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Denitrification of nitrite in a two-phase fluidized bed bioreactor
~
Pergamon
War. Sci. Tech. Vol. 34, No. 1-2, pp. 339-346.1996. Copyright © 1996 IAWQ. Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved. 0273-1223/96 $15'00 + 0'00
PH: S0273-1223(96)00524-0
DENITRIFICATION OF NITRITE IN A TWO-PHASE FLUIDIZED BED BIOREACTOR A. Hirata and A. A. Meutia Department of Chemical Engineering, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo 169, Japan
ABSTRACT Denitrification of nitrite-nitrogen carried out experimentally in an anoxic two-phase fluidized bed bioreactor is described, and the characteristics of the biological treatment were also theoretically studied. Methanol was used as the carbon source, and nitrite-degrading bacteria immobilized on CB particles were employed. A method for evaluating the characteristics of the biological treatment is proposed. Within the range of the experiment, the results show that denitrification of nitrite-nitrogen could be approximated by Monod-type reaction kinetics, characteristic values for the biological treatment of ~= 5.0 kg-Nekg-1-VSed- 1 and K/Km= 23.8 m3e kg- 1-VSed- 1 being obtained. There was good correlation between the experimental results and the calculated curves. A maximum volumetric denitrification rate for nitrite of 18.7 kg-N em-3e d- 1 was achieved, this high value demonstrating the high efficiency of an anoxic two-phase fluidized bed bioreactor to denitrify nitrite-nitrogen. Copyright © 1996 IAWQ. Published by Elsevier Science Ltd. KEYWORDS Biofilm; biological wastewater treatment; denitrification; fluidized bed bioreactor; nitrite-nitrogen.
INTRODUCTION An accumulation of nitrite concentration often occurs when nitrifying high-strength ammonium wastewater (Ganczarczyk, 1978; Cecen & Gonenc, 1995) and when denitrifying industrial wastewater (Blaszczyk et al., 1985; Wilderer et al., 1987). This accumulation of nitrite is undesirable because of its toxicity to aquatic life, and when this happens, further treatment is required to remove nitrite from the wastewater. This treatment involves the dissimilatory reduction of nitrite to nitrogen gas, and is also a shortened pathway for removing nitrogen from highly nitrogenous waste without nitrate reduction (Chen et al., 1991; Rahmani et al., 1995).
Most research on denitrification of nitrite has been carried out by using suspended-growth cultures (Beccari et al., 1983), packed bed reactors (Blaszczyk et aI., 1981; Blaszczyk, 1983; Mycielski et aL, 1983; Blaszczyk et al., 1985), or submerged biofilters (Chen et al., 1991; Cecen and Gonenc, 1995; Rahmani et al., 1995). Very little research has been done on using fluidized bed reactors. However, fluidized bed reactors offer such advantages as a high biomass concentration, resulting in 339
340
A. HIRATA and A. A. MEUTIA
higher volumetric removal with lower hydraulic retention time and greater compactness of the reactor when compared with conventional treatment systems (Hirata et al., 1990; Lazarova et aL, 1994). These advantages encouraged the use of a fluidized bed bioreactor in this study. Such re~ctors have been successfully used for treating wastewater containing phenol (Hosaka et al., 1985; H~ata. et al., 1990), coke oven waste (Hirata et al., 1991a), kitchen waste (Hirata et al., 1991b), ammonIa-nItrogen (Hirata et al., 1989) and washing of drums waste (Hirata et al., 1992). These reactors have also been used to study fluidization characteristics (Hirata and Bulos, 1990; Hirata et al., 1995) and reactor design (Hirata et al., 1985; Hirata and Noguchi, 1994). In order to understand the denitrification of nitrite in a fluidized bed, the characteristics of the biological treatment need to be clarified. In this study denitrification of nitrite-nitrogen. i~ evaluated experimentally in an anoxic two-phase fluidized bed bioreactor, and the charactenstlcs of the biological treatment is also theoretically studied.
MATERIALS AND METHODS
Reactor. The anoxic two-phase fluidized bed bioreactor system shown in Fig. 1 was used. The fluidized bed was a cylindrical acrylic column with a height of 320 cm and an internal diameter of 5 cm. Support particle. The support particle was CB (cement ball) particles made from aluminium silica (manufactured by Onoda Cement Co. Ud.) with an average 2.22 g cm-3 specific density and 0.194• 0.218 mm diameter. Microorganism. The denitrification reactor was started up with sludge from our enriched laboratory culture, this sludge having been acclimatized to a synthetic nitrite substrate for several months. The seeding sludge was added to the two-phase fluidized bed reactor and recycling operations begun with a feed of about 50 g em- 3 of the synthetic substrate. The biofilm was immobilized on the particle for several days, and recycling was then changed to continuous operation. Substrate. The synthetic substrate consisted of NaN02 (4926 g em-3), KH2P04 (2200 g em-3), NH4 HC03 (493 g em-3) and CH30H (8867 g em- 3). Excess methanol was used as the external carbon source in the reactor, the ratio by weight of methanol and nitrite being 1.8 (C/N=3.325). The substrate was continuously fed into the reactor, the nitrite-nitrogen influent concentration being between 15 and 300 g em- 3• The superficial liquid velocity (UJ varied from 400 to 950 med- 1• The calculation of some equations in this experiment used an effluent concentration of nitrite that did not reach zero. The keys used in Figures 3-7 are shown in Table 1. The water temperature was maintained at 30°C and the pH value of the influent was approximately 7. During the experiments, the pH value was increased to about 9 in the effluent. The average value for the dissolved oxygen concentration inside the reactor was around 0.2 g em-3 • Analyses. The nitrite-nitrogen concentration was measured by ion chromatography (Tosoh C8011 equipment) according to Japanese Industrial Standards (1IS). The ammonia concentration was regularly measured with an ion meter (IOC-lO, Denki Kagaku Keiki Co. Ud.), and pH was measured with a pH meter (Tpx-90 i, Toko Chemical Lab. Co. Ud.). RESULTS AND DISCUSSION Fig. 2 shows an example of the nitrite-nitrogen concentration according to the height in the reactor 3 column when Sin= 42.6 g em- and U\=441 med- 1• The nitrite-nitrogen concentration decreases gradually from the. bottom of the tw~-phase fluidized bed (influent) to the top of the reactor (effluent): .As .prevIOusly reported (HIrata et al., 1991a), it was ascertained that the hydraulic charactenstlcs m the. reactor could be approximated as plug flow, this approximation being valid throughout the expenmental range. The ammonia concentration was measured to check the removal
VI [med-1]
Sin [g·m-3]
15-25
400-450 450-500 500-550 550-600 600-700 850-950 Xb
:
.
