Anaerobic digestion of crop and waste biomass

192 Pages·2016·4.81 MB·English

by  Ivo Achu Nges

Anaerobic digestion of crop and waste biomass: Impact of feedstock characteristics
on process performance
Ivo Achu, Nges
Published: 2012-01-01
Link to publication
Citation for published version (APA):
Ivo Achu, N. (2012). Anaerobic digestion of crop and waste biomass: Impact of feedstock characteristics on
process performance Lund University (Media-Tryck)
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Anaerobic digestion of crop and waste biomass:
Impact of feedstock characteristics on process
performance

Ivo Achu Nges

Doctoral thesis
Department of Biotechnology

Akademisk avhandling för avläggande av teknologie doktorsexamen vid
tekniska fakulteten vid Lunds Universitet. Avhandlingen kommer att
offentligen försvaras torsdagen den 14 Juni 2012, kl.10:30 i hörsal B på
Kemicentrum, Sölvegatan 39, Lund.

Academic thesis, which by due permission of the faculty of Engineering
at Lund University, will be publicly defended on Thursday, the 14th of
June, 2012 at 10:30 a.m. in Lecture Hall B, at the Center of Chemistry
and Chemical Engineering, Sölvegatan 39, Lund, for the degree of
Doctor of Philosophy in Engineering.

The faculty opponent is Associate Professor Hinrich Uellendahl,
Aalborg University, Denmark.
Doctoral thesis
Department of Biotechnology
Lund University Sweden

© Ivo Achu Nges

ISBN 978-91-89627-83-3
ISRN LUTKDH/TKBT--12/1137-SE

Printed in Sweden by Media-Tryck, Lund University, Lund 2012

Cover photo: Courtesy of Emma Kreuger
To Nangah Ruphina M. (RIP)

Organization Document name
LUND UNIVERSITY DOCTORAL DISSERTATION
Date of issue
Department of Biotechnology 2012-05-21

P.O. Box 124 SE-221 00 Lund, Sweden
Author(s) Sponsoring organization

Ivo Achu Nges
Title and subtitle
Anaerobic digestion of crop and waste biomass: Impact of feedstock characteristics on process
performance
Abstract
Anaerobic digestion provides an array of positive environmental benefits such as reducing greenhouse gas
emissions, replacing mineral fertilizers, producing renewable energy and treating waste. However, pitfalls in
anaerobic digestion such as poor methane yields, process instability, process failure and regional shortages
of feedstock have limited the full exploitation of the anaerobic digestion process.
The research presented in this thesis deals with the assessment of the possible negative or positive
impacts of feedstock characteristics on the efficiency of anaerobic digestion. In addition, it investigates
ways of enhancing the methane yield of the feedstock by improving the feedstock characteristics. The
feedstocks investigated were various energy crops, food industrial waste and sewage sludge. The
improvement methods investigated were ensiling, nutrient supplementation, co-digestion and anaerobic
pretreatment.
It was found that ensiling crops results in insignificant losses in energy, total solid and wet weight. In
addition, no significant difference was found in methane yields between the ensiled and fresh crop samples.
The importance of correcting for losses of volatiles in total solids determination was pointed out and it was
shown that failing to do so could be the main reason why many previous publications report increased total
solid based methane yields after ensiling. Increased methane yield in silages may therefore be an effect of
an analytical error rather than an effect of using ensiling as a pretreatment prior to anaerobic digestion.
Anaerobic digestion of crop biomass is known to be particularly limited by nutrient availability. Direct
nutrient supplementation in crop mono- digestion in this research demonstrated an efficient biogas process
at the shorter hydraulic retention times commonly applied in co-digestion of crop biomass and manure. The
high degradation efficiency was evidenced by high methane yields, comparable to maximum expected
yields generated under controlled conditions, and low volatile fatty acids accumulation. As a result of
nutrient addition, the digestate could comply with certification standards for bio-fertilizer. Also, viscosity
problems commonly reported for crop mono-digestion were not observed in this study, which could be
another effect of nutrient addition.
Co-digesting of waste biomass and crop biomass led to significant improvement in methane yield per ton
of feedstock and carbon to nitrogen ratio as compared to digestion of only the waste biomass. Biogas
production from crops in combination with waste biomass also eliminated the need for addition of
micronutrients normally required in crop mono-digestion. Co-digestion was also presented as a means of
feedstock supplementation to curb feedstock shortages in waste-based anaerobic digestion processes. In
addition, inhibitors in anaerobic digestion such as free ammonia and light metal ions were diluted, a
condition which can lead to an overall viable biogas process
Anaerobic pre-treatment led to the solubilisation of particulate organic matter in sewage sludge. This
solubilisation could have led to the improved methane yield, methane production rate and reduction in
volatile solids.
Applying different feedstock improvement solutions to the various feedstocks investigated, i.e. nutrient
addition, co-digestion and pretreatment, were demonstrated as effective means of enhancing the methane
yield of the feedstock thereby improving the overall anaerobic digestion process.
Key words
Anaerobic digestion, Biofertilizer, Renewable energy, sustainable operation
Classification system and/or index terms (if any)

Supplementary bibliographical information Language: English

ISSN and key title ISBN
978-91-89627-83-3
Recipient´s notes Number of pages Price
198
Security classification

Distribution by (name and address)

I, the undersigned, being the copyright owner of the abstract of the above-mentioned dissertation, hereby grant to
all reference sources permission to publish and disseminate the abstract of the above-mentioned dissertation.

