STABILIZATION PONDS Eng. Dr. Erich Kellner November, 7 th – 2012 São Carlos - Brazil

1. STABILIZATION PONDSEng. Dr. Erich KellnerNovember, 7th – 2012São Carlos - Brazil Summer School on Wastewater Treatment Plants and Management Lector of Civil Engeneering Department of São Carlos Federal University (UFSCar)

2. Stabilization ponds: Figure 1: Stabilization ponds – Lins (SP) - Brazil Stabilization ponds are biological treatment systems in which stabilization of organic material is carried out by bacterial oxidation and/or photosynthetic reduction of algae.

3. Basic Configurations of Wastewater Treatment Systems by Stabilization Ponds: Figure 2: Configurations of wastewater treatment systems by stabilizations ponds Source: adapted from von Sperling (2000)

4. Pros and Cons of using stabilization ponds: PROS CONS • Need large areas; • Limited and dependent on weather; • Quality of effluent varies; • Simplicity to built, operate and maintain; • Low operational cost; • Good quality on effluent;

5. Anaerobic Ponds: • Basins of 3m to 5m (10 feet to 17 feet) depth receiving continuous organic load of wastewater so that anaerobic conditions are met. • Sedimentation pond. • High waste water loading – depletes all O2. • Solids settle at bottom of the to pond. • Anaerobic digestion of sludge occurs at the bottom of the pond. Figure 3: Anaerobic Pond– São Carlos (SP) - Brazil

6. Anaerobic Ponds: Hydrolysis - Complex organics (proteins and fats broken down to simpler compounds by various bacteria Acidogenesis (Fermentation) – Fatty acids and alcohols oxidized ,amino acids and carbohydrates fermented, produce volatile fatty acids and hydrogen Acetogenesis – conversion of complex fatty acids to acetic acid Methanogenesis - conversion of acetic acid to methane and CO2 and CO2 ,H2 to methane Figure 4: Metabolic process in anaerobic digestion Source: adapted from Pescod (1995)

7. Anaerobic Ponds - Design Criteria: Design is highly empirical – based on volumetric load (g BOD/m3/day) and Hydraulic Detention Time (day) • Time of Hydraulic Detention (q) = between 4 to 6 days for the final plan • Liquid depth = between 4 to 5m • Volumetric organic load (lv) = 0.08 and 0.4 kgDBO/m3pond.day • Superficial organic load(ls) > 1000 kgDBO/ha.day • Sludge accumulation = 0.01 to 0.03 m3/inhab.year

8. Anaerobic Ponds - Design Criteria: Table: Expected efficiency to reduce DBO due to average air temperature in the coldest month

9. Facultative Ponds: • Basins of 1.5m to 2m depth. • To have clear water, light penetration and photosynthetic production of oxygen to decompose organic material take place easier • Part of the solids present in the wastewater settle and are biodegradable in an anaerobic process Figure 5: Facultative ponds – Barretos (SP) - Brazil

10. Facultative Ponds:

11. Facultative Pond Interactions: Figure 6: Definition of interactions occurring in a facultative pond Source: Tchobanoglous and Schroeder (1985)

12. Facultative Ponds - Design Criteria: • PRIMARY FACULTATIVE PONDS: • Superficial application rate limit* (lS) = 20.T – 60 kgDBO/ha.day** • Expected efficiency to reduce DBO (Empirical equation based on complete mixture model)*: let e be the efficiency (%); ls superficial application rate (kgDBO/ha.day) • Notes: • Refers to half depth in the area • Average air temperature in the coldest month (oC).

13. Facultative Ponds - Design Criteria: • SECONDARY FACULTATIVE POND: • 14.T – 40 < 200 kgDBO/ha.day** p/T >17oC • Superficial application rate limit* (lS) = • 350. (1,107-0,002.T)T-25kgDBO/ha.day** p/T <17oC • Expected efficiency to reduce DBO (Empirical equation based on complete mixture model)*: let e be the efficiency(%); ls superficial application rate (kgDBO/ha.day) Notes: * Refers to half depth in the area. ** Average air temperature in the coldest month (oC).

