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Screening method for evaluation of inhibition of nitrification in Sweden
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Wal. Sci. Tech. Vol. 40, No.2, pp. 175-178, 1999 C 1999IAWQ
Pergamon
Publishedby ElsevierScience Ltd Printed in Great Britain. All rights reserved 0273-1223199 520.00 + 0.00
PII: S0273-1223(99)00477-1
SCREENING METHOD FOR EVALUATION OF INHIBITION OF NITRIFICATION IN SWEDEN K. Jonsson and J. la C. Jansen Department 0/Building and Environmental Technology, Lund Institute ofTechnology, 118, SE-221 00 Lund, Sweden
P.O. Box
ABSTRACT An investigation with respect to inhibition of nitrification of wastewater from 109 Swedish municipal wastewater treatment plants was performed. Flow proportional, 24·hour composite samples were collected during one week, and then analysed using the screening method. Inhibition of nitrification above 10% was found at only 20 plants. In general, the load of inhibiting substances is limited in Swedish munic ipal wastewater according to this study . The inhib ition found is not connected to any special category of treatment plants with respect to the size of the plant. Neither was any general pattern of inhibition during the week found in this investigation. It was also shown that the screening method can be used for detecting small quantities of inhibiting substances if different dilutions of the same sample are analysed.
KEYWORDS Inhibition; nitrification; nitrogen removal; screening method; toxicity; wastewater INTRODUCTION During the next decades, several wastewater treatment plants in Sweden will have to fulfil outlet demands of about 10-15 mg tot-Nil. Many plants will probably be reconstructed for biological nitrification and denitrification. As for every biological system, this can be affected by toxic substances occurring in incoming wastewater. Furthermore, nitrification is performed by two very limited groups of bacteria, which means that if one group of nitrifiers is inhibited, there is no other group of bacteria that can compensate for the loss. Another thing that characterises nitrifiers is the comparatively slow growth rate. This in its turn. means that the aerobic part of a wastewater treatment plant with nitrification is usually dimensioned with respect to the nitrification process, and a reduction of the process rate will affect the outlet of nitrogen, especially during winter. Inhibition of nitrification has been noticed at some wastewater treatment plants in Sweden, and a few local studies have been performed to measure inhibition of nitrification (JOnsson et al., 1996). A Danish investigation shows that inhibition of nitrification is a widespread phenomenon in our neighbouring country (Laursen and Jansen, 1995). A corresponding investigation has until now not existed in Sweden.
17S
K. JONSSON and J. LA C. JANSEN
176
MATERIAL AND METHODS In this study, wastewater from 109 different wastewater treatment plants in Sweden has been analysed. The 109 plants comprise about 6.3 million pe, and have been selected so that more than 98% of all municipal wastewater in Sweden that could possibly be subjected to outlet demands for nitrogen in the future are included. During a whole week, flow proportional, 24-hour composite samples were collected and frozen before analysis. At first, samples of three weekdays were analysed. If inhibition was found in any of the samples, the remaining four samples were tested . All samples have been tested twice with a concentration of 50% wastewater. The inhibition of nitrification was examined using a screening method developed in Denmark and Sweden (Arvin et al., 1994; Swedish EPA, 1995) . The basic principle of the method is that nitrifying activated sludge is mixed with a synthetic nutrient solution containing (NH4)zS04 and NaHC03 • The suspension is mixed with tap-water and the wastewater under consideration, in proportions which secure the proper dilution of the wastewater. The mixture is shaken for 120 minutes, and then the nitrification is stopped by filtration and cooling of the samples. Nitrification inhibition is found by comparing the nitrate production in samples containing wastewater with reference samples without wastewater (see Figure 1).
tap water , \ I-f 0
\4~ J i '.
r
.
ac tIvaled sind re
\,
~ ~ -. JI] ~ ~ J r: dupli ate (1%
sample I ur tap w l er t reference )
tJ
--1
....-.=0
['x-
X
-. ~
1J J
-.. Anal 'sis
1 1 ~ 1J 1
shakinu 120 m in
rer
110 11
coo ling
. lop ped hy
filtration
Figure 1_ Schematic description of the screening method for determination of inhibition of nitr ification.
Inhibition ('Xl) 100
o --
o
........-...a--...........
10.000
L.....LI.... W
~...IdIu.bLt1WlahI_~
10 .000 - 2 .000
:
2 -.000 - 100 .000
. 101l.OOO
Person equivalents connected to the plant Figure 2. Maximum inhibition determined for each plant as a function of the size of the plant.
