EVALUATION OF AERATORS FOR CITH4-NNEI CATFISH FARMING - -r '- - ;-,b' % ~i.: -: ~:: ::;; .;. : :_: 1:;-~ i. JUNL 1987 W' BULLETIN 584 ALABAMA AGRICULTURAL EXPERIMENT STATION AUBURN UNIVERSITY LOWELL T FROBISH, DIRECTOR AUBURN UNIVERSITY, ALABAMA CONTENTS Page INTRODUCTION ............................................... 3 Principles of Aeration............ Water Circulation............... Test Methods...................................10 Pump Sprayer Aerators........... Squirrel Cage Aerators........... Paddle Wheel Aerators ................. .................. ................ 4 9 12 TRACTOR-POWERED AERATORS .............................. 13 ................ 17 19 23 ............................ Comparison of Tractor-Powered Aerators................ 22 ELECTRIC AERATORS......................................... Paddle Wheel Aerators............................... 23 35 Vertical Pump Aerators .............................. Pump Sprayer Aerators ........................ 41 Propeller Aspirator Pumnp Aerators..................... Diffuser Aerators ................................... Comparison of Electric Aerators....................... Electric Paddle Wheel Aerator Design.................. SUMMARY ................................................... REFERENCES ................................................ 44 45 46 49 51 52 FIRST PRINTING 3M, APRIL 1987 Information contained herein is available to all without regard to race, color, sex, or national origin. Evaluation of Aerators For Channel Catfish Farming Claude E. Boyd and Taufik Ahmad' INTRODUCTION catfish farming is a profitable endeavor which is expanding rapidly in the United States. The acreage devoted to channel catfish ponds is increasing at a rate of about 10 percent per year, and production of fish per acre also is rising. CHANNEL A major problem in catfish farming is the low concentrations of dissolved oxygen (DO) which result from high fish stocking and feeding rates necessary to assure profit (4,19). For years, catfish farmers have relied on large, emergency aerators powered by power take offs (PTOs) of farm tractors to prevent fish stress and mortality at times when DO concentrations were low (4,8,19). This practice is expensive because a tractor must be available to power each emergency aerator, and many aerators are necessary for large catfish farms. To reduce dependence on tractor-powered aerators, some fish farmers have begun to invest heavily in smaller, floating, electric ones. When used at 1 to 3 horsepower (hp) per acre in research ponds, floating, electric aerators permit greater fish production, and they prevent most crises with low DO (10,12,14). In practice, fish farmers usually aerate at only 0.5 to 1.0 horsepower per acre, but even these rates result in improved fish production at these aeration rates. The overall cost of aeration is less with electric aerators than with tractor-powered aerators. However, tractor-powered aerators probably will not be replaced entirely, because they can be used when DO crises are too severe to be managed with smaller, electric aerators. Also, some catfish ponds do not have electrical services. Most aerators used in catfish farming have been designed and fabricated by fish farmers or 'Professor and Graduate Assistant, respectively, of Fisheries and Allied Aquacultures. 4 ALABAMA AGRICULTURAL EXPERIMENT STATION local machine shops. Tractor-powered aerators have been subjected to few performance tests (2,7,9,13), but even less information is available on the performance of electric aerators (6). Electric aerators are used widely in wastewater treatment. These aerators have been subjected to years of research, development, and testing, and performance information is available from their manufacturers. Aerators for wastewater treatment usually are too expensive for application in catfish farming, but a few pollution equipment companies have sold aerators to catfish farmers. During the past 3 years, performance tests on a number of tractorpowered and electric aerators which are used in catfish farming have been performed at the Alabama Agricultural Experiment Station. A description of these tests and results obtained are presented in this report, following an explanation of the principles of aeration. Principles of Aeration The air contains 20.95 percent oxygen. At standard barometric pressure (29.92 inches of mercury), the pressure of oxygen in air is 6.27 inches of mercury (29.92 x 0.2095). This, of course, varies with barometric pressure. The pressure of oxygen in the air drives oxygen into water until the pressure of oxygen in water is equal to the pressure of oxygen in the air. When the pressure of oxygen in water and air are equal, net movement of oxygen molecules from air to water ceases. The water is said to be at equilibrium, or at saturation, with DO when the oxygen pressure (sometimes called oxygen tension) equals that of the air. The concentration of DO in water at saturation varies with temperature and barometric pressure. As water temperature increases, the DO concentration at saturation decreases, table 1. DO concentrations in table 1 are given in parts per million (p.p.m.); 1 p.p.m. = 1 milligram per liter (mg/1). At a given temperature, the DO concentration at saturation increases in proportion to increasing barometric pressure. Plants growing in water produce oxygen by photosynthesis, and during daylight hours plants in fish ponds often produce oxygen so fast that DO concentrations in the water rise above saturation. Water containing more DO than expected for the water temperature and barometric pressure is said to be supersaturated with DO. When water is supersaturated with DO, the pressure of oxygen in water is greater than the pressure of oxygen in air. Water also may contain less DO than expected at saturation. At night respiration by fish, plants, and other pond organisms causes DO levels to decline. Thus, during warm months nighttime DO con- CATFISH POND AERATORS TABLE 1. DISSOLVED OXYGEN (DO) CONCENTRATIONS AT SATURATION FOR DIFFERENT TEMPERATURES (1) 5 Temperature, degree C' DO Temperature, degree C' DO 0(32) 1(34) 2(36) 3(37) 4(39) 5(41) 6 (43) 7(44) 8 (46) 9 (48) 10 (50) 11(52) 12(53) 13(55) 14(57) 15(59) 16(61) 17 (62) p.p.m. ..................... 14.60 ..................... 14.1.9 ..................... 13.81 ..................... 13.44 ..................... 13.09 ..................... 12.75 ..................... 12.43 ..................... 12.12 11.83 ..................... ..................... 11.55 ..................... 11.27 11.01 ..................... ................... 1.. 0.76 .................. .. 10.52 ............ ......... 10.29 ..................... 10.07 .................. ... 9.85 ...................... 9.65 18(64) 19(66) 20 (68) 21(70) 22 (72) 23(73) 24 (75) 25(77) 26 (78) 27 (80) 28 (82) 29 (84) 30(86) 31(88) 32(90) 33(92) 34 (93) 35 (95) ...................... ...................... ...................... ...................... ...................... ...................... ...................... ...................... ...................... ...................... ...................... ...................... ...................... ...................... ...................... ...................... ...................... ...................... p.p.m. 9.45 9.26 9.07 8.90 8.72 8.56 8.40 8.24 8.09 7.95 7.81 7.67 7.54 7.41 7.28 7.16 7.05 6.93 'Numbers in parenthesis are degrees F. centrations in ponds often are below saturation (the pressure of oxygen in water is less than the pressure of oxygen in the air). When water is below saturation with DO, there is a net movement of oxygen molecules from air to water. At saturation with DO, the number of oxygen molecules leaving the water equals the number entering (no net movement). There is net movement of oxygen molecules from water to air when water is supersaturated with DO. The greater the difference between the pressure of oxygen in water and air, the larger the movement of oxygen molecules from air to water or vice versa. The concentration of DO at saturation for a particular water tem- perature and atmospheric pressure may be calculated as follows: Cs = S Ctab BP t 29.92 where Cs = DO concentration at saturation (p.p.m.); Ctab = DO concentration at the existing temperature and standard barometric pressure, table 1 (p.p.m.); BP = barometric pressure (inches of mercury); 29.92 = standard atmospheric pressure at sea level (inches of mercury). For rigorous calculations, the vapor pressure of water must be subtracted from both the numerator and denominator of the above equa- 6 ALABAMA AGRICULTURAL EXPERIMENT STATION tion (11). However, for practical purposes, this adjustment may be ignored (1). The percentage saturation of water with DO may be estimated as: S= -CS x 100 where S = percentage saturation with DO; Cm = measured concentration of DO in water (p.p.m.). The pressure or tension of DO in water can be estimated as: Po 2 =C x 0.2095 x 29.92 Cs where Po2 = DO pressure in water (inches of mercury). The DO pressure in water can be thought of as the equivalent pressure of oxygen in air necessary to hold the observed concentration of DO in the water. The oxygen deficit is the difference between the measured DO concentration and the DO concentration at saturation. That is: OD = C, - Cm where OD = oxygen deficit (mg/1). The value for OD will be positive when the DO concentration in water is below saturation and negative when the DO concentration in water is greater than saturation. The value of OD may be expressed as a pressure difference if C s and C m are in pressure rather than concentration. Oxygen moves from air to water and vice-versa by diffusion, and the rate of oxygen diffusion depends upon the oxygen deficit. The oxygen deficit is the driving force causing oxygen to enter or exit the water surface. Obviously, at