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Irene Seco Manuel Gómez Alma Schellart Simon Tait

7th International Conference on Sewer Processes & Networks Wednesday 28 - Friday 30 August 2013 The Edge Conference Centre, Sheffield. Erosion resistance and behaviour of highly organic in-sewer sediment. Irene Seco Manuel Gómez Alma Schellart Simon Tait.

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Irene Seco Manuel Gómez Alma Schellart Simon Tait

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  1. 7th International Conference on Sewer Processes & Networks Wednesday 28 - Friday 30 August 2013 The Edge Conference Centre, Sheffield Erosion resistance and behaviour of highly organic in-sewer sediment Irene Seco Manuel Gómez Alma Schellart Simon Tait

  2. Wet weather pollution from combined sewer systems Releaseof in-sewer sediment deposits accumulated during dry-weather constitute a major source of pollutants that affect the water quality of receiving natural water bodies

  3. Wet weather pollution from combined sewer systems Particularities in the Mediterranean region in Spain: Long dry-weather periods Intense precipitation events Rain regime cumulative precipitation = 600 mm/year (concentrater 50 days/year) average dry-period between rain: 11 days ≈ 40% rainfall registered P(mm)>10mm

  4. Wet weather pollution from combined sewer systems Particularities in the Mediterranean region in Spain: Long dry-weather periods Intense precipitation events Rain regime In-sewer sediment accummulation and consolidation

  5. Wet weather pollution from combined sewer systems Particularities in the Mediterranean region in Spain: Low circulating flow (0.56 m3/s average Congost River. Vallès Oriental. Catalonia. Spain) Long dry-weather periods Intense precipitationevents Flow regime in rivers Rain regime Low dilution capacity

  6. Wet weather pollution from combined sewer systems Particularities in the Mediterranean region in Spain: Low circulating flow Low dilution capacity Long dry-weather periods Intense precipitationevents High percentage of impervious surface in Urban areas Flow regimein rivers Rain regime Urban pattern

  7. Wet weather pollution from combined sewer systems Particularities in the Mediterranean region in Spain: Low circulating flow Low dilution capacity Long dry-weather periods Intense precipitationevents High percentage of impervious surface in Urban areas Flow regimein rivers Rain regime Urban pattern Sewer solids mainly from wastewaters Relevant Organic composition

  8. Wet weather pollution from combined sewer systems Particularities in the Mediterranean region in Spain: Low circulating flow Low dilution capacity Long dry-weather periods Intense precipitationevents High percentage of impervious surface in Urban areas Flow regime in rivers Rain regime Urban pattern Significant volumes discharged in a short time from sewer network (CSO) Significant organic Pollutionin natural streams and sea Overflows during wet-weather

  9. Objectives of this study Particular conditions of Build-up/Wash-off affects the initiation of sediment motion

  10. Objectives of this study Particular conditions of Build-up/Wash-off affects the initiation of sediment motion Investigate erosion behaviour of real in-sewer organic-rich sediment collected in Spain • Analyse changes in transport potential for different lengths of antecedent dry-weather periods • Consider potential incidence of the environmental conditions in-sewer on the transport loads and initiation of motion

  11. Improve prediction of in-sewer sediment transport loads Objectives of this study • Long dry-weather • period/Build-up • Intense rainfall/Wash-off Suitable to be applied to the particular Mediterranean climate and urban pattern conditions

  12. Real in sewer sediment characteristics Sediment collected from a sewer system (residential and commercial area in Catalonia, Spain)

  13. Real in sewer sediment characteristics Sediment collected from a sewer system (residential and commercial area in Catalonia, Spain) relevant Organic content (O.M. around 80%) organic nature of solid particles from domestic wastewaters, and the presence of greases Cohesive properties

  14. Real in sewer sediment characteristics Sediment collected from a sewer system (residential and commercial area in Catalonia, Spain) relevantOrganic content (O.M. around 80%) Related with the organic nature of solid particles from domestic wastewaters, and the presence of greases Cohesive properties d50 = 0.31 mm (310 µm) Density = 1310 kg/m3

  15. Sediment with high organic content and cohesive properties Real in sewer sediment characteristics Consolidation, microbiological degradation, chemical-biological interactions (bonding forces between particles ) Effects on the transportof solids significant influence on the incipient motion

  16. Laboratory erosion measurement Evaluation Erosion Rate Assessment critical threshold of motion at solid-fluid interface Erosion meter devised (based on a design by Liem et al. 1997). Liem et al. (1997) investigation on erosional proecess of cohesive sediment using an in-situ measuring device. International Journal of Sediment Research, 12 (3), 139-147

