E ect of step geometry and water quality on e ciency of cascade aeration

Scientia Iranica A (2016) 23(3), 918{925 Sarif University of Tecnology Scientia Iranica Transactions A: Civil Engineering www.scientiairanica.com Researc Note E ect of step geometry and water quality on e ciency of cascade aeration V. Ratinakumara, G. Dinakaranb; and C.R. Suribabub a. Scool of Civil Engineering, SASTRA University, Tanjavur, 613401, India. b. Center for Advanced Researc in Environment, Scool of Civil Engineering, SASTRA University, Tanjavur, 613401, India. Received 11 April 2015; received in revised form 1 July 2015; accepted 25 August 2015 KEYWORDS Aeration; E ciency; Step geometry; Dissolved oxygen; Cascade. Abstract. In tis paper, te e ect of step geometry wit ve di erent tread values from 0.40 m to 0.60 m wit an increment by 0.05 m, and tree di erent types of water, namely potable, non-potable, and recycled water, on aeration e ciency of stepped cascade aeration was studied. Detailed experimental investigations were carried out for di erent ydraulic loading rates of 0.005 m2 /s to 0.035 m2 /s. All te experiments were conducted for nappe ow condition. Results revealed tat te overall aeration e ciency at standard conditions (E20 ) approaces te maximum for t= = 4, number of steps were 12 wit a ydraulic loading rate of 0.02 to 0.025 m2 /s for potable and non-potable water. In te case of recycled water, maximum e ciency was acieved for t= = 3:67. Results also revealed tat stepped cascade aeration was a very suitable option for enancing DO content in treatment of waste water before discarging it to water bodies to save aquatic life. 2016 Sarif University of Tecnology. All rigts reserved. 1. Introduction Aeration was found to be one of te important tecniques employed in water and wastewater treatment process, wic enabled supply of oxygen from gaseous pase to liquid pase. In te case of nappe ow, te energy dissipation occurs by te break-up of jet in te air. In te case of skimming ow, te ow is in an organized stream supported by te recirculation uid. It was found from experiments tat skimming ow occurred wen te ratio of critical dept to te eigt of te step (dc =) was greater tan 0.8 and smaller values of dc = caused nappe ow [1]. In stepped cascade system, water is permitted to fall on series of steps and during tis process, *. Corresponding autor. Tel. +91 9944082810; Fax: +91 4362 264120 E-mail addresses: ratinakumar@civil.sastra.edu (V. Ratinakumar); gd@civil.sastra.edu (G. Dinakaran); suribabu@civil.sastra.edu (C.R. Suribabu) bubbles are formed wic lead to dragging of air from te atmospere. Stepped cascade system was used to remove color and taste caused by volatile oil, carbon dioxide, ydrogen sulpide, and volatile organic compounds suc as clorine and metane in te potable water treatment process [2]. Stepped cascade ow is caracterized by its large residence time, vibrant mixing, and substantial air bubble entrainment. Fluctuation in turbulence acts next to air-water free surface and causes te air bubble entrainment wic is responsible for continuous tapping and releasing of air. It was observed tat ow due to gravity played a vital role in te air entrainment process [3]. Experiments were carried out on stepped cascade aeration system to investigate te e ect of air entrainment [4] and ydraulics of nappe ow [5], predict transition from nappe to skimming ow [6], and propose te condition for nappe ow [7]. Previous researc works, conducted by [8-17], focused on ydraulic aspects of cascade system and te existence of relationsip between ow rate and step geometry

V. Ratinakumar et al./scientia Iranica, Transactions A: Civil Engineering 23 (2016) 918{925 919 on aeration was reported. Appreciable results were obtained in te experiments conducted for removing te pollutants from grey water using cascade aeration and bio ltration. Good removal eciency of ions concentration and COD is witnessed in te experiments [18]. Experiments were also conducted to study te combinational eect of stepped cascade system wit limestone trickling lter in removal of toxic matters like Polyclorinated bipenyls (PCB's), Petroleum products and Penols [19]. An attempt at numerical modeling of stepped cascade wit end sill and ig rougness