Use of treated mine water for rainbow trout (Oncorhynchus mykiss) culture: a production scale assessment

In previous proof-of-concept work, it was shown that the use of treated coal mine water for rainbow trout (Oncorhynchus mykiss) culture in a cage was technically feasible, though only a 50-fish bioassay was grown and no work on production-related issues was conducted. To further advance the use of treated mine water, an under-utilized water resource throughout Mid Appalachia, work was conducted to assess the effects of using treated coal mine water for the intensive production of rainbow trout in a flow-through system. During this study, comprehensive water quality data were collected to supplement fish weight and length data taken during routine monthly sampling events. The 8000 fish grew well in the raceway system over the 9 months of production, where a feed conversion ratio of 1.4 and a condition factor of 5.1 × 10⁻⁴ were measured with stocking and harvest densities of 26.4 and 50.2 kg/m³, respectively. Further, total net production was 3275 kg (7220 lb) with 98.6% survival. Throughout the study, dissolved ion concentrations (Fe, Al, Mg, Ca, and SO₄) often exceeded recommended tolerance limits. Further, elevated ammonia nitrogen concentrations generated from a component of the mine water-treatment process were identified as a potential limiting factor for aquaculture development. However, when the non-ideal effects of high ionic strength and the speciation of dissolved metal–ligand complexes were taken into account, the concentrations of free metal ions were within recommended tolerance limits.     

Growth and the effect of grading, of turbot in a shallow raceway system

Juvenile turbot Scophthalmus maximus (L.), ranging in size from 30 to 407 g were graded into small, large, and unsorted groups in a low-water-level raceway system. Water depth was 7 cm. The rearing design proved self-cleaning and well suited for turbot ongrowing. Mean initial weights 146.2, 236.1, 162.7 g increased to 299.1, 465.6 and 343.1 g in the small, large, and unsorted groups respectively during the 86 day experiment. The corresponding SGRs were 0.84, 0.79 and 0.87% day-1. No positive effect of grading on biomass production was revealed. The coefficient of variance gave no indication of social interactions, but plotting the start weights against estimated individuals SGRs did, although the effect was minor.     

Analysis of sediment transport modeling using computational fluid dynamics (CFD) for aquaculture raceways

A simulation model to analyze the water flow and sediment transport in aquaculture raceways was developed using a computational fluid dynamics (CFD) software package. The simulation was used to evaluate the efficiency of solids settling in the quiescent zone of existing trout raceways. This efficiency was based on the percentage of solids removed, which corresponds to the percentage of solids introduced into the raceway that settle in it, with settling taking place primarily in the quiescent zone.

The raceway selected for model validation was a rectangular concrete raceway 30.0 m long, 3.0 m wide, 0.9 m deep, with a slope of 0.01. The raceway included a quiescent zone of approximately 5.3 m in length, which was separated from the rearing area by a screen. The water flow rate through the raceway was approximately 0.058 m³/s. Velocity measurements were recorded at 230 stations along the raceway using an acoustic Doppler velocimeter, for comparison with the results obtained from the simulations.

For the purpose of simulating sediment transport, six groups of particles were used to account for the total suspended solids. The sizes of the particles selected were based on an experimentally determined distribution for solids from a similar raceway, and were 692, 532, 350, 204, 61, and 35 μm for Groups 1–6, respectively. The particle density for each size was assumed to be 1150 kg/m³. Values of the percentage of solids removed for the different particle sizes were 100.0% for the largest particles, and 54.7, 0.9, and 0.1% for the three smallest particles, respectively. This methodology of analyzing the raceway sediment transport in terms of its percentage of solids removed based on CFD simulations can also be used to examine raceway design alternatives for improving the particle removal efficiency.     

Water quality and sludge characterization at raceway-system trout farms

Studies were conducted to characterize raceway water quality, effluent water quality, and waste solids within three, raceway-type trout farms. No significant differences were found in effluent water quality between the three farms during 7 months of monitoring. Average effluent quality over the course of the day was not found to be impaired. However, effluent quality was found to change significantly during times of feeding and harvesting. In a concrete/earthen-lined farm, normalized total suspended solids (TSS) concentrations were as high as 115 and 63 mg/l during harvesting and feeding events, respectively. Total Kjeldahl nitrogen (TKN) and ortho-phosphate (OP) also increased with higher TSS loads. The majority of particles (by weight) measured in effluent samples at all three farms were evenly divided between the smallest range (1.5–30 μm) and the largest (>210 μm). For settled sludge samples, the majority of the particles were in the size range of 1.5–30 μm. Particle size in the raceway was positively correlated with fish size during feeding events, but this correlation dissipated during the 4-h period after feeding. The accumulation and characteristics of sludge in a sediment trap were also monitored over a 22-day period.     

高速滚珠轴承动态特性求解的沟道控制理论修

从滚珠轴承高速运转时滚动体(钢球)与内、外沟道接触存在旋滚比出发,分析了高速滚珠轴承动态方程组沟道控制理论的不足.在根据滚动体所受内外圈摩擦力与陀螺力矩相平衡的关系得出的内外沟道控制参数表达式中,引入滚动体与沟道之间摩擦因数的半经验公式.为避免沟道控制理论的不足,滚动体姿态角的计算采用了按照达朗伯原理推导的计算公式,取代了由沟道控制理论得出的姿态角.使得摩擦因数和姿态角的计算同时耦合了滚动体法向载荷的影响而最终成为与方程组同时迭代的变量,并给出了迭代算法,实现了两者的精确表达和精确计算.最后通过算例比较了两种方法的区别,说明了本文方法的计算结果更加精确,适合于现代轴承分析与设计的精确化要求.     

First feeding of common wolffish on formulated dry feed diets in a low water-level raceway system

Wolffish (Anarhichos lupus) larvae were first fed in a low water-level raceway system, with two new types of formulated dry feed diets. Water level in the rearing tank was 1.5 cm. The fish showed a high preference for feeding from the surface. During the first week the fish experienced a drop in dry weights. The highest SGR of 5.8% was obtained between day 35–60. The best feeding regime gave a survival rate of 82 (2.5)%. Results indicate failure to initiate feeding as a main cause of mortality in the fed groups. Death by starvation occurred after 30–40 days. It is speculated whether the large difference in growth rates between the two feeding regimens is due to differences in carbohydrate levels between the two feed types. The rearing tank technology proved, with minor adjustments, to be self-cleaning and well suited for first feeding of wolffish.