Environmentally Compatible Cooling Water Treatment Chemicals 05-11-02
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Transcript of Environmentally Compatible Cooling Water Treatment Chemicals 05-11-02
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Environmental Research of theFederal Ministry of the Environment,
Nature Conservation and Nuclear Safety- Water Economy -
Research Report 200 24 233
Environmentally compatible cooling watertreatment chemicals
byDipl. Geogr./Hyd. Stefan Gartiser
Dipl. Hyd. Elke Urich
Hydrotox GmbH, Freiburg
On behalf of theFederal Environmental Agency
Berlin, April 2002
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IReport Cover Sheet1. Report No.
UBA-FB 200 24 2332.
Water economy3.
4. Report Title
Environmentally compatible cooling water treatment chemicals5. Autor(s) (Family Name(s), First Name(s))
Gartiser, Stefan; Urich, Elke6. Report Date
7. Publication Date
8. Performing Organisation(s) (Name, Address)
Hydrotox GmbH9. UFOPLAN-No.
200 24 233Boetzinger Str. 29D-79111 Freiburg
10. No. of Pages
106 + 91 (annex)11. No. of References
103 + 71 (annex)12. Sponsoring Agency (Name, Address)
German Federal Environmental Agency13. No. of Tables
20Postfach 33 00 22, D-14191 Berlin (Germany) 14. No. of Figures
1115. Supplementary Notes
This project was commissioned in the form of a grant on the basis of costs as partialfinancing to the recipients (Grant Decision Z 1.6-25106/182 of 31.01.00)In Germany about 32 billion m3/a cooling water are discharged from industrial plants andthe power industry. These are conditioned in part with biocides, scaling and corrosioninhibitors. Within the research project the significance of cooling water chemicals wasevaluated, identifying the chemicals from product information, calculating their loads fromconsumption data of more than 180 cooling plants and investigating the basic characteristicdata needed for an environmental hazard assessment. Additionally, the effects of coolingwater samples and products were determined in biological test systems. Batch tests (shocktreatments) were performed under defined conditions in order to measure the inactivationof cooling water biocides.Generally the cooling water samples only showed low ecotoxicity, upon considering theinactivation of the biocides with time. With systematic backtracking, the genotoxicity of thecooling water from one company in the umu test could be attributed to one biocide withisothiazolinones and Bronopol as ingredients. Measurement of the inactivation of biocides,with the luminescent bacteria toxicity test, revealed a strong correlation with the inoculumconcentration and enabled a better estimation of the importance of the elimination factorsdegradation and adsorption. An overall balance sheet of chemical loads confirmed that theprincipal amounts came from open recirculation cooling systems, whereas only
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II
Contents
0 Summary .............................................................................................. 1
1 Introduction.......................................................................................... 5
2 Current knowledge .............................................................................. 6
2.1 Fundamentals ........................................................................................ 6
2.2 Cooling water flow ................................................................................. 7
2.3 Minimum requirements for cooling water discharges in Germany ......... 9
2.4 General environmental hazards from cooling systems ........................ 10
2.5 Cooling water conditioning................................................................... 12
2.5.1 Dispersants and hardness stabilizers .................................................. 122.5.2 Scale inhibitors .................................................................................... 132.5.3 Biocides ............................................................................................... 14
3 Goals and investigative strategy ...................................................... 18
4 Methods .............................................................................................. 20
4.1 Laboratory investigations ..................................................................... 20
4.1.1 Cooling water samples ........................................................................ 204.1.2 Product investigations.......................................................................... 244.1.3 Chemical parameters........................................................................... 244.1.4 Fluorescent bacteria test according to DIN 38412-34 and
Nr. 404 of the AbwV............................................................................. 244.1.5 Alga test according to DIN 38412-33 and Nr. 403 of the AbwV ........... 254.1.6 Daphnia test according to DIN 38412-30 and Nr. 402 of the AbwV ..... 254.1.7 Ames test in conformance with DIN 38415-4 ...................................... 254.1.8 umu test according to DIN 38415-3 and Nr. 410 of the AbwV ............. 264.1.9 Elimination of biocides ......................................................................... 27
4.2 Drawing up an overall balance sheet................................................... 28
4.2.1 Compilation of production information materials .................................. 28
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III
4.2.2 Making a balance sheet of the emissions of cooling waterchemicals............................................................................................. 29
4.3 Literature and database-research........................................................ 33
5 Results................................................................................................ 36
5.1 Cooling water investigations ................................................................ 36
5.2 Product investigations.......................................................................... 38
5.2.1 Eco- and Genotoxicity.......................................................................... 385.2.2 Identifying the source of the genotoxicity in plant 6 ............................. 385.2.3 Decrease of the biocidal effect in the fluorescent bacteria test ........... 41
5.3 Evaluation of the product information sheets....................................... 52
5.4 Evaluation of the questionnnaires........................................................ 53
5.4.1 Open recirculation cooling systems ..................................................... 545.4.2 Once-through cooling systems ............................................................ 565.4.3 Closed circulation cooling systems ...................................................... 585.4.4 Estimation of the total loads for Germany............................................ 585.4.5 Overview and comparison ................................................................... 64