a given oxygen deficit, the amount of oxygen that can enter a given volume of water in a specified time interval depends upon the area of water surface relative to water volume. The amount of oxygen entering increases with greater surface area. Oxygen from the air readily enters the surface film, and the DO concentration in the surface film quickly reaches saturation. The movement of oxygen from the surface film throughout the entire volume of water is much slower than the initial entry of oxygen into the surface film. Thus, in still water, the surface film quickly saturates with DO, and the rate of diffusion of oxygen into water becomes slow, because no more ox- CATFISH POND AERATORS 7 ygen can diffuse from air into the surface film until some of the oxygen in the surface film diffuses into the greater volume of water. The importance of mixing of water on oxygen transfer between air and water should be apparent. Mixing makes the surface rough and thereby increases surface area. Mixing also causes mass transfer (convection) of water and DO from the surface to other places within the water body. Mixing of pond water by wind favors diffusion of oxygen, so more oxygen diffuses into or out of pond water on a windy day than on a calm day. The rate of change in the oxygen deficit (or the rate of change in mass oxygen transfer) with time depends upon the oxygen-transfer coefficient, and the oxygen-transfer coefficient depends upon turbulence of water (degree of mixing), area of water surface, and water volume. Surface area varies with turbulence, and neither variable can be estimated accurately. Nevertheless, it is possible to calculate the overall oxygen-transfer coefficient with the following equation: K _ In OD 1 - in OD 2 L (t 1 t 2 )/60 where KLa = overall oxygen-transfer coefficient (hour-); in = natural logarithm; OD 1 = oxygen deficit at t 1 (p.p.m.); OD2 = oxygen deficit at t2 (p.p.m.); tI = time 1 (minute); t2 = time 2 (minute). Aerators influence the rate of oxygen transfer from air to water by increasing turbulence and surface area of water in contact with air. Aerators are of two basic types: splashers and bubblers. An example of a splasher aerator is a paddle wheel aerator. It splashes water into the air to affect aeration. Splashing action also causes turbulence in the body of water being aerated. Bubbler aerators rely upon release of air bubbles near the bottom of a water body to affect aeration. A large surface area is created between air bubbles and surrounding water. Rising bubbles also create turbulence within a body of water. Aerators are tested to determine the rate at which they transfer oxygen to water. Tests are conducted in a tank of known volume. Water in the test tank is deoxygenated, and the aerator is operated to effect re-aeration. Concentrations of DO are measured at timed intervals during re-aeration. These data are used, as described later, to estimate the amount and efficiency of oxygen transfer under standard conditions (0 p.p.m. DO, 68°F, and clean tap water). The standard oxygen transfer rate (SOTR) is defined as the pounds 8 ALABAMA AGRICULTURAL EXPERIMENT STATION of oxygen that an aerator will transfer in 1 hour. The standard aeration efficiency (SAE) is obtained by dividing SOTR by power input to give the pounds of oxygen transferred per horsepower-hour. SOTR and SAE values are for aerators operating in clean water at 68°F and containing 0 p.p.m. DO. These conditions seldom exist in fish ponds. The rate that an aerator transfers oxygen to water decreases with increasing DO concentration and to a lesser extent with increasing temperature. Clean water often aerates faster than water from fish ponds. The cx value is a measure of the difference in the aeration rate of pond water and clean water when both are at the same temperature: Oxygen-transfer coefficient for pond water Oxygen-transfer coefficient for clean water = The actual oxygen transfer rate for an aerator operating in a fish pond can be estimated with the following equations: Cs-C OTR = SOTR " Px 1.024T-2 0 x 9.07 where OTR = Oxygen transfer rate in pond water (pounds O2/hour); Cp = DO concentration in pond water (p. p.m.); 9.07 = CS at 68°F and 29.92 inches of mercury (p.p.m.); T = Water temperature (°C). If one is interested in aerator performance in brackish or salt water, the CS value in the preceding equation must be adjusted for salinity. Also, the value for C at 68°F and 29.92 inches of mercury must be 5 determined for the existing salinity and this value used in place of 9.07 in the preceding equation. Strickland and Parsons (17) provided a nomograph for estimating DO concentration at saturation in waters of different salinities. Aeration efficiency (AE) for pond conditions can be estimated by using SAE instead of SOTR in the preceding equation. Estimation of OTR and AE is seldom attempted for fish ponds. The primary value of SOTR and SAE in fish farming is for comparing aerators. An aerator with a high SOTR value will transfer more oxygen than an aerator with a low SOTR value when aerators are operating under similar conditions. Likewise, for comparable operating conditions, an aerator with a high SAE will transfer oxygen more efficiently than an aerator with a low SAE. SOTR and SAE values are comparable to standard gas mileage ratings which are provided by automobile manufacturers. Gas mileage ratings permit prospective automobile buyers to compare cars, but buyers realize that under actual CATFISH POND AERATORS 9 driving conditions gas mileage will be less than the standard gas mileage rating. Water Circulation Circulation of pond water by aerators is beneficial for several reasons: (1) oxygenated water moves across the pond and fish can more readily find zones with adequate DO concentrations; (2)without constant movement of well oxygenated water away from the aerator, aeration will increase DO concentrations in the vicinity of the aerator and greatly reduce oxygen-transfer efficiency; and (3) mixing of pond water by aerators reduces vertical stratification of temperature and chemical substances. Boyd and Martinson (6) developed two techniques for estimating the water circulating abilities of aerators. One procedure involved pouring a brightly colored dye in the water around an aerator and determining how long it took an aerator to spread the dye over the entire pond surface. In the other method, a concentrated solution of salt (NaCl) was poured into the water around the aerator. Specific conductance values were measured at several sites and depths in the pond at timed intervals until specific conductance was uniform throughout the water volume. The time necessary to effect uniform specific conductance was taken as the time required to completely mix the pond water. The mixing rate was calculated as follows: MR - (A)(D) (P)(T) where MR = mixing rate (acre-foot/horsepower-hour) A = pond area (acres) D = average depth of pond (feet) P = aerator size (horsepower) T = time to homogenously mix salt throughout pond volume (hour) Boyd and Martinson (6) and Petrille and Boyd (13) determined mixing rates for several different types of tractor-powered and electrically powered aerators. In general, mixing rates increased with increasing SOTR values for tractor-powered aerators and with increasing SAE for electric aerators. This is logical because vigorous splashing or stirring of water is necessary for efficient oxygen transfer with surface aerators, and vigorous splashing will induce strong water circulation. Among tractor-powered aerators, the Airmaster (described later) and a paddle wheel aerator were most effective in mixing pond water (13). Electric propeller aspirator pump aerators 10 ALABAMA AGRICULTURAL EXPERIMENT STATION (Air-02 aerators) were more efficient in mixing pond water than vertical pump aerators and diffused-air aerators. Mixing tests were not conducted with electric paddle wheel aerators. If an aerator is efficient in oxygenating water, it will usually induce adequate water circulation. Excessive water circulation should be avoided, because turbidity from suspended soil particles may result. Therefore, in the present study, aerators were tested only for their abilities to transfer oxygen to water. Test Methods Aerator tests were conducted in small ponds (0.1 or 0.25 acre) or in concrete tanks (160, 784, or 1,400 or 5,400 square feet). Water depth averaged 3 feet in ponds. Water was of uniform depth in tanks; depths ranged from 2.5 to 3.5 feet in different tests. Ponds and tanks were rectangular in shape with lengths approximately twice widths. Tractor-powered pump sprayer aerators and squirrel cage aerators were tested in ponds; other aerators were tested in tanks. Aerator performance tests followed accepted guidelines (1,3,5,18). Water in ponds or tanks was deoxygenated by applying sodium sulfite and cobalt chloride. Sodium sulfite removes oxygen according to the following reaction: Na 2S03 + 1/2 02 - Na 2 SO . 