Water circulation induced by mechanical aerators in a rectangular vessel for shrimp aquaculture

A water streamer was designed for the purpose of enhancing cost-efficient circulation between the water surface and bottom of shrimp aquaculture ponds. We took direct measurements of the water current field induced by the designed aerator in a large rectangular reservoir of dimensions (L)50 × (W)19 × (D)1.3 m³ and compared the results with those of a standard Taiwanese paddle-wheel aerator. Vertical circulation between the surface and the bottom induced by the paddle wheel aerator was less than that by the designed aerator. Furthermore, the paddle-wheel aerator consumed more electric power than the designed aerator. The structures of water current induced by the two aerators are elucidated, and the advantages and disadvantages of the aerators are discussed.Auxiliary employment of the designed aerators may contribute to delivery of high DO water throughout the pond, which is more efficient than a paddle wheel aerator.     

Selection of aerators for intensive aquacultural pond

Aeration cost is the third largest cost in intensive aquaculture system after post larvae and feed cost representing about 15% of total production cost. Therefore, selection of aerators plays a major role in maximizing the profit in such system. Over the years, various types of aerators have been developed specifically to enhance the production of aquatic species. The performances of these aerators are generally compared in terms of standard aeration efficiency. However, suitability of a particular aerator at different pond sizes and water quality conditions can best be determined in terms of aeration cost per unit time of operation. In the present study, economic performance of five different aeration systems – circular stepped cascade (CSC), pooled circular stepped cascade (PCSC), 1-hp paddle wheel, 2-hp paddle wheel and propeller aspirator pump were evaluated and compared at different pond sizes, initial DO concentrations of pond and operating hours of aerators; assuming a typical Indian major carp (IMC) culture with commonly practiced stocking density and feeding. Both CSC and PCSC aerators were found to be suitable for pond size less than 1000 m³. However, for pond sizes more than 5000 m³, 1-hp paddle wheel and 2-hp paddle wheel aerators were found to be efficient.     

水车式增氧机性能试验研究

研究了水车式增氧机在清水试验中的增氧能力、动力效率以及实际养殖池塘试验中上下水层溶解氧变化。结果表明,水车式增氧机对于水深为1 m以内的养殖水体具有良好的增氧和搅拌效果,开启100 min左右,可使距增氧机10 m、水深0.9 m处水体溶氧值从6.5 mg/L左右上升到8.7 mg/L左右,和上层水体溶氧值趋于一致;运转时可形成一股较大的定向水流,对鳗鱼等喜好水流的鱼类较为适合。但水车式增氧机对<1.5 m的底层水体增氧作用较弱。本研究为水车式增氧机池塘养殖的运用提供了有益的借鉴。     

叶轮式增氧机性能研究

叶轮式增氧机具有增氧、搅拌和曝气等功能.通过对其近10年1.5 kW、3.0 kW两种型号的增氧能力和动力效率这两个主要性能指标每年的检测平均值进行统计,以及实际养殖池塘试验中上下水层溶解氧、水温变化的研究;结果表明,运转80 min左右,可使距增氧机10 m、1.5m深处底层水体的溶解氧和水温与上层水体一致,从7.3...     

叶轮式增氧机对鱼池溶氧日变化影响的模拟模型初步研究

针对鲜有鱼池溶氧模型考虑增氧机对鱼池溶氧日变化影响的现实,在传统的描述鱼池水温和溶氧日变化多层模型的基础上,通过分析叶轮式增氧机水跃和液面更新对鱼池多层水体中各能量要素和溶氧变化因子的影响,构建了能反映叶轮式增氧机增氧效果的鱼池水温和溶氧日变化模拟模型.通过实验数据对模型的校参和验证,发现溶氧逐小时模拟值与观测数据的均...     

