Design of a Simple Trickling Biofilter for Recirculating Aquaculture System (RAS)

Abstract

Recirculating aquaculture system (RAS) is an environment
friendly way of farming fish at a high
density in a controlled environment. An efficient
biofiltration system is the key for the success of any
recirculating aquaculture system. Trickling filters
are one of the oldest and widely used biofilter types
in aquaculture. In the present study a simple
trickling biofilter was designed and was tested with
two types of filter media i.e., river sand and charcoal
for rearing Litopenaeus vannamei in a closed RAS. The
experiment was carried out for a period of 90 days.
Ammonia – nitrogen (NH3-N) was not detected
from any of the tanks during the study. The mean
pH and nitrite-nitrogen (NH3-N) of both the types’
of filter tanks were 7.8 and 0.13 ppm respectively.
There was no significant difference in pH and
nitrite-nitrogen (NH3-N) between the charcoal based
filter tanks (C1 and C2) and sand based filter tanks
(S1 and S2). The sand based filter tanks (S1 and S2)
showed significantly lower hardness than charcoal
based filter tanks (C1 and C2). The average total
hardness of sand based filter tanks and charcoal
based filter tanks (C1 and C2) were 446.11 ppm and
504.78 ppm respectively. The mean length of the
shrimp harvested at the end of 90 days from charcoal
based filter tanks (C1 and C2) and sand based filter
tanks (S1 and S2) were found to be 8.97 cm and 10.03
cm respectively. The average weight of the shrimp
was 5.70 g in charcoal based filter tanks (C1 and C2)
and 7.27 g in sand based filter tanks (S1 and S2).
Statistical analysis shows that shrimp in sand based
filter tanks (S1 and S2) shows higher growth rate
than shrimp in charcoal based filter tanks (C1 and
C2). The survival rate in sand based filter tanks (S1 and S2) was also higher i.e., 47.5% and charcoal based filter tank (C1 and C2) was 39%.