2.4. Analytical methods
Liquid and solid sampling from various zones was carried out
at least twice per week and the reported values are the average of
at least three measurements. Liquid samples were filtered through
0.45 m syringe filters and the required dilutions were made for
concentrated samples. The COD concentration was measured using
closed reflux colorimetric method (EPA standard method 410.4).
Total nitrogen (TN) and total phosphorus (TP) in the liquid samples
were determined using colorimetric methods after digestion
of the samples at 100 ◦C for 1 h. Total nitrogen (TN) concentration
was determined according to the persulfate digestion method
(HACH method 10071). Total phosphorus (TP) concentration was
determined by the ascorbic acid method (EPA method 365.2). The
concentration of NH3-N was determined according to the Salicylate
Method (EPA method 350.1). NO2-N was measured by the diazotization
method (EPA method 354.1), while NO3-N was determined
according to the reaction of nitrate ions with 2,6-dimethylphenol
(EPA methods 353.2). Total Kjeldahl nitrogen (TKN) was calculated
from the difference of TN and the sum of nitrate and nitrite.
The phosphorus content of sludge was measured spectrophotometrically
using the vanadomolybdophosphate method [21]. The
VFA concentration was determined using esterification method
(HACH Method 10240), while the concentration of solids in the
sludge was determined using gravimetric methods (Standard
Methods 2540 B and D). The samples were oven-dried at