Engineering considerations for water circulation in crawfish ponds with paddlewheel aerators

Engineering considerations for paddlewheel aeration in vegetated shallow water ponds for the production of procambarid crawfish is necessary to ensure cost-effective application. Three experimental ponds (approximately 2 ha each) were planted with rice in August as forage for the resident pond population of red swamp crawfish, Procambarus clarkii, and flooded in October. Two 2.2 kW (3 hp), single-phase electric motor (110 V_ac) paddlewheel aerators were placed in each pond. The aerator rotors were 160-cm long and 95-cm in diameter. The aerator rotor had 36 paddles with half the paddles 27.3-cm long and half 34.9-cm long. Rotor speed was set at 83 rpm and operated at three paddle submergence settings: 7.6, 12.7, and 17.8 cm below the water surface. Over a 20-week period between November and April, channel velocity, head difference, and aerator amperage was measured for both one and two aerators in operation in each pond. Results indicated that circulation of oxygenated water from the aerators can be accomplished as efficiently with a single aerator set at a lower paddle depth (7.6-cm) compared to operating two aerators set at a greater paddle depth (12.7 or 17.8-cm). However, based on the apparent efficiency of the aerators and the calculated channel roughness coefficients values obtained from the channel velocities, paddlewheel aerators are an inefficient option for circulating the pond water especially when rice foliage dominants the total vegetative biomass of the pond.     

增氧机池塘增氧效果试验的研究

研究不同型式的增氧机性能,可使生产者根据不同养殖对象与模式针对溶氧的需求,选择配置合适的增氧方式。通过对使用最为广泛的叶轮式、水车式、射流式和曝气式增氧机产品性能的池塘实效试验,分析比较各类增氧机性能、工作特性和适用范围。结果表明,养殖水体溶解氧主要来自浮游植物的光合作用;叶轮式、水车式和射流式增氧机应用于服务水域,其增氧能力远远不能满足该水域养殖鱼类的氧需求,但可满足养殖鱼类的应急氧需求;曝气式增氧机因没有应急增氧作用和水体搅拌能力而不适合四大家鱼等常规鱼种的养殖需要。     

Assessment of the new generation aeration systems efficiency and water current flow rate,its relation to the cost economics at varying salinities for Penaeus vannamei culture

The selection of aerators and correct numbers can play an essential role in reducing the cost of production in aquaculture. The new generation aerators, namely spiral leaf, air‐jet, submersible and impeller, used in aquaculture, were assessed for its aeration efficiency and energy cost compared with the commonly used paddle wheel aerator. Of the aerators tested, the impeller had the highest aeration efficiency of 2.098 kg O₂/kW hr, followed by paddle wheel with 1.436 kg O₂/kW hr at 20‰ salinity. The spiral and air‐jet aerators had maximum aeration efficiency of 1.326 and 1.419 kg O₂/kW hr, respectively, at 35‰ salinity. The submersible aerator was not efficient as its maximum efficiency was 0.380 kg O₂/kW hr. The water flow by paddle wheel was 3 ft/sec and also provides better coverage than other types of aerators. The efficiency of aerators was high in optimum salinities (20‰ and 35‰) than the low or high saline condition. The average energy cost of shrimp pond aeration per hectare was lowest for impeller, followed by paddle wheel aerator. The study provided economic comparisons of vannamei culture using different aeration systems by keeping a uniform set of economic assumptions. Shrimp farms with impellors can give 14%–25% high returns across salinities, whereas spiral leaf can provide 5% high returns at 35‰ salinity. The combination of the type of aerators and the calculated use based on the salinity of the culture systems can result in energy‐saving and also a reduction in the production cost.     

