Environmental Engineering Reference
In-Depth Information
2.2 Water quality assays
Water samples collected for this study were passed through a 0.45
m filter and tested for
total ammonia nitrogen (TAN), nitrate-nitrogen (NO
3
-
-N) and nitrite-nitrogen (NO
2
-
-N)
content using a spectrophotometer (Hach DR 2400, Loveland, CO). Temperature and pH
were determined by using a pH/mV/
μ
C meter (Oakton
Acorn Meter Kit model pH 6,
Vernon Hills, Illinois). Alkalinity and hardness were measured using Hach Permachem
Reagent methods. Total Kjeldall nitrogen (TKN) was determined by using macro-Kjeldall
Standard Method 4500-N
org
B, (American Public Health Association [APHA] et al., 1998).
°
For statistical analyses, 95% simultaneous confidence intervals were determined to compare
means of water quality parameters after passage through each of the five main units of the
treatment train. We used a one-way ANOVA with the four treatments as the factor in the
model; the values of the parameters in the influent water were added as covariates for
ANOVAs performed for the sedimentation basin and the denitrification reactor. For the
units following the denitrification reactor, covariates were not used because they did not
improve the model.
2.3 Biological yields determination
The biological (anoxic) yield,
Y
b
(i.e., the amount of microbial biomass formed per unit of
substrate used), was determined using a bench-scale batch reactor for both methanol (as
COD) and NO
3
-
-N substrates. The biomass produced was quantified as volatile suspended
solids (VSS) and COD. A hermetically closed 5-L vessel was initially filled with water
seeded with biofilm sheared from a sample of coated sand from the denitrification reactor.
Potassium nitrate and methanol were added in amounts accounting for initial
concentrations of NO
3
-
-N and methanol (as dissolved COD) of 207 and 1666 mg/l,
respectively. Methanol was well in excess of stoichiometric requirements so that it would
not be a limiting factor. Continuous stirring and a constant temperature of 28±1ºC were
maintained. Pure nitrogen was injected for about 5 minutes to strip dissolved oxygen and to
replace the air from the space above the fluid. Gas exiting at the top was collected and
directed by a hose to a water bath, sealing the space. Any additional nitrogen gas produced
by denitrification followed the same path before entering the atmosphere. The operation of
purging nitrogen was repeated after any sample collection (i.e., at the beginning and at 12-
hour intervals through 48 hours). Total suspended solids (TSS), volatile suspended solids
(VSS), dissolved and total chemical oxygen demand (COD) were measured according to
Standard Methods 2540D, 2540E, and 5220C, respectively (APHA et al., 1998). NO
3
-
-N was
determined spectrophotometrically (Hach DR 2400, Loveland, CO). Filters of 1.5-μm pore
diameter were used for collecting TSS, and for obtaining samples for dissolved COD
determinations. The equations used to determine
Y
b
values (Grady et al., 1999) were:
Δ
VSS
g
Y
=
(1)
VSS
Δ
dissolvedCOD
g
and:
Δ
VSS
g
−
Y
=
(2)
NO
−
N
3
Δ
NO
−
−
N
g
3
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