Signature Date 2012-05-04

PREFACE

The research presented in this PhD thesis was conducted at the
Department of Biotechnology, Lund University, under the supervision
of Dr Lovisa Björnsson (main supervisor) and Dr Jing Liu (co-
supervisor). I greatly appreciate the financial assistance from Eon gas
Sverige.

The thesis has two main parts: an introduction, summarising my
research, its findings and applications, and a compilation of published
papers or papers earmarked for publication. The work described is the
result of the collaboration and support of a good many people. In
particular, I would like to thank my main supervisor, Lovisa Björnsson
for her encouragement, enthusiasm, availability and tireless efforts in
making this work a success. The support I received from you was truly
first rate. Jing Liu, my co-supervisor, thanks for introducing me into the
field of biomethanation or AD and for showing me how to write a
scientific article. Marika Murto, thanks for the guidance during the
potato waste project.

I would like to thank my colleagues, Emma and Carla, for suggesting
improvements in the methane potential test and in the analysis of
organics, respectively; and for sharing their great deal of expertise. I
would also like to thank Jesper Christensson, Nforngang, J. and
Toungwa, F. for their technical assistance at the pilot plant. Thanks to
Siv and Frans-Peder for their help with administration and technical
issues, respectively. A hearty thanks to all the staff and lecturers at the
Department of Biotechnology.

Thanks to all my lab mates, friends and fellow postgraduates for fond
times and wonderful camaraderie; especially Malik, Maryam, Valentine,
Rosa, Maria, Marisa, Linda (the ‘fikas’ and diners were soul lifting!),
i
Reza, Victor, Lesedi, Ally, Tarek, Roya, Pontus, Kosin, Solmaz,
Rawana, Tania, Anslem, Zeeshan, Sami, Peter, Gustav, Amin, Ramin,
Fabian, Sten, Hugo, Deepti, Ravi, Georgina, Serena, Maru, Harald,
Dimitry, Gashaw, Fatima etc. apologies to those I might have forgotten.

To you Cameroonians in Lund (CamLund) and Malmö (Camgrass),
especially the Kimbungs, the Lekunzes, the Bumus and the Tanahs, you
made Sweden (Lund/Malmö) a home away from home. Efetobore
Erukporo, you have always been a ‘big brother’, thanks for all the good
counsel.

I would like to extend special thanks to my family, especially my wife
Benedicta, my son Darin Achu, uncle Boss, Auntie Boss, uncle Joe, Mr
Ngang Cletus, Mr George Atanga, Manka, Chi, Yong, Dominic, Tche
etc. who have been extremely patient and have provided tremendous
support and love throughout the course of this project. Thanks to you all
and many more thanks to the rest of the extended family. Stella Mai,
Mrs Nkuo aka Na Jack, Mrs Ataindum aka Na Eric, Hyacintha Wallang
aka nawain, the warm fufu-corn and Kati Kati still warms my heart!
And you Mr Ngong Kits, Ngong Ludwig, and the Anbainbus, you have
been family!

Yotah Joana aka Auntie Joan, you have been a mother, counselor,
mentor, provider, etc. I couldn’t have asked for more, I appreciate!

Finally, all reverence and praise to Yahweh, the giver of wisdom,
knowledge and peace.

ii
Abstract

Anaerobic digestion provides an array of positive environmental
benefits such as reducing greenhouse gas emissions, replacing mineral
fertilizers, producing renewable energy and treating waste. However,
pitfalls in anaerobic digestion such as poor methane yields, process
instability, process failure and regional shortages of feedstock have
limited the full exploitation of the anaerobic digestion process.

The research presented in this thesis deals with the assessment of the
possible negative or positive impacts of feedstock characteristics on the
efficiency of anaerobic digestion. In addition, it investigates ways of
enhancing the methane yield of the feedstock by improving the
feedstock characteristics. The feedstocks investigated were various
energy crops, food industrial waste and sewage sludge. The
improvement methods investigated were ensiling, nutrient
supplementation, co-digestion and anaerobic pretreatment.

It was found that ensiling crops results in insignificant losses in energy,
total solid and wet weight. In addition, no significant difference was
found in methane yields between the ensiled and fresh crop samples.
The importance of correcting for losses of volatiles in total solids
determination was pointed out and it was shown that failing to do so
could be the main reason why many previous publications report
increased total solid based methane yields after ensiling. Increased
methane yield in silages may therefore be an effect of an analytical error
rather than an effect of using ensiling as a pretreatment prior to
anaerobic digestion.

Anaerobic digestion of crop biomass is known to be particularly limited
by nutrient availability. Direct nutrient supplementation in crop mono-
digestion in this research demonstrated an efficient biogas process at the
shorter hydraulic retention times commonly applied in co-digestion of
iii