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Public Health Engineering1 Wastewater Collection Systems Discuss the sources of wastewater Understand the relevant sections of the legislation relating.

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Presentation on theme: "Public Health Engineering1 Wastewater Collection Systems Discuss the sources of wastewater Understand the relevant sections of the legislation relating."— Presentation transcript:

1 Public Health Engineering1 Wastewater Collection Systems 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 On completion of this module you should be able to:

2 Public Health Engineering2 Wastewater Collection 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 Some definitions on wastewater systems

3 Public Health Engineering3 Wastewater Collection Systems Domestic flows Industrial and trade wastes Urban stormwater Infiltration/inflow Sources of wastewater

4 Public Health Engineering4 Wastewater Collection Systems Materials in wastewater Impurities 0.01% Physical form suspended dissolved Chemical inorganic organic Biological living Non-living bacteria, fungi, protozoa, algae

5 Public Health Engineering5 Wastewater Collection Systems 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 Qlds guidelines allow 14 – 28 m 3 / Infiltration/inflow (I/I)

6 Public Health Engineering6 Wastewater Collection Systems Hydraulic loading (ML/d) Organic loading (kg/m 3.d) Concept of equivalent person or population (ep) for design Wastewater presents a unique design problem

7 Public Health Engineering7 Wastewater Collection Systems 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 Relevant legislations

8 Public Health Engineering8 Wastewater Collection Systems 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 Discharge into sewers

9 Public Health Engineering9 Wastewater Collection Systems Subject to the Environmental Protection Act 1994 Administered by the Environmental Protection Agency Generally licence conditions of BOD 5 2 mg/L Quality of treated effluent

10 Public Health Engineering10 Wastewater Collection Systems Separate versus combined systems Gravity and pumped flows Small collection systems using pressure or vacuum Types of wastewater systems

11 Public Health Engineering11 Wastewater Collection Systems Pressure system

12 Public Health Engineering12 Wastewater Collection Systems Vacuum system

13 Public Health Engineering13 Wastewater Collection Systems Sewer alignment Depth of sewer House connection Location of manholes Testing of sewers and house drains Sewer installation

14 Public Health Engineering14 Wastewater Collection Systems Sewer installation

15 Public Health Engineering15 Self-cleansing velocity ie. minimum slope Minimum cover to protect the sewer Required depth to drain properties serviced Sufficient depth to avoid other services Factors that control the depth of sewers

16 Public Health Engineering16 House drain is the property sewer pipe that adjoins councils 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 House drain and connection

17 Public Health Engineering17 Wastewater Collection Systems Sewer installation Typical sewer and housedrain connection

18 Public Health Engineering18 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. Testing of sewers

19 Public Health Engineering19 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 Use of manholes and location

20 Public Health Engineering20 Wastewater Collection Systems Typical manhole configuration

21 Public Health Engineering21 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

22 Public Health Engineering22 Wastewater Collection Systems Average dry weather flow (ADWF) 275 L/c.d Peak dry weather flow, PDWF = C 1 x ADWF Peak wet weather flow, PWWF = C 1.ADWF + I/I Maximum flow at 3/4 pipe depth 150 mm min. dia gravity flow & min. slope dependent on pipe dia. Design for maximum flow (Queensland Planning Guidelines for Water Supply and Sewerage Schemes)

23 Public Health Engineering23 Peaking factors for maximum flows

24 Public Health Engineering24 Proportional velocity and discharge

25 Public Health Engineering25 Proportional geometry elements E E E d/D radian AdAd PdPd v/Vq/Q

26 Public Health Engineering26 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

27 Public Health Engineering27 Wastewater Collection Systems 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/m 2 shear stress for organic solids Owing to a mixture of solids and liquids, sewage flow velocities must be self-cleansing

28 Public Health Engineering28 Wastewater Collection Systems Slime growth under waterline will promote anaerobic bacteria and reduce sulfate to sulfides Downstream turbulence will release H 2 S into the air space Moist film above the waterline and aerobic bacteria will oxidise H 2 S to H 2 SO 4 Effects of long detention times Owing to the high O 2 demand of biodegradable organic matter, long HRT will deplete dissolved oxygen (DO)

29 Public Health Engineering29 Effects of long detention times

30 Public Health Engineering30 Effects of long detention times

31 Public Health Engineering31 Effects of detention times in rising mains

32 Public Health Engineering32 Wastewater Collection Systems Is it still environmentally responsible to use kg/day of drinking water to transport 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? Finally do we question:

33 Public Health Engineering33 End of Module 6 Wastewater Collection Systems

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