Study of the Septicity Problem throughout the
Tunnel Systems under the Harbour Area
Treatment Scheme (HATS)
Feng Jiang
Professor,
School of Chemistry and Environment
South China Normal UniversityEmail: [email protected] / [email protected] / Tel: +86-13760612488
2 Assess the sulfide generation in HATS SCS
3 Simulation of HATS SCS by SPMM
4 Summary
1 General introduction
Contents
As the water quality in Victoria Harbour affects many people in Hong Kong, the Government initiated the
Harbour Area Treatment Scheme(HATS). It improves the water quality of Victoria Harbour through the
collection, treatment and disposal of sewage from both sides of Harbour.
1. General introduction
Stage 2A: • commissioning in December 2015;
• upgrading 8 PTWs, construction of 21km-
long and -70 to -160 m deep tunnel system;
• treats the remaining 25% of sewage
Stage 1: • commissioned in December 2001;
• upgrading 7 PTWs, construction of 23km-long
and -70 to -140 m deep tunnel system;
• treats 75% of the sewage, the capacity to
move up to 1.7 million m3/d.
long-distance long-time of sewage conveyance obnoxious gas(H2S) and corrosion
H2S SO42-
H2S
SO42-
H2S
Sulfur Oxidizing Bacteria
Sulfate Reducing Bacteria
Sewer atmosphere
Bulk sewage
Biofilm
H2SO4
sulfide is generally bio-generated in sewer biofilm, due
to the growth of the SRB colonized in biofilm (Ito et al.,
2002).
Mechanism of H2S production in sewers
Sulfate reduction and sulfide production:
𝑆𝑂42− + 𝐶
𝑆𝑅𝐵𝑆2− + 𝐶𝑂2
Anoxic sulfide oxidation:𝑆2− + 𝑂2/𝑁𝑂3
− 𝑆0/𝑆𝑂42− + 𝑁2
Hydrogen sulfide dissociation:𝑆2− ↔ 𝐻𝑆− ↔ 𝐻2𝑆
Hydrogen sulfide emission:
𝐻2𝑆(aq) ↔ 𝐻2𝑆(𝑔)
H2S(g)
conc.(ppm)Harmful effects
0.13 Min concentration can be smelt
… …
200-300Continuous exposure after one hour, there was a noticeable
conjunctivitis, and respiratory irritation
500-700 Loss of consciousness, apnea, and even death
1000~Loses consciousness immediately, breathes stops and died in
several minutes
average
peakHATS
H2S
Co
ntr
ol
End-of-pipe treatment
Forced Ventilation
DeodourizationUnit
In-pipe treatment
Chemical Dosing
To transform dissolved sulfide
H2O2, O2, NO3-,
NO2-
To inhibit sulfide formation
FNA, Molybdate
To precipitate dissolved sulfide
Fe2+, Fe3+
To suppress H2Sg
emissionNaOH, Ca(OH)2
Hydraulic flushing
How to control H2S(g) in sewer ?
• High Cost
• Chemical pollution
• Risk to downstream WWTP and ecosystem
Over dosage
• Ineffective H2S control
• Infrastructure corrosion
• Human health risk
Insufficient dosage
A sewer processes math model is essential to cost-effective H2S control in HATS
0
5000
10000
15000
20000
25000
4/10/2015 9:00 5/10/2015 21:00 7/10/2015 9:00
Flo
wra
te (
m3/h
)
Time
CW
SKW
TKO
KT
TKW
KC
TY
• The Sewer Process Mathematical Model (SPMM)
– Developed by Dr. Feng Jiang (SCNU) and Prof. G H
Chen (HKUST) since 2007
– To simulate all the physical, chemical, and biological
processes related to sewage quality changing in sewers.
