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Introduction to Azo Dye Treatment

Aerobic Granular Sludge - A Possible Alternative

Project Objectives and Goals

Methods

Results & Discussion

Summary and Future Work

Outline

HKUST BIOENGINEERING GRADUATE PROGRAM

Sludge Granulation for

Azo Dye Wastewater Treatment

Lawrence, Yan KaiqiSupervisor : Prof. Ka Ming Ng

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Introduction to Azo Dye Treatment

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INTRODUCTION TO AZO DYE TREATMENT – Azo Dyes’ Structures

Mordant Orange 1

Coloring Azo Bond

Azo Dyes

Simple synthesis

Good technical performance

Wide color spectrum

70 % of synthetic colorants used in the

textile industry

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INTRODUCTION TO AZO DYE TREATMENT – Azo Dye Pollution

Dyeing Process

Wat

er

Unc

olor

ed P

rodu

cts

Colored Products

Azo Dyes Wastewater containing 2-50% of original azo dyes

Deeply Colored

Potentially Carcinogenic

and Mutagenic

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INTRODUCTION TO AZO DYE TREATMENT – Azo Dyes Wastewater Treatment

Azo

Dye

Was

tewa

ter

Trea

tmen

ts

Physicochemical Methods

Ozonation

Photochemical Treatments

Sonolysis

Fenton’s Reagent Oxidation

Adsorption

Chemical Coagulation/ Flocculation with Sedimentation

Biological Methods

Biosorption

Biodegradation

Advanced Oxidation Process

Economical and Environmentally Friendly Option

Require Expensive Equipment and Chemicals

Generate Secondary Waste

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CO2, H2O, N2 …

Colorless,Harmless

Aerobic Amine Mineralization

INTRODUCTION TO AZO DYE TREATMENT – Conventional Activated Sludge System

Conventional Activated Sludge System

AnaerobicTank

Sedimentation Tank

Sludge SedimentationColor Removal Aromatic Amine Removal

AerobicTank

N

N

R1

R2

NH2 R2

R1 NH2

Azo Dye Aromatic Amines

Colored Colorless, Toxic

Chromophore

Anaerobic Decolorization

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Aerobic Granular Sludge – A Possible Alternative

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Aerobic Sludge Granulation:A process of microbial self-

aggregation, by means of biological, physical and chemical phenomena, to help the community achieving better survivability

Microbial cell organized into dense and fast settling pellets with diameter 0.2 mm to around 5 mm

AEROBIC GRANULAR SLUDGE – Introduction to Sludge Granulation

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AEROBIC GRANULAR SLUDGE – Formation Mechanisms

Aerobic sludge granulation usually occurs in sequencing batch reactors with air aerated at a high superficial velocity

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AEROBIC GRANULAR SLUDGE – Granulation Process

Hydraulic Shearing

Forces

Flagella Movements

Gravitational Forces

Extracellular Polymeric Substances (EPS)

Chemical Forces Formation of ionic pairs or triplets

with divalent/ trivalent ions

Physical Forces van der Waals Forces, opposite

charge attraction

Biochemical Forces Surface Dehydration,

Membrane Fusion

Step 1Initiation of bacterium-

bacterium contact by physical movements

Step 2Maintaining stable bacterium-

bacterium contact with the establishment of attractive

forces

Step 3Maturation of aerobic granule structures by microbial forces

Step 4Formation of stable 3-

dimensional structure with granules shaped by

hydrodynamic shearing forces

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AEROBIC GRANULAR SLUDGE – Replication Mechanisms

Sludge growth and aggregation

Shearing forces acting on the

granules cause fragmentation

Internal decay of biomass

resulting in voids and cavities

Reformation of stable granule

structure

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AEROBIC GRANULAR SLUDGE – Anaerobic Zones in Aerobic Granules

Dead CellsPolysaccharides,

Lipids,

Proteins

Aerobic Zone

Anaerobic Zone

Living AnaerobicBacteria

Living AerobicBacteria

Modified from: Y. Li, Y. Liu, L. Shen and F. Chen, "DO diffusion profile in aerobic granule and its microbiological implications," Enzyme and Microbial Technology, pp. 349-354, 2008.