5.5 Elimination of chemicals in cooling systems and sewage plants ......... 70
5.6 Regulatory control of cooling water discharges ................................... 70
5.7 Literature and database research ........................................................ 71
6 Evaluation........................................................................................... 74
6.1 Composition of cooling water............................................................... 74
6.2 Emission route for cooling water chemicals ......................................... 75
6.3 Elimination behavior of cooling water biocides .................................... 75
6.4 Choice of active substances ................................................................ 77
6.4.1 Biocides ............................................................................................... 776.4.2 Cooling water conditioners................................................................... 82
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IV
7 Recommendations............................................................................. 89
7.1 Energy conservation measures ........................................................... 89
7.2 Technical solutions .............................................................................. 89
7.3 Process operation................................................................................ 91
7.4 Evaluation and selection of cooling water chemicals ........................... 93
7.4.1 Water risk classes, the VCI-concept for open cooling systems ........... 937.4.2 "Benchmarking"-concept ..................................................................... 947.4.3 Plant specific evaluation of cooling water chemicals ........................... 957.4.4 TEGEWA-concept for indirect dischargers .......................................... 967.4.5 Outlook ................................................................................................ 96
8 Sources............................................................................................... 98
9 Ackknowledgements ....................................................................... 105
List of TablesTable 1: Cooling water discharge in river basins (1995) [Mio. m3] .............................. 7Table 2: River flow volume balance for Germany in 1992 .......................................... 7Table 3: Ratio of used/discharged cooling water (1995) ............................................. 9Table 4: Charateristic data for the investigated systems .......................................... 23Table 5: Determination of the elimination of cooling water biocides ......................... 28Table 6: Summary of the wastewater investigations ................................................. 37Table 7: Results of the product investigations .......................................................... 39Table 8: Source of the genotoxicity in the cooling water from plant 6 ....................... 40Table 9: Dosing of biocides in the circulation cooling ............................................... 42Table 10: Experimental overview of the elimination curves of cooling
water biocides ........................................................................................... 43Table 11: Elimination of BCDMH depending on the inoculum .................................. 50Table 12: Characteristic data for the cooling systems investigated .......................... 53Table 13: Total amounts of the investigated chemicals in open circulation
cooling ...................................................................................................... 55Table 14: Consumption data in plants with flow-through cooling .............................. 57Table 15: Cooling water use for thermal power plants (1995 ) ................................. 60
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VTable 16: Concentrations of continuously added conditioners (concentrationin the circulation water in mg/l) ................................................................. 61
Table 17: Chemical usage in open circulation cooling systems in Germany ............ 63Table 18: Total load of cooling water chemicals in the once-through cooling
of the foodstuffs industry........................................................................... 64Table 19: Comparison of the estimated consumption data for certain biocides
with data from other countries (data in kg/a on a substance basis) .......... 69Table 20: Summarized evaluation of the eotoxicity and degradability of cooling
water chemicals ........................................................................................ 73
List of FiguresFigure 1: Investigative strategy ................................................................................. 19Figure 2: Decrease of the fluorescent bacteria inhibition with isothiazolinone .......... 44Figure 3: Decrease of the fluorescent bacteria inhibition with QAV .......................... 45Figure 4: Decrease of the fluorescent bacteria inhibition with DBNPA (10 mg/l) ...... 46Figure 5: Decrease of the fluorescent bacteria inhibition with DBNPA (48 mg/l) ...... 46Figure 6: Fluorescent bacteria inhibition with glutardialdehyde (30-160 mg/l) .......... 48Figure 7: Fluorescent bacteria inhibition with glutardialdehyde (30-1000 mg d.s./l) . 48Figure 8: Decrease of the fluorescent bacteria inhibition with Bronopol ................... 49Figure 9: Decrease of the fluorescent bacteria inhibition with BCDMH (4 mg/l) ....... 51Figure 10: Decrease of the fluorescent bacteria inhibition with BCDMH (37 mg/l) ... 51Figure 11: Proportion of biocidal active ingredients in 101 products ......................... 52
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VI
Abbreviations
AbwV Wastewater OrdinanceAMPA Aminomethylenephosphonic acidAOX Adsorbable organic halogens (X = Cl, Br, I)ATMP Aminotrimethylenephosphonic acidATV Abwassertechnische Vereinigung e. V.BAT Best available techniquesBCDMH 1-Bromo-3-chloro-5,5-dimethylhydantoinBgVV Bundesinstitut fr gesundheitlichen Verbraucherschutz
und VeterinrmedizinBIG Brandweerinformatiecentrum Gevaarlijke StoffenBUA Beratergremium fr umweltrelevante SchadstoffeCAS Chemical AbstractsCHEMIS Chemical information system of the BgVVCOD Chemical oxygen demandDBNPA DibromonitrilopropionamideDTPMP Dieethylenetriaminepentamethylenephosphonic acidDOSE Dictionary of Substances and Their EffectsECDIN Environmental Chemicals Data and Information NetworkEnviChem Data Bank of Environmental Properties of ChemicalsEC50 50% effect concentrationEDTA EthylenediaminetetraacetateEDTMP Ethylenediaminetetramethylenephosphonic acidEQS Environmental Quality StandardEC European CommunityGESTIS Gefahrstoffinformationssystem der gewerblichen
BerufsgenossenschaftenGSBL Gemeinsame Stoffdatenbank Bund/LnderGA Lowest ineffective dilution, alga test = lowest dilution
factor at which inhibition of algal biomass growth is below20%.
