Anaerobic Co-Digestion of Tannery and Dairy Industry Wastes for Bio Energy Production

235 Pages·2017·3.07 MB·English

Anaerobic Co-Digestion of Tannery and Dairy Industry Wastes for Bio
Energy Production: An Approach to Convert Waste to Energy in Agro
industrial Sector

Shifare Berhe

Addis Ababa University
Addis Ababa, Ethiopia
Septmber 4, 2017
Anaerobic Co-Digestion of Tannery and Dairy Industry Wastes for Bio
Energy Production: An Approach to Convert Waste to Energy in Agro
industrial Sector

Shifare Berhe

A Thesis Submitted to:
The Center for Environmental Science in Partial Fulfilment of the Degree of
Doctor of Philosophy in Environmental Science

Addis Ababa University
Addis Ababa, Ethiopia
Septmber 4, 2017
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ABSTRACT

Anaerobic Co-Digestion of Tannery and Dairy Industry Wastes for Bio Energy Production:
An Approach to Convert Waste to Energy in Agro industrial Sector

Shifare Berhe, PhD thesis
Addis Ababa University, 2017

The introduction of cleaner technologies through the reuse of wastes for energy recovery can
improve the environmental performance of agro processing industries. However, existing
waste treatment methods in Ethiopian agro processing industries do not innovatively add
value to the wastes by recovering bio-energy to contribute to the ever increasing energy
demands in the country and reduce greenhouse gas emissions. In this study anaerobic co-
digestion of agro-industrial wastes: tannery waste water (TWW), tannery solid waste (TSW)
and dairy waste water (DWW) was investigated using two phase anaerobic sequencing batch
reactor (ASBR) for enhanced waste to energy conversion. Laboratory scale anaerobic
digesters; one used for acidogensis and the other for methanogensis with 0.4L and 0.6L
working volumes, respectively, were used in semi continuous mode operation under
mesophilic range (38+20C) . Operational parameters such as mixing ratios of substrates,
hydraulic retention time (HRT) and organic loading rate (OLR) were optimized for improved
process performance and stability of both hydrolytic-acidogenic and methanogenic steps. The
optimum operational conditions of hydrolytic- acidogenic step at four mixing ratios of
substrates (100:0, 75:25, 50:50 and 25:75) and at HRT of 5, 3 and 1days were examined.
Based on the results obtained the highest process performance in terms of TVFA
concentration (3990mgCH COOH/L) with an acidification degree of 55.5% was achieved
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when hydrolytic- acidogenic reactor was fed with 50:50(TWW:DWW) and operated at HRT
of 3days (OLR of 2.63gCOD/L.day). Similarly, the substrate mixing ratio of
50:50(TWW:TSW), HRT of 5days and OLR of 1.20gCOD/L/day were found to be best values
for achieving maximum TVFA (2450mgCH COOH/L), degree of acidification (36.55%) and
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degree of hydrolysis(54.8%). The methanogenic process step also showed that methanogenic
reactor feed with 50:50(TWW:DWW) operated at HRT of 15 days exhibited improved process
stability in terms of pH (6.70), VFA accumulation i.e VFA/Alkalinity (0.363), alkalinity (3350
mgCaCO /L) and ammonia (231mg/L) in which all values were with in optimum operating
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range.
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The rector also exhibited best process performances in terms of daily biogas (647ml/day),
methane production (461ml/day), methane content (71.2%) and COD removal efficiency
(85.6%) when operated at HRT of 15 days and equivalent OLR (0.517gCOD/L.day). The
biogas production, methane content and COD removal efficiency during anaerobic co-
digestion of TWW and DWW (50:50) were enhanced by 94.3%, 47.4% and 22.5%,
respectively, as compared to mono digestion of TWW. The best overall process performance
efficiency (acidogenesis and methanogensis) for TCOD reduction (88.8%) was achieved
when methanogenic reactor (50% TWW and 50% DWW) operated at HRT of 18 days (3 days
for acidogenesis + 15 days for methanogensis). Similarly, methanogenic reactor feed with
substrate mixing ratio of 50%TWW and 50%TSW at HRT of 20 days (OLR =
0.280gCOD/L.day) exhibited pH of 6.8, VFA/Alkalinity of 0.305, alkalinity of
3210mgCaCO /L and ammonia of 246mg/L which were found within optimum operating
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range. In this methanogenic reactor (50:50 of TWW and TSW) best process performances in
terms of daily biogas (415ml/day), methane production (251ml/day), methane content
(60.5%) and COD removal efficiency (75%) were achieved when operated at HRT of 20 days
and OLR of 0.280gCOD/L.day. The highest overall TCOD reduction (77.3%) was obtained
when 50% TWW and 50%TSW in the two phase anaerobic system operated at HRT of 25days
(5days for acidogenesis + 20 days for methanogenensis). In general improved process
stabilities as well as performances were achieved during anaerobic co-digestion of TWW
with DWW and TSW as compared to mono digestion of TWW. Furthermore the results
obtained from this study provide fundamental information for scaling up the high
performance two phase anaerobic co-digestion system in these agro industries to recover bio
energy which can be used as fuel in their different unit operations.
Key words: Anaerobic co-digestion, dairy waste water, tannery solid waste, tannery waste
water

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ACKNOWLEDGEMENTS

Completion of this doctoral dissertation was possible with the support of several people and
organizations. I would like to express my sincere gratitude to all of them.

