- Email: [email protected]
Identifying and fighting inhibition of nitrification at Öresundsverket
~
Wat. Sci. Tech. Vol. 33. No. 12. pp. 29-38. 1996. Copyright C 1996IAWQ. Pubhshed by ElsevIer ScIence Ltd Printed in Great Britain. All rights reserved. 0273-1223196 SIS·OO + 0-00
Pergamon
PH: S0273-1223(96)00454-4
IDENTIFYING AND FIGHTING INHIBITION OF NITRIFICATION AT ORESUNDSVERKET Karin Jonsson*, Peter Magnusson**, Lars-Erik Jonsson**, Bengt Goran Hellstrom*** and Jes la Cour Jansent • Department of Water and Environmental Engineering. Lund Institute of Technology. Box 118. S-221 DO Lund. Sweden •• Helsingborg Water and Sewage Works. Gdseblicksviigen 4. S-252 27 Helsingborg. Sweden ... RUST VA.Projekt AB. Box 47D05. S·IDO 74 Stockholm, Sweden t Aved¢re Wastewater Treatment Plant. Kanalholmen 28. DK-2650 Hvidovre. Denmark
ABSTRACT After extension of Oresundsverket in Helsingborg severe nitrification problems have occurred. Complete inhibition of nitrification has been recognized once and a general reduction of nitrification capacity has been found compared to design, to other Swedish treatment plants and to internationally accepted design criteria. A comprehensive examination of inhibition of nitrification has identified industrial sourcc:s as the dominating contributors. Some industries have been identified as important sources but fighting inhibition of nitrification requires more than tracking down a few dominating industries, since examination shows that discharges of inhibitory substances are widespread among the industries in the catchment area. Naturally, fighting inhibition of nitrification requires the elimination of contributions from industries with identified discharge. Furthermore information campaigns directed towards the industries in general are required and fmally it is necessary to include requirements for inhibitory substances in the industrial discharge permits. Copyright 1996lAWQ. Published by Elsevier Science Ltd.
KEYWORDS Inhibition: nitrification: nitrogen removal: toxicity: wastewater.
INTRODUCTION The Wastewater Treatment Plant of Helsingborg, Oresundsverket, is the first plant in Sweden, which is designed for extended nitrogen removal. Since its extension in 1992, a comprehensive full scale test programme has been performed in order to establish experience under Swedish conditions with respect to combined nitrOgen and 29
K. JONSSON ~, al.
30
phosphorus removal. During the test programme it became obvious that inhibition of nitrification and poor sludge settling properties became important issues for examination since these problems very seriously influenced the test programme. Below, results from studies and strategies for fighting the inhibition of nitrification are presented.
ORESUNDSVERKET IN HELSINGBORG Oresundsverket was renewed in 1992. The former high loaded activated sludge system was extended into an activated sludge system for nitrogen and phosphorus removal designed for 220,000 p.e. The plant was further provided with postfiltration for polishing of suspended solids and phosphorus. The plant is constructed in four separate lines, which make an excellent basis for full scale experiments and optimization. Each line can be operated individually from inlet to filtration unit. Basically, the system comprises a recycling system for predenitrification which can be combined with phosphorus removal as pre-precipitation, simultaneous precipitation or biological phosphorus removal and completed with post-precipitation. Figure 1 shows an air photo of the plant. Table I and table 2 give the basic technical information of the plant and the characteristics of the influent and of the discharge requirements.
Fig. I. Air photo of Oresundsverket in Helsingborg. TABLE 1. TECHNICAL INFORMATION OF ORESUNDSVERKET. Number Primary clarifiers Activated sludge treatment anaerobic/anoxic anoxic anoxic/aerobic anoxic/aerobic aerobic anoxic Final clarifiers Filters
8 4 4 4 4 4 4 16 12
Area (m2)
Volume (ml )
8·300
8·1125
16·330 12· 50
4·1020 4·3100 4·1020 4·1020 4·1504 4· 535 16·1320
31
Identifying and fighting inhibition of nitrification
TABLE 2. CHARACTERISTICS OF THE INFLUENT AND DISCHARGE UMITS AT ORESUNDSVERKET. Influent 3
ClJIm (m /h)
Flow (m3/d) COD (mgtl) BOD, (mgll) Tot-N (mgll) Tot-P (mgtl) Temp. (monthly mean values, 0c)
3250 S4000 420 130 33 5.7 10-19
Discharge limits (annual mean values) Target value
Trial period criteria
10 8 0.3
10 12 0.3
INHIDITION OF NITRIFICATION The extended plant was started up in 1992. As a part of the test progranune many on-line sensors and a comprehensive programme for chemical analyses were established. During the first winter of operation poor sludge properties were noticed and consequently it was impossible to keep a sufficient amount of sludge to maintain the aerobic sludge age corresponding to the design capacity. The plant however is not fully loaded and, consequently, the nitrogen removal could be kept at an acceptable level. In March 1993 a severe case of inhibition of nitrification occurred. The on-line meteB for ammoniwn and nitrate showed that on the 2nd of March something stopped nitrification completely. The plant was operated with two lines with simultaneooS precipitation, one line with pre-precipitation and one line with biological phospholllS removal. Figure 2 shows the results of ammonia measurements from these three different processes. It is seen that the effluent normally shows a weekly variation, and that nitrification completely disappeared on the 2nd of March. Full nitriflC8tion was re-established three weeks later. The same pattern is seen for all lines, but it seems as if the pre-precipitation system re-established faster than the other systems. It was impossible to fmd the reason for the accident, but since the plant serves the Helsingborg Municipality, where several big industries are located, it was decided to initiate a progranune for examination of inhibition from the major industries and from selected industries from branches well represented in the catchment area. Based on the very comprehensive test programme at the treatment plant, it is possible to calculate the necessary aerobic sludge age to keep full nitrification. For the lines operated with simultaneooS precipitation, as well as for the line with biological phospholllS removal, the critical sludge age adjusted to lSoC is found to be around 12 days (Magnusson and JOnsson, 1995). This value is much higher than reported from other Swedish treatment plants where nitrogen removal experiments have been performed (Swedish EPA, 1991). Values in the range of 5-8 days are given in agreement with internationally accepted design figures in EPA (1975), where values around 6 days of aerobic sludge age are sufficient at 15°C. This fmding of an unusually high necessary sludge age compared to general accepted design rules understated the need for examination of the wastewater discharged to the plant.
