Watermatex To be Presented by: Professor Kin Man Ho Kingsford Environmental Hong Kong

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1 Watermatex 2015 To be Presented by: Professor Kin Man Ho Kingsford Environmental Hong Kong

Introduction Parts 1-3 CFD Modelling for of the Overall CEPT Capacity Maximization for the Increased Upgrading Part #1 2-D CFD Process Hydraulic modelling for Upgrading of Each PST Tank for

2 Introduction Parts 1-3 CFD Modelling for of the Overall CEPT Capacity Maximization for the Increased Upgrading Part #1 2-D CFD Process Hydraulic modelling for Upgrading of Each PST Tank for Increased Capacity Part #2 3-D CFD Flow Hydraulic Modelling for Flow Balancing to Each PST Part #3 - Integrated Process and Flow CFD Modelling for PST Upgrading Overall Summary and Conclusions

Stonecutters Island Sewage Treatment Works (SCISTW) Stage 1 currently

Ø Receives preliminary treated effluent from urban Kowloon, Kwai

23.6 km deep underground tunnel. Ø Design capacity of 1.

Ø Fully commissioned at the end of 2001.

3 Stonecutters Island Sewage Treatment Works (SCISTW) Stage 1 currently the world s largest Chemically Enhanced Primary Treatment (CEPT) Plant. Ø Receives preliminary treated effluent from urban Kowloon, Kwai Chung, Tsing Yi, Tseung Kwan O & North-Eastern HK Island conveyed by a 23.6 km deep underground tunnel. Ø Design capacity of 1.7 million m 3 /day Ø Maximum hydraulic peak factor of 2. Ø Fully commissioned at the end of Ø Water quality in the Harbor substantially improved. Cross-Harbor Swim Race Returns to HK in 2,011 on West Zone of Victoria Harbor.

Ove Arup & Partners Hong Kong Limited (Arup) was commissioned by Drainage Services Department (DSD) of Hong Kong Government to upgrade the SCISTW in 2007 - Stage 2A Works. Kingsford Environmental (H.

4 Ove Arup & Partners Hong Kong Limited (Arup) was commissioned by Drainage Services Department (DSD) of Hong Kong Government to upgrade the SCISTW in Stage 2A Works. Kingsford Environmental (H.K.) Ltd. was engaged by Arup to upgrade the existing CEPT tanks using CFD PST model Target upgraded capacity of 2.45 million m 3 /day (10 Million Population) with maximum hydraulic peak factor of 1.7. Additional sewage collected from the North and South-West shores HK Island conveyed via the constructed deep tunnel Site area is extremely restricted limiting expansion. of newly system.

5 56 x 7 x 3.5m 60.5 x 7 x 3.5m Cross-Section of Double-Deck PST

6 Key Component Parameter Existing CEPT Tanks (Stage 1) Design Criteria Upgraded CEPT Tanks (Stage 1 & Stage 2A) Design Criteria Design Flow Design ADWF 1,725,000 m 3 /d 2,450,000 m 3 /d Design PDWF 2,242,500 m 3 /d 3,185,000 m 3 /d Design PWWF 3,450,000 m 3 /d 4,165,000 m 3 /d Design PDWF / PWWF; Peak Factor 1.3 / / 1.7 Rapid Mixing Chambers Number of Chambers Flocculation Tanks Number of Tanks (Total) Primary Sedimentation Tanks Type of Tank Double Deck Double Deck Number of Tanks (Total) = 46 Number of Tanks (in Normal Operation) 34 (4 Standby) 40 (6 Standby) Capacity of Each / PWWF 50,735m 3 /d / 101,029 m 3 /d Volume of Each Tank 2,854 m 3 2,854 m 3 HRT of Each 1.35 hours 1.12 hours HRT of Each 0.68 hours 0.66 hours 61,250 m 3 /d /104,125m 3 / d Description Design Influent Content Effluent Discharge Criteria Total Suspended Solids (TSS) 5-day Biological Oxygen Demand (BOD 5 ) Average: 208 mg/l Average: 177 mg/l 95 percentile: 55 mg/l Max.: 110 mg/l 95 percentile: 75 mg/l Max.: 150 mg/l

7 Part 1: Original Scope 2-D CFD Process Hydraulic modelling for Upgrading of Each PST Tank for the Increased Capacity Part 2: Variation Order (Significant Flow Imblanace) 3-D CFD Flow Hydraulic Modelling for Flow Balancing to Each PST Part 3: Variation Order Integrated Process and Flow CFD Modelling for PST Upgrading

8 2-D CFD Process Hydraulic modelling for Upgrading of Each PST Tank for the Increased Capacity

9 Step 1: On-site Data Collection Step 2: PST CFD Model Selection, Development & Calibration Step 3: Identification of the Most Optimal (Cost-Effective) Hydraulic Enhancement Feature(s) Step 4: Validation and Fine-tuning of the PST Model

Kemmerer Samplers To evaluate the existing & upgraded performance & capacity of the CEPT process. Calibration of the CFD PST model.

nonsettleable TSS conc. reflecting the PST solids removal performance under ideal operating conditions.

