Rotary discs reactor for enhanced production of microbial cellulose

Abstract

Production of microbial cellulose is receiving great attention since microbial cellulose is comparable to the synthetic cellulose, source of medium is abundant and cellulose has wide applications. However, microbial cellulose is produced in Malaysia in the form of ‘nata’ as food using traditional method only. Furthermore, the use of trays for static fermentation in traditional method is not economical, laborious and the up-scale process for high yield productivity is limited. This study aims to develop a practical methodology for enhanced production of microbial cellulose by designing a Rotary Discs Reactor (RDR). One of the major factors that determine the success of fermentation process is aeration during fermentation. Therefore, RDR applies the concept of Rotating Biological Contactor (RBC) that widely used in wastewater treatment in order to exposing the bacteria to oxygen for better aeration. This reactor consists of an array of discs that is mounted to a shaft. The shaft is connected to a driven motor so that the rotation of the shaft together with the discs is achievable and controllable. The discs on the shaft are positioned in a horizontally set trough that contains a biological medium in which at least a portion of the contained discs are being submerged. In the preliminary study of discs selection, discs made from stainless steel fabricated with 0.3cm mesh sizes gave the highest result compared to others. In addition, it was found that smallest mesh in stainless steel type of discs was advantagous in assisting the Acetobacter xylinum attachment onto the discs which resulted in better aeration and higher cellulose production. To study effect of rotation speed in RDR, fermentation in prepared sucrose medium had been carried out at the rotational speeds of 7, 9 and 11 rpm. It was found that rotational speed gives significant effect towards microbial cellulose production where fermentation in RDR using 7 rpm gave the highest microbial cellulose production of 149.12gram per liter substrate. A series of static and RDR fermentation had been run in a fixed condition in order to compare the production yields. Results showed that fermentation carried out using RDR gave 86.78% higher production of microbial cellulose compared to static fermentation after 5 days of fermentation. This indicated that RDR could give better aeration process compared to static fermentation. However, too much Dissolved Oxygen resulted from too high rotational speed resulted in decrease of microbial cellulose production in RDR as this affected the stability of the culture. Hence, it can be concluded that fermentation using RDR did not depend solely on dissolved oxygen in the medium as the rotation of discs permitted direct exposure to air for A.xylinum during the fermentation process.