4 Cobalt chloride catalyzes the reaction between sodium sulfite and oxygen. To remove 1 p.p.m. of DO requires 8 p.p.m. of sodium sulfite. Cobalt chloride was added to provide 0.075 p.p.m. of cobalt. The two chemicals were dissolved in containers of water (5 to 35 gallons) and splashed over water surfaces of tanks or ponds. Chemicals were mixed with waters of test basins by running aerators. A polarographic DO meter (Yellow Springs Instrument Co., Model 57) was used to measure DO concentrations at timed intervals while DO rose from near 0 percent to 80 or 90 percent of saturation. Concentrations of DO were measured at three different places in tanks and at five different places in ponds. Time intervals ranged from 15 seconds to 4 minutes for different aerators; measurements were made over at least 10 time intervals in each test. Concentration of DO at saturation was calculated by adjusting the appropriate saturation concentration from table 1 for barometric pressure. Deficits of DO were estimated for each time interval by subtracting measured DO concentrations from concentration of DO at saturation. Natural logarithms of oxygen deficits were plotted ver- CATFISH POND AERATORS 11 sus time of aeration. The line of best fit was drawn by visual inspection of plotted points. The oxygen transfer coefficient was calculated with the following equation: (KLa)T = in ODIo - In OD7 0 t 7 0 - tlo where (KLa)T = overall oxygen-transfer coefficient for the existing water temperature (hour- ); ODIo = oxygen deficit at 10 percent of saturation (p.p.m.); OD70 = oxygen deficit at 70 percent of saturation (p. p.m.): tlo = time when DO reaches 10 percent of saturation (hour); t7o = time when DO reaches 70 percent of saturation (hour); Data for solution of the above equation were obtained from the graph of DO deficit versus time of aeration. The (KLa)T value was adjusted for 20°C (68°F) as follows: (KLa)20 = KLaT + 1. 0 2 4 T 20 where (KLa) 20 = overall oxygen-transfer coefficient at 20°C (hour- 1); T = water temperature for test (°C). Aerator tests were conducted in tanks filled with pond water. In order to adjust (KLa) 20 values to clean water conditions, values were determined. Water samples from test basins were brought to the laboratory and bench-scale aeration tests were conducted by aerating water in 4-liter beakers with an air pump and air stone (16). Comparison tests were conducted with tap water, and values were computed: (KLa) 20 pond water (KLa) 2o tap water 0 Next, the adjusted overall oxygen-transfer coefficient [(KLa)' 2o0 ] was obtained: (KLa)' 20 = (KLa)' 20 + o The standard oxygen-transfer rate (SOTR) in pounds oxygen per hour was estimated as follows: SOTR = (KLa)' 20 X 9.07 x V x 10-3x 2.205 12 ALABAMA 12 ALABAMA AGRICULTUA AGRICULTURAL EXPERIMENT XEIMN STATION TTO where 9.07 = DO concentration at 20 0C mospheric pressure (g/m 3) (68°F) and standard at(1 g/m 3 = 1 p.p.m.); V = tank volume (m3); 10-3 = factor for converting grams to kilograms; 2.205 = factor for converting kilograms to pounds. Standard aeration efficiency (SAE) in pounds of oxygen per horsepower-hour was obtained by dividing SOTR by horsepower applied to the aerator shaft. At least three oxygen-transfer trials were conducted for each aerator. Aeration tanks or ponds were drained after a maximum of eight oxygen-transfer trials and refilled. In tests with electric aerators, current (amperes) was measured to determine if the aerator was drawing the rated current. If it was, the horsepower applied to the aerator shaft was assumed to be the rated motor output horsepower, or if a gear reducer was used, the horsepower applied to the aerator shaft was estimated as motor output horsepower times the gear reducer efficiency Voltage readings were obtained with a voltmeter, and power measurements were made with a TIF Model 2000A clamp-on digital watt meter. In cases where the aerator was drawing less than the rated current, the horsepower supplied to the aerator shaft was estimated for three-phase motors by the equation: horsepower74 3_ I x x E x PF x Eff 746 where I = current (amperes); E = voltage (volts); PF = power factor; Eff = combined motor and gear reducer efficiency. For single-phase motors, the \/3 term was omitted from the above equation. No attempt was made to determine the power applied to the shafts of tractor-powered aerators. A Biddle speed indicator determined aerator shaft speeds. TRACTOR-POWERED AERATORS Tractor-powered aerators included pump sprayers, squirrel cages, and paddle wheels. These portable aerators were mounted on trailers and powered by PTOs of large farm tractors (50 horsepower or more). In practice, the use of tractor-powered aerators is restricted to emergency aeration during periods when DO concentrations are dangerously low. CATFISH POND AERATORS 13 suriedl 161-Itrac~t( Because the liorselpovxer applied to the aerator shaft was niot iaIopower(d aerato rs, Ski'. valuies wXere not (calclatldt(. Pump Sprayer Aerators (Crisafl -l ihe pump w i ni xhichi is manu factuired by)Crisaflli hinip Co., G.lenivc , Monitania, had1 a 16-inch-dtiamieter by 8.88-inch-wxidle im 1peller anid a 1'-iflcl-(hiamteflt Ii schar~(. figu're 1. The s~prayer wXas a 12-uicl-liaiflter pipe wxhich xten~dedI 5 tcet al ov e th( center ine of the prmivp ou t let Tle endi ol the pipe) was cappiedi wxith a cone which wxas p)erfor1ated wxith 127 0.5- inch diameter holes. Six larg(' slot's (0.5-inich x >-ilc) an stix~ i small slots (0.5- ic x11 1. ich1 w~emre cut inito the pipe just blohw the cap oni thme side o1-the pipe facing the pond. The pump was) operatedi with a 65-horsepowxer tractor. The tractor PT() turned at 540) n p. mi. ;the pumiip shaft rotated at the saume sped(. ' * FIG. 1.Crisafulli tractor-powered pump sprayer aerator. 14 ALABAMA AGRICULTURAL EXPERIMENT STATION SOTR for the Crisafulli pump sprayer aerator was 17.3 pounds of oxygen per hour, table 2. Spree - This pump sprayer was constructed by Thed Spree, Boligee, Alabama. It was similar in appearance, figure 2, to the Crisafulli pump sprayer. The pump has a 16-inch-diameter by 6-inch-wide impeller and an 18-inch-diameter discharge. The discharge outlet was fitted with an 18-inch-diameter pipe which extended 5 feet above the centerline of the pump outlet. The pipe was capped with a flat plate. The side of the pipe facing the pond was perforated with 14 slots (2inch x 4-inch). The pump shaft was rotated at 540 r.p.m. by a 65-horsepower tractor. A SOTR of 26.5 pounds of oxygen per hour was achieved for the Spree pump sprayer aerator, table 2. Airmaster - This aerator is manufactured by Mastersystems, Inc., Greenwood, Mississippi. The pump has an 18-inch-diameter by 8inch-wide double-intake impeller. The pump casing was connected to a 10-inch-diameter by 10-foot-long manifold which contained a 5.5inch-diameter hole in each end and 30 discharge ports in the top. Each port is constructed by cutting a 0.125-inch slit for 3000 around a radius of 2 inches. Water sprayed vertically through ports and laterally through holes at the end of the manifold, figure 3. The pump was powered by an 80-horsepower tractor which turned the pump shaft at 1,000 r.p.m. The Airmaster pump sprayer aerator had an SOTR of 46.9 pounds of oxygen per hour, table 2. Big John Aerator - Southern Machine Welding, Inc., Quinton, TABLE 2. STANDARD OXYGEN TRANSFER RATES (SOTR) FOR TRACTOR-POWERED EMERGENCY AERATORS ARE DESCRIBED IN THE TEST Aerator' Tractor size Aerator shaft speed SOTR2 SOTR2 Waterblower s .................... House Manufacturing(PV) ............ ) Auburn Univ., concave paddles(PV ... es AirmasterP ) ........................ (P Auburn Univ., flat paddles w) ........ McCray(sc).......................... .. Spree(Ps)........................... .. Big John(PS) ° 45 elbow sprayer.................. .. ( ) Horsepower 200 65 65 80 65 65 65 50 r.p.m. 1,000 540 540 1,000 540 400 540 540 Lb. 0 /hr. 162.8 65.7 58.0 46.9 43.3 37.3 26.5 2 ± 8.9 ± 3.2 + 3.5 ± 2.4 ± 2.6 ± 4.2 + 0.9 20.2 ± 3.1 Tee sprayer...................... McClendon(sc)..................... Crisafulli(Ps)....................... Mean + 1 standard error. 19.7 + 2.9 17.3 1.3 17.3 1.1 'PS = pump sprayer aerator; PW = paddle wheel aerator; SC = squirrel cage aerator. 2 50 65 65 540 400 540 ± ± CATFISH POND AERATORS * 3' r ..:.- FIG. 2. Spree tractor-powered pump sprayer aerator. 1 FIG. 3. Airmaster tractor-powered pump sprayer aerator. ALABAMA AGRICULTURAL EXPERIMENT STATION Alabama, manufactured this aerator, figure 4. The pump had an 18inch-diameter bxy 5-inchwide dolbie intake impeller with an 8-inchdiameter discharge. The sipray er was falbricated of 8-inch-diameter PVC pipe. Two types of sprayers were tested. One consisted of a pipe fitted at its discharge end with a tee. The other was fitted at its discharge end with a 4,50 elbow. 'The aerator was powered rei a 50horsepowxer tractor; the1p11np shaft was rotated at 540 r.p. m. The 450 elbo)w sprayer had a SOTR of 20.2 pounds of oxy gen per hour, while the tee spra er had a SOTH of 19.7 poLuls of oxvgen per hour, table 2. Water Blower - '[his aerator was built ly Rlichardi Koehn, Walnut Crove, Florida. The punp had an 18-inch-diamneter b 4-inch-wide loule-intake impeller. The spray er was a continuation of the pump casing which gradually reduced in size to 6.5-inch-diameter at its discharge end figure 5. The angle of the spraayer x with the water surface was adijustable. In tests, tte discharge end of the spra\ er was I i- If L;' FIG. 4. Big John tractor-powered pump sprayer aerator. CATFISH POND AERATORS 17 FIG. 5. Waterblower tractor-powered pump sprayer aerator. foot ab)ove ad p~arallel to the' pond1 surface. fihe aerator was poee to approximuatex 200 by a large tractor wxhich xxas t iirlocharg(I horsepowxer. Tile pomp si aft xxas rotatedI at 1,000 r. p).])]. Thew Water Blower had iavcrv high SOTH of 162.8 pounds of oxx gen per lhour, tablle 2. Squirrel Cage Aerators 'McLendon - This aerator, figure 6, wxas built byx\\ayne Mfend1(on, O)pelika, Alab ama. The sqirrel cage was origrinll the fan fir at large air-conditioneir. It wxa~s .30 inches long and 28 inches in diamneter; there were (64 sligily cturved vanes, each 2 inches wvide. The squiirr'el cage was attaced at its Center of, rotation to the end of' a shaft. In tests the 18 ALABAMA AGRICULTURAL EXPERIMENT STATION .,:* . FIG. 6. McLendon tractor powered squirrel cage aerator. b~ack edIge of the squirrel cage extended 2 inches into the wxater, but the front edIge was not as dlep)becauLse the aerator wxas set at an angle when b)ackedl into the p)ond(. The 65-horsepower tractor- could only rotate the aerator at 400 r. p. in. The aerator pro~pelled water approximnately 40 feet inlto the air. SO TR for this aerator was 17.3 pounIds of oxygen per hour, tab~le 2. CATFISH POND AERATORS 4, , ~A2[ k FIG. 7 McCray tractor powered squirrel cage aerator. McCraw - I larold M~cCra, Greensboro, Alabamna, fabr icatedl this aerator, figure 7. It consistedl of two squirrel cages attacied at their centers of rotation to a shaft One squirrel cage was 24 inches in outsidIe diameter; the other was 28 inches in outside diameter. Inaside diamneters were 15~ and 17 inches, respectix (IX. Voles we re tear-drop) shaped inl cross section. 