Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE
A system to produce feedstock for biogas production
BACKGROUND
In industrial production of biogas the availability of feedstock is limited.
Biogas is defined in
literature as a gas mixture mainly consisting of methane (CH4) and carbon
dioxide (C02), which
is produced by bacterial breakdown of a biological substrate. Industrial
biogas plants are forced
to buy biomass, e.g. ley and wheat, from farmers to produce biogas. This means
that the product,
biogas, can be uneconomic to produce. The area of arable land is also limited
since there is a
competition situation between crops for food and for energy production. The
loss in production
is also strongly weather dependent, since bad weather is decreasing the crops.
These factors
lead to that the product, biogas, may become uneconomical to produce.
Earlier ideas, about alternative marine biomass for anaerobic digestion, have
dealt with
microalgae, macroalgae or blue mussels. All these have drawbacks as feedstock
for production of
biogas; Microalgae have a high cost of culturing considering that specific
nutrient must be added
under sterile conditions as well as a need for extra illumination since day
light is insufficient.
Macroalgae has been shown to be a good feedstock for anaerobic digestion but
can, if they are
harvested from beaches, contain high concentrations of heavy metals such as
cadmium. By
culturing macroalgae offshore it is possible to improve the economical
prerequisites by
fertilizing the water and hence enhance the growth rate. Blue mussels have a
large draw back in
that they have non-organic shells which a biogas plant does not want to
include in the process
since the shells clogs process pipes as well as increase the sedimentation of
not digestible
matter.
Producers of biogas always strive to increase the production of gas given a
certain amount of
biomass to maximize the yield. The problem to be solved is how the producer
can increase the
gas production. The most beneficial solution of biomass production is energy
efficient, increases
the yield of methane gas and gives other environmental positive effects at the
same time.
Prior art aiming to harvest biomass from the sea has only discussed
macroalgae, gathered by
culturing or harvest (Boudewijn et al. 1983; Schramm and Lehnberg 1984; Gao
and McKinley
1994; Yokoyam et al. 2007; The Crown Estate 2009) as well as macroalgae that
has been driven
ashore (Detox AB 2009). Even anaerobic digestion of microalgae taken from the
algal blooms in
the Baltic Sea has been proposed (Grondahl 2009) as well as anaerobic
digestion of blue mussels
cultured in the Baltic Sea (Hansson 2008; Radio Kalmar 2009). Also an idea
based on culturing
microalgae in nutrient rich waste water from sewage plants has been presented
(Nyberg 2008;
Clear Water Energy Nordic AB 2009). Among filed patent applications several
can be mentioned
claiming the exclusive right to use biomass based on micro- or macroalgae as
well as their
extracts (US2008/0050800, CN101418316, US2009081744, EP2014759, CN101285075,
CN101255075, UA24106, DE102007007131, W02007014717, W09851814, PT100012,
DE3607864, CN101418315).
MARINE BIOMASS - ASCIDIANS
Sea squirts, Ascidiacea, is a class of tunicates with approx 2300 species
around the world, of
which approximately 50 at the Swedish west coast. They are sessile, solitary
or colony forming
suspension feeders. The body is sack like and completely surrounded by the
tunica. The genus
Ciona consists of following species: Ciona edwardsi, Ciona fascicularis, Ciona
gelatinosa, Ciona
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imperfecta, Ciona intestinalis, Ciona mollis and Ciona savignyi. As an example
the ascidian Ciona
intestinalis L. is mentioned which occurs in very high abundances and has been
reported in
densities over 5000 individuals per m2 (Millar 1971). The weight of biomass
has been estimated
to -7kg DW/m2 (Gulliksen 1972) and in Canadian water to 200kg wet weight / m2
(Ramsay,
Davidson et al. 2009). If we use the dry matter composition of 4% (Petersen et
al. 1997) this
value corresponds to 8kg DW/m2. They live by filtering plankton from the water
and has a very
rapid growth compared to many other animals. Their daily growth in length can
be 2-3% and a
doubling time of weight in 10 days (Petersen et al. 1995). Ciona intestinalis
reproduces in boreal
waters two times per year and in warmer water three times, possibly four times
(Dybern 1965).
