2.3. Assessment of water quality parameters
Water temperature, dissolved oxygen (portable DO meter WTW
Oxi 340i) and pH (portable HANNA pH/ORP/Temperature meter HI
991002) were determined twice weekly. Total alkalinity was measured
by acid titration on a weekly basis followingStirling (1985). Total
ammonia nitrogen (TAN), nitrite (NO2–N) and nitrate (NO3–N) were
analyzed spectrophotometrically with an autoanalyzer (BRAN LUBBE
AutoAnalyzer 3) according to standard methods (APHA, 1998). Water
samples (50 ml) were collected weekly at around 12:00 h from each
tank and filtered under vacuum pressure through pre-dried and preweighed
GF/C filter paper. The filtered water was used for nutrient
analysis and the filter paper for total suspended solid (TSS)
determination.
Total suspended solid (TSS) and biochemical oxygen demand
(BOD5) of water were measured on a weekly basis followingStirling
(1985). After filtering water for nutrient analysis, the pre-dried and
weighed filter paper containing suspended materials was dried in an
oven until constant weight. Dried samples were weighed to 0.01 mg
using a Mettler AC 100 balance. The TSS was calculated from the
weight differences. For BOD determination, water samples were
collected in plastic bottles from each tank. Two diluted samples in
each tank and two controls (with only distilled water) were used in
170 ml BOD bottles. Samples were diluted 10 times initially and 20
times at the end of the experiment with distilled water. The initial
oxygen concentrations in the samples were determined using a BOD
YSI probe and DO meter (YSI model 57). The necessary chemicals were
added to each bottle in case of diluted samples according toStirling
(1985). The samples were firmly closed with stopper and placed in an
incubator (Gallenkamp Cooled Incubator) in the dark at 22 °C for
5 days. At the end of this time, the dissolved oxygen level was
determined again and BOD5 was calculated in mg l−1 (Stirling, 1985).