INDUSTRIAL DISCHARGE TO QRESUNDSVERKET The industry in Helsingborg is dominated by a few big factories in chemical, pharmaceutical and food industry and by a great number of small industries where especially printing companies are common. Figure 3 shows the contribution from the industry and from households to the treatment plant related to flow, organic matter (BOD,) and nitrogen. It is seen that the industry makes up a very significant part of the mass flow to the plant.
K. J6NSSON ~, al.
32
NH.-N in the outlet (mgtl) 25 T 20 -
15 10-;-
5
oLa~~iiY I-mar
IS-feb -M-
Bio-P
IS-mar __ Pre-precipitation
I-apr
IS-apr
.~ Simultaneous precipitation
Fig. 2. Inhibition accident in March 1993.
Flow Average: 54,000 mJtd
BOD 7 Average: 7,000 kgtd
Tot-N Average: 1,800 kgtd
() . .
_Industrial wastewater DLeachate _ Domestic wastewater c::::ILeakage
Fig. 3. Industrial and household contribution to the load of Qresundsverket.
EXAMINATION OF INHIBmON OF NITRIFICATION FROM INDUSTRIES IN THE CATCHMENT AREA OF ORESUNDSVERKET As a way to find methods how to judge the effect of different industries discharge of wastewater to the municipal wastewater treatment plants. Swedish EPA did carry out a study of the toxicity of wastewater from about ten different industries in Helsingborg during November 1992. Different methods for evaluation of the toxicity from industrial effluent were used and tests for inhibition of nitrification were included since such methods are believed to be closer to the processes in wastewater treatment plants than traditional ecotoxicology tests. During one week samples were taken from 10 industries. the local dump site and influent and effluent at the treatment plant. The whole examination is reported in Swedish EPA. 1993. and in figure 4 the nitrification inhibition found in a 20 % solution from the most important industries is shown. The dump site and the effluent from the treatment plant showed no inhibition on nitrifying bacteria. It is seen that the different industries exhibit a very different inhibition pattern. Some industries have almost constant inhibition (on different levels) whereas others vary much from day to day. Furthennore several industries have no discharge of wastewater during weekends. (n table 3 the six most important industries are ranked according to emission of substances which inhibit nitrification.
33
Identifying and fighting inhibition of nitrification
,~~~~:r--------l18 ~ 1ZI ClMmIal l\.1---....__- - - - - 1 ~ Food l1!IPrlalin&
'-"
l\.Jl...AN--l\.N'I-----~
MIXl
TIIlI
Wed
1bu
Fri
Sal
1ZI ClMmIal ~ ClMmIal
s..
Fig. 4. Inhibition of nitrification found during one week at six industries. The inhibition was found using a slightly modified version of ISO 9509 (1989) and a new screening method (Swedish EPA. 1995) close to the Minntox method presented in Arvin et al. (1994). The two methods gave similar results. Figure 4 is based on results from the screening method, which later on was established as a routine measurement at the laboratory of the plant. The basic principles of the screening method is that nitrifying activated sludge is mixed with a synthetic IDltriem solution containing (NHJ1S04 and NaHC03• The suspension is mixed with tap-water and the wastewater under consideration in proportion which secure the proper dilution of the wastewater. The mixture is shaken during 120 minutes, the nitrification is stopped by filtration and cooling of the samples. Nitrification inhibition is found by comparing the nitrate production (or ammonia removal) in samples containing wastewater with reference samples without wastewater.
