2.3. Sampling and analysis
Water samples for chemical analyses were collected from the
influent tank and from the outlet of each system every 3 d, respectively.
All water samples were transferred immediately to the lab
and stored at 4 C before analysis. Water samples were analyzed
for nitrogen (NH4 + -N, NO3
-N, NO2
-N and TN) and organic matter
(COD). Water temperature and dissolved oxygen (DO) were measured
in situ by a DO meter (HQ 30d 53LEDTM HACH USA). All of
the analyses were performed according to standard methods