25-30
30-35
35-45
50-60
65-70
85-90
(l-
f)-
¢Ia
ea ~c
J;;.a
Vb
Separation tank
SOcm
TABLE 1 KEYS USED IN FIGURES 3-7
..". t
_t. Effluent't •
'; r
250-300
Two-phase fluidized bed
.,1_
320Cm
~
~a b
Bioparticle Sampling spot
@c
©1
(a)7.8-11.4 kg-VS·m-3, (b)20.35 kg-VS·m-3, (c)33.60 kg-VS·m-3
Fig. 1. Two-phase fluidized bed bioreactor. 1:1
0
TABLE 2 PREVIOUS STUDIES ON mE DENITRIFICATION OF NITRATE- AND NITRITE-NITROGEN IN BIOFILM REACTORS
g: ::l
::tl
0
Type of reactor
Carbon source
Fonn of NOx-N Influent cone.
Temperature
[gom-3]
[OC]
Submerged bioflter Submerged filter Fixed film Packed bed Packed bed Packed bed
acetate molasses benzoic acid methanol acetic acid ethanol
NOz-N N03 -N, NOz-N NOz-N NOz-N NOz-N NOz-N
8.8- 35.0 - 850.0 194.0-1033.0 1000.0 1000.0 1000.0
20 13-23 25-27
Fluidized bed Fluidized bed
methanol methanol
N03 -N, NOz-N N03 -N
5.0- 100.0 6.6- 30.0
18-23
Fluidized bed
methanol
NOz-N
15.0- 300.0
-
penitrification rate Based on biomass Based on volume R./~V
[kg-N°kg-1-VSod-1]
Reference
2.
g.
[kg-Nom-3 od-1]
0-
0.20- 0.38 8.22- 9.88 0.42- 3.99
Rahmani et aI., 1995 Cecen & Gonenc, 1995 Chen et al., 1991 Blaszczyk et al., 1985 Blaszczyk et al., 1981 Mycielski et aI., 1983
0.185 (max.)
0 ::l 0
...,
R.jV
2.10 (max.) 0.36 (max.)
II> :::.
-
0.033-0.243
5.40-20.70 0.69- 3.28
Jeris & Owens, 1975 Hennanowicz & 01eng, 1990
30
0.141-2.575
3.23-18.70
This study w
....
~
A. HIRATA and A. A. MEUTIA
342
of nitrite caused by the denitrification or ammonification process. However, no ammonia was found inside the reactor, nor in the effluent during this experiment, it was thus ascertained that the removal of nitrite-nitrogen was caused by denitrification. The denitrification rate of nitrite-nitrogen in the two-phase fluidized bed was obtained in th~s l experiment on a biomass basis (R/XbV) as 0.141-2.75 kg-Nekg-1-vSed- , and for. the volu~etnc denitrification rate (~/V) as 3.23-18.70 kg-N em-3e d- l . Table 2 shows several ~revlOus studIes ~n the denitrification of nitrite and nitrate, the rate obtained in this study being hIgh compared wIth those obtained in other research work.
......
10.............."I'""'P"'l,..,.,..,.,..,.,..,~.,.,..,.,
Z
~
'e
I
cJ
= = = c:J
,,
,,
'0,
~
Cf)
.-==
I.
,,
,,
..-• Z I.
00
6
I
,,
~
'<0
~
8
> !J ....... 4
0"',..
I
e
100 200 Height [em]
~
2
~
'iiK~OO
300
150 200 In (Sin/Sout)/(Sin-Sout) [m e kg-l_N]
Fig. 2. An example of nitrite-nitrogen conc. along the height of the reactor. Sin= 42.6 g • m-3, U I= 441 m • dol
50
100
3
Fig. 3. Evaluation of biological wastewater treatment and determination ofKu and Ku/K m values.
Method for evaluating the characteristics of biological treatment in an anoxic biofilm reactor An analysis of the biological treatment characteristics of nitrite-nitrogen denitrification in an anoxic two-phase fluidized bed bioreactor was conducted according to the following assumptions: (a) steady-state conditions (b) negligible substrate inhibition and a Monod-type reaction being applicable (c) negligible contribution of free-cell (suspended) microorganisms to the overall removal rate (d) plug flow characteristics in the reactor Basic equation:
U dS +X "'._S_ I dz. b Y K +S
=
0
•
(1)
Boundary conditions:
.,.,
"'=0 S=S •
~,
::=8, 8=S.",
(2)
The following equation for evaluating the biological treatment characteristics then results:
X.v _
1
K.ln(SJS.,,)
-- - -+----R,
where
K.= /..I. ,JY
Ku K. S.,. -S.ut
(3)
Denitrification of nitrite
343
Ku and KJKm are characteristic values for quantifying denitrification, high values indicating that denitrification is well conducted. Therefore, K" and KJKm are the characteristics values for the biological treatment. While these characteristic values vary depending on the character and condition of the wastewater, environmental conditions such as temperature and pH, and on the microorganisms applied, the values are constant with varying wastewater concentration, flow rate, or biomass. From Equation 3, it can be shown that the reactor volume (V) can be rationally designed with the given values of biomass concentration (Xb), K" and KJKm obtained from the experiment, depending on the flow rate (QJ, influent concentration (SJ and effluent concentration (SouJ. The values of K" and KJKm were obtained from the experimental data resulting from Sin' Q. and Xb being varied and the other conditions being constant. In the case of plug flow, these data can be plotted as XbVJR, for the ordinate and In(Su/Soul)I(Sin-SouJ for the abscissa. With a certain character and condition of the wastewater, environmental conditions, and microorganism for which the values of Ku and KJKm are constant, a straight line can be constructed. K,jK,. can then be obtained from the slope of the straight line, and 1JKu from the intercept.
