#18

january 2011
#18
le gouessant
aquaculture
technical
newsletter
› What is an organic fish ?
› CO2, how to efficiently degas ?
Organic trout farm in open sea water – Ireland
This new INF’EAU Issue is willing to
evaluate the situation on two quite
different subjects. Organic aquaculture is expending rapidly in
Europe. This article lows down on the differences between the
previous French standard and this new European regulation in force
since the 1st of July, 2010.
The CO2 subject in aquaculture is sometimes a neglected constraint by
fish farmers. Consequences, in particular in hatcheries, yet can be tragic.
Removing CO2 with simple techniques is possible, with the exception
Defined since the 1920’s, organic farming is on a world
scale set for almost 40 years now (International Federation
of Organic Agriculture Movements - IFOAM)(1). The French
organic agency (Agence Bio), in charge of the development
and the promotion of organic farming in France, defines it
as follows “organic farming is a specific way of agricultural
production, that is to say a set of farming practices being
respectful towards ecological balance and the autonomy of
farmers. Aiming at soil and natural resources conservation,
environment protection and the maintaining of farmers,
organic farming is often considered as a the spark of sustainable
agriculture”. Organic farming involves applying to a standard.
On a general point of view, France lags behind its European
neighbours with an utilized agricultural area devoted
(1)
that the water and fish farm parameters are well set at the beginning.
2010 will have been a year of transition in an difficult economical context :
confirmation on structural tensions on raw material prices, leading to
a price explosion. We have now to learn to live with this situation and
keep on developing new and innovative feeds on both economical and
performance aspects. Products will evolve as well to face another major
issue : the hardening of the environmental regulation. That will be one of
our goals for 2011. Happy new year !
Dominique CORLAY, Aquaculture Manager
to organic farming of around 2 %, versus about 6 % for
Germany and Spain, 9 % in Czech Republic and Italy and more
than 13 % in Austria (2007 figures – source : Agence Bio).
As a reminder, the Grenelle Environment Round Table in 2007 set
the objective to reach in France 6 % in 2012 and 20 % in 2020.
Finally, the global value for organic food products sales
has doubled in France between 2005 and 2009 from 1,5
billion to 3 billions Euros, while the demand for conventional
food was only growing by 3,6 % according to Agence Bio.
Hence comes out a very favourable tendency to organic farming
development in Europe. Aquaculture can as well follow that path. In
order to get a clearer view, thanks to the help of CIPA (French InterProfessional Committee for Aquaculture Products), we have decided to
make a point on the latest changes of organic fish farming standards.
summary
what is an organic fish ?
Development ot the organic fish-farming
requirements
The requirements of the new european standard
Labelling of the products
Practical details for an organic conversion
Conclusion
Key figures
p.1
p.2
p.2
p.3
p.3
p.3
p.3
Degassing columns :
stripping CO2 efficiently
Basic principles of a C02 degassing column
Natural vs Artifial aeration
Additional remarks
p.4
p.5
p.6
p.7
http://fr.wikipedia.org/wiki/Agriculture_biologique#Dans_l.27Union_europ.C3.A9enne
What is an organic fish ?
Dominique Corlay, Le Gouessant Aquaculture manager | Marine Levadoux, CIPA | Sylvain Delord, Le Gouessant Aquaculture
о
Organic fish farming was, until the 5th
of august 2009, governed in France by CC
REPAB F, standard of compliance set in 2000
by the French Agriculture Depar tment,
fish -f armers, cer tif ying agencies and
professionals of the organic farming sector.
At that time, no European standard was set
and were coexisting several private, regional
or national standards in various countries of
the European Union.
2
LE GOUESSANT, commitment for a sustainable fish farming
Development ot the organic fishfarming requirements
› Articificial polyploïd animals ;
› Hormones or hormones derivatives.