Ø What types of particles should be settled out of the influent under different selected operating conditions.

10 Kemmerer Samplers To evaluate the existing & upgraded performance & capacity of the CEPT process. Calibration of the CFD PST model. Flocculation Test Ø To identify the optimal chemical dosing rate(s) & HRT in which would achieve the practical lowest effluent nonsettleable TSS conc. reflecting the PST solids removal performance under ideal operating conditions. Sludge Settling Velocity Distribution Test Ø To provide an indication of how much TSS settling should be expected in the PST tanks. Ø What types of particles should be settled out of the influent under different selected operating conditions. Ø The hydraulic capacity of the PSTs. Solids Profile Test Ø To determine the extent of floc aggregation & breakup throughout the flow paths of the treatment process units. Ø to identify possible location(s) to enhance re-flocculation.

11 High Accuracy Clarifier Model (HACM ) was selected. Ø Verified worldwide by applications to many PSTs & has been peer reviewed Ø Detailed description of the model can be found in literature The CFD PST Model was developed & calibrated using: Ø As-built drawings Ø Historical plant data from 2004 to 2006 Ø On-site Data Collection conducted in February 2008 Ø Settling velocity assumed to be 1.2 m/hr Ø Influent TSS: 200 mg/l

12 In-tank hydraulic enhancement features were selected - potential effectiveness & cost-efficiency: Ø Inlet energy-dissipating & flocculation baffles (CFD Model Designed) Ø Inboard effluent launders Lamella plates/tubes were not considered because: Ø Not be effective to the existing shallow configuration of the PSTs. Ø Solids trapping/accumulation inside the plates/tubes may be an operational problem particularly as the PSTs are to be covered.

13 Hydraulic Enhancement Features of Primary Sedimentation Tanks (Cont d) Inlet Energy Dissipating & Flocculation Baffles Mid-Tank Baffles In-Board Launders Inlet Zone Transitional Zone Uniform Velocity Zone Effluent Zone

14 To compare the TSS removal efficiency between the predicted & the real achievable max. capacities. On-site validation using One (1) each of the identical PST with & without hydraulic enhancement feature(s). The PST CFD Model re-calibrated with the validation test results. The re-calibrated PST Model was then used to further fine-tuned the design of the selected hydraulic enhancement feature(s) for the design upgrade of the existing PSTs.

Creating a re-flocculation chamber for the NSS at the front end of the PST.

15 Eliminating density currents & flow entrainment from the inlet into the settling zone. Distributing the flow more evenly across the full width. Creating a re-flocculation chamber for the NSS at the front end of the PST. Improving the flow patterns by providing good vertical flow distribution. Dissipating the energy of incoming flow through its perforated surface. Combining the energy dissipating & reflocculating zone to optimize area for the settling zone for maximum capacity.

16 Hydraulic Enhancement Feature(s) Upper Deck Improvement* Lower Deck Improvement* Inlet Energy-Dissipating & Flocculation Baffles 9% 12% Inboard Effluent Launder Inlet Energy-Dissipating & Flocculation Baffle & Inboard Effluent Launder 8% 4% 13% 13% * In terms of effluent TSS concentrations, in mg/l.

17 Hydraulic Enhancement Feature(s) Max. Operating Capacity Under DWF Conditions Unit Existing Unmodified PST Modified PST m 3 /d 3,268,000 3,594,800 m 3 /d/pst 81,700 89,870 Allowed Diurnal Peak Factor 1.33 (1.3) 1.47 (1.3) No. of PSTs of 1.3 Unit 39 (40) 36 (40) Max. Operating Capacity Under PWWF Conditions m 3 /d 4,040,000 4,444,000 m 3 /d/pst 101, ,100 Allowed Wet Peak Factor 1.65 (1.7) 1.81 (1.7) No. of PSTs Peak Design Flow Unit 42 (40) 38 (40)

18 Conducted on January Two (2) identical, completely self-contained Prototype CEPT systems were used for the validation of the HACM PST Model. Validation Test were conducted on three (3) separate days under both average & peak flow conditions. Upgraded PST performed significantly better than the Non-Upgraded PST: - Ø Significant drop in TSS level between the PST inlet Ø Provided a good flocculation environment for the incoming TSS Ø On the basis of NSS concentration, the Inlet Energy-Dissipating & Flocculation Baffles increased the capacity by: Ø Peak flow conditions: >22% Ø Average flow conditions: >20% (12±5%)

CFD PST model allowed selection of the most optimal hydraulic enhancement feature(s) for the upgrading of the existing PSTs & design of the PSTs for the expansion.