养殖池塘增氧机制与装备性能比较研究

水产养殖过程中,池塘生态系统可分为自成熟期和人工维持期。在养殖容量提高的情况下,养殖生物呼吸需氧量在不断增加,缺氧条件下有机物分解成有害物质,影响养殖生产。维持池塘生态系统稳定的主要工程机制为:通过上下水层交换、平衡营养元素等方法,强化光合作用,提高营养物质转化规模,提升初级生产力;形成生态增氧为主、机械增氧为辅的高效增氧机制。以中国养殖池塘生态系统为研究对象,分析探讨养殖池塘生态机制、水体溶氧理论、增氧机作用机理、不同类型增氧机的机械性能等,提出了大宗淡水鱼混养池塘及几种典型单养池塘增氧机配置方式,从而为池塘养殖系统增氧机的配置提供技术参考。     

Author index

Oxygen-transfer rates (tap water, 0 mg/l dissolved oxygen, 20°C) for four tractorpowered emergency aerators tested in a 820-m³ pond were: blower-fan aerator, 12.2 kg O₂/h; Crisafulli^® pump and sprayer, 12.3 kg O₂/h; Airmaster^® aerator (centrifugal pump and sprayer), 21.3 kg O₂/h; paddlewheel aerator, 26.3 kg O₂/h. Times required for aerators to homogeneously mix salt in a 6000-m³ pond were: blower-fan aerator, 96 min; Crisafulli pump and sprayer, 94 min; paddlewheel aerator, 53 min; and Airmaster aerator, 38 min. The Airmaster aerator and the paddlewheel aerator did not differ in their abilities to transfer oxygen and circulate pond water (P > 0.05); they were both superior to the blower-fan aerator and the Crisafulli pump and sprayer (P < 0.01).     

Aquaculture economics research in Asia: Proceedings of a workshop held in Singapore, 2–5 June 1981: IDRC,Ottawa, Canada, 1982. 128 pp., ISBN 639-3-003-(5). Available in the U.S.A. from Unipub,New York,NY, $15.00; in other countries from IDRC,Ottawa, Canada, $12.00

Propeller-aspirator-pump aerators of 0.38, 1.5, and 2.24 kW transferred averages of 1.73 to 1.91 kg oxygen/kW · h in standardized oxygen transfer tests (tap water; 20°C; 0 mg/l dissolved oxygen) conducted in a shallow basin (1.04 m of water depth). In comparison tests, spray-type surface aerators transferred 1.34 to 1.41 kg oxygen/kW · h and a diffused-air system transferred 1.08 kW · h. The water-mixing capabilities of aerators were estimated from the time to completely mix salt (NaCl) throughout the volumes of ponds, and from the time required to spread a dye over surfaces of ponds. The propeller-aspirator-pump was effective in mixing pond water. A 1.5-kW propeller-aspirator-pump spread dye over a 0.4-ha pond in 32 min and mixed salt throughout 3000 m³ of water in 90 min. A larger spray-type surface aerator (2.24 kW) required 1.5 h to spread dye and 1.75 h to mix salt in the same pond.     

Assessment of standard aeration efficiency of different aerators and its relation to the overall economics in shrimp culture

Aerators are essential for maintaining the dissolved oxygen level in shrimp culture operations. Many types of aerators are promoted as suitable for shrimp culture, but their comparative efficiencies and water circulation patterns are least understood. The aerators viz, modified paddlewheel, Scorpion jet, Venture jet, Wavesurge were evaluated to compare the standard aeration efficiency at different saline conditions with the commonly used paddle wheel. The modified paddlewheel had the highest mean aeration efficiency of 2.018 kg O₂/ kWh at 35‰, followed by the paddlewheel with 1.434 kg O₂/ kWh at 20‰ water salinity. Compared to this, the Scorpion jet and the Wavesurge have shown the highest aeration efficiency of 0.667 and 0.412 kg O₂/ kWh at 20 and 35‰ water salinities, respectively, whereas the Venture jet has given only. The aerator's performance was better at medium water salinities (20 and 35‰) than low (5‰) or high saline (50‰) conditions. In addition to aeration, the paddlewheel aerator has given the maximum water circulation speed 3 ft/sec and coverage distance of 24 m. The cost economics were derived by keeping all other expenses constant except aeration associated costs. The internal rate of returns in shrimp culture with a modified paddle wheel was 127 % compared to the commonly used paddle wheel (120 %). However, the scorpion and wavesurge aerators have shown returns of 47 % and 27 % respectively across the salinities. The selection and sizing of aerators based on the biomass and efficiency of the aeration systems can make considerable headway in decreasing the cost of production and energy use.     

