Zymomonas mobilis Biofilm Reactor for Ethanol Production Using Rice Straw Hydrolysate Under Continuous and Repeated Batch Processes.

Tatsaporn Todhanakasem,Verawat Champreda,Piyawit Koomphongse,Pattanop Kanokratana,O-lan Salangsing,Sanya Kaewket

doi:10.3389/fmicb.2019.01777

Abstract

Plastic composited corn silk was developed as a biotic/abiotic carrier for Zymomonas mobilis biofilm formation for the purpose of ethanol production. Furthermore, we explored the use of rice straw hydrolysate as substrate in both multistage continuous culture and repeated batch processes and compared the ethanol production efficiency by two strains of Z. mobilis. Biofilm formed by bacterial strains Z. mobilis ZM4 and TISTR551 were detected, and its proficiencies were compared under various conditions by scanning electron microscopy (SEM) and crystal violet assays. The greatest biofilm formed by both strains was found on day five after the inoculation. Z. mobilis strain ZM4 grown in repeated batch biofilm reactors produced higher yields of ethanol than TISTR551 grown under the same conditions, while TISTR551 produced higher yields of ethanol in the multistage continuous process. The yields were highly maintained, with no significant differences (p < 0.05) among the three consecutive repeated batches. These experiments highlight exciting uses for agricultural byproducts in the production of ethanol using Z. mobilis biofilm reactors.

Highlights

Lignocellulosic materials are abundant renewable resources that mainly contain cellulose, hemicellulose and lignin, in which cellulose and hemicellulose are the main carbohydrate sources
Zymomonas mobilis ZM4 and TISTR551 were cultivated in a biofilm medium to allow development of biofilms on plastic composited corn silk carriers
Fermentation processes can be classified into two categories according to the morphological state of the microbial biomass

Summary

Introduction

Lignocellulosic materials are abundant renewable resources that mainly contain cellulose, hemicellulose and lignin, in which cellulose and hemicellulose are the main carbohydrate sources. Cellulose is a long chain of crystalline glucose molecules, while hemicellulose is mainly composed of a mixture of five- carbon sugars. This makes lignocellulosic material a potential carbon source that contributes significantly to various bioprocesses to produce many value-added products, including bioethanol and other commodities without competition for food demand (Isikgor and Becer, 2015). Bioethanol and other commodities could be produced from many agricultural waste products obtained from rice milling. Lignocellulosic materials are not readily accessible to enzymatic hydrolysis, and processing them requires physical, chemical and enzymatic pretreatments. The pretreatment processes cause an extensive modification of the lignocellulosic

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