Enhancing biogas production from lawn grass by optimizing selected factors involved in anaerobic ...

130 Pages·2016·2.23 MB·English

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Surname, Initial(s). (2012) Title of the thesis or dissertation. PhD. (Chemistry)/ M.Sc. (Physics)/
M.A. (Philosophy)/M.Com. (Finance) etc. [Unpublished]: University of Johannesburg. Retrieved
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Enhancing biogas production from lawn grass by optimizing
selected factors involved in anaerobic digestion
By
Noxolo Thandeka Sibiya
Submitted in fulfillment of the requirement for the Degree of
Master of Technology
In
Chemical Engineering
In the Faculty of Engineering and Built Environment
University of Johannesburg
Supervised by
Prof. E. Muzenda & Dr. H. Tesfagiorgis

2016
DECLARATION
I, the undersigned, hereby declare that the work contained in this dissertation, except where
otherwise indicated, is my own original work and has not been submitted for any degree
examination at any other university.
Signature:
Date: 07/06/2016
i
ACKNOWLEDGMENT

Firstly, I would like to thank God Almighty for giving me the opportunity to achieve higher
education at this level and giving me courage and strength during the course of my M.Tech study
at UJ.
I would like to express my profound gratitude to my academic supervisors Prof Edison Muzenda
and Dr Habtom Tesfagiorgis for their valuable guidance, stimulating advice and encouragement
during this research.
A special thank is addressed to my colleagues Ireen Maile and Ishmael Ramatsa for their
assistance with laboratory work.
I gratefully acknowledge the University of Johannesburg Global Excellence Scholarship (GES)
and South Africa National Energy Development Institute (SANEDI) for funding my studies.
Deepest and sincere gratitude goes to my parents (Mr Sibiya, Mrs Sibiya & Ms Mathonsi) for
their support, love, encouragements and prayers. I would also like to extend my appreciation to
my siblings and friends for their support and encouragements throughout the study.

ii
RESEARCH OUTPUT

 Sibiya, N.T., Tesfagiorgis, H.B., & Muzenda, E. “Influence of alkaline (NaOH) pre-
treatment on biogas production and bio-methane potential of lawn grass under
anaerobic condition.” South Africa Journal of Chemical Engineering, Submitted, June,
2016.
 Sibiya, N.T., Tesfagiorgis, H.B., & Muzenda, E. “Influence of co-digestion of lawn
grass with cow dung and pig manure on biogas production.” Studia Universitatis
Babes-Bolyai Seria Chemia, Submitted, May, 2016.
 Sibiya, N.T., Muzenda, E., & Mbohwa, C. “Evaluation of potential substrates for
biogas production via anaerobic digestion: A review.” World congress on Engineering
& Computer Science, San Francisco, United State of America, 19-21 October, 2016.
 Sibiya, N.T., Tesfagiorgis, H.B., & Muzenda, E. “Application of different pre-
treatment techniques for enhanced biogas production from lawn grass: A review.”
Advancements in Energy, Environment and Climate Change Research: Making
Connections and Building Thematic Links, Book Chapter, April, 2016.
 Sibiya N.T., Tesfagiorgis, H.B., & Muzenda, E. “Influence of nutrients addition for
enhanced biogas production from energy crops: A review.” nternational Conference
on atest Trend Energy Technologies, retoria, South Africa, November, 2015.
 Sibiya, N.T., Tesfagiorgis, H.B., & Muzenda, E. “Influence of digestate recirculation
and recirculation percentage on biogas production from lawn grass via anaerobic
digestion.” World Congress on Engineering, San rancisco, United States of America,
October, 2015.
 Sibiya, N.T., Tesfagiorgis, H.B., & Muzenda, E. “Application of different pre-
treatment techniques for enhanced biogas production from lawn grass: A review.”
nternational Conference on Energy, Environment and Climate Change, Mauritius,
July, 2015.
 Sibiya, N.T., Tesfagiorgis, H.B., & Muzenda, E. “The effects of organic loading rate
and retention time on anaerobic digestion of lawn grass.” nternational Conference on
Energy, Environment and Climate Change, Mauritius, July, 2015.
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 Sibiya, N.T., Muzenda, E., & Tesfagiorgis, H. B. “Effect of temperature and pH on the
anaerobic digestion of grass silage.” nternational Conference on Chemical Engineering
& Advanced Com utational Technologies, Ca e Town, November, 2014.
 Sibiya, N. T., & Muzenda, E. “A review of biogas production optimization from grass
silage.” International Conference on Chemical Engineering and Advanced
Computational Technologies, Pretoria, South Africa, 24 25 November, 2014.
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ABSTRACT

Biogas technology via anaerobic digestion (AD) is considered as an alternative option to reduce
the emission of greenhouse gases, improve energy efficiency and address increasing dependency
on imported fossil fuel. Although biogas can be produced easily, numerous researches have
shown that the efficiency of methane production, especially from grass, is not optimal due to
some factors affecting the AD rocess directly and indirectly. Therefore, this master’s
dissertation focuses on evaluating the techniques that can be used to enhance the
biodegradability of lawn grass, and subsequently improves biogas and methane production under
anaerobic condition.

