sludge reduction

84
NEW APPROACHES TO MINIMIZE EXCESS SLUDGE IN ACTIVATED SLUDGE SYSTEMS G H Chen, K J An, S. G H Chen, K J An, S. Saby Saby , and H K Mo , and H K Mo Department of Civil Engineering The Hong Kong University of Science and Technology (HKUST) Clear Water Bay, Kowloon, Hong Kong

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Page 1: Sludge reduction

NEW APPROACHES TO MINIMIZE EXCESS SLUDGE IN ACTIVATED SLUDGE SYSTEMS

G H Chen, K J An, S. G H Chen, K J An, S. SabySaby, and H K Mo , and H K Mo

Department of Civil EngineeringThe Hong Kong University of Science and Technology

(HKUST)Clear Water Bay, Kowloon, Hong Kong

Page 2: Sludge reduction

Introduction

Activated sludge production, treatment and disposal

Page 3: Sludge reduction

Sludge Production

Primary Settling

Effluent toSecondary Treatment

Raw WastewaterBOD (100%) Screens

Primary Sludge(35% BOD)

Primary Treatment Effluent(BOD 65%) Bio-reactor

Secondary Effluent(BOD 10%)Secondary

Settling

Secondary Sludge(30% BOD)

CO2+ H2O (25% BOD)

Primary sludge:110-170 kg dry solids /103 m3

of wastewater treated

microorganisms

cellsnewOHCOnutrientsOmatterorganic222 ++++

Secondary sludge:70-100 kg dry solids /103 m3

of wastewater treated

3 m3/103m3

wastewater treated

8 m3/103m3

wastewater treated

Page 4: Sludge reduction

Sludge Treatment

Gravity Anaerobic digestion

Chemical conditioning

Primary sludge (5% solids)

Flotation

Aerobic digestion

Heating

Centrifuge

Filter press

Drying bed

Lagoon

Centrifuge

Thickening Stabilization Conditioning Dewatering

optional

7-9% solids

Secondary sludge (1% solids)

Primary sludge + secondary sludge (3% solids)

Anaerobic digestion

~ 30% solids contentReducing the sludge

volume greatly

Sludge reuse or disposal

Page 5: Sludge reduction

Sludge Disposal

Incineration

Ocean dumpingLand application

•The most preferred means• Capacity is limited• Lack of new location

• Practiced in large municipalities• Air pollution

Landfill

Water pollution control regulationsReuse of sludge nutrientSoil amendment Sludge should be less contaminated

Page 6: Sludge reduction

Sludge Disposal

Incineration

Ocean dumping

Landfill

Land application

•The most preferred means• Capacity is limited• Lack of new location

• Practiced in large municipalities• Air pollution

Water pollution control regulationsReuse of sludge nutrientSoil amendment Sludge should be less contaminated

Incineration

Ocean dumping

Landfill

Land application

•The most preferred means• Capacity is limited• Lack of new location

• Practiced in large municipalities• Air pollution

Water pollution control regulations

Incineration

Ocean dumping

Landfill

Land application

•The most preferred means• Capacity is limited• Lack of new location

• Practiced in large municipalities• Air pollution

Water pollution control regulationsReuse of sludge nutrientSoil amendment Sludge should be less contaminated

Best solution will be reducing excess sludge production during the wastewater treatment, or recovering energy and resources from sludge

Page 7: Sludge reduction

Major Approaches of Excess Sludge Reduction

Page 8: Sludge reduction

Major Approaches of Excess Sludge Reduction

(1) Sludge pretreatment through thermal, mechanical, or ozone treatment

(2) Restricting/limiting sludge growth in an aeration tank

Disintegration:Sludge Secondary substrate

Page 9: Sludge reduction

recycled sludge recycled sludge

secondary substratessecondary substrates

dissolvingozonation

Thermal

COCO22 + H+ H22OO

catabolism

new biomassnew biomass

anabolismO2 O2

Why Sludge Why Sludge SolubilizationSolubilization//disintrgationdisintrgationcan Reduce Excess Sludge Productioncan Reduce Excess Sludge Production

As a result, excess sludge can be reducedAs a result, excess sludge can be reduced

Page 10: Sludge reduction

[1] Applied force for sludge pretreatment

– Heat treatment under a high temperature up to 180ºC[R. T. Haugh et al.,1978][J. Pinnekamp ,1989], [U. Kepp et al., 2000], [A. Canales et al., 1994]

– Mechanical pretreatment using ultrasonication, mills and homogenizers[G. Lehne, A. Muller and J. Schwedes 2001], [K. Nickel et al., 1998][U. Basier and P. Schmidheiny, 1997]

• Stirred Ball Mills (SBM) • High Pressure Homogenizers (HPH)• Ultrasonic Homogenizers (UH)• Mechanical Jet Smash Technique (MJS)• High Performance Pulse Technique (HPP)• Lysat-Centrifugal-Technique (LC)

– Ozonation [H. Yasui and M. Shibata,1994], [E. Egemen et al., 2001][T. Kamiya, and J. Hirotsuji, 1998], [M. Weemaes et al., 2000]

