Comparison of Different Strategies for Selection/Adaptation of Mixed Microbial Cultures Able to Ferment Crude Glycerol Derived from Second-Generation Biodiesel.

C Varrone,S B Le,I V Skiadas,S Markussen,T Haugen,H N Gavala,T M B Heggeset

doi:10.1155/2015/932934

Abstract

Objective of this study was the selection and adaptation of mixed microbial cultures (MMCs), able to ferment crude glycerol generated from animal fat-based biodiesel and produce building-blocks and green chemicals. Various adaptation strategies have been investigated for the enrichment of suitable and stable MMC, trying to overcome inhibition problems and enhance substrate degradation efficiency, as well as generation of soluble fermentation products. Repeated transfers in small batches and fed-batch conditions have been applied, comparing the use of different inoculum, growth media, and Kinetic Control. The adaptation of activated sludge inoculum was performed successfully and continued unhindered for several months. The best results showed a substrate degradation efficiency of almost 100% (about 10 g/L glycerol in 21 h) and different dominant metabolic products were obtained, depending on the selection strategy (mainly 1,3-propanediol, ethanol, or butyrate). On the other hand, anaerobic sludge exhibited inactivation after a few transfers. To circumvent this problem, fed-batch mode was used as an alternative adaptation strategy, which led to effective substrate degradation and high 1,3-propanediol and butyrate production. Changes in microbial composition were monitored by means of Next Generation Sequencing, revealing a dominance of glycerol consuming species, such as Clostridium, Klebsiella, and Escherichia.

Highlights

The exponential growth of biodiesel production in the last decade has led to a concomitant increase in crude glycerol [1, 2]
For the quantification of volatile fatty acids (VFAs), filtered samples were acidified with H3PO4 (30 μL of 17% H3PO4 was added in 1 mL of sample) and analyzed on a gas chromatograph (PerkinElmer, Clarus 400), equipped with a flame ionization detector and a capillary column (Agilent HPFFAP, 30 m long, 0.53 mm inner diameter)
The strategy of Kinetic Control coupled with Minimal Medium (MM-KC) led to a maximum ethanol yield of 4.6 g/L, together with a 1,3 PD yield of around 3 g/g, with complete substrate degradation within 21 h

Summary

Introduction

The exponential growth of biodiesel production in the last decade has led to a concomitant increase in crude glycerol [1, 2]. New uses of crude glycerol are required in order to overcome the problem of glycerol glut. Environmental biotechnologies are going to provide a significant contribution to tackle the challenge of a more efficient use of by-products and waste streams. In this frame, a so-called “ecobiotechnological approach” has been recently proposed as an interesting tool for a more effective exploitation of wastes and wastewaters [4]

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Conclusion