The effects of operational parameters such as temperature, pH, loading rate, and retention time
were evaluated. Techniques including recirculation of digestate, alkaline (NaOH) pre-treatment
and co-digestion were also investigated. The characteristics of the substrate were determined in
order to verify the suitability of the substrate for AD process. Biogas production from lawn grass
was studied in the batch laboratory scale digester (1000 mL) with the working volume of 800
mL. Automatic Methane Potential Test System (AMPTS II) was used to measure bio-methane
potential and methane content was measured using gas chromatography (GC, claurus 580).
Although all the techniques have proven to enhance biogas and methane production from lawn
grass, co-digestion has been considered as the most preferable method for enhanced biogas and
methane production. The highest biogas yield was obtained when grass was co-digested with
cow dung, while the maximum methane was observed when pig manure was a co-substrate with
grass at the ratio of 1:1 (25:25 g). The suitable environmental condition for AD on this study was
found to be at 45 ºC and pH of 6.5, while the optimal retention time was found to be 8 days,
regardless of the effect of temperature and pH. An increase of biogas and methane production by
10% was observed when the digester loading rate was increased from 20 g/L to 60 g/L, whereas
higher methane content was obtained in a digester with 30 % recycled solid digestate. It was also
found that pre-treating lawn grass with 0.093 M NaOH at 40 and 55 ºC prior the AD process
resulted in a significant increase in bio-methane potential from 813 to 1204 NmL and methane
content from 40 to 52 %.
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TABLE OF CONTENTS
Contents
DECLARATION ..................................................................................................................................... i
ACKNOWLEDGMENT ......................................................................................................................... ii
RESEARCH OUTPUT........................................................................................................................... iii
ABSTRACT ............................................................................................................................................ v
TABLE OF CONTENTS........................................................................................................................ vi
LIST OF FIGURES ................................................................................................................................ ix
LIST OF TABLES ................................................................................................................................ xii
LIST OF ACRONYMS ......................................................................................................................... xiii
Chapter 1 ................................................................................................................................................. 1
INTRODUCTION ................................................................................................................................... 1
1.1 Background and motivation .................................................................................................. 1
1.2 Problem statement ................................................................................................................ 4
1.3 Aim and Objectives .............................................................................................................. 5
1.4 Scope of the study ................................................................................................................ 5
1.5 Justification of the research .................................................................................................. 6
1.6 Structure of dissertation ........................................................................................................ 6
References ........................................................................................................................................... 8
Chapter 2 ................................................................................................................................................. 9
LITERATURE REVIEW .................................................................................................................... 9
2.1 Grass as a feedstock for AD process ..................................................................................... 9
2.2 History of biogas production .............................................................................................. 10
2.3 Biogas ................................................................................................................................ 12
2.4 Biogas production process (anaerobic digestion) ................................................................. 13
2.5. Parameters that affect anaerobic digestion .......................................................................... 17
2.6. Optimization of biogas production ...................................................................................... 25
References............................................................................................................................................. 36
Chapter 3 ............................................................................................................................................... 51
EFFECT OF TEMPERATURE AND pH ON BIOGAS PRODUCTION FROM GRASS .................. 51
vi
3.1. Introduction........................................................................................................................ 51
3.2. Materials and Method ......................................................................................................... 52
3.3. Results and Discussion ....................................................................................................... 55
Conclusion ............................................................................................................................................ 60
References............................................................................................................................................. 61
Chapter 4 ............................................................................................................................................... 63
THE EFFECTS OF ORGANIC LOADING RATE AND RETENTION TIME ON ANAEROBIC
DIGESTION OF LAWN GRASS ...................................................................................................... 63
4.1. Introduction........................................................................................................................ 64
4.2. Materials and Method ......................................................................................................... 65
4.3. Results and Discussion ....................................................................................................... 66
Conclusion ............................................................................................................................................ 71
Chapter 5 ............................................................................................................................................... 74
INFLUENCE OF DIGESTATE RECIRCULATION ON BIOGAS PRODUCTION FROM LAWN
GRASS VIA ANAEROBIC DIGESTION ......................................................................................... 74
5.1. Introduction........................................................................................................................ 74
5.2. Materials and Method ......................................................................................................... 75
5.3. Results and Discussion ....................................................................................................... 77
Conclusion ............................................................................................................................................ 81
References............................................................................................................................................. 82
Chapter 6 ............................................................................................................................................... 83
INFLUENCE OF CO-DIGESTION OF LAWN GRASS WITH COW DUNG AND PIG MANURE
ON BIOGAS PRODUCTION ........................................................................................................... 83
6.1. Introduction........................................................................................................................ 83
6.2. Materials and Method ......................................................................................................... 84
6.3. Results and Discussion ....................................................................................................... 88
Conclusion ............................................................................................................................................ 94
References............................................................................................................................................. 95
Chapter 7 ............................................................................................................................................... 99
INFLUENCE OF ALKALINE (NaOH) PRE-TREATMENT ON BIOGAS PRODUCTION AND BIO-
METHANE POTENTIAL OF LAWN GRASS UNDER ANAEROBIC CONDITION ...................... 99
7.1. Introduction........................................................................................................................ 99
7.2. Materials and Method ....................................................................................................... 100
vii
7.3. Results and Discussion ..................................................................................................... 102
Conclusion .......................................................................................................................................... 110
References........................................................................................................................................... 110
Chapter 8 ............................................................................................................................................. 112
GENERAL CONCLUSIONS AND COMMENDATIONS .............................................................. 112

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