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2.1 Quantification of wastewater flow, design of wastewater sewers

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• 1. 18-9-2013 Challenge the future Delft University of Technology CIE4491 Lecture. How to quantify wastewater flow Marie-claire ten Veldhuis Source: news.bbc.co.uk Source: www.nu.nl
• 2. 2CIE4491 Lecture Quantifying wastewater flow Learning objective of this course: design urban drainage system 1. Available principles for urban drainage: stormwater and wastewater collection 2. How to quantify flows incl. flow variations: stormwater and wastewater 4. Available transport principles: gravity flow, pressurised flow 6. Principles of hydraulic calculations: design pipe dimensions and vertical profile 5. Layout of urban drainage system 3. Design requirements
• 3. 3CIE4491 Lecture Quantifying wastewater flow Foul sewer design Terminology: wastewater flow; dry weather flow; wastewater sewer/foul sewer Design steps for wastewater sewers:  Determine design capacity: dry weather flow  Determine appropriate design diameter: max filling rate  Determine bottom gradient: “self-cleansing” capacity
• 4. 4CIE4491 Lecture Quantifying wastewater flow Dry weather flow Design steps for wastewater sewers:  Quantify dry weather flow  start from drinking water consumption, assume peak factor to allow for daily variation  add industrial ww (if relevant)  add groundwater infiltration (+wrong connections), based on assumption/best guess
• 5. 5CIE4491 Lecture Quantifying wastewater flow Foul/wastewater sewer design Design steps for separate wastewater sewers:  Determine design capacity: dry weather flow  Determine appropriate design diameter: max filling rate  max filling rate 50% at design flow: allow for future increase + backup in case of system failure
• 6. 6CIE4491 Lecture Quantifying wastewater flow Foul/wastewater sewer design Design steps for wastewater sewers:  Determine design capacity: dry weather flow  Determine appropriate design diameter: max filling rate  Determine bottom gradient: “self-cleansing” capacity  NB: wastewater particles with hard-to-predict behaviour
• 7. 7CIE4491 Lecture Quantifying wastewater flow Foul/wastewater sewer design – bottom gradient Minimum bottom gradient: “self-cleansing” capacity (esp. critical in more or less flat areas)  UK: min self-cleansing velocity 0.6 m/s  Better: min shear stress:  = 0.5-1.5 N/m2  Rule of thumb: i=1/D (D: pipe diameter in mm)  Or: min gradient 1:250 (1st section); 1:500 (other sections) N.B.: 25 years of sewer sedimentation research – unable to predict sedimentation processes!
• 8. 8CIE4491 Lecture Quantifying wastewater flow Wastewater flow, remember: Small compared to stormwater flow High organic matter content (good for wwtp bacteria, not for CSO) Sticky: sedimentation/erosion unpredictable Foul sewers sensitive to blockage Wastewater systems in flat areas: pumping