Part B | 12.5
356 Part B Tools and Methods in Marine Biotechnology
observed. The PBBR system was energy optimized for
continuous operation by limiting energy input to a single stage pumping of water and aeration to the aeration
cells.
Both the PBBRs have the same configuration and
are identical to the PBBRs used in Kumar et al. [12.47],
as are the PS beads used for immobilization. The AOB
and NOB reactors were connected in series. Water
flowed from a large OHT into the AOB and therefrom
into the NOB by gravity. The outflow from the NOB
flows into a CT and from there into the larval rearing tank (LRT). From the LRT, water is pumped out
into the OHT. The major components of the nitrifying bacterial consortia (NBC) were the marine genus,
viz., Nitrosococcus and Nitrobacter. A noteworthy operational flexibility of the PBBRs was that they were
interchangeable between prawn (salinity 15 g L
1 ) and
shrimp (salinity 30 g L
1 ) larval rearing systems simply
by changing the NBC based on salinity.
Silapakul et al. [12.49] examined a novel packed
bed external loop airlift bioreactor (PBEL-ALBR) (volume 60 L) as an integrated system with simultaneous nitrification/denitrification for treatment of marine
aquaculture wastewater containing ammonia and nitrate
compounds. The PBEL-ALBR consisted of both aeration and nonaeration zones in the same unit, that served
as nitrification and denitrification compartments (where
ammonia and nitrate were biodegraded, respectively),
which were packed with plastic bioballs to increase the
surface area for microbial attachment, on the surface of
which nitrifying and denitrifying microorganisms were
immobilized.
The reactor (Fig. 12.24) consists of one aerated column (riser) interconnected by conduits with two unaerated columns (downcomer) – the cross-sectional area
of the downcomers being almost 10 times larger than
the riser to ensure adequate retention time for denitrification which is known to require 510 times longer
reaction time than nitrification. The aerated and unaerated columns were packed with 200 and 2000 bioballs
(per column), respectively. A porous gas sparger for air
dispersion was located at the bottom of the aerated column. The airflow rate was determined as a minimum
that could induce liquid circulation between the aerated and unaerated sections. The recirculation of water
was driven from the aerated riser where water moved
up as aeration was provided and down through the unaerated downcomer. In the riser, nitrifying bacteria fed
on wastewater containing high dissolved oxygen, oxidizing ammonia to nitrate. The low dissolved oxygen
effluent from the riser flowed through the downcomer
where denitrifying bacteria removed the nitrate. The
authors noted that no nitrite/nitrate accumulation occurred in any experiment, indicating rapid and effective
denitrification. Overall, the reactor performance was
satisfactory and comparable with other treatment systems, however, where the PBEL-ALBR stands out is
in providing nitrification and denitrification in a single setup without requiring a two-reactors-in-series
cascade.
Seo et al. [12.50] examined the nitrification performance of an NBC (comprising mainly Nitrosomonas
species) immobilized in boric acid treated PVA beads,
for a marine RAS, by employing a continuous
immobilized-cell ALBR (volume 45 L) for acclimation
of the NBC from activated sludge and estimation of ammonia removal rate. In addition, four three-phase, completely mixed, fluidized bed-type bioreactors (FBBR)
(volume 2:5 L each) were also employed for acclimation of the immobilized nitrifiers from freshwater to
seawater system, with increasing salt concentration. Immobilization in support gel is an effective technique for
maintaining high cell density and preventing washout of
slow-growing autotrophic nitrifiers (ATN) under a low
water temperature or high water flow rates. Although
ATNs are sensitive to low temperatures, immobilization
(a) improves tolerance to low temperatures and also, (b)
provides protection against various toxic agents. In the
operational range of values for the HRT, an optimum
HRT was found for the marine nitrification process at
which the highest ammonia removal rate was reached.
The four reactors were used to determine nitrification activity at four different salt concentrations. Each
FBBR consisted of two separate compartments – one
for beads settling and the other for airlift of the beads.
Air was supplied through acrylic pipes (0:1 vvm). Influent NH 3 concentration was maintained at 10 mg L
1 .
Nitrification activity decreased during the immobilization process due to centrifugation, transportation by
pump, shear stress arising out of stirring, toxicity from
the immobilization support material, and low pH of the
boric acid solution. However, nitrification activity gradually recovered with operating time. It was observed
that, nitrification activity of recovered nitrifier beads
was higher than that of free nitrifiers due to high ammonia loading.
Polysaccharide-based gels and reticulate foams are
usually considered as the preferred immobilization matrices for photosynthetic cell systems. Although five
major immobilization techniques (viz., entrapment, microencapsulation, covalent coupling, aggregated cells,
and adsorption) are in vogue, for growth of photosyn-
356 Part B Tools and Methods in Marine Biotechnology
observed. The PBBR system was energy optimized for
continuous operation by limiting energy input to a single stage pumping of water and aeration to the aeration
cells.