Page 11: Sludge reduction

[1] Specific energy consumption with various pretreatment methods [J. Müller,2000]

Specific energy input (kJ/kg SS)

Deg

ree

of s

ludg

e re

duct

ion

(%)

Page 12: Sludge reduction

[1] Comparison of various sludge pretreatment methods

Poor sludge settlingOdor generation

Relatively low

Relatively lowHighOzonation

High costSuitability of the machines for practical application is major concern

HighHighHighMechanical

Produce non-biodegradable organic matter at high temperature Odor generation

HighHighLowThermal

DisadvantagesOperational cost

Energy requirement

Sludge reductionefficiency

Sludge pretreatment method

Page 13: Sludge reduction

[2] Restricting/limiting sludge growth in an aeration tank

A significant reduction in sludge production could be achieved by restricting/limiting sludge growth under the following conditions:

1. at high temperatures [P. Coultate and K. Sundaram,1975], [I. Nioh and C. Furusaka,1968]

2. with the presence of metabolic inhibitory substances [G.H Chen et al., 2000];3. with nutrients limitation [S. P. Tsai, 1990]4. with the presence of higher forms of microorganisms such as protozoa and

metazoa [C. H. Ratsak et al., 1994]; [J. H. Rensink et al., 1997]5. with a long SRT as in an extended aeration process and MBR process [S.

Chaize and A. Huyard , 1993].

Page 14: Sludge reduction

[2] Concept of restricting/limiting sludge growththrough futile cycle or energy uncoupling

EnergyEnergy

Catabolism Anabolism

Energy Conditions to induce futile cycle:

Extreme or unfavorable environmentLimitation of nutrientsPresence of certain chemicalsFutile

Cycle

Page 15: Sludge reduction

Sludge Pretreatment Sludge Pretreatment vsvs Sludge Growth RestrictionSludge Growth Restriction

Sludge Pretreatment Sludge Growth Restriction

60-100% excess sludge reduction

50-80% excess sludge reduction

High energy input Lower energy input

Require modification of treatment plant

Little modification of treatment plant

Page 16: Sludge reduction

Major Shortcomings of the Present Methods

• Poor Sludge Settling

• Higher Oxygen Requirements

• Reduced Nutrient and Substrate Removal

• Alternative method for reducing excess sludge production, which is feasible and cost-effective, is necessary

Page 17: Sludge reduction

New Approaches to Reduce Excess Sludge Studied at HKUST

1. Chemically stimulated futile cycle

2. Chlorination pretreatment of sludge

3. Oxic-Settling-Anaerobic (OSA) process

4. Autotrophic denitrification

Page 18: Sludge reduction

Ideal Chemicals to Stimulate Futile CycleIdeal Chemicals to Stimulate Futile Cycle

Low cost

High efficiency

Low toxicity

Less impact on substrate removal capacity

3, 3’, 4’, 5-tetrachlorosalicyanide (TCS)

Page 19: Sludge reduction

Chemical Structure of TCS

A chemical compound, 3,3A chemical compound, 3,3’’,4,4’’,5,5--ttetrachlorosalicylanilideetrachlorosalicylanilide (TCS) can (TCS) can stimulate futile cycle in stimulate futile cycle in Streptococcus Streptococcus bovisbovis

CONH

Cl Cl

Cl

Cl CH

One of the formulations of soaps, rines, polishes, shampoo, deodorants

Page 20: Sludge reduction

Work Scope

to investigate the effect of TCS on sludge growth rate and

substrate utilization rate

to find out an appropriate TCS dosage to induce excess sludge

reduction

to examine the response of microbial activity to the TCS

dosage

Page 21: Sludge reduction

Methodology:

pure culture of E.Coli

batch and continuous mixed cultures cultivated with and without TCS

endogenous decay coefficient study

Page 22: Sludge reduction

-1

-0.5

0

0.5

1

0 0.1 0.2 0.3 0.4 0.5TCS (ppm)

Yob

s (m

g P-

CO

D/m

g S-

CO

D)

Effect of TCS on the observed growth yield (Yobs) of E. coli at different TCS concentration

S0/ X0 = 2X0 = 500 mg/L

Page 23: Sludge reduction

Change of ATP content in E. coli at different TCS concentrations

TCS concentration (ppm)

∆ATP content (µg/mg SS)

0.0 -1.59 0.02 -1.62 0.05 -1.77 0.1 -1.90 0.2 -1.88 0.4 -2.16

Page 24: Sludge reduction

Effect of TCS on Sludge Growth Rate and Substrate Effect of TCS on Sludge Growth Rate and Substrate RemovalRemoval RateRate

1

1.1

1.2

1.3

1.4

1.5

0 30 60 90 120 150 180Time (min.)

Rel

ativ

e bi

omas

sco

nc. (

X/X

o)

Control0.2 ppm TCS0.4 ppm TCS0.6 ppm TCS0.8 ppm TCS

S0/ X0 = 2X0 = 500 mg/LContinuous aeration

significant effect on sludge growth when TCS > 0.4 ppm

0.5

0.6

0.7

0.8

0.9

1

0 30 60 90 120 150 180Time (min.)