Sewer Process Mathematical Model
Biofilm/sediment
Water phase
Gas phase H2S(g)
SO42-
S2-//HS-/H2S(ag)
NO3-
S2-
Diffusion
emission
Attachment /Detachment
Biomass / particulate
biofilm-process
Schematic diagram of the main reaction related to sulfide in sewer
CorrosionH2SO4
Substance
concentrations
in biofilm
Changes in
biofiom
composition
(1) Agreement No. DEMP09/06 - Sewer Biofilm Modeling for sulfide Formation in Sewers
• Tung Chung pressured main sewer (TCS) and Tuen Mun gravity sewer (TMS)
(2) HKIA Sewer Network Study
• The sewer networks in the Hong Kong International Airport (HKIA)
SPMM can be used to simulate the biochemical process of biofilm and
wastewater, and also can predict the sulfide production and H2S releases,
e.g. the previous Applications of this SPMM
sulfide H2S(g)
Sampling Locations: SCISTW and 7 PTWs
Analyzing parameter: 20 parameters include
TS, DS, VSS, H2S(g), flowrate etc.
Sampling time: Every 2 or 12h for 7 days
• Data (2015.10.4 9:00 to 2015.10.7 9:00) for model
calibration
• Date (2015.10.7 9:00 to 2015.10.11 9:00) for model
verification
Sampling Locations: SCISTW and 8 PTWs
Analyzing parameter: 20 parameters include
TS, DS, VSS, H2S(g), flowrate etc.
Sampling time: Every 2 or 12h for 2 days
• (2015.12.7 14:00 to 2015.12.9 14:00)
HATS 1
HATS 2A
2. Assess the sulfide generation in HATS SCS
KC
PTW
TY
PTW
TKW
PTW
KT
PS
KT
PTW
TKO
PTW
CW
PTW
SKW
PTW
TUNNEL A
TUNNEL B
TUNNEL C
TUNNEL D
TUNNEL E
TUNNEL F
TUNNEL G
SCI
STW
Inverted Syphon
Pressured Main
Both (KT Riser Shaft)
HATS Stage 1
0 500 1000 1500 2000
SCISTW
output
PTWs input
Net sulfide input or output (kgS/d)
CW input KC input KT input SKW input
TKO input TKW input TY input SCISTW output
228
kgS2-/d
~70% DS were generated in the HATS 1
48
kgS2-/d
27
kgS2-/d
191
kgS2-/d
108
kgS2-/d
43
kgS2-/d
18
kgS2-/d
2089
kgS2-/d
Field experiment and data analysis
Liquid sampling
H2Sg monitoringat SCISTW MPS No.1
H2S(g) Conc. at MPS No.1
Average: 219 ppm
Maximum: 720 ppm
Wet well
H2S(g) conc. in HATS 1 outlet
0
5000
10000
15000
20000
25000
4/10/2015 9:00 5/10/2015 9:00 6/10/2015 9:00 7/10/2015 9:00
Flo
wra
te (
m3/h
)
Time
CW
SKW
TKO
KT
TKW
KC
TY
SCISTW output (10/4-10/7)
Based on the different sewer with different water quality and hydraulic conditions (e.g. pH,
flowrate, and dissolved sulfide), model should be used to predict and effective control H2S(g).
