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9 Introduction to Wastewater disposal

Technische Universität Dresden. Peter Krebs. Department of Hydro Sciences, Institute for Urban Water Management. Urban Water Systems. 9 Introduction to Wastewater disposal. 9.1 Overview of wastewater system 9.2 Goals of wastewater disposal 9.3 Costs of sewers and wastewater treatment

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9 Introduction to Wastewater disposal

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  1. Technische Universität Dresden Peter Krebs Department of Hydro Sciences, Institute for Urban Water Management Urban Water Systems 9 Introduction to Wastewater disposal 9.1 Overview of wastewater system 9.2 Goals of wastewater disposal 9.3 Costs of sewers and wastewater treatment 9.4 Interface between sewer and wastewater treatment plant 9.5 The receiving water as a goal system 9 Introduction to wastewater disposal

  2. 9 Introduction to wastewater disposal 9.1 Overview of wastewater system 9 Introduction to wastewater disposal

  3. Sedimentation Treatment Clean water inflow Sludge disposal In-/Exfiltration Urban water system Urban region Retention Sewage retention tank Rain-runoff process Reservoir Combined sewer Water distribution Sewer system Retention tank CSO structure Infiltration Overflow Water purification WWTP Receiving water Ground water 9 Introduction to wastewater disposal

  4. Sewage retention Overflow structure Overflow Combined water storage The urban drainage system WWTP WWTP effluent Receiving water 9 Introduction to wastewater disposal

  5. The reality at overflow structures… 9 Introduction to wastewater disposal

  6. 9 Introduction to wastewater disposal 9.2 Goals of wastewater disposal 9 Introduction to wastewater disposal

  7. Goals of wastewater disposal Hygiene Hygienic disposal Flood protection No backwater effects in and from sewers Water protection Minimising of pollutants impact Minimising oxygen depletion Maintaining hygienic water quality 9 Introduction to wastewater disposal

  8. „Classical“ drainage approach Iit is the task of urban drainage to collect and remove all kinds of wastewater from housing areas completely and as quickly as possible, (…) without impacts on surface and sub-surface waters.“ „Wastewater includes sewage from domestic and industrial areas, rainwater, snow melt water, infiltration, effluent water from fountains, enclosed running waters (…), irrespective whether they are polluted or not.“ Hörler (1966) 9 Introduction to wastewater disposal

  9. Problem-oriented drainage „only these wastewaters should be collected and disposed which cannot be infiltrated in the catchment without impact on groundwater. Moreover, the runoff should be subject to retention and deceleration in order to decrease the runoff peaks.“ „Instead of purely technical approaches to solve the wastewater disposal problem, it is the aim to consider the entire water cycle in urban areas.“ VSA (1989) 9 Introduction to wastewater disposal

  10. 9 Introduction to wastewater disposal 9.3 Costs of sewers and wastewater treatment 9 Introduction to wastewater disposal

  11. Investment costs for the wastewater system 9 Introduction to wastewater disposal

  12. Annual costs Fixed costs • Depreciation • Payment of interest • Personnel • Energy • Operation means, e.g. chemicals • Repairs, spares • Sludge disposal • Administration Operation costs 9 Introduction to wastewater disposal

  13. Depreciation and operation costs 9 Introduction to wastewater disposal

  14. 9 Introduction to wastewater disposal 9.4 Interface between sewer and wastewater treatment plant 9 Introduction to wastewater disposal

  15. 400 Capacity of WWTP = 2 (85%) + Q Q Q m S,max f 300 WWTP capacity for stormwater Inflow rate (l/s) inflow 200 Dry-weather flow Q t Average inflow rate 100 Q Q s,m s Q f 0 0 4 8 12 16 20 24 Time (h) Capacity of WWTP 9 Introduction to wastewater disposal

  16. Capacity of WWTP Combined water inflow according to DWA A131 (2000) decisive Qsfor design One-hours peak dry-weather flow, which is matched or exceeded at 15% of days „hidden“ extra capacity • hourly flow rate below the daily peak value for 23 hours per day • hourly peak value at 85% of days below design inflow • Design for increasing wastewater flow in the future 9 Introduction to wastewater disposal

  17. Extraneous water flow Qf • Groundwater infiltration • Drainage • Small rivers • Water from fountains • Cooling water • Excess water from drinking water reservoirs  Extraneous water flow is variable Rough estimate, if no data available 9 Introduction to wastewater disposal

  18. 70 7 60 6 NH -Load 4 50 5 COD-Load 40 4 -Load (kg/h) COD-Load (kg/h) 30 3 4 COD NH Daily mean load and 20 2 4 NH 10 1 0 0 00:00 04:00 08:00 12:00 16:00 20:00 00:00 Time (hh:mm) Sewage flow: diurnal loads variation 9 Introduction to wastewater disposal

  19. 9 Introduction to wastewater disposal 9.5 The receiving water as a goal system 9 Introduction to wastewater disposal

  20. Approach of Water Framework Directive „Immission“ Emission 9 Introduction to wastewater disposal

  21. Hydrology of receiving water Flow rate • Important with regard to dilution of wastewater input •  Mean flow rate •  Variations, minimum and maximum Rain-runoff process • Response time • Quicker runoff process and CSO than flow increase in river 9 Introduction to wastewater disposal

  22. 0,8 0,7 River 0,6 /s) 3 0,5 0,4 Flow rate (m 0,3 CSO 0,2 0,1 0,0 0 1 2 3 4 5 6 Time (h) Response time of CSO and river Critical phase 9 Introduction to wastewater disposal

  23. Impervious area bATV = Area of hydrologic catchment Impact to rivers by CSOs: hydraulic effects Changed hydrology • Frequency of high flow rates • Flow rate Gradients are steeper due to intense CSO events River bed erosion • Potentially more frequent • Local erosion • Effects on biocenosis  Intense events are decisive 9 Introduction to wastewater disposal

  24. Development of flies (Gammeter, 1995) LF town area LP natural, upstream 9 Introduction to wastewater disposal

  25. Event Concentration Load weak high small medium medium high intense low high Number of inhabitants aATV = Low-flow discharge Impacts to rivers by CSOs: polluting effects Particulate matter • Accumulation on catchments surface and in sewer • First flush = f (dry-weather period, runoff rate) Dissolved matter originating from sewage 9 Introduction to wastewater disposal

  26. Time scale Effect Indicator acute hydraulic Flow rate, sher rate, erosion (hours) chemical Toxic substances (NH3) in water physical Suspended matter, turbidity bio-chemical Oxygen depletion in water hygienic Bacteria, viruses aesthetic Smell, floatables delayed chemical toxic Substances (NH3, NO2) in river bed (days) bio-chemical Oxygen depletion in sediment hygienic Bacteria, viruses in sediment aesthetic Floatables, oil, grease accumulative hydrologic Flow regime, morphology (weeks, chemical Heavy metals, org. Subs. in sediment years) bio-chemical Oxygen depletion (eutrophication) Effects in rivers (Schilling et al., 1997) 9 Introduction to wastewater disposal

  27. Ecological river quality Morphology • Layout • Shading • Erosion frequency • Flow shadow Hydrology • Flow regime • Rain-runoff characteristics Physics • Temperature and temperature variations • Conductivity Chemistry • NH4+, NH3 , Nutrients • Heavy metals Biology • Species variety • Species numbers 9 Introduction to wastewater disposal

  28. River water quality in Saxony (Source: LfUG (1998)) 9 Introduction to wastewater disposal

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