TABLE 3. RANKING OF INDUSTRIES ACCORDING TO DISCHARGE OF INHIBITORY SUBSTANCES. Branch
Chemical Food industry Chemical Chemical Printing Pharmaceutical
Inhibition in 20 % solution mean value (%)
Mean flow (m3/d)
28 20 60 43 60 9
679 562 18 18 3.6 30
K. JONSSON et aI.
34
MEASURES TAKEN TO FIGHT THE NlTRIFICAnON INHmITION The results from the examination showed such dramatic inhibition from some industries that action had to be taken. The action comprised of three parts: - Start up of a programme for routine measurement of inlubition at the influent of the plant and detailed examination of variation of nitrification capacity of the sludge. - Direct contact to and examination of industries where previous examinations showed high inhibition. - General awareness campaigns directed towards the industries to minimize discharge of substances toxic for biological processes. The programme for routine measurement of inlubition of the influent started in May 1993 and has now been running for more than one year. A flow proponional. 24-hour composite sample from the influent is collected every day and then frozen for later analysis of inhibition of nitrification. The sludge used for the examination is sludge from Oresundsverket. but sludge from the Klagshamn Wastewater Treatment Plant in MalmO is tested in parallel. The industrial load to this plant is minor and investigations have shown that inhibition is negligible. Figure 5 shows one and a half year of nitrifICation inhibition measured using sludge from Oresundsverket. The wastewater is tested in a high concentration (SO % wastewater). It is seen that great variation exists. However. a general trend is immediately visible. During summer holidays and other periods. when the industries are closed. the inhibition decreases. Figure 6 furthermore shows the mean inhibition for the days of the week. It is seen that inhibition decreases during weekends. when the industries are closed. and that Fridays are especially critical. The reason for this could be that the discharge of inhibitory substances is related to cleaning procedures. and that these especially take place just before the week~nds. Inhibition (%)
20
o
May93 Jun93 Jul93 Aug93 Sep93 Oct93 N0v93 Dcc93 Jan94 Fcb94 Mar94 Apr94 May94 Jun94
Fig. S. Daily measurements of nitrifICation inhibition at Oresundsverket. Measurements of inhibition of sludge from the Klagshamn Plant as well as sludge from Oresundsverket give a possibility to see if any adaptation of the sludge takes place. Figure 7 shows the inhibition found on the Klagshamn sludge as a function of the inhibition found on the sludge from Oresundsverket. It is seen that inhibition is signifICant on both sludges. It seems to be the case that the effect al moderate inhibition is highest on the Klagshamn sludge. but equal when the inhibition is high.
35
Idenlifying and fighting inhibilion of nitrification
Inhibition (%)
40 35 30
I I
25 20 15 10 5
o
I
I
Monday
I
Tuesday
•• ••
Wednesday
Thursday
Friday
Saturday
Sunday
Fig. 6. Variation of nitrification inhibition during the week.
This observation could be consistent with a supposition that some kind of acclirnatisation takes place for substances which are common in the sewer system. whereas accidents or random serious spill of inhibitory substances have more or less the same effect on different sludges. The conclusion from the routine programme is that inhibition is a very serious problem. that the industry can be expected to be the main contributor and that several/many industries are expected to contribute to the problem. but that few days with especially high inhibition could be caused by single industries. Four industries. where the examination showed significant inhibition and where it was known that potential harmful substances are used in the production. were contacted and a programme for identification of their discharge of inhibitory substances was established. For the most important industry (chemical) a programme was established with daily testing of the inhibitory effect of the effluent before discharge to the sewer system and of several inplant streams. The test technique used at the industry was the same as the one used at the plant. Figure 8 shows the inhibition at the industrial plant for the same period as shown in figure 5. It is seen that the industry discharges inhibitory substances most of the days.
100 I I
80
i
Inhibition (%) Klagsharnn
•
I
60
I
• • •. • . .../,.•.. • . .. .
•
/.
"
-20
'#.,l"t.
-20.:
•• ~
•
•
/
..... .... .. . ••
~~, #. ~/
••
1:1 /
40
~
//
/.
•
/
••
•
• 60
Inhibition (%) 6resundsverltet
80
100
Fig. 7. Inhibition of wastewater from the influent on sludge from Klagshamn Wastewater Treatment Plant as a function of inhibition found on sludge from Oresundsverket. The line indicating equal inhibition of both sludges is given too.
K. JONSSON et al.
36
Inhibition (%)
100 80 60 40 20
o May93 Joo93 Jul93 AUi93 Sep93 Oct93 N0Y93 Dcc:93 Jan94 Feb94 Mar94 Apt94 May94 Joo94
Fig. 8. Inhibition found at the effluent from a big chemical industry. However comparison between figure 8 and 5 shows that no direct connection exists between the discharge from the industry and the effect measured at the inlet to the treatment plant. The industry is assumed to be the most important source of inhibitory substances to the plant but many other industries have to contribute in order to explain the effects noticed at the treatment plant. The general awareness campaign includes several actions. More than 100 industries were visited, and their handling of potential harmfu1 substances were controlled and discussed. A brochure explaiping the effect of discharge of toxic substances from the industry was sent out to all industries in the catchment area. Finally, limits for discharge of substances inhibitory for nitrifICation have been established and will be applied for all new discharge pennissions and for old ones when they have to be renewed.