Definitions
DW: Abbreviation for Dry Weight which is the water free weight the organism
has after drying
(-80 C, 1 day).
Wet weight: The weight of the biomass in wet condition which is weighed within
1 hour after
harvest when the biomass is at least half the time in a colander.
Marine / marine environment: Defined as the water environment which is not
pure lake water
or consists of fresh water. i. e. all water environment which has a salinity
over 0.5 %o NaCl.
Sea: Same definition as marine environment.
Organism: Defined as all living organisms of the groups Eukaryota, Archea and
Procaryote.
Animal: A group of organisms belonging to the group Animalia.
Sea squirt / ascidians: Animals belonging to the group Ascidia
Artificial seeding: A by man controlled production of egg and sperms in
organisms whose
zygotes (the fertilized egg) develops to larvae which settles on hard surfaces
in water before
they grow to adult animals.
Water: All environments consisting of H2O which includes marine environment
and lakes, both
environments includes both natural as well as artificial environments, e. g.
ponds and other
water constructions.
Plankton: All organisms living suspended in water is the scientific correct
definition as we use in
this text. The plankton can be divided into, and embraces, zooplankton,
phytoplankton and
bacterioplankton depending on which organism is referred to.
Settla: Is a Swedish translation of the English term settle which is
translated to the Swedish bli
fast, satta sig. The term settla (infinitive - att settla) is used by Swedish
marine biologists.
Ascidia: The organism group is named sjopungar in Swedish. Ascidia is
synonymous with
Ascidiacea and is defined by Tree-of-life (http://tolweb.org/tree) and
references therein.
Anthozoa: The organism group is named "koraller" in Swedish. Defined by Tree-
of-life and
references therein.
Porifera: The organism group is named "svampdjur" in Swedish. Defined by Tree-
of-life and
references therein.
Macroalgae: Visible algae. A unifying term for the organism groups red algae
(rhodophyta),
green algae (chlorophyta) and brown algae (phaeophyta).
Microalgae: Unicellular organisms which are not visible to the naked eye and
are living
suspended in the sea. Are not related with macroalgae but belongs to several
different organism
groups such as dinoflagellates, diatoms etc.
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BRIEF DESCRIPTION OF THE FIGURES
Figure 1: Large scale culturing of ascidians in the sea for biomass
production. Ascidians are
growing on culture lines (a) which are submersed in the water. A horizontal
rope (b) fastened to
floats (c) holds the culture lines up. The horizontal lines is trenched
outwards by a rope (d)
which is hold by moorings and anchors (d).
Figure 2: Description of a method for artificial seeding of ascidian larvae on
culture lines
submersed in water. Mature individuals of ascidians (a) are fastened on a net
(b) inside the
water tank (c). Water is entering by a pipe (d) and is exiting by a pipe (e)
Culturing lines (f) is
hung over a pole (g) which can be removed from the tank.
SUMMARY
The invention consists of a procedure composed of anaerobic digestion of water
living
organisms to be used as feedstock for biogas production. The said procedure
can also include the
culture and harvest of the organisms before anaerobic digestion. A very
suitable organism for
this is in Swedish waters is the sea squirt organism, Ciona intestinalis,
based on 1. A very fast
growth which allows for several harvests annually, even during winter time 2.
No hard internal
structures such as shell or bones which prevent the biomass to be pumped 3.
The biomass has
been shown to increase the biogas production during anaerobic digestion with
multiple
biomasses 4. Possibility to be cultured in existing culture systems for blue
mussels 5. Production
ensurement in that it is possible to avoid losses of biomass due to harsh
weather which happens
to land based agriculture 6. Continuous culturing and harvest season by an, in
this patent,
described procedure which allows the sea squirts to settle on the culture
ropes under controlled
conditions which allows for continuous harvest 7. Culturing is without
competition to
agriculture 8. Culturing and harvest in the sea gives much more biomass per
area and demands
less energy for culturing and harvest compared to agriculture.
