400
Y. Argaman et al.
mgPO/-P L· 1 • The substrate was prepared using dechlorinated tap water
containing all the nitrifiers' requirements of micro- and macronutrients. This
substrate composition was used in all further experiments. Constant pH of 7.6 ±
0.2 was maintained using sodium carbonate solution.
Specific nitrification activity was determined immediately after bacteria
immobilization, and was related to the specific nitrification activity of free
biomass. The specific ammonium rate was used for determining the nitrifying
biomass activity. The rates were determined in short-term batch tests, under
nonlimiting substrate conditions. If the remaining activity was less than 10% of
the free biomass nitrification rate, the respective method of immobilization was
considered as highly toxic to the nitrifiers; and, corresponding, 10-40% and above
40% were assumed to be of moderate and low toxicity, respectively.
Physical properties were mostly related to the gel's durability, and its stability
over time. The gel was of low stability if the gel-bead dimensions and the
nitrifying activity were the same for only less than I week. Moderate stability was
defined when the above were stable for up to 3 months, and high stability for more
than 3 months, since Wijffels (1993) demonstrated that 3 months is the least
period of time that makes nitrification by immobilized biomass cost-effective. The
gel-beads' stability was estimated through the operation of a continuous-flow
reactor fed with ammonia synthetic wastewater.
4.2 Process-Related and Cost-Determining Parameters
Two process- and cost-related parameters were studied in this work: minimum
concentration of the seeded nitrifying biomass providing effective nitrification,
and durability of the immobilized biomass. The effect of seeded biomass
concentration on the steady-state activity of the immobilized nitrifiers was studied
in continuous-flow experiments and employing synthetic inorganic ammonia
wastewater. Three parallel experiments were conducted for Lentisol (GeniaLab,
Braunschweig, Germany) and PVA-glycerol beads and for PVA-glycerol threads
(immobilization methods selected as appropriate). Each experiment employed five
to seven cylindrical vessels of 1.4-L equipped with diffused aeration and operated
as continuous-flow reactors. All the reactors contained 10% and 2.5% V dVR
(volume of gel/volume of reactor) of the gel beads and threads, respectively. Each
reactor had a different concentration of seeded biomass and was fed with
ammonium synthetic wastewater (100 mgNH/-N L· 1 ). The influent and effluent
ammonia, nitrite and nitrate concentrations were measured daily. When chemical
steady state was reached, specific nitrification activity was evaluated as the
ammonia oxidation rate related to the seeded biomass.
Durability of the immobilized nitrifier's operation was studied using two
aerated reactors similar to those described above. The reactors contained 10%
VdVR of lens-shaped beads prepared from Lentisol and PVA-glycerol gel with a
concentration of 109 L· 1 of seeded nitrifying biomass. These reactors were fed
with synthetic ammonia wastewater during first 2 weeks of the experiment.
Y. Argaman et al.
mgPO/-P L· 1 • The substrate was prepared using dechlorinated tap water
containing all the nitrifiers' requirements of micro- and macronutrients. This
substrate composition was used in all further experiments. Constant pH of 7.6 ±
0.2 was maintained using sodium carbonate solution.
Specific nitrification activity was determined immediately after bacteria
immobilization, and was related to the specific nitrification activity of free
biomass. The specific ammonium rate was used for determining the nitrifying
biomass activity. The rates were determined in short-term batch tests, under
nonlimiting substrate conditions. If the remaining activity was less than 10% of
the free biomass nitrification rate, the respective method of immobilization was
considered as highly toxic to the nitrifiers; and, corresponding, 10-40% and above
40% were assumed to be of moderate and low toxicity, respectively.
Physical properties were mostly related to the gel's durability, and its stability
over time. The gel was of low stability if the gel-bead dimensions and the
nitrifying activity were the same for only less than I week. Moderate stability was
defined when the above were stable for up to 3 months, and high stability for more
than 3 months, since Wijffels (1993) demonstrated that 3 months is the least
period of time that makes nitrification by immobilized biomass cost-effective. The
gel-beads' stability was estimated through the operation of a continuous-flow
reactor fed with ammonia synthetic wastewater.
4.2 Process-Related and Cost-Determining Parameters
Two process- and cost-related parameters were studied in this work: minimum
concentration of the seeded nitrifying biomass providing effective nitrification,
and durability of the immobilized biomass. The effect of seeded biomass
concentration on the steady-state activity of the immobilized nitrifiers was studied
in continuous-flow experiments and employing synthetic inorganic ammonia
wastewater. Three parallel experiments were conducted for Lentisol (GeniaLab,
Braunschweig, Germany) and PVA-glycerol beads and for PVA-glycerol threads
(immobilization methods selected as appropriate). Each experiment employed five
to seven cylindrical vessels of 1.4-L equipped with diffused aeration and operated
as continuous-flow reactors. All the reactors contained 10% and 2.5% V dVR
(volume of gel/volume of reactor) of the gel beads and threads, respectively. Each
reactor had a different concentration of seeded biomass and was fed with
ammonium synthetic wastewater (100 mgNH/-N L· 1 ). The influent and effluent
ammonia, nitrite and nitrate concentrations were measured daily. When chemical
steady state was reached, specific nitrification activity was evaluated as the
ammonia oxidation rate related to the seeded biomass.
Durability of the immobilized nitrifier's operation was studied using two
aerated reactors similar to those described above. The reactors contained 10%
VdVR of lens-shaped beads prepared from Lentisol and PVA-glycerol gel with a
concentration of 109 L· 1 of seeded nitrifying biomass. These reactors were fed
with synthetic ammonia wastewater during first 2 weeks of the experiment.