DISCUSSION The examination of combined nitrogen and phosphorus removal at Oresundsverket has been seriously influenced by problems with inhibition of nitrifICation. The problems have been displayed in detail due to the significant use of on-line sensors and the comprehensive test programme. One important question is if the problem is wide spread or more severe in Helsingborg than in other cities where nitrogen removal has been introduced. Only very few problems like the actual ones have been reported in the literature. Figure 9 shows the nitrification inhibition from a screening examination of 38 Danish wastewater treatment plants with nitrogen removal (Laursen and Jansen, 1995). In each case the incoming wastewater was tested using the sludge from the corresponding plant. It is seen that about one third of the plants receive wastewater which exhibit significant acute nitrifICation inhibition. From other studies, problems with short term inhibition of nitrification caused by accident or spill of chemicals have been reported (Swedish EPA, 1991). A study in Stockholm (Swedish EPA, 1994) has shown a similar picture of inhibition from the industries. It is believed that the discharge of toxic substances at Oresundsverket is higher than typical for wastewater treatment plants due to the high industrial connection. However many treatment plants is expected to have similar loadings of inhibitory substances. The specifIC conditions for the operation of Oresundsverket are assumed to have emphasized the problem. Any problem with inhibition of nitrifICation is recognized very easily due to the cold climate and the poor sludge properties which means that the plant is operated close to the design capacity for nitrification. Furthermore the comprehensive test programme has enabled detection of all distul'baoces and effects in the plant and detection of important sources.
37
Identifying and fighting inhibition of nitrification
Inhibition (%) 60
50
40 -
30
ZO
I
3
5
7
9
II
13
15
17
19
ZI
Z3
Z5
Z7
Z9
31
33
35
37
Plant number Fig. 9. Inhibition of nitrification found at 38 Danish wastewater treatment pIants. During the very comprehensive programme of examination of inhibition of nitrification at Oresundsverket it is demonstrated that the nitrification capacity of the plant is significantly reduced and that the incoming wastewater contains inhibitory substances at various levels which can explain the reduced capacity and also an accident where nitrification was completely inhibited. Examination of several industries has identified a few important contributors but also shown that many industries from different branches discharge wastewater which has an acute toxic effect on nitrification. Fighting the inhibition of nitrification consequently requires a comprehensive programme of examination of the iIK:oming wastewater and of the sludge in order to identify the problems and their consequences. Furthermore. it is necessary to keep track of the industrial loading to the system in order to be able to find important contributors. Adjustment of the permissions to discharge industrial effluents to the sewer system is also necessary when treatment plants are extended for nitrogen removal.
CONCLUSIONS Oresundsverket in Helsingborg has been seriously influenced by discharge of substances causing inhibition of nitrification. Shon term deterioration of the effluent quality with respect to ammonia has been observed and a general signifICant reduction of the nitrification capacity has been documented. More than one year of measurements of inhibition of nitrification on daily samples from the inlet have shown a varying but sometimes very high level of acute inhibition. Up to 90 % inhibition is found several times for a 80 % solution of incoming wastewater. Inhibition is reduced during week-ends and holidays supporting a proposition that industrial contribution to inhibition is dominating. Parallel examinations of inhibition on sludge from Oresundsverket and from Klagsbamn Wastewater Treatment Plant have shown reduced inhibition at low levels of inhibition when acclimated sludge from Oresundsverket is used but equal inhibition at high levels of inhibition.
K. JONSSON tt aI.
38
Examination of wastewater from industries in the catchment area has shown significant acute inhibition of nitrification at several industries from different branches. A detailed examination of discharge of inlubitory wastewater of one big chemical industry has rendered that it is an important contributor but the examination has also shown that other industries have to contribute. Fighting the inhibition of nitrification is complicated and has to include activities to track down significant contributors, to adjust discharge permits in order to prevent future problems and to inform the industries about the possible effects at the treatment plant of spill or illegal discharge of inhibitory substances.
REFERENCES Arvin. E., Dyreborg, S., Menck. C. and Olsen, J. (1994). A mini-nitrification test for toxicity screening, MINNTOX. Water Research vol.28, No.9, pp. 2029-2031. EPA (1975). Process Design Manual for Nitrogen Control. U.S. Envirorunental Protection Agency, Washington D.C. ISO 9S09 (1989). (E) Method for assessing the inhibition of nitrifICation of activated sludge-organisms by chemicals and wastewaters. Laursen, K.D., and Jansen, J. la C. (1995). IJ 50% of Danish wastewater treatment plants inhibited? (In Danish). Stads- og havneingenioren, No.2.
Magnusson, P. and J~nsson, L-E. (1995). Full-scale experiences from nutrient removal at Oresundsverket. Nordic Seminar on nitrogen removal from municipal wastewater. Espoo, Finland. Swedish EPA (1991). Nitrogen Removal at Municipal Wastewater treatment plants. Final Report (In Swedish). Report 3975. Swedish EPA (1993). Industrial loading of municipal wastewater treatment plants. Data from an examination in Helsingborg. (In Swedish). Report 4235. Swedish EPA (1994). Industrial loading of municipal wastewater treatment plants. Examination at Bromma Wastewater treatment plant. (In Swedish). Report 4376. Swedish EPA (1995). Screening-method for estimation of inlubition of nitrification at municipal wastewater treatment plants. (In Swedish). Report 4424.