Both the PBBRs have the same configuration and
are identical to the PBBRs used in Kumar et al. [12.47],
as are the PS beads used for immobilization. The AOB
and NOB reactors were connected in series. Water
flowed from a large OHT into the AOB and therefrom
into the NOB by gravity. The outflow from the NOB
flows into a CT and from there into the larval rearing tank (LRT). From the LRT, water is pumped out
into the OHT. The major components of the nitrifying bacterial consortia (NBC) were the marine genus,
viz., Nitrosococcus and Nitrobacter. A noteworthy operational flexibility of the PBBRs was that they were
interchangeable between prawn (salinity 15 g L
1 ) and
shrimp (salinity 30 g L
1 ) larval rearing systems simply
by changing the NBC based on salinity.
Silapakul et al. [12.49] examined a novel packed
bed external loop airlift bioreactor (PBEL-ALBR) (volume 60 L) as an integrated system with simultaneous nitrification/denitrification for treatment of marine
aquaculture wastewater containing ammonia and nitrate
compounds. The PBEL-ALBR consisted of both aeration and nonaeration zones in the same unit, that served
as nitrification and denitrification compartments (where
ammonia and nitrate were biodegraded, respectively),
which were packed with plastic bioballs to increase the
surface area for microbial attachment, on the surface of
which nitrifying and denitrifying microorganisms were
immobilized.
The reactor (Fig. 12.24) consists of one aerated column (riser) interconnected by conduits with two unaerated columns (downcomer) – the cross-sectional area
of the downcomers being almost 10 times larger than
the riser to ensure adequate retention time for denitrification which is known to require 510 times longer
reaction time than nitrification. The aerated and unaerated columns were packed with 200 and 2000 bioballs
(per column), respectively. A porous gas sparger for air
dispersion was located at the bottom of the aerated column. The airflow rate was determined as a minimum
that could induce liquid circulation between the aerated and unaerated sections. The recirculation of water
was driven from the aerated riser where water moved
up as aeration was provided and down through the unaerated downcomer. In the riser, nitrifying bacteria fed
on wastewater containing high dissolved oxygen, oxidizing ammonia to nitrate. The low dissolved oxygen
effluent from the riser flowed through the downcomer
where denitrifying bacteria removed the nitrate. The
authors noted that no nitrite/nitrate accumulation occurred in any experiment, indicating rapid and effective
denitrification. Overall, the reactor performance was
satisfactory and comparable with other treatment systems, however, where the PBEL-ALBR stands out is
in providing nitrification and denitrification in a single setup without requiring a two-reactors-in-series
cascade.
Seo et al. [12.50] examined the nitrification performance of an NBC (comprising mainly Nitrosomonas
species) immobilized in boric acid treated PVA beads,
for a marine RAS, by employing a continuous
immobilized-cell ALBR (volume 45 L) for acclimation
of the NBC from activated sludge and estimation of ammonia removal rate. In addition, four three-phase, completely mixed, fluidized bed-type bioreactors (FBBR)
(volume 2:5 L each) were also employed for acclimation of the immobilized nitrifiers from freshwater to
seawater system, with increasing salt concentration. Immobilization in support gel is an effective technique for
maintaining high cell density and preventing washout of
slow-growing autotrophic nitrifiers (ATN) under a low
water temperature or high water flow rates. Although
ATNs are sensitive to low temperatures, immobilization
(a) improves tolerance to low temperatures and also, (b)
provides protection against various toxic agents. In the
operational range of values for the HRT, an optimum
HRT was found for the marine nitrification process at
which the highest ammonia removal rate was reached.
The four reactors were used to determine nitrification activity at four different salt concentrations. Each
FBBR consisted of two separate compartments – one
for beads settling and the other for airlift of the beads.
Air was supplied through acrylic pipes (0:1 vvm). Influent NH 3 concentration was maintained at 10 mg L
1 .
Nitrification activity decreased during the immobilization process due to centrifugation, transportation by
pump, shear stress arising out of stirring, toxicity from
the immobilization support material, and low pH of the
boric acid solution. However, nitrification activity gradually recovered with operating time. It was observed
that, nitrification activity of recovered nitrifier beads
was higher than that of free nitrifiers due to high ammonia loading.
Polysaccharide-based gels and reticulate foams are
usually considered as the preferred immobilization matrices for photosynthetic cell systems. Although five
major immobilization techniques (viz., entrapment, microencapsulation, covalent coupling, aggregated cells,
and adsorption) are in vogue, for growth of photosyn-