Efficacy of Pilot-Scale Wastewater Treatment upon a Commercial Recirculating Aquaculture Facility Effluent - Aquaculture and the Environment: A Shared Destiny - page 153

Y (Biomass COD/
Dissolved COD)
This study 0.69 0.29 0.41
Semon et al. (1997) 0.62 0.17 - 0.18 0.24 - 0.26
Jeris et al. (1977) 0.57 0.17 0.24
Moore & Schroeder (1971) 0.53 - 1.4 0.14 - 0.29 0.17 - 0.35
Coelhoso et al. (1992) 0.5 - 1.3 - -
Stephenson & Murphy (1980) 1.0 - -
Grady et al. (1999) - 0.27 0.39
Table 11. Comparison of biological yield ( Y b ) estimates from this study (batch reactor tests)
and from the literature under NO 3 - -N saturation conditions.

Y (Biomass VSS/
NO 3 - -N)

Y (Biomass VSS/
Dissolved COD)

Source

Y VSS and Y COD were determined to have values of 0.29 and 0.41 g/g, respectively. These
values agree only with those reported by Grady et al. (1999), and are larger than values
reported by other authors (Table 11). For example, Jeris & Owens (1975) suggested that
between 15 and 20% of the methanol consumed is expected to be converted into cell mass,
while Karnchanawong & Polprasert (1990) found this conversion to be between 20 and 28%.
The difference could be explained by noting that Grady et al.'s (1999) values were obtained
under conditions similar to those in this study, such as excess NO 3 - -N, and continuously-
stirred, batch tank reactors. Such conditions exploited the maximum potential for ATP
formation under anoxic conditions, resulting in a higher yield for anoxic growth. In contrast,
other authors (Table 10) derived their results from steady-state operating conditions in
fluidized bed biological reactors, which have much higher denitrification rates than
continuously-stirred tank reactors. Lower denitrification rates coincide with high solids
production rates (Stephenson & Murphy, 1980), helping to explain the larger Y VSS and Y COD
values observed in continuously-stirred tank reactor tests.

We also determined Y NO3-N using denitrification reactor data in order to confirm the results
and interpretations above, and also to characterize the behavior of the denitrification reactor
under conditions of diurnal NO 3 - -N variations. Our findings (Table 12) confirmed that the
denitrification reactor worked at an NO 3 - -N dose lower than saturation and resulted in a
larger Y NO3 -N. Additionally, the largest yields were obtained for the afternoon
measurements, i.e., the lowest NO 3 - -N influent, regardless of experimental treatment or
working stream flow.

The weighted average biomass production for the denitrification reactor (as VSS) was
estimated at 20.2 kg VSS m 3 /day for the 6 Lpm working flow rate, and 15.8 kg VSS m 3 /day
for 4 Lpm. The difference was probably due to the different percent of recirculation, which
resulted in different working streams. As was suggested by the biofilter Y NO3 -N (i.e.,
approximately one), nitrogen removal values approximated those of VSS removal. Nitrogen
removal was between 23.4 kg NO 3 - -N m 3 /day for the 6 Lpm working flow, and 16.2 kg NO 3 -
-N m 3 /day for 4 Lpm. Our maximum nitrogen removal was higher than generally expected
from denitrification for domestic wastewater treatment. For example, Coelhoso et al. (1992)
obtained nitrogen removal of 5.4 to 10.4 kg NO 3 - -N m 3 /day. Semon et al. (1997) suggested a
maximum design loading of 6.4 kg NO 3 - -N m 3 /day. Jeris & Owens (1975) reported nitrogen
removal of 20.7 kg NO 3 - -N m 3 /day in fluidized sand biological reactors. The higher removal
rate in our study was probably because of the higher operating temperature, which drove