RESULTS AND DISCUSSION Compared to the previously mentioned Danish study, inhibition of nitrification occurs much less frequently in Swedish wastewater. Values of 10% inhibition of nitrification or above were only found at 20 plants. The
Screening method for evaluation of inhibition of nitrification
177
results show that in general the load of inhibiting substances is limited at Swedish wastewater treatment plants . It does not mean that occasional cases of high inhibition of nitrification, caused by accidents or spills of chemicals, will not exist, but it means that there are not constantly large quantities of inhibiting substances in Swedish wastewater. In Figure 2, the maximum inhibition determined for each plant is plotted versus the size of the plant, and it is seen that the inhibition found is not connected to any special category of treatment plants.!n this study, no general pattern of inhibition can be distinguished for the treatment plants where inhibition is found. For some plants, essential inhibition is found most days of the week (Figure 3a) while other plants are affected by inhibition only occasionally (Figure 3b). For the treatment plant represented by Figure 3b, the highest inhibition value occurs on the Friday. This was also the case in a previous investigation with daily sampling at a wastewater treatment plant for more than one year, see Figure 3c (Jonsson et al., 1996). The reason for the "Friday effects" like these could be that discharge of inhibitory substances is related to cleaning procedures, and that these take place especially just before weekends . Figures 3a and 3c represent the same wastewater treatment plant, and it is seen that different strategies of sampling can lead to significantly different results. Inlnbition (%)
a
100
50 0
Inhibition (%)
50
kJJ,.,.lJ
0
M T W T F S S
Inhibition (%)
b
100
100 50
f
0
[ -[ - I
MTWTFSS
C
~ M T W T F S S
Figure 3. Variation of inhibition for a) treatment plant I during one week and b) treatment plant II during one week. c) The mean inhibition for the days of the week when daily sampling for more than one year was performed at plant
Inhibiting substances in municipal wastewater are often very diluted, and in order to detect the existence of these small amounts, a sensitive method is needed . The limit of detection for the screening method in this study has been calculated to be 5% (Jonsson et al., 1999).
Inhibit"m ' (%)
Planlt\
10
5
0 20% 50%
o -5
on
. 'uc
cd
u
•
0%
- 10
Inhibition (%) 10
..lU ll
/I
5
0 20%
o -5 - 10
0%
ion
TIm
Fri
at
lUI
•
0%
Figure 4. Variation of inhibition when the samples from two plants with moderate inhibition were analysed in different dilutions .
As a part of this investigation, some of the wastewater samples were analysed in different dilutions . In Figure 4, the results obtained with samples from two different treatment plants are shown . For plant A. a larger percentage of wastewater corresponds to a higher inhibition value . This means that even though most values are below the limit of detection , it is possible to draw the conclusion that inhibiting substances are
K. JONSSON and J. LA C. JANSEN
178
present in the influent of this treatment plant. For plant B, the inhibition of nitrification varies at random below and above zero. This indicates that the results reflect the uncertainty of the method rather than presence of inhibiting substances in the sample. CONCLUSIONS In this study, 10% inhibition of nitrification or above was only found at 20 out of 109 plants. In general, the load of inhibiting substances is limited in Swedish municipal wastewater. The inhibition found is not connected to any special category of treatment plants with respect to the size of the plant. No general pattern of inhibition during the week was found in this investigation. It is possible to detect even small quantities of inhibiting substances if different dilutions of the same sample are analysed.
ACKNOWLEDGEMENTS The authors would like to thank VA-FORSK and NUTEK (the STAMP-programme) for financial support. REFERENCES Arvin, E., Dyreborg, S., Menck, C. and Olsen, J. (1994). A mini-nitrification test for toxicity screening, MINNTOX. Wat. Res. 28(9), 2029-203 t. Jonsson, K., Grunditz, c., Dalhamrnar, G. and Jansen, 1. la C. (1999). Occurrence of mtnfication inhibition in Swedish municipal wastewaters. (submitted) Jonsson, K., Magnusson, P., Jonsson, L-E., Hellstrom, B. G. and Jansen, J. la C. (1996). Identifying and fighting inhibition of nitrification at Oresundsverket. Wat. Sci Tech., 33(12), 29-38. Laursen, K. D. and Jansen, J.la C. (1995). Are 50% of the Danish wastewater treatment plants inhibited? (Er 50 % af danske renseanleeg hremmede?). Stads- og havneingenieren, 2, 41-43. (In Danish) Swedish EPA (1995). Screening method for estimation of inhibition of mtnfication at municipal wastewater treatment plants. (Screemngmetod for bestamning av nitrifikanonshamnmg - vid dnft av kommunala avloppsrenmgsverk). Report No. 4424. (In Swedish)
Wal. Sci. Tech. Vol. 40, No.2, pp. 175-178, 1999 C 1999IAWQ
Pergamon
Publishedby ElsevierScience Ltd Printed in Great Britain. All rights reserved 0273-1223199 520.00 + 0.00
PII: S0273-1223(99)00477-1
SCREENING METHOD FOR EVALUATION OF INHIBITION OF NITRIFICATION IN SWEDEN K. Jonsson and J. la C. Jansen Department 0/Building and Environmental Technology, Lund Institute ofTechnology, 118, SE-221 00 Lund, Sweden
P.O. Box
ABSTRACT An investigation with respect to inhibition of nitrification of wastewater from 109 Swedish municipal wastewater treatment plants was performed. Flow proportional, 24·hour composite samples were collected during one week, and then analysed using the screening method. Inhibition of nitrification above 10% was found at only 20 plants. In general, the load of inhibiting substances is limited in Swedish munic ipal wastewater according to this study . The inhib ition found is not connected to any special category of treatment plants with respect to the size of the plant. Neither was any general pattern of inhibition during the week found in this investigation. It was also shown that the screening method can be used for detecting small quantities of inhibiting substances if different dilutions of the same sample are analysed.