is made using Volume Of Fluid (VOF) multipase ow model [20]. Te application of stepped cascade along wit trickling lter lled wit termo-stone removed te concentration of toxic matters in te range 0.074 nm-0.156 nm [21]. Te stepped cascade system as become very versatile in recent years because of its speedy construction. It is also proved tat te system is a cost eective aeration system in replenising dissolved oxygen. From te available literature, it is understood tat previous studies focused on ydraulic properties of water and step geometry. Hence, in te present work, eect of stepped cascade aeration on water quality, especially waste water after post-treatment, was considered. Te adaptability of te cascade system in suc situations was also studied. 2. Materials and metods Experimental model for te rectangular stepped cascade aeration system consisted of two tanks, called stilling basin and collecting tank, tted on te upstream and downstream sides, respectively. Bot tanks were made up of steel. Te size of te upstream tank was 0:60 m 1:20 m 1:0 m and downstream tank was 0:60 m 0:60 m 0:60 m. Bot tanks were connected by a sloped waist arrangement made up of steel frame, on wic RCC precast slab was placed to provide a rm base for construction of steps. Steps were constructed using brick masonry to reect te reality of te eld. Perspex seets were used as side walls of te stepped cascade system to facilitate better visualization from outside wen experiment was on. A 5 HP capacity monoblock pump was used to lift te water from te collection tank to te tank in te upstream side. A magnetic ow meter, capable of measuring 0.040 m 3 /s wit an accuracy of 0.0001 m 3 /s, was used to measure te rate of ow. Two dissolved oxygen meters (HANNA make - model HI 9146) were used to measure concentration of dissolved oxygen in te measuring locations (one at upstream tank and te oter at downstream tank) of te stepped cascade system by inserting probes to a dept of 0.20 m [13]. Te calibration of DO meters was daily done by air calibration metod in ambient air conditions. Tree readings were taken at te upstream and downstream locations for eac and every sample and average value was used for te analysis. Te total eigt of te stepped cascade system used in te present work was 1.80 m. Experiments were conducted for tree dierent qualities of water, namely Potable Water (PW), Non- Potable Water (NPW), and Recycled Water (RW). Te water, collected from te Reverse Osmosis (RO) plant in SASTRA university campus, was designated as PW. Te water quality parameters of PW were fullling its requirements. Te water collected from te bore well of SASTRA university was named NPW. It ad iger cloride content and total dissolved solids. However, BOD and COD of NPW were well witin te permissible limit. Te water collected from euent treatment plant was designated as Recycled Water (RW). It ad iger values of water quality parameters exceeding permissible limit. For eac and every type of water, readings were taken for two dierent eigts of steps (0.15 m and 0.18 m) wit ve dierent treads of steps (0.40 m, 0.45 m, 0.50 m, 0.55 m, and 0.60 m). In total, tere were 210 trials performed in te present work. Potable and non-potable water was added wit 10 mg/l of sodium sulte and 0.010 mg/l of cobalt cloride for te purpose of deoxygenation to maintain 1 mg/l of DO concentration. Since no reduction in DO concentration was observed in recycled water due to te addition of cemicals, no deoxygenation was performed as recycled water, collected from te euent treatment plant, contained iger TDS and surface agents. It retarded te process of deoxygenation even after te addition of Sodium Sulte. Figure 1 sows te experimental model used for te present researc work. Table 1 lists te design parameters adopted in te experiment. Table 2 provides te cemical caracteristics of dierent types of water used in conducted experiments. Taking te eect of temperature into account, te following equation was used to nd te aeration eciency at a standard temperature of 20 C [22]. Table 3 provides te calculation of [d c =] for te steps used in tis experiment, i.e. 0.15 m and 0.18 m for various ydraulic loading rates. Figure 1. Experimental model for te laboratory stepped cannel.

