Review & Design of the Apia Pressure Sewer System

Transcription

1 Review & Design of the Apia Pressure Sewer System Presented by Tainau Moefaauo Taputoa Titimaea - Samoa Water Authority & Paul Edwards Urban Water Solutions 1

2 Contents Project Background Project Team Data Collection Physical Inspections Modelling Existing System Analysis On Property Design Reticulation Design 2

3 Introduction to Pressure Sewers A pressure sewer is a network of fully sealed pipes, which are fed by grinder pump located at each property. The grinder pump grinds the solids into a slurry, which is then pumped through a small diameter pipeline from the house to the reticulation pressure sewer in the street Pipes are sized to accommodate a limited number of pumps operating at one time. 3

4 Pressure Sewer Configuration 4

5 Pressure Sewer Configuration 5

6 Apia Pressure Sewer System Client Samoa Water Authority (SWA) SWA provides water to 80% of Samoa s population. SWA provides wastewater services to 120 commercial customers connected to 80 pump units in the CBD of Apia. Population of Apia 37,000 Population of Samoa 180,000 6

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8 Project Background Flooding frequent problem in Apia due to high rainfall and inadequate drainage. Septic tanks releasing wastewater into the environment. Adverse ground conditions & high water table. Pressure Sewer System and WWTP constructed in

9 Project Drivers WWTP designed to treat 1ML/day based on design assumptions by previous consultant. Average flows of 500kL/day currently received at WWTP. Large wet weather inflow to the system. Need for comprehensive review of the system performance & operation. Assessment of system capacity so more connections be made to the system. Knowledge transfer to SWA Modelling, design, analysis & operation 9

10 Project Scope Existing System Conduct a physical survey of the existing system. Develop a hydraulic model in InfoWorks CS of the existing PSS Determine system constraints and recommend improvements. Assessment of system capacity so more connections be made to the system. Future System Review & Update O&M Procedures Provide training to SWA staff in modelling, design and operation of the PSS. Design future extensions to the system 10

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12 Project Team Urban Water Solutions Modelling of existing system in InfoWorks System Performance Analysis Training of SWA staff in modelling & PS Reticulation Design Design of extensions to the pressure sewer system Pressure Sewer Services Australia Specialist Subconsultant Physical inspections & pump diagnostics checks Review of current O&M procedures Training of SWA staff in O&M procedures On property design for future extensions 12

13 Physical Surveys & Inspections UWS team & SWA staff carried diagnostic checks on all pump units in the system. Verification of Voltage and Amperage against the pump curve. Verification of audible & visual alarm system Verification of level sensing devices. Inspection of control panel condition. Inspection of pump well, pump and cutter condition. Inspection of boundary valve and operation of boundary valve. 13

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16 Smoke Testing & Drainage Inspections UWS team & SWA staff carried out smoke testing to locate entry points for storm water inflows. Identification of direct cross connections into the PSS. On property drainage inspections undertaken to identify drainage system infiltration points. 16

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20 Infiltration Points Manhole covers - Plastic manhole covers used at new government building. Rodding Points - Unsealed covers. Grease Traps (Septic Tanks) Low points on properties 20

21 Cross Connections Roof drainage directly connected to pump wet well. Direct connection of a roof drainage down pipe into the overflow relief gully. 21

22 Outputs from Physical Inspections Defects Summary List Property Defect Forms Infiltration Defects Summary Updated Asset Register 22

23 Data Collection Water Usage & Pump Run Times To determine system inflows, water meters, electricity meters and pump run meters were read over an 8 day period. High pump run hours noted 23

24 Data Collection Inlet Flow Data from the WWTP Flow Data extracted from SCADA at the WWTP 8 days at 90 second timestep 6 months of historical flow data extracted at 10 min timestep 24

25 Inlet Flow Data 25

26 Data Collection Pressure Data For use in model calibration. UWS installed 6 pressure loggers across the system. Set to record pressures at a 30 second timestep Installed over an 8 day period. 26

