KOSEN 한인과학기술자네트워크

직접 발효기로 미생물을 배양하면서 나오는 데이터를 갖고 계산하면 비교적 쉽습니다만...말로 아주 쉽게 설명하라고 하면 정말 어렵네요.. KLa에 대하여 생물공학책에 흔히 나오는 식이 아래의 식입니다.. KLa = Rr/(Cs-CL) KLa는 물질전달계수인데... 발효에서는 산소전달계수(hr-)로 많이 이용되지요.. Rr : 배양액의 산소이용속도[mgO₂/ℓ·hr] Cs : 발효기내 배양액의 포화 DO농도[㎎/ℓ] CL : 발효기내 배양액의 DO농도[㎎/ℓ] 그러면 KLa를 구하려면 Rr. Cs, CL을 모두 알아야한 구할 수 있겠지요.. DO Probe 사용해서 KLa 구하는 방법이 있지만... 엄청나게 쉽지는 않고... 어느정도의 발효기의 운영과 여기서 나오는 데이터에 대한 연산이 수반되어야 합니다. DO값은 변화더라도 KLa 값은 안 변하는 것이 아니고 변하지요.. Cs는 대략 25도 1atm에서 7 mg/l로 정해져 있는데 CL이 높아지거나 낮아지면... (Cs-CL)이 변해서 KLa 값이 달라지겠지요.. 그리고 vvm값과 KLa 값의 연관 관계는 글쎄요?? VVM은 aeration volume/medium volume/minute로 즉 1분당 발효조 부피 당 유입되는 공기량입니다.. KLa에서는 배양액의 산소이용속도도 주요 인자로 작용하기 때문에 이 VVM 만으로 KLa와 어떤 직접적인 연관관계를 찾는 것은 어려울 것 같네요... 아래가 DO probe를 이용해서 KLa를 구하는 실험방법입니다만... 질문하신 분에게는 많이 어렵지 않을까하는 생각이 듭니다.. Measurement of Kla in a Sparged Bioreactor Introduction Dissolved oxygen is an important substrate in aerobic fermentations. Since oxygen is sparingly soluble in water, it may be the growth-limiting substrate in these fermentations. For bacteria and yeast cultures, the critical oxygen concentration is about 10% to 50% of the saturated DO (dissolved oxygen concentration). Above this critical concentration, the oxygen concentration no longer limits growth. For optimum growth it is therefore important to maintain the DO above this critical level by sparging (bubbling gas through) the fermentor with air or pure oxygen. Of course, to be effective, the mass transfer rate from the gas bubbles to the liquid broth must equal or exceed the rate at which growing cells take up the oxygen. Oxygen transfer is usually limited by the liquid film surrounding the gas bubbles. The rate of transport is given by: NO2=kLa(c*-CL) (1) where kL is the oxygen transport coefficient (cm/h), a is the gas-liquid interfacial area (cm2/cm3), kLa the volumetric oxygen transfer coefficient (h-1), C* is saturated DO concentration (mg/l) (approx. 7 mg/l at 25 deg. C and 1 atm.), CL is the actual DO concentration in the liquid (mg/l), and NO2 is the rate of oxygen transfer (mg O2/ l· h) (Shuler and Kargi, 1992) In this lab you will use a “gassing-in” method to measure kLa. Linek, Sinkul, and Benes describe this method in several excellent review articles. The fermentor should be filled approximately 2/3 full with water. Valves on the back of the fermentor allows you to first de-gas the liquid by sparging with nitrogen, and then introduce a step change to pure oxygen. The rate of gas transfer to the liquid is determined by using a DO probe that is mounted in the fermentor head. This probe is connected to a DO meter, which in turn is connected to a data acquisition (DAQ) system on the PC. Note that the DO probe we are using has a relatively slow response time, and you may want to take probe dynamics into account. The value of kLa may be determined by analysis o f the concentration vs. time data. The DAQ system is also set up to automatically monitor impeller (stirrer) speed and fermentor temperature, and to store it in an Excel spreadsheet. You will want to check the calibration on these parameters to make sure you are getting accurate data. Assignment 1) Design and perform an experiment to measure probe response time. 2) Design and perform an experiment to characterize the dependence of kLa on impeller speed. 3) Design and perform an experiment to characterize the dependence of kLa on superficial gas velocity *design the experiments so that they measure, to the extent possible, the interaction of the two variables also) 4) Use the results of items 1-3 to determine coefficients/exponents a, b, c in an equation of the form: KLa = aebVc5 where e is power dissipated in volume of liquid phase (W/m3) and ns is the superficial gas velocity in meters per second (note, you will need to measure the appropriate variables to obtain power input). Compare to literature values, etc. 5) Use the article by Brown as a guide to investigating and discussing alternative forms of correlations, the assumptions that are required in those forms and their applicability to our experimental system Starting References: Linek, V, Sinkule, J, and Benes, P, 1991, Critical Assessment of Gassing-In Methods for measuring kLa in Fermentors, Biotechnology and Bioenginering 38, 323-330 Linek, V and Benes, P, 1987, Critical Review and Experimental Verification of the Correct Use of the Dynamic Method for the Determination of Oxygen Transfer in Aerated Agitated Vessels to Water, Electrolyte Solutions and Viscous Liquids, Chemical Engineering J. 34, 11-34 Perry’s Handbook, 50th ed., section 28 Shuler, ML and Kargi, F., 1987, Bioprocess Engineering: Basic Concepts, Prentice Hall, NJ *Also any other good biochemical engineering text (i.e. Bailey and Ollis) , Perry’s Handbook (Liquid-Gas Systems, Biochemical Engineering), and misc. journal articles. >안녕하세요. > >지금 발효를 공부하고 있는 사람입니다. > >KLa 값을 구하려고 하는데 책에 너무 어렵게 되어 있네요. > >혹시 DO Probe 사용해서 쉽게 KLa 구하는 방법이 없나요. > >그리고 초기 KLa 값이 시간이 지나면 변하나요? > >제 생각엔 DO값은 변화더라도 KLa 값은 안 변할 것 같은데.. > >그리고 vvm값과 KLa 값의 연관 관계 좀 알려 주시면 감사하겠습니다. > >솔찍히 KLa 값에 대한 정의가 잘 안 잡히네요. > >답변 부탁드립니다.