Evaluation of the characteristics of biological wastewater treatment An evaluation of the experimental results with Equation 3 is shown in Fig. 3. Although there is some scatter, which is quite common with biological treatment, the plot approximates to a straight line that does not pass through the origin. The best-fit line between Equation 3 and the experimental results proves that the denitrification of nitrite could be regarded as a Monod-type reaction. Vossoughi et al. (1982) have reported that the reduction of nitrite was a first-order reaction, while other researchers have explained denitrification in a fixed film with a simplified half-order and zero• order reaction concept (Cecen and Gonenc, 1995; Jansen and Harremoes, 1984). According to their work, nitrate-nitrogen removal was a half-order reaction at low bulk concentration, becoming a zero-order reaction when the biofilm had been fully penetrated by the substrate. Within the range of experimental conditions at which the influent nitrite-nitrogen concentration was up to 300 g-m-3, the reaction was neither first- nor zero-order; therefore, it had to be treated as a Monod-type reaction. The slope and the intercept of the straight line in Fig. 3 enabled the following characteristic values of the biological treatment to be obtained: K" = 5.0 kg-N-kg-1-VS-d- 1 Km = 0.21 kg-N-m-3 KJKm = 23.8 m3 -kg- 1-VS-d- 1 Based on the foregoing theoretical analysis, Fig. 4 shows the relationship between (Sin-SouJlln(Sj./SouJ and the denitrification rate of nitrite-nitrogen on a biomass basis (R/XbV). It can be seen that R/X., V increases as (Sin-SouJlln(SjJSouJ increases, enabling the reaction to be categorized as first• order when (Sin-SouJlln(Si./SouJ is below 0.06 kg-N-m-3• Figure 5 shows the effect of biomass per unit flow rate (~VIQJ on the effluent nitrite-nitrogen concentration (SouJ with varying influent nitrite-nitrogen concentration (SJ. The curves in Fig. 5 were plotted according to Equation 3 with the characteristic values obtained from the experiment, and the plots show that these curves were simulated very well by the experimental results. From Fig. 5, within the range of experimental conditions, SOUl could reach nearly zero when Sjn was nearly 90 g-m-3 and Xt, VIOl was greater than 0.2 kg-VSed-m-3• In the case of Sin being between 90 and 300 g-m-3 and Xt, VIOl being greater than 0.3 kg-VS-d-m- 3, SOUl could be treated as nearly zero. Using the same experimental results, Fig. 6 shows the effect of ~V/QI on the nitrite-nitrogen removal efficiency (Tl) when Sin is varied. The best-fit line between the measured points and the 3 calculated curves shows good correlation. With XbV/Q, greater than 0.3 kg-VS·d-m- , the removal efficiency was found to be almost 1. Therefore, when the influent concentration is low and the effect
A. HIRATA and A. A. MEUTIA
q-l
of S on 1] is small, the reaction can be ,n . concentration is greater, the reaction cannot of Xb V/0" 1] will decrease as the influent
. n the approximated to a first-or der type. Whe . influent 1 be approximate . d to a fiIrs t-order type . For a given va ue concentration increases.
2 •
1
Fig. 5. Effects of biomass per flow rate (X bVIQI) and influent concentration (Sin) on effluent concentration (Sout)·
Fig. 4. Relationship between (Sin-Sout)/ln(SiJSout) and denitrification rate of nitrite on a biomass basis (R/XbV).
-"'7'"
1,..,....or-T"'"'I"""'T':~~~tp.t~
-
;:0.8
I
.-=0.6
/
/
tf'l
QJ
'e z•
~
-=
ct.
QJ
Sin [g • m- 3] _. ·,-300 -. -- 200 - - -90 ... 60 --- 30 15
~ 0.4
e ~
z 0.2 o I N
0
15
't:S
CJ
Z
/
......
~
o
0.1
0.2
X bV/QI [kg-VS • d • m-
3
10
,/
I
-!J
/
~
.......
0.3
]
Fig. 6. Effects ofXbV/Q, and influent concentration on nitrite-nitrogen removal efficiency ( 1] ).
.. -:A
0""""'
1.o.I.
0.2
~
0.3 (Sin- Sout)/In (Sin/Sout) [kg • m -3]
o
0.1
3
X b [kg-VS • m- ] -40.0 ---30.0 . - . 20.0 ---10.0 - .. - 7.5 -' .. - 5.0
Fig. 7. Effects of biomass concentration (Xb) and (Sin-Sout)!ln (SdSout) on volumetric denitrification rate (RtM.
The effects of biomass concentration (Xb) and (Sin-SouJl1n(SiJSouJ on the volumetric denitrification rate (~N) shows that R/V increases as ~ increases (Fig. 7). Within the range of the experimental
Denitrification of nitrite
345
conditions, a maximum value of 18.7 kg-N em-3e d- 1 was achieved for the volumetric nitrite denitrification rate with this reactor. This value is 2 to 15 times as high as the results obtained by other researchers who studied the denitrification of nitrite (Table 2) in a suspended-growth culture (Beccari et al., 1983), packed bed reactor (Blaszczyk et al., 1981; Blaszczyk, 1983; Blaszczyk et al., 1985; Mycielski et al., 1983), or submerged biofilter (Cecen and Gonenc, 1995; Chen et aI., 1991; Rahmani etal., 1995). However, this is almost the same value as that obtained for the volumetric denitrification rate for nitrate in a fluidized bed reactor (Jeris and Owens, 1975), proving that the use of the two-phase fluidized bed bioreactor enhanced the capacity to denitrify nitrite-nitrogen.
CONCLUSIONS The following conclusions could be drawn from the results. 1. Equation 3 for evaluating the characteristics of biological treatment in a plug flow type of anoxic biofilm reactor is proposed. A method for evaluating the characteristic values of biological treatment, K,. and KJKm, is also proposed. 2. The experimental results arranged by using the proposed evaluation equation show that the denitrification of nitrite-nitrogen must be treated as a Monod-type reaction within the experimental range considered. Characteristic values to quantify the biological treatment of K,.= 5.0 kg-Nekg-1-VSed- 1 and KJKm = 23.8 m3e kg- 1-VSed- 1 were obtained. The experimental results correlate well with the calculated line. 3. The maximum volumetric nitrite denitrification rate of 18.7 kg-N em-3e d- 1 was achieved within the range of the experimental conditions used. This value is higher than the results from other biofilm research because of the greater efficiency of the anoxic two-phase fluidized bed bioreactor for carrying out the denitrification of nitrite.