Wat. Sci. Tech. Vol. 33. No. 12. pp. 29-38. 1996. Copyright C 1996IAWQ. Pubhshed by ElsevIer ScIence Ltd Printed in Great Britain. All rights reserved. 0273-1223196 SIS·OO + 0-00
Pergamon
PH: S0273-1223(96)00454-4
IDENTIFYING AND FIGHTING INHIBITION OF NITRIFICATION AT ORESUNDSVERKET Karin Jonsson*, Peter Magnusson**, Lars-Erik Jonsson**, Bengt Goran Hellstrom*** and Jes la Cour Jansent • Department of Water and Environmental Engineering. Lund Institute of Technology. Box 118. S-221 DO Lund. Sweden •• Helsingborg Water and Sewage Works. Gdseblicksviigen 4. S-252 27 Helsingborg. Sweden ... RUST VA.Projekt AB. Box 47D05. S·IDO 74 Stockholm, Sweden t Aved¢re Wastewater Treatment Plant. Kanalholmen 28. DK-2650 Hvidovre. Denmark
ABSTRACT After extension of Oresundsverket in Helsingborg severe nitrification problems have occurred. Complete inhibition of nitrification has been recognized once and a general reduction of nitrification capacity has been found compared to design, to other Swedish treatment plants and to internationally accepted design criteria. A comprehensive examination of inhibition of nitrification has identified industrial sourcc:s as the dominating contributors. Some industries have been identified as important sources but fighting inhibition of nitrification requires more than tracking down a few dominating industries, since examination shows that discharges of inhibitory substances are widespread among the industries in the catchment area. Naturally, fighting inhibition of nitrification requires the elimination of contributions from industries with identified discharge. Furthermore information campaigns directed towards the industries in general are required and fmally it is necessary to include requirements for inhibitory substances in the industrial discharge permits. Copyright
KEYWORDS Inhibition: nitrification: nitrogen removal: toxicity: wastewater.
INTRODUCTION The Wastewater Treatment Plant of Helsingborg, Oresundsverket, is the first plant in Sweden, which is designed for extended nitrogen removal. Since its extension in 1992, a comprehensive full scale test programme has been performed in order to establish experience under Swedish conditions with respect to combined nitrOgen and 29
K. JONSSON ~, al.
30
phosphorus removal. During the test programme it became obvious that inhibition of nitrification and poor sludge settling properties became important issues for examination since these problems very seriously influenced the test programme. Below, results from studies and strategies for fighting the inhibition of nitrification are presented.
ORESUNDSVERKET IN HELSINGBORG Oresundsverket was renewed in 1992. The former high loaded activated sludge system was extended into an activated sludge system for nitrogen and phosphorus removal designed for 220,000 p.e. The plant was further provided with postfiltration for polishing of suspended solids and phosphorus. The plant is constructed in four separate lines, which make an excellent basis for full scale experiments and optimization. Each line can be operated individually from inlet to filtration unit. Basically, the system comprises a recycling system for predenitrification which can be combined with phosphorus removal as pre-precipitation, simultaneous precipitation or biological phosphorus removal and completed with post-precipitation. Figure 1 shows an air photo of the plant. Table I and table 2 give the basic technical information of the plant and the characteristics of the influent and of the discharge requirements.
Fig. I. Air photo of Oresundsverket in Helsingborg. TABLE 1. TECHNICAL INFORMATION OF ORESUNDSVERKET. Number Primary clarifiers Activated sludge treatment anaerobic/anoxic anoxic anoxic/aerobic anoxic/aerobic aerobic anoxic Final clarifiers Filters
8 4 4 4 4 4 4 16 12
Area (m2)
Volume (ml )
8·300
8·1125
16·330 12· 50
4·1020 4·3100 4·1020 4·1020 4·1504 4· 535 16·1320
31
Identifying and fighting inhibition of nitrification
TABLE 2. CHARACTERISTICS OF THE INFLUENT AND DISCHARGE UMITS AT ORESUNDSVERKET. Influent 3
ClJIm (m /h)
Flow (m3/d) COD (mgtl) BOD, (mgll) Tot-N (mgll) Tot-P (mgtl) Temp. (monthly mean values, 0c)
3250 S4000 420 130 33 5.7 10-19
Discharge limits (annual mean values) Target value
Trial period criteria
10 8 0.3
10 12 0.3
INHIDITION OF NITRIFICATION The extended plant was started up in 1992. As a part of the test progranune many on-line sensors and a comprehensive programme for chemical analyses were established. During the first winter of operation poor sludge properties were noticed and consequently it was impossible to keep a sufficient amount of sludge to maintain the aerobic sludge age corresponding to the design capacity. The plant however is not fully loaded and, consequently, the nitrogen removal could be kept at an acceptable level. In March 1993 a severe case of inhibition of nitrification occurred. The on-line meteB for ammoniwn and nitrate showed that on the 2nd of March something stopped nitrification completely. The plant was operated with two lines with simultaneooS precipitation, one line with pre-precipitation and one line with biological phospholllS removal. Figure 2 shows the results of ammonia measurements from these three different processes. It is seen that the effluent normally shows a weekly variation, and that nitrification completely disappeared on the 2nd of March. Full nitriflC8tion was re-established three weeks later. The same pattern is seen for all lines, but it seems as if the pre-precipitation system re-established faster than the other systems. It was impossible to fmd the reason for the accident, but since the plant serves the Helsingborg Municipality, where several big industries are located, it was decided to initiate a progranune for examination of inhibition from the major industries and from selected industries from branches well represented in the catchment area. Based on the very comprehensive test programme at the treatment plant, it is possible to calculate the necessary aerobic sludge age to keep full nitrification. For the lines operated with simultaneooS precipitation, as well as for the line with biological phospholllS removal, the critical sludge age adjusted to lSoC is found to be around 12 days (Magnusson and JOnsson, 1995). This value is much higher than reported from other Swedish treatment plants where nitrogen removal experiments have been performed (Swedish EPA, 1991). Values in the range of 5-8 days are given in agreement with internationally accepted design figures in EPA (1975), where values around 6 days of aerobic sludge age are sufficient at 15°C. This fmding of an unusually high necessary sludge age compared to general accepted design rules understated the need for examination of the wastewater discharged to the plant.