I am deeply indebted to my adviser Dr. Seyoum Leta for his fundamental role in my PhD
dissertation. Dr. Seyoum provided me with every bit of guidance, assistance, meticulous
comments and expertise that I needed during my doctoral work. Dr. Seyoum, a person with
an amicable and positive disposition; has always made himself available to clarify my doubts
despite his busy schedules and I consider it as a great opportunity to do my doctoral
dessertation under his scientific guidance and to learn from his research expertise. In addition
to our academic collaboration, I greatly value the close personal connection that Dr. Seyoum
and I have forged over the years. Staff members of Center for Environmental Science have
been very kind enough to extend their help at various phases of this research, whenever I
approached them, and I do hereby acknowledge all of them.

I also gratefully acknowledge Environmental Science Laboratory Technicians Mr Temesgen
Aragi, W/ro Mingizeam Tsegaye and W/ro Tsigie Yadessa for their unlimited assistance and
support during the experimental work. The following institutions and organizations: Addis
Ababa University Food Science and Nutrition programs, Addis Ababa University Chemistry
Department, Mekelle University Chemistry Department, Leather Industry Development
Institute (LIDI), Modjo Tannery Industry, Lame Dairy PLC are highly acknowledged for
their cooperation during this research work. I would also like to express my gratitude for
financial support provided by Addis Ababa University, School of Graduate Studies and
Center for Environmental Science. My gratitude also extended to Jigjiga University for
sponsoring me to pursue my PhD at Addis Ababa University. I owes a lot to my parents, my
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wife W/ro Birhan Hailu, my children Elon Shifare and Loza Shifare who encouraged and
helped me at every stage of my personal and academic life and longed to see this
achievement come true. I would like to extend my heartfelt thanks to Dr Dori Woldu, Ato
Hailesiasie Suba, Ato Huluf Weldesilasie and Ato Eyasu Weldesilasie with their family for
their eldless moral and material support which can not be expressed in words. In addition, the
generous support and contribution of all my colleagues are deeply acknowledged and
emphasized in all cases of my future life.

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DEDICATION
This PhD dissertation is dedicated to the memory of my father Berhe Gebru

