costs for installation and operation of the denitrification reactor
are outweighed by the reduction in costs for discharge to the local
sewer, groundwater permits restricting groundwater extraction at
one production location and the increasing energy costs for heating
groundwater to 28
◦
C(Martins et al., 2009b).
Considering the nutrient balance before and after on-farm
implementation of denitrification on an hypothetical 100 MT/year
tilapia farm (Eding et al., 2009), performance of a 100 MT/year
tilapia RAS with and without denitrification was compared for
the sustainability parameters nutrient utilization efficiency (%),
resource use and waste discharge per kg fish produced (Table 4). It
can be seen that the RAS with denitrification has substantially lower
requirements for heat, water and bicarbonate. Although the RAS
with denitrification has somewhat higher requirements for electricity, oxygen and labour (and investments), the actual production
costs per kg harvested fish are approximately 10% lower than for
the conventional RAS. Waste discharge is reduced by integration