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

• Published in: Materials Vol. 16; no. 7; p. 2693
• Main Authors: Jin, Yong, de Leeuw, Kasper D, Strik, David P B T B
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 28.03.2023; MDPI
• Subjects: anaerobic fermentation; Bioconversion; Biodegradable materials; Biodegradation; Biogas; Bioplastics; Carbon; Carboxylates; Chemical oxygen demand; Climate change; Computer industry; End of life; Esters; Fermentation; Germany; Hydrolysates; Hydrolysis; Microorganisms; Netherlands; Nutrients; PHA recycling; PHBV; Plastics; Polyhydroxyalkanoates; Polymers; Pretreatment; Recycling; Recycling (Waste, etc.); Substrates; United States; United States; Netherlands; Germany; anaerobic fermentation; PHA recycling; PHBV; carboxylates; hydrolysis
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma16072693

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.