7 PTWs input (10/4-10/7)
Flowrat
e
DS
H2S(g)
pH
0
0.5
1
1.5
2
2.5
3
3.5
4/10/2015 9:00 5/10/2015 9:00 6/10/2015 9:00 7/10/2015 9:00
Dis
solv
ed s
ulf
ide
(mg
S/L
)
Time
CW
SKW
TKO
KT
TKW
KC
TY
DS
Flowrate
Strong fluctuation
Average sulfide Concentration:
H2S(g) measured: 219 ppm
simulated: 221 ppm
DS measured: 1.82 mgS/L
simulated: 1.94 mgS/L
Model Calibration of HATS stage 1 (10/4-10/7)
3. Simulation of HATS SCS by SPMM
Model Verification of HATS stage 1 (10/7-10/11)
Simulated well
Average sulfide Concentration:
H2S(g) measured: 207 ppm
simulated: 214 ppm
DS measured: 1.89 mgS/L
simulated: 1.79 mgS/LPredictedwell
H2S(g)
H2S(g)
DS
DS
Flowrate
Flowrate
1. Locate the position of sulfide generation
2. Case study Case 1: Ultimate Flow Simulation
Case 2: Temperature effect
Case 3: Water Flushing
3. H2S control by chemical dosing Case 4: Super-oxygenation system(TKO) ;
Case 5: Nitrate dosing(TKW) ;
Case 6: NaOH (TKW) ;
Case 7: Nitrate + NaOH (TKW) ;
Case 8: Nitrate + NaOH (TKW) + Forced Ventilation (MPS1)
Overview
Model Application of HAST Stage 1
TunnelAverage flowrate
(m3/h)
Hydraulic
retention time(h)Lengh (km)
Calculated DS-in
(average mgS/L)
Calculated DS-out
(average mgS/L)
Net sulfide
production
(kgS/d)
A CW 2446 1.1 2300 0.81 2.35 90
B CW SKW 5357 0.7 2500 1.29 2.02 94
C TKO 5812 2.6 5300 1.64 2.93 180
D CW SKW TKO KT 25754 0.8 3300 1.36 1.57 130
E CW SKW TKO KT TKW 35390 1.5 5500 1.27 2.04 654
F KC TY 12210 1.3 3600 0.18 1.70 445
G KC 9643 0.3 800 0.19 0.15 -8
The position of sulfide generation
Long HRT result in high
sulfide concentration
Short HRT and high DO result in very
low sulfide concentration
Largest
Due to 35,390m3/h wastewater
HATS Stage 1
• The ultimate flow is predicted to be 1.4 times of current flow (average);
• sulfide production in Tunnels decreased by 12%, DS concentration decreased
by 27% (drop from 1.94 mgS/L to 1.42 mgS/L).
Current flow Ultimate peak flow
TunnelFlowrate
(m3/h)AverageHRT(h)
Simulated DS-out(mgS/L)
Net sulfideproduction(kgS/d)
Flowrate(m3/h)
AverageHRT(h)
Simulated DS-out(average mgS/L)
Net sulfideproduction(kgS/d)
A 2,446 1.1 2.35 90 2,556 1.0 2.13 81
B 5,357 0.7 2.02 94 7,083 0.5 1.69 87
C 5,812 1.3 2.93 180 6,869 1.1 2.78 188
D 25,754 0.8 1.57 130 34,560 0.6 1.28 50
E 35,390 1.5 2.04 654 52,201 1.0 1.44 539
F 12,210 1.3 1.70 445 16,066 1.0 1.38 463
G 9,643 0.3 0.15 -8 12,789 0.2 0.14 -15
HATS 1 47,599 1.94 1,585 68,267 1.42 1,393
Ultimate Flow Simulation
HATS 1Case Study 1
SCISTW
DS (mgS/L)DS variation(%)
Net sulfide production
(kgS/d)
28.7° C-
simulated1.94 0% 1,585
32.0° C-
simulated2.16 11% 1,837
25.0° C-
simulated1.61 -17% 1,207
18.0° C-
simulated1.16 -40% 692
Winter: 18° C
Spring-Autumn: 25° C
Summer: 32° C
Field experiment: 28.7° C
Temperature Bioactivity sulfide generation
Temperature Effect
HATS 1Case Study 2
Case Study 3Water Flushing
Tunnel E Tunnel F
Length (km) 5.5 3.6
Flowrate (m3/h)(10/4-10/7)
35,390 12,210
HRT (hour) 1.5 1.3
Unsatisfactory control effects
- Enormous flow requirement: 10 to 20 times of the average
flow, and increase with tunnel size;
- Flushing frequency: every 3~4 days, lasting for 1h;
Negative impact
- Stress the downstream treatment capacity
- High energy consumption
Flushing
EF
H2S control by chemical dosing
Q1: Where ?