KEYWORDS Inhibition; nitrification; nitrogen removal; screening method; toxicity; wastewater INTRODUCTION During the next decades, several wastewater treatment plants in Sweden will have to fulfil outlet demands of about 10-15 mg tot-Nil. Many plants will probably be reconstructed for biological nitrification and denitrification. As for every biological system, this can be affected by toxic substances occurring in incoming wastewater. Furthermore, nitrification is performed by two very limited groups of bacteria, which means that if one group of nitrifiers is inhibited, there is no other group of bacteria that can compensate for the loss. Another thing that characterises nitrifiers is the comparatively slow growth rate. This in its turn. means that the aerobic part of a wastewater treatment plant with nitrification is usually dimensioned with respect to the nitrification process, and a reduction of the process rate will affect the outlet of nitrogen, especially during winter. Inhibition of nitrification has been noticed at some wastewater treatment plants in Sweden, and a few local studies have been performed to measure inhibition of nitrification (JOnsson et al., 1996). A Danish investigation shows that inhibition of nitrification is a widespread phenomenon in our neighbouring country (Laursen and Jansen, 1995). A corresponding investigation has until now not existed in Sweden.
17S
K. JONSSON and J. LA C. JANSEN
176
MATERIAL AND METHODS In this study, wastewater from 109 different wastewater treatment plants in Sweden has been analysed. The 109 plants comprise about 6.3 million pe, and have been selected so that more than 98% of all municipal wastewater in Sweden that could possibly be subjected to outlet demands for nitrogen in the future are included. During a whole week, flow proportional, 24-hour composite samples were collected and frozen before analysis. At first, samples of three weekdays were analysed. If inhibition was found in any of the samples, the remaining four samples were tested . All samples have been tested twice with a concentration of 50% wastewater. The inhibition of nitrification was examined using a screening method developed in Denmark and Sweden (Arvin et al., 1994; Swedish EPA, 1995) . The basic principle of the method is that nitrifying activated sludge is mixed with a synthetic nutrient solution containing (NH4)zS04 and NaHC03 • The suspension is mixed with tap-water and the wastewater under consideration, in proportions which secure the proper dilution of the wastewater. The mixture is shaken for 120 minutes, and then the nitrification is stopped by filtration and cooling of the samples. Nitrification inhibition is found by comparing the nitrate production in samples containing wastewater with reference samples without wastewater (see Figure 1).
tap water , \ I-f 0
\4~ J i '.
r
.
ac tIvaled sind re
\,
~ ~ -. JI] ~ ~ J r: dupli ate (1%
sample I ur tap w l er t reference )
tJ
--1
....-.=0
['x-
X
-. ~
1J J
-.. Anal 'sis
1 1 ~ 1J 1
shakinu 120 m in
rer
110 11
coo ling
. lop ped hy
filtration
Figure 1_ Schematic description of the screening method for determination of inhibition of nitr ification.
Inhibition ('Xl) 100
o --
o
........-...a--...........
10.000
L.....LI.... W
~...IdIu.bLt1WlahI_~
10 .000 - 2 .000
:
2 -.000 - 100 .000
. 101l.OOO
Person equivalents connected to the plant Figure 2. Maximum inhibition determined for each plant as a function of the size of the plant.
