The feasibility of using algae as a co-substrate for biogas production

56 Pages·2015·1.03 MB·English

The feasibility of using
algae as a co-substrate
for biogas production

Laboratory experiments of the co-digestion of algae
and biosludge
Möjligheten av att använda alger som samsubstrat for
biogasproduktion
Laboratoriska experiment av samrötning mellan alger
och bioslam

Lisa Arkelius
Health, Science & Technology
Master of science in industrial management and engineering
Master Thesis: 30 ECTS
Andreas Nilsson & Karin Granström
Mikael Johnson
2015-06-08

Prologue
This master thesis represents the last and final part of my education at
Karlstad’s University, within Industrial Management and Energy- and
Environmental Engineering. The thesis coves 30 university points and has
been conducted during spring of 2015 at Karlstad’s University.
I would like to thank my supervisors Andreas Nilsson and Karin Granström,
for their mentorship, support and endless patience. Without their help and
expertise this work had been much harder.
I would also like to thank Susanne Ekendahl at SP, Technical Research
Institute of Sweden, for her help answering questions about the cultivation of
algae at Bäckhammars bruk. Also thanks to some of the other interests in the
algae project, Nordic Paper, Region Värmland and The Paper Province, for an
interesting meeting about the algae project.
Last I want to thank my family for their endless support during my five year of
education. Without their love and help, this would not been possible.
Lisa Arkelius 2015-06-08

4
Abstract
Today 88 % of the world energy comes from fossil fuels. Greenhouse gas
emissions are increasing and the fossil fuels energy sources will decrease at
some point. Other alternatives must be found, to substitute and lower the
usage of fossil fuels. Biogas is one of these other options. It is a versatile fossil
free fuel that can be used for heat, power and fuel for vehicles. Many different
substrates have been used for biogas production over the years, and now algae
are examined as a substrate. Algae have advantages over the former substrates
used for biogas production. Laboratory experiments were conducted to
examine the co-digestion potential of algae and biosludge, which is a rest
product from a wastewater treatment plant at a pulp and paper mill. The
profitability aspect of using algae and biosludge for biogas production has
been examined as well.
The result shows that unmixed algae were the highest methane producing
substrate, which produced a maximum of 203,5 Nml/g VS. An interesting
result was that both algae and biosludge separately produced more methane
gas than the mixtures. The profitability aspect of the thesis showed that it is
not profitable to use algae primarily for biogas production, based on the
conditions of today.

5
Sammanfattning
Idag kommer 88 % av världens energi från fossila bränslen. Utsläppen av
växthusgaser ökar och de fossila bränslenas energikällor kommer att minska
inom en viss tid. Andra alternativ måste hittas, för att ersätta och minska
användningen av fossila bränslen. Biogas är ett av dessa alternativ, det är ett
mångsidigt fossilfritt bränsle som kan användas för värme, el och bränsle för
fordon. Många olika substrat har använts för biogasproduktion under årens
lopp, och nu har alger undersöktes som ett nytt substrat. Alger har fördelar
jämfört med de tidigare substrat som används för biogasproduktion.
Laboratorieförsök genomfördes för att undersöka samrötning av alger och
bioslam, som är en restprodukt från en avloppsanläggning vid ett massa- och
pappersbruk. Lönsamhetsaspekten av att använda alger och bioslam för
biogasproduktion har också undersökts .
Resultatet visar att alger utan inblanding av bioslam gav mest metan och
producerade maximalt 203,5 Nml/g VS. Ett intressant resultat var att både
alger och bioslam rötade separat producerade mer metangas än blandningarna.
Lönsamhetsaspekten av rapporten visade att det inte är lönsamt att använda
alger för endast biogasproduktion, baserat på villkoren i dag.

6
Table of content
1. Introduction 11
1.1. Background 11
1.2. Problem discussion 13
1.3. Purpose 14
1.3.1. Research questions: 14
1.4. Delimitations 14
2. Theoretical framework 15
2.1. Biogas 15
2.2. Anaerobic Digestion 15
2.2.1. Inhibition of anaerobic digestion 17
2.3. Substrate 18
2.3.1. Algae 19
2.3.2. Biosludge 21
2.4. Digestate 22
3. Research methodology 25
3.1. Research strategy 25
3.2. Literature study 25
3.3. Experimental setup 26
3.3.1. Substrates and inoculum 26
3.3.2. AMPTS2 28
3.3.3. VS and TS 29
3.3.4. Round 1 30
3.3.5. Round 2 32
3.3.6. Round 3 33
3.3.7. pH and TAN 33
3.3.8. Digestate 34
3.4. Economy 35
4. Results 37
4.1. Experimental results 37
4.1.1. Round 1 37
4.1.2. Round 2 39
4.1.3. Round 3 41
7
4.1.4. Summary of the experimental results 43
4.1.5. Digestate 45
4.2. Economics 45
5. Analysis and discussion 47
6. Conclusions and future research 51
7. References 52