Rel

ativ

e su

bstr

ate

conc

. (S/

So)

Control 0.2 ppm TCS0.4 ppm TCS0.6 ppm TCS0.8 ppm TCS

S0/ X0 = 2X0 = 500 mg/L Continuous aeration

Significant effect on substrate uptake rate when TCS >0.4 ppm

Page 25: Sludge reduction

Effect of TCS on Observed Growth YieldEffect of TCS on Observed Growth Yield

0.3

0.5

0.7

0 0.2 0.4 0.6 0.8TCS dose (ppm)

Yob

s (m

g M

LSS/

mg

CO

D) So/Xo =2

X0 = 500 mg MLSS/L TCS reduces the Yobs

A shape drop of Yobs is detected between 0.4 and 0.6 ppm TCS introduction

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8TCS dose (ppm)

u/u

0 or

q/q

0

u/u0

q/q0

TCS reduces both the µ and q

The change of µ resemble that of Yobs

Page 26: Sludge reduction

Effect of TCS on Sludge Decay RateEffect of TCS on Sludge Decay Rate

400

450

500

550

600

0 1 2 3 4 5Time (day)

MLS

S (m

g/L)

control1.0 ppm TCS

Page 27: Sludge reduction

Effect of TCS on Cumulative Excess Effect of TCS on Cumulative Excess Sludge Production of Batch Cultures Sludge Production of Batch Cultures

0

30

60

90

120

0 5 10 15 20 25 30Time (day)

Acc

umul

ativ

e Ex

cess

Slu

dge

(g S

S/d)

Bc 2Bc 1Bc 0

S0/X0 = 0.25X0 = 2,000 mg SS/L

y = 1.94 g SS/d

y = 3.41 g SS/d

y = 2.66 g SS/d

Page 28: Sludge reduction

Nomenclatures in the Results and DiscussionNomenclatures in the Results and Discussion

Symbol Description

Bc 0 Batch cultivation without the presence of TCS (control)

Bc 1 Batch cultivation with the presence of 0.5 ppm TCS

Bc 2 Batch cultivation with the presence of 1.0 ppm TCS

Cc 0 Continuous cultivation without the presence of TCS

Cc 1 Continuous cultivation with the presence of 1.0 ppm TCS

Page 29: Sludge reduction

Observed Growth Yield of Batch Cultures Cultivated Observed Growth Yield of Batch Cultures Cultivated with TCS at Different Dosages with TCS at Different Dosages

0

0.2

0.4

0.6

0.8

0 10 20 30Time (d)

Yobs

(g S

S/g

CO

D)

Bc 2Bc 1Bc 0

Page 30: Sludge reduction

Effect of TCS on Cumulative Excess SludgeEffect of TCS on Cumulative Excess SludgeProduction of Continuous Cultures Production of Continuous Cultures

0

30

60

90

0 10 20 30Time (d)

Cum

ulat

ive

Exc

ess

Sldu

ge(g

)

Cc 1Cc 0

y = 3.06 g SS/d

y = 1.90 g SS/d

Page 31: Sludge reduction

Observed Growth Yield Analysis of Continuous CulturesObserved Growth Yield Analysis of Continuous Cultures

0

0.2

0.4

0.6

0 10 20 30Time (d)

Yobs

(mg

SS/ m

gC

OD

/d)

Cc 1Cc 0

Experiments were conducted at a period of 3 hoursDuring the experiment, TCS was not added

Page 32: Sludge reduction

Effect of TCS on Substrate Removal Efficiency of Continuous CultEffect of TCS on Substrate Removal Efficiency of Continuous Culturesures

55

65

75

85

95

0 10 20 30Time (d)

Cc 1Cc 0C

OD

rem

oval

ef

ficie

ncy

(%)

TCS dose (ppm) Parameter

0 1.0

Mean Substrate removal (mg COD /L /d) 920 880

Daily Sludge Production 383 238

Overall yield (g SS / g COD) 0.41 0.27

Effluent SS conc. (mg/L) 35.7±15.4 43.3±23.1

Page 33: Sludge reduction

Effect of TCS on SOUR of Batch and Continuous CulturesEffect of TCS on SOUR of Batch and Continuous Cultures

SOUR (mg O2/g SS/hr)Measurement Day

0ppm TCS (control) 0.5ppm TCS 1.0ppm TCS

0 58.6 61.2 58.95th 52.1 57.1 49.3

10th 63.1 75.3 97.020th 63.7 79.7 90.830th 60.1 81.3 96.1

Batch CultureINCREASE

SOUR (mg O 2/g SS/hr)M easurement Day

0 ppm TCS (control) 1.0 ppm TCS

0th 61.2 63.75th 62.2 72.4

10th 66.7 77.820th 64.8 79.530th 62.6 78.3

Continuous Culture

Page 34: Sludge reduction

Microbial Activity of Batch Cultures (DAPI & CTC Data)Microbial Activity of Batch Cultures (DAPI & CTC Data)