INDUSTRIAL DISCHARGE TO QRESUNDSVERKET The industry in Helsingborg is dominated by a few big factories in chemical, pharmaceutical and food industry and by a great number of small industries where especially printing companies are common. Figure 3 shows the contribution from the industry and from households to the treatment plant related to flow, organic matter (BOD,) and nitrogen. It is seen that the industry makes up a very significant part of the mass flow to the plant.
K. J6NSSON ~, al.
32
NH.-N in the outlet (mgtl) 25 T 20 -
15 10-;-
5
oLa~~iiY I-mar
IS-feb -M-
Bio-P
IS-mar __ Pre-precipitation
I-apr
IS-apr
.~ Simultaneous precipitation
Fig. 2. Inhibition accident in March 1993.
Flow Average: 54,000 mJtd
BOD 7 Average: 7,000 kgtd
Tot-N Average: 1,800 kgtd
() . .
_Industrial wastewater DLeachate _ Domestic wastewater c::::ILeakage
Fig. 3. Industrial and household contribution to the load of Qresundsverket.
EXAMINATION OF INHIBmON OF NITRIFICATION FROM INDUSTRIES IN THE CATCHMENT AREA OF ORESUNDSVERKET As a way to find methods how to judge the effect of different industries discharge of wastewater to the municipal wastewater treatment plants. Swedish EPA did carry out a study of the toxicity of wastewater from about ten different industries in Helsingborg during November 1992. Different methods for evaluation of the toxicity from industrial effluent were used and tests for inhibition of nitrification were included since such methods are believed to be closer to the processes in wastewater treatment plants than traditional ecotoxicology tests. During one week samples were taken from 10 industries. the local dump site and influent and effluent at the treatment plant. The whole examination is reported in Swedish EPA. 1993. and in figure 4 the nitrification inhibition found in a 20 % solution from the most important industries is shown. The dump site and the effluent from the treatment plant showed no inhibition on nitrifying bacteria. It is seen that the different industries exhibit a very different inhibition pattern. Some industries have almost constant inhibition (on different levels) whereas others vary much from day to day. Furthennore several industries have no discharge of wastewater during weekends. (n table 3 the six most important industries are ranked according to emission of substances which inhibit nitrification.
33
Identifying and fighting inhibition of nitrification
,~~~~:r--------l18 ~ 1ZI ClMmIal l\.1---....__- - - - - 1 ~ Food l1!IPrlalin&
'-"
l\.Jl...AN--l\.N'I-----~
MIXl
TIIlI
Wed
1bu
Fri
Sal
1ZI ClMmIal ~ ClMmIal
s..
Fig. 4. Inhibition of nitrification found during one week at six industries. The inhibition was found using a slightly modified version of ISO 9509 (1989) and a new screening method (Swedish EPA. 1995) close to the Minntox method presented in Arvin et al. (1994). The two methods gave similar results. Figure 4 is based on results from the screening method, which later on was established as a routine measurement at the laboratory of the plant. The basic principles of the screening method is that nitrifying activated sludge is mixed with a synthetic IDltriem solution containing (NHJ1S04 and NaHC03• The suspension is mixed with tap-water and the wastewater under consideration in proportion which secure the proper dilution of the wastewater. The mixture is shaken during 120 minutes, the nitrification is stopped by filtration and cooling of the samples. Nitrification inhibition is found by comparing the nitrate production (or ammonia removal) in samples containing wastewater with reference samples without wastewater.