920 V. Ratinakumar et al./scientia Iranica, Transactions A: Civil Engineering 23 (2016) 918{925 Table 1. Design parameters used in te experiment. S. no Independent Range Dependent 01. Hydraulic loading rate (m 2 /s) 0.005, 0.01, 0.015, 0.02, 0.025, 0.03 and 0.035 02. Rise of eac step (m) 0.15 and 0.18 03. Tread of eac step (m) 0.60, 0.55, 0.50, 0.45 and 0.40 04. Widt of te cannel (m) 0.60 05. Total eigt of te system (m) 1.80 06. Number of steps 12 and 10 Aeration eciency (E 20 ) Table 2. Cemical properties of te used water. Parameter Potable Water (PW) Non-Potable Water (NPW) Recycled Water (RW) ph 7.5 8.77 9.2 Temperature ( C) 26.2 28.2 29.3 TDS (mg/l) 30 1800 930 Salinity (mg/l) 102 670 1023 Cloride (mg/l) 81 385 120 DO (mg/l) 6.00 6.40 4.90 COD (mg/l) 10 12 170 BOD (mg/l) 0 2 65 Table 3. Dimensionless discarges (d c =) based on ow per unit widt and step eigt. Flow rate per Dimensionless discarge unit widt For step eigt For step eigt (m 3 /s/m) of 0.15 m of 0.18 m 0.005 0.0911 0.0759 0.01 0.1446 0.1205 0.015 0.1894 0.1578 0.020 0.2295 0.1912 0.025 0.2663 0.2219 0.030 0.3007 0.2506 0.035 0.3332 0.2777 Oxygen transfer eciency (E T ) for a ydraulic structure at any temperature, T ( C), was expressed by te following equation: E T = [C d C u ] [C s C u ] ; (1) were: E T C d C u Transfer eciency at actual water temperature; Concentration of DO in te downstream (mg/l); Concentration of DO in te upstream (mg/l); C s E 20 = Saturation concentration (mg/l). i 1 (1 E) f 1 ; (2) were E 20 is aeration eciency for 20 C; f is exponent described by: 1 + 0:02103(T 20) + 8:261x10 5 (T 20) 2 ; (3) and T is ambient temperature in C. Canson (2002) proposed an equation for nappe ow condition, wic was followed in te present researc work and is given below: dc were: d c d c = q 2 w g q w L 0:89 1 3 L ; (4) Dimensionless discarge; Critical dept in a rectangular cannel (m); Hydraulic loading rate (discarge per unit widt)(m 2 /sec); Heigt of steps (m); Lengt of steps (m). 3. Results and discussion 3.1. Eect of step geometry Te variations of overall aeration eciency (E 20 ) wit respect to a non-dimensional parameter (d c =) are depicted in Figures 2-4 for te eigt of step = 0.15 m, and in Figures 5-7 for te eigt of step = 0.18 m, respectively. Te variation of aeration eciency E 20 wit a non-dimensional parameter (d c =) increases wit increase in (d c =) up to certain values beyond wic it as sown reverse trend. It was applicable for bot te eigts of step of 0.15 m and 0.18 m. It migt be due to te following reasons. A decline trend was observed in te aeration eciency wen te ow was subjected to increased ydraulic loading rate and

V. Ratinakumar et al./scientia Iranica, Transactions A: Civil Engineering 23 (2016) 918{925 921 Figure 2. Aeration e ciency of potable water wit Figure 6. Aeration e ciency of non-potable water wit Figure 3. Aeration e ciency of non-potable water wit Figure 7. Aeration e ciency of recycled water wit respect to dc = for 0.15 m of rise. respect to dc = for 0.15 m of rise. respect to dc = for 0.18 m of rise. respect to dc = for 0.18 m of rise. Figure 4. Aeration e ciency of recycled water wit respect to dc = for 0.15 m of rise. Figure 8. E ect of step geometry on te overall aeration e ciency. Figure 5. Aeration e ciency of potable water wit respect to dc = for 0.18 m of rise. tis could be due to transition from nappe to skimming ow and widt of te cannel. It was also seen tat for a particular eigt of step, size of tread played a role in deciding about aeration e ciency. Higer e ciency was observed for smaller values of tread. Furter increase of tread values sowed a reverse trend in e ciency. From te e ect of step geometry, it was understood tat increase in eigt of step from 0.15 m to 0.18 m resulted in reduction in e ciency. It was due to increase in number of steps for lesser eigt of 0.15 m. Since more number of steps was used for 0.15 m eigt of step, aeration e ciency got accelerated and was very muc e ective. To understand te e ect of step geometry on overall aeration e ciency of stepped cascade aeration system, a typical example is explained in te following lines by taking te result of potable water. Te results are discussed for a step tread of 0.60 m wit eigts of 0.15 m and 0.18 m, respectively, as sown in Figure 8. Te results were compared for almost closer values of dc =. For a ow rate of 0.009 m3 /s, te aeration