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AEROBIC GRANULAR SLUDGE – Comparing to Conventional Activated Sludge

Conventional ActivatedSludge

Granular Sludge

Well – Established Faster Settling Velocity

Higher Biomass Retention

Less Space Consuming

Lower Construction and Operating Costs

Possible to perform simultaneous AN/A reactions

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AEROBIC GRANULAR SLUDGE – Proposed Azo Dye Degradation Mechansim

Living CellsLiving

AnaerobicBacteria

Living AerobicBacteria

Dead CellsPolysaccharides,

Lipids,

Proteins

MassTransfer

Dye

AnaerobicDecolorization

AromaticAmine Aerobic

Aromatic Amines

Mineralization

HarmlessEnd Products

Fast Settling Velocity

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Project Objectives and Goals

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PROJECT OBJECTIVES & GOALS

• To devise a method towards successful cultivation of aerobic granules for azo dye wastewater treatment;

• To demonstrate the developed granules capabilities in performing simultaneous anaerobic decolorization and aerobic aromatic amines mineralization;

• To investigate the effects of different operating parameters to the process performances, including:

• 1. Sludge granular size • 2. Saturated bulk dissolved oxygen

concentration (DO)• 3. Biomass concentration• 4. Organics loading concentration

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Methods

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METHODS – Schematic Diagram of the Experiment

Granules Characterization

Morphology and Size Particle Density

Volatile Solid/Solid

Dry Mass/Wet Mass

Sludge Granular Size

Biomass Loading

Bulk Dissolved Oxygen

Organic Loading

Color

Aromatic Amine

COD

Cultivation and Acclimation of

aerobic granules

Performance Tests

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METHODS – Conventional Granulation of Aerobic Sludge

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METHODS – Revised Method of Acclimation and Sludge Granulation

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METHODS – Photo of Aerobic Granules Cultivated in the Project

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METHODS – Granular Size Control

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METHODS – Dissolved Oxygen Control

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METHODS – Verification of the Dissolved Oxygen Control

To verify the method of dissolved oxygen control Mixed gases with different

compressed air to nitrogen ratios were used to maintain a certain oxygen content (%) in it.

The dissolved oxygen concentration of the reactor content was measured by a ODO probe (YSI ProODO™)

For the verifying the method, dissolved oxygen concentrations of different oxygen contents in the mixed gases were also predicted using the Henry’s Law.

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METHODS – Color Removal Monitoring by UV-Vis Spectrometry

To measure the color intensityThe absorbance at 371.5nm, which is the characteristic peak of the model pollutant Mordant Orange 1, was measured using a UV-Vis spectrophotometer

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METHODS – Aromatic Amines Monitoring by Diazonium Coupling Reaction

To measure the aromatic amines concentration• Diazonium coupling reaction was

employed to measure the colorless aromatic amines concentration generated during the anaerobic decolorization. The reaction couples the colorless primary aromatic amines with coupling agent and form purplish-pink products, which was then measured using a UV-Vis Spectrometer.

• With different aromatic amines, the reaction is known to produced products with slightly different intensities at different wavelengths of maximum absorbance.

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METHODS – Diazonium Coupling Reaction Modification

To make accurate measurement of aromatic amines concentration:The theoretical reduction products of mordant orange 1, 4- Nitroaniline (4-NA) and 5- Aminosalicylic acid (5 –ASA), were used to produce a calibration curve for amines monitoring.

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Results and Discussions -Size, Morphology and Physical Properties of

Aerobic Granules

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RESULTS & DISCUSSSIONS – Size and Morphology

Diameter and shape descriptors of different sizes granules.

