of the frustum cone in HAR in cm
CD - Drag coefficient
COD - Chemical oxygen demand
d or dp - Diameter of the particle or biogranule in cm
D - Column diameter in cm
De - Effective diffusion coefficient in cm2/h
ECP - Extracellular polymer
EDX - Energy-dispersive X-ray spectroscopy
FBR - Fluidized bed reactor
fs - Fraction of electron donor associated with cell synthesis
g - Acceleration due to gravity in cm/s2
h - Fluidized bed height in cm
HAR - Hybrid anoxic reactor
HDratio - Ratio of height to diameter of the HAR
HRT - Hydraulic retention time
k' - Denitrification rate in mg NO3-N/L.day
k - Zero order denitrification rate constant in mg NO3-N/g VSS.day
ks - Monod constant in mg/L
n - A parameter in Richardson Zaki equation
N - Number of microbial granules
NO2-N - Nitrite nitrogen NO3-N - Nitrate nitrogen
xii
NR - Nitrogen removal in mg/L
Q - Feed flow rate in L/day
r - Radial position within the bead in cm
R - Radius of the microbial granule in cm
rc - Surface free energy of microbe
Ret - Particle Reynolds number
rl - Surface free energy of liquid
rs - Surface free energy of inert particle
S - Substrate concentration within the granule/compartment in mg/L Sb - Substrate concentration in the bulk liquid phase in mg/L
SBR - Sequencing batch reactor
SND - Simultaneous nitrification and denitrification
SRT - Solid retention time
SVI - Sludge volume index
TSS - Total suspended solids
UASB - Up-flow anaerobic sludge bed
ui - A parameter in Richardson Zaki equation
us - Up-flow liquid superficial velocity in cm/day
ut - Terminal settling velocity in cm/s
v - Denitrification rate in mg NO3-N/g VSS.day
vb - Component flux at the surface of the granule in mg/day
Vs - Volume of the granule in L
VSS - Volatile suspended solids
X - Biomass concentration in mg/L
YN/C - YN2/COD
YN/N - YN2/NO3-N
YX/C - YBiomass/COD
xiii YX/N - YBiomass/NO3-N
ΔGa - Free energy of adhesion
ε - Bed porosity
θ - Angle of inclination of frustum cone with respect to axis of HAR
μ - Specific growth rate in h-1
μl - Liquid viscosity in g/cm.s
μmax - Maximum specific growth rate in h-1
ξ - COD/NO3-N ratio
ρl - Density of the liquid in g/L
ρp - Density of the particle in g/L
ϕ - Thiele modulus