Dosing Location : SCISTW or
KT, TKO, TY,…?
Q2: What ?
Dosing chemical: Ca(NO3)2,
NaOH, O2….
Q3: When and how?
Dosing strategy: dosage,
stable or dynamic?
Objective:• H2S(g) at SCISTW MPS 1 ≤ 20 ppm
• DS concentration at SCISTW MPS 1 ≤ 1.5 mg/L
The location selection for septicity control mainly considered:
The target H2S(g) control location - SCISTW
The net sulfide production contribution- tunnel E contribute 41% of the net sulfide production in HATS 1 system
The mixing and reaction time of dosage;
3050 kg/h dosing rate at six PTWs: TKW, KT, TKO, SKW, CW and TY, respectively.
610 kg/h dosing rate at TKW, KT, TKO, SKW and CW simultaneously
Best dosing location:TKW
Dosing Location Selection- Trial with Nitrate Dosing
HATS 1
Oxygen
o Only TKO can install this system;
o Long distance transportation consumed too much
oxygen dosage.
o Low control efficiency to SCISTW
Case 4: Super-Oxygenation System (TKO) HATS 1
Case 5: Nitrate Dosing (TKW)
0
50
100
150
200
250
0 500 1000 1500 2000 2500 3000
H2S
(p
pm
)
Dosage (kg/h)
Oxygen
Calcium nitrate
Sodium hydroxide
Case 6: NaOH Dosing (TKW)
Nitrate or
NaOH
• For DS control (<1.5 mg/L), it works
• Increasing nitrate dosage is inapplicable to
control H2S(g) at < 20 ppm
Add NaOH at a rate of 998 kg/h at TKW
Little change of DS concentration;
H2S(g) dropped from 221ppm to 18 ppm.
Forced Ventilation
Nitrate + NaOH
Case 8: Nitrate + NaOH (TKW) +
Forced Ventilation (SCISTW)
Case 7: Nitrate + NaOH dosing (TKW)
Nitrate + NaOH
HATS 1
To achieve the control target of :
H2S(g) ≤ 20 ppm
DS ≤ 1.5 mg/L
Ca(NO3)2 :1250 kg/h + NaOH : 848 kg/h.
√√
To achieve the control target:
H2S(g) ≤ 20 ppm
DS ≤ 1.5 mg/L
Ca(NO3)2 : 1250 kg/h + NaOH 498 kg/h + forced
ventilation: ACH of 5
√√
Case Note Recommendation
1Ultimate Flow Simulation
Flowrate sulfide H2S(g) -
2 Temperature effect T sulfide H2S(g) -
Objective:• H2S(g) at SCISTW MPS 1 ≤ 20 ppm
• DS concentration at SCISTW MPS 1 ≤ 1.5 mg/L
3 Water Flushing Unsatisfactory control effects X
4Super-oxygenation system(TKO)
Low efficiency X
5 Nitrate dosing(TKW) H2S(g) at < 20 ppm X
6 NaOH (TKW) H2S(g) at < 20 ppm, but little change of sulfide
X
7Nitrate + NaOH
(TKW) sulfide √ H2S(g) √ √
8Nitrate + NaOH
(TKW) + Forced
Ventilation (MPS1)sulfide √ H2S(g) √ √
4. Summary
The developed SPMM well predicted the sulfide production and H2S releases in
HATS stage 1 tunnels.
By model simulation, the recommended strategy for septic control in HATS stage
1 is combined dosing of calcium nitrate and sodium hydroxide at To Kwa Wan
PTW, with forced ventilation at MPS 1 of SCISTW
The SPMM is an efficient and helpful tool to identify the key factors to the
serious septic problem and reduce hydrogen sulfide pollution in the HATS
system