0.5 ppm TCS1.0 ppm TCS

Control

Day Batch Culture Active microbialportion (%)

no. of active microbes/ VSS(no./mg)

15 Control 5.7 1.39 x 108

0.5 ppm TCS 10.3 3.45 x 108

1.0 ppm TCS 10.5 4.07 x 108

30 Control 3.9 1.09 x 108

0.5 ppm TCS 4.3 1.22 x 108

1.0 ppm TCS 7.6 2.72 x 108In

crea

se

Incr

ease

Page 35: Sludge reduction

Microbial Activity of Continuous CultureMicrobial Activity of Continuous Culture

Control1.0 ppm TCS

Day ContinuousCulture

Active microbialportion (%)

no. of active microbes/VSS (no./mg)

15 control 7.4 1.49 x 108

1.0 ppm TCS 11.2 2.99 x 108

30 control 5.6 1.42 x 108

1.0 ppm TCS 10.1 2.69 x 108In

crea

se

Incr

ease

Page 36: Sludge reduction

Enzyme complex I, III and IV

+ + + + + + + + + + + + + + + + + + + + +

- - - - - - - - - - - - - - - - - --

1/2 O2 + 2 H+ + 2 e- H2O

2 NADH +2 H+ 2 NAD+ +2 e-

F0

F1

I, III,IV

H+H+

H+ H+H+

H+

ATP

H+

ADP+Pi

H+ H+

H+

H+

TCS interacts with

membrane

H+

H+

H+

Proposed Mechanism: Futile Cycle Induced by TCS

INNER AREA

OUTER AERA

MITOCHONDRIA

F0, F1-ATP synthase

Page 37: Sludge reduction

[2] Chlorination pretreatment of Excess Sludge

Excess sludge

Compressed air

Treated Water

40 L/daySynthetic wastewater

Flow meter

Automatism

Pressurecaptor

40 L/day

Hollow fibermembrane

2L sludge

Cl2

N2KI solution (1N)

Magnetic stirrer

99%

For washing

Chlorinated sludge

2 L/day

Reactor for sludgechlorination

MembranebioreactorB A

Figure 2-1. Membrane biological reactor (A) and chlorination setup (B) used in this study.

Page 38: Sludge reduction

Chlorine dose and residual during the sludge chlorination.

65.019.10.33237.85.80.26612.91.80.1999.00.30.1335.50.30.066

(mg Cl2/L)(mg Cl2/L)(g Cl2 /g MLSS)

Total Cl2residual

Free Cl2Residual

Chlorine Dose

Page 39: Sludge reduction

y = 1.71x - 0.41R2 = 0.99

y = 5.14x - 6.88R2 = 0.99

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25 30 35 40

Time (days)

Cum

ulat

ive

exce

ss s

ludg

e (g

)Reference system

With chlorinated sludge recirculation

Reduction 67%

Figure 2-2. Sludge production rates in the continuous systems without (the reference system) and with (testing line) the chlorination treatment of excess sludge.

Page 40: Sludge reduction

0

100

200

300

400

500

600

700

800

0 5 10 15 20 25 30 35 40

Time (days)

Solu

ble

CO

D in

slu

dge

(mg

O2/L

)

-10

0

10

20

30

40

50In sludge from aerated sludgeIn treated water

Solu

ble

CO

D in

trea

ted

wat

er (m

g O

2/L)

Figure 2-3. Variations of the COD concentration in the sludge and treatedwater of the testing system.

(Errors bars present the standard deviation of the COD measurement).

Page 41: Sludge reduction

A

C

B

50

60

70

80

90

100

0 5 10 15 20 25 30 35

Time (days)

% M

LSS/

TS

Sludge from aerated tank

Figure 2-4. Change of MLSS/TS during the operation of the testing system. Figure 2-5. Particle distribution in

activated sludge (A) prior to chlorination study; (B) after recirculation

of chlorinated excess sludge for 20 days;

(C) just after chlorination step.

Page 42: Sludge reduction

0.0E+00

5.0E+11

1.0E+12

1.5E+12

2.0E+12

2.5E+12

3.0E+12

Sludge from reference system

Numb

er of

cells

per g

of M

LSS

Cells (DAPI counting)

Respiring bacteria(CTC counting)

Sludge in pilot unit with chlorinated sludge recirculation

29%

34%

Figure 2-8. Total number of cells and the number of active bacteria in both the reference and testing systems (the results represent the mean values of five independent analyses).

THMs concentrations in the treated water and sludge.

8606808301280Sludge after NaClO addition (150 mg Cl2/L)

<200<200230*<200Chlorinated sludge (after 10 min reaction)

270*310<200260*Chlorinated sludge (just after chlorination)

<200<200<200<200Treated water

Analysis 4Analysis 3Analysis 2Analysis 1Sample

THMs concentration (µg/L)

Page 43: Sludge reduction

[3] Oxic-Settling-Anaerobic (OSA) System

Aerationtank

Settling

Influent Effluent

Excess sludge

Sludge holding tank

• No additional substrate• High sludge

concentration • Longer retention time

Important factors

•Biomass level •Anaerobic sludge exposure time (SAET)•ORP

Sludge settleability and nutrient removal?What extent of reduction?