'The two 0squirrel cages we re separated by a distance of':3 feet along the shaft. The aerator was b~ackedl into the pond until the b~ottomn edge of the squirrel cage nearest the tractor was subImergedI to a depth of 11 inches. The (65-horsepower tractor trnedI the squirrel cage at onlyX 400 r. pin. Water wXas prop1elledI ab~out .50 feet into the air. The SOTH for the MceCray squirrel cage aerator wvas :37.3 pounds of oxygen perF houri, tale 2. Paddle W~heel Aerators Auburn Uiversity - The two aerators we rc of almost ideintical constriiction, except that one aerator had flat p~add(les and the other had 20 ALABAMA AGRICULTURAL EXPERIMENT STATION sbightly concav e paddles. Aerators were conistructedl by local machine shops. Paddle wheels consistedl of 18-inch-diameter by 18-inch-long llubs5 mounted on axles of truck dlifferentials, figure 8. Twelve 14-inchlong byv 6-inch-wide paddles were weldled to each hub. There were four paddles, each 90° apart in each row of paddles around the 1ub. The middle row of p)add~les was rotated 430 on the circumference of the hub~s to the other twxo rows to provide a staggered arrangement of paddles. A dIrive shaft connected to the truck (lifleren~tial was fitted at its other end wxith a PTO shaft. Speed reduction byv the differential was 4.5:1; this prov ided at paddle wheel speed of 120 r. p. in. wxhen the tractor PTO) rotated at .540 r.p.mi. Paddle wheels were sublmerged to the centerlines of the hubs. A 65-horsepowver tractor pr~ovided poer Values of SOTH were 43.3 and 58.0 p)ound~s of oxygen per hour for p)addlle wheel aerators with flat and concave padd~les, resp~ectively, table 2. FIG. 8. Auburn University tractor-powered paddle wheel aerator. CATFISH POND AERATORS 21 H-ouse Manufacturing - This aerator, figure 9, was manufacetured Cherry alle, Arkansas. Two 4.5-inchlong by 20-inch-diameter hub~s w~ere motunted otn a heavy du~t, 0.75ton truck (differential with a gear redu~ction ratio of 4.5:1. Paddles w~ere 12-inches-long and made of 6-inch-wide x 1.5-inch-deep channel iron. Thte paddles wer e welded oni each hub in six rows of fouir p)addles per~ roxx. Each p~add~le in a row was 900 apart on the circumference of the huhl. In the first row, the first paddle w\as weldedl at (0 ° (360°) on the circumference of the luhl. In the secondl rowx, the first by loulse Mlanuftacturing (Co., FIG. 9. House Manufacturing tractor-powered paddle wheel aerator. 22 ALABAMA AGRICULTURAL EXPERIMENT STATION paddle was welded at 15° . For the third row, the first paddle was welded at 30 ° . The procedure was continued for all six rows to provide a spiral arrangement of paddles. A drive shaft was connected to the differential and fitted at the other end with a PTO shaft. In tests, the paddle tips were submerged to a depth of 9.88 inches and rotated at 110 r.p.m. with a 65-horsepower tractor. The House Manufacturing Co. paddle wheel aerator had a SOTR of 65.7 pounds of oxygen per hour, table 2. Comparison of Tractor-Powered Aerators Values for SOTR are summarized in table 2. Standard errors of the mean provided for SOTR values reveal that good precision was achieved in oxygen-transfer tests. The highest SOTR was obtained for the Water Blower, but this aerator required a 200-horsepower tractor to drive it. Tractor sizes for other aerators were similar (50 to 80 horsepower). Of the three paddle wheel aerators, one had paddles of channel iron (rectangular in cross section), one had paddles concave in cross section, and one had flat paddles. All three paddle wheel aerators were powered by the same 65-horsepower tractor. The aerator with channel iron paddles had the highest SOTR value; the paddle wheel aerator with concave paddles was superior to the one with flat paddles. The Airmaster aerator had a SOTR comparable to the paddle wheel aerator with flat paddles; however, other pump sprayer and squirrel cage aerators powered by 50- and 65-horsepower tractors had lower SOTR values than paddle wheel aerators. Busch et al. (9) tested a few tractor-powered aerators, and they also found paddle wheel aerators to have greater SOTR values than pump sprayer aerators. However, the Airmaster aerator, a pump sprayer, was equally as effective in transferring oxygen, table 2. In addition, it directs water in two directions along the shoreline. During oxygendepletions, fish.often congregate in shallow water along pond edges. The Big John aerator does not require a lot of power; it can be operated with a 35-horsepower tractor. It transfers enough oxygen to make it useful in aerating small ponds (1 to 5 acres). An attachment for the Big John aerator permits it to be used effectively in applying chemicals to fish ponds. Gears in the differential of paddle wheel aerators serve to reduce the speed of the tractor PTO, and these gears are the major maintenance problem with paddle wheel aerators. The pump of pump sprayer aerators is driven directly by the tractor PTO and gear reduction is unnecessary. Therefore, pump sprayer aerators require CATFISH POND AERATORS 23 less maintenance than paddle wheel aerators. In addition, the sprayer device may be removed from most pump sprayer aerators, and the pump used for pumping water. These desirable features should spur efforts to develop more efficient pump sprayer aerators. ELECTRIC AERATORS Electric aerators included paddle wheel, vertical pump, pump sprayer, propeller aspirator pump, and diffuser aerators. A paddle wheel aerator splashes water into the air as the paddle wheel rotates. A vertical pump aerator consists of a motor with an impeller (propeller) attached to its shaft. The impeller jets water into the air without imparting much velocity to the water. A pump sprayer aerator employs a centrifugal pump to spray water at high velocity through holes in a manifold and into the air. A propeller aspirator pump aerator uses the venturi principle to introduce air bubbles into turbulent water created by an uncased impeller. A diffuser aerator discharges fine bubbles of air into the water near the pond bottom. Paddle Wheel Aerators House Manufacturing - This aerator, figure 10, was fabricated by House Manufacturing Co., Cherry Valley, Arkansas. It had a 12-footlong hub. The hub was 8.62 inches in diameter and each end was fitted with a short, 2.25-inch-diameter shaft. Paddles were 14 inches long and 6 inches wide and were triangular (120 ° ) in cross section. There were four paddles welded 90 ° apart in each row around the circumference of the hub making 24 rows of paddles. The paddles were spiralled on the hub; the first paddle in each row was offset 200 from adjacent paddles to produce the spiral. A spiral paddle arrangement is illustrated in figure 11. The paddle wheel was mounted in take-up bearings, and bearings were mounted on a metal frame. The metal frame was attached to metal boxes filled with styrofoam to provide floatation. The 10-horsepower, 230/460-volt, 3-phase electric motor was connected to a gear reducer by a belt drive. The gear reducer output shaft was attached to the aerator shaft with a flexible coupling. The aerator was operated at 84 r.p.m.. and at three paddle depths: 3.25, 3.62, and 4.0 inches. The motor was fully loaded at a paddle depth of 3.62 inches, table 3. At a paddle depth of 3.62 inches, SOTR and SAE were 48.1 pounds of oxygen per hour and 4.8 pounds of oxygen per horsepower-hour, respectively. Geddie's Machine and Repair Shop - The aerator, which was manufactured by Geddie's Machine and Repair Shop, Hollandale, Mississippi, had a 12-foot-long x 8-inch-diameter hub which had TABLE 3. PERFORMANCE DATA ON FLOATING ELECTRIC PADDLE WHEEL AERATORS TESTED Design FeaturesPw Power at 3 Operating Costs SAE' aerator SOTR' HubPoe Per hr. Per lb. 0, Legh Diameter Speed Depth Consumption shaft H~I '. I P I\l~ ~IYlnlul .r. I Int r\ lu I-I .~ Ilu~r-11.1 111\I r\lllll.l r r\l .~ .I . . lhp Lb.0/hr. Lb. O2hp-hr. Dol. r,p.mi. Kw Dol. In. Ft. In. 9.04 9.12 38.3 ± 1.4 0.018 3.25 4.2 0.68 36 84 12 House 3.62 9.44 .015 4.8 .71 36 84 0.2 10.0 12 .015 10.58 4.5 .79 4.0 11.4 4.0 36 84 12 .61 .015 4.25 8.18 9.2 41.4 ± 0.1 4.5 32 12 89 Geddie 2.75 108 22.4 ± 0.2 3.5 .42 .019 37 5.61 6.4 10 Dan .015 67 4.0 7.76 8.6 39.9 ± 1.1 4.6 .58 36 12 Martar 10.0 1.6 4.4 .71 .016 78 4.0 9.46 12 36 .014 37.5 7.5 83 8.60 8.55 42.0 ± 1.5 4.9 .60 10.5 S and N .107 5.5 4.2 .60 10.5 37.5 98 8.62 8.55 36.3 -± 1.6 .020 120 3.0 .59 37.5 29.6 ± 2.5 3.5 8.41 8.40 10.5 .035 2.3 .71 32 150 6.0 9.43 9.00 20.5 -± 1.1 Beaver Tail 4.0 .042 190 16.7 ±! 1.3 1.8 .70 32 3.0 9.70 9.30 4.0 .033 2.2 .54 34 78 7.15 7.5 16.5 ± 1.2 8.0 Rogers 6 110 9.83 .038 6.0 -1.9 .74 46 10.0 19.4 ± 1.0 4 Spree .030 3.5 .16 24 109 2.09 2.0 5.4 ± 0.2 2.7 Fritz 2 .73 .026 28.4 ± 0.5 2.8 32 105 9.69 10.0 8.0 AEMCO, PVC 10 0.2 2.0 .71 .036 4.5 9.48 10.0 32 110 15 .022 110 3.5 32 7.85 7.5 26.5 ± 0.7 3.5 .59 1(1 15 AEMCOSteel 12 32 .016 79 4.5 9.18 43.1 -} 0.9 4.9 .69 8.8 'Standard oxygen transfer rate. 'Standard aeration efficiency; SOTR dlivided by power applied to aerator shaft. 'Based on electricity cost of $0. 