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. 2023 Mar 28;16(7):2693.
doi: 10.3390/ma16072693.

Microbial Recycling of Bioplastics via Mixed-Culture Fermentation of Hydrolyzed Polyhydroxyalkanoates into Carboxylates

Yong Jin  1 , Kasper D de Leeuw  1   2 , David P B T B Strik  1
Affiliations

Microbial Recycling of Bioplastics via Mixed-Culture Fermentation of Hydrolyzed Polyhydroxyalkanoates into Carboxylates

Yong Jin et al. Materials (Basel). .

Abstract

Polyhydroxyalkanoates (PHA) polymers are emerging within biobased biodegradable plastic products. To build a circular economy, effective recycling routes should be established for these and other end-of-life bioplastics. This study presents the first steps of a potential PHA recycling route by fermenting hydrolyzed PHA-based bioplastics (Tianan ENMATTM Y1000P; PHBV (poly(3-hydroxybutyrate-co-3-hydroxyvalerate)) into carboxylates acetate and butyrate. First, three different hydrolysis pretreatment methods under acid, base, and neutral pH conditions were tested. The highest 10% (from 158.8 g COD/L to 16.3 g COD/L) of hydrolysate yield was obtained with the alkaline pretreatment. After filtration to remove the remaining solid materials, 4 g COD/L of the hydrolyzed PHA was used as the substrate with the addition of microbial nutrients for mixed culture fermentation. Due to microbial conversion, 1.71 g/L acetate and 1.20 g/L butyrate were produced. An apparent complete bioconversion from intermediates such as 3-hydroxybutyrate (3-HB) and/or crotonate into carboxylates was found. The overall yields of the combined processes were calculated as 0.07 g acetate/g PHA and 0.049 g butyrate/g PHA. These produced carboxylates can theoretically be used to reproduce PHA or serve many other applications as part of the so-called carboxylate platform.

Keywords: PHA recycling; PHBV; anaerobic fermentation; carboxylates; hydrolysis.

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Conflict of interest statement

The authors declare no conflict of interest. Kasper D. de Leeuw is a researcher at ChainCraft which is a company developing a platform technology to produce fatty acids from organic residues; he is, as well, a lecturer and postdoctoral researcher at Wageningen University and Research.

Figures

Figure 1
Figure 1
Proposed new route for recycling PHA via the formation of carboxylates after PHA application.
Figure 2
Figure 2
(A). Comparison of soluble COD (SCOD) after three pretreatments for PHBV. (B). COD (TCOD is the total COD of PHBV, and SCOD is measured soluble COD); and pH change between the start and end of alkaline pretreatment.
Figure 3
Figure 3
(A). Total SCOD of supplied PHBV (as hydrolysate), SCOD (as carboxylates), and pH during mixed-culture fermentation, (B). Total supplied SCOD (as hydrolysate) and pH change in the control group experiment.
See this image and copyright information in PMC

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