  17. Laboratory erosion measurement A prepared sample is exposed to a consolidation period and subsequently subject to increased shear stress, to simulate increased flows through sewer pipes at the start of a storm event. • Simulation of dry-weather periods • Different lengths: 16, 64, 140 hours • Environmental conditions: • Anaerobic and Aerobic • Constant low shear stress: • 0.15 N/m2 (dry-weather flows inside conduits) Consolidation period Erosion phase Sampling and Analysis

  18. Laboratory erosion measurement A prepared sample is exposed to a consolidation period and subsequently subject to increased shear stress, to simulate increased flows through sewer pipes at the start of a storm event. • Simulation of dry-weather periods • Different lengths: 16, 64, 140 hours • Environmental conditions: • Anaerobic and Aerobic • Constant low shear stress: • 0.15 N/m2 (dry-weather flows inside conduits) Simulation flows at start of storm event Increasing shear stress is applied in a stepwise way Consolidation period Erosion phase Sampling and Analysis

  19. Laboratory erosion measurement A prepared sample is exposed to a consolidation period and subsequently subject to increased shear stress, to simulate increased flows through sewer pipes at the start of a storm event. • Simulation of dry-weather periods • Different lengths: 16, 64, 140 hours • Environmental conditions: • Anaerobic and Aerobic • Constant low shear stress: • 0.15 N/m2 (dry-weather flows inside conduits) Simulation flows at start of storm event Increasing shear stress is applied in a stepwise way Sediment samples collected during erosion tests at each shear stress interval Remaining sediment after tests collected Consolidation period Erosion phase Sampling and Analysis

  20. Erosion rate of sediments monitored in terms of Suspended Sediment concentration Main Results Average erosion rate (q) linked to the applied shear stress (tb) Anaerobic T1 16h T2 64h T3 140h Aerobic T4 16h T5 64h

  21. Main Results Erosion Rate values Comparison between tests with increasing length of periods of consolidation. 16h (T1) 64h (T2) 16h (T4) 140h (T3) 64h (T5) Anaerobic Aerobic

  22. Main Results Erosion Rate values Comparison between tests with increasing length of periods of consolidation. 16h (T1) 64h (T2) 16h (T4) 140h (T3) 64h (T5) Anaerobic Aerobic drop in overall values of Erosion Rates as length dry-periodincrease

  23. Main Results Tests with the same consolidation period and different environmental ambience. (T1) Anaerobic (T2) Anaerobic (T4) Aerobic (T5) Aerobic 16h consolidation period 64h consolidation period

  24. Main Results Tests with the same consolidation period and different environmental ambience. (T1) Anaerobic (T2) Anaerobic (T4) Aerobic (T5) Aerobic 16h consolidation period 64h consolidation period

  25. Conclusions Laboratory tests to estimate erosional resistance from highly organic sediment beds under storm runoff conditions Improvements in prediction of in-sewer sediment transport loads (Mediterranean conditions)

  26. Conclusions Environmental conditions influence over sediment-bed nature and structure

  27. Conclusions Environmental conditions influence over sediment-bed nature and structure Increment of resistance against erosion (as consolidation dry-period lengthen and oxygen is available) Increase of erosional strength with depth

  28. Conclusions Environmental conditions influence over sediment-bed nature and structure Increment of resistance against erosion (as consolidation dry-period lengthen and oxygen is available) Increase of erosional strength with depth comparing with results obtained with low-organic sediment and synthetic sediment (differences in sediment properties) Lesser magnitudes of Critical Shear Stresses

  29. Conclusions • Future investigations aimed to: • asses critical shear stress in highly organic sediment beds • analyse influence of temperature in dry-period

  30. Concerned about pollution control Thank you for your attention

  31. Wet weather pollution from combined sewer systems Particularities in the Mediterranean region climate in Spain: Long dry-weather periods Intense precipitaction events Rain regime day-precipitation = 4 day/month cumulative precipitation = 600 mm/year (concentrater in spring and fall) average dry-period between rain: 11 days Max. dry-period: 70 days (2010-2012) Intense precipitation events following long dry-periods ≈ 40% rainfall registered P(mm)>10mm

  32. Erosion of sediments from bed during tests were monitored in terms of Suspended Sediment concentration and related with Erosion Rate Main results • q: average Erosion Rate in a applied Shear Stress • step (tb) linked to Suspended Sediment • Concentration (CSS) • V : water volume of the column over • sediment sample • AS : surface area bed subjected to erosion

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