NOMENCLATURE H
=
reactor height [m] saturation constant for nitrite-nitrogen [kg-N em-3] K,. = f.1 mlY [kg-Nekg-1-VSed- l ] O. = volumetric liquid flow rate [m 3e d- l ] ~ OI(Sin-SouJ [kg-Ned-I] S = nitrite-nitrogen concentration [kg-N em-3] VI = superficial liquid velocity [m ed-I] V = bed volume [m3] Xb = biomass concentration [kg-VSem-3] Y = yield factor based on nitrite-nitrogen [kg-VSekg-1-N] = distance from bottom of fluidized bed reactor [m] z 1] = nitrite-nitrogen removal efficiency TJ == I-Sou/Sin [-] f.1 m = maximum specific growth rate [d- l ] Subscripts in = influent out = effluent
Km
=
REFERENCES Beccari, M., Passino, R., Ramadori, R. and Tandoi, V. (1983). Kinetics of dissimilatory nitrate and nitrite reduction in suspended growth culture. J. Water Pol/ut. Control Fed., 55 (1), 58-63. Blaszczyk, M., Przytocka-Jusiak, M., Kruszewska, V. and Mycielski, R. (1981). Denitrification of
346
A. HIRATA and A. A. MEUTIA
high concentrations of nitrites and nitrates in synthetic medium with different sources of organic . carbon I. acetic acid. Acta Microbiologica Polonica, 30 49-58. Blaszczyk, M. (1983). Effect of various sources of organic carbon and high nitri~e and mtrate concentrations on the selection of denitrifying bacteria. II. Continuous cultures In packed bed reactors. Acta Microbiologica Polonica, 32 (1) 65-71. Blaszczyk, M., Galka, E., Sakowicz, E. and Mycielski, R. (1985). Denitrification of hi~ concentrations of nitrites and nitrates in synthetic medium with different sources of organic carbon III. methanol. Acta Microbiologica Polonica, 34 195-206. Cecen, F. and Gonenc, I. E. (1995). Criteria for nitrification and denitrification of high-strength wastes in two upflow submerged filters. Water Environ. Res., 67 (2) 32-142. Chen, S. K, Juaw, C. K and Cheng, S. S. (1991). Nitrification and denitrification of high-strength ammonium and nitrite wastewater with biofilm reactors. Wat. Sci. Tech., 23 (7-9) 1417-1425. Christensen, F. R, Kristensen, G. H. and Jansen, J. la C. (1989). Biofilm structure-an important and neglected parameter in wastewater treatment. Wat. Sci. Tech., 21(8/9),805-814. Ganczarczyk, J. J. (1978). Second-stage activated sludge treatment of coke-plant effluents. Wat. Res., 13 337-342. Hermanowicz, S. W. and Cheng, Y. W. (1990). Biological fluidized bed reactor: hydrodynamics, biomass distribution and performance. Wat. Sci. Tech., 22 (1/2) 193-202. Hirata, A, Bolus, F. B. and Noguchi, M. (1995). Correlation for bed voidage in three-phase fluidized bed. J. Chern. Eng. Japan, 28 (4) 400-404. Hirata, A. and Noguchi, M. (1994). Biological wastewater treatment by three-phase fluidization• characteristics and basic design method. Wat. Sci. Tech., 30 (11) 91-100. Hirata, A., Umezawa, H., Endou, E. and Hosaka, Y. (1992). Biological treatment of wastewater from the washing of oil and chemical drums in a three-phase fluidized bed. Int. Chern. Eng., 32 (3) 578-584. Hirata, A, Takahashi, C. and Arai, M. (1991a). Biological treatment of coke oven wastewater in a three-phase fluidized bed. Environ. Conservation Eng., 20 183-192. Hirata, A, Takahashi, C. and Takahashi, T. (1991b). Treatment of kitchen wastewater in complete mixing three-phase fluidized bed bioreactor. Suishitsu Odaku Kenkyuu, 14 730-736. Hirata, A, Hosaka, Y. and Umezawa, H. (1990). Characteristics of simultaneous utilization of oxygen and substrate in a three-phase fluidized bed bioreactor. J. Chern. Eng. Japan, 23 (3) 303-307. Hirata, A. and Bulos, F. B. (1990). Predicting bed voidage in solid liquid fluidization. J. Chern. Eng. Japan, 23 (5) 599-604. Hirata, A, Hosaka Y., Basuki, B. T., Maeda, K (1989). Nitrification of ammonia nitrogen in a three-phase fluidized. Suishitsu Odaku Kenkyuu, 12 (9) 575-58l. Hosaka, Y., Kaihou M. and Hirata, A. (1985). Biological treatment of phenolic wastewater in a three-phase fluidized bed. Wat. Sci. Tech., 17(8), 1437-1439. Jansen, J. la C. and Harremoes, P. (1984). Removal of soluble substrates in fixed films. Wat. Sci. Tech. 17(2/3), 1-14 Jeris, J. S. and Owens, R W. (1975). Pilot-scale, high-rate biological denitrification. J. Water Pollut. Control Fed., 47 (8) 2043-2057. Lazarova, V. and Manem, J. (1994). Advances in biofilm aerobic reactors ensuring effective biofilm activity control. Wat. Sci. Tech., 29 (10-11) 319-327. Mycielski, R, Blaszczyk, M., Jackowska, A and Olkowska, H. (1983). Denitrification of high concentrations of nitrites and nitrates in synthetic medium with different sources of organic . carbon II. ethanol. Acta Microbiologica Polonica, 32 381-388. Rahmani, H., Rols, J~ L., Capdeville, B., Cornier, 1. C. and Deguin, A. (1995). Nitrite removal by a fixed culture m a submerged granular biofilter. Wat. Res., 29 (7) 1745-1753. Vossoughi, M., Laroche, M., Navarro, J. M., Faup, G. and Leprince, A. (1982). Continuous denitrification by immobilized cells. War. Res., 16 995-1002. Wilderer, ~. A., Jones, W. L. and Dau, U. (1987). Competition in denitrification systems affecting reductIOn rate and accumulation of nitrite. Wat. Res., 21 (2) 239-245.
