Aerobic Methane Oxidation Coupled to Heterotrophic Denitrification for the Treatment of Secondary Effluent
- 주제(키워드) Aerobic methane oxidation , Denitrification , Secondary effluent , Methane , Nitrous oxide
- 발행기관 고려대학교 대학원
- 지도교수 이재우
- 발행년도 2016
- 학위수여년월 2016. 8
- 학위구분 박사
- 학과 대학원 환경기술.정책협동
- 원문페이지 157 p
- 실제URI http://www.dcollection.net/handler/korea/000000069283
- 본문언어 영어
- 제출원본 000045881873
초록/요약
This study aimed to investigate a potential of application of aerobic methane oxidation coupled to denitrification (AeOM-D) and to estimate its applicability for treating the real secondary effluent as an alternative. In order to study AeOM-D, a sequencing batch reactor (SBR) was operated under various conditions, including hydraulic retention time (HRT) and CH4 loading rate. Methanotrophic denitrification under a non-aerated condition (without external supply of oxygen or air) was investigated in a bioreactor coupled with a membrane diffuser. Activted and anaerobically digested sludge were selected as seed sludge in this study. A batch experiment demonstrated that, while both methane consumption and nitrogen production rates were not high in the absence of oxygen, most of nitrate was reduced into N2 with 90% recovery efficiency. The methane utilized for nitrate reduction was determined at 1.63 mmol CH4/mmol NO3--N, which was 2.6 times higher than the theoretical value. In spite of the absence of oxygen supply, methanotrophic denitrification was well performed in the bioreactor, due to the enhanced mass transfer of the methane by the membrane diffuser and utilization of oxygen remaining in the influent. The maximum denitrification efficiency and specific denitrification rate were 69% and 1.69 mg NO3--N/g VSS·hr, respectively, which were slightly lower than for methanotrophic denitrification under the aerobic condition. The average concentration of total organic carbon in the effluent was as low as 2.45 mg/L, which indicates that it can be applied as a post-denitrification method for the reclamation of the secondary effluent. The dominant fatty acid methyl ester of mixed culture in the bioreactor was C16:1ω7c and C18:1ω7c, which was predominantly found in type I and II methanotrophs, respectively. Due to the requirement of oxygen for higher performance of AeOM-D, the selected mixed culture was investigated with various hydraulic retention time (HRT) and CH4 loading rate under the aerobic condition. The experiments were conducted under three different HRTs (0.25, 0.5 and 1.0 d) and two different methane loading rates (5 and 20 mmol/L•hr). Both the HRT and CH4 loading rate played an important role in the overall denitrifying performance. A higher denitrification efficiency and biomass growth rate were achieved at a longer HRT and a higher CH4 loading rate. The ∆NO3--N varied in a relatively narrow range: from 0.96 to 2.69 mg N/g VSS∙hr; however, the maximum ∆NO3--N occurred at the middle HRT of 0.5 d, regardless of CH4 loading rate. The fraction of CH4 utilized for denitrification was estimated based on the chemical oxygen demand (COD) fractionation. Due to a greater mass transfer rate, a longer HRT and a higher CH4 loading rate resulted in a higher methane transformation fraction by methanotrophs; however, it did not lead to a higher utilization faction due to the rapid exhaustion of nitrate. The effluent soluble COD concentration presumably related to methanotrophic by-products was lower than 15 mg/L in all experimental conditions except for 1 day HRT at a high CH4 loading rate. A higher CH4 loading rate at 1 d HRT led to a higher diversity of microbial community structure for both methanotrophs and denitrifiers. Type II methanotrophs, including Methylocystis, was the most dominant methanotrophs, regardless of CH4 loading rate; however, the dominant denitrifier shifted from Hyphomicrobium to Sterolibacterium_f with the increase of CH4 loading rate. Emission of three major greenhouse gases (GHGs), including CH4, CO2, and N2O, was evaluated during operation of a sequencing batch reactor for AeOM-D. the maximum specific denitrification rate (SDNR) increased as HRT increased from 0.25 to 1.0 d. However, the highest overall SDNR during the entire reaction time occurred at the medium HRT of 0.5 d since that of the longer HRT tended to be lowered due to the deficiency of residual nitrate. Dissolved N2O concentration increased and then leveled-off or slightly decreased. Concentration of the dissolved N2O was higher at the shorter HRT, which was highly associated with the lowered C/N ratio. A longer HRT leads to a higher C/N ratio with a sufficient carbon source produced by methanotrophs via methane oxidation, which provides a favorable condition for reducing N2O formation. Similar to the dissolved N2O formation, N2O emission rate was higher at a shorter HRT condition. Opposite to N2O emission, the emission rates of CH4 and CO2 were higher at a longer HRT. A longer HRT resulted in a greater total GHGs emission as CO2 equivalent due to the higher emission rate of CH4. It was doubled when HRT increased from 0.5d to 1.0 d. The contribution of CH4 onto the total GHGs emission was most dominant, accounting for 98 - 99% as compared to that of N2O (< 2%). AeOM-D SBR was operated using a real secondary effluent. The experiments were conducted under two different HRT at CH4 loading rate of 20 mmol/L•hr. The performance of AeOM-D was evidently lower than that of the synthetic wastewater system. Nitrification was occurred as well as denitrificaiton and its efficiency in HRT of 0.5 and 1day, was 82.0 and 90.7%, respectively. Buildup of NO2--N was observed in all HRT conditions. In order to investigate nitrogen transformation in AeOM-D, a track study was conducted under HRT of 0.5 day. The overall specific denitrification rate (SDNR) was 10% lower than under the synthetic wastewater system. It was found that NO2--N was accumulated in AeOM-D, it might be produced from both of nitrification and denitrification steps. MMO activity was obviously inhibited by NH4+-N oxidation and accumulation of NO2--N.