In other countries and waters, other species of ascidians (or corals or
sponges) can be most
suitable to culture and harvest to achieve the benefits by means of
cultivability, rapid growth
and the possibility to use industrial pumps in combination with an energy
system to produce
biogas by anaerobic digestion. Examples on such organisms are Ascidia
sydneiensis, salps,
apendicularians and desmosponges. By using experience and techniques from
industrial
culturing of mussels this invention secures the industrial production of
ascidians. In addition
new technical solutions have been incorporated to secure an industrial
production of ascidians
during the whole year and not only during the ascidians ordinary period of
reproduction.
The invention relates to a procedure for biogas production, which comprising
anaerobic
digestion of water living organisms belonging to the group ascidiacea.
The procedure for biogas production comprises anaerobic digestion and
utilization of the
produced gas during anaerobic digestion. The digester gas (so called raw gas)
consists of
methane and carbon dioxide, of this mixture the methane is purified for the
production of
biogas.
In one embodiment, the procedure includes culture and harvest ascidians before
they are
anerobically digested.
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Culturing of ascidians may be performed by using a number of surfaces
submersed in water, on
which said surfaces the ascidians can be cultured before harvest.
According to a preferred embodiment, the procedure includes fastening
ascidians in larval stage
on culturing surfaces, by storing said culturing surfaces submersed in water
tanks together with
adult individuals of ascidians, regulating the water temperature in the tank,
causing the adult
individuals to start spawning, and larvae produced by the fusion of gametes,
are settling on the
surfaces, which are there after placed on the culture site.
Further, the culture can also be achieved according to methods described by
Aypa (1990); rack
culture, hanging method, bitin culture, tulus culture, stake culture, tray
culture, wig-wam
culture, rope-web culture, bouchout culture, raft culture and long-line
culture.
According to another aspect, the method includes to utilize solid and fluid
digestate. The method
can further include utilizing the solid and fluid digestate to produce a
fertilizer.
The invention also relates to a method for producing fertilizer, comprising
anaerobic digestion
of water living organisms belonging to the groups ascidians and thereafter
utilize solid and fluid
digestate for fertilizer production.
Another aspect of the invention relates to a method comprising to culture
ascidians together
with macroalgae of the groups rhodophyta, chlorophyta and phaeophyta. Combined
culture
leads to higher growth rate of the macroalgae due to the dissolved nutrients
excreted by the
ascidian metabolism.
This method can further relate to anaerobically digest the macroalgae together
with said
ascidians.
The invention also relates to a method for production of fertilizer,
comprising culturing and
anaerobic digestion of ascidians and macroalgae together, and to utilize solid
digestate to
produce fertilizer.
In one form of practice the said methods is the organisms filter feeding
animals of the groups
anthozoa and porifera.
The invention also relates to a method of fastening ascidians in larval stage
on culturing
surfaces, by storing said culturing surfaces submersed in water tanks together
with adult
individuals of ascidians, regulating the water temperature in the tank,
causing the adult
individuals to start spawning, and larvae produced by the fusion of gametes,
are settling on the
surfaces, which thereafter are placed on the culture site.
Another aspect of the invention comprises anaerobic digested biomass from
anaerobic digestion
of water living animals from the group Ascidia.
In one embodiment, the invention relates to anaerobic digested biomass from
ascidians derived
by any of the above mentioned methods.
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DETAILED DESCRIPTION
Below, the present invention will be described in detail with reference to
specific embodiments
of the invention. This description is provided to increase the understanding
of said specific
embodiments, and is in no way meant to limit the scope of the present
invention. The scope of
the present invention is defined by the claims as appended.