Pergamon
War. Sci. Tech. Vol. 34, No. 1-2, pp. 339-346.1996. Copyright © 1996 IAWQ. Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved. 0273-1223/96 $15'00 + 0'00
PH: S0273-1223(96)00524-0
DENITRIFICATION OF NITRITE IN A TWO-PHASE FLUIDIZED BED BIOREACTOR A. Hirata and A. A. Meutia Department of Chemical Engineering, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo 169, Japan
ABSTRACT Denitrification of nitrite-nitrogen carried out experimentally in an anoxic two-phase fluidized bed bioreactor is described, and the characteristics of the biological treatment were also theoretically studied. Methanol was used as the carbon source, and nitrite-degrading bacteria immobilized on CB particles were employed. A method for evaluating the characteristics of the biological treatment is proposed. Within the range of the experiment, the results show that denitrification of nitrite-nitrogen could be approximated by Monod-type reaction kinetics, characteristic values for the biological treatment of ~= 5.0 kg-Nekg-1-VSed- 1 and K/Km= 23.8 m3e kg- 1-VSed- 1 being obtained. There was good correlation between the experimental results and the calculated curves. A maximum volumetric denitrification rate for nitrite of 18.7 kg-N em-3e d- 1 was achieved, this high value demonstrating the high efficiency of an anoxic two-phase fluidized bed bioreactor to denitrify nitrite-nitrogen. Copyright © 1996 IAWQ. Published by Elsevier Science Ltd. KEYWORDS Biofilm; biological wastewater treatment; denitrification; fluidized bed bioreactor; nitrite-nitrogen.
INTRODUCTION An accumulation of nitrite concentration often occurs when nitrifying high-strength ammonium wastewater (Ganczarczyk, 1978; Cecen & Gonenc, 1995) and when denitrifying industrial wastewater (Blaszczyk et al., 1985; Wilderer et al., 1987). This accumulation of nitrite is undesirable because of its toxicity to aquatic life, and when this happens, further treatment is required to remove nitrite from the wastewater. This treatment involves the dissimilatory reduction of nitrite to nitrogen gas, and is also a shortened pathway for removing nitrogen from highly nitrogenous waste without nitrate reduction (Chen et al., 1991; Rahmani et al., 1995).
Most research on denitrification of nitrite has been carried out by using suspended-growth cultures (Beccari et al., 1983), packed bed reactors (Blaszczyk et aI., 1981; Blaszczyk, 1983; Mycielski et aL, 1983; Blaszczyk et al., 1985), or submerged biofilters (Chen et al., 1991; Cecen and Gonenc, 1995; Rahmani et al., 1995). Very little research has been done on using fluidized bed reactors. However, fluidized bed reactors offer such advantages as a high biomass concentration, resulting in 339
340
A. HIRATA and A. A. MEUTIA
higher volumetric removal with lower hydraulic retention time and greater compactness of the reactor when compared with conventional treatment systems (Hirata et al., 1990; Lazarova et aL, 1994). These advantages encouraged the use of a fluidized bed bioreactor in this study. Such re~ctors have been successfully used for treating wastewater containing phenol (Hosaka et al., 1985; H~ata. et al., 1990), coke oven waste (Hirata et al., 1991a), kitchen waste (Hirata et al., 1991b), ammonIa-nItrogen (Hirata et al., 1989) and washing of drums waste (Hirata et al., 1992). These reactors have also been used to study fluidization characteristics (Hirata and Bulos, 1990; Hirata et al., 1995) and reactor design (Hirata et al., 1985; Hirata and Noguchi, 1994). In order to understand the denitrification of nitrite in a fluidized bed, the characteristics of the biological treatment need to be clarified. In this study denitrification of nitrite-nitrogen. i~ evaluated experimentally in an anoxic two-phase fluidized bed bioreactor, and the charactenstlcs of the biological treatment is also theoretically studied.
MATERIALS AND METHODS
Reactor. The anoxic two-phase fluidized bed bioreactor system shown in Fig. 1 was used. The fluidized bed was a cylindrical acrylic column with a height of 320 cm and an internal diameter of 5 cm. Support particle. The support particle was CB (cement ball) particles made from aluminium silica (manufactured by Onoda Cement Co. Ud.) with an average 2.22 g cm-3 specific density and 0.194• 0.218 mm diameter. Microorganism. The denitrification reactor was started up with sludge from our enriched laboratory culture, this sludge having been acclimatized to a synthetic nitrite substrate for several months. The seeding sludge was added to the two-phase fluidized bed reactor and recycling operations begun with a feed of about 50 g em- 3 of the synthetic substrate. The biofilm was immobilized on the particle for several days, and recycling was then changed to continuous operation. Substrate. The synthetic substrate consisted of NaN02 (4926 g em-3), KH2P04 (2200 g em-3), NH4 HC03 (493 g em-3) and CH30H (8867 g em- 3). Excess methanol was used as the external carbon source in the reactor, the ratio by weight of methanol and nitrite being 1.8 (C/N=3.325). The substrate was continuously fed into the reactor, the nitrite-nitrogen influent concentration being between 15 and 300 g em- 3• The superficial liquid velocity (UJ varied from 400 to 950 med- 1• The calculation of some equations in this experiment used an effluent concentration of nitrite that did not reach zero. The keys used in Figures 3-7 are shown in Table 1. The water temperature was maintained at 30°C and the pH value of the influent was approximately 7. During the experiments, the pH value was increased to about 9 in the effluent. The average value for the dissolved oxygen concentration inside the reactor was around 0.2 g em-3 • Analyses. The nitrite-nitrogen concentration was measured by ion chromatography (Tosoh C8011 equipment) according to Japanese Industrial Standards (1IS). The ammonia concentration was regularly measured with an ion meter (IOC-lO, Denki Kagaku Keiki Co. Ud.), and pH was measured with a pH meter (Tpx-90 i, Toko Chemical Lab. Co. Ud.). RESULTS AND DISCUSSION Fig. 2 shows an example of the nitrite-nitrogen concentration according to the height in the reactor 3 column when Sin= 42.6 g em- and U\=441 med- 1• The nitrite-nitrogen concentration decreases gradually from the. bottom of the tw~-phase fluidized bed (influent) to the top of the reactor (effluent): .As .prevIOusly reported (HIrata et al., 1991a), it was ascertained that the hydraulic charactenstlcs m the. reactor could be approximated as plug flow, this approximation being valid throughout the expenmental range. The ammonia concentration was measured to check the removal
VI [med-1]
Sin [g·m-3]
15-25
400-450 450-500 500-550 550-600 600-700 850-950 Xb
:
.