19 CFD PST model allowed selection of the most optimal hydraulic enhancement feature(s) for the upgrading of the existing PSTs & design of the PSTs for the expansion. Full-scale validation confirmed the upgrading approaches. The un-modified PSTs will not meet the upgraded capacity requirement under ideal balanced flow between all of the PSTs. However, 100% equal flow distribution conditions is impossible w/ 2 close to 200-m long main distribution channels & 46 PSTs w/ upper & lower decks (or a total of 92 PSTs). For upgrade design, use only ~10-15% increase in treatment capacity of the upgraded PSTs w/ perforated energy-dissipating & flocculation inlet baffles will be on the safe side. A further CFD modelling is required to identify the exact impact of flow imbalance on the process performance.

20 3-D CFD Flow Hydraulic Modelling for Flow Balancing to Each PST

imbalance; Photo was taken from PST#16 on 26 Feb.

21 Observed severe flow imbalances between stacked PSTs during Onsite Data Collection; Preliminary evaluation showed > ±30% imbalance; Photo was taken from PST#16 on 26 Feb. 08 at 11:44 a.m. Photo was taken from PST#46 on 26 Feb. 08 at 11:41 a.m.

22 Step 1: 3-D CFD Model Data Preparation for Flow3D Step 2: 3-D CFD Model Set-up & Calibration of Flow3D Step 3: Optimization for Equal Flow Balance with Enhancement Features Step 4: Model Operation

Various modelling scenarios to investigate flow imbalance

23 Flow3D CFD Modelling for Hydraulic Performance Existing CEPT Tanks New CEPT Tanks New Rapid Mix & Floc Tanks Various modelling scenarios to investigate flow imbalance and hydraulic performance of existing CEPT tanks and new CEPT tanks.

24 Ø New PSTS and MDC combined with old PSTS and MDC Ø Flow imbalance cannot be completely resolved. Ø Flows from new system did not reduce the imbalance between old tanks. Ø Tanks near point of zero velocity get high flows Ø The peak factors of 1.7, 1.35 and 1.0 are used for flow imbalance evaluation to determine the following: - Ø To determine the extent of flow imbalance; Ø To identify flow distribution efficiency to each PSTs; 80,000 Agreement No. CE 8/2006 (DS): Historical Plant Data of Stonecutters Island Sewage Treatment Works Influent Diurnal Flow in 2007 Peak flow: 68,381 m 3 22:00 (P.F.=1.30) 70,000 60,000 Ave. flow: 52,700 m 3 /hr 50,000 40,000 30,000 20,000 10, :00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 Flow (m3/hr) Time

25 1.79M m 3 /d x M m 3 /d x1.7

PST # 45 PST # 9 Flow rate (cms) 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 42 % 1.51 44 % Ideal Flow Rate = 1.05 cms 0.6 PST # 9 PST # 45 Primay Sedimentation Tanks Flow Rate (CMS) 2 1.8 1.

26 PST # 45 PST # 9 Flow rate (cms) % % Ideal Flow Rate = 1.05 cms 0.6 PST # 9 PST # 45 Primay Sedimentation Tanks Flow Rate (CMS) PST # 45 Flow Rate = 1.51cms Ideal Flow rate = 1.05 cms PST # 9 Flow Rate = 0.6 cms Time to Steady State (Secs)

27 Part 2 Approach Summary and Recommendations The integrated results on flow imbalance & primary eff. TSS under steadystate conditions are: - Condition Under ADWF Condition Under PWWF Condition Ultimate 2.44 M m 3 /d w/ diurnal P.F. of M m 3 /d w/ diurnal P.F. of 1.7 Settling Velocity 1.1 m/hr 1.8 m/hr MDC modification No No # of PST Online 36 PSTs 40 PSTs No. of PST Offline (for MDC maintenance) 10 PSTs 6 PSTs Predicted Primary Effluent TSS Level (flow-weighted) 48 mg/l (35 57 mg/l) Up to 57 mg/l To meet 95 percentile, the percentage of time which may exceed the peaking factor of are summarized below, according to SCISTW flow data from : Ø Exceeding 1.3 PF is 8.0% (Only need to consider a peak factor of 1.35) Ø Exceeding 1.4 PF is 2.2% Ø Exceeding 1.5 PF is 1.0% Ø Exceeding 1.6 PF is 0.6% Ø Exceeding 1.7 PF is 0.3% Ø Exceeding 1.8 PF is 0.2 Upgrading design needs to allow a larger safety factor for contingency.