075 per kilowatt-hour. Demand changes for electricity were not used in computing operating costs in any aerator test. Aerator 48.1 51.3 44.4 20.0± CATFISH POND AERATORS 25 rrr F 't*j j/ r~ £ ; a;: if FIG. 10. House Manufacturing electric paddle wheel aerator. FIG. 11.Spiral arrangement of paddles on hub. 26 ALABAMA AGRICULTURAL EXPERIMENT STATION 12. s1ho rt , 1.5- inch-diamneter shafts at (each end, figurei Paddles we re 12 inches long x 4.75 inches wXide and triangular (1200) in cross sectio)n. Padd(les wxere weldedl 900 apart in each row around the lul; there wXere 23 rows. Each of the fouir lines ol paddles wXas spiralled silightl. The p'fadd1le wheel wxas supported in lbearings mounted 01n a metal f ame. Fiberglass boxes prov ided flotation. The imotor wxas a 10liorsep)owXer, 2:30/460-v olt. 3-phase gearmotor. Padd~le whl~ speed w~as S9 r.1p.m., andl p~addle silergence was 4.25 inches. The' motor was sl ighlyi under loaded (9.2 horsepower). SOTI1 and SAXL v aluies were 41.4 p)olilds of oxygen~ per hour and 4.5 pounds of o\xygen per' horsepower-hour. respectiv el, table .3. D~an's Nicehanics - This aerator, figure 13, wXas produced by lban's lrgaii Cit, MIiss issipp~i. The aerator hub1 w~as 10 feet Mechanics, Xas long< anl 6.7.5 inches in diamueter. The hub11 w~elded to at 1.755-inchore 15 inches (ha u'eter sh af't Xwhichi ran tlhrough the lubl. P~addles we loi g and~ trapezoidlal in cross section. The trapezoidlal section was 4.25 inches wXide across the open face and :3.5 inches wXidIe across the hack of the paddle: it wXas 1.2.5 inches dleep. There wXere' our paddl~les prrowX (90° apart) and 24 rowXs of paddles. Each line of' paddles dppd 900 to the id~dle of the huib and then rose 90° to the other end1( prov ide a chex ion-shaped paddle arrangement. figure 1:3. The to aerator wXas supp)1ortedl in bearings 1111mted on a metal f'ainc. Flotat ion was prov idled by water-tight metal b~oxes. The 10)-horsepower, FIG. 12. Geddie's Machine and Repair Shop electric paddle wheel aerator. CATFISH POND AERATORS FIG. 13. Dan's Mechanics electric paddle wheel aerator. 230/ 460-v olt, 3-phase gearwiotor wxas connectedI to the aerator shaft wxith a flexible coupling. P~addle wxheel speed was 108 r.p. mn., and the paddle subm)Ifergence dlepthl wxas 2.75 inches. [he padd~le d1epth wxas not stufficient to properly loadl the motor at a paddle wheel speed ol 108 r. p. mn.Power appliedl to the aerator shaft was estimated at 6.4 horsepower, tab~le 3. Values for SO TN and SAE were 22.4 pounds of ox\ gen per hour and 3.5 pounds of oxy gen pcr lh)rse1)ower-ho)Ir, resp~ect ivel. Nltartar - TIhe aerator, figure 14, was huilt b\x Nartar Brothers, Lake Village, Arkansas. The hub xwas 12 feet long and 8 inches in diamneter wxith 1.5.-inch-(lialneter shafts at each end(. Paddles xwere 14 inches long, 5.5 inches xwide, and triangular ( 127°) in cross section. There xwere four p~addlles p~er roxw (90° apart) and 23 roxws. Each line of paddles wxas spiralledl slightly from each end( to the middle of' the 1l111 to p~roducL' a chexvron-shapedI p)addle arrangement. Thie mtetal aerator supp)lort frame xxas attachedl to stx rofoam floats. One end of 28 ALABAMA AGRICULTURAL EXPERIMENT STATION FIG. 14. Martar electric paddle wheel aerator. the paddle wheel wxas sulported Iby a b~eariilg. The other end was flange mounted to the spindle of a finial (irive from a John D~eere comnb~ine. The finial drlive servedi as a gear reduceer. The 10-horsepowver, 2:30/460 volt, 3-phlase motor was eonnectedl to the final (Irive wxith lbelts. The paddle wheel wxas operated at a paddle dlepthl of' 4 ielhes and at 67 or 78 r.p.lin. A greater SOTli (44.4 pounds of'oxx gen per hour) load was ob~tained for 78 r.p. lin., and the motor operated near 11111 at this paddle wxheel speed, table :3. \'alimes fin- SAE were 4.6 pounids5 of' o\\ gemi per horsepowxer-hour at 67 r.p. mu. and 4.4 pounds of oxygen per horsepower-hour at 78 r.p.lin. S and N Sprayer - 11e aerator, figure 15, wxas construceted by the S and N Sprayer Coh., G;reenwood, Mississippi. The huh wxas 10.5 feet long and 8 inches in dijamneter. Paddles, figure 16, were pr'essedc from inehes wvide and of polygonal cross-seetion. sheet metal. T'hex wxere ~3 Tips wxere flat anid 1bent at a 22.5so angle. Paddles xx ere either 10.7.5 or 1:3. 75 inches long. I Iene, maximum paddle wheel diameter wxas :37 5 inches. Paddles wvere .weldel to the huh wvith four p~add~les 9f0° apart ini each r'ow around the hubl eireumferemmee. Padd~les ini adjaen t rows wxere welded on 4.5-inch centers. Progressing fr-om one end of, the were attached 1.02 inehes furhi11l) other, padldles in each i'oxw to the ther' around the c'imrcumf erenee of' tim huhi in the same dlimrection of' motation to produce a spiral. Paddles wxere attached in altei'mating i'ows of' long (1 3 .7'5 inches) and short (10.75 inches) p)addcles. A short, 1.5- CATFISH POND AERATORS 29 kwhBE tn,~ FIG. 15. S and N Sprayer electric paddle wheel aerator. inch-diameter shaft at the outside eud of the hul fit into a pillow Ilock bearing. The bearing was inouiited to a 2-inch-square tllbing frame. A 1.75-inch-diameter shaft was mounted on the chive end of the huh and attached directly to the gear reducer. The gear reducer was colnnectedI by lelt drive to a 10-horsepower, 3-phase, 230/460 volt, electric motor. The metal frame was attaehed at each end to 8foot-long by 29-inch-diameter aluminum tanks. Attachment was with rods through holes which permitted the frame to lbe raisedl or lowered with turlbuckles. Thus, paddle depth could lbe regulated. Tests were conducted at three paddle wheel speeds: 83, 98, and 120 r. p. In. At these speeds, paddle depths for long paddlles were 7.5, 5.5, and 3.0 inches, respectivel. The greatest SOTR (42.0 pounds of oxygen per hour) and SAE (4.9 poullds of oxygen per horsepowerhour) were achieved when the paddle wheel was rotated at 8:3 r.p.m. with 7.5-inch paddle depth, talble 3. Rogers - The aerator depicted in figure 17 was con structed by Willie Rogers, Ralph, Alabama. The aerator huh was 6 feet long and 8.5 inches inldiameter. The hub was fitted with 1.5-inch-diameter shafts. Paddles were of angle iron which was 2.75 inches wide across the open face; they were 12.75-inches long. There were three paddles 30 30 ALABAMA ALABAMA AGRICULTRLEPIMNSAIO AGRICULTURAL EXPERIMENT STATION FRONT .A .8" IESIDE . c 1.8 CROSS SECTION FIG. 16. Long paddle for S and N Sprayer aerator. per row, so paddles were 120° apart around the circumference of the hub, making 25 rows. Each line of paddles was spiralled slightly The motor was 75-horsepower, 220-volt, and single-phase; it was connected to the gear reducer unit by belts. The gear reducer was joined directly to the aerator shaft. Bearings which supported the paddle wheel were attached to an angle iron frame which was positioned on styrofoam floats. Paddle depth was 8 inches, and the paddle wheel speed was 78 r. p.m. SOTR and SAE were 16.5 pounds of oxygen per hour and 2.2 pounds of oxygen per horsepower-hour, respectively, table 3. CATFISH POND AERATORS FIG. 17 Rogers electric paddle wheel aerator. Spree Aerator - Thed Spree of Boligee, Alabama, fab~ricated the aerato~r shown in figure 18. The aerator was constructed from a truck dIiferential and axles attached to an angle iron frame and floated with stx roloam blocks. Hubs, each 2 feet long and( 16 inches in diameter, we re attached to the axles. Paddles were of angle iron (interior angle of 1620) which was 6 inches wide across the open face and 15 inches long. There were four paddles per row (900 ap1art) andl 4 rows of pad(lies pe hub in a staggered arrangement. The 10-horsepower, 220 volt, single-phase imotor was connlectedl by a b~elt dIrive to the (lifferential (drive shaft. Paddle dlepth was 6 inches, andl paddle wheel sp~eed xvas 110 r. p. in. Respective xvaluies for SOTR and SAE were 19.4 pounds of oxygen per hour andl 1.9 pounds of oxy gen per horsepower-hour, talble :3. 32 ALABAMA AGRICULTURAL EXPERIMENT STATION IT o~ree electric paddle wheel aerator. Beaver Tail - This aerator wxas manuflactulred by the Beaxver Tail MIanufacturting (Co., Selina, Alabama. An Impala Chexvrolet differential wxith a :3:1 sp~eedl reduction ratio was attachedl to an angle iron frame wxhich restedl on stx rofoam floats, figure 19. 1Hubs (20 inches in dliamneter by 24 inches long) wxere attachled to the axles of the dliflerential. Six, 24-inch-wxide by 6-inch-long p)adles wxere wvelded to each huh11 to form twxo, 24-inch-long by 32-inch-dliamcter paddle wxheels. A drixve shaft from the dliflerential wxas belt dIriv en bx a 10-horsepowver, single-p)hase, 220-volt motor. The paddle wxheel aerator wxas tested at twxo operating conditions: 190 r.p.mi. and 3-inch paddle dlepth or 150) r. p. in. and 6-inch paddle depth. Best results wxere achiev ed at 130 r.p.m. (SOTR 20.5 p~oundls of oxygen per hour: SAE =2.:3 p~ounds( of' oxy gen per horsepowxer-hour), tab~le 3. Fritz - This aerator xvas sold in the United States by Fritz Chemical Co., Dallas, Texas, buit it wxas manufactuired by the Nan Rong Fishing CATFISH POND AERATORS 33 FIG. 19. Beaver Tail electric paddle wheel aerator. Machinery Co., Tainan Hsiang, "Tiwxan. Brief description of the aerator, figure 20, is dihfiut. It consisted of for- plastic paddle wheels mouintedl two each on two stainless steel shafts. Each paddle wheel was 24 inches in diamneter and was compLrisedl of fonir, 6-inch-wide, flat paddles. The 2-horsepower, 110/220 v olt, single-phase mohtor was coupled to at gear redulcer wxhich, in turn, wxas coupled to the shafts. Paddle wxheels rotated at 109 . p.mi. with at paddle tip subm)Iergence of :3.5 inches. The F'ritz aerator had an SOTH of .5.4 p)oundsI of oxygen per hour and an SAE of 2.7 p)ounds( of oxygen per horsepower-hour,; tab~le .3. 