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Design and Investigation of an Automatic Cultivating Reactor of the microalga
本研究旨在設計開發一套自動化微藻類反應器系統，連續生產微藻類細胞；系統主要由培養槽本體、曝氣裝置、pH值回饋控制、攪拌裝置、新培養液儲存槽、進排液控制裝置、溫度控制系統、光照裝置、外部遮蔽本體、PLC(可程式邏輯控制器)自動控制系統及各項感測器等所建構而成，並經由全光照之前導試驗，攪拌軸轉速可變頻控制在0至60Hz之間，其轉速經實際量測介於0至352.7rpm，同時建立轉速與變頻值之迴歸關係式(y=-0.04899 +5.87296x)；系統曝氣量之供給可依培養需求設定為0至4l/min；光照條件可依其需要作4、8與12只燈源切換，經量測其光照強度分別為2600、3600與5000 lux；系統水體溫度設定27℃時，可保持系統溫度介於25至29℃範圍之間；pH值可經由CO2注入調控在其設定範圍內，目前控制在6.5至7.5pH之間；進排液可依其培養週期，作循環模式、手動切換、定時與濁度控制，進而啟動進液與排液之電磁閥，完成收穫與新液注入等功能；反應器培養槽與新培養液儲存槽有效水體分別為150與120公升(l)。研究並以大溪地等鞭金藻，進行相關批次式基礎試驗，其中包括海水滅菌ヽ接種量ヽ鹽度ヽ光週期ヽ溫度、培養液濃度等試驗，進而獲致批次試驗時以接種量25%、鹽度30ppt、全光照、溫度25℃及正常培養液濃度條件下為較佳之培養條件；經實際培養測試微藻類反應器其放大培養程序、光照強度、最大增殖濃度與半連續試驗，獲致本系統在有效水體約為120公升(l)、不同光照強度、鹽度28±0.5ppt、pH值回饋範圍為7±0.5與溫度範圍25至29℃時，以批次式培養時發現放大培養週期以不超過5天與使用較高光照強度條件下培養為佳，且於最大增殖試驗時，可獲致藻細胞濃度約1192×104cell/ml；並進一步以半連續式培養測試時發現稀釋率以較低為佳，因此本研究之自動化半連續培養試驗採稀釋率16.66%進行31天培養，結果獲致每日可收穫定量高濃度藻體溶液，平均藻細胞生長濃度與乾物重(純水清洗)約為548×104 cell/ml及0.0015g/ml，而稀釋後平均藻濃度約為395×104cell/ml，即單日之藻細胞增殖濃度平均約為150×104cell /ml；同時發現生長速率以培養前階段(第0至15天)有較大之單日平均值，約為0.43，而培養後階段(第16至30天)生長速率單日平均則為0.24，但其生長則為呈較穩定之趨勢，因此證實本研究之自動化半連續式反應器已具有良好且穩定之長時間培養微藻能力。
An automatic cultivating reactor system which can be used to continuously produce the microalgal cells has been designed and developed in this research. The system was constructed and combined together with the parts of the cultivating tank, the aeration equipment, the pH value feedback control device, the stirring device, the new cultivating solution storage unit, the solution inlet and outlet control equipment, the temperature control system, the illumination device, the outer cover unit, the PLC (programmable logical controller) automatic control system and other sensors. Through the pilot tests using the set of continuous illumination, the rotation speed of the stirring shaft measured was varying between 0 and 352.7rpm and which could be adjusted and controlled using an indirect circuit frequency controller between frequencies of 0 and 60Hz. A regression equation (y=-0.04899+5.87296x) between the relation of rotation speed and frequency was also established. According to the need of the cultivating requirement, the air supply amount could be chosen from 0 to 4 l/min and the illumination condition could be changed to 4, 8 or 12 light sources with the illuminance of 2600, 3600 or 5000 lux respectively. The system temperature could be maintained between 25 and 29℃ while setting the reactor temperature at 27℃. The pH level was also held between the range of 6.5 and 7.5 as controlled by injecting an appropriate amount of the CO2 gas. Based on the cultivation period of the microalga, the ignition point of the replenishment of the new cultivating solution and the delivery of the harvesting solution could depend on the choice of the controlling methods such as the continuous mode, hand-operation, timing and turbidity, to turn on and off the solution inlet and outlet electromagnetic valves respectively to complete each cultivating cycle. The valid capacities of the cultivating tank of the reator and the storage tank of the new cultivating solution storage unit were 150 and 120 litters, respectively. This research applied Tahiti Isochrysis galbana affinis to process the foundamental tests of the effects of each relevant batch type rearing, including the factors of the inoculation amount, the salinity, the illumination period, the cultivation temperature and the ingredient concentration of the cultivating solution, and the relevant rearing tests of the reactor system. The experimental results of the foundamental batch tests showed that the optimal cultivating conditions of the inoculation amount, the salinity and the temperature were 25%, 30ppt and 25℃, respectively with continuous illumination and normal ingredient concentration of the cultivating solution. The results from the testing of the enlarging cultivation, the illumination intensity, the most growing concentration and the semi-continuous rearing of the reactor system also showed that under the cultivating conditions used with the valid cultivating volume 120 l, different illumination intensities, salinity 28±0.5ppt, pH value 7±0.5 and temperature range 25-29℃ of the reactor, the cultivation period was found under 5 days in the batch cultivation, the higher illumination intensity was better, and the most growing concentration was up to 1192×104 cell/ml. The semi-continuous cultivating tests also demonstrated that the lower dilution ratio was better. During 31 days of the automatic semi-continuous cultivating test with daily dilution ratio 16.67％, the reactor could produce a high concentration solution of the algal cell. The daily average growing concentration was up to 548×104 cell/ml with the dry weight (washing with pure water) of 0.0015g/ml, and the average concentration of the agal cell after dilution was about 395×104cell/ml. It showed that an average increasing rate per day was 150×104 cell/ml. The average daily growth rate of the front section (from day 0 to 15) was higher with the value of 0.43; however, the growth of the rear section (from day 16 to 30) was more stable with a lower daily average growth rate of 0.24. The experiments also verified that the reactor system presently developed in this reseach obtained the capability of stable and long-term cultivating functions.
Keywords : Microalgae, Automatic semi-continuous, Reactor
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