25-30
30-35
35-45
50-60
65-70
85-90
(l-
f)-
¢Ia
ea ~c
J;;.a
Vb
Separation tank
SOcm
TABLE 1 KEYS USED IN FIGURES 3-7
..". t
_t. Effluent't •
'; r
250-300
Two-phase fluidized bed
.,1_
320Cm
~
~a b
Bioparticle Sampling spot
@c
©1
(a)7.8-11.4 kg-VS·m-3, (b)20.35 kg-VS·m-3, (c)33.60 kg-VS·m-3
Fig. 1. Two-phase fluidized bed bioreactor. 1:1
0
TABLE 2 PREVIOUS STUDIES ON mE DENITRIFICATION OF NITRATE- AND NITRITE-NITROGEN IN BIOFILM REACTORS
g: ::l
::tl
0
Type of reactor
Carbon source
Fonn of NOx-N Influent cone.
Temperature
[gom-3]
[OC]
Submerged bioflter Submerged filter Fixed film Packed bed Packed bed Packed bed
acetate molasses benzoic acid methanol acetic acid ethanol
NOz-N N03 -N, NOz-N NOz-N NOz-N NOz-N NOz-N
8.8- 35.0 - 850.0 194.0-1033.0 1000.0 1000.0 1000.0
20 13-23 25-27
Fluidized bed Fluidized bed
methanol methanol
N03 -N, NOz-N N03 -N
5.0- 100.0 6.6- 30.0
18-23
Fluidized bed
methanol
NOz-N
15.0- 300.0
-
penitrification rate Based on biomass Based on volume R./~V
[kg-N°kg-1-VSod-1]
Reference
2.
g.
[kg-Nom-3 od-1]
0-
0.20- 0.38 8.22- 9.88 0.42- 3.99
Rahmani et aI., 1995 Cecen & Gonenc, 1995 Chen et al., 1991 Blaszczyk et al., 1985 Blaszczyk et al., 1981 Mycielski et aI., 1983
0.185 (max.)
0 ::l 0
...,
R.jV
2.10 (max.) 0.36 (max.)
II> :::.
-
0.033-0.243
5.40-20.70 0.69- 3.28
Jeris & Owens, 1975 Hennanowicz & 01eng, 1990
30
0.141-2.575
3.23-18.70
This study w
....
~
A. HIRATA and A. A. MEUTIA
342
of nitrite caused by the denitrification or ammonification process. However, no ammonia was found inside the reactor, nor in the effluent during this experiment, it was thus ascertained that the removal of nitrite-nitrogen was caused by denitrification. The denitrification rate of nitrite-nitrogen in the two-phase fluidized bed was obtained in th~s l experiment on a biomass basis (R/XbV) as 0.141-2.75 kg-Nekg-1-vSed- , and for. the volu~etnc denitrification rate (~/V) as 3.23-18.70 kg-N em-3e d- l . Table 2 shows several ~revlOus studIes ~n the denitrification of nitrite and nitrate, the rate obtained in this study being hIgh compared wIth those obtained in other research work.
......
10.............."I'""'P"'l,..,.,..,.,..,.,..,~.,.,..,.,
Z
~
'e
I
cJ
= = = c:J
,,
,,
'0,
~
Cf)
.-==
I.
,,
,,
..-• Z I.
00
6
I
,,
~
'<0
~
8
> !J ....... 4
0"',..
I
e
100 200 Height [em]
~
2
~
'iiK~OO
300
150 200 In (Sin/Sout)/(Sin-Sout) [m e kg-l_N]
Fig. 2. An example of nitrite-nitrogen conc. along the height of the reactor. Sin= 42.6 g • m-3, U I= 441 m • dol
50
100
3
Fig. 3. Evaluation of biological wastewater treatment and determination ofKu and Ku/K m values.
Method for evaluating the characteristics of biological treatment in an anoxic biofilm reactor An analysis of the biological treatment characteristics of nitrite-nitrogen denitrification in an anoxic two-phase fluidized bed bioreactor was conducted according to the following assumptions: (a) steady-state conditions (b) negligible substrate inhibition and a Monod-type reaction being applicable (c) negligible contribution of free-cell (suspended) microorganisms to the overall removal rate (d) plug flow characteristics in the reactor Basic equation:
U dS +X "'._S_ I dz. b Y K +S
=
0
•
(1)
Boundary conditions:
.,.,
"'=0 S=S •
~,
::=8, 8=S.",
(2)
The following equation for evaluating the biological treatment characteristics then results:
X.v _
1
K.ln(SJS.,,)
-- - -+----R,
where
K.= /..I. ,JY
Ku K. S.,. -S.ut
(3)
Denitrification of nitrite
343
Ku and KJKm are characteristic values for quantifying denitrification, high values indicating that denitrification is well conducted. Therefore, K" and KJKm are the characteristics values for the biological treatment. While these characteristic values vary depending on the character and condition of the wastewater, environmental conditions such as temperature and pH, and on the microorganisms applied, the values are constant with varying wastewater concentration, flow rate, or biomass. From Equation 3, it can be shown that the reactor volume (V) can be rationally designed with the given values of biomass concentration (Xb), K" and KJKm obtained from the experiment, depending on the flow rate (QJ, influent concentration (SJ and effluent concentration (SouJ. The values of K" and KJKm were obtained from the experimental data resulting from Sin' Q. and Xb being varied and the other conditions being constant. In the case of plug flow, these data can be plotted as XbVJR, for the ordinate and In(Su/Soul)I(Sin-SouJ for the abscissa. With a certain character and condition of the wastewater, environmental conditions, and microorganism for which the values of Ku and KJKm are constant, a straight line can be constructed. K,jK,. can then be obtained from the slope of the straight line, and 1JKu from the intercept.