RESULTS AND DISCUSSION Compared to the previously mentioned Danish study, inhibition of nitrification occurs much less frequently in Swedish wastewater. Values of 10% inhibition of nitrification or above were only found at 20 plants. The
Screening method for evaluation of inhibition of nitrification
177
results show that in general the load of inhibiting substances is limited at Swedish wastewater treatment plants . It does not mean that occasional cases of high inhibition of nitrification, caused by accidents or spills of chemicals, will not exist, but it means that there are not constantly large quantities of inhibiting substances in Swedish wastewater. In Figure 2, the maximum inhibition determined for each plant is plotted versus the size of the plant, and it is seen that the inhibition found is not connected to any special category of treatment plants.!n this study, no general pattern of inhibition can be distinguished for the treatment plants where inhibition is found. For some plants, essential inhibition is found most days of the week (Figure 3a) while other plants are affected by inhibition only occasionally (Figure 3b). For the treatment plant represented by Figure 3b, the highest inhibition value occurs on the Friday. This was also the case in a previous investigation with daily sampling at a wastewater treatment plant for more than one year, see Figure 3c (Jonsson et al., 1996). The reason for the "Friday effects" like these could be that discharge of inhibitory substances is related to cleaning procedures, and that these take place especially just before weekends . Figures 3a and 3c represent the same wastewater treatment plant, and it is seen that different strategies of sampling can lead to significantly different results. Inlnbition (%)
a
100
50 0
Inhibition (%)
50
kJJ,.,.lJ
0
M T W T F S S
Inhibition (%)
b
100
100 50
f
0
[ -[ - I
MTWTFSS
C
~ M T W T F S S
Figure 3. Variation of inhibition for a) treatment plant I during one week and b) treatment plant II during one week. c) The mean inhibition for the days of the week when daily sampling for more than one year was performed at plant
Inhibiting substances in municipal wastewater are often very diluted, and in order to detect the existence of these small amounts, a sensitive method is needed . The limit of detection for the screening method in this study has been calculated to be 5% (Jonsson et al., 1999).
Inhibit"m ' (%)
Planlt\
10
5
0 20% 50%
o -5
on
. 'uc
cd
u
•
0%
- 10
Inhibition (%) 10
..lU ll
/I
5
0 20%
o -5 - 10
0%
ion
TIm
Fri
at
lUI
•
0%
Figure 4. Variation of inhibition when the samples from two plants with moderate inhibition were analysed in different dilutions .
As a part of this investigation, some of the wastewater samples were analysed in different dilutions . In Figure 4, the results obtained with samples from two different treatment plants are shown . For plant A. a larger percentage of wastewater corresponds to a higher inhibition value . This means that even though most values are below the limit of detection , it is possible to draw the conclusion that inhibiting substances are
K. JONSSON and J. LA C. JANSEN
178
present in the influent of this treatment plant. For plant B, the inhibition of nitrification varies at random below and above zero. This indicates that the results reflect the uncertainty of the method rather than presence of inhibiting substances in the sample. CONCLUSIONS In this study, 10% inhibition of nitrification or above was only found at 20 out of 109 plants. In general, the load of inhibiting substances is limited in Swedish municipal wastewater. The inhibition found is not connected to any special category of treatment plants with respect to the size of the plant. No general pattern of inhibition during the week was found in this investigation. It is possible to detect even small quantities of inhibiting substances if different dilutions of the same sample are analysed.
ACKNOWLEDGEMENTS The authors would like to thank VA-FORSK and NUTEK (the STAMP-programme) for financial support. REFERENCES Arvin, E., Dyreborg, S., Menck, C. and Olsen, J. (1994). A mini-nitrification test for toxicity screening, MINNTOX. Wat. Res. 28(9), 2029-203 t. Jonsson, K., Grunditz, c., Dalhamrnar, G. and Jansen, 1. la C. (1999). Occurrence of mtnfication inhibition in Swedish municipal wastewaters. (submitted) Jonsson, K., Magnusson, P., Jonsson, L-E., Hellstrom, B. G. and Jansen, J. la C. (1996). Identifying and fighting inhibition of nitrification at Oresundsverket. Wat. Sci Tech., 33(12), 29-38. Laursen, K. D. and Jansen, J.la C. (1995). Are 50% of the Danish wastewater treatment plants inhibited? (Er 50 % af danske renseanleeg hremmede?). Stads- og havneingenieren, 2, 41-43. (In Danish) Swedish EPA (1995). Screening method for estimation of inhibition of mtnfication at municipal wastewater treatment plants. (Screemngmetod for bestamning av nitrifikanonshamnmg - vid dnft av kommunala avloppsrenmgsverk). Report No. 4424. (In Swedish)