14. Maturation Ponds: • Basins of between 0.8m and 1.5m depth. Normally, 1.0 m depth is used. • The main objective of maturation ponds is to remove pathogenic microrganisms present in the wastewater, which occur mainly due to sunlight in the water column. Figure 7: Maturation ponds – Barretos (SP) - Brazil

15. Maturation Ponds - Design Criteria: • Superficial organic load (ls) < 50 kgDBO/ha.day • HDT for each pond (qm) > 7 days, with at least 3 maturation ponds in sequence. • Decrease of pathogenic microrganisms: Continuously Stirred Tank Reactor (CSTR)

16. But what kind of reactor do we have here?

17. Hydrodynamic Test: FP2 FP1 AP Figure 8: Stabilization Ponds in Novo Horizonte (SP) Source: Moreira (2006) Figure 9: Rodamina B injection in FP1 Source: Moreira (2006)

18. Hydrodynamic Test: Figure 10: Non-dimensional concentration curve of Rodamina B in function of measured time in FP1 exit Source: Kellner, Moreira & Pires (2009). • Theoretical hydraulic Detention Time teórico was 164 hours. • Real hydraulic Detention Time resulted in 55 hours, with dispersion number(d) equal to 11.034.853.603 !!!. • Active volume of 33.6% (3.5h) and recuperation of dye mass of 95.6%. • Source: (Kellner, Moreira & Pires, 2009).

19. Influence of Thermal Stratification in the Distribution of Rodamina B in the Water Column of FP1 Temperature (oC) Depth (m) Concentration (mg/l) [Animation done from results presented by Kellner, Moreira & Pires (2009).]

20. Thermal Stratification of a stabilization pond affects… …the useful volume, …the dispersion number, …the HDT, etc. According to Kellner & Pires (2000), temperature gradient 0.6oC/m, in stabilization ponds with temperature of 25oC, can lead to a thermal stratification state.

21. Design and Operational Problems: Figure 11: Facultative Pond built in shaded area

22. Design and Operational Problems: Figure 12: Infiltration problem in anaerobic pond

23. Design and Operational problems: • Facultative Pond with red brown colour • Possible causes: • Organic material overload • Presence of photosynthetic bacteria that oxidates sulphyte and does not produce oxygen does not contribute to reducing BOD

24. Design and Operational Problems: • Facultative Pond withmilky green colour • Possible causes: • The pond is in an autofloculation process due to increase in pH and temperature • Precipitation of hydroxide magnesium or calcium dragging algae and other microrganisms with it

25. Design and Operational Problems: • Facultative Pond with yellow green colour • Possible causes: • Growth of rotifers, protozoas or crustaceans which feed on algae; • There could be a significant decrease in the DO and possibly a bad odor from the anaerobic decomposition of OM.

26. Design and Operational Problems: • Facultative Pond with green blue colour • Possible causes: • Significant growth of cianobacteria; • Appearance of native certain species which decompose easily, causing bad odors, reducing the penetration of sunlight and diminishing oxygen production.

27. Design and operational problems: • Facultative pond with grey colour • Possible causes: • Overload of organic material and/or short detention time • Fermentation in sludge layer incomplete.

28. Design and operational problems:: Absence of Grit Removal System Not having desanders can cause silting in the ponds

29. Design and operational problems:: Absence of Grit Removal System …is able to change the flow and wastewater in the ponds

30. Anaerobic pond – Problems of bad odor Free surface makesexchange of gases easier (CH4, H2S,…) for the atmosphere

31. Anaerobicpond - Problems with bad odor (possibility of using methane)

32. Sludge:

33. Sludge conditioning (Solution or Environmental passivity?) Sludge conditioning in materia lsacks can make it passive. Figure: Sludge conditioning

34. Thank You! E-mail: erich.kellner@ufscar.br