The regulatory framework of the
entire organic agriculture has recently
changed with the release of several
regulations aiming at homogenizing
the requirements of organic agriculture
within the EU and in the third countries
exporting organic products in the EU
(in force since the 1st of july, 2010) :
The following requirements apply :
The maximum percentage of nonorganic aquaculture juveniles
introduced to the farm shall be 80 % by
31 December 2011, 50 % by 31 December
2013 and 0 % by 31 December 2015,
For on-growing purposes and when
organic aquaculture juvenile animals are
not available non-organic aquaculture
juveniles may be brought into a holding.
At least the latter 2/3 of the duration of
the production cycle shall be managed
under organic management.
Regulation (EC) n°834/2007 : It contains the the general
Framework regulation for principles enforceable to
organic agriculture organic agriculture, and then
to aquaculture.
Regulation (EC) n°889/2008 :
Implementing regulation
(production, processing,
labelling, control) completed by
REC n°710/2009 for fish-farming, shellfish and seaweed
(excluding spirulina) and REU
n°271/2010 on labelling
It contains the requirements
addressing all productions
covered by the previous
regulation, particularly
aquaculture.
CCF BIO
French Organic Standard (decree of the 5/01/2010) replacing
the CCREPAB-F for animal
production not covered by the
REC n°889/2008 (rabbit, snail,
ostrich, aquaculture during the
derogation period) and It is left
to member states to decide how
to apply the provisions.
Organic producers under the
french standard to the date
of publication of the european
concerning organic aquaculture (5th of august 2009) have
the choice between :
> applying the new regulation
now,
> or keeping on applying the
French standard (CC REPAB F
being now CCF BIO) until the
30th of June 2013.
Furthermore, it is left to
member states to decide
how to apply the provisions.
They have been defined within
the INAO and inserted in the
CCF BIO. Some of them concern
aquaculture.
Those texts are available on INAO’s
website : www.inao.gouv.fr.
The requirements of the new
european standard
о Simultaneous production
> Both organic and non-organic
production may be permitted on the
same holding during the conversion
period (knowing that it shall not exceed
the rotation of the batches already on
farm. In a raceway farm, organic batches
are kept up-stream non-organic ones.)
and in hatcheries and nurseries (with a
clear physical separation).
> Organic and non-organic facilities
land-based and/or in fresh water, have
to be separated by a minimal distance
of 3 km along the river, if the organic
farm is located down-stream, and of 1
km bird’s-eye. For sea water ongrowing,
a minimal distance of 5 km (or less on
the basis of a study) has to be respected
between organic and non-organic farms
in order to guaranty the absence of
water exchanges.
о Conversion of a farm
о Environmental practises
The requirement to follow the production
authorization’s order is completed by the
obligation to treat the water discharge
for inland facilities.
> Farm i n g co n d i t i o ns
о Caracteristics of the
farming facilities
Closed recirculation aquaculture animal
production facilities are prohibited, with
the exception of hatcheries and nurseries.
Artificial heating or cooling of water
shall only be permitted in hatcheries
and nurseries. Natural borehole water
may be used to heat or cool water at all
stages of production.
Aeration is permitted to ensure
animal welfare and health, under the
condition that mechanical aerators
are preferably powered by renewable
energy sources.
The use of oxygen is only permitted for
uses linked to animal health requirements
and critical periods of production and
transport, in the following cases :
› an exceptional case of temperature
rise or drop in atmospheric pressure or
accidental pollution,
› occasional stock management
procedures such as sampling and sorting,
› in order to assure the survival of the
farm stock.
о Stocking density
The stocking density is calculated on the
biological production unit of the entire
tanks or cages used.
Type of holding Conversion period
This part is a synthesis of the above
texts but cannot be considered as
exhaustive. For further details, it is
advised to have a look to those texts.