TABLE OF FIGURES
FIGURE 1 BIOGAS USAGE IN SWEDEN 2013 12
FIGURE 2 THE DIFFERENT STAGES DURING ANAEROBIC DIGESTION 16
FIGURE 3 THE EQUIPMENT AMPTS2. 28
FIGURE 4 ACCUMULATED METHANE PRODUCTION, ROUND1 37
FIGURE 5 AVERAGE METHANE PRODUCTION OF THE TRIPLICATES,ROUND1 38
FIGURE 6 ACCUMULATED METHANE PRODUCTION,ROUND2 39
FIGURE 7 AVERAGE METHANE PRODUCTION OF THE TRIPLICATES,ROUND2 39
FIGURE 8 ACCUMULATED METHANE PRODUCTION, ROUND3 41
FIGURE 9 AVERAGE METHANE PRODUCTION OF THE TRIPLICATES, ROUND3 42

TABLE OF TABLES
TABLE 1 RESTRICTIONS OF HEAVY METALS FOR DIGESTATE USAGE 23
TABLE 2 RESTRICTIONS OF NUTRIENTS IN DIGESTATE 23
TABLE 3 TS AND VS VALUES FOR THE INOCULUMS 27
TABLE 4 TS AND VS VALUES FOR THE ALGAE 27
TABLE 5 TS AND VS VALUES FOR THE BIOSLUDGE 28
TABLE 6 THE AMOUNT OF SUBSTRATE IN EACH OF THE TRIPLICATES 32
TABLE 7 THE AMOUNT OF SUBSTRATE IN EACH OF THE TRIPLICATES 33
TABLE 8 THE AMOUNT OF SUBSTRATE IN EACH OF THE TRIPLICATES 33
TABLE 9 HEAVY METAL CONTENT IN BIOSLUDGE IN 2007 34
TABLE 10 NUTRIENT CONTENT OF ALGAE AND BIOSLUDGE 35
TABLE 11 ANALYSES OF THE DIGESTATE AFTER ANAEROBIC DIGESTION 38
TABLE 12 ANALYSIS OF THE DIGESTATE AFTER ANAEROBIC DIGESTION 40
TABLE 13 ANALYSIS OF THE DIGESTATE AFTER ANAEROBIC DIGESTION 42
TABLE 14 MAXIMUM METHANE PRODUCTION, AVERAGE PRODUCTION AND STANDARD
DEVIATION OF THE MIXTURES. 43
TABLE 15 AVERAGE VALUE AND STANDARD DEVIATION OF PH, TAN AND FAN 44
TABLE 16 COMPARING THE SUBSTRATES AGAINST RESTRICTIONS FOR USAGE OF DIGESTATE 45
TABLE 17 REVENUES AND COSTS FROM BIOGAS PRODUCTION BY ALGAE AND BIOSLUDGE 46
TABLE 18 REVENUES AND COSTS FROM BIOGAS PRODUCTION BY BIOSLUDGE 46

8
Nomenclature and list of words
AMPTS2 Autometic Methane Potential Test
System
Anaerobic A process where microorganisms
digestion break down organic material in the
absence of oxygen
Anaerobic A process where microorganisms
fermentation break down organic material in the
absence of oxygen
Bioenergy Renewable energy that derives from
biological sources
Biogas A gas fuel which is produced during
anaerobic digestion
C/N-ratio The relation between carbon and
nitrogen
FAN Free Ammomium Nitrogen (NH ) (mg/l)
3
H S Hydrogen Sulfide (mg/l)
2
Lignocellulosic Biomass from trees, bushes and
material grass.
NH + Ammonium Nitrogen Ion (mg/l)
4
TAN Total Ammonium Nitrogen (NH - (mg/l)
3
N)
TS Total Solids (%), (g VS/g sub),
(g)
VFA Volatile Fatty Acids (mg/l)
VS Volatile Solids (%), (g VS/g sub),
(g)
9
10