Efficacy as feedstock for anaerobic digestion
The background for the invention to use ascidians as biomass in anaerobic
digestion lies in the
fact that Swedish producers of biogas are using waste from the seafood
industry, in the form of
brine and rest products, and so increases the biogas production, both in
volume produced biogas
as well as a higher percentage of methane in the gas. Waste from the seafood
industry is
considered to be a very good biomass complement in combined anaerobic
digestion with waste
sludge, a possible explanation for this could be that the said waste is rich
in nitrogen which
promotes the overall anaerobic digestion if the combined biomass has a higher
composition of
carbon. In anaerobic digestion a general rule is that the molar quota between
carbon and
nitrogen shall be between 30:1 and 20:1 (C:N). Ascidians have a carbon -
nitrogen quota of 4:1
which is too low for optimal anaerobic digestion using ascidians alone. But
ascidian biomass is
very suitable for anaerobic digestion in combination with more carbon rich
biomasses such as
waste sludge from sewage treatment plants or crops from agriculture. The waste
from seafood
industry has a carbon - nitrogen quota of 5:1 which is an argument that the
low carbon-nitrogen
quota of ascidians is not a problem in industrial anaerobic digestion
processes.
The salinity of biomass from newly harvested ascidians is more or less the
same as the
surrounding water. This is caused by the fact the ascidians close their body
openings and
enclosures a volume of water. In ascidians from the sea outside Lysekil,
Sweden, which we have
used in tests of anaerobic digestion, the salinity has ranged between 20 and
30 %o but can vary
between 10 and 35 %o in these waters. The waste from seafood industry has a
salinity of 60 -
70 %o and this salinity has not been shown to decrease the efficacy of
anaerobic digestion if the
digester is given time to adjust for the amount of saline biomass. The fact
that a anaerobic
digestion process accepts fair amounts of saline biomass is known (Schramm and
Lehnberg
1984; The Crown Estate 2009). It is also known that a small degree of salinity
enhance the
production of biogas. A general rule is that the bacterial community can
handle a wide range of
different biomasses given time to adjust. Methane producing bacteria comes
evolutionary from
the sea but occurs in stomachs of animals as well as in marine and brackish
waters.
Marine biomass - other species of ascidians and corals and sponges
As well as culturing the species we have chosen as an example, Ciona
intestinalis, which is
suitable to culture in Swedish waters, other species of Ciona or other
ascidians can be cultured
where the environmental conditions so demand or if Ciona intestinalis is not
naturally occurring.
See table 1 for a phylogenetic overview of the class Ascidia.
In the genus Ciona, as mentioned above, following species is included: Ciona
edwardsi, Ciona
fascicularis, Ciona gelatinosa, Ciona imperfecta, Ciona intestinalis, Ciona
mollis and Ciona savignyi,
which all is suitable for similar use as Ciona intestinalis.
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Table 1 Phylogenetic overview of the class ascidians (Ascidiacea) which all
are possible to use as biomass for
anaerobic digestion.
Kingdom: Animalia
Phylum: Chordata
Subphylum: Tunicata
Class: Ascidiacea
Order: Enterogona
Suborder A lousobranchia Family Claveliniclae
Family Didemniclae
Family Polycitoridae
Family Polyclinidae
Suborder Phlebobranchia Family Agnesiidae
Familj Ascidiidae
Family Cionidae
Family Corelliclae
Family Diazonidae
Family H ob hiidae
Family Pero horidae
Genus Didemnum
Order Pleurogona
Suborder Stolidobranchia
Family Pyuridae
Family Styelidae
Genus Eusynstvela
Genus S e/a
Family Botrvllidae
Genus Bot-vlloides
Genus Botivllus
Other fast growing species of both corals and sponges can also be cultured in
the sea, or in lakes,
with the same methods as described herein, aiming at producing biogas for
anaerobic digestion
or production of bioethanol. Some of these animals can be suitable for
culturing off-shore at
larger depths. In expanding the examples given here, we point at the high
abundance and
productivity of animals around so called "thermal vents" (hot underwater
volcanoes) where
many life forms is using chemotrophic bacteria as primary producers. In this
patent application
we have chosen to use ascidians as examples. The invention is thereby not
limited to the use of
ascidians, but includes coral and sponge animals which neither is industrial
cultured to
producing biomass.
