Impact of aeration and alkalinity on the water quality and product quality of transported tilapia—A simulation study

The effects of aeration and alkalinity on water quality and product quality of Nile tilapia (Oreochrmis niloticus) were determined for simulated commercial hauling conditions. Three types of aeration were tested: pure oxygen aeration with a fine bubble diffuser (Oxygen), air aeration with medium bubble diffusers (Air), and a combination of both pure oxygen aeration with a fine bubble diffuser and air aeration with a medium bubble diffuser (Mixed). Simulated transport hauls were conducted at two initial alkalinities: 1.74 ± 0.11 meq/L (Low) and 8.84 ± 0.55 meq/L (High).The Air treatments resulted in the lowest carbon dioxide concentration, and the highest pH and un-ionized ammonia concentrations. At high alkalinities, the Air treatments were unable to maintain adequate dissolved oxygen levels. The Mixed treatment resulted in reduced carbon dioxide and dissolved oxygen concentrations. The Oxygen treatment resulted the highest dissolved oxygen, highest carbon dioxide, and lowest pH and un-ionized ammonia. Un-ionized ammonia concentrations were higher with the High Alkalinity treatments because of higher pH. Significant mortality was observed in the Air treatments in both the Low- and High-Alkalinity treatments. Mortality in the Oxygen and Mixed treatments for both low and high alkalinities were comparable to that observed in commercial tilapia transport using fine bubble diffusers and pure oxygen.These results indicate that mortality due directly to hauling water quality will not be increased at high alkalinity, if pure oxygen aeration is used. The potential effects of water quality during hauling on survival and product quality may be less than the impact from (a) physical damage from loading and un-loading and (b) physiological problems resulting from pH and temperature shock during the transfer from the hauling tanks to retail holding systems, especially for fish of reduced fitness.     

An evaluation of three paddlewheel aerators used for emergency aeration of channel catfish ponds

Oxygen transfer rate, power requirement and fuel consumption were determined for three paddlewheel aerators used for emergency aeration of channel catfish ponds. The power requirement of the tractor-powered units was directly related to the diameter of the paddlewheel drum and the paddle immersion depth. Oxygen transfer rates ranged from 6·9 to 41 kg h^?1 and increased linearly with the power requirement. The largest paddlewheel aerator, operated at the maximum paddle depth, produced the highest oxygen transfer rate (41 kg h^?1). Oxygen transfer efficiencies ranged from 1·29 to 1·97 kg kWh^?1.     

Estimation of Oxygen Transfer Rates for Mechanical Aerators in Brackishwater Aquaculture Ponds

Oxygen transfer rates for mechanical aerators are usually determined by standard aeration tests conducted in concrete tanks. Results from standard tests are then extrapolated to field application of the aerators in aquaculture ponds, but these extrapolations have not been verified. In this study, oxygen transfer rates were estimated for propeller-aspirator-pump aerators deployed in brackish water aquaculture ponds under normal pond conditions. Estimation was accomplished by fitting the Whole Pond Respiration Diffusion (WPRD) model to nighttime observations of dissolved oxygen concentration for ponds in which artificial aeration had been initiated during the night. Application of this new technique revealed that oxygen transfer rate determined from a standard aeration test was similar to that estimated from trials in aquaculture ponds. Preliminary results suggest that oxygen transfer rates were higher when the aerator was placed in the deep end of the ponds than when the aerator was situated in the shallow end. Aeration efficiencies ranged from 1.45 to 1.8 kg O ₂ per kW-hour.     

The relationship between feeding rate, paddlewheel aeration rate and expected dawn dissolved oxygen in intensive shrimp ponds

Determination of the proper level of supplemental aeration in intensive shrimp culture is critical for maintaining adequate concentrations of dissolved oxygen while minimizing equipment and operating costs. Little quantitative information is available on sizing the amount of aeration equipment to various levels of intensification.

Results indicate that dawn dissolved oxygen (mg/liter) can be predicted based upon the amount of feed applied (kg/ha day) per unit aeration (hpday/ha). The amount of feed which can be applied with a given amount of supplemental aeration and a reasonable expectation that dawn dissolved oxygen will not be below a targeted concentration is expressed by the equation F/A = 28·83 − (4·31 × DO).     