> Production framework
о Origin of the animals
The main principles of organic agriculture
prohibit the use of :
› Genetically Modified Organisms (GMO) ;
For facilities that cannot be drai- 24 months
ned, cleaned and disinfected (lake,
permanent pond…)
For facilities that have been drai- 12 months after the last
ned, or fallowed (earthen ponds, drainage or fallowing
drainable plonds…)
For facilities that have been 6 months after the last
drained, cleaned and disinfected drainage, cleaning and
(concrete tanks, resin tanks…) disinfection.
For open water facilities including 3 months
those farming bivalve molluscs
(cage farms in open water or
shellfish farming)
Species or type of species Maximum stocking density
Freshwater salmonids Salmon :20 kg/m3
Brown trout and rainbow
trout : 25 kg/m3
Arctic charr : 20 kg/m3
Other salmonids : 15 kg/m3
Sea water salmonids
10 kg/m3 in cages
Cod and other Gadidae, sea 15 kg/m3
bass, sea bream, meagre, red
porgy, red drum, spinefeet
Turbot 25 kg/m2
Freshwater sturgeons 30 kg/m3
3
Inf’eau 18 - january 2011
> Feeds
Feeds for carnivorous aquaculture
animals shall be sourced with the
following priorities :
› organic feed products of aquaculture
origin ;
› fish meal and fish oil from organic
aquaculture trimmings ;
› fish meal and fish oil and ingredients of
fish origin derived from trimmings of fish
already caught for human consumption in
sustainable fisheries ;
› organic feed materials of plant origin
- 60 % max of the ration - and of animal
origin.
If feed mentioned above is not available,
fish meal and fish oil from non-organic
aquaculture trimmings, or trimmings of
fish caught for human consumption may
be used for a transitional period until the
31 December 2014. Such feed material
shall not exceed 30 % of the daily ration.
о Disease prevention and
veterinary treatment
The use of allopathic treatments, with
the exception of antiparasitic products, is
limited to :
two courses of treatment per year,
with the exception of vaccinations and
compulsory eradication scheme, for
animal living more than a year,
one course of treatment per year, for
animals living less than a year.
The use of parasite treatments, not including
compulsory control schemes operated by
Member States, shall be limited to :
two courses of treatment per year for
animals living more than 18 months,
only one course of treatment per year
for fish living less than 18 months.
If the mentioned limits for allopathic
treatments are exceeded the concerned
aquaculture animals can not be sold as
organic products.
The withdrawal period for allopathic
veterinary treatments and parasite
treatments, including treatments under
compulsory control and eradication schemes
shall be twice the legal withdrawal period
compared to the law in force or in a case in
which this period is not specified, 48 hours.
Vaccination is authorized.
The list of substances for use in the
presence of aquaculture animal is
limited to limestone for pH control.
> Majors changes
compared to CC REPAB F
The European standard has significant
differences compared to CC REPAB F.
Here below are listed of a few them that
have to be highlighted :
› While CC REPAB F defined some water
quality specifications for the water inlet
of organic farms, the European standard
does not impose such constraints.
› The European regulation does not
impose any production tonnage limit
per year.
› The use of triploïde fish is prohibited
while it was allowed in the CC REPAB F
(on condition that no use mono-sex
females shall be done).
› Almost all external treatment
substances are now prohibited.
Labelling of the products
A few cases have to be distinguished :
Practical details for an
organic conversion
It is necessary to closely read through
the different texts concerning organic
production in order to see if the
requirements needed can fit with the
facility.
The organic certification imposes the
commitment to respecting the organic
standard but as well to respect a control
plan carried out by a certifying agency
that delivers the certificate.
Conclusion
Having done this run down through
the new EU organic standard, it appears
that some of the restraints to the
development of organic aquaculture
have been removed (water quality and
tonnage limit as an example) – yet, the
part on external treatments remains
quite problematic.
This new standard combined to the fact
that the organic sector has the wind
in its sails, organic aquaculture has to
spark interest. The conversion of some
facilities to organic production would
probably revitalize the aquaculture
sector in some countries.