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Table of Contents Pages
ABSTRACT ............................................................................................................................. iii
ACKNOWLEDGEMENTS ....................................................................................................... v
DEDICATION .......................................................................................................................... vi
List of Tables ........................................................................................................................... xv
ACRONYMS .......................................................................................................................... xvi
CHAPTER ONE ...................................................................................................................... 18
1. INTRODUCTION ............................................................................................................... 18
1.1 Background .................................................................................................................... 18
1.2 Statement of the Problem ............................................................................................... 21
1.3 Objective of the Study .................................................................................................... 27
1.3.1 General objective ..................................................................................................... 27
1.3.2 Specific objectives ................................................................................................... 27
CHAPTER TWO ..................................................................................................................... 28
2. LITERATURE REVIEW .................................................................................................... 28
2.1 Tannery Industry ............................................................................................................ 28
2.2 Processes Involved in Leather Production ..................................................................... 28
2.2.1 Beam house operations ............................................................................................ 29
2.2.2 Tanning Operation ................................................................................................... 31
2.2.3 Drying and finishing operation ................................................................................ 33
2.2.4 Finishing .................................................................................................................. 35
2.3 Environmental impacts of leather industry .................................................................... 35
2.3.1 Waste water ............................................................................................................. 35
2.3.2 Gaseous emission .................................................................................................... 36
2.3.3 Solid wastes ............................................................................................................. 37
2.4 Technological Options for Cleaner Production in Tannery Industry ............................. 38
2.4.1 Clean technology options ........................................................................................ 38
2.4.2 Solid waste management options ............................................................................ 39
2.4.3 Waste water treatment options ................................................................................ 40
2.5 Agro processing Industry and their Environmental Performances in Ethiopia .............. 42
2.5.1 Tannery industries in Ethiopia ................................................................................. 43
2.5.1.1 Waste generation capacity of tannery industry in Ethiopia .................................. 44
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2.5.1.2 Waste management techniques in Ethiopian tanneries ......................................... 45
2.5.2 Dairy industry .......................................................................................................... 46
2.5.2.1 Processes involved and waste generation during milk processing ................... 46
2.5.2.2 General characterization of dairy waste water .................................................. 47
2.5.2.3 Environmental concerns of dairy industry ........................................................ 48
2.5.2.4 Dairy waste treatment technologies .................................................................. 49
2.5.2.5 Dairy industry waste management in Ethiopia ................................................. 49
2.6 Anaerobic Digestion Technology................................................................................... 51
2.6.1 Biochemical Process of Anaerobic Digestion ......................................................... 51
2.6.1.1 Hydrolysis ......................................................................................................... 51
2.6.1.2 Acidogenesis ..................................................................................................... 52
2.6.1.3 Acetogenesis ..................................................................................................... 52
2.6.1.4. Methanogensis ................................................................................................. 53
2.6.2 Types anaerobic digester based on design ............................................................... 54
2.6.2.1 Fixed dome digester .......................................................................................... 54
2.6.2.2 Floating drum digester ...................................................................................... 55
2.6.2.3 Plug flow digester ............................................................................................. 56
2.6.3 Anaerobic Reactors .................................................................................................. 57
2.6.3.1 Anaerobic sequencing batch reactor (ASBR) ................................................... 57
2.6.3.2. Continuous stirred tank reactor (CSTR) .......................................................... 59
2.6.3.3. Anaerobic plug-flow reactor (APFR) .............................................................. 60
2.6.3.4 Anaerobic contact reactor (ACR) ..................................................................... 61
2.6.3.5. Up-flow anaerobic sludge bed (UASB) reactor) ............................................. 62
2.6.3.6 Anaerobic filter (AF) reactor ............................................................................ 64
2.6.3.7 Expanded granular sludge bed (EGSB) reactor ................................................ 65
2.6.3.8. Anaerobic baffled reactor (ABR)..................................................................... 66
2.6.3.8 Anaerobic fluidized bed reactor (AFBR) .......................................................... 68
2.6.3.9 Anaerobic membrane bio reactors (AnMBR) ................................................... 69
2.6.4 Factors affecting biogas production ........................................................................ 70
2.6.4.1 Microbial population ......................................................................................... 71
2.6.4.2 pH ...................................................................................................................... 71
2.6.4. 3. Carbon-to-nitrogen mass ratio (C:N) .............................................................. 72
2.6.4.4 Temperature ...................................................................................................... 72
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2.6.4.5. Hydraulic retention time (HRT) ....................................................................... 74
2.6.4.6 Organic loading rate (OLR) .............................................................................. 74
2.6.4.7 Inhibitors ........................................................................................................... 75
2.7 Research Approach to Enhance Performance of AD ..................................................... 79
2.7.1 Use of additives ....................................................................................................... 80
2.7.2 Variation in operational parameters ........................................................................ 83
2.7.3 Pre-treatment ........................................................................................................... 86
2.7.4 Multi-stage digestion systems ................................................................................. 90
2.7.6 Use of fixed films .................................................................................................... 91
2.7.7 Anaerobic Co-digestion approach ........................................................................... 92
2.7.7.1. Co-digestion of meat industry wastes: ............................................................. 93
2.7.7.2 Anaerobic co-digestion of food wastes ............................................................. 98
2.7.7.3 Livestock manure ............................................................................................ 104
CHAPTER THREE ............................................................................................................... 108
3. METHODS AND MATERIALS ....................................................................................... 108
3.1 Experimental Set up ..................................................................................................... 108
3.1.1 Bench scale AD set up ........................................................................................... 108
3.1.2 Start up and Operating Procedures ........................................................................ 109
3.1.3 Inoculums .............................................................................................................. 112
3.2 Samples and Sampling Site .......................................................................................... 113
3.2.1 Samples .................................................................................................................. 113
3.2.1.1 Tannery waste water (TWW) .......................................................................... 113
3.3.1.2 Tannery solid wastes (TSW) ........................................................................... 114
3.2.1. 3 Dairy waste water (DWW) ............................................................................ 114
3.2.2 Sampling site ......................................................................................................... 115
3.2.2.1 Description of tannery waste sampling site .................................................... 115
3.2.2.1 Description of dairy waste sampling site ........................................................ 116
3.3 Laboratory Analysis ..................................................................................................... 117
3.4 Operational Parameters Calculations ........................................................................... 118
3.4.1 Organic loading rate (OLR) ................................................................................... 118
3.4.2 Hydraulic retention time (HRT) ............................................................................ 118
3.5 Process Stability Parameters Calculations ................................................................... 118
3.5.1 Degree of hydrolysis .............................................................................................. 119
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