more목차
ABSTRACT i
LIST OF TABLES viii
LIST OF FIGURES ix
CHAPTER 1. BACKGROUND 1
1.1. Background of the Research 1
1.2. Literature review 3
1.2.1. Methane oxidation by methanotrophs 3
1.2.2. Methane monooxygenase (MMO) 6
1.2.3. Degradation of methane and ammonia by methanotrophs 7
1.2.3.1. Methane 7
1.2.3.2. Ammonia 7
1.2.4. Denitrification 9
1.2.4.1. Denitrifier 9
1.2.4.2. Reducatase involved in denitrification 9
1.2.4.3. Metabolism of nitrate reduction by denitrifier 10
1.2.5. Aerobic methane oxidation coupled to denitrification (AeOM-D) 12
1.2.6. Energetic estimation for methane utilization in AeOM-D 13
1.2.6.1. Methane oxidation 13
1.2.6.2. Denitrification 16
1.2.6.3. Fraction of energetic in AeOM-D 17
1.3. Objectives and scope of the research 19
CHAPTER 2. MEMBRANE DIFFUSER COUPLED BIOREACTOR FOR METHANOTROPHIC DENITRIFICATION UNDER NON-AERATED CONDITION: SUGGESTION AS A POST-DENITRIFICATION OPTION 29
2.1. Introduction 29
2.2. Materials and Method 33
2.2.1. Seed culture and medium 33
2.2.2. Selection of seed culture and anaerobic batch test 33
2.2.3. CH4 dissolution test: Kinetic assessment 34
2.2.4. Continuous operation of bioreactor coupled with membrane diffuser 35
2.2.5. Analytical methods 37
2.2.6. Fatty acid methyl esters (FAMEs) of mixed culture 38
2.3. Results and Discussion 39
2.3.1. Comparison of seed culture 39
2.3.2. Batch experiment 40
2.3.3. Kinetics for CH4 dissolution of two different diffusers 43
2.3.4. Operation of non-aerated bioreactor 46
2.3.5. FAMEs analysis for methanotrophs in bioreactor 51
2.4. Conclusions 54
CHAPTER 3. EFFECTS OF HYDRAULIC RETENTION TIME (HRT) AND METHANE LOADING RATE ON METHANOTROPHIC DENITRIFICATION OF SECONDARY EFFLUENT: UTILIZATION OF METHANE AND SHIFT OF MICROBIAL COMMUNITY STRUCTURE 60
3.1 Introduction 60
3.2 Materials and Method 64
3.2.1. Mixed culture consortium and medium 64
3.2.2. Setup and operation of bioreactor for AeOM-D 64
3.2.3. CH4 dissolution test 66
3.2.4. DNA extraction, PCR amplification and pyrosequencing analysis 67
3.2.5. Analytical methods 68
3.3 Results and Discussion 69
3.3.1. Performance of AeOM-D 69
3.3.2. Transformation and utilization of methane 71
3.3.3. Shift of Microbial community structure 79
3.4 Conclusions 84
CHAPTER 4. GREENHOUSE GASES (GHGs) EMISSION FROM AEROBIC METHANOTROPHIC DENITRIFICATION (AeOM-D) IN SEQUENCING BATCH REACTOR (SBR) 89
4.1 Introduction 89
4.2 Materials and Method 92
4.2.1. Mixed culture consortium and medium 92
4.2.2. Track study for AeOM-D 93
4.2.3. CH4 dissolution test 94
4.2.4. Analytical methods 95
4.3 Results and Discussion 96
4.3.1. Denitrification rate in AeOM-D 96
4.3.2. CH4 utilization and N2O formation in AeOM-D 98
4.3.3. Greenhouse gases (GHGs) emission in AeOM-D SBR 104
4.3.4. Impact of AeOM-D on climate change 108
4.4 Conclusions 111
CHAPTER 5. APPLICATION OF AEROBIC METHANE OXIDATION COUPLED TO DENITRIFICATION ON REAL SECONDARY EFFLUENT 117
5.1 Introduction 117
5.2 Materials and Method 120
5.2.1. Operation of sequencing bioreactor 120
5.2.2. Track study for AeOM-D 121
5.2.3. MMO activity test 121
5.2.4. Analytical methods 122
5.3 Results and Discussion 124
5.3.1. Performances of AeOM-D on real secondary effleunt 124
5.3.2. Track study in AeOM-D 126
5.3.3. Effect of NH4 oxidation for MMO activity 129
5.4 Conclusions 134
CHAPTER 6. FINAL CONCLUSIONS AND FUTURE WORKS 138
ACKNOWLEGEMENT 142
