Research On The Air-lift Artificial Upwelling Technology And Its Sea Trials

In recent years,the coastal ecological environment has gradually deteriorated,and how to improve the coastal environment has become the hot domain for scientists.As a geoengineering method,artificial upwelling can effectively increase primary productivity and enhance the capacity of marine carbon sinks by placing artificial equipments to transport nutrient-rich deep ocean water to the upper euphotic layer,promoting the uptake of nutrients by phytoplankton and algae.Some achievements of artificial upwelling in theory and laboratory experiments has been obtained in China,while almost few researches on the application technology and sea trials of artificial upwelling have been carried out yet.With the support of the National Key Research and Development Plan " Processes of coastal ecosystem carbon sequestration and approaches for increasing carbon sink”(Grant No.2016YFA0601400)and the National Natural Science Foundation of China "Mechanism research on the artificial upwelling and its effects on the marine environment"(Grant No.51120195001),we conduct some researches on the key technologies of air-lift artificial upwelling,and design efficient and reliable artificial upwelling devices for different applications.Furthermore,we combine the air-lift artificial upwelling technology with the marine ranch in China,and carry out some sea trials in mariculture zone.Through sea trials of artificial upwelling,we can test the application feasibility of the artificial upwelling technology and equipment in the ocean,gather some valuable technologies and experience for the future,and explore the application prospects of artificial upwelling technology in increasing aquaculture production,nutrient removal and marine carbon sink.The main contributions of this dissertation are as follows:1.Focusing on the plume control in air-lift artificial upwelling,we study the theories of two kinds of air-lift artificial upwelling,including bubble curtain and air-lift pump,and propose a method to control the plume movement by adjusting the amount of air injected or the deploy depth of upwelling pipe.For the bubble curtain,we extend the theory of bubble plume in still water to the crossflow to study the separation phenomenon,and deduce a theoretical model of its trajectory.For the air-lift pump,we comprehensively analyse the energy budget of each part in the air-lift system through energy conservation equation,and obtain a simplified relationship between the lifted water flow rate and the air injection flow rate.Furthermore,a method for calculating the optimal deploy depth of upwelling pipe is also proposed.2.An experimental device for bubble plume was built in this dissertation,and some experiments have been carried out in a circulating flume to study the motion characteristics of bubble plume in crossflow and the effects of air flow rate and cross flow velocity on the separation of bubble plume.In the experiment,the tracer is photographed to track the trajectory of entrained plume,and experimental results are compared with theoretical calculation results to verify the validity and applicability of the theoretical model of bubble plume.3.In order to explore the application feasibility of air-lift artificial upwelling technology in lifting deep ocean water,we carry out a sea trial near Dongji island of the East China Sea.The reliability and survivability of i1proved air-lift upwelling device with "Upper Rigid and Lower Flexible" and”Shallow Air Injection" have been verified.Besides,with experiment data from the sea trial and previous lake trials,a comprehensive study on the effects of different engineering parameters(pipe diameter and submerged depth)and air injection method(nozzle shape,hole size,and submergence ratio)on the efficiency of air-lift artificial upwelling has been conducted.4.To explore the application prospects of bubble-curtain artificial upwelling technology in coastal areas,we combine bubble-curtain artificial upwelling technology with the kelp culture in coastal marine ranch.Aiming at the problem of nutrient deficiency during the peak season of kelp growth,a bubble-curtain artificial upwelling system based on in-situ energy supply by solar floating platform is designed,including the overall scheme design,the structure and function design of solar energy platform and air injection system design,etc.In the design,different kinds of air injection system are proposed,including marine cable,main air pipe and single air pipe,and all of them are nirther studied through deploy tests in sea trials.In addition,by combining the theory of bubble plume and tidal current conditions in mariculture zone,we propose an efficient air injection strategy under regular semi-diurnal tides to i1prove the efficiency of bubble-curtain artificial upwelling.5.In the dissertation,we carry out a sea trial of bubble-curtain artificial upwelling in Aoshan bay?Jimo,Qingdao city.Detailed process of the sea trial is described,and the difficulties encountered and solving experience are summarized.The advantages and disadvantages of different air injection systems are discussed and some measures for further improvement are proposed.In addition,the effect of bubble-curtain artificial upwelling is preliminarily evaluated by means of multi-site water sampling and physical and chemical sensor measurement,through which the application feasibility of bubble-curtain artificial upwelling technology in marine ranch is verified.The successful development of artificial upwelling in the sea trials proves the engineering feasibility to alleviate coastal ecological environment.Meanwhile it has extracted some technologies and accumulated valuable engineering experience,which paves the way for the future development of coastal environment restoration projects.Furthermore,the research results in this dissertation can also be applied in the fields of seabed resource exploitation,lake and river environmental restoration.