GEA Lowest ineffective dilution, Ames test = lowest dilutionfactor at which an induction difference as compared withnegative controls of
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VII
GL Lowest ineffective dilution, luminescent bacteria test =lowest dilution factor at which inhibition of luminescenceis below 20%
GD Lowest ineffective dilution, Daphnia test = lowest dilutionfactor at which 90% of Daphnia retain their mobility
HSDB Hazardous Substances Data BankHEDP Hydroxyethanediphosphonic acid
IR Induction rate in the Ames and umu tests
IUCLID International Uniform Chemical Information DatabaseIUPAC International Union of Pure and Applied ChemistryIPPC directive EC-directive Integrated Pollution Prevention and Control
KBwS Kommission zur Bewertung wassergefhrdender StoffeLAGA Lnderarbeitsgemeinschaft WasserLC50 50% lethal concentrationMW Molecular weightMQ Mean water flowNTA NitrilotriacetateOECD Organisation for Economic Co-operation and
DevelopmentOSPAR Oslo/Paris Convention for the protection of the marine
environment of the Northeast AtlanticPBTC Phosphonobutanetricarbonic acidPEC Predicted environmental concentrationsPNEC Predicted no effect concentrationQAV Quarternary ammonium compoundsRTECS Register of Toxic Effects of Chemical SubstancesSCAS-Test Semi-continuous activated sludge testTEGEWA Verband der Textilhilfsmittel-, Lederhilfsmittel,- Gerbstoff-
und Waschrohstoff-Industrie e.V.VCI Verband der Chemischen IndustrieVGB Technische Vereinigung der Grokraftwerksbetreiber e.V.WF Growth factor in the umu testWGK WassergefhrdungsklasseVwVwS Verwaltungsvorschrift wassergefhrdender Stoffe
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10 Summary
In power plants and industrial processes non-recoverable heat released during the
use and conversion of energy is removed from the industrial processes by cooling
systems. Water is the most important coolant medium used. In Germany about 27
billion. m3 cooling water (109 m3) are discharged per year from power plants mainly
via once-through cooling systems. To this, about 5 billion m3 from industrial plants
must be added, of which about 376 million m3 comes from plants with open
recirculation cooling systems. The water consumption of open recirculation systems
amounts to only 2-5% of that of open cooling systems at equal cooling capacities.
Nevertheless, the water added to the system to compensate the loss of water due to
evaporation or blow down ("make-up water") regularly has to be conditioned with
biocides, scale inhibitors, dispersants and/or corrosion inhibitors, in order to prevent
disturbances of processes by depositions (scaling), corrosion or bio-mass growth
(fouling).
Within the research project the input of cooling water chemicals was evaluated,
identifying the chemicals from product information, calculating their loads from
consumption data of more than 180 cooling plants and investigating the basic
characteristic data needed for an environmental hazard assessment. Additionally, 12
water samples from 7 companies and 11 products have been evaluated in biological
test systems. The elimination of eight cooling water biocides has been determined,
using the luminescent bacteria assay and batch tests with defined inoculum
concentrations (30-1000 mg d.s./l).