Size Category (a) 0.3 – 1.0 mm

(b) 1.0 – 1.7 mm

(c) 1.7 – 2.4 mm

(d) > 2.4 mm

Area-averaged Diameter (mm) 0.730.22 1.51 0.33 2.420.46 4.120.93

Aspect Ratio 1.690.48 1.490.38 1.380.27 1.300.20

Roundness 0.630.15 0.700.14 0.750.12 0.790.10

Size and morphology of granules• Granules developed in this study had

area-averaged diameters of 0.3 – 5 mm

• The decreasing aspect ratios and increasing roundness with increases in granular size indicate larger granules were more spherical in shape.

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RESULTS & DISCUSSSIONS – Physical Properties

Physical properties of the cultivated aerobic granules• By Stokes Law, V and d2

• Where V= settling velocity of a spherical particle;

• and d = the particle density and particle diameter;

• The particle density of aerobic granules (1.01 to 1.04 g/cm3) is similar to the density of activated sludge ((1.01-1.06 g/cm3)

• The improved settling velocity is due to the increase in particle diameter instead of the improvement of particle density

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Results and Discussions -Effect of Sludge Granular Size and Bulk

Dissolved Oxygen Concentration

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RESULTS & DISCUSSSIONS – COD Removal

% of COD removal of different size granules under different DO• DO , % of COD removal

• Activation of oxygen dependent metabolic pathway that is more energetically efficient.

• Granular size , No significant impact to the % of COD removal in 48 hours, but with COD removal rate.

• Smaller mass transfer resistance in smaller granules

COD removal kinetics of different sizes granules under a dissolved oxygen of 1 ppm

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RESULTS & DISCUSSSIONS – General Trends of Dye Removal Kinetics

General Trends of Dye Removal Kinetics

Where D = dye content of the commercial dye• Dye equiv. is a collective

measurement of the total amount of dye related compound in the wastewater

• Sudden drop of dye and dye equiv. conc. (120 to 100 ppm) immediately after aerobic granules added

• Initial rapid biosorption• Continuous decolorization with

aromatic amines generation • Reductive decolorization

• Aromatic amines concentration built up faster at the beginning, but dropped later in the experiment

• Simultaneous production and consumption of aromatic amines

Dye remediation kinetics using different sizes granules under different dissolved oxygen levels (▲ represents the Dye Equiv. concentration; represents the color; represents the aromatic amines concentration)

Dye removal kinetics of granules in the size of 1.7 – 2.4 mm under a DO conc of 1 ppm

Sudden drop

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RESULTS & DISCUSSSIONS – Color Removal

% of Color removal of different size granules under different DO• DO, % of color removal

• Reductive decolorization is favored by the –ve redox potential provided by anaerobic condition

• Oxygen is better e- acceptor

than azo bond• Granular size , % of color removal

• Better synergy in more mature, larger granules

• Granular size , % of color removal is less sensitive to the change in DO concentration

• Smaller change in the anaerobic region to aerobic region ratio

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RESULTS & DISCUSSSIONS – Color Removal (cont.)

Anaerobic zone in aerobic granules• The thickness of aerobic layer on

aerobic granules is independent to the sludge granular size (Li et. al. (2008))

• Larger granules have larger portions of anaerobic zone in a high DO conc.;

• With the change of the bulk DO conc., smaller granules may change from completely anaerobic to completely aerobic, while larger granules might only change to partially aerobic

• Larger granules have a more stable ratio of anaerobic zone to aerobic zone

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RESULTS & DISCUSSSIONS – Aromatic Amine Removal

% of Aromatic amines removal of different size granules under different DO• Granular size , % of aromatic amines

removal is less sensitive to the change in DO concentration

• Smaller change in the anaerobic region to aerobic region ratio

• DO , % of aromatic amines removal • Oxygen is required for the

destruction of aromatic structures by the enzymes hydroxylase and oxygenase;

• In low DO, larger granules showed better aromatic amines removal;

• Better synergy in the bacterial community;

• In high DO, smaller granules showed better aromatic amines removal;

• Smaller granules have larger portion of aerobic region in high DO

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RESULTS & DISCUSSSIONS – Equivalent Dye Removal

% of Equivalent dye removal of different size granules under different DO• DO , Decolorization rate and

aromatic amines mineralization rate ;

• In low DO, the dye removal is limited by the aromatic amines mineralization; In high DO, the dye removal is limited by the decolorization;

• To achieve an optimized dye removal, the decolorization rate and aromatic amines mineralization rate have to be balanced.

