Enhanced Anaerobic Biodegradation and Biomethane Production from Bioplastics by the Addition of Aerobically Prepared Triacylglycerol Lipase

Abstract

This study aimed to overcome the limited biodegradability of bioplastics under anaerobic conditions. With polycaprolactone (PCL) as a model system, the effect of a bioplastic-degrading enzyme, triacylglycerol lipase (TGL), on its degradation and biomethane production was investigated. As the PCL film did not show evidence of any degradation over 14 days under anaerobic conditions in the sludge, TGL from Bacillus sp. JY35 was added to promote PCL breakdown into its monomeric form, which could be used for methane production. Application of 200 units/mg of TGL in the sludge led to a 33% increase in PCL degradation over 7 days, with sustained lipase activity despite the decreasing trend in effectiveness after 72 h. Across all type of samples, methane production in the TGL-supplemented sludge increased 1.8-fold across sludge types and up to 2.2-fold when bioplastics other than PCL underwent degradation, compared with that in the untreated sludge. Our result showed the addition of concentrated enzyme could effectively improve bioplastics biodegradability concomitant with methane production under anaerobic conditions, thus offering a feasible approach for optimizing anaerobic degradation with various bioplastics such as Polybuthylene succinate (PBS), and Polybutylene adipate-co-terephthalate (PBAT) although it will take longer time than PCL.

Keywords: Anaerobic degradation; biomethane; enzymatic treatment; polycaprolactone; sludge; triacylglycerol lipase.

Fig. 1. PCL degradation and lipase activity under aerobic and anaerobic conditions.

(A) Degradation yield after 7 days of degradation under aerobic and anaerobic conditions. (B) TGL activity under both conditions using substrates of varying chain lengths (C6, C8, C10, and C12).

Fig. 2. Comparison of methane production by the sludge with or without PCL film and ε-caprolactone over time.

(A) Biomethane production and degradability tests with or without PCL film. (B) Biomethane production with or without ε-caprolactone.

Fig. 3. Comparison of PCL degradation with different concentrates of culture filtrates.

(A) Degradation yield (%) of PCL films and, (B) lipase enzyme activity of degradation strains conducted using p-nitrophenyl hexanoate (C6).

Fig. 4. Application of TGL concentrates (200 U/mg) to sludge for PCL degradation.

(A) Time dependent methane production and biodegradability of PCL films by sludge. (B) lipase activity of degrading strains conducted using p-nitrophenyl hexanoate (C6).

Fig. 5. Biomethane production and degradability test using different sludges with or without TGL.

(A) Biomethane production and degradability between sludge (control) and supplemented sludge in sludge samples of various provenances. (B) lipase enzyme activity of degradation strains conducted using p-nitrophenyl hexanoate (C6).

Fig. 6. Biomethane production and degradability tests using various types of plastic films with or without TGL.

(A) Biomethane production and degradability between sludge (control) and PBS, PBAT and PHB plastic film. (B) lipase enzyme activity of degrading strains conducted using p-nitrophenyl hexanoate (C6).