Methane and Hydrogen Production from Crop Biomass through Anaerobic Digestion

153 Pages·2011·1.67 MB·English

by  Outi Pakarinen

JYVÄSKYLÄ STUDIES IN BIOLOGICAL AND ENVIRONMENTAL SCIENCE
229
Outi Pakarinen
Methane and Hydrogen Production
from Crop Biomass through
Anaerobic Digestion
JYVÄSKYLÄ STUDIES IN BIOLOGICAL AND ENVIRONMENTAL SCIENCE 229
Outi Pakarinen
Methane and Hydrogen Production
from Crop Biomass through
Anaerobic Digestion
Esitetään Jyväskylän yliopiston matemaattis-luonnontieteellisen tiedekunnan suostumuksella
julkisesti tarkastettavaksi yliopiston Ylistönrinteen salissa YAA303
marraskuun 4. päivänä 2011 kello 12.
Academic dissertation to be publicly discussed, by permission of
the Faculty of Mathematics and Science of the University of Jyväskylä,
in Ylistönrinne, hall YAA303, on November 4, 2011 at 12 o'clock noon.
UNIVERSITY OF JYVÄSKYLÄ
JYVÄSKYLÄ 2011
Methane and Hydrogen Production
from Crop Biomass through
Anaerobic Digestion
JYVÄSKYLÄ STUDIES IN BIOLOGICAL AND ENVIRONMENTAL SCIENCE 229
Outi Pakarinen
Methane and Hydrogen Production
from Crop Biomass through
Anaerobic Digestion
UNIVERSITY OF JYVÄSKYLÄ
JYVÄSKYLÄ 2011
Editors
Anssi Lensu
Department of Biological and Environmental Science, University of Jyväskylä
Pekka Olsbo, Ville Korkiakangas
Publishing Unit, University Library of Jyväskylä
Jyväskylä Studies in Biological and Environmental Science
Editorial Board
Jari Haimi, Anssi Lensu, Timo Marjomäki, Varpu Marjomäki
Department of Biological and Environmental Science, University of Jyväskylä
URN:ISBN:978-951-39-4460-5
ISBN 978-951-39-4460-5 (PDF)
ISBN 978-951-39-4459-9 (nid.)
ISSN 1456-9701
Copyright © 2 0 1 1 , by University of Jyväskylä
Jyväskylä University Printing House, Jyväskylä 2011
ABSTRACT
Pakarinen, Outi
Methane and hydrogen production from crop biomass through anaerobic digestion
Jyväskylä: University of Jyväskylä, 2011, 96 p.
(Jyväskylä Studies in Biological and Environmental Science
ISSN 1456-9701; 229)
ISSN 978-951-39-4459-9 (nid.)
ISBN 978-951-39-4460-5 (PDF)

Yhteenveto: Metaanin ja vedyn tuottaminen energiakasveista anaerobiprosessissa
Diss.
The feasibility of methane and hydrogen production from energy crops through
anaerobic digestion was evaluated in this thesis. The effects of environmental
conditions, e.g. pH and temperature, as well as inoculum source on H yield were
2
studied in batch assays. In addition, the effects of pre-treatments on methane and
hydrogen yield as well as the feasibility of two-stage H + CH production was
2 4
evaluated. Moreover, the effect of storage on methane yield of grasses was evaluated.
Monodigestion of grass silage for methane production was studied, as well as shifting
the methanogenic process to hydrogenic. Hydrogen production from grass silage and
maize was shown to be possible with heat-treated inoculum in batch assays, with
highest H yields of 16.0 and 9.9 ml gVS –1 from untreated grass silage and maize,
2 added
respectively. Pre-treatments (NaOH, HCl and water-extraction) showed some potential
in increasing H yields, while methane yields were not affected. Two-stage H + CH
2 2 4
producing process was shown to improve CH yields when compared to traditional
4
one-stage CH process. Methane yield from grass silage monodigestion in continuously
4
stirred tank reactor (CSTR) with organic loading rate (OLR) of 2 kgVS (m3d)–1 and
hydraulic retention time (HRT) of 30 days was at most 218 l kgVS –1. Methanogenic
fed
process was shifted to hydrogenic by increasing the OLR to 10 kgVS (m3d)–1 and
shortening the HRT to 6 days. Highest H yield from grass silage was 42 l kgVS –1
2 fed
with a maximum H content of 24 %. Energy crops can be successfully stored even for
2
prolonged periods without decrease in methane yield. However, under sub-optimal
storage conditions loss in volatile solids (VS) content and methane yield can occur.
According to present results energy crops such as grass silage and maize can be
converted to hydrogen or methane in AD process. Hydrogen energy yields are
typically only 2-5 % of the methane energy yields, but the overall energy yield of the
process can be increased by two-stage H + CH producing process. In addition, the
2 4
ongoing methanogenic process can be shifted towards hydrogen production by
increasing the OLR and shortening the HRT. However, the process needs further
research to optimize especially the H production.
2

