1. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 1 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 Technische Universität Dresden Department of Hydro Sciences, Institute for Urban Water Management Peter Krebs Urban Water Systems

2. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 2 9.1 Overview of wastewater system 9 Introduction to wastewater disposal

3. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 3 Urban region Rain-runoff process Sewage retention tank Water distribution Reservoir Sewer system Combined sewer Retention tank CSO structure Water purification WWTP Receiving water Ground water Urban water system Infiltration Overflow Retention Sedimentation Sludge disposal In-/Exfiltration Clean water inflow Treatment

4. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 4 The urban drainage system Overflow structure Receiving water Overflow Combined water storage WWTP WWTP effluent Sewage retention

5. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 5 The reality at overflow structures…

6. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 6 9.2 Goals of wastewater disposal 9 Introduction to wastewater disposal

7. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 7 Goals of wastewater disposal Hygiene Flood protection Water protection Hygienic disposal No backwater effects in and from sewers Minimising of pollutants impact Minimising oxygen depletion Maintaining hygienic water quality

8. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 8 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) „Classical“ drainage approach

9. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 9 „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) Problem-oriented drainage

10. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 10 9.3 Costs of sewers and wastewater treatment 9 Introduction to wastewater disposal

11. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 11 Connected inhabitants5000 inh50‘000 inh200‘000 inh Population density50 inh/ha100 inh/ha200 inh/ha SewerLength per person(m/inh)74.53 Costs per m(EUR/m)400500600 Costs per inh(EUR/inh)260022501800 StorageVolume / inh(m 3 /inh)0.20.150.13 tanksCosts / inh(EUR/inh)200150135 WWTPsIndustry add-on(PE)250025000100000  (inh+PE) (PE)750075000300000 costs / PE tot (EUR/PE)450340250 costs / inh(EUR/inh)675510375 Investment costs for the wastewater system

12. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 12 Annual costs Fixed costs Operation costs Depreciation Payment of interest Personnel Energy Operation means, e.g. chemicals Repairs, spares Sludge disposal Administration

13. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 13 Depreciation and operation costs Connected inhabitants5‘000 inh50‘000 inh200‘000 inh EUR / (inh · a) DepreciationSewer system (2%/a)1059072 Storage tanks (3%/a)13109 WWTP (5%/a)625038 Total180150119 OperationSewer system30159 Storage tanks433 WWTP382014 Total723826

14. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 14 9.4 Interface between sewer and wastewater treatment plant 9 Introduction to wastewater disposal

15. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 15 Capacity of WWTP

16. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 16 Capacity of WWTP Combined water inflow according to DWA A131 (2000) decisive Q s for 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

17. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 17 Extraneous water flow Q f 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

18. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 18 Sewage flow: diurnal loads variation

19. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 19 9.5 The receiving water as a goal system 9 Introduction to wastewater disposal

20. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 20 Emission „Immission“ Approach of Water Framework Directive

21. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 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

22. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 22 Response time of CSO and river Critical phase

23. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 23 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 b ATV = Impervious area Area of hydrologic catchment

24. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 24 Development of flies (Gammeter, 1995) LF town area LP natural, upstream

25. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 25 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 Event Concentration Load weak high small medium medium high intense low high a ATV = Number of inhabitants Low-flow discharge

26. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 26 Oxygen depletion (eutrophication)bio-chemical Heavy metals, org. Subs. in sedimentchemical Flow regime, morphologyhydrologic Floatables, oil, greaseaesthetic Bacteria, viruses in sedimenthygienic Oxygen depletion in sedimentbio-chemical toxic Substances (NH 3, NO 2 ) in river bedchemical Smell, floatablesaesthetic Bacteria, viruseshygienic Oxygen depletion in waterbio-chemical Suspended matter, turbidityphysical Toxic substances (NH 3 ) in waterchemical Flow rate, sher rate, erosionhydraulic IndicatorEffect years) (weeks, accumulative (days) delayed (hours) acute Time scale Effects in rivers (Schilling et al., 1997)

27. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 27 Ecological river quality Morphology Layout Shading Erosion frequency Flow shadow Hydrology Flow regime Rain-runoff characteristics Physics Temperature and temperature variations Conductivity Chemistry NH 4 +, NH 3, Nutrients Heavy metals Biology Species variety Species numbers

28. Urban water systems9 Introduction to wastewater disposal© PK, 2005 – page 28 River water quality in Saxony (Source: LfUG (1998))