微孔曝气增氧技术应用现状

微孔增氧技术与传统增氧方式相比,不仅能增加水产养殖水体中的溶解氧量,尤其是中、下层水体均匀增氧,还能改善养殖池塘的生态环境。本文主要介绍微孔增氧机的工作原理及与其他增氧设备配套使用的优点。     

The Effect of Continual,Nocturnal, or No Aeration on Water Chemistry and Plankton Standing Crops in Highly-Fertilized Sunshine Bass,Morone chrysops × M. saxatilis,Fingerling Production Ponds Without Fish

ABSTRACT

Production of fingerlings from very small fry depends upon an initial high concentration of rotifers followed by high densities of crustacean zooplankton. High fertilization rates lead to increased zooplankton production but often cause poor water quality conditions that aeration may alleviate. This study was designed to determine the effects of constant, nocturnal, and no aeration on water quality, primary productivity, and standing crops of phytoplankton and zooplankton in heavily fertilized nursery-size ponds that contained no fish.

Four 0.04-ha ponds were aerated continually; four ponds were aerated only at night with a 372-W (1/2 hp) paddlewheel aerator; and four ponds were not aerated. For 21 days after they were filled on July 21, 1999, the ponds received 1,224 kg/ha rice bran and 581kg/ha liquid 9-27-0 fertilizer. Water quality variables, primary production, chlorophyll-a and zooplankton were sampled daily.

Constant aeration resulted in several conditions more conducive to survival of fish fry, such as higher zooplankton densities, more moderate temperatures, and safer dissolved oxygen levels than did nocturnal aeration or no aeration. However, the development of a higher standing crop of phytoplankton and higher total ammonia concentrations in the turbulent, constantly aerated ponds resulted in higher un-ionized ammonia levels that were not favorable to survival and growth of fry. The high concentrations of zooplankton that developed in the aerated ponds have good potential for cropping to inoculate other ponds or to provide live foods for tank culture of zooplanktivorous fish.     

Diversified aeration facilities for effective aquaculture systems—a comprehensive review

The growing intensive aquaculture system around the world maintains a high stocking density, wherein it is essential to increase and sustain the optimum dissolved oxygen concentration (DO) through the provision of artificial aeration systems. The selection of an aerator is a crucial aspect of aquaculture operations. The selected aerator must be economically efficient and should be able to fulfill the requirement of oxygen supply in the pond water. The present study provides an extensive literature review on the importance of artificial aeration in aquaculture, the standard method of test for performance evaluation of an aerator, various aeration systems and their mechanisms, method to determine the numbers of aerator requirement, comparative studies of different type of aerators, and economic consideration in selection of aerators. In addition, a thorough analysis has been done to suggest the type of aerator that is economically viable and efficient for different pond volumes based on the performance data reported in the reviews. Therefore, this study may help the end-users (fish farmers) to select the best aerator based on their requirements.

     

底充式增氧对改善池塘水质效果的初步研究

在凡纳滨对虾（Litopenaeus vannamei）和三疣梭子蟹（Portunus trituberculatus）养殖池塘中进行了底充式增氧对池塘水质改善效果试验。结果表明,增氧2～3h能减小或消除池塘温度和溶解氧（DO）跃层,显著提高池塘底层水体的ρ（DO）（P〈0.05）。在上午8：00～11：00这段时间开增氧机的效果最佳;试验池塘的氨氮（NH4＋-N）和亚硝酸盐（NO2--N）的质量浓度为对照池塘的72.5%～74.1%和2.6%～2.7%,能促进池塘氧化反应,降低有害物质的含量,改善池塘环境条件。     

Total gas pressure and oxygen and nitrogen saturation in warmwater ponds aerated with airlift pumps