Evaluation of the characteristics of biological wastewater treatment An evaluation of the experimental results with Equation 3 is shown in Fig. 3. Although there is some scatter, which is quite common with biological treatment, the plot approximates to a straight line that does not pass through the origin. The best-fit line between Equation 3 and the experimental results proves that the denitrification of nitrite could be regarded as a Monod-type reaction. Vossoughi et al. (1982) have reported that the reduction of nitrite was a first-order reaction, while other researchers have explained denitrification in a fixed film with a simplified half-order and zero• order reaction concept (Cecen and Gonenc, 1995; Jansen and Harremoes, 1984). According to their work, nitrate-nitrogen removal was a half-order reaction at low bulk concentration, becoming a zero-order reaction when the biofilm had been fully penetrated by the substrate. Within the range of experimental conditions at which the influent nitrite-nitrogen concentration was up to 300 g-m-3, the reaction was neither first- nor zero-order; therefore, it had to be treated as a Monod-type reaction. The slope and the intercept of the straight line in Fig. 3 enabled the following characteristic values of the biological treatment to be obtained: K" = 5.0 kg-N-kg-1-VS-d- 1 Km = 0.21 kg-N-m-3 KJKm = 23.8 m3 -kg- 1-VS-d- 1 Based on the foregoing theoretical analysis, Fig. 4 shows the relationship between (Sin-SouJlln(Sj./SouJ and the denitrification rate of nitrite-nitrogen on a biomass basis (R/XbV). It can be seen that R/X., V increases as (Sin-SouJlln(SjJSouJ increases, enabling the reaction to be categorized as first• order when (Sin-SouJlln(Si./SouJ is below 0.06 kg-N-m-3• Figure 5 shows the effect of biomass per unit flow rate (~VIQJ on the effluent nitrite-nitrogen concentration (SouJ with varying influent nitrite-nitrogen concentration (SJ. The curves in Fig. 5 were plotted according to Equation 3 with the characteristic values obtained from the experiment, and the plots show that these curves were simulated very well by the experimental results. From Fig. 5, within the range of experimental conditions, SOUl could reach nearly zero when Sjn was nearly 90 g-m-3 and Xt, VIOl was greater than 0.2 kg-VSed-m-3• In the case of Sin being between 90 and 300 g-m-3 and Xt, VIOl being greater than 0.3 kg-VS-d-m- 3, SOUl could be treated as nearly zero. Using the same experimental results, Fig. 6 shows the effect of ~V/QI on the nitrite-nitrogen removal efficiency (Tl) when Sin is varied. The best-fit line between the measured points and the 3 calculated curves shows good correlation. With XbV/Q, greater than 0.3 kg-VS·d-m- , the removal efficiency was found to be almost 1. Therefore, when the influent concentration is low and the effect
A. HIRATA and A. A. MEUTIA
q-l
of S on 1] is small, the reaction can be ,n . concentration is greater, the reaction cannot of Xb V/0" 1] will decrease as the influent
. n the approximated to a first-or der type. Whe . influent 1 be approximate . d to a fiIrs t-order type . For a given va ue concentration increases.
2 •
1
Fig. 5. Effects of biomass per flow rate (X bVIQI) and influent concentration (Sin) on effluent concentration (Sout)·
Fig. 4. Relationship between (Sin-Sout)/ln(SiJSout) and denitrification rate of nitrite on a biomass basis (R/XbV).
-"'7'"
1,..,....or-T"'"'I"""'T':~~~tp.t~
-
;:0.8
I
.-=0.6
/
/
tf'l
QJ
'e z•
~
-=
ct.
QJ
Sin [g • m- 3] _. ·,-300 -. -- 200 - - -90 ... 60 --- 30 15
~ 0.4
e ~
z 0.2 o I N
0
15
't:S
CJ
Z
/
......
~
o
0.1
0.2
X bV/QI [kg-VS • d • m-
3
10
,/
I
-!J
/
~
.......
0.3
]
Fig. 6. Effects ofXbV/Q, and influent concentration on nitrite-nitrogen removal efficiency ( 1] ).
.. -:A
0""""'
1.o.I.
0.2
~
0.3 (Sin- Sout)/In (Sin/Sout) [kg • m -3]
o
0.1
3
X b [kg-VS • m- ] -40.0 ---30.0 . - . 20.0 ---10.0 - .. - 7.5 -' .. - 5.0
Fig. 7. Effects of biomass concentration (Xb) and (Sin-Sout)!ln (SdSout) on volumetric denitrification rate (RtM.
The effects of biomass concentration (Xb) and (Sin-SouJl1n(SiJSouJ on the volumetric denitrification rate (~N) shows that R/V increases as ~ increases (Fig. 7). Within the range of the experimental
Denitrification of nitrite
345
conditions, a maximum value of 18.7 kg-N em-3e d- 1 was achieved for the volumetric nitrite denitrification rate with this reactor. This value is 2 to 15 times as high as the results obtained by other researchers who studied the denitrification of nitrite (Table 2) in a suspended-growth culture (Beccari et al., 1983), packed bed reactor (Blaszczyk et al., 1981; Blaszczyk, 1983; Blaszczyk et al., 1985; Mycielski et al., 1983), or submerged biofilter (Cecen and Gonenc, 1995; Chen et aI., 1991; Rahmani etal., 1995). However, this is almost the same value as that obtained for the volumetric denitrification rate for nitrate in a fluidized bed reactor (Jeris and Owens, 1975), proving that the use of the two-phase fluidized bed bioreactor enhanced the capacity to denitrify nitrite-nitrogen.
CONCLUSIONS The following conclusions could be drawn from the results. 1. Equation 3 for evaluating the characteristics of biological treatment in a plug flow type of anoxic biofilm reactor is proposed. A method for evaluating the characteristic values of biological treatment, K,. and KJKm, is also proposed. 2. The experimental results arranged by using the proposed evaluation equation show that the denitrification of nitrite-nitrogen must be treated as a Monod-type reaction within the experimental range considered. Characteristic values to quantify the biological treatment of K,.= 5.0 kg-Nekg-1-VSed- 1 and KJKm = 23.8 m3e kg- 1-VSed- 1 were obtained. The experimental results correlate well with the calculated line. 3. The maximum volumetric nitrite denitrification rate of 18.7 kg-N em-3e d- 1 was achieved within the range of the experimental conditions used. This value is higher than the results from other biofilm research because of the greater efficiency of the anoxic two-phase fluidized bed bioreactor for carrying out the denitrification of nitrite.