Regulation or standard applied between the 8
August 2009 and the 30 June 2010
Producer under CCF BIO CCF BIO
bio before the 8 August
2009
Regulation or standard applied from the 1 July 2010
CCF BIO
(with the information of
the Auditing Body)
RCE 710/2009
RCE 710/2009
Producer converting to RCE 710/2009
organic farmin after the
8 August 2009
RCE 710/2009
Key figures (Source : AgenceBio) :
› 126 organic aquaculture facilities within Europe (225 in the world) in 2008.
› Around 50 000 tonnes of organic products in Europe in 2008
› Ireland is the world leader for organic salmon production – 8000 tonnes in 2008
› France has 29 organic fish-farms (2009).
Le Gouessant Aquaculture’s organic feeds : sea bass, sea bream,
trout, salmon, sturgeon and shrimp. See page 8
!
4
LE GOUESSANT, commitment for a sustainable fish farming
Degassing columns :
stripping CO2 efficiently
In a fish farm, the CO2 concentration in
the water can vary according to the water
source. Ground water may have CO2 in
excess resulting from a stay at a higher
temperature/pressure in a particular rock
bed (like chalk for instance) or from a
particularly high biological activity while
filtered through a rock bed.
Surface waters generally have a more
equilibrated carbonic gas content even
though rivers or channels having seasonal
vegetation developments may have a
considerable fluctuation in their carbonic
gas content. In open sea water, it is unlikely
to find high carbonic gas content except at
night when heavy algal blooms occur.
In fish holding facilities, the CO2 content
is also related to the fish stock and all
organisms present in the tank (aquatic
plants, algae, bacteria…) as respiration
produces CO2 and consumes O2.
Here below are the rough concentrations
in fresh water of the main air gases in
equilibrium with air (Patm = 760 mm Hg,
T=14°C) :
Nitrogen = 17 mg/l
Oxygen = 10 mg/l
CO2 = 0,70 mg/l
For precise values according to salinity and temperature see tables here below
Table 1 : Solubility of Nitrogen (mg/l) in water at different temperatures and salinities
from moist air with pressure of 760 mmHg (Colt, 1984).
T (°C) 1
Salinity (‰)
0
5
10
15
20
25
30
35
40
0
23.04
22.19
21.38
20.60
19.85
19.12
18.42
17.75
17
5
20.33
19.61
18.92
18.26
17.61
16.99
16.40
15.82
15.26
10
18.14
17.53
16.93
16.36
15.81
15.27
14.75
14.25
13.77
15
16.36
15.82
15.31
14.81
14.32
13.86
13.40
12.97
12.54
20
14.88
14.41
13.96
13.52
13.09
12.68
12.28
11.89
11.52
25
13.64
13.22
12.82
12.43
12.05
11.69
11.33
10.99
10.65
30
12.58
12.21
11.85
11.50
11.17
10.84
10.52
10.21
9.91
Table 2 : Solubility of Carbon dioxide (mg/l) in water at different temperatures and
salinities from moist air with pressure of 760 mmHg (Colt, 1984).
T (°C)
Salinity (‰)
0
5
10
15
20
25
30
35
40
0
1.09
1.06
1.03
1
0.98
0.95
0.93
0.90
0.88
5
0.89
0.87
0.85
0.83
0.81
0.79
0.77
0.75
0.73
10
0.75
0.73
0.71
0.69
0.68
0.66
0.64
0.63
0.61
15
0.63
0.62
0.60
0.59
0.57
0.56
0.54
0.53
0.52
20
0.54
0.53
0.51
0.50
0.49
0.48
0.47
0.46
0.45
25
0.46
0.45
0.44
0.43
0.42
0.41
0.41
0.40
0.39
30
0.40
0.39
0.39
0.38
0.37
0.36
0.35
0.35
0.34
Source : C.E. Boyd, Water Quality in Ponds for Aquaculture, 1990.
These concentrations reflect a situation where the gases are
in “normal proportion” in the surrounding atmosphere, i.e. the
following rounded up figures Nitrogen: 79 %; Oxygen 21 %.