Culturing of organisms in water
A general system for culturing sessile organisms in sea, either marine or
brackish, is that it
consists of a surface submersed in water where organisms from the ambient
water settle as
larvae or that larvae or spores settles on the surfaces in water tanks on land
by manipulating the
parental generation. Generally at harvest the surfaces, as ropes, lines,
poles, nets, etc., is
removed from the water so the organisms can be harvested onto a boat or to
land. Another
occurring method is to culture organisms on natural substrates and bottoms
which also give the
possibility for production of biomass.
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To culture ascidians, corals or sponges, the general system for culturing
mentioned above, is
sufficient if the submersed surface has the right properties for the organisms
to settle and grow
and not to fall of the surface. The suitable time for submersion of the
surfaces is important
regarding water temperature, salinity or other physical parameters to ensure a
good growth of
the animals. The time for submersion is also important regarding the presence
of larvae in the
water due to their life cycle. Below are a number of culture methods given as
examples for
methods suitable for ascidian culture which also is suitable for culturing of
corals and sponges.
Several of these methods are given in aqua culture literature (see e.g. Aypa
1990).
The long-line method is most commonly used for mussel culturing in Sweden and
the method as
we find, in Swedish waters, as the most suitable. This is based on that the
method is used in
industrial scale for culture and harvest of approx. 3000 tons blue mussels
annually and the
methods is therefore reliable. All equipment is commercial available and
harvest boats is
possible to rent as well as experienced personnel. The long-line method
consists of a
polypropylene band, 5 cm width, which is submersed into water in a long
unbroken chain. In a
Swedish long-line culture with dimensions 20*200 meters the total length of
culture lines is 24
km. The lines is fastened with regular intervals on a carrier rope which in
turn is uphold by
floats, see Figure 1. The ends of the carrier ropes are anchored to keep the
culture outstretched.
The method is also named "one dragon method" in China. By placing the culture
lines hanging
above the bottom, bottom living animals is efficiently hindered to come up
onto the lines and
feed, for Ciona intestinalis this is valid for e.g. Asterias rubens which
feeds on the said species.
Other methods that can be used for efficient culture and harvest can include
(according to Aypa
1990): Rack culture, hanging method, bitin culture, tulus culture, stake
culture, tray culture, wig-
wam culture, rope-web culture, bouchout culture, raft culture, long-line
culture.
Integrated culture
A specific embodiment of the method to culture ascidians in the sea with the
purpose to produce
biomass for anaerobic digestion is to have an integrated culture of ascidians
and macro algae.
Different techniques for culturing macro algae are well known and are
described well in the
specialist literature (Lucas and Southgate 2003; Pillay and Kutty 2005). It is
also known that
macroalgae have a higher growth rate when there are higher concentrations of
nutrients in the
water, mostly nitrogen and phosphorus compounds. It is also known that animals
excrete
nutrients as byproducts of their metabolism in the form of e.g. urine, urea or
substances with
similar purpose to remove excess metabolites from organisms. These excretions
are rich in easy
available nitrogenous substances; compare e.g. the use of manure as fertilizer
in agriculture.
With this background knowledge we state that there is an enhancing effect in
integrated culture
of ascidians, or the organisms chosen for the production of biomass for
anaerobic digestion, with
macro algae. The ascidians are excreting nutrients that make macroalgae grow
faster which is
preferable for industrial producers. In an environmental perspective, said
integrated culture
increases the capacity to remove nutrients from the sea for the whole cultures
which is positive
if emission credits is sold based on the facto amount of nitrogen and
phosphorus that is removed
from the sea. No one has previously used an integrated culture of ascidians
with macroalgae as
biomass for anaerobic digestion to achieve the said effect.