Generally, the cooling water samples showed only low ecotoxicity in the algae,
Daphnia and luminescent bacteria assays if the elimination time of the biocides is
considered. With systematic backtracking, the genotoxicity of the cooling water from
one company in the umu-assay could be attributed to one biocide with
isothiazolinones and Bronopol as ingredients. No effects of the water samples have
been detected with the Ames test, although several products proved to be mutagenic
in the Ames test. The elimination of biocides in batch tests, as measured with the
luminescent bacteria toxicity test, showed that isothiazolinones and quarternary
ammonium compounds were better removed with higher inoculum concentration due
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2to their adsorption to activated sludge. In contrast, the elimination velocity for 2,2-
dibromo-3-nitrilopropionamide (DBNPA) increased with increasing pH. For the
oxidative biocide bromochlorodimethylhydantoin (BCDMH) only a weak dependence
on inoculum concentration was observed, while Bronopol showed a distinct toxicity at
low inoculum concentrations even after 8 days. Therefore, the test conditions for the
determination of elimination curves, which determine the period the circuit must be
closed after a shock treatment with non-oxidizing biocides according to Annex 31 of
the German Waste Water Ordinance, must be clearly defined. Inactivation curves
performed applying the test conditions of the VCI-working group "Biocides in cooling
systems" with high inoculum density (activated sludge with 500 mg d.s./l) favor
elimination by adsorption, and the test design corresponds to an inherent bio-
degradation test. Comparable biomass concentrations normally were not found in
cooling systems. If additional information is required, especially for directly
discharged cooling water, results about ready bio-degradation and/or elimination
curves at lower inoculum concentrations (i.e., 30 mg d.s./l corresponding to the test
conditions of the OECD 301 "Ready bio-degradability" tests) should be demanded.
The overall accounting of chemical loads in a balance sheet confirmed that the
principal amounts came from open recirculation cooling systems, whereas only
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3power plant using salt water as coolant, as well as plants of the chemical and
foodstuff industries. Of course, for foodstuffs hygiene requirements (product safety)
are more important than the prevention of biofouling in the cooling system.
According to the operators statements, the recirculation water of closed cooling
systems is often discharged indirectly via municipal treatment plants and only in
isolated cases directly into the recipient water. No luminescent bacteria test results
were available for two thirds of the cooling systems, although 40% of them directly
discharged the cooling water. Only in some cases did operators indicate that
elimination curves of the biocides used have been submitted. As a rule, only the
period of time for which the circuit must be closed after a treatment with biocides is
documented as specified by the producers of conditioning chemicals. Concrete
examples have also been presented in which the usage of chemicals has been
reduced up to 90% by simple technical or organizational measures (cleaning,
shading of cooling towers from the sun).
Basic substance data sheets were documented for all chemicals applied, based on
extensive literature and data bank/database researches, enabling first assessments
of environmental relevance using several approaches of hazard assessment.
For some chemicals (e.g., butylbenzotriazole, chlorotolyltriazole, tetraalkylphos-
phonium chloride) considerable data gaps exist. With reference to the BREF-
document of the EU-Commission about "the application of best available techniques
to industrial cooling systems", different approaches regarding the selection and
optimizing of cooling water chemicals are described. There is a clear confirmation
that this issue cannot be examined separately from the complex thermodynamic
processes, the water quantity available and the site specific characteristics. A
combination of emission- and water-quality-based criteria is recommended to assess
cooling water chemicals. The advantage of emission-based approaches based on
the classification system of harmful water pollutants according to the European R-
phrases of the dangerous substances directive is that, along with the aquatic
ecotoxicity, other protection areas such as health aspects or soil conservation are
considered. Additionally, insufficient databases were considered for the assessment,
following the precautionary principle. However, in order to draw attention to the loads
emitted, both the consumption amount as well as the elimination in cooling systems
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4and (for indirectly discharged water) municipal treatment plants should be
emphasized, as described in the TEGEWA-concept for indirect discharges. The
advantage of water-quality based approaches such as the "benchmarking"-concept
based on the predicted environmental and effect concentrations is that the intrinsic
properties of chemicals such as bio-degradability and ecotoxicity are combined and
the site specific characteristics are considered. Nevertheless, this approach focuses
on the environmental quality standards for surface water derived from chemical risk
assessment, and the rule of load minimizing seems to be less important when the
water flow capacity of the recipient water is considered to be sufficient. The
determination of toxicity loads (=effect concentration multiplied by load) is a possible
further development of the "benchmarking"-concept. Prequisites for the assessment
of conditioning cooling chemicals are that chemicals can be identified unambiguously
in product descriptions and that data gaps will be closed.
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51 Introduction
In power plants and industrial processes non-recoverable heat released during the
use and conversion of energy is removed from the processes by cooling systems.
Due to its high heat capacity water is the most important coolant medium used. Apart
from surface water from rivers and lakes also sea, ground or drinking water is used
for cooling purposes.