Carbonic gas 0,3 %.
If these usual proportions in the surrounding atmosphere
change, then the solubility of the different gases in water will
change accordingly. Each gas exerts a partial pressure in function
of its concentration in the atmosphere; the total sum makes the
atmospheric pressure or the total gas pressure as being measured
with so called “saturometer” or “total gas pressure meter”(1).
(1)
Biological and/or physical changes in/around the water body
may drastically change the water content of the different gases.
One gas can then be temporarily in “supersaturation”, meaning
the quantity of gas dissolved in the water exceeds the normal
quantity that should be dissolved under the exact circumstances.
It can also be “undersaturated” or “desaturated” according to
specific situations.
It can be roughly estimated that each mole of oxygen consumed
by the respiratory activity will generate a mole of carbonic gas.
This means in a rough approach that every gram of oxygen
La sursaturation des gaz dissous, un phénomène souvent mal connu en aquaculture, Hussenot, J. ; Leclercq, D. Aquarevue N°11 Février-Mars 1987, pp27-30.
Inf’eau 18 - january 2011
consumed will generate around 1,375
gram of CO2.
CO2 elimination off the fish body is
a passive process depending on the
concentration gradient between inside
and outside the barrier formed by the
fish’s gills. It implies that when the
CO2 concentration increases in the
water, its concentration increases as
well it the fish’s blood because being
less eliminated by the gills : it is called
hypercapnia.
This results in the diminution of the
blood pH (acidosis), leading to a negative
effect on the affinity of the haemoglobin
with oxygen and thus on its transport in
the fish’s tissues.
Moreover, during the filtration of the
blood in the kidney, this blood acidosis
leads as well to a compensatory reaction
in the renal tubules where some
mineral deposits of calcium phosphate
are formed causing what is called a
nephrocalcinosis. The consecutive
inflammation of the kidney, of a variable
importance, progressively interferes with
the renal function and the metabolism
of the fish. The lesions weakens it
(especially towards diseases) and impairs
its growth performances.
it causes a drop of the respiratory frequency
of the fish (led by the oxygen rate) and
therefore diminishes the removing of CO2
from the blood by the gills.
So, oxygen is needed but first CO2 has
to be degassed with a sufficient aeration
in order to avoid this infernal spiral.
It is generally accepted that CO2 levels
lower than 10 mg/l are well tolerated
by fish ; yet, the sensitivity to dissolved
gasses varies according to species(2).
A concentration of 20 mg/l lowers by
10 % the specific growth rate (SGR) of
bass(3) and average to high rates impairs
significantly the growth of trout(4).
Basic principles of a C02
degassing column
The aim of a degassing column is to
bring the gas content of water closer
to their normal equilibrium at the
prevailing physical situation. It will thus
strip the gases in excess (nitrogen if any,
and carbon dioxide most of the time
in aquaculture) and allow for oxygen
dissolution up to saturation (or close by).
To reach this result, the water flow has to
be closely in contact with the ambient
air. A maximized contact between air
and water is usually obtained by the
formation of a thin water film on a
plastic media developing an important
specific area (m2/m3).
A packed column consists of a vertical
vessel filled with packing medium or a
proper height of self-sustaining plastic
media.
1 – The pipe and/or the bulk of structured
media has to stand perfectly vertical in
order to avoid any flow along the pipe
skin itself.
Diagram of a basic degassing tower
Calcium phosphate mineral deposits
A typical case of a nephrocalcinosis on a trout
The lower the oxygen concentration, the
higher the CO2 toxicity. So the oxygen
level in the water has to be monitored.