27 Pressure Logger Locations 27

28 Pressure Logger Installation 28

29 Pressure Data 29

30 Rainfall Data Installed a rain gauge at the WWTP Obtained historical rainfall data from the Samoa Met Office 30

31 Model Configuration 100mm PVC Pressure sewer main Manufacturer's pump curve links each wet well node to the service line 90mm HDPE service line Pump wet well modelled as a node Sanitary flows from the building are loaded to the pump wet well node Each property modelled as a subcatchment 31

32 Model Layout WWTP 32

33 Model Calibration (Red = WWTP Inlet Meter Data, Green = Model Data) 33

34 Pressure Verification (Red = Pressure Logger Data, Green = Model Data) 34

35 System Analysis Calibrated model used to analysis system performance. Model run for 7 days to assess peak velocities. The WSAA pressure sewer code states the minimum flow velocity, which shall be achieved at least once in every 24 h, shall be 0.60 m/s. 35

36 Predicted Velocities 36

37 Target I/I Removal Foreshore Line Tooa Salamasina Blg Seal Manhole Diabetes Clinic Low Gully Seal rag screen Central Bank Infiltration into tank TTTE Building Direct Roof Connection RSA Club Infiltration through pump lid Library Tree root intrusion Low Gully 37

38 Summary of Existing Review In Dry Weather, the WWTP is only running at approx 50% capacity. Analysis showed plenty of available capacity in major reticulation network. On property defects and major locations of I/I identified. 38

39 Knowledge Transfer Incorporation of SWA staff into the Project Team. On the Job Training & Mentoring. Training provided in Hydraulic Modelling, Analysis and Design. Development of Detailed O&M procedures. Training in O&M Procedures. 39

40 Operations & Maintenance PSSA have provided ongoing operation and maintenance support & training to SWA staff. Convent Street Realignment 40

41 Operations & Maintenance Convent Street Realignment 41

42 Operations & Maintenance Service Line Repairs 42

43 Operations & Maintenance PE Pipe Welding 43

44 Operations & Maintenance Ififi Street Nightworks 44

45 Operations & Maintenance Pump Repair Training 45

46 Operations & Maintenance Driver Training 46

47 Design Process Two design streams: On property design Reticulation design and analysis Future Connections: 108 new properties connected 3 mains extensions 47

48 On Property Designs Plumbing Audit undertaken at each property to be connected. 48

49 On Property Designs 49

50 On Property Designs 50

51 On Property Designs 51

52 On Property Designs 52

53 On Property Designs 53

54 Reticulation Design Survey Surveyor engaged to undertake topographic survey. Model Update New pipelines added. Future properties digitised into the model. Pump locations & service lines modelled. 54

55 Reticulation Design 55

56 Reticulation Design Sewage Loading Estimates Water consumption data sourced and average long term water usage estimated. 56

57 Reticulation Design Design Criteria Sewage estimates generally 80% ave daily water consumption. Seasonal facilities (eg. hotels) used peak 4 month average daily water consumption. Diurnal profile assigned to reflect business type 57

58 Design Criteria Reticulation Design Aquatec OGP pumps exclusively across the system. All new mains PE100 PN16 pipe in sizes 63mm, 90mm and 110mm. Minimum velocities as per WSAA standards 58

59 Daily Scouring Velocity 59

60 Daily Flows to WWTP 60

61 Septicity Assessment The age of the sewage has been assessed against the following WSSA Pressure Sewer code guidelines: < 4 hours Low / minimal septicity risk 4-8 hours Medium septicity risk > 8 hours High septicity risk Existing System Future System Average Sewage Age Septicity Risk 5.1 hours Medium 3 hours Low 61

62 Reticulation Design Plans 62

63 Pressure Sewer Systems A Pacific Solution! Appropriate technology for Pacific conditions. High ground water table. Flat or hilly terrain. Poor ground conditions. Overflows to the environment contained. Energy efficient. Flexibility allows for phased development. Operation & maintenance staff have developed proficiency with appropriate training. 63

64 Summary Operation, performance and capacity assessment successfully undertaken on the existing PSS. Using hydraulic model enables design of future extension to be undertaken with confidence (predicted velocities and pressure etc.) Modelling analysis has enabled double the customers to be connected to the system. SWA now have skills to manage and operate the system. 64

65 Thank You 65