Anaerobic digestion of aliphatic polyesters

Abstract

Anaerobic processes for the treatment of plastic materials waste represent versatile and effective approach in environmental protection and solid waste management. In this work, anaerobic biodegradability of model aliphatic polyesters, poly(L-lactic acid) (PLA), and poly(ɛ-caprolactone) (PCL), in the form of powder and melt-pressed films with varying molar mass, was studied. Biogas production was explored in batch laboratory trials at 55 ± 1°C under a nitrogen atmosphere. The inoculum used was thermophilic digested sludge (total solids concentration of 2.9%) from operating digesters at the Central Waste Water Treatment Plant in Prague, Czech Republic. Methanogenic biodegradation of PCLs typically yielded from 54 to 60% of the theoretical biogas yield. The biodegradability of PLAs achieved from 56 to 84% of the theoretical value. High biogas yield (up to 677 mL/g TS) with high methane content (more than 60%), comparable with conventionally processed materials, confirmed the potential of polyester samples for anaerobic treatment in the case of their exploitation in agriculture or as a packaging material in the food industry.

Methane Production from Poly(lactic Acid) (PLA) and Polyhydroxybutyrate (PHB) Biodegradable Plastics with Anaerobic Granulated Sludge

“…The CH4(g) conversion of PLA under thermophilic conditions was more effective than under mesophilic conditions. A high level of biodegradation of 82% to 90% was reported in a mean digestion time of 90 days, [14], [96], [97], [98], [99]. Other authors have found a lower level of biodegradation, between 40 and 60%, with a similar timeframe for the digestion, [18], [81], [84], [100].…”

“…However, it should be noted that the biodegradation levels were presented to 60% and 40%, respectively, were not the final biodegradation levels, as the BMP tests were stopped before they reached the plateau of methane production, [81], [84]. A decrease in the molecular weight of PLA was had a positive effect on the biodegradation kinetics, [98]. Thermophilic degradation of rigid pieces of PLA (1 x 1, 2 x 2, and 3 x 3 cm) assessed and observed negligible CH4(g) production of approximately 10 to 30 L CH4 / kg VS, [15].…”

Anaerobic Biodegradability of Commercial Bioplastic Products: Systematic Bibliographic Analysis and Critical Assessment of the Latest Advances

“…Pre-incubation of the inoculum with 20 mL of sludge acclimated to PLA 100 3 biogas x [ 101 ] PBS PBS 1 mm sheet 58 I/S = 2.85 (VS basis); working volume = 300 mL 100 0 0 CH 4 x [ 95 ] PCL PCL (Mn 58.1 kg.mol −1 ) 10 × 10 × 0.7 mm film 55 Plastic to inoculum ratio: 0.38 g COD/g VSS. Inoculum: thermophilic digested sludge from a digester 140 663 60 biogas DSC, SEM [ 160 ] …”

“… 75 --- 60.0 SEM x [ 159 ] PLA PLA (Mn 44.5 kg/mol) 10 × 10 × 0.7 mm film 55 Plastic to inoculum ratio: 0.15 g COD/g VSS. Inoculum: thermophilic digested sludge from a digester 120 677 74 biogas DSC, SEM [ 160 ] PLA PLA (Mn 3.4 kg/mol) Powder 55 Plastic to inoculum ratio: 0.15 g COD/g VSS. Inoculum: thermophilic digested sludge from a digester 90 520 56 biogas DSC, SEM PLA PLA (Mn 0.35 kg/mol) …”