But, conversely, the use in excess of
liquid oxygen can make things worse at
two levels :
it favours high stocking densities, increasing
the CO2 level excreted in the water
The importance of measuring carbon dioxyde in aquaculture, Pete Southgate, Fish Vet Group, july 2005
Gas control in land based aquaculture, physiological and technical aspects, Blancheton & Al, WAS-2006
(4)
Effects of Carbon Dioxide Exposure on Intensively Cultured Rainbow Trout Oncorhynchus mykiss : Physiological Responses and Fillet Attributes, Melody L. Danley & al, Journal of the World Aquaculture Society, Vol. 36 Issue 3 – april 2007.
(2)
(3)
5
6
LE GOUESSANT, commitment for a sustainable fish farming
2 – The water has to be spread over
the media at best to trickle over most
of the media.
3 – The column diameter is adapted
according to the water flow knowing
that the apparent trickling water speed
should be within 100-600m/h. In the
lower range, there is a risk that the
water doesn’t trickle over 100 % of the
media.
In the upper range, there is a risk
of hydraulic clogging of the pipe,
stopping any air to flow through with
the water. It is therefore recommended
to dimension the columns closer to
200-300m/h.
PP type Pall-rings Physical
properties :
> Diameter : 50 mm.
> Spécific area : 110 m2/m3.
> Apparent density : 65 kg/m3.
> Void factor : 93 %.
Available from Acui-T.
yield is obtained. A number of trials have
shown that the higher the column, the
better is the result.
!
Alternately, structured packing material
can be used. They come shaped into
cubes or box-like and can be piled
above each other. They work better if
cross-piled (change the direction at
every new level). They are sold under
various commercial names.
Diameter =2x√[Q/(πxv)]
Q = water flow in m3/h
V = apparent trickling water speed in m/h
Diameter in m
4 – If a “random” type packing is used,
the medium size should be 1/8 to 1/10
to the column diameter and should
have a large void characteristic (about
85-90 percent). It should be packed in a
way that allows the water flow to break
up randomly into a thin film that trickles
down through the column avoiding
short-cuts.
Various packing media are sold under
the names of rings, barrels, pall rings,
spheres and other commercial names
(see picture below).
Blocks - Each block is 0,9x0,6x0,45m
5 – A dispersion plate should be used
on top of the column to optimize the
repartition of the water flow. Mostly, a
plate with a number of holes (diameter
according to the size of the column).
Alternately, other options can be taken
to break the kinetic energy of the water
arriving at the top of the column and
disperse it at best over the media
upper area.
(5)
Oxygen and Nitrogen move also faster
in/out the water than CO2. Therefore a
given column height will not perform
the same yield on oxygen and CO2.
Regarding CO2 degassing, the column
effect might also be impaired by
the chemical profile of the water. In
a surface sea water loaded with a
CO2 excess originating from the fish
biomass itself there will be no or little
interferences and a good degassing
could be obtained with around 0,6 to
1,5 m of head.
For the treatment of ground waters,
a specific study has to be made as a
function of the content of CO2 in excess
of an acceptable level. Up to 3 m of
head might be required.
For columns up to 315 mm water can be
delivered on top of the media without
a diverting plate, but above this size it
is highly recommended to add one.
Pall type rings
However, there is always an economic
optimum according to species and
stages being considered.
6 – The height of the columns is the main
parameter from which the degassing
Note d’Alexander Rose, Fischtechnik International Engineering, GmbH
The yield (Y) of a column is expressed
as a percentage by the following
equation :
Y = [1-(FC-CS)/(IC-SC)]x100
Concentrations are expressed in ppm or saturation %
FC : final concentration
SC: saturation concentration
IC : initial concentration
For example, if the CO2 content is
initially 80 ppm and should be 4 ppm at
equilibrium (fresh water from a specific
spring) and after passing it through the
column, it came down to 20ppm, the
yield is :
Y = [1-(20-4)/(80-4)]x100 = 79 %
Which means that “79 % of the excess of
CO2 has been eliminated to atmosphere”.
