Biofilter
start-up and ammonia carrying capacity test
European Network for the Dissemination of Aquaculture
RTD Information (Q5CA-2000-30105) and previously FAIR-3837, Aquaflow ref. :
TL2003-179
In
closed recirculating systems, the water needs to be continuously treated in
order to avoid the accumulation of harmful substances. Recently, biological
filters are widely used in many types of aquaculture operations. Integrating
the nitrification unit into a fish rearing system is a matter of
calculations but the way the biofilter start up is being carried out can be
both beneficial and crucial for the subsequent production phases. The aim of
this project was to test and develop a rapid and safe method for biofilter
start-up on low costs, without using bacteria concentrates and to test the
ammonia carrying capacity.
The
experiment was carried out in a pilot scale recirculating system with a
total volume of 10m3 using a circular up-flow fix bed biofilter.
The total volume of the biofilter was 3m3 and round plastic
filter media was applied (Danpak, 300m2 /m3). The
water was pre-filtered through a 30µm drum filter and it was aerated from
the bottom of the biofilter. The temperature was 23±0,5ºC and the average
flow rate was 3,6m3.h-1. The salinity was kept at
1,6-1,7g.l-1.
In
order to facilitate bacterial growth, predetermined amounts of carbide and
pelletised food were administered frequently. Through microbial breakdown of
carbide, the ammonia was provided and by the slow dilution and degradation
of the feed the micro- and macronutrients were also supplied.
The
experiment consisted of two phases: (i) The startup of the biofilter; (ii)
Testing the ammonia carrying capacity.
In
the first phase of the experiment, ammonia concentration reached the peak
level by day 12, which was in compliance with the applied starter dose of
carbide. On days 13-15 the
ammonia was fully converted into nitrite and the further application of
carbide resulted in increasing nitrite, but steadily low ammonia levels. On
days 26-29, nitrate appeared in the system water; the nitrification process
was well established. Thereafter,
the applied carbide portions resulted in uniformly low levels of both
nitrite and ammonia. The pH decreased continuously during the experiment,
but this was controlled by dissolved sodium bicarbonate. The time required
for biofilter startup without bacteria concentrates is in compliance with
those found in the relevant references. However, the costs of the applied
method are six times lower that of using bacteria concentrates. Nevertheless
the bacteria populations established on the biofilter are better adapted to
the local conditions. Even if the period of the start-up could be shorter by
applying concentrates, the costs and reliability are of great concern.
In
the second phase of the experiment, which was started on day 40, the ammonia
carrying capacity was tested by administering increasing doses of ammonium
chloride daily. The doses were calculated from the maximum theoretical
carrying capacity for ammonia. The removal rate for ammonia was observed and
the results showed that the biofilter was able to remove about the half of
the calculated maximum theoretical ammonia load. However, the dynamics of
ammonia removal efficiency showed an increasing tendency in time. The
results suggest that if increasing doses are applied for a longer period,
the removal capacity can be enhanced; thus the carrying capacity of the
biofilter can be set close to the planned fish load.
For more information, contact:
Árpád Peley
Research Institute for Fisheries
Aquaculture and Irrigation (HAKI)
P.O.B. 47, H-5541 Szarvas - Hungary
Tel.: +36 66 515 334
Fax: +36 66 312 142
E-mail:
pelleya@haki.hu