Economic Assessment of Alternative Aquaculture Aeration Strategies

Oxygen depletion is a serious problem for the catfish industry, especially as producers attempt to increase their production intensity. Aeration, either emergency or continuous, is the most common method used to address oxygen depletion.
A risk-programming model using Target MOTAD methodology was developed to study the aquacultural producer's aeration decision-making process. Effects of stocking rate, aeration yield response and availability of labor, capital and electricity on the selection of aeration strategy were analyzed.
Continuous aeration with electric paddlewheels was most often selected as the best aeration strategy. However, as farmers become increasingly concerned with financial risk, they apply continuous aeration with pump sprayers first, then no aeration and lastly emergency aeration with tractor-powered paddlewheels. Emergency aeration was only used when: 1) electricity was not available and the producer desired a highly conservative financial strategy, and 2) the relative efficiency of continuous aeration in the field was dramatically reduced from experimental results.     

Use of Air Stripping Technology to Remove Ammonia from Biologically Treated Blue Crab Processing Wastewater

Abstract

Crab cooker wastewater contains high concentrations of chemical oxygen demand (COD), total suspended solids (TSS), and total Kjeldahl nitrogen (TKN). Anaerobic biological treatment of the wastewater releases high concentrations of ammonia. In this study, the potential for air stripping to remove ammonia from wastewater which was treated biologically under anaerobic conditions was evaluated. An air stripping tower's ammonia removal efficiency increased from 50 to 72 percent as the air flowrate was increased from 9 to 21 m³/min. The average liquid loading rate and liquid temperature were 25 L/m²/min and 14^GC, respectively. Ammonia stripping efficiency increased as the stripping factor was increased from one to three; however, under the conditions of this study (2,3 inch LanPac packing and countercurrent tower), stripping factors from two to three were only possible at low liquid loading rates (less than 41 m-Vm²/min) due to pressure drop considerations. At liquid loading rates less than 41 m-Vm²/min, the product of the overall mass transfer coefficient (KL) and the specific interfacial area (a) increased with increasing liquid loading rate, probably because more of the packing surface was wetted at higher liquid loading rates.     

Economic Assessment of Alternative Aquaculture Aeration Strategies

Oxygen depletion is a serious problem for the catfish industry, especially as producers attempt to increase their production intensity. Aeration, either emergency or continuous, is the most common method used to address oxygen depletion.
A risk-programming model using Target MOTAD methodology was developed to study the aquacultural producer's aeration decision-making process. Effects of stocking rate, aeration yield response and availability of labor, capital and electricity on the selection of aeration strategy were analyzed.
Continuous aeration with electric paddlewheels was most often selected as the best aeration strategy. However, as farmers become increasingly concerned with financial risk, they apply continuous aeration with pump sprayers first, then no aeration and lastly emergency aeration with tractor-powered paddlewheels. Emergency aeration was only used when: 1) electricity was not available and the producer desired a highly conservative financial strategy, and 2) the relative efficiency of continuous aeration in the field was dramatically reduced from experimental results.     

池塘养殖中不同机械增氧技术的组合及效果验证

为解决河南中牟县万滩镇养殖池塘机械增氧技术单一的问题,通过试验研究微孔式、水车式、涌浪式等几种增氧机的性能及使用方式,以达到提升增氧效果和提高养殖效益的目的。结果表明,该地区池塘溶氧含量高而利用率低,养殖户传统增氧方法不当。适宜增氧方式为:涌浪式增氧机适合在晴天下午使用3~6 h,可有效提升周边20 m范围内底层水体的溶氧水平;投食前后半小时开启和关闭微孔式、水车式增氧机,可提升投食期间投饵区溶氧水平1~2 mg/L,保证鱼群的进食效果;夜间搭配使用微孔式和低功率叶轮式增氧机增氧,可使微孔区域底层水体溶氧比不增氧状态高出1 mg/L以上。     

