Wastewater Collection Systems

1. Wastewater Collection Systems On completion of this module you should be able to: • Discuss the sources of wastewater • Understand the relevant sections of the legislation relating to sewer collection systems and wastewater • Plan and design a wastewater collection system Public Health Engineering

2. Wastewater Collection Systems Some definitions on wastewater systems • Sewerage – a system comprising of collection and treatment facilities • Sewage – spent water or wastewater • Sewers – a collection system of pipes to convey wastewater to a central point of treatment Public Health Engineering

3. Wastewater Collection Systems Sources of wastewater • Domestic flows • Industrial and trade wastes • Urban stormwater • Infiltration/inflow Public Health Engineering

4. Wastewater Collection Systems Materials in wastewater Impurities 0.01% Chemical Biological Physical form inorganic suspended organic dissolved living Non-living bacteria, fungi, protozoa, algae Public Health Engineering

5. Wastewater Collection Systems Infiltration/inflow (I/I) • Ingress of groundwater or rainwater from pipe defects, joints etc • Ground condition also dictates I/I • I/I peaks during and after storms and varies with season • Extraneous water from illegal connections • Qld’s guidelines allow 14 – 28 m3/d.km Public Health Engineering

6. Wastewater Collection Systems • Hydraulic loading (ML/d) • Organic loading (kg/m3.d) • Concept of equivalent person or population (ep) for design Wastewater presents a unique design problem Public Health Engineering

7. Wastewater Collection Systems Relevant legislations • Plumbing & Drainage Act 2002, and Standard Plumbing & Drainage Regulation 2003, that relate to licensing and assessing of work • Environmental Protection Act 1994 that relates to quantity and quality of flows into the environment Public Health Engineering

8. Wastewater Collection Systems Discharge into sewers • Governed by the local authority (trade officers) • Industrial and trade effluent are considered on a case by case basis • Land discharge is subject to the Environmental Protection Act 1994 Public Health Engineering

9. Wastewater Collection Systems • Subject to the Environmental Protection Act 1994 • Administered by the Environmental Protection Agency • Generally licence conditions of BOD5 < 20 mg/L; NFR < 30 mg/L; DO > 2 mg/L Quality of treated effluent Public Health Engineering

10. Wastewater Collection Systems Types of wastewater systems • Separate versus combined systems • Gravity and pumped flows • Small collection systems using pressure or vacuum Public Health Engineering

11. Wastewater Collection Systems Pressure system Public Health Engineering

12. Wastewater Collection Systems Vacuum system Public Health Engineering

13. Wastewater Collection Systems Sewer installation • Sewer alignment • Depth of sewer • House connection • Location of manholes • Testing of sewers and house drains Public Health Engineering

14. Wastewater Collection Systems Sewer installation Public Health Engineering

15. Factors that control the depth of sewers • Self-cleansing velocity ie. minimum slope • Minimum cover to protect the sewer • Required depth to drain properties serviced • Sufficient depth to avoid other services Public Health Engineering

16. House drain and connection • House drain is the property sewer pipe that adjoins council’s sewer • Minimum house drain dia. is 100 mm with a min. slope of 1:60 allowing 0.5 invert depth at the head • House drains must be vented at the head • House connection is made at the lowest point Public Health Engineering

17. Wastewater Collection Systems Sewer installation Typical sewer and housedrain connection Public Health Engineering

18. Testing of sewers • Water test - apply a pressure equal to 2 m head at the higher section of the length under test. Loss of water shall not exceed 1 L/m diameter. m length in 30 minutes • Air test – apply a pressure of 30 kPa and hold for 3 mins. Time taken for a drop from 25 kPa to 20 kPa shall be not less than 90 secs for pipes less than 225 mm. Public Health Engineering

19. Use of manholes and location • Inspection and maintenance • Changes in vertical and horizontal alignment • Intersections • Spaced not greater than 90 m for 375 mm pipes • Spaced not more than 150 m for larger pipes Public Health Engineering

20. Wastewater Collection Systems Typical manhole configuration Public Health Engineering

21. Wastewater Collection Systems • System must drain all points of the catchment • Peak wet weather flow capacity • Self-cleansing flow velocity • gravity flow at minimum slope • Pressure mains where necessary Design parameters Public Health Engineering

22. Wastewater Collection Systems Design for maximum flow(Queensland Planning Guidelines for Water Supply and Sewerage Schemes) • Average dry weather flow (ADWF) 275 L/c.d • Peak dry weather flow, PDWF = C1 x ADWF • Peak wet weather flow, PWWF = C1 .ADWF + I/I • Maximum flow at 3/4 pipe depth • 150 mm min. dia gravity flow & min. slope dependent on pipe dia. Public Health Engineering

23. Peaking factors for maximum flows Public Health Engineering

24. Proportional velocity and discharge Public Health Engineering

25. d/D radian  Ad Pd v/V q/Q 0.015 0.4911 28 5.48648E-05 0.0368 0.1164 0.00036 0.016 0.5073 29 6.04235E-05 0.0380 0.1215 0.00042 0.017 0.5230 30 6.61557E-05 0.0392 0.1265 0.00047 Proportional geometry elements Public Health Engineering

26. Wastewater Collection Systems • About 60 – 80% of the daily water demand appears as spent water • There is a diurnal pattern in the collection system • Minimum 150 mm pipe with a minimum slope of 1:150 in the collection system • Minimum slopes relate to self-cleansing velocity Public Health Engineering

27. Wastewater Collection Systems Owing to a mixture of solids and liquids, sewage flow velocities must be self-cleansing • 0.75 PDWF at least once a day to promote self-cleansing flow • Generally, self-cleansing velocity is achieved at 0.6 – 0.75 m/s • Use of 0.15 kg/m2 shear stress for organic solids Public Health Engineering

28. Wastewater Collection Systems Effects of long detention times Owing to the high O2 demand of biodegradable organic matter, long HRT will deplete dissolved oxygen (DO) • Slime growth under waterline will promote anaerobic bacteria and reduce sulfate to sulfides • Downstream turbulence will release H2S into the air space • Moist film above the waterline and aerobic bacteria will oxidise H2S to H2SO4 Public Health Engineering

29. Effects of long detention times Public Health Engineering

30. Effects of long detention times Public Health Engineering

31. Effects of detention times in rising mains Public Health Engineering

32. Wastewater Collection Systems Finally do we question: • Is it still environmentally responsible to use 50 - 80 kg/day of drinking water to transport 1 - 1.5 kg/d of human waste to a treatment plant? • Do we have to continue improving the wrong solution or do we have the intelligence for new solutions? Public Health Engineering

33. End of Module 6 Wastewater Collection Systems Public Health Engineering