Along with the organic and inorganic constituent compounds of this water, non-
negligible amounts of air pollutants, which might cause scaling, growth of
microorganisms and corrosion, are also washed out by cooling water due to the high
air turnover of cooling towers. Hence, the cooling water often is conditioned with
dispersants, corrosion inhibitors and biocides. As wastewater treatment of cooling
water is usually not applied, these chemicals are discharged with the blow down
into the sewer or (from directly discharging plants) into the receiving water.
Within the project a systematic evaluation of the input of cooling water chemicals into
German surface water was carried out. To accomplish this, the chemicals used were
identified from product information, their loads were calculated from consumption
data of more than 180 cooling plants, and the basic characteritic data needed for an
environmental hazard assessment were compiled. Additionally, the effects of cooling
water samples and products were determined in biological test systems. Batch tests
were performed under defined conditions in order to measure the elimination of
cooling water biocides.
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62 Current knowledge
2.1 Fundamentals
Cooling systems can be distinguished as once-through systems, as well as open and
closed recirculation systems, and their combinations (Held and Schnell 2000,
Anonymous 2001c). In once-through cooling systems cooling water is used without
recirculation, i.e., the warmed water is directly discharged into the receiving water.
Often once-through cooling is applied in combination with a cooling tower, where the
cooling water is trickled in order to remove part of the heat via evaporation cooling.
Once-through cooling systems demand a large water supply. For instance, power
stations with a difference between in- and outlet temperature of 10C consume, as a
rule, about 3.5 m3 cooling water per 100 MW installed electric capacity (Fichte et al.
2000).
Open recirculating cooling systems are wet cooling circuits open to the air, where the
water used for cooling purposes is cooled down by evaporation. As a first
approximation one can assume that in open recirculating systems 70% of the heat
amount is removed by evaporation. The evaporation loss depends on the cooling
capacity and the climatic conditions. As a rule of thumb it can be assumed that, per
10C temperature elevation, 1.1% to 1.6% of the circulating water flow evaporates in
Central Europe (Fichte et al. 2000, Sommer 1988). Additionally, droplet losses of
about 0.1% of the circulating water flow are emitted. Hereby, cooling water
ingredients are usually concentrated by a factor of 2-4. The concentration factor is
adjusted via the blow down (draining of cooling water to the recipient water body or
municipal treatment plant). The evaporation losses and the blow down are
compensated by the make-up water. The fresh water supply of open recirculating
systems amounts to only 2-5% of that from once-through cooling systems at equal
cooling capacity.
Besides the above mentioned, there are also closed circuit cooling systems (dry air-
cooling), which are operated without wastewater emissions and are usually applied
at high process temperature levels above 50C. Hybrid cooling systems combine the
wet and dry cooling principles.
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72.2 Cooling water flow
The discharge of cooling water into surface water has substantial significance for
water economy. The water resource balance shows that about 40% of the
precipitation drained off in Germany is used for cooling purposes, whereas significant
differences in the river basins can be observed because of to regional industrial main
areas and the varying water flow of the principal water recipients. For example, the
proportion of cooling water from the total flow of the Elbe and Rhine Rivers is above
60%, while the proportion from the Danube River amounts only to about 10% (Table
1; Table 2).
Table 1: Cooling water discharge in river basins (1995) [Mio. m3]
Table 2: River flow volume balance for Germany in 1992
The power plants for public supply, with 84% of all cooling water discharges, are the
most important dischargers. Only 219 million m3 cooling water from mostly small
companies were indirectly discharged via municipal sewage treatment plants, so the
cooling water proportion of municipal wastewater amounts to only 2-3 % of the total
by volume. Thus, nearly all the volume of cooling water (>99%) is discharged directly
River basin Donau Rhein Maas Ems Weser Elbe
coast and sea Oder sum
Cooling water discharges of mining and industry 536,7 3.621,7 17,1 34,8 175,9 597,4 16,7 45,5 5.045,9
direct dischargers 500,5 3.527,7 15,1 33,0 156,4 532,8 15,6 45,4 4.826,4indirect dischargers 36,3 93,9 2,0 1,8 19,6 64,6 1,2 0,1 219,4
Cooling water discharges from power industry for public supply 1.974,6 12.603,0 n.a. 62,1 4.647,8 7.178,9 880,3 1,0 27.347,7Source: Statistisches Bundesamt Fachserie 19, Reihe 2.2, 1998Maas=sum of cooling water of the Rur, Schwalm and Niers Rivers
River basin Donau Rhein Maas Ems Weser Elbe
coast and sea Oder sum
Average runoff into BRD [m3/s] 579 1225 253 n. a 2057Average runoff from BRD [m3/s] 1346 2043 32 111 347 610 201 11 4701Runoff from area of BRD [m3/s] 767 818 32 111 347 357 201 11 2644Cooling water effluents in total [m3/s] 80 514 1 3 153 247 28 1 1027Proportion of cooling water from MQ with runoff into BRD 6% 25% 40% 14% n. a 22%Proportion of cooling water from MQ from area of BRD 10% 63% 2% 3% 44% 69% 14% 13% 39%Source: Statistisches Bundesamt Fachserie 19, Umweltkonomische Gesamtrechnungen, August 1994
Statistisches Bundesamt Fachserie 19, Reihe 2.2, 1998, changed to m3/sMQ = Average runoff in 1992 of the respective draining areas of rivers; BRD=Federal Republic of Germany
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8into the receiving water course. Conequently the chemicals used for cooling water
conditioning immediately enter the receiving water, so that a particular risk potential
might arise, unless the chemicals are inactivated in the cooling system itself.
