不同增氧方式对精养池塘溶氧的影响

当前对于在精养池塘中如何配制和合理使用不同机械增氧方式缺乏系统的比较研究。该文为了探讨高温季节晴好天气不同机械增氧方式对池塘溶氧全天调控的影响,试验设计如下：于夏天高温季节集中对精养池塘应用3种不同增氧方式,在晴好天气的白天和夜间进行增氧效果试验。结果发现：无论增氧机开启与否,池塘的溶氧都存在明显的昼夜起伏,且在午后出现峰值。增氧机的开启增强了上下水层交换,削减了氧差,减少了上层溶氧的逸出损失,提升了下层水体的低溶氧水平。池塘上层溶氧起伏程度大于下层,下层溶氧变化滞后于上层（下层溶氧出现峰值落后于上层约2～5 h）,且这种滞后性为增氧机运行所削弱。夜间增氧能向池塘补充溶氧,但仍不足以弥补鱼类和浮游生物的代谢、微生物的生长及有机物的氧化分解造成的溶氧损耗。单从机械增氧能力来看,叶轮式＞微孔式＞耕水机。综合分析节能和增氧效果,在精养池塘养殖环境下,白天开机增氧选择耕水机较为合适,而夜间应急增氧选择叶轮式更可取。试验通过对不同机械增氧方式增氧效果和能耗的系统比较,为合理选择和使用增氧方式提供了一定的参考价值。

Impact of different aeration approaches on dissolved oxygen for intensive culture ponds

Aerators are essential in semi-intensive and intensive aquaculture to maintain an environment congenial to the physiological requirements of the cultured organisms. In an intensive aquaculture, the full oxygen demand of the cultured species cannot be met through natural aeration only. Therefore, artificial aeration is essential. In past years, various types of aerators have been developed to maintain the desired concentration of dissolved oxygen (DO) in the pond water to improve the energy efficiency of the oxygen mass-transfer process. In the present study, it is intended to compare the dynamical efficiency and economic performance of three different aeration approaches, including paddle wheel aerators, diffused-air systems, and water cultivators at different initial DO concentrations of ponds and operating durations of aerators. The study involved a typical Chinese grass carp culture with commonly practiced stocking density and feeding. The comparison included two parts: daytime and nighttime experiments with a repeated measurement design for each one. In the daytime experiment, the paddle wheel aerators and diffused-air systems were operated between 12:00 and 16:00 and the water cultivators between 8: 00 and 18:00. In the nighttime experiment, the three aeration systems were all operated between 0:00 and 6:00. Based on the investigation, phytoplankton photosynthesis on sunny days was still the main source for DO replenishment in such intensive culture ponds since aerators were not operated all day. The operation of aerators enhanced water exchange between the upper and lower layers of water, decreased the escape of DO in the daytime due to over-saturation, and increased the total stock of DO. Accordingly, aerators reduced the risks of fish raising their heads above water to breathe in the night/dawn and were beneficial for fish feeding. The diurnal variation of DO in the upper layer of water was greater than that in the lower layer and displayed dis-synchronization which could be attenuated by mechanical mixing/aeration. The mixing/aeration capacity of paddle wheel aerators and diffused-air systems were significantly higher than that of cultivators, but the paddle wheel aerators also increased the oxygen consumption rates during the night in comparison to the cultivators, possibly due to the enhanced decomposition of organic matter promoted by water circulation. In the current case, the mechanical aeration capacity of cultivators, diffused-air systems, and paddle wheel aerators were 0.22, 3.2, and 4.53 kg/h, corresponding to a decrease rate of DO 0.58 mg/h for the cultivators, 0.43 mg/h for the diffused-air systems, and 0.27 mg/h for the paddle wheel aerators during nighttime. Energy consumption in the daytime was in the following order: paddle wheel aerators (12.0 k W?h) > diffused-air systems (6.4 k W?h) > cultivators (0.8 k W?h). Based on the dynamic efficiency and energy savings, the cultivator is more suitable for mixing/aeration in the daytime, while the paddle wheel more effectively mitigates oxygen depletion during the night.