What is the cause for the reduction?

• It is relatively easy to modify conventional activated sludge process

• Neither chemical addition nor heat energy is required

• The treatment efficiency is NOT affected

• Great potential in full-scale application

Page 44: Sludge reduction

• To examine the capacity of OSA system in reducing excess sludge production

• To investigate the performance of an OSA system under different operating conditions

• To study the impact of the anaerobic sludge zone on bacterial activity

• To identify the cause of the reduction of excess sludge production in an OSA system

Study Objectives

Page 45: Sludge reduction

Experimental Set-up

Working Volume = 10.0 L

AERATION TANK

SETTLING TANK

STOCKSOLUTION

Volume = 4.0 L

DILUTIONWATER

SLUDGE HOLDING TANK

Working Volume = 4.5 L

NITROGENGAS TANK

Effluent Overflow

RecirculatedSupernatant

Air inlet

Concentrated Sludge

ORP Electrode

Effluent Permeate

Hollow Fiber MembranePore size 0.4 µmFacilitate the precise measurement of sludge production

MLSS : 7-9 g/LORP : 100, -100, and -250mV

SAET 6,10, and 12 hrMLSS : 7-9 g/LORP : -250mV

HRT : 6 hr, MLSS:2 g/L, DO: >2 mg/L

Wastage excess sludge

Page 46: Sludge reduction

Observed Growth Yield at Different ORP in Sludge Holding Tank

0.1812.772.30-250

0.2212.272.70-100

0.3212.183.90+ 100

Yobs(g SS/g COD)

COD removal rate (g COD/day)

Net sludge production rate

(g SS/day)

ORP in sludge holding tank (mV)

Page 47: Sludge reduction

Observed growth yieldat different SAET in Sludge Holding Tank

at -250 mV ORP

0.1712.72.012

0.1912.32.410

0.2712.23.56

Yobs(g SS/g COD)

COD removalrate (g COD/day)

Net sludgeproduction rate

(g SS/day)

SAET in sludge holding tank (hours)

Page 48: Sludge reduction

Comparisons of Performance of OSA System with Reference System under same COD Loading

Operating conditions

Reference System I OSA System

Influent

Effluent

Effluent

SettlingTank

Aeration Tank

Wastage sludge

Influent

Aeration Tank

Wastage sludge

Sludge Holding Tank

HRT : 6 hrMLSS : 2 g/L

HRT : 6 hrMLSS : 2 g/L

SAET : 10 hrMLSS : 8 g/LORP : -250mV

Membrane filtration was used to facilitate the precise measurement

Page 49: Sludge reduction

COD Removal

0

50

100

150

200

250

300

350

400

0 10 20 30 40 50 60 70 80

Time (day)

CO

D (m

g/L)

Effluent average (Reference system I) = 41 mg/L

Effluent average (OSA system) = 18 mg/L

Influent average =330 mg/L

Page 50: Sludge reduction

Sludge Production Rate

0

100

200

300

400

500

0 10 20 30 40 50 60 70 80Time (day)

Cum

ulat

ive

Exce

ss S

ludg

e Pr

oduc

tion

(g M

LSS)

Excess sludge production (Reference system I)@ 4.8 g/day

Excess sludge production (OSA system)@ 2.3 g/day

Page 51: Sludge reduction

Observed Growth Yield

0.20.4Yobs ( g SS/g COD)

1312Substrate utilization rate (g COD/day)

2.34.8Net sludge production rate(g SS/day)

OSA SystemReference System I50 % of reduction !!!How about the sludge settleability and bacteria activity?

Page 52: Sludge reduction

Sludge Settleability

0

50

100

150

200

250

300

0 10 20 30 40 50 60 70 80

Time (day)

SVI

Reference system IMean 180

Mean 110

OSA system

Page 53: Sludge reduction

SOUR

0

10

20

30

40

50

60

70

80

SOU

R (m

gO2 /g

VSS

-hr)

1 2 3 4 5 6 7 8 9 10

Time (week)

OSA system Reference system I

60

50

At temperature 20oC

Page 54: Sludge reduction

Comparisons of Performance of OSA System with Reference System under same Sludge Quantity

Operating Conditions

Reference System II OSA System

Influent

Effluent

Effluent

SettlingTank

Aeration Tank

Wastage sludge

Influent

Aeration Tank

Wastage sludge

Sludg Holding Tank

HRT : 6 hrMLSS: 7~8 g/L

HRT : 6 hrMLSS: 2 g/L

20 g

80 g

30 g

30 g

Higher sludge quantity will generally result in low sludge production? is it the main cause for the OSA system for reducing the excess sludge production?