Inf’eau 18 - january 2011
On a pure scientific point of view, the
height of a column is determined by
the Height of Transfer Unit (HTU) that
varies with the medium and the gas
according to the following equation(5) :
H=HTUxln[(Cl-Ce)/(Cl-Ca)]
Height (H) & HTU in m
Cl = concentration at saturation of the gas, Ce = concentration of the
gas in incoming water, Ca = desired gas concentration
For example, at 20°C HTU (CO2) =
0,88 m for a trickling body with the
following dimensions : 80x80x2 mm, 75
m2 /m3 and open gap of 94 %.
Natural vs Artifial aeration
The height of the column creates a
chimney effect that strips more efficiently
CO2. Without air extractor or ventilator, the
chimney effect works due to the height of
the column but as well the temperature
difference between the air and the water.
Most of the time, the degassing columns
aiming at stripping CO2 have air blowers (at
the bottom of the column) or air extractors
(at the top of the column) to set up a
constant air counter-flow. To improve the
efficiency of a packed column, the air flow
has to be above 10 fold the water flow(6).
The air-flow can also be used as a lateral
cross-flow, which is easier and requires
cheaper instrument. An example of
lateral air flow obtained with a chicken
house ventilator is illustrated on the
photo below.
it has to be excluded as salt will also add
difficulties for the vacuum equipment.
To implement the air cross flow from
the bottom of the column, a turbine
will be installed at a distance, with
a protected air intake, and will blow
through a properly dimensioned pipe.
A water tight join will be established to
force air to rise up into the column and
escape from the top exit.
additional Remarks
When CO2 is stripped off fresh water,
hard and alkaline waters have a high
tendency to deposit lime.
Thus it is necessary to clean on a regular
basis the degassing tower in order to
prevent clogging. To do so, the media
can be put in a cylinder made of a
chicken wire that can be easily taken
down and cleaned in an acid solution.
With any sea water, algae might
establish on the top of the column if
light is available.
A well sized and efficient column
Ventilated column
The ventilator will push air through from
a small distance.
A bad example
To implement an extraction from
above, the top of the column has to be
tightly closed. The air extraction being
made by an horizontal pipe sucking air
from the chamber.
This method is efficient but the vacuum
equipment usually doesn’t last as it sucks
very humid air permanently. In sea water,
Evaluation of full-scale carbon dioxide stripping columns in a cold water recirculating system, Summerfelt & al,
Aquacultural engineering 28, March 2003
(6)
Another process often seen is the
development of bacterial slime as the
media also allows for a biofilm to develop.
The shear force expressed by the trickling
water is never sufficient to avoid this
and slime may build up to clogging the
column, breaking its degassing effect.
Columns should always be made easily
“washable”.
Developing an adapted pack column
for CO2 degassing is a multi-parameter
task and is more difficult than a simple
degassing for oxygen recovery. The help
of a specialist for the diagnosis and the
design should be asked for.
Didier Leclercq, Aquaculture engineering | Acui-T
contact : acui.t@free.fr | +33 (0)6 09 028 724
Antoine Barnaud, Veterinarian doctor | Le Gouessant Aquaculture
Sylvain Delord, Agricultural engineer | Le Gouessant Aquaculture
7
january 2011
#18
Le Gouessant aquaculture’s
organic feeds
› www.agencebio.org
› http://agriculture.gouv.fr/l-agriculture-biologique
› http://ec.europa.eu/agriculture/organic/home_fr
› www.qualite-france.com/page.php?p=4
› www.ecocert.fr/-Tout-sur-la-Bio-et-le-.html
› www.fnab.org/
› www.inao.gouv.fr
le gouessant aquaculture
Société Coopérative d’Intérêt Collectif Agricole à forme civile et capital variable - SIREN 306 957 168
sica du gouessant - z.i. - b.p. 40228 - f-22402 lamballe cedex
Tél. +33(0)2 96 30 74 74 - Fax +33(0)2 96 30 74 32 - contact.aqua@legouessant.fr
www.aqua.legouessant.fr
willy.b7@gmail.com © décember 2010
Places to surf on the web…