一种新型管式曝气装置的设计与试验

随着水产养殖业逐渐向高密度、集约化方向的发展,为实现氧气(O_2)高效溶解、二氧化碳(CO_2)调控、流态改善等目的,急需研制新型高效曝气装置,开发高效节能的曝气技术。基于气水两相溶解的双膜理论和文丘里原理,设计开发了一种管式曝气装置,经初步试验获得了影响增氧性能的关键技术参数,并以此为基础对曝气装置进行优化设计,研究新型节能增氧技术。试验结果表明,管式曝气装置中影响曝气效果的因素有水面高程(Hw)、缩径(D_1/D_2)、旋混结构、进气口大小、进气量等。水面高程、缩径、进气口越大,进气量越充足,曝气装置的增氧效果越高;而额外增加延长结构和旋混结构后,曝气装置水头损失增大、进气量下降,从而导致增氧效果显著下降。该装置利用额外水流动力实现增氧,是一种高效、节能、经济的新型曝气装置,可为水产养殖提供一种新的增氧方法。     

Dissolved Oxygen and Aeration in Ictalurid Catfish Aquaculture

Feed‐based production of ictalurid catfish in ponds is the largest aquaculture sector in the USA. Feed has an oxygen demand, and increases carbon dioxide, ammonia nitrogen, and phosphate inputs to ponds. Major sources of oxygen in ponds are phytoplankton photosynthesis and mechanical aeration; the major sink for oxygen is respiration by fish and by microorganisms in the water column and sediment. Dissolved oxygen concentrations decline when respiration exceeds photosynthesis, and the most crucial time for low dissolved oxygen concentration is at night. Mechanical aeration is applied to avoid nighttime dissolved oxygen concentrations from falling below the critical level for catfish of 3 mg/L. Electrically powered paddlewheel aerators are used by most catfish producers. The oxygen‐transfer efficiency of these aerators is known, but calculations of aeration requirement from stocking and feeding rates are not reliable because of variation in phytoplankton abundance and in weather conditions. Dissolved oxygen concentrations must be monitored, and when measurements suggest that nighttime dissolved oxygen concentration will be unacceptably low, tractor‐powered emergency aerators must be operated to supplement dedicated aeration. Dissolved oxygen concentration also is important in hatcheries, and small aeration systems have been developed for hatchery application.     

一种大水体太阳能自动增氧装置的研发与试验

研发一种大水体太阳能自动增氧装置,为大水体的缺氧、水体污染提供一种解决方法。太阳能自动增氧装置由太阳能光伏发电系统、检测与智能增氧系统、自动化驱动系统组成。光伏发电系统充分利用太阳能资源,解决了电能消耗问题;检测与智能增氧系统实现了增氧过程中氧溶解浓度检测和智能感应运行;自动化驱动系统通过智能感应信号和电子差速控制系统实现增氧机原地转向、转弯和直行3种运动模式的移动,增加了增氧面积。使用太阳能自动增氧装置增氧试验表明,80 min内1 m水深处溶氧量增加0.79 mg/L,2 m水深处溶氧量增加0.78 mg/L,3m水深处溶氧量增加0.77 mg/L,4 m水深处溶氧量增加0.78 mg/L;改善水质试验表明能有有效提高水体溶氧,降低氮磷含量;养殖试验表明,增加鲤产量35.3%、鲢鳙产量31.2%。     

Supplementary oxygen and temperature management during live transportation of greenlip abalone, Haliotis laevigata (Donovan, 1808)

Live greenlip abalone, Haliotis laevigata , are highly valued in Australian export markets with demand increasingly being met with cultured stock. Live transportation of abalone requires the maintenance of favourable conditions within transport containers for periods exceeding 35 h. We examined the combined effects of temperature regulation (ice provision) and of supplemental oxygen (60% and 100% concentrations) on mortality rates of abalone over 7 days following a 35-h simulated live-transport experiment. We also examined the physiological condition of greenlip abalone (oxygen consumption rate, haemolymph pH and weight) during the simulation experiment. The provision of ice and supplementary oxygen reduced abalone mortalities. Omission of ice and supplementary oxygen during the transport simulation resulted in mortality rates ranging from 70% to 100%. The addition of ice to containers with ambient oxygen concentrations decreased average mortality rates by 50%. While supplementary oxygen further reduced these rates, the provision of both ice and 100% oxygen was by far the most effective combination, reducing mortalities to between 2% and 6%. Supplementary oxygen increased oxygen consumption rates of abalone above those transported at ambient oxygen concentrations. Live-transport decreased haemolymph pH in all treatments but was most pronounced in treatments without ice or supplementary oxygen. On average, abalone lost 7–13% of their weight during the simulation but this loss was independent of transport treatment.     