Gas bubble disease and improper inflation of swim bladders in larval striped bass Morone saxatilis have been recently related in laboratory studies to very low levels of gas supersaturation. In other species, kills resulting from gas supersaturation have been reported in natural waters as large as Galveston Bay. We monitored warmwater ponds during spring to determine the extent of naturally occurring gas supersaturation and compared these levels with levels of gas saturation in ponds equipped with airlift pumps. Total gas pressure averaged 110% in the morning at the surface of non-aerated ponds and in the afternoon in ponds with airlift pumps. At other times of the day total gas pressure averaged 106–107% at the surface and bottom, morning and afternoon, in both aerated and non-aerated ponds. No evidence of gas bubble disease was found in 15-day-old striped bass fry cultured for 42 days in either aerated or non-aerated ponds.     

Design Characteristics of Spiral Aerator

In this study, the performance of a spiral aerator, a modified design of the paddlewheel aerator, was evaluated to determine its applicability in aquaculture ponds. The aeration characteristics of the spiral aerator were determined by conducting aeration experiments in a cement concrete tank of dimension 5 × 5 × 1.5 m. Nondimensional numbers related to oxygen transfer (E) and power consumption (Ne) were proposed and expressed as functions of geometric (number of handles per shaft, n) and dynamic (Froude and Reynolds number) parameters. Simulation equations for oxygen transfer and power consumption based on the Froude criterion were developed. The maximum brake power standard aeration efficiency was achieved at n = 13. Finally, an economic analysis was performed assuming a typical Indian major carp culture pond to determine the optimum rotational speed of the aerator at different pond volumes and dissolved oxygen concentration present in the pond at which the aeration cost is minimized. The results showed that the least aeration cost is achievable when rotational speed of the spiral aerator is only 70 rpm for pond volumes up to 700 m³ and from 120 to 220 rpm for pond volumes exceeding 700 m³.     

底部微孔增氧管布设距离和增氧时间对刺参养殖池塘溶氧的影响

为明确刺参养殖池塘中微孔增氧的效果以及增氧管的布设间距、增氧时间对水体溶氧的影响,研究测定了在夏季刺参养殖池塘一个增氧周期内(每天23:00—7:00增氧8 h,7 d一个周期)水体中溶氧(DO)、亚硝酸盐氮(NO_2~--N)、COD的变化。结果显示:连续充气增氧的8 h内DO持续增加,增氧2 h上升速率缓慢,增氧2~6 h上升速率迅速提高,增氧6~8 h上升速率下降,连续充气8 h能够显著改变夜间溶氧降低现象;增氧7 d时间内,NO_2~--N和COD持续下降,分别由0.025 mg/L下降到0.014 mg/L、18.46 mg/L下降到14.15 mg/L。对充氧管道不同距离处DO的测定结果表明,距离增氧管1~2 m处DO较高,3~4 m处缓慢下降,与1~2 m处差异不显著(P0.05),DO保持在5.22 mg/L左右,距离5 m以上时DO下降速度较快,与1~2 m处差异显著(P0.05)。研究表明:微孔增氧可以明显增加水体DO,减少COD、NO_2~--N;微孔增氧机充氧时间6~8 h效果较好;微孔增氧管之间的布设距离在6~8 m可以实现高效增氧。     

WATER CIRCULATION—AN ALTERNATIVE TO EMERGENCY AERATION

A management system, replacing emergency aeration practices with gentle pond circulation, has been employed over an entire catfish growing season. Five waterblenders were used to provide pond circulation for a 1.42 ha catfish pond stocked at a density of nearly 10,000 finger-lings/ha. Pond water circulation during the daytime hours mixed oxygen-rich surface waters with the deeper oxygen-poor waters. The waterblending operation continued long enough after dark to decrease the thermal gradients, so that the diurnal temperature change provided top-to-bottom mixing on most nights during the season. Comparisons of yield data, power requirements, and oxygen and temperature profiles show the advantages of the pond receiving water circulation over a neighboring pond that was aerated only on an emergency basis. Comparisons of waterblending with recent aeration studies of other investigators show an order of magnitude reduction in energy uses.