34 ALABAMA AGRICULTURAL EXPERIMENT STATION 11 FIG. 20. Fritz electric paddle wheel aerator. AEMCO) - This un~i(IIe aerator, figure 21, wvas Inanhlfacturedl by the A(itacu ltural En gineering and MIarnufctuiring Co., G reenwoo00(, MIississippi. The 11111 consistedI of' PVC pipe (10) inchies in (diamneter). Short shafts wvere attachled to flanges, and a flange and shaft were p)ressedl into each end of the pipe andl seculred1 %vith1)o1ts. Paddles consistedl of 3..5-inch dliamneter PV\C pipe (32 inches long) which had been cut longitudinally and at an angle oni each end. Paddles were insertedl through holes in the hull andl secured xx ith pop riv ets. Cunt endls of the pipes serv ed as paddles. Paddles spiralled slightly around the lubl. '111c foatation assemly was fabricated h-or fib~erglass and filled wxith foam . The iniotor wxas a 230/460) volt, 3-phase, (gearn otor. Three aerators we rc testedl. One had a 10-h1orsepoxxer motor andl a 10foot-long 1mb wvith 66 paddles; rotation speed wxas 10.5 r. p. m. wxitlh a paddle depth of' 8 inches. The other twxo aerators had 1.5-fot-long hubhs with 98 padd~les. Both aerators had paddle wheel speeds of' 110o n.p). tin. b~ut one had a 7. 5-horsepowxer motor and the other had a 10horsepoxxer mnotor-; paddle depths were 3 inches and 4.5 inches, respectivecl. CATFISH POND AERATORS 35 FIG. 21. AEMCO plastic (PVC) electric paddle wiiee aerator. Rest results (SOTR =26.5 pounds of o\\ geii p)er hour, SAE :3.5 pounds of oxy gen per horsepower('-hour) were achiev ed with the 1.5foot-long PV\C paddle wxheel operated at :3.5-inceh paddlie depth and 110 r.p. m., table 3, lbut ia I. fot hng PV C paddle wheel is imnpractical. The l0-f0ot-long PV C paddle wheel had art SOTR of 28.-4 po01nds1 of oxy gen per hou r and ant SAE of 2.8 potunds of oxx gen per ho rseSince these tests were ru n, AM L( has startedl manufaceturiutg a \l paddle wxheel aerator wi~th atsteel hu b and p)add~les. The paddle wxheel is sim ilar to the one illuistratedl in fi gure 11. Values lot- SO TR and SA E wxere 43.1 pounds of ox\-geut per hour- and 4.9 pounds of oxy gen per horsepower1-hour, resp~ect ivel. H ence, the AFB \C( aerator wxith E steel paddle wXheel is htighlix efficient. Vertical Pump Aerators Air-o-later - This aerator, figu re 22, is mnanuifact ured1 b\ Air-ou-later CoprtoKansias Cit, MIissoui. The sublmnersib le notor and11 impeller wxere attached in the center of'a hole wxithtin ia molded pol\ sty rene float. A (diffuiser xx as mouuntedl ab~ove( the imotor and impeller assem l. The impeller tumrnued at 3,450 in.p. in. and jettedl water through the( hole in the float and the dliffuser produced at circular dlisclharge p)at tern. TIhe Air-o-later is ax ailable in 0.:3:3 and 1.0-horsepoxxer sizes; tests xxere muade for- a 0.33-horsepoxxer uniit. The 0.33-horsepoxwer units haxe 110-xolt, single-phase motors. Values for SOTB and SAE wxxere 0.7 pound of' o\xgen per hour and 2.2 pounds of o\ygeni per horsepower-hur, respeti'e, table 4. ALABAMA AGRICULTURAL EXPERIMENT STATION FIG. 22. Air-o-later vertical pump aerator. nm;_ H~r~c i Hrill iu ')iii lAriX lili', ii',l Aera.toii cnup Power i Po~ccXaIt artor S(OT13R I' Lb. 0,/Il) lit. 2.2 2.3 2.2 2.-1.SO) 2.5 19 1.I2 Opcirating Dol. (11)25 .11 cost',t Kir Xir-o-lt r Otcb .. .... lip 0.33 I 2.0 :3.0 1().() 0.75 1175 210 ri',. . * 11:3 t S6 2.79 UIer. .. . .. IceUii . Vae .. I )ouihd. . . Rogers . . . .. 1 ..71) .(is 195 (0.1 16 1)2 6.G- 0I.3 24. I~ 0.9'L9 '0.1 I 1. 01 1 1. 0.7 (.1 lr. )){i (..036 0)30 .21 .05 .05 2. .15 (132 .033 .026 .03)6 .)62 Stanidard oI i' 'u trsi Otterbine - The O)tterbine, manulfacturedI byX odale hesouirces, '.Iiinaiis, Pennllsylvan) ia, conlsisted (If at 5!llnilrsihl ini otor anim fpeller mounllited in at dlollt-shaped plastic float, figure 2:3. 'N( dliffuser' Xater simly jetted into)thle air'. O)tterbilic aerators are l. wXas u sed, adi w iiialulfactlre(I in) severasl sizes; 2 and~ .3-horWsepower units werte testedi. liw 2-horsepowxer unit had at 110/120-vo(lt sinlgle-p)hase motor. The 3- hoIrsepowXer unit hadl a 2;30/460 vo(lit. 3-phase mol~to. MIotors operatedi at 1, 7()0Ir. p. 11. The effiiec of' the 2- and :3-horsepowxer ()tterhine aerators wxas essentially tihe same (2.2 and 2.3 poundts (of'oxy gen per hiouin). Of' eou rse, S(T )IIwas gr'eater' for' tihe 3-hor)isepowerI aer'ator, table 4. Power H-ouse - 1111 Powe''Ilot sc.' Baltimore, M ary landt or'ltinally fX prodluced~ tiis dev ice, figu re 24, as a (deicer for bo at hou sts. It eon- sisted (If a 0. 75-lliwsepower(1 subinersible, 110/220 Xv(lit, single-phase, ;3,400 r. p.mi. inotor aind plastic im~peller' uiioliiitte inside ia plastic' plastic' floatationi unit. shrloud. lTe slhroudi wXas imonttedi insidle at CATFISH POND AERATORS 37 FIG. 23. Otterbine vertical pump aerator. Water wxas jettedl into the air and no diflulser wxas used. The Powxer House had a SOTR of 1.9 pounds of ox\ gen per hour and(a SAE of 2.5 pounds(I of oxyge ~er horsepower-hour, tab~le 4. Dyer - This aerator, figure 25, wxas Mnanufactoired lxy Dyxer WVell and Irrigation Service, Greenwoo00(, Mississippi. The 10-horsepowver, 230/460) volt, 3-phase motor wvas anoitntedl ab~ove the floatation sy stem wxhich con sistedl of a sqluare frame mnade of 10-inch dliameter PV'C pipe. The motor was positioned ab~ove a cone-shaped dilluser and a 10-inch-diameter aluujinuin pip~e extended 2 feet b~elowv the wxater leveli to the pump bowl s. The motor shaft extendecd to the pump bl)v and the impeller was an 8.5-inch-diameter, 1.3-pitch propeller. hnIpeller speed~ wxas 1, 750 r. p.ma. 38 ALABAMA AGRICULTURAL EXPERIMENT STATION k d a1 (4~a~ ' 1 r 'l n"" ,I 4 Fi FIG. 24. Power House vertical pump aerator. CATFISH POND AERATORS 39 The I)\er aerator had a SOTRi of 24.0 p)ounds of oxy gen per hour and an SAE of 2.4 p~oundcs of oxy gen per horsepower-hour, tah~le 2. Rogers - 'Ihis aerator, figure 26, was built byV Willie Rogers, Ralph, Alabama. The 2-horsepowver, 110/220 volt, single-phase motor was supported by a metal framne wxhich was attached to and extended ab~ove the sty rofoam float. A shaft connected the p~ropeller to the outpunt shaft of the motor which turned the propeller at 3,400 r.p. in. This aerator had SOTR and SAE v alues of2. 4 pounds of oxy gen per hour and 1.2 pounds of oxy gen per horsepower-hor, respectivel, tale 4. FIG. 25. Dyer vertical pump aerator. 40 ALABAMA AGRICULTURAL EXPERIMENT STATION M~clonald - The MlcIonald Co)., Erin, Tennessee, mnainufct i red this acirator (no) fpictii avdailab~le ). It consisted of, a 110-volt, singlep)hase, 0. T.3horsefpow\er, :3,450)r. p. in. mo~tor mounlifted ab)o\ a h ousing of 'C pip~e. \\ater intake slots wer crc(lt in~ the housing. Theu impci hr was fhtted in to theI housing and at tach ed to the motor shalt.A 2-inch-diameter PV\C discharge pipe fr-om tihe 1ottom of the housing exteilded ab~out 1 foot abov.e the w'.ater su rface. The aerator was iixxlmte(I on a sh. rofoam float. The diev.ice simply spray ed w5ater inito the ai. Resp~ectivec SO TB and SAE valoes wwerc 1.4 pounds of oxygeni per hour and 1.9 pounds of o\\ gen per horscpowser hour, tab~le 4. , * f FIG. 26. Rogers vertical pump aerator. CATFISH POND AERATORS Pump Sprax er Aerators 55 Airmaster stemos, Inc., (rcenx Thec aerator, figure 27 wxas mfanulfacturedl by Master00(, MIississipp1i. Thie aerator wxas essenitially the same as the trailer-munted, tractor-powe'red kiru aster aerator (described tinder tractor-powxeredi aerators) excep~t that thme pump and Manifold were mouitted on floats andi the pump powxered by at 10horsepower, 23() 460 xolt, 3-phase electric motor. Thme pump shaft wNas connected to thme motor output shaft by p~ulleys an b0llelts. TIhe pm p had at 16-inch-dliamneter b)\ 4-inch-wxidle (lou ble intake impeller that was rotatedI at 582 i-.p. m. Thme 10-inch-dliamneter discharge mnanifi)Id1 had onec 6-inch-diameter hole in each end and four rows of (lischarge ports along the top). lihe Ai ri iaster had at SO )T11 of :32.0 pounds of oxygen per hou r and at SAE, of 3.2 potuinds o oxge pe horsepow\er-houir, talie 5. Water Miaster - TIhis aerator, figure 28, wxas fab~ricatedl by tihe I rrigatiton Ito jt mniit Co. , Inrdianiola, MIissi ssippIi . A 20-h orsepowxer, 2:30/16() slt. :3-phase muotor and deep wxell tuirbinie pumpit \xere inserted into a 10-inch(1-dialimeter sect ion of P~VC pipe. O ne end of the pip)e wxas fittedl wxith ia screen andl the other end wxas fitted with at 4,5° Twi .5. I'imtu~\N i Irrr ~FJutOP'mt I~m I0Mm 5m~r~vI;ii \mixuh i;,"Maria Xittmastem .. .. SN I latcr ... atc, Ilo .... Kit' 7. 15. 59 l) 10I.U1 16.3 30.0 Lb.(I Iii 32 U( ± 2.2 ± 39.--S 21 Lb. (1) -r :32U 1.(i 1. I.s Ip 05; I. 1i 1.12 ~ Ool).1 U)()I5 OM Ut 1ti 'Basedt ton clecit'i t cost of S0. (15 per kilowt t-hour.il FIG. 27. Airmaster pump sprayer aerator. ALABAMA AGRICULTURAL EXPERIMENT STATION ellbowx and a short piece of pip~e wxas insertedl inlto the elbow. A teeshaped manifold wxas attaced(to the short piece of pipe. The maifold was drilled with 18, 1-inch-diameter holes. The entire dev ice comp~rised the pump spraver; and it was suspended by\ brackets from two, cappLed1, 10-inch-diameter PVC pipes xvhich serv ed as floats. When placed in the water, the manifo~ld extendled a fewx inches above the surface. In operation, the puimp forced water through the holes in the manifold. The pump wvas ratedl at 1,400 g. p. in. at 4.5 iot-head, hut the actual dlischarge of the aerator cold not b~e calculated because the head was not known. Because the aerator wxas large, it had a high SOTR, but its efficiency xwas lowv (SAEF 1.6 pounds of oxygen per horsepowxer-hour), tab~le 5. 11 I -4- FIG. 28. Water Master electric pump sprayer aerator. CATFISH POND AERATORS 1-ouse - This floating pump sprayer aerator, figure 29, wxas fabrihaedb House Mlanuifacturing Co., Cherry Vally rass h centrifugal p)Lmp~ had an 18-inch-diameter impeller, and it was driv en by a 20-horsepowxer, 230/460-volt, 3-phase motor. 'Water was discharged through two, 10-inch-diameter, galvanized iron p~ipe~s. Each pip~e was capped, andI each cap contained a 4. 