The Hydrodynamic Characteristics of the Vamvakofito Stabilization Ponds System

Transcription

1 The Hydrodynamic Characteristics of the Vamvakofito Stabilization Ponds System Maria Gratziou, Kyriakos Kopasakis, Maria Chalatsi Laboratory of A Hydraulics Department of Civil Engineering Democritus University of Thrace

2 Waste Stabilization Ponds (WSPs) Hydrodynamic characteristics of a WSP system (temperature in the water column, flow velocity, HRT, geometry): important factors in the systems efficiency, in pollutants removing and in the sludge accumulation and distribution at the bottom of the s Treatment efficiency often hydraulically compromised, according to prior researchers The majority of hydraulic studies on WSPs performed on full-scale field s, with transient flows and large surface areas exposed to wind and temperature variations A number of numerical models reported in the literature, helping to quantify and elucidate WSPs performance Important to validate the hydraulic design of the WSPs either through pilot-scale experimental tracer tests or numerical modeling

3 Greece Small number of researches Insufficient information Only a few WSPs in Greece Just 8% of all Urban Wastewater Treatment Plants in the country 90% of them situated in North Greece Objectives of the study Investigation of the hydrodynamic characteristics of a WSP system situated in Vamvakofito (North Greece), by simulation with the 3D hydrodynamic model ELCOM Examined hydrodynamic characteristics: temperature HRT flow speed ELCOM (Estuary and Lake Computer Model) Designed for practical numerical simulation of hydro- dynamics and thermodynamics for lakes and reservoirs Mainly used to predict the variation of water temperature and salinity in space and time

4 Layout of Vamvakofito WSP system as it was constructed Lowland area, in the mainland of northern Greece with latitude φ: 41º N longitude λ: 23º E altitude from 30 m, in a Mediterranean climate One facultative (62 x 39.5 m) and two maturation s (61.5 x 29 m each one) in series Treatment only of domestic wastewater Total Hydraulic Retention Time (HRT) 68.7 d Length aligned on a east west axis

5 Vamvakofito facultative maturation maturation

6 DESCRIPTION OF THE NUMERICAL MODEL ELCOM Governing Hydrodynamic Equations Continuity Equation Momentum Equation in -x, -y and -z direction Equation of State

7 DESCRIPTION OF THE NUMERICAL MODEL ELCOM Governing Hydrodynamic Equations Continuity Equation Momentum Equation in -x, -y and -z direction Equation of State

8 DESCRIPTION OF THE NUMERICAL MODEL ELCOM Basic assumptions Incompressive fluids Ignoring the non-hydrostatic terms Boussinesq Assumption

9 Water temperature(ºc) Bathymetry file ELCOM Model Inputs Boundary condition file Meteorological data file Inflow point Outflow point Data input file Τιμές Πεδίου Time (days)

10 ELCOM MODEL SET UP Horizontal Discretization: 1x1 m 2. Vertical Discretization: 15 horizontal layers 0.2m layer depth. Maximum Depth: 2.5 m. Time Step: 6O sec. Maximum simulation time: 7 months ( March 30 th September 2005).

11 Wastewater Temperature field ( C) Wastewater temperature ( C) Calibration of ELCOM for Vamvakofito WSP system Observed values Model Values Comparison of the hydrodynamic characteristics of the s water column, concerning the water s temperature, with the corresing field values (March September 2005) Very satisfactory calibration Time (days) Calculation of the determination coefficient r 2, concerning water temperature s profile r 2 = 0,9887 Satisfactory reproduction of the field values Wastewater column R² = 0, Wastewater Temperature produced by ELCOM simulation ( C)

12 Distance Distance Wastewater Temperature ( C) Temperature of the s water column at Vamvakofito WSP system The temperature of the water column of the affected by the colder water entering from the point of inflow Temperature of incoming water masses < those kept at the s for a long time Inlet point temperature Ponds temperature Hotter wastewater column during summer months Smaller effect of solar radiation to the water column s temperature of the facultative, than the maturation s, from 1 to 2 ºC, due to their smaller depth Drop of the water column s temperature during the night Highest water column s temperature during the afternoon Time (date) Distance Surface layer , 00:00 Distance Surface layer , 18:00 Points of temperature control

13 Depth (m) Depth (m) Depth (m) Depth (m) Depth (m) Profile of wastewater temperature variation in May 2005 at Vamvakofito WSP Temperature (ºC) Temperature (ºC) Temperature (ºC) Date Point Κ1 Date Point Κ2 Date Point Κ3 Temperature (ºC) Temperature (ºC) Effect of strong sunlight and hot winds in the temperature of s water column during 17, 18 and 19 May Lower temperature in facultative rather than in maturation s (~ 2 ºC) No temperature variations in the different s depths, no risk of stratification Date Point Κ4 Date Point Κ5

14 Distance (m) Distance (m) Distance (m) Distance (m) Distance (m) Distance (m) Distance (m) Evolution of Tracer 1 from March to September 2005 in the surface layer of Vamvakofito WSPs Distance (m) Distance (m) Distance (m) Distance (m) March 2005 April 2005 May 2005 June 2005 Six months required for Tracer 1 to obtain the maximum value of the surface level and throughout the water column of the s Distance (m) Distance (m) Distance (m) July 2005 August 2005 September 2005

15 Wastewater retention time in Vamvakofito WSP system Scenario of clean s (as they were constructed) HRT in the (facultative): HRT in the (maturation): HRT in the (maturation): 63 d 75 d 85 d 12 days 10 days Total HRT coincides with the actual calculated HRT Scenario of s with accumulated sludge (current situation) HRT in the (facultative): HRT in the (maturation): HRT in the (maturation): 50 d 60 d 69 d 10 days 9 days Total HRT coincides with the actual calculated HRT

16 scenario- Bathymetry scenario- Bathymetry

17 The magnitude and the direction of WSPs instantaneous flow velocities April 2005: (a) Surface layer June 2005: (a) Surface layer August 2005: (a) Surface layer April 2005: (b) Bottoming layer 0,01 0,125 m/sec June 2005: (b) Bottoming layer 0,01 0,03 m/sec August 2005: (b) Bottoming layer 0,01 0,06 m/sec No significant differences in the magnitude of the velocity between surface and bottoming layer or between the s Slightly larger velocities at the bottom than at the surface layer in April, mainly at the walls of the maturation Low velocities in June, both on the surface and the bottom s layer No significant differences at flow velocities between surface and bottoming layer in August

18 Very satisfactory calibration of the model CONCLUSIONS Satisfactorily reproducing the values of the field measurements (r 2 = 0,9887) The temperature of the water mass entering the WSP lower than that of the water mass staying longer into the Temperature variation up to 7 C, during hot summer period Water column s temperature at the facultative affected by the colder water volumes that enter the Smaller effect of solar radiation to the water column s temperature at the facultative than at the maturation s, by 1 to 2 C Higher water column temperatures during afternoon hours at all the s Same temperature at the s water column avoidance of danger of stratification at the s different depths Calculated HRTs by ELCOM in accordance with the real wastewater s HRTs into the s The route and the dynamics of a conservative pathetic pollutant which enters the system and then shed or diffused to the interior of the s requires 6 months until the pollutant gets its maximum value at the surface layer and at all the water column of the system s s (partly explains the instability at heavy metals and some other trace element s removal) No significant differences of velocity measures between surface bottom layer, neither among the s Flow velocities range 0,01 to 0,125 m/sec

19 Thank you you for for your your attention attention