Page 55: Sludge reduction

Sludge Production Rate

Reference system II@ 2.2 g/day

OSA system@ 2.0 g/day

0

20

40

60

80

100

120

0 10 20 30 40 50Time (day)

Cum

ulat

ive

Exce

ss S

ludg

e Pr

oduc

tion

(g M

LSS)

Page 56: Sludge reduction

COD Removal

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30 35 40 45 50 55 60

Time (day)

CO

D (m

g/L)

Influent average 330 mg/L for both systems

Effluent average(Reference system II)= 12 mg/L

Effluent average(OSA system) = 18 mg/L

Sludge loading is 4 times higher

Page 57: Sludge reduction

Observed Growth Yield

0.18Yobs ( g SS/g COD) 0.2

1313Substrate utilization rate(g COD/day)

2.02.2Net sludge production rate(g SS/day)

OSA systemReference System II

However, the operating principle of the two systems are different !

Let’s look at the other parameters…

Page 58: Sludge reduction

SOUR

0

10

20

30

40

50

60

70

80SO

UR

mgO

2/g

VSS-

hr

1 2 3 4 5 6 7 8 9 10Time (week)

OSA system Reference system IISOUR

Substrate oxidation and cell synthesis:

COHNS + O2 + nutrients →bacteriaCO2 + H2O + NH3 + )tissuecellnew(NOHC 275 + other end products

60

40

At Temperature 20oC

Page 59: Sludge reduction

Endogenous Respiration

Endogenous respiration:

C5H7O2N (Cells) + 5 O2 →bacteria 5CO2 + NH3 + 2H2O

0

2

4

6

8

10

12SO

UR

mg

O 2/

g VS

S-hr

1 2 3 4 5 6 7 8 9 10

Time (week)

OSA system Reference system II

8

5

At Temperature 20oC

Page 60: Sludge reduction

The diluted SVI (DSVI) test has been used for the reference system II since MLSS concentration in the aeration tank was very high (Wastewater Engineering 4th edition)

Sludge Settleability

0

100

200

300

400

0 10 20 30 40 50 60Time (day)

SVI/D

SVI

DSVI for reference system II

SVI for OSA system

Page 61: Sludge reduction

Microscopic Observation

1,260<100Actinomycete (CFU/mL)

13,750absentProtozoa and metazoa (counts/mL)

Reference System IIOSA SystemType of microorganism

Ciliates in Ref IIActinomycete

Page 62: Sludge reduction

Nutrients Removal

45±25.5±19.5±0.510±1PO43-

(mg P /L)80±318±212±2330±10COD (mg/L)

0.2±0.0536±155±11.6±0.3NO3-

(mg N/L)

0.02±0.0050.05±0.050.05±0.020NO2-

(mg N/L)

25±0.50.04±0.050.04±0.535±0.5NH4+-

(mg N/L)

26±0.538±0.555±160±1TN (mg N/L)

Effluent of the sludge

holding tankSystem effluentEffluentInfluentParameter

OSA systemReference system II

Page 63: Sludge reduction

COD Balance Batch Test Set-Up

P

ORP & pH Recorder

GC/FID

Magneticstirrer

Nitrogen gas

Reactor I ORP :-250 mV Reactor III

ORP : 0~ -20 mV

Reactor IIORP :-150 mV

Measured Parameters

- pH and ORP- MLSS and COD- Nitrite, Nitrate, Phosphate, Sulfate- Organic Carbon content in the produced gas

Page 64: Sludge reduction

MLS

S an

d C

OD

(a)

Initial, 9 Initial, 9 Initial, 9

Final, 7.9Final, 8.7 Final, 8.9

0

1

2

3

4

5

6

7

8

9

10

Reactor I (ORP at -250 mV) Reactor II (ORP at -150mV) Reactor III (ORP at -20 mV)

MLS

S (g

/L)

10% 4% 1.2%

(b)

Final, 15

Final, 147

Final, 512

Initial, 35Initial, 35Initial, 350

100

200

300

400

500

600

Reactor I (ORP at -250 mV) Reactor II (ORP at -150mV) Reactor III (ORP at -20 mV)

CO

D c

once

ntra

tion

(mg/

L)

Page 65: Sludge reduction

7.932.0 37.87.6PO43--P(mg/L)

120.9 0.434.5NO3--N(mg/L)

00.0 0.00NO2--N(mg/L)

7.06.5 7.57.3pH

01444632VFA (mg as COD/L)

11,64011,477 11,12811,674TCOD (mg/L)

1216534539SCOD (mg/L)

8,1297,9667,5938,194MLVSS (mg/L)

8,8988,6788,254.08,906MLSS (mg/L)

Reactor IIIReactor IIReactor I

Final sample after 16 hoursInitial sampleParameter

1. initial and final COD (soluble + particulate) was estimated, their difference gives a total COD loss

2. COD consumptions in the corresponding reactions were estimated

3. The amount of COD released as gaseous products was estimated

Typical Results

SO42--S(mg/L) 7.2 3.6 6.3 7.0

Organic carbon (%) in the gas - 2.03 - -

Total COD removed in Step (2) and (3) was compared with the total COD loss of the system in Step (1).