Keywords: Energy crop; grass silage; hydrogen; methane; pre-treatment; storage; two-
stage anaerobic process.

Outi Pakarinen, University of Jyväskylä, Department of Biological and Environmental
Science, P.O. Box 35, FI-40014 University of Jyväskylä, Finland
Author’s address Outi Pakarinen
Department of Biological and Environmental Science
P.O. Box 35
FI-40014 University of Jyväskylä
Finland
[email protected]

Supervisor Professor Jukka Rintala
Department of Biological and Environmental Science
P.O. Box 35
FI-40014 University of Jyväskylä
Finland

Reviewers Professor Jaakko Puhakka
Department of Chemistry and Bioengineering
Tampere University of Technology
P.O.Box 541
FI-33101 Tampere
Finland

Dr. Sonia Heaven
Faculty of Engineering and the Environment
University of Southampton
Southampton SO17 1BJ
United Kingdom

Opponent Professor Alan Guwy
Faculty of Health, Sport and Science
University of Glamorgan
Pontypridd CF37 1DL
United Kingdom
CONTENTS
LIST OF ORIGINAL PUBLICATIONS
ABBREVIATIONS
1 INTRODUCTION ..................................................................................................... 9
1.1 Background ...................................................................................................... 9
1.2 Anaerobic digestion pathways ................................................................... 10
1.2.1 Hydrolysis ......................................................................................... 10
1.2.2 Acidogenesis ...................................................................................... 11
1.2.3 Acetogenesis ...................................................................................... 12
1.2.4 Methanogenesis ................................................................................ 12
1.3 Hydrogen production in acidogenesis ...................................................... 13
1.3.1 Theoretical hydrogen yield and hydrogen producing
micro-organisms ............................................................................... 13
1.3.2 Inoculum for hydrogen production ............................................... 14
1.3.3 The effect of pH and substrate concentration on
hydrogen production ....................................................................... 15
1.3.4 Effect of temperature on hydrogen production ........................... 17
1.3.5 The effect of HRT on hydrogen production ................................. 17
1.3.6 Partial pressure of hydrogen ........................................................... 18
1.3.7 The effect of nutrients on hydrogen production .......................... 18
1.3.8 Hydrogen production from model substrates ............................. 18
1.4 Two-stage hydrogen and methane production ........................................ 19
1.5 Crop biomass for methane and hydrogen production ........................... 21
1.5.1 Composition of crops ....................................................................... 21
1.5.2 Storage of energy crops.................................................................... 22
1.5.3 Pre-treatments of energy crops ....................................................... 23
1.5.4 Methane production from crop biomass ....................................... 24
1.5.5 Hydrogen production from crop biomass .................................... 25
2 OBJECTIVES ............................................................................................................ 29
3 MATERIALS AND METHODS ............................................................................ 30
3.1 Main experiments of the thesis ................................................................... 30
3.2 Substrates and inocula ................................................................................. 31
3.3 Experimental set-up ..................................................................................... 32
3.3.1 Storage experiments (I) .................................................................... 32
3.3.2 Pre-treatments (III, IV) ..................................................................... 33
3.3.3 Methane and hydrogen potential batch assays (I-IV) ................. 33
3.3.4 CSTR reactors (V).............................................................................. 34
3.4 Analyses and calculations ........................................................................... 34
4 RESULTS .................................................................................................................. 37
4.1 The effect of storage on methane yield of grasses ................................... 37
4.2 Hydrogen production from grass silage and maize ................................ 44
4.2.1 The effect of inoculum on hydrogen production from
grass silage ......................................................................................... 44
4.2.2 The effects of VS ratio, temperature and initial pH on
hydrogen yield from grass silage ................................................... 46
4.2.3 The effects of pre-treatments on hydrogen production
from grass silage and maize ............................................................ 47
4.3 Methane production from grass silage and maize .................................. 53
4.3.1 Methane yield in batch assays, the effect of pre-
treatments .......................................................................................... 53
4.3.2 Methane production after hydrogen stage ................................... 53
4.3.3 Methaneproduction from grass silage in CSTRs ......................... 55

