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

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

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

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

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

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

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

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

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

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

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) Costs per inh(EUR/inh) StorageVolume / inh(m 3 /inh) tanksCosts / inh(EUR/inh) WWTPsIndustry add-on(PE)  (inh+PE) (PE) costs / PE tot (EUR/PE) costs / inh(EUR/inh) Investment costs for the wastewater system

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

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) Storage tanks (3%/a)13109 WWTP (5%/a) Total OperationSewer system30159 Storage tanks433 WWTP Total723826

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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