Page 66: Sludge reduction

COD Balance

Reactor I

1.93467.26213.70 77.69.6166.36 476.48

-0.72434.41194.18 70.610.4159.22 431.32

9.30497.4266.75 60.47.2163 536.32

Total COD consumption

Gas production

Phosphorus release

Sulfate reductionDenitrificationSTo-STe (mg/L)

Unaccounted COD (%)

COD consumption (mg/L)COD loss

Reactor II

2.19209.330441.2164.13214.02

5.91202.79045.40.4156.99215.54

4.79200.46048.81.8149.86210.54

Total COD consumption(4)(3)(2)(1)STo-STe (mg/L)

Unaccounted COD (%)

COD consumption (mg/L)COD loss

Page 67: Sludge reduction

Expected Sludge Production under Anaerobic and Aerobic Conditions

Removal of substrate under anaerobic condition

Removal of substrate under aerobic condition

Theoretical sludge production (mg/L)

Theoretical sludge production (mg/L)

Reaction COD consumed (mg/L)

Y(g VSS/g COD)

Y(g VSS/g COD)

Denitrification 163 0.3 48.9

Sulfate reduction 7.2 0.2 1.4

0.55 251.3Phosphorus release 60.4 0.18 10.88

Gas production 266.8 0.05 13.34

Total ∑ 497.4 ∑ 74.5 ∑ 251.3

Page 68: Sludge reduction

Conceptual Representation of OSA System

Influent

COD =330 mg/LNH4

+-N =36 mg N/LNO3

- -N =2 mg N/LPO4

2--P= 10 mg P/L

Biomass =8.8 g/LCOD < 30 mg/LSludge wastage

Aeration Tank

CO2

Biomass

Settling Tank Sludge Holding Tank

ORP = -250 mVSAET = 10 hours

Soluble COD

Decay Biomass Soluble COD (100%)

Denitrification Sulfate reduction Phosphorus release Gas production( 33%) (2%) (15%) (50%)

Overall growth yield is significantly lower as compared to aerobic oxidation

Biomass =8.3 g/LCOD = 70 mg/L

Effluent

day/12.0g4.39

day/g5sludgeofamount

decaytoduelossSS ==Ka=

Achromobacter, Acinetobacter, Agrobacterium, Alcaligenes, Arthrobacter, Paracocus etc (Payne, 1981)

Halobacterium, Methanomonas. Pseudomonas spp. Gayle (1987)

Most of these bacteria are able to use oxygen as well as nitrate or nitrite and also can carry out fermentation in the absence of nitrate or oxygen..

Page 69: Sludge reduction

Economic Aspect

1.6 *107 USD/year [2,3]1.02×107 USD/year[2,3] (40USD/ton)

Sludge Treatment and disposal cost

Calculation based on 100,000 m3/d of flow rate for two systems[1] Metcalf and Eddy, Inc. Wastewater Engineering: Treatment, Disposal and Reuse 4th edition, McGraw-Hill. Inc,

2003.[2] D. G. Christoulas, A. D. Andreadakis, A. Kouzeli-Katsiri, E. Aftias and Mamais, Alternative schemes for the

management of the sludge produced at Psyttalis WWTP, Water Sci. Techol., 42(9), 29-36, 2000.[3] A. M. Springer, D. V. Guillerom, Feasibility study of sludge lysis and recycle in the activated sludge process, T.

Journal May 1996 162-170

330 m3/d210 m3/dDisposal capacity(Landfill)

1100 m3 * 15d= 16,500 m3 [1]

700 m3/d *15d =10,500 m3 [1]

Digester volumeCost saving

NOYesORP control unit

NOAdditional for sludge pumping

Pumping

NOQ:25,000m3/d,HRT 10h= 10,416 m3

Sludge holding tank construction

Cost increase

Typical activated sludge process

OSA

Page 70: Sludge reduction

[5] A new solution to Hong Kong Sewage- A Feasibility Study of Autotrophic Denitrification

Hong Kong sewage has unique characteristics due to the use of seawater in toilet flushing: sulfate level ~ 500 mg/L, COD ~ 300 mg/L, and chloride ~ 6000 mg/LThis sulfate level enables efficient sulfidogenic reactions under anaerobic condition, thereby resulting in a very low sludge yield (0.17) and eliminating oxygen demand for carbon oxidation in the subsequent treatment steps. If sufficiently produced sulfide, mostly in dissolved form, could be utilized by “Autotrophic Denitrification” as the electron donor, sludge production can be further reduced up to 75% as compared to conventional aerobic-anaerobic processesKey point is to shut out carbon source completely from heterotrophic oxidation and denitrification that feature a high sludge yield (0.4-0.5).