Bubble size distribution in a bubble column applied to aquaculture systems

Bubble size distribution affects the gas-liquid mass transfer rates during aeration and foam fractionation processes employed in recirculating aquacultural systems. The effects of air flow rate, protein concentration and air stone pore size on bubble characterization were investigated. Bubble size was measured photographically in conjunction with image-processing techniques. The study indicated that bubble size increased with air flow rate and air stone pore size, but decreased with protein concentration. Within the tested range of these variables, the geometric diameters of the majority of the bubbles (90%) were within the range of 0·5–3·0 mm, and the bubble sizes followed a normal distribution.     

Performance of a recirculating fish production system stocked with tilapia hybrids

To demonstrate whether practical quantities of food fish could be produced in an inexpensive closed system suitable for family-scale use, 424 tilapia hybrid fry weighing a total of 177 g were stocked on 8 May 1981 into a 7600-liter (10·7 m²) steel-walled, vinyl-lined pool equipped with a rotating biological contactor, a settling basin, supplemental aeration and a passive solar collector. Ammonia, nitrite, nitrate, oxygen, temperature, pH and turbidity were monitored. New water was added at intervals during the experiment, at an average rate equivalent to 4% per day. Floating catfish chow was fed. To establish a growth curve and biomass estimate, 30 fish were removed, weighed and restocked every two weeks. After 146 days of grow-out, 48·6 kg of fish were harvested. Food conversion was 1·25:1. With suitable temperatures, 2·5 crops totaling at least 121 kg could be produced at a rate equal to 121000 kg/ha/yr of water surface.     

Respiratory and hematological response of tench, Tinca tinca (L.) to a short-term cadmium exposure

The effects of 3 h exposure to 96hLC50 of cadmium (4.5 mg dm⁻³) on oxygen consumption rate, and hematological parameters (RBC, WBC, erythrocyte and leukocyte pattern) of juvenile tench were evaluated. Oxygen consumption significantly decreased beginning from 24 h postexposure, and remained reduced until the end of the experiment (96 h postexposure). RBC gradually increased, together with the percentage of juvenile cells in circulation. On the other hand, cadmium induced damage to the red cells – the share of cellular anomalies significantly increased with time postexposure. They included abnormal cell shape, vacuolization, swelling, chromatin disintegration in the nucleus, and nucleus indentation. The exposed fish showed a gradual and significant decrease in WBC without a shift of lymphocyte/neutrophil proportion. No significant changes in thrombocyte count occurred. The results show that short-term exposure to cadmium reduced fish energetic metabolism, and suppressed immune abilities. The symptoms gradually developed after the end of exposure, and no recovery took place until␣96 h.     

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。     

Ammonia removal in selected aquaculture water reuse biofilters

Four fixed-film biological filters (rotating biological contactor, biodrum, trickling filter, and a submerged anaerobic filter) were tested for the removal of ammonia using a simulated warmwater fish and invertebrate culture water supply. Filter design may be determined based on the results of ammonia removal efficiency over a wide range of hydraulic loads. The rotating biological contactor (RBC) provided the best ammonia removal (over 90%) up to about 0·06 m³ m^?2 day^?1 (1·2 gpd ft^?2). The biodrum removed over 80% of the ammonia to a hydraulic load of 0·05 m³ m^?2 day^?1 (0·9 gpd ft^?2). The trickling filter removed 50% of the ammonia at a hydraulic loading of 0·012 m³ m^?2 day^?1 (0·3 gpd ft^?2).     