Considering the different industrial sectors of cooling water dischargers (cf., table 3)
it is evident that, next to the power plants for public supply, in particular the chemical,
mining and metal industries are the principal dischargers of cooling water. From the
proportion of "used" and "discharged" cooling water a "utilization factor" can be
calculated. This factor gives an indication of the importance of open recirculating
cooling systems in the respective industrial sector. (The data on cooling water
utilization also contain the recirculated volume and multiple-shift uses for different
purposes.)
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9Table 3: Ratio of used/discharged cooling water (1995)
2.3 Minimum requirements for cooling water discharges in Germany
In Germany the discharge of cooling water is regulated in Annex 31 of the
Framework regulation for wastewater. Here inter alia the following requirements are
given:
With the exception of phosphonates and polycarboxylates exclusively complexing
agents which are readily bio-degradable may be used,
The wastewater must not contain chromium, mercury or organometallic
compounds,
The concentrations for chlorine, AOX, COD, phosphorus and zinc are limited,
Water used for cooling purposes
Water used for cooling
Discharged cooling water
without treatmentUtilisation factor *)
*1000 m3 *1000 m3
Power plants for public supply 61.759.994 27.347.665 2,3
Mining industry 5.616.335 812.998 6,9Foodstuff and tobacco industries 905.610 161.889 5,6Textile industry 176.554 145.123 1,2Leather industry 4.170 317 13,2Wood manufacturing 41.723 11.609 3,6Paper and printing industry 683.511 390.528 1,8Coking plant and petroleum processing 2.415.387 127.419 19,0Chemical industry 11.333.036 2.488.627 4,6Rubber ware production 640.606 65.111 9,8
Glass, ceramics and stone commerce 382.479 28.497 13,4Metal products and manufacturing 5.091.455 616.186 8,3Engine construction 236.904 26.284 9,0Production of office machines, electrical engineering 393.444 59.964 6,6Vehicle construction 1.143.730 108.069 10,6
Production of furniture etc., recycling 50.581 3.261 15,5Sum of industrial cooling systems 29.115.525 5.045.882 5,8
Grand total of all cooling systems 90.875.519 32.393.547 2,8Reference: Statistisches Bundesamt Fachserie 19, Reihe 2.2, 1998*) The Utilisation factor here refers to the discharged cooling water and not to the make-up water!
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10
For fresh water cooling systems a shock treatment with microbicidal substances
is limited to oxidative biocides (chlorine, chlorine dioxide, hydrogen peroxide,
ozone).
After a shock treatment with a biocidal substance the blow down of recirculating
cooling systems is only allowed if the luminescent bacteria toxicity does not
exceed GL =12 (GL= Lowest ineffective dilution factor, LID).
Annex 31 currently is being revised and will be in force in 2002 (Anonymous 2001). A
background paper (draft of the Bund/Lnder GK 21/41 from 17.12.2001) will also be
published in 2002.
In the course of the implementation of the EC-directive 96/61/EC concerning
Integrated Pollution Prevention and Control (IPPC-directive) an extensive "Reference
Document on the Application of Best Available Techniques to Industrial Cooling
Systems" was elaborated, which is available in the internet (http://eippcb.jrc.es). The
aim of the IPPC-directive is to optimize the operation of industrial plants, so that
while considering energy efficiency and waste avoidance no substantial pollution of
the environment will be generated. Hereby measures for the improvement of one
environmental compartment (e.g., water) shall not lead to additional stress of another
compartment (e.g., air). The reference document offers a comprehensive
documentation for the selection of cooling systems, technical descriptions and
potential environmental effects. It is clear that the cooling system cannot be
considered separately from the industrial process and location. By optimizing the
overall process substantial amounts of energy can often be saved. In addition, the
excess energy should be used insofar as possible, for example for hydrothermal
heating projects. Although in the reference document approaches for evaluating the
chemical additives in cooling systems are described (cf., sect. 7.4), until now there
has been no systematic presentation of the basic data required for this, both on the
input side (consumption data), as well as on the material, chemical side
(degradability, ecotoxicity, genotoxicity, bioaccumulation).