The integrated culture is obtained by the following description: 1. Ascidians
and macroalgae is
cultured on different rope/band within the same culture unit so the macroalgae
comes in
proximity to the release of nutrients from the ascidians and the ascidians
does not compete for
planktonic food 2. Ascidians and macroalgae is cultured on separate but
closely located units.
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The maximum distance between culturing units, when culturing separately, is
determined by the
size of the culturing units as well as water currents and hydrography of the
area so the
macroalgae can utilize the nutrients that the ascidians excrete.
Artificial seeding
Ciona intestinalis is reproducing in temperatures between 8 and 23 (Dybern
1965) and
releases larvae in Swedish and Norwegian waters between May and September with
maximum
larval production in June (Dybern 1965; Gulliksen 1972).
The method of artificial seeding is today used for cultivation of macroalgae
such as species of
Porhyra among which one is the popular Japanese Nori-algae used for sushi
(Kelly and
Dworjanyn 2008). Artificial seeding means that by performing a certain
technical procedure,
such as manipulating the amount, quality and temperature of the light, the
lifecycle of the
macroalgae can be regulated to produce reproductive bodies (spores). For a
person skilled in the
art it is possible to perform such a method.
However, no one has used the mentioned method to ensure settling on culture
surfaces in the
sea for ascidians. Knowledge of the physical properties of the water that is
needed for ascidians
to release their egg and sperms in laboratory is well known. This knowledge
has been used to
rear new individuals of ascidians for research purposes. But since no one has
had the idea to
culture ascidians in large scale at sea, no one has had the idea to improve
such method by
artificial seeding.
The method is performed by storing adult individuals of ascidians in a water
tank where the
water temperature is kept below 8 , at which temperature ascidians get
sexually mature if the
temperature is exceeded. In those tanks the culture band, culture ropes or
other culture
surfaces, onto which the ascidians shall settle as a new generation larvae,
are submersed.
Thereafter the temperature is raised over 8 and the adult individuals of
ascidians after a period
of time releases egg and sperm which is conjugated to larvae. The larvae will
thereafter settle on
the submersed culture band, culture ropes or other culture surfaces.
The ascidians can be contained in the same tank as the culture bands or be
contained in a tank
with communicating water connection.
After the settling of larvae on the submersed band the larvae are growing for
a suitable
delimited time until they have had an enough growth to stand transportation to
the new water
environment where they shall grow to adult age before harvest.
Results
The growth rate of Ciona intestinalis has been measured by the applicant and
was found to be
8.5 cm (n=350, s.d. = 3.2 cm) during 93 days and a increase of biomass,
measured as wet weight
per m2, of 33 kg during the same period of time (location: Lysekil, Sweden,
time May 2009 to
August 2009, depth 1-2 meter on a vertical concrete construction, approximate
salinity 20-34
psu, approximate temperature 10-20 ).
The inventor has further conducted anaerobic digestion tests where the
production of biogas
after 10 days was 600 ml CH4/g VS with biomass from ascidia mixed with 30 %
(weight) carbon
rich biomass.
The inventor has also conducted test for harvest of ascidians (Ciona
intestinalis) on an ascidian
culture in Ljungskile on the Swedish west coast during April 2010. The culture
was using the
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long-lines method. During the harvest test a boat ordinary used for blue
mussel harvest did
harvest 10m3 ascidians per hour.
The inventor has conducted a test for anaerobic digestion of 10m3 ascidians
during April 2010.
The ascidian biomass was digested in combination with sludge waste from a
waste water plant.
The results did show that the biogas production after mixing with 5% Ciona
intestinalis was
retained at previous levels as before the addition. The concentration of
methane was unchanged
and varied between 58 and 64%.
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