Anaerobic Membrane Bioreactor for Continuous Lactic Acid Fermentation.

Rong Fan,Peter Czermak,Mehrdad Ebrahimi

doi:10.3390/membranes7020026

Rong Fan, Peter Czermak + Show 1 more

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https://doi.org/10.3390/membranes7020026

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Abstract

Membrane bioreactor systems can enhance anaerobic lactic acid fermentation by reducing product inhibition, thus increasing productivity. In batch fermentations, the bioconversion of glucose is strongly inhibited in the presence of more than 100 g·L−1 lactic acid and is only possible when the product is simultaneously removed, which can be achieved by ceramic membrane filtration. The crossflow velocity is a more important determinant of flux than the transmembrane pressure. Therefore, to stabilize the performance of the membrane bioreactor system during continuous fermentation, the crossflow velocity was controlled by varying the biomass concentration, which was monitored in real-time using an optical sensor. Continuous fermentation under these conditions, thus, achieved a stable productivity of ~8 g·L−1·h−1 and the concentration of lactic acid was maintained at ~40 g·L−1 at a dilution rate of 0.2 h−1. No residual sugar was detected in the steady state with a feed concentration of 50 g·L−1.

Highlights

Membrane bioreactors (MBRs) are hybrid systems comprising a bioreactor for bioconversion and a membrane device for separation
The settling tank in a conventional activated sludge process was replaced with a membrane device, improving the effluent quality, increasing volumetric loading rates and solid retention times, and reducing hydraulic retention times and sludge production [3,4,5,6]
System for wastewater treatment, anaerobic MBRs can be used in fermentation processes to produce organic acids such as itaconic [11], propionic [12], and lactic acids [13,14], because the fermentation of these organic acids generally takes place in anaerobic environments

Summary

Introduction

Membrane bioreactors (MBRs) are hybrid systems comprising a bioreactor for bioconversion and a membrane device for separation. Dorr-Olivier Inc. reported the first application of crossflow membrane filtration in an activated sludge bioreactor for wastewater treatment [1,2] In this system, the settling tank in a conventional activated sludge process was replaced with a membrane device, improving the effluent quality, increasing volumetric loading rates and solid retention times, and reducing hydraulic retention times and sludge production [3,4,5,6]. The submerged membranes rely on coarse bubble aeration to minimize fouling, while aeration transfers oxygen to the biomass and maintains the solids in suspension, improving the efficiency of biodegradation Since these early applications, MBR systems have devolved rapidly to meet diverse requirements in different bioprocesses, reflecting their advantages in terms of biocatalyst immobilization, and simultaneous product generation and recovery. In addition to the aerobic MBR system for wastewater treatment, anaerobic MBRs can be used in fermentation processes to produce organic acids such as itaconic [11], propionic [12], and lactic acids [13,14], because the fermentation of these organic acids generally takes place in anaerobic environments

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