المقارنة بالتجارب المعملية والعملية بين الزيوليت والكربون النشط فى ازالة الامونيا من المزارع السمكية

Comparison of Zeolite (Clinoptilolite)
and Activated Carbon
as Ammonia Absorbants in Fish Culture

technolab el-bahaa group

general.dr

bahaa badr

chemical consultant

01229834104

Introduction

Ammonia at relatively low
concentration can have negative
effects on fish tissues and
physiological factors such as growth
rate, oxygen consumption and
disease resistance (Piper et al. 1984)

and can restrict yields in intensive
fish culture (Delistraty et al. 1977;
Colt and Armstrong 1981).

The two principal methods of
removing ammonia in water are:

(1)
nitrification,

and

(2)

ion exchange.

Nitrification is a two-step oxidation
of ammonia to nitrate by autotrophic
bacteria, and is an essential part of a
recirculating fish culture system
(Bower et al. 1981).

For nitrification,
materials such as oyster shell, rock,
sand, activated carbon, etc. are used
to prepare a substrate for bacteria.

Ion exchange is a process in
which ions of an exchanger (synthetic
or natural resin) are exchanged with
certain ions in wastewater.

Some
natural resins, such as zeolite, are
used in removing ammonia from
wastewater culture systems.

One of
the best zeolites in ammonia removal
is clinoptilolite.

Activated carbon
needs to be conditioned before use.
At 20-22 ºC, 60 days of conditioning
is needed; a longer time is needed at
lower temperatures (Bower et al.

1981). Clinoptilolite does not need
conditioning.

Bower and Turner (1982) showed
that the use of clinoptilolite in sealed
plastic bags for the transport of live
fish can be effective in reducing
ammonia.

Turner and Bower (1982)
examined the influence of bacterial
nitrification during the transport of
live fish and showed that addition of
a substrate containing nitrifying
bacteria to sealed plastic bags is a
practical way for reducing ammonia.

No study has yet been carried out
to compare carbon and zeolite
simultaneously.

This study was
therefore undertaken to compare the
response of activated carbon
containing nitrifying bacteria and
zeolite (clinoptilolite) under similar
conditions.

---------------------------------------------------------------------------

Materials
and Methods

To cultivate nitrifying bacteria,
four all-glass aquariums were
equipped with airstone and
immersion heater, each aquarium
was allocated a certain salinity, i.e.
0, 10, 20 and 30 ppt.

The aquaria
were filled with 0.5 l of water from
a trout farm.

Ammonium chloride
was added to the water as a source
of ammonia (Turner and Bower,
1982) until the bacteria was capable
of oxidizing at a rate of 5 ppm per
24 hrs.

Water temperature was
maintained at 22-24ºC.

As the pH
of water was maintained above 8.0
no buffer was added.

To accelerate
bacterial propagation, activated
carbon was placed in the underwater
aquarium pump (filter), through
which the water passes
(Landau,1992).

The carbon used was of
commercial grade and the utilized
zeolite was a product of Afrand
Tooska Co. Ltd., Iran. The average
diameter of the grains for both
materials was 1-2 mm.

In 24 three-liter plastic buckets,
solutions of different salinities, i.e. 0,
10, 20 and 30 ppt were prepared.

Total
ammonia nitrogen (TAN) was added
at 1, 3 and 5 ppm.

Ten ppt (30 g)
activated carbon was added to half the
number of buckets and 10 ppt zeolite
was added to the remainder.

Every 4 hrs, a 100 cc sample was
taken and replaced with the same
volume of water of same salinity.

Samples were preserved with
sulphuric acid and stored in a fridge
for later analysis (Clesceri et al. 1989).

TAN was determined spectro
photometrically by the method of
Indirect Nesslerisation (Clesceri et
al., 1989).

The statistical significance of the
differences between mean values for
various treatments was determined
with Duncan’s multiple range test
and student’s t-test.

-----------------------------------------------------------------------------
Results
and Disscussion

Over time, efficiencies of both
materials declined.

The highest
amount of TAN was removed in the
first 4-hour period(Fig.1).

After 4
hrs, TAN decline was not significant
(P>0.05); after 8 hrs, TAN decline
continued constantly and was not
significant (P>0.05).

There was no
change in TAN concentration after
8 hrs in the buckets containing
zeolite.

Zeolite is an ion exchanger
and in the presence of a large amount
of ammonia, ion exchange will take
place quickly, after which it loses its
ion exchange ability.

In the case of
activated carbon, nitrifying bacteria
need oxygen to oxidize ammonia;
therefore dissolved oxygen
decreases over time.

In other words,
oxygen depletion leads to a
reduction in nitrification rate
(Lawson, 1994).

Nitrification is a
process which produces acid and it
was noted that there was a definite
decrease in pH in the buckets
containing activated carbon,
sometimes falling below seven.

The effect of salinity on the two
materials studied was highly
significant (P<0.0001).

With
increasing salinity, the capability of
both materials was reduced.

This
could be due to the fact that other
cations in seawater may be
competing with ammonium (NH4+).

The decrease in activated carbon
efficiency due to salinity may be
related to two factors:

(1) biomass of
bacteria was low

or

(2) bacteria
species were not suitable for saline
water.

For conditioning of activated
carbon in freshwater, effluent of a
trout raceway was added to the
aquaria.

By increasing salinity from
0 to 30 ppt, the difference between
the two materials decreased and at 30
ppt, no significant difference was
observed (P>0.05).

It seems that at
salinities higher than 30 ppt, activated
carbon can be more promising than
zeolite

With regard to the
interaction of ambient ammonia and
salinity , at each concentration
of ammonia and at salinities more
than 10 ppt, it is recommended that
activated carbon be used.

With increasing initial ambient
ammonia, after a certain period,
residual ammonia was further
decreased.

After 24 hrs, TAN in
containers containing 1, 3 and 5 ppm
decreased by 80.8%,65.4% and
58.8%, respectively.

Although this study showed that
zeolite generally acts better than
activated carbon, it does not indicate
that it is incapable of nitrification.

Conditioning qualifications of
activated carbon have effects on the
results of this process; especially the
material used for seeding of bacteria
is very important.

Environmental
history of bacteria in seed media may
be the primary determinant of the
effectiveness of seeding (Bower and
Turner 1981).

As mentioned earlier,
lack of access to a material as a
suitable seed, especially for saline
waters may be the main reason for
the lack of effectiveness of activated
carbon observed in this study.

Zeolite
has great potential for removing
ammonia from water, especially at
salinities lower than 10 ppt but the
main obstacle in using zeolite is its
uselessness after a few hours.

This
does not mean that it should not be
used in fish culture as it is easy to
regenerate.

Zeolite is cheaper than activated
carbon and does not need conditioning
before use This makes use of zeolite
in fish culture facilities a better option
for reducing ammonia concentration.