5-inch (liameter outlet hole. Tw enty-eight 0.125-inch slits were cut halfway through the p)ipes. The pump was rated at 3,400 g. p. in. at 14-foot head, butt the actual aerator discharge could not be calclated. The pump sprayer assemly wxas mnounted on stx rot oain floats. This aerator also had a high SOTR (29.8 pounds(l of oxy gen per hour), but the SAE of 1.5 p)oundls of oxygen per horsepjower-hoiur was low, tale 5. FIG. 29. House electric pump sprayer aerator. ALABAMA AGRICULTURAL EXPERIMENT STATION Propeller Aspirator Pump Aerators Aeration Indulst ries, (Chaska, MIin nesota, mnatiettlrd the Airc0,aerators, figutre 30. Tihe prilnr\ aerator parts wXere a mo to r, a hiollow shaft wXhich rotatedl at 3,45(0 r.p.n. a hollowx houisiiig inside wxhiech the rotating shaft fit, and an impeller wXhieb wXas attached at the (11( of tihe rotat in g shaft. Aerators wXere suipported on pontoons or P~VC fhoats wXith tihe mvotor albove thle wXater su1rface. In operat ion the ipeller acceleratedl the wXater' to a X eloei ty high e' nugh to cause at dIrop in pressure within the hIollow, rotating shaft. Air wXas fored~ dIownI the hollowX shaft byatosphieric pressuire and fine ICbu11ble5 enrAer ators wijth less teredl the turb l)In t wXater around1( the inll)llen than 2-horsepow er i iotors operated oil I10-volt, single-phase powXer. Larger aerators hiad 2:30/46(0 volt, 3-phase imotoirs. * Aerators ranlginig in size from 0.1253 to 20-horsepowXer had SAE v allies of 2.1 to :3.1 pounds(1 of o\\ gen per horsepower-hiour,~ talble 6i; and the average Ski'. wXas 2.6 pounds of' oxx gein per horsepow~er-hour. SO )TR iinereased wX aerator horsepowxer and rangedl from 0.26 to ith 533.9 p)oundI(s oi'oxvgen per hour. r S FIG. 30. Aire-OZ propeller aspirator pump aerators. CATFISH POND AERATORS 45 TABLE 6. PERFORMANCE DATA ON PROPELLER ASPIRATOR PUMP (AIRE-0 2) AERATORS TESTED Power at aerator shaft, hp SOTR' Lb. 02/hr. 0.26 ± 0.02 0.65 ± 0.07 1.4 ± 0.1 2.2 ± 0.2 5.6 ± 0.1 9.3 + 0.4 11.0 + 0.7 21.8 ± 2.1 23.2 + 1.1 45.1 + 3.1 53.9 + 2.5 SAE 2 3 Operating costs Per hr. Dol. 0.009 .017 .035 .07 .14 .21 .35 .52 .70 1.05 1.40 Per lb. 02 Dol. 0.035 0.125............ .026 0.25 ............. .025 0.5 .............. .032 1.0 .............. .025 2.0 .............. .023 3.0 .............. .032 5.0 .............. .024 7.5.............. .030 10.0.............. .023 15.0.............. .026 20.0 .............. 'Standard oxygen transfer rate. 2Standard aeration efficiency; SOTR divided by power applied to aerator shaft. 3Based on electricity cost of $0.075 per kilowatt-hour. Lb. O0/hp-hr. 2.1 2.6 2.8 2.2 2.8 3.1 2.2 2.9 2.3 3.0 2.7 Diffuser Aerators Hinde - Hinde Engineering, Highland Park, Illinois, fabricated this diffuser aerator (no picture available). It consisted of a 0.75horsepower low pressure blower to force air through tubing that had 0.5-inch-long slits at 18-inch intervals along its top side. A lead filled keel on the bottom of the tubing prevented the tubing from floating. Air was released through four, 29-foot-long lines of tubing at the bottom of the aeration tank. Air flowed into the tubing at 3 square feet per minute and 3 pounds per square inch of pressure. Water depth in the tank was 47 inches. Values for SOTR and SAE were 1.4 pounds of oxygen per hour and 1.9 pounds of oxygen per horsepower-hour, respectively, table 7. Microshear - This prototype aeration system was produced by Aeras Water Resources, Eden Prairie, Minnesota. The system, figure 31, was quite complex. It employed an air diffuser nozzle to inject air through an exchange surface into a high velocity stream of water. Converging venturi action reduced water pressure and film forces for TABLE 7. PERFORMANCE DATA FOR DIFFUSER AERATORS TESTED 3 Aerator Power SOTR' SAE 2 Operating costs o Per lb. Per hr. Dol. Dol. hp Lb. 02/hr. Lb. 02/hp-hr. 0.036 0.05 1.9 1.4 + 0.1 0.75 Hinde ............ .050 .12 1.7 2.4 + 0.2 1.7 Microshear ........ 'Standard oxygen transfer rate. "Standard aeration efficiency; SOTR divided by power applied to aerator shaft. 3Based on electricity cost of $0.075 per kilowatt-hour. 46 ALABAMA AGRICULTURAL EXPERIMENT STATION FIG. 31. Microshear diffuser aerator. bubb)lle form ation andc 1 )eiilitted air to pass from tihe injecto)r in the torm ofa high v'oluime stream of sllearedl mierolbiiib1le',. The full-scale sys5temi empl)oyedl a 10-horsepowxer, 2:30-volt, 3-phase motor to powe\r the air supp)ly (Hoots Universal HAl Blowxer, 150 cuic~ feet per udnmte) and wxater siipple (Hyxpro MIodcl 920:30 Centrifiigal Pump, 125 g. p.mi.). The dev ice was monolitedI on a floatinig fiberglass platform. Air was in jectedl through si\ nozles that were 1 foot apart and ab ott 1.5 fe~et belowv the water surface. O)'xygen-transfer tests wxere conduceted with at sealed-diown model of' the aerator that was rated at 1.7 horsepower(1. Ihe Micjroshear su it produ ced a S()TR of 2.4 pounds oflo\\gemi per hour and a SAE of' 1.4 pounds of oxvx gem per horsepower-hour,; tab~le 7. Since these tests wxere conducted, the M1icroshear aer'ator has been mlodlified. Preimnmarx tests inidicate that thle inew vers~ion of' the Microshmear' aerator' is niucih more efficient than thle pmrototype unait descrilbed ab~ove. Comparison of Electric Aerators D~ata on oxygen transfer (S( )TI and SAE), p~ower reqiredI at tihe aerator shaft, power coinsuimption, and~ operating cost are smininaizcd ini tab~les .3-7. InI tatble S, SAE x aluies airc preseinted for tihe differemnt aeratomr typ1es. Tlhe order' of ineireasing ('flieim te (SA F,) follo ws: diffimser aerators, pump spraver aerators vertical pup aerators, x pr'opeller' aspirator pump11 aerators, aind paddle wheel aerators. O per'atinig cost in dollars per pound of oxy gen decireasedl as ficiemiex increased, tab le 8. IDifhisem' aerators of tenl are lmigly (]hciemit ini aeratimig wxastewxater treatment b~asimns. 'Ihese b~asinls are 10 to :30 fact deep, so thlere is a fairlxy lo~ng contact time be(tweenl rising aimr1) ibubbes amnd wxater (hang CATFISH POND AERATORS 47 TABLE 8. AVERAGES OF STANDARD AERATION EFFICIENCY (SAE) VALUES AND OPERATING r COSTS FOR ELECTRIC AERATORS Type of aerator Average SAE Average operating Paddle wheel .... ............ Propeller aspirator pump ........ Vertical pumps ................. Pump sprayer .................. Diffused air .................... . Lb. Os/hp-hr. 3.5 2.6 2.1 2.1 1.6 Dol. 0.024 .027 .036 .036 .043 time). Fish ponds are seldom more than 5 feet deep, so the hang time for bubbles is much less than in wastewater treatment basins. Therefore, diffuser aerators are less efficient in fish ponds than in wastewater treatment basins, because of insufficient time for absorption of oxygen from the rising bubbles. The tubing of diffuser aerators is easily clogged by sediment and by benthic organisms which encrust the tubing. Furthermore, the tubing obstructs seining operations. One pump sprayer aerator, the Airmaster, had a high SAE, the other two were inefficient because too much energy was spent in accelerating water. For a pump style aerator, the pump should discharge a high volume of water at low or medium head. At high head, discharge is reduced and oxygen transfer efficiency declines. The sprayer is not essential for aeration with a low or medium head pump, but the sprayer improves water circulation. The Airmaster aerator is especially efficient in circulating pond water (13). The Airmaster also is operated by a belt drive without a gear reducer and flexible coupling; hence, it should seldom have mechanical failures. Vertical pump aerators are appealing because of their simplicity. The impeller usually is connected directly to the motor output shaft, eliminating the need for gear reducers. Propeller speeds of 1,750 and 3,450 r.p.m. have been used, but a 1,750 r.p.m. motor is probably the best choice. Motors can be mounted above or below the water surface. Motors mounted above the water surface are easier to service. For maximum oxygen transfer efficiency, the aerator should pump as much water into the air as possible for the rated pump horsepower. Therefore, impeller selection is critical. The height of the water jet is not critical, the pumping rate is much more important. White water (shearing of water) must be produced if a vertical pump aerator is to transfer appreciable oxygen, but once shearing is produced, as much water as possible should be pumped through the shear zone. Formation of a high jet of water wastes energy that could be used more efficiently for pumping. The cone-shaped diffuser on some aerators is useful in developing a nice water discharge pattern. 48 ALABAMA AGRICULTURAL EXPERIMENT STATION Because diffusers are inexpensive, their use is desirable. A number of companies manufacture vertical pump aerators for use in waste water treatment. These aerators typically have SAE rates of 2.5 to 3.5 pounds of oxygen per horsepower-hour (15). Unfortunately, they usually are too expensive for use in fish farming. Small vertical pump aerators are particularly useful for aerating fish ponds of 0.1 to 2 acres which are common on fish hatcheries and research stations. The Power House and Air-o-later aerators are small enough and sufficiently efficient for this task. Propeller aspirator pump aerators (Aire-0 2) have good oxygentransfer efficiencies and excellent water circulation capabilities (6). They are of rugged construction and have low service requirements. Aire-0 2 aerators have been improved by several years of research and development, and the authors can offer no suggestions for improving their performance. This Air-0 2 is available in a variety of sizes, and it should have a wide range of applications in fish culture. Paddle wheel aerators tested in this study covered a wide range of SAE values (1.9 to 4.9 pounds of oxygen per horsepower-hour). Paddle wheel aerators specified as House, Geddie, Martar, and S and N, table 3, were similar in design to the optimum design features for paddle wheel aerators described by Boyd and Ahmad in an unpublished manuscript. These paddle wheel aerators clearly were superior to all