922 V. Ratinakumar et al./scientia Iranica, Transactions A: Civil Engineering 23 (2016) 918{925 eciency wit step eigt of 0.15 m was found to be 0.62, wereas for step eigt of 0.18 m, it was found to be 0.28. Tis dierence in aeration eciencies due to step geometry is signicant. However, for te igest d c = value, te eect of step geometry pronounces less due to increase in ydraulic loading rate were ow is subjected to transition stage. 3.2. Eect of water quality For potable water, te maximum eciency of 62% was observed for t= = 4 wit d c = = 0:189 for 0.15 m eigt of a step. It was also observed tat for a ydraulic loading rate from 0.005 to 0.025 m 2 /s, te aeration eciencies were good and furter increase of ow led to transition zone; ence, tere was a reverse trend. Tere was not muc variation in aeration eciency from t= = 4 to 3.33 and furter reduction of tese values sowed a iger reduction in eciency wic was due to decrease in tread values below 0.45 m were sucient space was not available for aeration process. In a similar sense, for t= = 3 wit a ydraulic loading rate of 0.005 m 2 /s, a minimum eciency of 15% was observed. As te turbulence, directly related wit velocity and spreading of water on step, was like tin lm over te larger area, te performance of cascade system for low ydraulic loading rate was found to be very low. In general, ow wit lower velocity will lead to greater residence time of te cascade and will result in greater air transfer. But, te geometry of te cascade was unable to produce greater turbulence and ence lesser eciency. Improved performance of cascade systems was observed for ydraulic loading rate 0.01 m 2 /s and 0.015 m 2 /s. It was due to formation of ydraulic jump witin te tread and ultimately yielded sizable quantity of aeration. However, te eciency of cascade aeration signicantly improved wen ydraulic loading rate increased to 0.02 m 2 /s and 0.025 m 2 /s. By furter increase in ydraulic loading rate to 0.03 and 0.035 m 2 /s, te eciency was found to be low wen compared wit eciency for ydraulic loading rates of 0.02 m 2 /s and 0.025 m 2 /s. Wit increased velocity of ow on te cascade, te residence time and aeration eciency decreased. It was evident from te above results tat step geometry was optimized based on ydraulic loading rate and considered to be te main governing parameter in te design stage. In te case of non-potable water wit a eigt of step = 0.15 m, more aeration eciency was acieved for t= = 4 and for oter t= values, te eciency was found to be less. Increase in d c = up to 0.266 increased te aeration eciency for all t= values and furter increase in d c = sowed a reverse trend. It was due to increased ydraulic loading rate. Also, similar trend was observed for a eigt of 0.18 m. Maximum eciencies of 56% and 47% were observed for eigts of steps 0.15 m and 0.18 m, respectively. Figure 9. Eect of water quality on te overall aeration eciency. Also, similar trend was seen in recycled water as non-potable water, but tere was no muc variation among eciencies of dierent t= values. Except t= = 2:22, for all te oter t= values, aeration eciency was above 30% and maximum eciency was 63% for a eigt = 0.18 m. For a eigt of step = 0.15 m, tese values were falling between 46 and 57%. Hence, it was inferred tat stepped cascade aeration system was eective in recycled water wit addition of no cemicals and it was te eld reality. Te aeration eciency of recycled water was found to be a little bit less tan eciency of potable and non-potable water; it migt be due to te reason tat recycled water as sediments, wereas potable and non-potable water does not ave tis. To understand te eect of water quality on te overall aeration eciency, Figure 9 depicts te results of aeration eciency wit respect to t= values for a ydraulic loading rate of 0.03 m 2 /s. It was understood from te results tat water quality ad eect on aeration eciency and was ranging from 10 to 20%, except for t= = 2:67 (tread = 0.40 m and eigt = 0.15 m). It was also inferred tat aeration eciency of recycled water under stepped cascade aeration system attracted considerable attention. 