NOMENCLATURE H
=
reactor height [m] saturation constant for nitrite-nitrogen [kg-N em-3] K,. = f.1 mlY [kg-Nekg-1-VSed- l ] O. = volumetric liquid flow rate [m 3e d- l ] ~ OI(Sin-SouJ [kg-Ned-I] S = nitrite-nitrogen concentration [kg-N em-3] VI = superficial liquid velocity [m ed-I] V = bed volume [m3] Xb = biomass concentration [kg-VSem-3] Y = yield factor based on nitrite-nitrogen [kg-VSekg-1-N] = distance from bottom of fluidized bed reactor [m] z 1] = nitrite-nitrogen removal efficiency TJ == I-Sou/Sin [-] f.1 m = maximum specific growth rate [d- l ] Subscripts in = influent out = effluent
Km
=
REFERENCES Beccari, M., Passino, R., Ramadori, R. and Tandoi, V. (1983). Kinetics of dissimilatory nitrate and nitrite reduction in suspended growth culture. J. Water Pol/ut. Control Fed., 55 (1), 58-63. Blaszczyk, M., Przytocka-Jusiak, M., Kruszewska, V. and Mycielski, R. (1981). Denitrification of
346
A. HIRATA and A. A. MEUTIA
high concentrations of nitrites and nitrates in synthetic medium with different sources of organic . carbon I. acetic acid. Acta Microbiologica Polonica, 30 49-58. Blaszczyk, M. (1983). Effect of various sources of organic carbon and high nitri~e and mtrate concentrations on the selection of denitrifying bacteria. II. Continuous cultures In packed bed reactors. Acta Microbiologica Polonica, 32 (1) 65-71. Blaszczyk, M., Galka, E., Sakowicz, E. and Mycielski, R. (1985). Denitrification of hi~ concentrations of nitrites and nitrates in synthetic medium with different sources of organic carbon III. methanol. Acta Microbiologica Polonica, 34 195-206. Cecen, F. and Gonenc, I. E. (1995). Criteria for nitrification and denitrification of high-strength wastes in two upflow submerged filters. Water Environ. Res., 67 (2) 32-142. Chen, S. K, Juaw, C. K and Cheng, S. S. (1991). Nitrification and denitrification of high-strength ammonium and nitrite wastewater with biofilm reactors. Wat. Sci. Tech., 23 (7-9) 1417-1425. Christensen, F. R, Kristensen, G. H. and Jansen, J. la C. (1989). Biofilm structure-an important and neglected parameter in wastewater treatment. Wat. Sci. Tech., 21(8/9),805-814. Ganczarczyk, J. J. (1978). Second-stage activated sludge treatment of coke-plant effluents. Wat. Res., 13 337-342. Hermanowicz, S. W. and Cheng, Y. W. (1990). Biological fluidized bed reactor: hydrodynamics, biomass distribution and performance. Wat. Sci. Tech., 22 (1/2) 193-202. Hirata, A, Bolus, F. B. and Noguchi, M. (1995). Correlation for bed voidage in three-phase fluidized bed. J. Chern. Eng. Japan, 28 (4) 400-404. Hirata, A. and Noguchi, M. (1994). Biological wastewater treatment by three-phase fluidization• characteristics and basic design method. Wat. Sci. Tech., 30 (11) 91-100. Hirata, A., Umezawa, H., Endou, E. and Hosaka, Y. (1992). Biological treatment of wastewater from the washing of oil and chemical drums in a three-phase fluidized bed. Int. Chern. Eng., 32 (3) 578-584. Hirata, A, Takahashi, C. and Arai, M. (1991a). Biological treatment of coke oven wastewater in a three-phase fluidized bed. Environ. Conservation Eng., 20 183-192. Hirata, A, Takahashi, C. and Takahashi, T. (1991b). Treatment of kitchen wastewater in complete mixing three-phase fluidized bed bioreactor. Suishitsu Odaku Kenkyuu, 14 730-736. Hirata, A, Hosaka, Y. and Umezawa, H. (1990). Characteristics of simultaneous utilization of oxygen and substrate in a three-phase fluidized bed bioreactor. J. Chern. Eng. Japan, 23 (3) 303-307. Hirata, A. and Bulos, F. B. (1990). Predicting bed voidage in solid liquid fluidization. J. Chern. Eng. Japan, 23 (5) 599-604. Hirata, A, Hosaka Y., Basuki, B. T., Maeda, K (1989). Nitrification of ammonia nitrogen in a three-phase fluidized. Suishitsu Odaku Kenkyuu, 12 (9) 575-58l. Hosaka, Y., Kaihou M. and Hirata, A. (1985). Biological treatment of phenolic wastewater in a three-phase fluidized bed. Wat. Sci. Tech., 17(8), 1437-1439. Jansen, J. la C. and Harremoes, P. (1984). Removal of soluble substrates in fixed films. Wat. Sci. Tech. 17(2/3), 1-14 Jeris, J. S. and Owens, R W. (1975). Pilot-scale, high-rate biological denitrification. J. Water Pollut. Control Fed., 47 (8) 2043-2057. Lazarova, V. and Manem, J. (1994). Advances in biofilm aerobic reactors ensuring effective biofilm activity control. Wat. Sci. Tech., 29 (10-11) 319-327. Mycielski, R, Blaszczyk, M., Jackowska, A and Olkowska, H. (1983). Denitrification of high concentrations of nitrites and nitrates in synthetic medium with different sources of organic . carbon II. ethanol. Acta Microbiologica Polonica, 32 381-388. Rahmani, H., Rols, J~ L., Capdeville, B., Cornier, 1. C. and Deguin, A. (1995). Nitrite removal by a fixed culture m a submerged granular biofilter. Wat. Res., 29 (7) 1745-1753. Vossoughi, M., Laroche, M., Navarro, J. M., Faup, G. and Leprince, A. (1982). Continuous denitrification by immobilized cells. War. Res., 16 995-1002. Wilderer, ~. A., Jones, W. L. and Dau, U. (1987). Competition in denitrification systems affecting reductIOn rate and accumulation of nitrite. Wat. Res., 21 (2) 239-245.