other aerators. The aerator produced by Dan's Mechanics, table 3, would be more efficient if the paddle wheel was turned slower and the paddle depth increased. The Beaver Tail aerator had an excessive paddle wheel speed; and the short paddle wheels employed on this aerator lead also to inefficiency. The Fritz paddle wheel aerator was not highly efficient, but it would be suitable for aerating 1- to 2-acre ponds. Aerators designated Rogers and Spree were built by fish farmers for their own use rather than as commercial ventures. Although inefficient, these aerators transfer enough oxygen to be useful. The AMECO PVC paddle wheel aerator was unique. The PVC and fiberglass construction was lightweight, sturdy, and resistant to corrosion. Unfortunately, extensive research on variations in design and operating conditions for PVC paddle wheels (Boyd, Ahmad, and Lafa, unpublished manuscript) suggested that it was not possible to build a PVC paddle wheel that was as efficient as a steel paddle wheel. CATFISH CATFISH POND AERATORS.4 POND AERATORS 49 Electric Paddle Wheel Aerator Design Results of aeration tests suggest that 10- or 12-foot-long paddle wheels with paddles of triangular or polygonal cross section and a total diameter of about 36 inches is a good design. The paddle wheel speed should be 80 to 90 r. p. m. with a paddle depth sufficient to load the motor. Once the speed is selected, the optimum paddle depth can be determined as the depth necessary to draw the rated amperes of the motor. To prolong the service life of the motor, it should only draw 90 percent of its full-load amperes rating. Even though most electric motors have a service factor of 1.10 or 1.15, they will last longer if they are not fully loaded. Shafts of most electric motors used for paddle wheel aerators rotate at 1,750 r.p.m., so some method must be used to reduce the motor speed to the desired aerator shaft speed. Some aerators described above had gearmotors. In a gearmotor, the gear reducer is built onto the motor and the motor output shaft rotates at the desired aerator shaft speed. For other aerators, a separate gear reducer was employed, and a belt drive was used to connect the motor and gear reducer. Also, a flexible coupling should connect the gearmotor or gear reducer output shaft to the aerator shaft. Gearmotors or separate gear reducers are both suitable means of obtaining the desired aerator shaft speed. However, both techniques are expensive. An alternative method of motor speed reduction is to mount a jackshaft on the aerator frame and connect the motor shaft to the jackshaft with a belt. Double or triple cog belt drives are best. By selecting a large pulley for the jackshaft and a small pulley for the motor, the jackshaft speed will be much slower than the motor output shaft speed. The aerator shaft can be driven by the jackshaft with a roller chain. A small sprocket can be mounted on the jackshaft and a large sprocket on the aerator shaft to obtain the desired aerator shaft speed. For example, an aerator shaft speed of 90 r.p.m. may be obtained as follows: 4-inch-diameter pulley on motor, 18.5-inch pulley on jackshaft, 16tooth sprocket on jackshaft, and 70-tooth sprocket on aerator shaft. A thin metal cover over the drive assembly will protect belts, roller chain, and bearings from water. The jackshaft means of achieving the desired aerator shaft speed is less expensive than other methods, because it eliminates the need for a gear reducer (or gearmotor) and flexible coupling. Most electric paddle wheel aerators are mounted on floats, but some fish farmers have used electric motors to power trailer-mounted 50 ALABAMA AGRICULTURAL EXPERIMENT STATION paddle wheel aerators. Such piaddle wheel aerators look like a tractorp~owered padldle wvheel aerator, lbut an electric mo(tor is in untedl on the trailer and( connected to the aerator (Ihive shaft through belts and( pullleys. This eliminates the necessity of-a tractor to power each aerator. Another- variation in paddle wheel aerators is shown in figure 32. This aerator was faIbricated 1by researcher-s at the I)elta Branch Exp)erimnent Station, MIississippi Agricultural and Forestry Experimnt Station, Stoneville, MIississipp1i. 'The paddle wxheel was mioumntedl on floats, but the motor and jackshafts for speed reduction we re anchored on the pond bank. The paddle wheel was driven by a long shaft which was connectedl by universal joints to the jackshaft and the aerator shaft. This is an excellent design; the mnotor, ele'ctrical connections, and~ speed reduction mechanism are easy to serv ice, and they can he better protected from splashing wvater. Further research nmay provide some additional imp~rovemments in paddle wheel aerator perfrmanmce, bult dIrastic imuprov emnents are not exp~ectedl. Efforts to dev elop better floatation devices and more suit- FIG. 32. Paddle wheel aerator with motor and speed reduction assembly on pond bank. CATFISH CATFISH PON.AERATORS.5 POND AERATORS 51 able methods for anchoring and stabilizing paddle wheel aerators could be fruitful. Paddle wheel aerators can create turbidity in ponds, and research on techniques for reducing the potential of paddle wheel aerators to create turbidity is needed. SUMMARY Emergency aerators powered by tractors (65 horsepower or larger) had standard oxygen transfer rates (SOTR) of 17.3 to 162.8 pounds of oxygen per hour. Standard aeration efficiencies (SAE) were not determined for tractor-powered aerators. Several of the emergency aerators were well suited for use in channel catfish farming. Electric aerators (0.33 to 20 horsepower) included paddle wheel aerators, propeller aspirator pump aerators, vertical pump aerators, pump sprayer aerators, and diffused air aerators. Paddle wheel aerators generally were more efficient in transferring oxygen than other types of electric aerators. The best 10-horsepower electric paddle wheel aerators had SOTR values of 38.3 to 51.3 pounds of oxygen per hour and SAE values greater than 4.0 pounds of oxygen per horsepower-hour. Hence, these aerators transferred almost as much oxygen per hour as tractor-powered aerators which required much more energy. Other types of electric aerators had SAE values of 3.2 pounds of oxygen per acre or less, but propeller aspirator pump aerators, one pump sprayer aerator, and some vertical pump aerators were efficient enough for use in fish farming. Aeration efficiency is not the only consideration in selecting aerators. Some fish farmers prefer an aerator that produces strong water currents, and aeration efficiency must be sacrificed to some extent to obtain maximum water circulation. Other factors are initial cost, durability, availability of parts, and service provided by supplier. Many of the aerators described above can be used effectively in fish farming, and one cannot identify one aerator as clearly being superior to all others. As with any piece of equipment, facts must be considered, but the prospective buyer must ultimately decide which aerator he prefers. REFERENCES (1) American Public Health Association, American Water Works Association, Water Pollution Control Federation. 1980. Standard Methods for the Examination of Water and Wastewater, 15 ed. Amer. Pub. Health Assoc., Washington, D.C., 1,134 pp. (2) Armstrong, M.S. and C.E. Boyd. 1982. Oxygen Transfer Calculations for a Tractor-powered Paddlewheel Aerator. Trans. Amer. Fish. Soc. 111:316-366. (3) Boyle, W.C. 1979. Proceedings: Workshop Towards an Oxygen Transfer Standard. EPA-600/9-78-021, Nat. Tech. Information Serv., Springfield, Va. 271 pp. (4) Boyd, C.E. 1982. Water Quality Management for Pond Fish Culture. Elsevier Sci. Pub. Co., Amsterdam. 318 pp. . 1986. A Method for Testing Aerators for Fish Tanks. Prog. Fish(5) Culturist. 48:68-70. and D.J. Martinson. 1984. Evaluation of Propeller-aspirator(6) pump Aerators. Aquaculture 36:283-292. and C.S. Tucker. 1979. Emergency Aeration of Fish Ponds. (7) Trans. Amer. Fish. Soc. 108:297-304. , J.A. Steeby, and E.W. McCoy. 1979. Frequency of Low Dissolved Ox(8) ygen Concentrations in Catfish Ponds. Proc. Ann. Conf. Southeastern Assoc. Fish Wildlife Agencies 33:591-599. (9) Busch, R.L., C.S. Tucker, J.A. Steeby, and J.E. Reames. 1984. An Evaluation of Three Paddlewheel Aerators Used for Emergency Aeration of Channel Catfish Ponds. Aquacultural Eng. 3:59-69. (10) Cole, B.A. and C.E. Boyd. 1986. Feeding Rate, Water Quality, and Channel Catfish Production in Ponds. Prog. Fish-Culturist 48:25-29. (11) Colt, J. 1984. Computation of Dissolved Gas Concentrations in Water as Functions of Temperature, Salinity, and Pressure. Amer. Fish. Soc., Bethesda, Md., Spec. Pub. No. 14, 154 p. (12) Hollerman, W.D. and C.E. Boyd. 1980. Nightly Aeration to Increase Production of Channel Catfish. Trans. Amer. Fish. Soc. 109:446-452. (13) Petrille, J. and C.E. Boyd. 1984. Comparisons of Oxygen-transfer Rates and Water-circulating Capabilities of Emergency Aerators for Fish Ponds. Aquaculture 37:377-386. (14) Plemmons, B. P. 1980. Effects of Aeration and High Stocking Density on Channel Catfish Production. M.S. Thesis, Louisiana State Univ., Baton Rouge, La. 35 pp. (15) Shell, G. 1979. Momentum: Innovative Concept for Surface Aeration. Ind. Wastes, May/June 1979. (16) Shelton, J.L., Jr. and C.E. Boyd. 1983. Correction Factors for Calculating Oxygen-transfer Rates of Pond Aerators. Trans. Amer. Fish. Soc. 112:120122. (17) Strickland, J.D.H. and T.R. Parsons. 1972. A Practical Handbook of Sea Water Analysis, 2nd ed. Fisheries Research Board of Canada, Ottawa, Bull. No. 167. (18) Stuckenburg, J.R, V.N. Wahbeh, and R.E. McKinney. 1977. Experiences in Evaluating and Specifying Aeration Equipment. J. Water Poll. Cont. Fed. 49:66-82. (19) Tucker, C.S. and C.E. Boyd. 1985. Water Quality, p. 135-228. In: C.S. Tucker, (ed.). Channel Catfish Culture. Elsevier Sci. Publ. Co., Amsterdam.