TABLE 3. RANKING OF INDUSTRIES ACCORDING TO DISCHARGE OF INHIBITORY SUBSTANCES. Branch
Chemical Food industry Chemical Chemical Printing Pharmaceutical
Inhibition in 20 % solution mean value (%)
Mean flow (m3/d)
28 20 60 43 60 9
679 562 18 18 3.6 30
K. JONSSON et aI.
34
MEASURES TAKEN TO FIGHT THE NlTRIFICAnON INHmITION The results from the examination showed such dramatic inhibition from some industries that action had to be taken. The action comprised of three parts: - Start up of a programme for routine measurement of inlubition at the influent of the plant and detailed examination of variation of nitrification capacity of the sludge. - Direct contact to and examination of industries where previous examinations showed high inhibition. - General awareness campaigns directed towards the industries to minimize discharge of substances toxic for biological processes. The programme for routine measurement of inlubition of the influent started in May 1993 and has now been running for more than one year. A flow proponional. 24-hour composite sample from the influent is collected every day and then frozen for later analysis of inhibition of nitrification. The sludge used for the examination is sludge from Oresundsverket. but sludge from the Klagshamn Wastewater Treatment Plant in MalmO is tested in parallel. The industrial load to this plant is minor and investigations have shown that inhibition is negligible. Figure 5 shows one and a half year of nitrifICation inhibition measured using sludge from Oresundsverket. The wastewater is tested in a high concentration (SO % wastewater). It is seen that great variation exists. However. a general trend is immediately visible. During summer holidays and other periods. when the industries are closed. the inhibition decreases. Figure 6 furthermore shows the mean inhibition for the days of the week. It is seen that inhibition decreases during weekends. when the industries are closed. and that Fridays are especially critical. The reason for this could be that the discharge of inhibitory substances is related to cleaning procedures. and that these especially take place just before the week~nds. Inhibition (%)
20
o
May93 Jun93 Jul93 Aug93 Sep93 Oct93 N0v93 Dcc93 Jan94 Fcb94 Mar94 Apr94 May94 Jun94
Fig. S. Daily measurements of nitrifICation inhibition at Oresundsverket. Measurements of inhibition of sludge from the Klagshamn Plant as well as sludge from Oresundsverket give a possibility to see if any adaptation of the sludge takes place. Figure 7 shows the inhibition found on the Klagshamn sludge as a function of the inhibition found on the sludge from Oresundsverket. It is seen that inhibition is signifICant on both sludges. It seems to be the case that the effect al moderate inhibition is highest on the Klagshamn sludge. but equal when the inhibition is high.
35
Idenlifying and fighting inhibilion of nitrification
Inhibition (%)
40 35 30
I I
25 20 15 10 5
o
I
I
Monday
I
Tuesday
•• ••
Wednesday
Thursday
Friday
Saturday
Sunday
Fig. 6. Variation of nitrification inhibition during the week.
This observation could be consistent with a supposition that some kind of acclirnatisation takes place for substances which are common in the sewer system. whereas accidents or random serious spill of inhibitory substances have more or less the same effect on different sludges. The conclusion from the routine programme is that inhibition is a very serious problem. that the industry can be expected to be the main contributor and that several/many industries are expected to contribute to the problem. but that few days with especially high inhibition could be caused by single industries. Four industries. where the examination showed significant inhibition and where it was known that potential harmful substances are used in the production. were contacted and a programme for identification of their discharge of inhibitory substances was established. For the most important industry (chemical) a programme was established with daily testing of the inhibitory effect of the effluent before discharge to the sewer system and of several inplant streams. The test technique used at the industry was the same as the one used at the plant. Figure 8 shows the inhibition at the industrial plant for the same period as shown in figure 5. It is seen that the industry discharges inhibitory substances most of the days.
100 I I
80
i
Inhibition (%) Klagsharnn
•
I
60
I
• • •. • . .../,.•.. • . .. .
•
/.
"
-20
'#.,l"t.
-20.:
•• ~
•
•
/
..... .... .. . ••
~~, #. ~/
••
1:1 /
40
~
//
/.
•
/
••
•
• 60
Inhibition (%) 6resundsverltet
80
100
Fig. 7. Inhibition of wastewater from the influent on sludge from Klagshamn Wastewater Treatment Plant as a function of inhibition found on sludge from Oresundsverket. The line indicating equal inhibition of both sludges is given too.
K. JONSSON et al.
36
Inhibition (%)
100 80 60 40 20
o May93 Joo93 Jul93 AUi93 Sep93 Oct93 N0Y93 Dcc:93 Jan94 Feb94 Mar94 Apt94 May94 Joo94
Fig. 8. Inhibition found at the effluent from a big chemical industry. However comparison between figure 8 and 5 shows that no direct connection exists between the discharge from the industry and the effect measured at the inlet to the treatment plant. The industry is assumed to be the most important source of inhibitory substances to the plant but many other industries have to contribute in order to explain the effects noticed at the treatment plant. The general awareness campaign includes several actions. More than 100 industries were visited, and their handling of potential harmfu1 substances were controlled and discussed. A brochure explaiping the effect of discharge of toxic substances from the industry was sent out to all industries in the catchment area. Finally, limits for discharge of substances inhibitory for nitrifICation have been established and will be applied for all new discharge pennissions and for old ones when they have to be renewed.
