Optimization Of Cultivation Conditions And Development Of An Efficient Photobioreactor For Chlorella Emersonii

Chlorella,single-celled autotrophic organism of Chlorophyta,is an important raw material for the production of nutrient-balanced food,high-quality biodiesel and bioactive substances,and also widely used in environmental remediation and other industrial fields.The establishment of a large-scale cultivation system based on a photobioreactor is one of the key objectives for the commercialization of high-value products derived form Chlorella.The existing photobioreactors used for the cultivation of Chlorella have some defects such as high cost,low efficiency and poor monitoring system.In order to establish a high-efficient cultivation system of Chlorella in large scale,firstly,the current study was conducted to optimize various parameters for efficient cultivation of Chlorella.Secondly,based on these parameters,the theoretical model was designed,following by developing a new type of photobioreactor suitable for Chlorella growth and the related large-scale cultivation and monitoring system.Finally,CFD(Computational Fluid Dynamics)software was used to characterize several key parameters of this new photobioreactor including the algae flow field and the mixture of gas-liquid mass transfer.The reliability of the system was also tested qualitatively and quantitatively The main results are described as the followings.1.The oil-enriched Chlorella Emersonii strain Ce-sx-028 was selected as a test material of microalgae.The control variable method was used to screen the single factor variable for the optimal culture conditions of Chlorella.The desirable culture parameters obtained for Chlorella include the fowllowings:temperature 30±5?,light intensity 8000 lux,pH 5-9,N/P ratio 10:1,CO2 concentration of 10%(ventilation 1L/min),and inoculation amount of seed algae 12.5%(v/v).2.Accoding to the controllability of the optimum conditions for the microalgae cultivation,a new type of microalgae photobioreactor was designed and developed.This photobioreactor combined the advantages of higher-productivity and lower-energy consumption from flat-panel reactors and bubbling reactors,respectively.Moreover,such photbioreactor were accordingly equipped with some components for CO2-controlled aeration,and clearing of algae stiching on the wall,as well as multiple control systems of temperature,illumination,circulation,pH adjustment,and nutrient supply.Finally,an intelligent monitoring system was constructed for this photoreactor system to collect a variety of real-time data.3.CFD(Computational Fluid Dynamics)software was used to simulate the efficiency and reliablility of the photobioreactor.The mixing efficiency was selected as the key parameter for this analysis because it is the most important factor limiting the efficiency of photobioreactor.The flow field modeling and validation using aeration capacity as the variable by the bubbling-type photoreactor demonstrated,(1)the turbulent kinetic energy(TKE)was positively correlated to the turbulence dissipation rate(TDR);(2)the turbulence intensity in the reactor was suitable,and the effect of mixed mass transfer is obvious;(3)the small aeration rate in the reactor was enough to form the algae circulation,showing a higher turbulence intensity and a smaller dead area;(4)increasing aeration volume resulted obvious changes of variousparameters in the reactor.One of such changes was the increasing gas holdup and the decreasing dead-zone ratio.Therefore,the newly developed reactor has a strong gas-liquid mass transfer capability and a high mixing degree,which can meet the high efficiency cultivation of ChlorellaToken together,this study developed a new type of microalgae photobiorector with low-cost,high-efficient carbon fixation and high-biomassyield.The photobiorector also equipped with light-temperature control,algae circulation and pH adjustment,and intelligent Monitoring System.This photobiorector-based system established here provide scientific reference for large-scale cultivation of Chlorella and other economic microalgae and the commercial production of high-valued microalgae products.