28 Part 2 Approach Summary and Recommendations (Cont d) Provide energy-dissipating baffles with a maximum head loss of 500mm available; Other modifications were not allowed due to high headlosses of 500mm: - The perforated baffle only in the MDC (flow imbalances can be minimized to +20%/-12%); The orifice plate with 250 mm modifications (+18%/-10%); The combined MDC perforated baffle and the orifice plate with 250 mm modifications (+8.6%/-3.3%); To conduct Part 3 CFD Modelling to integrate the FLow3D results with HACM PST Process Model.

29 Ultimate Flow with 500mm Headloss Baffle (Ultimate Flow = 2.44M m3/d, PF=1.7) Energy Dissipating Baffle 1.79M m 3 /d x M m 3 /d x1.7 CFD Predicted Flow Distribution along MDC with 500mm Headloss Baffle (Ultimate Flow x 1.7 P.F.) 250% +29% of Ave Flow 200% Flow Distribution to each PST (Percentage to Average Flow) 150% 100% 50% 0% PST # 9 PST # 11 PST # 13 PST # 15 PST # 17 PST # 19 PST # 21 PST # 23 PST # 25 PST # 27 PST # 29 PST # 31 PST # 33 PST # 35 PST # 37 PST # 39 PST # 41 PST # 43 PST # 45 PST # 47 PSt # 49 PST # 51 PST # 53-19% of Ave Flow Average Flow

30 Integrated Process and Flow CFD Modelling for PST Upgrading

31 Part 3 Approaches to Integrated Process and Flow CFD Modelling for PST Upgrading To integrate the FLow3D results with HACM PST Process Model with: - Install 2 intermediate (mid-tank) perforated flocculation baffles for the upper & lower decks of the existing PSTs. Additional HACM simulations were conducted w/ 1 PST s inlet energy-dissipating & flocculation baffle & 2 mid-tank baffles in each of the PST s upper & lower decks to allow estimation of the overall effluent TSS levels. Normal Flow w/ Settling Velocity of 1.1 m/hr: P.F. 0.65, 1.0 & 1.35 Peak Flow w/ Settling Velocity of 1.8 m/hr: P.F. 0.65, 1.0, 1.35 & 1.7 Three capacity curves had been developed: - Flow imbalance vs Influent Flow per PST Effluent TSS vs Influent Flow per PST Flow-Weighted Final Effluent TSS level Need to look at the worse case scenarios with: - MPS#1 off-line 10 PSTs at 1 MDC & half MDC are offline (SV = 1.1 m/hr, P.F. = 1.35) 9 PSTs at 1 MDC & half MDC are offline (SV = 1.1 m/hr, P.F. = 1.35)

32 Simulations of the 2 Mid-Tank Baffles for the upper & lower decks of each existing & new PST to provide further treatment capacity enhancement.

33 Effluent TSS Content vs Influent Flow Under Dry and Wet Weather Flow Conditions (with Recommended Modifications)

34 Combined Results of HACM & Flow-3D Model on Effluent TSS Content vs Influent Flow Condition (with Recommended Modifications) and Under Different Worst Case What-If Scenarios Scenarios Daily Flow (m3/d) x PF # of PST On-line # of PST Off-line Settling Velocity (m/hr) Flow Weighted TSS (mg/l) Remarks With 500mm HeadLoss Energy Dissipating Baffle (WWF Condition) 2.44M x Steady-State MPS#1 Offline (DWF Condition) 2.44M x Steady-State 2.44M (33-48) Diurnal PF PST Offlined for MDC Maintenance (DWF Condition) 2.44M x Steady-State 2.44M (35-59) Diurnal PF PST Offlined for MDC Maintenance (DWF Condition) 2.44M x Steady-State 2.44M (35-57) Diurnal PF 1.3

35 MPS1 Offline (Ultimate Flow = 2.44M m3/d, PF=1.35) 0.45M m 3 /d x M m 3 /d x1.35 CFD Predicted Flow Distribution along MDC (Ultimate Flow x 1.35 P.F., MPS1 Offline) % +42% of Ave Flow % -23% of Ave Flow % % 50.00% 0.00% PST # 9 PST # 11 PST # 13 PST # 15 PST # 17 PST # 19 PST # 21 PST # 23 PST # 25 PST # 27 PST # 29 PST # 31 PST # 33 PST # 35 PST # 37 PST # 39 PST # 41 PST # 43 PST # 45 PST # 47 PSt # 49 PST # 51 PST # 53 Flow Distribution to each PST (Percentage to Average Flow) Average Flow

