402
Y. Argaman et al.
received any ammonia feed during the entire feed interruption period. All the
reactors were continuously aerated. Nitrification activity of these reactors was
tested after 3 months of interruption by determination of the volumetric
ammonium oxidation rate.
All the analytical tests for determination of TSS, VSS, ammonium, nitrite,
nitrate, BOD, COD, etc. were performed following ASTM standard methods
(1997).
5
Results and Discussion
5.1
Selection of the Appropriate Gel Material
Recently, artificially immobilized nitrifiers have attracted much attention.
Nitrifying bacteria were encapsulated in both the natural matrices (Ca-alginate
{ClzH1401ZCa}n, k-carrageenan {ClzH7SZ01ZK}n, Agarose {ClzHlS09}n), and the
synthetic polymers (polyacrylamide, P AA, {CHz=CHCONHz}n, polyethylene
glycol, PEG, {CHz=C(CH)3CO(OCHzCHZ)nOzCC(CH)3)=CHz}, polyvinylalcohol, PYA, {CHz=CHOH}n, polyurethane (PU), epoxy and silicon film)
(Libman 1998).
The data of Table 1 indicate that practically all methods of autotrophic biomass
immobilization may provide a higher nitrification rate than that of the
conventional activated sludge process. In order to select suitable gel material,
nitrifying bacteria harvested from the chemostate cultivation were immobilized
according to the procedures reported by the above authors. Properties of the most
successful and characteristic gel materials are presented in Table 2. It should be
noted that unsuccessful immobilization in some of the cases resulted from the
unavailability of specific compounds. For example, a key factor of PEG
application is the prepolymer with minimized content of toxic polymerization
inhibitors. This can be possible only if PEG is manufactured near the laboratory,
which is not the case in Israel.
Based on the extended literature review and experimental work, PV A gel was
selected due to its relatively low toxicity, low cost, and good physical properties.
In fact, this polymer meets practically all the requirements defined by Akin (1987)
and Leenen et al. (1996). PYA-drying method (as described by Jekel et al. 1998)
was employed in the present work applying two prepolymers: Lentisol (PV Abased prepolymer produced by GeniaLab, Braunschweig, Germany) and its
modified and simplified version, PV A-glycerol solution.
Y. Argaman et al.
received any ammonia feed during the entire feed interruption period. All the
reactors were continuously aerated. Nitrification activity of these reactors was
tested after 3 months of interruption by determination of the volumetric
ammonium oxidation rate.
All the analytical tests for determination of TSS, VSS, ammonium, nitrite,
nitrate, BOD, COD, etc. were performed following ASTM standard methods
(1997).
5
Results and Discussion
5.1
Selection of the Appropriate Gel Material
Recently, artificially immobilized nitrifiers have attracted much attention.
Nitrifying bacteria were encapsulated in both the natural matrices (Ca-alginate
{ClzH1401ZCa}n, k-carrageenan {ClzH7SZ01ZK}n, Agarose {ClzHlS09}n), and the
synthetic polymers (polyacrylamide, P AA, {CHz=CHCONHz}n, polyethylene
glycol, PEG, {CHz=C(CH)3CO(OCHzCHZ)nOzCC(CH)3)=CHz}, polyvinylalcohol, PYA, {CHz=CHOH}n, polyurethane (PU), epoxy and silicon film)
(Libman 1998).
The data of Table 1 indicate that practically all methods of autotrophic biomass
immobilization may provide a higher nitrification rate than that of the
conventional activated sludge process. In order to select suitable gel material,
nitrifying bacteria harvested from the chemostate cultivation were immobilized
according to the procedures reported by the above authors. Properties of the most
successful and characteristic gel materials are presented in Table 2. It should be
noted that unsuccessful immobilization in some of the cases resulted from the
unavailability of specific compounds. For example, a key factor of PEG
application is the prepolymer with minimized content of toxic polymerization
inhibitors. This can be possible only if PEG is manufactured near the laboratory,
which is not the case in Israel.
Based on the extended literature review and experimental work, PV A gel was
selected due to its relatively low toxicity, low cost, and good physical properties.
In fact, this polymer meets practically all the requirements defined by Akin (1987)
and Leenen et al. (1996). PYA-drying method (as described by Jekel et al. 1998)
was employed in the present work applying two prepolymers: Lentisol (PV Abased prepolymer produced by GeniaLab, Braunschweig, Germany) and its
modified and simplified version, PV A-glycerol solution.