4.4 Shifting methanogenic process to hydrogenic process ........................... 58
5 DISCUSSION ........................................................................................................... 60
5.1 Main findings of the thesis .......................................................................... 60
5.2 Effect of storage on methane yield of grasses ........................................... 60
5.3 Hydrogen production from grass silage and maize in batch process .. 63
5.3.1 Hydrogen production from grass silage and maize .................... 63
5.3.2 The effect of inoculum on hydrogen production from
grass silage ......................................................................................... 63
5.3.3 The effect of temperature on hydrogen production .................... 64
5.3.4 The effect of substrate concentration and pH on
hydrogen production ....................................................................... 65
5.3.5 The effect of pre-treatments ............................................................ 66
5.3.6 Pattern of hydrogen production and consumption ..................... 66
5.3.7 Effects of methodology on hydrogen yield in batch
assays .................................................................................................. 68
5.4 Shifting methanogenic process to hydrogenic ......................................... 69
5.5 Methane production from grass silage and maize .................................. 70
5.5.1 Methane yield in batch assays, the effect of pre-
treatments .......................................................................................... 70
5.5.2 Methane production after hydrogen stage ................................... 71
5.5.3 Methane production from grass silage in CSTRs ......................... 72
5.6 Energy aspect of hydrogen and methane from energy crops ................ 74
6 CONCLUSIONS ...................................................................................................... 77
Acknowledgements ............................................................................................................ 79
YHTEENVETO (RÉSUMÉ IN FINNISH) .................................................................... 80
REFERENCES .................................................................................................................. 82
LIST OF ORIGINAL PUBLICATIONS
The thesis is based on the following original papers, which will be referred to in
the text by their Roman numerals I-V.
I planned the experimental work with my supervisor and co-authors and
did the main part of the experimental work. I wrote the first draft of all the
papers and finalized them with my co-authors and supervisor.

I Pakarinen O., Lehtomäki A., Rissanen S. & Rintala J. 2008. Storing energy
crops for methane production: effects of solids content and biological
additive. Bioresource Technology 99: 7074–7082.

II Pakarinen O., Lehtomäki A. & Rintala J. 2008. Batch dark fermentative
hydrogen production from grass silage: the effect of inoculum, pH,
temperature and VS-ratio. International Journal of Hydrogen Energy 33: 594–
601.

III Pakarinen O., Tähti H. & Rintala J. 2009. One-stage H and CH and two-
2 4
stage H + CH production from grass silage and from solid and liquid
2 4
fractions of NaOH pre-treated grass silage. Biomass & Bioenergy 33: 1419–
1427.

IV Pakarinen O., Kaparaju P. & Rintala J. Hydrogen and methane yields of
untreated, water-extracted and acid (HCl) treated maize in one and two-
stage batch assays. International Journal of Hydrogen Energy. In press.

V Pakarinen O., Kaparaju P. & Rintala J. 2011. The effect of organic loading
rate and retention time on hydrogen production from a methanogenic
CSTR. Bioresource Technology 102: 8952–8957.