Research On Techniques Of Using Rainwater In Aeroponics System For Leaf Vegetables

Based on the significance of rainwater resource utilization for water resources utilization,the advantages of soilless cultivation technology,and the preliminary research of our research group,this article combines rainwater utilization with vegetable aeroponics technology,and takes Italian lettuce(Lactuca sativa L.var.ramosa Hort.)as the cultivation object to analyze the feasibility of using rainwater in Changchun City for aeroponics.Then designed and processed a rainwater utilization type aeroponics device integrating rainwater treatment and aeroponics nutrient solution recycling.The device was applied to cultivation experiment to evaluate the effect.The specific conclusions are as follows:(1)Based on the analysis of precipitation data in Changchun during the past ten years(2008-2017),combined with the test results of natural rainwater sampling analysis and inspection of two typical sampling points in the year of 2018,comparing with the water quality requirements of soilless cultivation,farmland irrigation and drinking water,and the aeroponics experiment of leafy vegetable using rainwater was conducted.The experiment results showed that the rainwater in Changchun City is a high-quality water source for soilless cultivation;the indexes of rainwater cultivation group(treatment 1)were all higher than the equal mixed group of rainwater and aerated tap water group(treatment 2)and tap water cultivation group(control group).The relative chlorophyll content and net photosynthetic rate in treatment 1 were the highest,while those in control group were the lowest,and treatment 2 was between the two;compared with control group,the contents of soluble sugar and nitrate nitrogen in treatment 1 and treatment 2 increased with the addition of rainwater,while the contents of soluble protein decreased with the addition of rainwater,and the contents of nitrate nitrogen in treatment 1 increased by nearly 50%;(2)Combining rainwater utilization with aeroponics technology,a set of rainwater utilization aeroponics device was designed and manufactured.The device is composed of a pre-sedimentation tank,an adsorption filtering tank,a transition tank,a reverse osmosis tank,a clear water tank,a tap water tank,a nutrient solution tank,a nutrient solution lifting pump,the nutrient solution regulating tank(include an acid solution tank,an alkali solution tank and a concentrated nutrient solution mother solution tank),an aeroponics box,a buffer disinfection tank and a control unit.The device can pretreat the supplied rainwater through the natural sedimentation and adsorption filtration,and the rainwater with a larger EC value can be further treatedby reverse osmosis.The device can realize the recycling of nutrient solution,sterilize the nutrient solution through ultraviolet and ozone,it takes the rainwater as priority water source and takes tap water as standby water source,and ensure the stability of water supply by complementing each other.(3)Through the design of hardware and software,the control system of rainwater utilization type aeroponics device is developed.The system is based on PLC control,which can distinguish EC value of rainwater after pretreatment in transition tank,and control the preparation and regulation of nutrient solution in the nutrient solution tank,which is the core part of the control system.The control system uses S7-200 SMART SR20 CPU as the processor,he CPU with EM AE08 analog input module,with the sensors of pH,EC,liquid level and temperature.It can realize the preparation of initial nutrient solution and the automatic control of nutrient solution components.It conforms to the principle of less use of nutrient solution and less supply on demand,it can save nutrient solution while ensuring the stability of nutrient solution components.(4)In order to study the pretreatment effect of the device on rainwater and provide suggestions for the use of the device,five different turbidity waters were prepared with an equal gradient in the range of 10NTU~130NTU,and the pre-sedimentation and adsorption filtration tests were carried out to determine the relationship between the pre-sedimentation time of turbidity water and the pre-sedimentation effect within the range.According to the research results,combined with the characteristics of vegetable water requirement in the growing season,it is suggested that the rainwater with a turbidity greater than 100 NTU should not be used directly under the premise of ensuring economic benefit.In addition,cultivation experiments were carried out,the results showed that the growth condition and quality of rainwater utilization aeroponics system were better than traditional aeroponics system.