2.4 General environmental hazards from cooling systems
In the operation of cooling systems a complex field of tensions between various
usage interests and environmental conflicts arises. The water consumption is highest
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11
for once-through cooling systems and for larger power plants this can exceed several
m3/s. Depending on the mesh width of the inflow rates to the cooling system and the
flow rate, substantial numbers of fish, especially young ones, can be sucked in and
killed (up to 25 fish per 1000 m3; Anonymous 2000). The temperature increase in the
surface water leads to a reduction of the oxygen solubility in the water together with
an increase in the metabolic activity. Since this can lead to a shift in the species
spectrum in the waters (LAWA 1991), heat load plans have been prepared for the
waters. The EU-Guideline 78/659/EWG specifies for Salmonid and Cyprinid waters,
among other things, the maximal permissible temperature elevations (1.5C and 3C)
and maximal temperatures (21.5C and 28C, and, during the spawning period of
cold-water fish, for certain waters 10C; 78/659/EWG 1978).
For cooling towers a large part of the heat burden is released as latent heat
(evaporation) and causes an increase of the air temperature, which can lead to
changes in the local microclimate (VDI 3784: 1986). For large power plants natural-
draft wet cooling towers are used, for which the construction height provides
sufficient force to drive the air current. For ventilator cooling towers the necessary
amounts of air are, in contrast, introduced by forced air blowers, for which electrical
energy must be provided (corresponding to 0.5-2% of the amount of emitted heat
energy, Anonymous 2000). For open recirculation cooling systems the water
consumption is usually reduced by ca. 95%-98% compared to once-through cooling
systems at equal cooling capacity. At the same time, however, the electrical energy
needed for the pumps is increased by ca. 50% thus amounting to ca. 1.5% of the
amount of emitted heat energy. The evaporation losses can be taken to be ca. 0.4-
0.7 l/s per 1000 MW of output electricity (Wunderlich 1978b). This leads to an
increase in the concentration of the constituent compounds in the water, so that
often a purification of the water and/or a conditioning of the cooling water is
necessary, which then requires the addition of chemicals to the receiving waters.
The most urgent goal of the plant management of cooling systems, however, is their
efficiency and protecting the system against depositions (scaling), corrosion and
biomass growth (fouling). The formation of depositions on the cool water side of a
heat exchanger or pipeline interferes with heat transfer and increases the loss of
pressure, so that the performance is substantially reduced. Ultimately, this leads to a
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12
higher water consumption and must be compensated by an increased application of
energy. Thus, a calcium deposit 0.5 mm in thickness reduces heat transfer in
condensers by ca. 20% (Todutza and Steinlein 1990). Corrosion processes not only
damage the system, but also increase the risk of leaks on the production side. In
addition, the corrosion products endanger the waters.
A control of the biomass growth is performed with the additional goal of minimizing
the microbiological risks arising from the cooling plant. It is known, for example, that
thermophilic human pathogens, especially Legionella pneumophilia, which causes a
severe pneumonia (Legionnaires disease), can be found in cooling systems (States
et al. 1987, Kusnetsov et al. 1997, Werner and Pietsch 1991, Howland and Pope
1983, Kusnetsov et al. 1993). Guidelines for controlling Legionella in cooling systems
are available (Anonymous 2001a).
2.5 Cooling water conditioning
For the prevention of scaling in recirculation cooling systems, dispersants and
hardness stabilizers are added. In addition, corrosion inhibitors and biocides are
used, whereby there are overlaps between the individual groups (e.g., phosphates
act both as hardness stabilizers and corrosion inhibitors).
2.5.1 Dispersants and hardness stabilizers
The precipitation of salts due to their exceeding their solubility limits is termed
scaling. Of particular interest in cooling systems is the precipitation of calcium
carbonate and calcium phosphate, and to a limited extent also calcium sulfate and
silicates. The hardness of the water can also be reduced by active decalcification
(precipitation with calcium hydroxide). The residual hardness is either removed by
conversion of the carbonate hardness into non-carbonate with acids (primarily
hydrochloric and sulfuric acid) or stabilized through the addition of hardness
stabilizers such as orthophosphate, polyphosphates and phosphonic acids. The
ready hydrolysis of polyphosphates to orthophosphate and the associated danger of
calcium phosphate deposition led to the development of stable phosphonic acids,
which are added in sub-stoichiometric amounts (Andres et al. 1980). The most
important phosphonic acids used in the field of cooling water treatment are aminotri-
methylenephosphonic acid (ATMP), hydroxyethanediphosphonic acid (HEDP) and
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13
phosphonobutanetricarbonic acid (PBTC). Organic polymers based on polyacrylic
acid, polymetacrylic acid, polymaleic acid and polyacrylamide (so-called
polycarboxylates) also have a certain hardness stabilizing effect and are often used
in combination with phosphonic acids.