36 10 PSTs with half MDC Offline (Ultimate Flow = 2.44M m3/d, PF=1.35) CFD Predicted Flow Distribution along MDC (Ultimate Flow x 1.35 P.F., 10 PSTs offline, Odd No. PST) % % -34% of Ave Flow +41% of Ave Flow Flow Distribution to each PST (Percentage to Average Flow) % % Average Flow 1.79M m 3 /d x M m 3 /d x % 0.00% PST # 9 PST # 11 PST # 13 PST # 15 PST # 17 PST # 19 PST # 21 PST # 23 PST # 25 PST # 27 PST # 29 CFD Predicted Flow Distribution along MDC (Ultimate Flow x 1.35 P.F., 10 PSTs offline, Even No. PST) PST # 31 PST # 33 PST # 35 PST # 37 PST # 39 PST # 41 PST # 43 PST # 45 PST # 47 PSt # 49 PST # 51 PST # % % -67% of Ave Flow +16% of Ave Flow % % 50.00% 0.00% PST # 10 PST # 12 PST # 14 PST # 16 PST # 18 PST # 20 PST # 22 PST # 24 PST # 26 PST # 28 PST # 30 PST # 32 PST # 34 PST # 36 PST # 38 PST # 40 PST # 42 PST # 44 PST # 46 PST # 48 PST # 50 PST # 52 PST # 54 Flow Distribution to each PST (Percentage to Average Flow) Average Flow

37 9 PSTs with half MDC Offline (Ultimate Flow = 2.44M m3/d, PF=1.35) CFD Predicted Flow Distribution along MDC (Ultimate Flow x 1.35 P.F., 9 PSTs offline, Odd No. PST) % % -52% of Ave Flow +26% of Ave Flow Flow Distribution to each PST (Percentage to Average Flow) % % Average Flow 1.79M m 3 /d x M m 3 /d x % 0.00% PST # 9 PST # 11 PST # 13 PST # 15 PST # 17 PST # 19 PST # 21 PST # 23 PST # 25 PST # 27 PST # 29 CFD Predicted Flow Distribution along MDC (Ultimate Flow x 1.35 P.F., 9 PSTs offline, Even No. PST) PST # 31 PST # 33 PST # 35 PST # 37 PST # 39 PST # 41 PST # 43 PST # 45 PST # 47 PSt # 49 PST # 51 PST # % +55% of Ave Flow % -22% of Ave Flow % % 50.00% 0.00% PST # 10 PST # 12 PST # 14 PST # 16 PST # 18 PST # 20 PST # 22 PST # 24 PST # 26 PST # 28 PST # 30 PST # 32 PST # 34 PST # 36 PST # 38 PST # 40 PST # 42 PST # 44 PST # 46 PST # 48 PST # 50 PST # 52 PST # 54 Flow Distribution to each PST (Percentage to Average Flow) Average Flow

38 CFD PST process and Flow Hydraulic models were proven to be time-efficient & cost-effective for upgrading design and capacity evaluation. CFD PST model allowed : - Selection of the most optimal hydraulic enhancement feature(s) for the upgrading; the effluent TSS levels from the PSTs at different flows to be computed. Full-scale validation confirmed the upgrading approaches. 3-D Flow3D allows the flow imbalance to be quantified and minimized; Integrating the Flow3D flow and HACM process models allowed the upgrading design to be confirmed revealed with the actual effluent flow-weighted TSS concentration of 55 mg/l, with the 500mm Head Loss Baffle at the MDC as an extra safety factor, if required; However, optimal options for flow imbalance reduction are not practical for SCI STW due to the available free board and extent of modification works involved; Use of 500mm Head Loss Baffle at the MDC significantly reduced the flow imbalance from +100% to +29%. However, this option is expensive in term of the OPEX; HACM and Flow3D have already been combined to provide 3-D PST Modelling.

39 Acknowledgement Thanks to the Drainage Services Department of Hong Kong Government for assigning funding for the CFD Modelling and for allowing the data to be presented.

Multilayer Energy Dissipating Inlet Column in Center-Feed Clarifiers 1

Multilayer Energy Dissipating Inlet Column in Center-Feed Clarifiers 1 References 6,276,537 08/21/2001 Esler et al 210/519 6,800,209 10/05/2004 Wright 210/801 Field of Invention Clarifiers are tanks where