循环曝气压力与活性剂浓度对滴灌带水气传输的影响

Impact of working pressure and surfactant concentration on air-water transmission in drip irrigation tape under cycle aeration

适宜的工作压力及表面活性剂浓度对循环曝气效率的提高及地下滴灌水气传输优化具有重要意义。利用循环曝气系统,设置工作压力和活性剂浓度2因素3水平共9个曝气组合,每组均进行非曝气对照试验,分析曝气组合条件对掺气比例、氧传质效率、滴灌带水气传输均匀性的影响。结果表明:循环曝气条件下,不添加活性剂时,压力提高有利于掺气比例增加,添加后,趋势相反;压力一定时,掺气比例随活性剂浓度升高而增加;滴灌带出水均匀性和出气均匀度分别在95%和70%以上;活性剂浓度及压力对氧传质系数分别起到了促进和抑制作用,活性剂的添加大大缩短了曝气时间;掺气比例计算方法能够准确反映曝气滴灌系统中水气传输特性。研究结果对循环曝气滴灌系统水气传输效率的提高及运行成本的降低有重要指导。

Aerated subsurface drip irrigation （ASDI） refers to the irrigation with aerated water based on Venturi principle by the use of subsurface drip irrigation （SDI） system. ASDI provides a source of oxygen to root environment that may suffer from temporary hypoxia, and therefore unlocks yield potentials of crops. But the efficiency of ASDI is dependent on a number of factors. Among which, proper operating pressure and surfactant concentration are of great significance for aeration efficiency and the uniformity of air and water flow in the aerated irrigation water stream. Proper control of air-water transmission will offer the industry an opportunity to further optimize the use of ASDI system and improve water use efficiency and minimize the environmental impacts of irrigation. The primary objective of this study was, therefore, to explore optimum working pressure and a surfactant sodium dodecyl sulfate - SDS addition on the flow uniformity of water-air irrigation in the drip pipeline. Nine combination were tested （3 working pressure at 0.05, 0.10, 0.15 MPa and 3 concentration level of SDS of 0, 5, and 16 mg/L, respectively）. Each combination has aeration treatment and non-aeration treatment. Results showed that the aerated concentration was increased with increasing operating pressure even without surfactant addition. However, aerated concentration decreased with increasing operating pressure under surfactant addition. Under the same operating pressure, the aerated concentration increased with increasing surfactant concentration. The addition of surfactant significantly increased the equilibrium concentration in aeration treatment. The average value of water flow uniformity under aerated drip irrigation was greater than 95%, suggesting that there was no negative impact of surfactant addition on the water flow during oxygation. And the air flow uniformity of each combination remained above 70%. The oxygen transmission efficiency was improved with the addition of SDS. The surfactant concentration had a positive effect on the oxygen mass transfer coefficient, while the operating pressure had a negative effect on the oxygen mass transfer coefficient. The surfactant addition has greatly shortened the aeration time. The deviation between the observed and calculated aerated concentration were less than 5%, indicating that the calculation method was reliable for the aerated irrigation water stream. The operating pressure at 0.1 MPa and surfactant concentration of 5 mg/L was optimal combination. This research demonstrates great importance of the improvement of aeration efficiency and the air-water transfer for oxygation that can significantly reduce the cost of operation.