Anaerobic biodegradation tests of poly(lactic acid) and polycaprolactone using new evaluation system for methane fermentation in anaerobic sludge

The anaerobic biodegradation tests of polycaprolactone (PCL) and poly(lactic acid) (PLA) powders were done at thermophilic temperature (55 °C) under aquatic conditions (total solid concentrations of the used sludge were 1.73% (undiluted sludge) and 0.86% (diluted sludge)) using a newly developed evaluation system. With this system, the evolved biogas is collected in a gas sampling bag at atmospheric pressure. This method is more convenient than using a pressure transducer or inverted graduated cylinder submerged in water. The biodegradation of PCL powder (10 g, 125-250 μm) in the diluted sludge stopped in about 47 days when the biodegradability reached 92%. The biodegradability of PLA powder (10 g, 125-250 μm) in undiluted sludge was 91% at about 75 days. The biodegradability of PLA powder (10 g, 125-250 μm) in diluted sludge was 79% at about 100 days. The biodegradability of PLA powder (5 g, 125-250 μm) in diluted sludge was 80% at about 85 days. It was found that the PCL and PLA powders were quite degraded using the new evaluation method. In addition, the smaller particle size PCL powder was biodegraded faster.