Page 71: Sludge reduction

REACTION I REACTION I –– HeterotrophicHeterotrophic Sulfate ReductionSulfate Reduction

REACTION II REACTION II –– Autotrophic DenitrificationAutotrophic Denitrification

Y=0.17 COD + SO42- H2S + HS-

Y=0.5 COD + O2 CO2 + H2O

Y=0.4 COD + NO3- CO2 + N2

Y=0.15 H2S + HS- + NO3- SO4

- + N2

Page 72: Sludge reduction

Proposed New Treatment System for Hong Kong Saline Sewage

COD Removal(Low sludge yield)

Nitrification(Low sludge yield)

Autotrophic denitrification(Low sludge yield)

Up to 75% excess sludge can be reduced than conventional aerobic-anaerobic processes

Page 73: Sludge reduction

Advantages of Proposed Treatment

Integration of sulfate reduction, autotrophic denitrification, and nitrification to achieve a very low sludge yield

Efficient COD removal and complete nitrogen removal are possible.

Neither chemical nor physical forces are needed, oxygen demand is also reduced greatly. Thus, a very low operation cost can be expected.

Page 74: Sludge reduction

Objective of this study

• To confirm efficiency of COD removal through sulfate reduction(Phase I)

• To study efficiency of autotrophic denitrification (AD) and its affecting factors (Phase I)

• To investigate performance of the integrated system for nitrogen and COD removal and excess sludge reduction(Phase II)

• To identify SRB and ADB bacteria (Phase II)• Pilot study of the proposed system at sewage treatment works

(Phase III)

Page 75: Sludge reduction

Reactor I

1 cm

Phase I Results

Reactor I (SR Bioreactor)Diameter = 10 cm, Height = 40 cmVolume = 3LFeeding synthetic sewage (TOC ~ 100mg/L, SO4

- ~ 500mg/L)

Page 76: Sludge reduction

Reactor II

Reactor II (Submerged AD Bio-filter)Diameter = 10 cm, Height = 30 cmVolume ~ 2.15 L Feeding effluent from reactor I with external nitrate source (30 N-mg/L)

Transition

Zone

Working

Zone

Page 77: Sludge reduction

Summary of Reactor I (SRB) Performance

ParametersHydraulic Retention Time

4 hrs 6 hrsInfluent Flow Rate (L/hr) 0.8 0.53

TOC (mg/L)

Influent (Average) 95 90

Effluent 16.3 ± 4.2 14.6 ± 2.7

TOC Removal % 82.4 ± 0.1 86.9 ± 5.1Sulfate (mg/L)

Influent 480.4 ± 116.7 660.6 ± 166.1

Effluent 220.3 ± 110.2 382.2 ± 111.9

Sulfate Removal 260.1 ± 113.4 278.4 ± 139.0

Average organic loading rate

kg TOC/m3-day 0.57 0.35

Sludge Yield (g VSS / g COD) 0.17 0.16

Page 78: Sludge reduction

COD / SO42- Ratio in Reactor I

• Theoretical COD / SO42- ratio for sulfidogenic reaction= 0.67

• Experimental COD / SO42- Ratio ~ 0.65 – 0.93

• Majority of COD was utilized by sulfate reducers

y = 0.7289x

y = 0.6938x

0

50

100

150

200

250

300

350

0 100 200 300 400 500Sulfate (mg/L)

CO

D (m

g/L)

HRT=4hrs HRT=6hrs

Page 79: Sludge reduction

Sulfur Balance in Reactor I

Measured Sulfur Source• Influent

– Sulfate ~ 154.2 mg S/L• Effluent

– Sulfate ~ 64.2 mg S/L– Total dissolved sulfide ~ 72.5 mg S/L

• Sulfate Reduced = 90 mg S/L• About 80% of the sulfide produced is in

the dissolved form

The remaining sulfur may include:hydrogen sulfide gasbiomass sulfurMetal sulfide

Page 80: Sludge reduction

Performance of Reactor II (SADB)

HRT = 4hrs

0

10

20

30

40

50

0 2 4 6 8 10 12 14

Time (days)

Nitr

ate

(N

-mg/L

)

Influent NO3-

Effluent NO3-

Page 81: Sludge reduction

Summary of SADB Performance

373.2259.7SO42- (mg/L)

124.486.6SO42- (mg S/L)

Dissolved Sulfide (mg S /L)

NO3- (N-mg/L)

72.5

33.8

Influent

-

1.3

Effluent

96%

Efficiency

Sufficient NO3- removal

in HRT = 4 hrs

TOC removal < 5mg/L

Theoretical Ratio: SO42- / NO3

- = 1.92 – 2.51 mg S/ mg N

Experimental Ratio:SO42- / NO3

- = 2.1 ± 1.19 mg S / mg N

Page 82: Sludge reduction

Acknowledgement

• Following organizations should be acknowledged for financially supporting our work:

Hong Kong Research Grants CouncilHKUSTVivendi Water

Page 83: Sludge reduction

The end

Thank you very much for your attention and patience.

Page 84: Sludge reduction

Sludge Production and Landfill CapacityExample of Hong Kong

Projected daily sludge production from water and wastewater treatment works in Hong Kong

Others

Wastewater workWater work

Sludge production and landfill assimilative capacity in Hong Kong

2050180015001690Landfill capacity (ton/day)

212018501200510Sludge quantity (ton/day)

2015200820011991Year