Environmental Engineering Reference
In-Depth Information
SB
DR
OR
OR %
TF
Total 3
(%)
removal
Treatment
mg/l
mg/l (%)
mg/l (%)
Increase 2
mg/l (%)
1
3.64 (+173.6) a
29.1
1.69 (-53.6) a
34.5 a
2.58
1.33 (-48.4) a
2
3.92 (+194.7) a
34.2
1.59 (-59.4) a
38.4 a
3
4.21 (+234.1) a
39.9
1.52 (-63.9) a
39.9 a
2.53
1.26 (-50.2) a
4
4.00 (+217.5) a
36.8
1.63 (-59.3) a
35.6 a
1 Abbreviations: SB = sedimentation basin, TF = trickling filter, OR = ozonation reactor, and DR =
denitrification reactor.
2 Percent increase of TAN concentration after ozonation from the initial TAN concentration in the
sedimentation basin.
3 Percent decrease of TAN concentration after ozonation from the initial TAN concentration in the
sedimentation basin.
Table 8. Total ammonia nitrogen (TAN) dynamics through the pilot plant 1 for all treatments
(unit outlet values). Means in a column with the same superscript are not significantly
different ( p >0.05).
In the trickling filter, partial nitrification occurred, removing 54-64% of TAN along with
organics. The organic loading of the trickling filter was estimated at 0.43 kg cBOD 5 /m 3 -d in
treatments 1 and 2, and 0.65 kg cBOD 5 /m 3 -day in Treatments 3 and 4. At these loadings,
conditions were not permissive for nitrifiers to grow and compete effectively with
heterotrophs, which made the nitrification performance of the trickling filter surprisingly
good. In comparison, Metcalf & Eddy (1979, as cited in Karnchanawong and Polprasert,
1990) obtained 75-85% TAN removal in a trickling filter at lower volumetric loadings of 0.10
to 0.16 kg BOD 5 /m 3 -day. Parker & Richards (1986) suggested a maximum threshold of 27
mg/l BOD 5 in order for any nitrification to occur in a trickling filter. Our results also
showed more efficient TAN removal when the stream had less organics, as in Treatment 3,
although we measured cBOD 5 instead of soluble BOD 5 .
The final effluent had TAN treatment averages between 1.52 and 1.69 mg/l, which is
generally undesirable in water used for exchange in aquaculture systems. However, were
this treated water used for exchange, only 0.84% of daily TAN production would be
reintroduced and the rotating biological contactors in the fish production systems would be
able to remove these amounts (Sandu et al. 2008).
3.7 NO 2 -N
Nitrite results from incomplete nitrification in the aquaculture systems' rotating biological
contactors. The average concentration was between 0.92 and 0.96 mg/l NO 2 - -N in BRA
effluent. NO 2 - -N concentration fluctuated through the treatment train (Table 9).
In the denitrification reactor, between 72-76% of influent NO 2 - -N was reduced to nitrogen.
This reduction suggests that the external carbon source was supplied in an amount
sufficient to support the completion of denitrification (van Rijn & Rivera 1990) and that
influent nitrite also was reduced in this process. Another mechanism for nitrite reduction
could be its utilization as a source of nitrogen by heterotrophic organisms in the upper
part of the biofilter due to the relatively low concentration of TAN in the stream. While
we cannot conclude which of these factors drove it, we regard NO 2 - -N reduction in the
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