2.1. Aquaponic system
Aquaponic is a special form of recirculating
aquaculture systems (RAS), namely a polyculture
consisting of fish tanks (aquaculture) and plants
148 A. Graber and R. Junge / Desalination 246 (2009) 147–156that are cultivated in the same water circle (hydroponic) [3–5]. The primary goal of aquaponic is to
reuse the nutrients released by fishes to grow crop
plants. Most systems separate fish faeces as
quickly as possible to reduce the BOD load in
the RAS, to enhance nitrification performance
and to reduce clogging of plant roots, which
could lead to loss of crop productivity.
Our aquaponic system established in Waedenswil, Zurich, was a new concept using lighlightexpanded clay aggregate (LECATM) [13] as filter
medium for the trickling filter. LECA is a type
of clay, which is super-fired to create a porous
medium. It is heavy enough to provide secure support for the plants’ root systems and was used in
indoor and outdoor hydroponic systems [13–17].
LECA was filled in standard boxes (0.4 0.6
0.4 m, green PVC), aligned in three rows in an
adjoining greenhouse (Fig. 1). In total, 74 boxes
were used, holding 3.0 m3
of LECA.
A primary goal of the system was to test a
completely closed RAS, making use of fish faeces, too. The raw effluent from the 2.5 m3
fish
tank (2 2 m square, water depth 0.65 m,
green fibre glass with central outlet at the bottom) was pumped and distributed in the LECA
filter at a rate of 10–15 m3
h
1
with a specially
developed irrigation system. To achieve a homogenous load of Total Suspended Solids (TSS)
distribution to the plant boxes, standard sewage
piping (d = 0.11 m, orange PVC) was levelled
horizontally over the LECA rows and each box
irrigated through a drilling hole of 6 cm diameter. The water exchange rate was set to zero,
and the system was operated as a closed looped
system. Only evaporation water was replaced
with tap water. Technical details were described
only in an unpublished report so far [18].
Fish species cultivated were tilapia (Oreochromis niloticus) during aubergine production
in 2004 and eurasian perch (Perca fluviatilis) in
the later experiments with tomato and cucumber.
Tilapia was a natural strain imported from Lake
Turkana, Kenya, perch was obtained from Percitech S.A., a Swiss company specialized in perch
breeding. The fish were fed ad libitum with a
swimming pelleted feed (Trouvit Tilapia Starter,
3.5 mm, 45% raw protein).
As a control, a row of 29 boxes in a hydroponic
system was installed, holding 1.2 m3
LECA
(Fig. 2). Tap water was pumped from a separate
0.3 m3
water reservoir at a rate of 5 m3
h
1