DISCUSSION The examination of combined nitrogen and phosphorus removal at Oresundsverket has been seriously influenced by problems with inhibition of nitrifICation. The problems have been displayed in detail due to the significant use of on-line sensors and the comprehensive test programme. One important question is if the problem is wide spread or more severe in Helsingborg than in other cities where nitrogen removal has been introduced. Only very few problems like the actual ones have been reported in the literature. Figure 9 shows the nitrification inhibition from a screening examination of 38 Danish wastewater treatment plants with nitrogen removal (Laursen and Jansen, 1995). In each case the incoming wastewater was tested using the sludge from the corresponding plant. It is seen that about one third of the plants receive wastewater which exhibit significant acute nitrifICation inhibition. From other studies, problems with short term inhibition of nitrification caused by accident or spill of chemicals have been reported (Swedish EPA, 1991). A study in Stockholm (Swedish EPA, 1994) has shown a similar picture of inhibition from the industries. It is believed that the discharge of toxic substances at Oresundsverket is higher than typical for wastewater treatment plants due to the high industrial connection. However many treatment plants is expected to have similar loadings of inhibitory substances. The specifIC conditions for the operation of Oresundsverket are assumed to have emphasized the problem. Any problem with inhibition of nitrifICation is recognized very easily due to the cold climate and the poor sludge properties which means that the plant is operated close to the design capacity for nitrification. Furthermore the comprehensive test programme has enabled detection of all distul'baoces and effects in the plant and detection of important sources.
37
Identifying and fighting inhibition of nitrification
Inhibition (%) 60
50
40 -
30
ZO
I
3
5
7
9
II
13
15
17
19
ZI
Z3
Z5
Z7
Z9
31
33
35
37
Plant number Fig. 9. Inhibition of nitrification found at 38 Danish wastewater treatment pIants. During the very comprehensive programme of examination of inhibition of nitrification at Oresundsverket it is demonstrated that the nitrification capacity of the plant is significantly reduced and that the incoming wastewater contains inhibitory substances at various levels which can explain the reduced capacity and also an accident where nitrification was completely inhibited. Examination of several industries has identified a few important contributors but also shown that many industries from different branches discharge wastewater which has an acute toxic effect on nitrification. Fighting the inhibition of nitrification consequently requires a comprehensive programme of examination of the iIK:oming wastewater and of the sludge in order to identify the problems and their consequences. Furthermore. it is necessary to keep track of the industrial loading to the system in order to be able to find important contributors. Adjustment of the permissions to discharge industrial effluents to the sewer system is also necessary when treatment plants are extended for nitrogen removal.
CONCLUSIONS Oresundsverket in Helsingborg has been seriously influenced by discharge of substances causing inhibition of nitrification. Shon term deterioration of the effluent quality with respect to ammonia has been observed and a general signifICant reduction of the nitrification capacity has been documented. More than one year of measurements of inhibition of nitrification on daily samples from the inlet have shown a varying but sometimes very high level of acute inhibition. Up to 90 % inhibition is found several times for a 80 % solution of incoming wastewater. Inhibition is reduced during week-ends and holidays supporting a proposition that industrial contribution to inhibition is dominating. Parallel examinations of inhibition on sludge from Oresundsverket and from Klagsbamn Wastewater Treatment Plant have shown reduced inhibition at low levels of inhibition when acclimated sludge from Oresundsverket is used but equal inhibition at high levels of inhibition.
K. JONSSON tt aI.
38
Examination of wastewater from industries in the catchment area has shown significant acute inhibition of nitrification at several industries from different branches. A detailed examination of discharge of inlubitory wastewater of one big chemical industry has rendered that it is an important contributor but the examination has also shown that other industries have to contribute. Fighting the inhibition of nitrification is complicated and has to include activities to track down significant contributors, to adjust discharge permits in order to prevent future problems and to inform the industries about the possible effects at the treatment plant of spill or illegal discharge of inhibitory substances.
REFERENCES Arvin. E., Dyreborg, S., Menck. C. and Olsen, J. (1994). A mini-nitrification test for toxicity screening, MINNTOX. Water Research vol.28, No.9, pp. 2029-2031. EPA (1975). Process Design Manual for Nitrogen Control. U.S. Envirorunental Protection Agency, Washington D.C. ISO 9S09 (1989). (E) Method for assessing the inhibition of nitrifICation of activated sludge-organisms by chemicals and wastewaters. Laursen, K.D., and Jansen, J. la C. (1995). IJ 50% of Danish wastewater treatment plants inhibited? (In Danish). Stads- og havneingenioren, No.2.
Magnusson, P. and J~nsson, L-E. (1995). Full-scale experiences from nutrient removal at Oresundsverket. Nordic Seminar on nitrogen removal from municipal wastewater. Espoo, Finland. Swedish EPA (1991). Nitrogen Removal at Municipal Wastewater treatment plants. Final Report (In Swedish). Report 3975. Swedish EPA (1993). Industrial loading of municipal wastewater treatment plants. Data from an examination in Helsingborg. (In Swedish). Report 4235. Swedish EPA (1994). Industrial loading of municipal wastewater treatment plants. Examination at Bromma Wastewater treatment plant. (In Swedish). Report 4376. Swedish EPA (1995). Screening-method for estimation of inlubition of nitrification at municipal wastewater treatment plants. (In Swedish). Report 4424.