3.3. Eect of cemical properties of water on aeration eciency From Table 2, it was observed tat Total Dissolved Solids (TDS) and Salinity of te NPW and RW were ig. Comparing te aeration performances of cascade systems for enancing DO content of dierent types of water, potable water was found to be better tan te non-potable and recycled water. It migt be due to te reason tat potable water was free from TDS and salinity, and ence it ad better aeration. In case of PW, te minimum and maximum aeration eciencies were found to be 32 and 62%, respectively, wic give an idea about te eectiveness of cascade system in enancing DO. In case of NPW, tese values ranged from 19% to 47% and reduction in eciency was due to iger values of TDS and salinity wit dissolved

V. Ratinakumar et al./scientia Iranica, Transactions A: Civil Engineering 23 (2016) 918{925 923 organic matter. In RW, te dierence between maximum eciency (63%) and minimum eciency (17%) was found to be more signicant tan tose in oter two types of water. Better aeration eciency was acieved as no deoxygenation was performed for RW before te start of experiment. Te initial DO concentration of RW ranges from 4 to 5 mg/l, wereas in cases of PW and NPW, te DO concentration as been set to a value from 1 to 2 mg/l by deoxygenation. 3.4. Comparison of te present results wit earlier researc Te predictive equation given by Nakasone [23] wit combination of fall eigt, discarge, and tail water dept to analyze te aeration eciency was compared wit our present work. Good agreement in results was not observed. Tis is due to te ydraulic properties adapted to tat equation. Te results of te present study were also compared wit te results of an earlier study by Moulick et al. It was inferred from teir results tat aeration eciency was very ig (from 0.8 to 0.9) compared wit te present study and it migt be due to te dierence in quality of water used and scale eect. Moulick et al. (2010) [15] studied a 3 m ig stepped cascade system wit step eigt value of 0.6 m, wereas in te present study, te total eigt of stepped cascade was restricted to 1.8 m wit eigts of 0.15 m and 0.18 m. Anoter equation, given by El-Monayeri (2011) [24], was also compared wit te present study, wic did not establis a good rapport wit our results due to iger value of COD. 3.5. Statistical analysis A regression analysis was made to analyze te results of te experiments, i.e. parameters like d c = and r=c s, to calculate te aeration eciency (E 20 ). All te parameters considered in tis equation are nondimensional parameters, wic will be useful to balance te equation E 20. Te measured aeration eciency was compared wit values of Eqs. (5)-(7). Good agreement was found between te observed values and predicted values form te developed equation. In addition, condence level in te correlation was seen in Figure 10. It was also indicated in te comparison of measured and predicted values tat tey fell well below te upper and lower bound (10% of peak values) lines and ence results were found to be reliable. From te obtained data for all te tree types of water, keeping E 20 as a dependent variable and function of d c and C r s, te following equations were developed for PW, NPW, and RW, respectively: E 20P W = 0:0119 + 0:0880 d c + 1:06 r C s ; (5) E 20NP W = 0:0175 + 0:0436 d c + 1:05 r C s ; (6) Figure 10. Comparison of te measured and predicted E 20 values. E 20RW = 0:0146 + 0:440 d c + 0:829 r C s ; (7) d c = 0:04 to 