Abstract
Given the large amount of crude glycerol formed as a by-product in the biodiesel industries and the concomitant decrease in its overall market price, there is a need to add extra value to this biorefinery side stream. Upgrading can be achieved by new biotechnologies dealing with recovery and conversion of glycerol present in wastewaters into value-added products, aiming at a zero-waste policy and developing an economically viable process. In microbial bioelectrochemical systems (BESs), the mixed microbial community growing on the cathode can convert glycerol reductively to 1,3-propanediol (1,3-PDO). However, the product yield is rather limited in BESs compared with classic fermentation processes, and the synthesis of side-products, resulting from oxidation of glycerol, such as organic acids, represents a major burden for recovery of 1,3-PDO. Here, we show that the use of an enriched mixed-microbial community of glycerol degraders and in situ extraction of organic acids positively impacts 1,3-PDO yield and allows additional recovery of propionate from glycerol. We report the highest production yield achieved (0.72 mol1,3-PDO mol−1glycerol) in electricity-driven 1,3-PDO biosynthesis from raw glycerol, which is very close to the 1,3-PDO yield reported thus far for a mixed-microbial culture-based glycerol fermentation process. We also present a combined approach for 1,3-PDO production and propionate extraction in a single three chamber reactor system, which leads to recovery of additional 3-carbon compounds in BESs. This opens up further opportunities for an economical upgrading of biodiesel refinery side or waste streams.
Highlights
Biodiesel production, as a promising alternative and renewable fuel, has continuously grown over the past decade (Clomburg and Gonzalez, 2013)
Glycerol (2.2 g chemical oxygen demand (COD) L−1) was still detected after 11 days. It was only after a second subsequent transfer (Transfer 2; Figure 2A) into fresh growth medium that glycerol was removed for 98% (0.3 g COD L−1), which coincided with a high 1,3-PDO concentration (13.0 g COD L−1) and a lower butyrate production (3.0 g COD L−1) compared with the previous transfer
Production rates for 1,3-PDO were slightly higher in HA medium (4.3 vs. 3.1 g COD L−1day−1), while butyrate production rates were similar between the two media (0.5 vs. 0.4 g COD L−1day−1)
Summary
As a promising alternative and renewable fuel, has continuously grown over the past decade (Clomburg and Gonzalez, 2013). Growth in its production has been less than the anticipated target and has increased at a slower pace during the last few years (Yang et al, 2012). The expansion of the biodiesel industry has, created a surplus of glycerol, resulting in an abundance of waste glycerol considered as a waste stream with associated disposal costs and a concomitant decrease in its overall market price. During 2004–2011, the biodiesel production has increased by 25 times and the market price of crude glycerol (80% pure) has decreased by a factor three in the USA (Clomburg and Gonzalez, 2013). It is of major importance to find a recycling solution for this waste glycerol to make biodiesel production more sustainable and economically viable
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