Title Page
Contents
ABSTRACT 9
Ⅰ. Introduction 11
Ⅱ. Materials and Methods 15
2.1. Isolation of polylactic acid (PLA) degradation-potential strains 15
2.1.1. Materials 15
2.1.2. Media 15
2.1.3. Isolation of strains from soil and compost samples 16
2.1.4. Comparative growth of PLA-degrading microorganisms in culture media with different carbon source 17
2.1.5. Identification of potential PLA-degrading bacteria 17
2.2. Selection of microbial strains 18
2.2.1. Strains 18
2.2.2. Enzyme activity 18
2.3. Preparation of microbial complex 18
2.4. Composition for compost manufacturing in pilot test 19
2.5. Layout of composting test site and compost management 22
2.6. On-site composting experiment 24
2.6.1. Measurement of environmental and composting temperatures 24
2.6.2. Measurement of odorous gases and carbon dioxide 24
2.7. Physicochemical analysis of compost samples at different stages 25
2.7.1. Determination of moisture content and pH in compost samples 25
2.7.2. Physicochemical analysis of compost samples 25
2.8. Degree of PLA particle disintegration in compost 26
2.9. Statistics 26
Ⅲ. Results and Discussion 27
3.1. Selection of complex microbial strains 27
3.1.1. Enzyme activity 27
3.1.2. Comparative growth of PLA-degrading microorganisms in culture media with different carbon sources 33
3.2. Composting assessment 38
3.2.1. Temperature and heating trends of compost piles during the composting period 38
3.2.2. The physical characteristics of compost piles during the composting period 41
3.3. The generation of odorous gases and carbon dioxide during the composting process 48
3.3.1. Ammonia and amine gases 48
3.3.2. Carbon dioxide 49
3.4. Compost quality 55
3.4.1. O rganic matter 55
3.4.2. Total nitrogen 56
3.4.3. Carbon-to-nitrogen ratio 57
3.4.4. The contents of potassium and phosphorus 57
3.5. The degradation level of polylactic acid in compost 60
Ⅳ. Conclusion 63
References 64
Appendix 68
Abstract (in Korean) 69
Table 1. Composition of raw materials for composting 21
Table 2. Characteristics of PLA-degrading potential strains used in microbial agent 29
Table 3. Characteristics of strains for improving the composting used in microbial agent 30
Table 4. Comparative growth of PLA-degrading microorganisms on BMM agar media with different carbon sources 34
Table 5. Growth of PLA-degrading microorganisms in BMM liquid culture with different carbon sources 36
Table 6. Temperature ranges of air and compost piles during composting period 40
Table 7. Change of water content in compost piles 44
Table 8. pH change in compost piles 45
Table 9. Change of electrical conductivity value in compost piles 46
Table 10. Change of ammonia gas production in compost piles 51
Table 11. Change of amine gas production in compost piles 52
Table 12. Change of carbon dioxide production in compost piles 53
Table 13. Change of nutrient content in compost piles 59
Figure 1. Structure of polylatic acid (PLA). 14
Figure 2. Place of pilot test (A) and compost piles (B). 23
Figure 3-1. The extracellular enzyme activity of strains on agar plate assay. 31
Figure 3-2. The protease activity of strains on agar plate assay. 32
Figure 4. Growth of PLA-degrading microorganisms on BMM agar media with different carbon sources for 5 days. 35
Figure 5. Growth of PLA-degrading microorganisms in BMM liquid culture with different carbon sources. 37
Figure 6. The variations in the physical characteristics of compost piles during the composting period. Temperature (A), water content and pH value (B), and EC value (C). 47
Figure 7. Changes of odorous gases and carbon dioxide production in compost piles. Ammonia (A), amine (B), and CO₂ (C). 54
Figure 8. Disintegration of PLA during 6 months of composting. Total number and weight of samples (A) and degree of PLA disintegration (B). 61
Figure 9. Direct observation of the change of PLA quantity during 6-month composting. 62