การผลิตเอธานอลโดยระบบ pH-auxostat: ผลของรูปแบบการควบคุมอัตโนมัติและความเป็นกรดด่างต่อการเจริยของ Zymomonas mobilis

Ethanol Fermentation in pH-Auxostat Culture: Influence of Automatic Controllers and pH on the Growth of Zymomonas mobilis

Name: ทัศนพร แก้วทองมา

Organization : มหาวิทยาลัยเทคโนโลยีพระจอมเกล้าธนบุรี

keyword: Zymomonus mobilisl pH-auxostatl ethanol fermentation

; automatic controller

; culture pH

; cassava starch

Abstract: A pH-auxostat continuous culture is known as a system employing growth-dependent pH changes to control rate of medium addition. A major problemencountered in pH-auxostat control for continuous ethanol fermentation ofZymomonas mobilis was that the estimated dilution rate could be too low and thusaffected ethanol productivity. In this system, rate of medium feed is very muchsensitive to even little change in pH. Therefore, to control the rate of ethanolproduction, the effect of automatic control systems and a variation in culture pHwere investigated. In this controlled system, two alternative methods which were pHmediated control feed with two pH difference feed media and pH control usingautomatic controllers with proportional (P), proportional plus integral (PI),proportional plus derivative (PD), and proportional plus integral plus derivative(PID) controllers, for maintaining the culture at set point (pH 5.5), were investigated.In the culture pH experiment, the following culture pH were varied as follows; 4.5,5.0, 5.5, 6.0 and 6.5. In addition, the feasibility of cassava starch as substrate forethanol production was evaluated as well.Using two buffered feed media (pH5.5 and 6.5) for the control, the pH in theculture could not be maintained at the set point although a high dilution rate (0.33h-1) was achieved in the system. The residual glucose was wasted through theeffluent and cells were eventually washed out. For the pH-auxostat culture using thefour controlling systems, the biomass concentration and dilution rate obtained werenot only determined by the growth rate of the culture ~ i t h respect to a change of pHbut also by the buffering capacity regulated by the following process parameters, PB(Proportional band), T (heat side proportional cycle), Ti (Integral time), Ar (Anti-reset windup), and Td (Derivative time) under an automatic controller. A 0.4% of PBwas observed to be the optimum value for controlling pH within the system withoutoffset. However, for other process parameters, small values of those T, Ti, Ar, andTd, resulted in low dilution rate and low ethanol productivity. An experimental setupusing the PID system demonstrated advantage over another with a feedback control(the P, PI, PD systems). Under the optimum condition using the PID controller, highethanol productivity of over 11 g R1 h-1 could be obtained. Furthermore, whencomparing the growth in pH-auxostat cultures at pH 4.5, 5.0, 5.5, 6.0 and 6.5, thefermentation rate and ethanol productivity were highest during the growth at pH 5.5.It could be suggested that the culture pH affected to the ratio between the inflows offresh medium and the base solution (r). As a result, "wash out" was observed at thedilution rate below or above pH optimum range.Under optimum condition of PID controller at pH 5.5, the ethanolfermentation in pH -auxostat culture using Z. mobilis could be operated at dilutionrate higher than 0.3 h-1, for a longer period of time (as long as 40 h) and withoutproduct inhibition. The ethanol productivity obtained from glucose medium andcassava starch hydrolysate under these conditions was about 11 and 10 g r1 h-1,respectively. This suggested that cassava starch materials are feasible for effectivesubstitutes of glucose for ethanol production using Z mobilis.

มหาวิทยาลัยเทคโนโลยีพระจอมเกล้าธนบุรี

Address: กรุงเทพมหานคร (Bangkok)

Email: info.lib@mail.kmutt.ac.th

Name: Asst.Prof.Dr.Sudarut Tripetchkul

Role: Supervisor

Created: 2544

Issued: 2005-10-26

Modified: 2019-06-24

วิทยานิพนธ์/Thesis

ISBN: 9746284916

CallNumber: BIT356

tha

DegreeName: วิทยาศาสตรมหาบัณฑิต

Level: ปริญญาโท

Descipline: เทคโนโลยีชีวภาพ

Grantor: มหาวิทยาลัยเทคโนโลยีพระจอมเกล้าธนบุรี

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