0:44; and r C s = 0:80 to 1:10: Te above equations could be used to predict te aeration performance of te cascade system by sligtly varying te geometry and ydraulic loading rates. From te detailed study, it was understood tat te aeration eciency was governed by step geometry, ydraulic loading rate, and also quality of water. Stepped cascade aeration was found to be eective in enancing DO in recycled water wic as sown a positive sign for natural treatment of wastewater before discarging it to water bodies to save aquatic life. 4. Conclusions From te detailed investigations carried out on rectangular stepped cascade aeration system to study te eect of ydraulic loading rate, d c =, eigt and tread of step, and water quality, te following conclusions were obtained: ˆ Increase of dimensionless discarge (d c =) increased te overall aeration eciency up to 0.266 and furter increase sowed a reverse trend wic was due to te fact tat ow approaced transition condition wit increased ydraulic loading rate; ˆ Te overall aeration eciency increased wit increase in te number of steps in wic better aeration process was on and vice versa; ˆ Te overall aeration eciency at standard conditions (E 20 ) approaced maximum for t= = 4 and

924 V. Ratinakumar et al./scientia Iranica, Transactions A: Civil Engineering 23 (2016) 918{925 number of steps were 12 wit ydraulic loading rate of 0.02 to 0.025 m 2 /s for potable and non-potable water. In te case of recycled water, maximum eciencies were acieved for t= = 3:67 bot for 0.15 m and 0.18 m as eigts of step; ˆ Overall aeration eciency was iger for recycled water among tree types of water used. Hence it was concluded tat stepped cascade aeration was very suitable for enancement of DO content. Acknowledgement Te autors wis to acknowledge te INCH division of Ministry of Water Resources, Government of India, for te researc funding it provided (Sanction No. 22/50/2010-R&D/405-414). Autors express teir gratitude and sincere tanks to te Vice-Cancellor of SASTRA University for giving te permission to use te laboratory facilities in tis researc work. Nomenclature L C d C u C s d c d c E Widt of cannel (m); Concentration of DO in downstream (mg/l); Concentration of DO in upstream (mg/l); Saturation concentration (mg/l); Critical ow dept (m); Dimensionless discarge; Transfer eciency at water temperature (%); E 20 Oxygen transfer eciency at 20 C (%); f Correction factor for temperature; g Acceleration due to gravity (m/s 2 ); K L Q q w t Heigt of te step (m); Liquid lm coecient for oxygen; Flow rate (m 3 /s); Hydraulic loading rate (m 3 /m/s); Tread of te step (m); T Ambient temperature in C; r Oxygen decit. Abbreviations BOD COD DO HP NPW Biological Oxygen Demand; Cemical Oxygen Demand; Dissolved Oxygen; Horse Power; Non-Potable Water; ph PW RW TDS VOC References Hydrogen ion concentration; Potable Water; Recycled Water; Total Dissolved Solids; Volatile Organic Compounds. 1. Rajaratnam, N. \Skimming ow in stepped spillways", J. Hyd. Eng., 116(4), pp. 587-591 (1990). 2. Toombes, L. and Canson, H. \Air-water mass transfer on a stepped waterway", J. Env. Eng., 131(10), pp. 1377-1386 (2005). 3. Canson, H. \Hydraulic design of stepped spillways and downstream energy dissipaters", Dam Eng., 11(4), pp. 205-242 (2001). 4. Canson, H. \Stepped spillway ow and air entrainment", Can. J. Civ. Eng., 20(3), pp. 422-435 (1993). 5. Canson, H. \Hydraulics of nappe ow regime above stepped cutes and spillways", Aus. Civ. Eng., Trans. Inst. Eng., 36(1), pp. 69-76 (1994). 6. Canson, H. \Prediction of transition nappe/skimming ow on a stepped cannel", J. Hyd. Res., 34(3), pp. 421-429 (1996). 7. Canson, H. and Toombes, L. \Energy dissipation and air entrainment in stepped storm waterway- Experimental study", J. Irri. & Drge. Eng., 128(5), pp. 305-315 (2002). 8. Boes, R.M. and Hager, W.H. \Hydraulic design of stepped spillways", J. Hyd. Eng., 129(9), pp. 671-679 (2003). 