Research On The Key Sensing Technology Of The Available Nutrients In Hydroponic Solution For Plant Factory

With the continuous expansion of facility agriculture hydroponic planting scale,there is increasing need for water and fertilizer management.The studies on nutrient detection methods and sensing technology of hydroponics in facility agriculture are of great significance to control nutrient and environmental factors more comprehensively and accurately.However,there are some limitations in the nutrient detection,such as the immature nutrient sensor,the ion-selective electrode(ISE)cannot be directly used for nutrient measurement in hydroponic solution,and the complicated operation and high cost of optical instruments.Therefore,the present study aims to optimize nitrogen,phosphorus and potassium sensor that is based on solid-ISE,to establish the prediction models of main nutrients concentrations in hydroponic solution,to develop the optical detection chips and portable detection system,and to construct a facility agriculture model with closed-loop automatic detection and control system of nutrients.The key findings and achievements are summarized as follows:(1)A layer of cobalt nanoparticles has been modified on the surface of the cobalt electrode by electrodeposition.The mechanism of electrode change during repeated use was studied by electrochemical impedance spectroscopy.The electrochemical impedance spectroscopy method was used to explore the change mechanism of the electrode during repeated use.The characterization data demonstrated that:cobalt nanoparticles improved the detection limit of phosphate ISE;electrodeposition time affected the performance of phosphate ISE.The best electrodeposition time is 60 minutes.The sensitivity(S)is about 27.28 mV/decade,the detection limit is 1×10-5.29 mol/L,and the response time is around 30 seconds.A disposable phosphate concentration detection chip based on carbon-based screen-printed electrode has been developed.The consistency of disposable phosphate detection chip is verified to be good.The maximum coefficient of variation within the same production batch is only 0.4992%.(2)Graphene and graphene-gold nanoparticle composites were modified on glass carbon electrode(GCE)substrate to investigate their effects on nitrate,ammonium,and potassium ISEs.We found that the charge transfer ability of GR-AuNPs-GCE is better than those of GCE and graphene modified glassy carbon electrode after comparing the electrodes with different charge transfer layers.The detection limit of ISE based on GR-AuNPs-GCE is improved as compared with those of the other two.The S of nitrate ISE is about 49.62 mV/decade,the detection limit is 1×10-4.88 mol/L.The S of ammonium ISE is about 53.39 mV/decade,and the detection limit is 1×10-5.52 mol/L;the S of potassium ISE is about 48.58 mV/decade,and the detection limit is 1 ×10-5.23 mol/L.(3)The classical bacterial foraging optimization algorithm(BFO)has been improved by bionics.The support vector regression has been optimized by using improved BFO to establish the nutrient prediction model of hydroponic solution.The improved BFO is a breakthrough in the optimization accuracy,stability and convergence speed;the nutrient prediction model can accurately predict the nutrient concentration using the information of ISEs and auxiliary sensor.The minimum determination coefficient of the model is 97.43%,which indicates high accuracy and generalization ability.(4)Based on the above findings,an electrochemical sensor was used to establish a detection system that can accurately control the nutrient concentration of hydroponic solution.Two different types of nutrient detection chips and portable optical nutrient detection equipment has been developed based on microfluidic chip.An example of facility agriculture with environmental regulation function has been successfully established.