Feng Jiang Professor, School of Chemistry and Environment South - - PowerPoint PPT Presentation

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 University Email: jiang.feng@foxmail.com / jiangfeng@scnu.edu.cn Mobile / 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

• bnoxious gas(H2S) and corrosion

H2S SO4

2-

H2S SO4

2-

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： 𝑇𝑃4

2− + 𝐷 𝑇𝑆𝐶𝑇2− + 𝐷𝑃2

Anoxic sulfide oxidation： 𝑇2− + 𝑃2/𝑂𝑃3

−

𝑇0/𝑇𝑃4

2− + 𝑂2

Hydrogen sulfide dissociation： 𝑇2− ↔ 𝐼𝑇− ↔ 𝐼2𝑇 Hydrogen sulfide emission: 𝐼2𝑇(aq) ↔ 𝐼2𝑇(𝑕)

H2S(g) conc.(ppm) Harmful effects 0.13 Min concentration can be smelt … … 200-300 Continuous 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 peak

HATS

H2S Control End-of-pipe treatment Forced Ventilation Deodourization Unit 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 emission NaOH, 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

5000 10000 15000 20000 25000 4/10/2015 9:00 5/10/2015 21:00 7/10/2015 9:00 Flowrate (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) SO4

2-

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

Corrosion H2SO4 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

500 1000 1500 2000 SCISTW

• utput

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 monitoring at 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

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 Flowrate (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

0.5 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 Dissolved sulfide (mgS/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/L

Predicted well

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

Tunnel Average 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 Tunnel Flowrate (m3/h) Average HRT(h) Simulated DS-out (mgS/L) Net sulfide production （kgS/d） Flowrate (m3/h) Average HRT(h) Simulated DS-out (average mgS/L) Net sulfide production （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 1

Case Study 1

SCISTW DS (mgS/L) DS variation(%) Net sulfide production （kgS/d） 28.7°C- simulated 1.94 0% 1,585 32.0°C- simulated 2.16 11% 1,837 25.0°C- simulated 1.61

• 17%

1,207 18.0°C- simulated 1.16

• 40%

692

Winter: 18°C Spring-Autumn: 25°C Summer: 32°C Field experiment: 28.7°C

 Temperature Bioactivity sulfide generation

Temperature Effect

HATS 1

Case Study 2 Case Study 3

Water 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

E F

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

• Only TKO can install this system;
• Long distance transportation consumed too much
• xygen dosage.
• Low control efficiency to SCISTW

Case 4: Super-Oxygenation System (TKO)

HATS 1

Case 5: Nitrate Dosing (TKW)

50 100 150 200 250 500 1000 1500 2000 2500 3000 H2S (ppm) 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 1 Ultimate 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 4 Super-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 7 Nitrate + NaOH (TKW) sulfide √ H2S(g) √ √ 8 Nitrate + 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