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Results and Discussions -Effect of Biomass Concentration and

Organics Loading Concentration

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RESULTS & DISCUSSSIONS – Effect of Biomass Concentration

Effect of biomass concentration• Biomass conc. , process

performances ;• From 1.25 g/L to 5 g/L, significant

improvements was observed in all parameters

• More degradation enzymes can be produced with higher biomass concentration.

• Similar % of pollutant removal after 5g/L

• The process may be limited by other factors, including the trace element concentration in the wastewater

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RESULTS & DISCUSSSIONS – Equivalent Dye Removal

Effect of organic loading concentration• Organic loading played two roles on

the bacterial dye removal, which are:

• (a) Carbon, nitrogen and energy source;

• (b) Electron donors for the reductive decolorization.

• Organic loading conc. , % of color removal , % of aromatic amines removal ;

• More e- generated for reductive decolorization;

• Preferential utilization of organic loadings with simpler structures, instead of aromatic amines

• The optimized organic loading concentration was determined to be 4000 ppm, as which balance the organic loading effect on color and aromatic amines removal.

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Conclusions and Future Work

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Conclusions

1. An integrated acclimation and granulation scheme was devised to cultivate aerobic granules for simultaneous anaerobic decolorization/ aerobic aromatic amines mineralization with its performances optimized by varying sludge granular size, bulk dissolved oxygen concentration, biomass concentration and organics loading concentration.

2. A good equivalent dye mineralization (61 2%), decolorization (88 1%), aromatic amines removal (70 3%) and COD removal (88 2%)within 48 hours reaction was obtained by using 5 g/L, 1.0 mm – 1.7 mm granules under a bulk dissolved oxygen concentration of 1 ppm, supplemented with 4000 ppm organic loadings from nutrients.

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Future Work

1. Although many factors may affect the size of granules cultivated in the reactor, no technique is currently available to control granular size. The design of sludge granular size controlling method may be important towards a better performances of aerobic sludge granulation system using in azo dye wastewater treatment.

2. Only a single model pollutant, Mordant Orange 1, was used in this study. In real life textile wastewater, other constituents, including surfactants, may exist and damage the developed granulation system. A further investigation of using the developed system for treating real textile wastewater may also be necessary.

3. The techniques of sludge granulation may not only applicable in wastewater treatment, but also in mass production of other bacterial metabolite. The faster settling velocity, higher biomass concentration and easier separation of the biomass from the liquid content may lead to the development of production process with more efficient conversion and easier downstream processes.

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Acknowledgements

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Acknowledgement

SupervisorProf. Ka Ming NG

Thesis examination committee Prof. Guohua CHEN and Prof. Henry LAM

Thesis supervision committeeProf. Xi Jun HU and Prof. David HUI

Wastewater treatment teamDr. Kelvin FUNG, Dr. Judy Zhang, Ms. Pinky Sin

Technical Staff in CBMEMr. Hoi Yau CHENG, Mr. Wing Li LEUNG, Mr. Kam Tim TANG

Technical and administrative Staff in BIENMs. Inez TSUI, Ms Zoei CHU, Ms Winnie LEUNG

Labmates and FriendsMy family members

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Thank You

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METHODS – Selective Pressure Theory

By Stokes Law:The free settling velocity of a spherical sediment is given by:

Where V = the settling velocity of the sediment= the allowed Settling Time L = the liquid level above the disposal porti.e. Volumetric Exchange Ratio Dp = the diameter of the sediment particle the density of the sediment = the density of the settling medium the viscosity of the settling Medium

• Settling time and volumetric exchange ratio were known to be influential to the granule formation and thus be regarded as the selective pressures of the aerobic sludge granulation,

• As short settling time and high volume exchange ratio will result in a larger wash out of reactor content, such conditions were also known as with high selective pressures