waste stabilization ponds

waste stabilization ponds-facultative pond

1. Waste Stabilization Ponds By- EARNEST F GLOYNA From- VINOD KUMAR SAKET & NAGENDRA KUMAR JILAGAM To – Dr. Sandip Mondal

2. DEFINITIONS: A pond designed to treat waste water biologically. ANAEROBIC PONDS FACULTATIVE PONDS : pond with upper aerobic and lower anaerobic conditions. PRIMARY FACULTATIVE : untreated waste water SECONDARY FACULTATIVE : pretreated waste water MATURATION PONDS

3. MODES OF OPERATION OF WASTE STABILIZAATION PONDS If BOD removal is major consideration combination of anaerobic and facultative ponds are used. If pathogen removal is major consideration facultative and maturation ponds are used. TEMPERATURE AND DETENTION TIME ARE ESSENTIAL PARAMETERS THAT CONTROL BIOLOGICAL PROCESS

4. MODES OF DECOMPOSITION AEROBIC PROCESS: AEROBIC OXIDATION In aerobic process, much of the cellular carbon serves as energy and respired as CO 2 To decrease organic content in dilute liquid waste aerobic oxidation is more efficient. ( CHO ) X + OXYGEN = CO 2 + H 2 O Oxygen must be supplied to waste stabilization ponds by Algal photosynthesis or by air water interface or by oxygen containing Compounds such as nitrates phosphates and sulphates

5. MODES OF DECOMPOSITION ANAEROBIC PROCESS : ANAEROBIC REDUCTION Putrefactive breakdown of organic compounds by anaerobic fermentation. For highly concentrated wastes or in case of settled solids anaerobic process is efficient. This is a two step process. Facultative heterotrophs degrade organic matter into fatty acids, aldehydes, alcohols etc. (CHO) x = CH 3 COOH Then these intermediate products are converted into methane, co2, ammonia. CH 3 COOH = CH 4 + CO 2 . THIS CO 2 IS UTILISED BY ALGAE AND PRODUCE OXYGEN NEEDED FOR AEROBIC PROCESS.

6. BACTERIAL DECOMPOSTION CHONP + O 2 = CO 2 + H 2 O + NO 3 + PO 4 Autotrophic organisms produce organic material from inorganic compounds. CO 2 + H 2 O + NO 3 + PO 4 + LIGHT = C X H Y O N A P B + O 2 (algal reaction).

7. BIOLOGICAL REACTIONS Oxidation of organic matter by aerobic bacteria Nitrification of protein by aerobic bacteria Reduction of organic matter by anaerobic bacteria Oxygenation of surface liquid by algae.

8. FACULTATIVE WASTE STABILIZATION POND

9. KINETICS OF POND BREAKDOWN If influent BOD is stabilized and complete mixing occurs, the breakdown occurs in first order reaction S = S O /(1+K.DT) Breakdown rate depend on temperature K 35 / K = 0 35-T = DT/ DT 35 0 = temperature reaction coefficient = 1.085 Removal efficiency = (S O - S)/S O

10. SLUDGE LAYER Rate of gas evolved is a measure of biological activity of bottom layer of facultative pond. K S = 0.002 (1.35) T-20 During early life of primary facultative pond, BOD removed is by settled organics solids then anaerobic fermentation takes place releasing organic material again into aerobic zone. During winter, sludge digestion rate or rate of gas evolved is reduced causing sludge accumulation During summer, sludge reduction takes place. As the digestion rate increases, more fermented organic material gets resuspended into aerobic zone. If this re-suspension rate exceeds reoxygenation rate ponds behaves as anaerobic pond.

11. Design Methods The actual design of a facultative pond depends on a great variety of local conditions, but a number of useful and rational design procedures are available. Four such procedures are described in this section - Load per unit area. Empirical procedure. South African practice. Suggestions made by the Indian Central Public Health Engineering Research Institute ( CPHERI ).

12. Load per unit area Experience has shown that certain generalizations can be made concerning the acceptable organic load of a facultative waste stabilization pond. Unpleasant odors may occur as a result of extremes in seasonal temperatures, inadequate surface area, uneven distribution of settleable solids, or inadequate liquid depth The distribution of settleable solids can be improved. through the use of multiple inlets and deeper ponds (1.5-2 m). Maintenance of liquid depth depends principally on the control of seepage and evaporation. Understandably the operation of the entire pond system is dependent on the volumetric loading, BOD loading per unit area, and the concentration of organic matter in the wastewater. ( Where the water content is low it may be difficult to maintain sufficient liquid over the settled solids.) In this case, water must be added or the pond should be designed to function without any overflow.

13. Above table shows BOD loading values that have been used successfully in various geographical areas, but obviously great care must be exercised in using these values for design purposes.

14. Empirical procedure After observing the results of many small laboratory ponds, larger pilot plants, and over 200 operating ponds, the author of this monograph and his collaborators have developed formulations that can be used to relate pond volume to temperature, BOD, influent volume and toxicity. The first of these equations, in which the estimated BOD removal efficiency is 85-95 %, was published by Hermann & Gloyna (1958)

15. With the help of above figure the required volume of a facultative pond can be estimated.

16. A loading factor (L.F.) is computed by multiplying the number of persons contributing waste (N) by the product of the per caput contribution in litres per day (q) and the BOD (La). A reasonably accurate design can be developed from this graph. When the required volume has been estimated in accordance with Equation of pond volume, the depth is selected with the aid of table given below.

17. A specimen calculations of pond design using the Gloyna procedure are shown below. Alternative solutions are provided to show the influence of temperature.

18. South African procedure C riteria for the design of facultative ponds in southern and central Africa, Marais & Shaw (1961) noted that: With low wastewater flow and a large surface area per caput , the pond did not attain the required liquid depth on account of losses through seepage and evaporation; The effluent BOD remained substantially constant irrespective of the seasonal variations in temperature. BOD loadings per unit area could be increased above those frequently reported in the literature. Anaerobic conditions developed in the summer, while during the winter the ponds appeared to operate satisfactorily.

19. In this method the maximum BOD load for a facultative pond is related to the depth: Marais & Shaw later reduced the dividend in this equation from 1000 to 750. On the basis of a study of the long-term behavior of the ponds, Shaw, Meiring & van Eck (1962) reduced this value still further to 600, so that above equation is now written as follows:

20. A specimen calculation of facultative pond design using the South African procedure is given below.

21. If these results are compared with those obtained by the empirical procedure; It can be seen that there is considerable uniformity. In both cases, the settleable solids must never be exposed to the air and sunshine. There must be adequate liquid present to fill the ponds and ensure satisfactory operation, otherwise alternative pretreatment is required.

22. Procedure based on suggestions by the Central Public Health Engineering Research Institute ( CPHERI ), India In tropical India, the design of facultative waste stabilization ponds for domestic waste-waters has been based on a loading of 336 kg BOD 5 /ha per day and an operating depth of 1.22 m (Dave & Jain, 1967). A study of 8 ponds has shown a BOD reduction for this loading of 70-85 %. To increase the BOD removal to 90% usually requires a significant increase in detention time. Indian practice suggests that it is desirable to have 2 ponds wherever possible to facilitate servicing, cleaning, etc.

23. QUERIES 1. Anaerobic fermentation and respiration. 2. Is mixing necessary? Because if there is no mixing then only DO concentration gradient occurs which helps in maintaining anaerobic conditions at bottom. 3. In order to maintain maximum BOD value, it is important use proper dilution to ensure that any toxic effect is removed and that no all DO is used. When increasing dilutions show increase in BOD values, the dilution should be increased until BOD levels off at its maximum.

24. Thank You…