Effects of different layouts of fine-pore aeration tubes on sewage collection and aeration in rectangular water tanks

Sewage collection and dissolved oxygen (DO) management have always been the focus of industrialized recirculating aquaculture. However, there are still no reports on how to achieve efficient sewage collection and increase DO in rectangular water tanks. In the present study, the performance of sewage collection and aeration in rectangular water tanks were compared among three fine-pore aeration tubes (disc-type diffuser, four corner-type diffuser and distribute-type diffuser) layouts at three airflow rates, 6, 18, and 30 m³/h. The results of computational fluid dynamics (CFD) modeling and bait collection tests revealed that sewage collection using the four corner-type diffuser was better than using the disc-type diffuser and the distribute-type diffuser. Using the four corner-type diffuser, a strip-shaped sewage collector could be set up at the bottom of the tank to collect sewage at an airflow rate of 18 m³/h and a disc-shaped sewage collector could be set up at the bottom of the tank to collect sewage at an air flow rate of 30 m³/h. In terms of aeration, volumetric oxygen transfer coefficient (K_La₂₀), standard oxygen transfer rate (SOTR), and standard oxygen transfer efficiency (SOTE) of the distribute-type diffuser were all the highest at the three airflow rates, followed by four corner-type diffuser, and finally the disc-type diffuser, indicating that the aeration performance in the distribute-type diffuser was optimal. However, there were no significant differences in K_La₂₀, SOTR, and SOTE between the four corner-type diffuser and the distribute-type diffuser at both 18 and 30 m³/h airflow rates. Therefore, four corner-type diffusers were the optimal choice for recirculating aquaculture, considering the sewage collection and aeration requirements. The results of the present offer novel insights on the application of CFD in recirculating aquaculture, in addition to basic data and theoretical guidance on how to achieve efficient sewage collection and aeration in recirculating aquaculture.     

Estimation of flow in a rearing tank of marine fish larvae by simplified numerical computation—a case of two-dimensional flow

Marine fish larvae are fragile against physical stress. However, few studies have been conducted to evaluate the flow field in a rearing tank, which is assumed to provide a high degree of physical stress to marine fish larvae. The flow field in a rearing tank (volume of 1 m³) is generated by aerators, which are commonly used to provide oxygen.

This paper is a report on the estimation of stationary flow in the rearing tank of marine fish larvae. The larvae are seven band grouper larvae of Epinephelus septemfasciatus, which have a very low survival rate immediately after the hatching of eggs. The experiments of rearing of seven band grouper larvae were carried out using rearing tanks with four aeration rates (1000, 200, 50 ml/min, and no aeration). The effects of aeration on the survival and floating death of seven band grouper larvae were examined. The experiments confirmed that the mass mortality of seven band grouper larvae depends on the flow rate in the rearing tank. Aeration at 200 ml/min resulted in the highest survival and growth rates of grouper larvae.

Larvae-rearing experiments provided evidence that the flow rates of the rearing tanks are very important design aspects of rearing tanks. The estimation of flow in a rearing tank for an aerating rate of 200 ml/min was carried out by numerical calculation. The computation was simplified by a two-dimensional flow based on experimental results. The calculated flow in the rearing tank was compared with the experimental one. The calculation of the stationary flow in the rearing tank showed good qualitative and quantitative agreement with the experimental results. The numerical estimation of the flow in a rearing tank of marine fish larvae was confirmed to be effective and satisfactory for the design of a tank that would provide optimum performance.     

Development and Evaluation of Diets for Crustacean Aquaculture

Effective purified and unrefined diets have been developed and evaluated for use in studying the nutrition of lobsters ( Homarus sp.). A 4-month growth experiment showed that the purified diets yielded weight increases nearly 80% of that achieved on a live food diet, with concomitant high survival rates. Lower-cost unrefined diets supported growth over half of that observed on live food diets. Supplementation of a purified diet with an astaxanthin concentrate derived from crayfish waste enhanced growth significantly, and all the diets tested promoted growth and survival with only 0.2% dietary cholesterol.
Growth and survival are the most useful criteria for evaluating crustacean diets, but other factors such as proximate analyses of feeds, physical characteristics such as pellet leaching rates, and measurable physiological effects can provide important supplemental information. Our analysis of some of these factors suggests that pellet integrity and resistance to leaching may not be directly related either to growth, or to levels of binder in the diets.