9. Baylar, A. and Emiroglu, M.E. \Study of aeration eciency at stepped cannels", Proc. Ins. Civil Eng., Water & Maritime Eng., 156(WM3), pp. 257-263 (2002). 10. Baylar, A. and Emiroglu, M.E. \Study of aeration performance of open cannel cutes equipped wit a ip bucket", Tur. J. Eng. & Env. Sci, 27, pp. 189-200 (2003a). 11. Baylar, A. and Emiroglu, M.E. \An investigation of eect of stepped cutes wit end sill on aeration performance", Wat. Qual. Res. J. Can., 38(3), pp. 527-539 (2003b). 12. Baylar, A. and Emiroglu, M.E. \Self-aeration in smoot and stepped cutes", Int. J. Sci. and Tec., 1(2), pp. 105-113 (2006). 13. Baylar, A., Bagatur, T. and Emiroglu, M.E. \Aeration eciency wit nappe ow over stepped cascades", Proc. Inst. Civ. Eng., Water & Maritime Eng., 160(WM1), pp. 43-50 (2007). 14. Baylar, A., Unsal, M. and Ozkan, F. \Te eect of ow patterns and energy dissipation over stepped cutes

V. Ratinakumar et al./scientia Iranica, Transactions A: Civil Engineering 23 (2016) 918{925 925 on aeration eciency", KSCE J. Civ. Eng., 15(8), pp. 1329-1334 (2011). 15. Moulick, S., Nares, V.T., Sing, B.K. and Mal, B.C. \Aeration caracteristics of a rectangular stepped cascade aeration system", J. Water Sci. & Tec., 61(2), pp. 415-420 (2010). 16. Ratinakumar, V., Dinakaran, G. and Suribabu, C.R. \Assessment of aeration capacity of stepped cascade for selected geometry", Int. J. Cem. Tec. Researc, 6(1) pp. 254-262 (2014). 17. Ratinakumar, V., Dinakaran, G., Suribabu, C.R. and Velmurugan, P. \Experimental Investigation on performance of stepped cascade aeration", Asian J. App. Sci., 7(6), pp. 391-402 (2014). 18. Abbood, D.W., Mustafa, A.S. and Jouda, R.A. \Modication of grey water using combination of stepped cascade and bio ltration", J. Env. Sci. & Eng. B., 2, pp. 473-481 (2013). 19. Abbood, D.W., Baqer, A.M.T. and Jasim, E.A. \Marginal treatment using sludge recycling from combination of stepped cascade weir and Limestone trickling lter", World Academy of Sci. Eng. & Tec, Civ. and Env. Eng., 2(1) (2015). 20. Abbood, W.D. and Abood, H.H. \Multipase ow model for 3D numerical model using ANSYS for ow over stepped cascade wit end sill", World Academy of Sci. Eng. & Tec, Civ. and Env. Eng., 2(5) (2015). 21. Abbood, W.D., Baqer, A.T.M. and Jasim, E.A. \Removing of toxic matter from marginal water using combination of stepped cascade and trickling lter", World Academy of Sci. Eng. & Tec, Civ. and Env. Eng., 2(10) (2015). 22. Doiron, T. \20 C - A Sort istory of te standard reference temperature for industrial dimensional measurements", J. Res. Nat. Inst. of Stan. and Tec., 112(1), pp. 1-24 (2007). 23. Nakasone, H. \Study of aeration at weirs and cascades", J. Env. Eng. ASCE, 113(1), pp. 64-81 (1987) 24. Kalifa, A., Bayoumi, S. and El. Monayeri, O. \Matematical modeling of aeration eciency and dissolved oxygen provided by stepped cascade aeration", J. Water Sci. and Tec., 63(1), pp. 1-9 (2011). Biograpies Vedacalam Ratinakumar is a PD candidate in te Scool of Civil Engineering at SASTRA University. He received is BE degree in Civil Engineering from SASTRA University and ME degree in Environmental Engineering from Anna University in 2005 and 2008, respectively. He works in te area of stepped cascade aeration. Govindasamy Dinakaran is a Professor in te Scool of Civil Engineering at SASTRA University. He received is BE in Civil Engineering from Baratidasan University, ME degree from National Institute of Tecnology and PD degree from Indian Institute of Tecnology Madras in Osore Structures in 1988, 1990, and 2003, respectively. His researc interests include sustainable materials and materials in aggressive environment. Conety Ravi Suribabu is a Professor in te Scool of Civil Engineering at SASTRA University. He received is BE degree in Civil Engineering from Baratidasan University, ME degree from Anna University, Cennai, and PD degree from SASTRA University in Water Resources Engineering in 1991, 1993, and 2006, respectively. His researc interests include sustainable water resources development and environment.