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Improving Anaerobic Digestion with Biochar for Decentralised Food Waste Management.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Improving Anaerobic Digestion with Biochar for Decentralised Food Waste Management./
Author:	Yang, Lim Ee.
Description:	1 online resource (174 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 84-09, Section: A.
Contained By:	Dissertations Abstracts International84-09A.
Subject:	Reactors. -
Online resource:	click for full text (PQDT)
ISBN:	9798374487985

Improving Anaerobic Digestion with Biochar for Decentralised Food Waste Management.
Yang, Lim Ee.

Improving Anaerobic Digestion with Biochar for Decentralised Food Waste Management. - 1 online resource (174 pages)

Source: Dissertations Abstracts International, Volume: 84-09, Section: A.

Thesis (Ph.D.)--National University of Singapore (Singapore), 2022.

Includes bibliographical references

Food waste remains a challenging problem in megacities. Anaerobic digestion is a matured technology that holds great promise to recover energy and nutrients from such waste. However, the dynamic nature of food waste causes anaerobic systems to perform sub-optimally, resulting in inhibition and eventual souring of the digester. This dysfunction affects the waste management process and has a huge economic impact. An improvement in the process is, therefore, very much warranted, in order to ensure more stable and economic waste management, and a more efficient (or productive) energy recovery system. In this PhD project, studies on gasification biochar were done with the objective of enhancing methane production and improving the stability of the start-up phase of thermophilic AD. A recovery strategy is proposed for the anaerobic system to handle organic overloading and thermal shock.Firstly, biochar from gasification, which is considered waste, was explored as an additive to enhance the stability of the anaerobic digestion system. The gasification biochar was compared with another biochar produced from pyrolysis. The results of the study suggested that the gasification biochar performed better than the pyrolytic biochar and the control. Specifically, the maximum specific methane yield increased by 35-130% and 21-272% for pyrolytic biochar and gasification biochar, respectively, for different dosages. A low dosage of 5 g/L of gasification biochar was found to be optimal while the optimal amount of pyrolytic biochar was 15 g/L. However, higher concentrations of biochar resulted in a decreased methane yield and increased the lag phase. Further investigation revealed that the calcium and potassium concentration on the biochar exceeded the inhibitory values. Although the biochar dosage also resulted in a significant increase in some of the trace element concentrations, which would be beneficial for methanogens, it was also discovered, however, that the relative distribution of the bioavailable trace elements was lesser compared to that of the control reactor. The conclusion was that it might aggravate the impact of some trace elements which were lacking in both the AD systems and the biochar.Secondly, the start-up of the thermophilic anaerobic digester from mesophilic sludge requires exposing the microorganisms to thermal shock. Accordingly, this can greatly impact the microbial dynamics, affecting the stability and performance of the anaerobic digestion. The key microbial networks were elucidated through thermochemical and microbial analysis. In particular, the addition of biochar was found to promote the growth of electroactive Clostridia and other electroactive bacteria, while the absence of biochar facilitated the growth of homoacetogenic Clostridia and syntrophic acetate oxidizing bacteria. It was found that biochar promoted direct interspecies electron transfer between the microbes and was responsible for the faster degradation of volatile fatty acids. Furthermore, reactors with biochar also enhanced the thermodynamically favourable acetoclastic methanogenic pathway due to the higher abundance of Methanosarcina.Thirdly, a study on the recovery of acidified anaerobic digesters was conducted. Although the high alkali metal content of biochar provided the necessary pH buffer and the possibility of facilitating the direct interspecies electron transfer mechanism, these factors alone could not fully restore the reactors to a fully functional state. Instead, biochar was loaded with nano-zero valent iron, which was shown to be capable of alleviating acid stress. Reactors with biochar yielded 105% more methane than the control reactors while the addition of the modified biochar accumulated 205% more than the control reactors.Lastly, the use of biochar was tested in a pilot-scale off-grid AD system. The use of biochar in AD under different operating conditions (ambient, mesophilic, and thermophilic) were finally evaluated using life cycle analysis and technoeconomic analysis. The results indicated that thermophilic anaerobic digestion with biochar was capable of operating at a high organic loading rate, with more favourable environmental and economic impacts. The study also identified improvements required by the pilot-scale system, such as better heat recovery and insulation, to improve its economic viability.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798374487985Subjects--Topical Terms:

1372700
Reactors.
Index Terms--Genre/Form:

554714
Electronic books.

Improving Anaerobic Digestion with Biochar for Decentralised Food Waste Management.
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520 $a Food waste remains a challenging problem in megacities. Anaerobic digestion is a matured technology that holds great promise to recover energy and nutrients from such waste. However, the dynamic nature of food waste causes anaerobic systems to perform sub-optimally, resulting in inhibition and eventual souring of the digester. This dysfunction affects the waste management process and has a huge economic impact. An improvement in the process is, therefore, very much warranted, in order to ensure more stable and economic waste management, and a more efficient (or productive) energy recovery system. In this PhD project, studies on gasification biochar were done with the objective of enhancing methane production and improving the stability of the start-up phase of thermophilic AD. A recovery strategy is proposed for the anaerobic system to handle organic overloading and thermal shock.Firstly, biochar from gasification, which is considered waste, was explored as an additive to enhance the stability of the anaerobic digestion system. The gasification biochar was compared with another biochar produced from pyrolysis. The results of the study suggested that the gasification biochar performed better than the pyrolytic biochar and the control. Specifically, the maximum specific methane yield increased by 35-130% and 21-272% for pyrolytic biochar and gasification biochar, respectively, for different dosages. A low dosage of 5 g/L of gasification biochar was found to be optimal while the optimal amount of pyrolytic biochar was 15 g/L. However, higher concentrations of biochar resulted in a decreased methane yield and increased the lag phase. Further investigation revealed that the calcium and potassium concentration on the biochar exceeded the inhibitory values. Although the biochar dosage also resulted in a significant increase in some of the trace element concentrations, which would be beneficial for methanogens, it was also discovered, however, that the relative distribution of the bioavailable trace elements was lesser compared to that of the control reactor. The conclusion was that it might aggravate the impact of some trace elements which were lacking in both the AD systems and the biochar.Secondly, the start-up of the thermophilic anaerobic digester from mesophilic sludge requires exposing the microorganisms to thermal shock. Accordingly, this can greatly impact the microbial dynamics, affecting the stability and performance of the anaerobic digestion. The key microbial networks were elucidated through thermochemical and microbial analysis. In particular, the addition of biochar was found to promote the growth of electroactive Clostridia and other electroactive bacteria, while the absence of biochar facilitated the growth of homoacetogenic Clostridia and syntrophic acetate oxidizing bacteria. It was found that biochar promoted direct interspecies electron transfer between the microbes and was responsible for the faster degradation of volatile fatty acids. Furthermore, reactors with biochar also enhanced the thermodynamically favourable acetoclastic methanogenic pathway due to the higher abundance of Methanosarcina.Thirdly, a study on the recovery of acidified anaerobic digesters was conducted. Although the high alkali metal content of biochar provided the necessary pH buffer and the possibility of facilitating the direct interspecies electron transfer mechanism, these factors alone could not fully restore the reactors to a fully functional state. Instead, biochar was loaded with nano-zero valent iron, which was shown to be capable of alleviating acid stress. Reactors with biochar yielded 105% more methane than the control reactors while the addition of the modified biochar accumulated 205% more than the control reactors.Lastly, the use of biochar was tested in a pilot-scale off-grid AD system. The use of biochar in AD under different operating conditions (ambient, mesophilic, and thermophilic) were finally evaluated using life cycle analysis and technoeconomic analysis. The results indicated that thermophilic anaerobic digestion with biochar was capable of operating at a high organic loading rate, with more favourable environmental and economic impacts. The study also identified improvements required by the pilot-scale system, such as better heat recovery and insulation, to improve its economic viability.
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