Autoclaving treatment of wasted disposable bamboo chopsticks

• Dry-basis reductions of bamboo chopstick BC and its combustibles increase with autoclaving time and temperature.
• For mild autoclaving, large portions of combustibles CBs are still kept, maintaining the utilization properties of BC.
• Autoclaving of BC at 428 K and 60 min is proper, preserving 84.11 wt.% CBs.
• The energy densitification ratio of BC mildly increases to 1.06–1.17 after autoclaving.
• The pyrolysis characteristics of autoclaved BCs under the conditions of this study are closed to that of un-autoclaved BC.

The autoclaving combined with mechanical separation, known as the mechanical heat treatment, is one of the promising alternatives to treat the mixed wastes consisting of organics and inorganics. After autoclaving, the organics can then be sorted, separated and recovered for the re-utilization. In this study, the steam autoclaving of bamboo chopstick (BC), which is one of the major biomasses in the municipal solid waste, was performed. The effects of steam autoclaving temperature (T) and autoclaving reaction time (t) on the characteristics of BC were examined. The thermal gravimetric and differential thermo-gravimetric analyses were conducted to assess the pyrolysis behavior of autoclaved BC which can be further treated to produce up-graded refuse derived fuel or bio-char. The results indicated that the autoclaving extent of BC (=(initial mass − mass at t)/initial mass, in dry basis) increases with increasing T and t. The high heating value per mass in dry basis (HHMD) of raw BC after autoclaving increases from 4365 kcal/kg to about 4975 kcal/kg at T = 428 K with t = 60 min (A428-60) and to 5044–5158 kcal/kg at 453 K with 30 (A453-30) and 60 min (A453-60), enhancing the energy densification ratio (ratio of HHMD after to that before autoclaving) to 1.06–1.17. However, on the wet basis, the water content of autoclaved product for the case of A428-60 is 35.85 wt.% being less than those of A453-30 and A453-60 of 45.33–55.20 wt.%. The comparison indicated that the conditions at 428 K with 60 min are more appropriate than the others, giving satisfactory HHMD with less water content. The pyrolysis behaviors of autoclaved BCs employing T = 428–453 K and t = 15–60 min are closed to that of raw BC, thus retaining the pyrolytic quality of BC. The information obtained in the present study is useful for the rational design and proper operation of autoclaving system for treating the wasted BC.