The calcium carbonate hardness can be stabilized with, e.g., carboxymethylcellulose.
To a limited extent complex formers (NTA) are used; EDTA is however excluded de
facto from use because of its poor degradability.
Further depositions can also be caused by the precipitation of suspended organic
and inorganic particles and iron oxides. To prevent this, dispersants based on the
above mentioned polycarboxylates as well as low-molecular weight anionic acids
(e.g., succinates) are added. These are to be distinguished from natural products,
such as lignins and tannins, and from synthetic polymers of the polyacrylic,
polymetacrylic, and polymaleic acids as well as sulfonates. The transition between
the hardness stabilizers and the dispersants is not clear-cut.
2.5.2 Scale inhibitors
The corrosion of metals is enhanced by the presence of oxygen, salt content
(especially chlorides) and a low pH, but also by deposits. During oxygen corrosion
metal ions are dissolved at the metal surface, which acts as the anode, while in the
cathodic reaction oxygen is reduced to hydroxide ion and a high pH is produced
locally (Anonymous 1991). Of particular importance is microbially induced corrosion,
which is caused by acidic metabolic products as well as the anoxic/anaerobic
conditions within biofilms. Sulfate-reducing bacteria of the genus Desulfovibrio act
corrosively, by reducing the sulfate while forming hydrogen sulfide. These bacteria
are among the most important in cooling systems (Koppensteiner 1973). However,
corrosion can also be induced by sulfur bacteria (Thiobacillus), iron bacteria
(Ferrobacillus, Gallionella) and nitrifying bacteria (Nitrosomonas, Nitrobacter).
Passive (anodal) corrosion inhibitors, such as phosphates, phosphonates, nitrite,
silicates and molybdates form a passive protective layer on the metal surface. The
use of chromate is no longer permitted. In contrast, cathodic inhibitors like zinc or
calcium carbonate, and to a limited extent also orthophosphate, form insoluble
deposits which protect the metal surface by reacting with the corrosive hydroxyl ions.
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14
Especially for copper and copper alloys, 1,2,3-triazoles are used as inhibitors.
Mercaptobenzthiazoles may no longer be used for this purpose according to Annex
31 of the AbwV regulations.
2.5.3 Biocides
The mean temperature in water cooling systems is ca. 35C and thus lies just below
the temperature optimum of most microorganisms (Mattila-Sandholm and Wirtanen
1992). Biocides are used to control biologically induced deposits and corrosion
processes. For cooling water systems algicides, fungicides and molluscicides are
relevant.
2.5.3.1 Biology in cooling systems
The growth of autotrophic algae is dependent on the presence of mineral nutrients,
carbon dioxide and light energy, while the growth of heterotrophic bacteria requires
organic material, which is composed of dead algae and/or the existing burden of the
water or air. In principle, bio-degradable conditioning agents can also function as a
carbon source. Many bacteria secrete a highly hydrated slime consisting of
polysaccharides, which leads to the formation of biofilms on surfaces (biofouling).
Biofilms decrease heat exchange, promote corrosion and hinder control by means of
biocides. Protozoa such as Ciliates or Ambae colonize affected cooling towers as
consumers, as do higher organisms such as mussels and snails, which can lead to
serious disturbances.
In once-through cooling systems, because of the short retention time and the
requirement for a rapid elimination, fast-acting oxidative biocides are used; and in
open cooling systems, non-oxidative, more stable organic biocides are called for.
2.5.3.2 Oxidative biocides
The most commonly used oxidative biocide, owing to its effectiveness and low price,
is chlorine or cholorine bleach (sodium hypochlorite). At the pH-values of > 8 typical
for cooling system circulation, there is a reduction of the biocidal effect of the active
substance, hypochlorous acid (HOCl), while hypobromous acid is still effective at pH
9. Hypobromous acid is generally generated on site by adding sodium bromide to
sodium hypochlorite (NaOCl). The use of free halogens as biocides may, depending
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15
on the water composition (e.g., DOC- and ammonium concentration), pH-value and
contact time, lead to the formation of disinfectant by-products such as
trihalomethanes, chloro- and bromoamines as well as absorbable organic halogen
compounds (AOX).
In the purification of drinking water chlorine is replaced in part by chlorine dioxide, in
order to minimize the formation of AOX, especially halogen methanes. Chlorine
dioxide reacts noticably more weakly with complex organic molecules and
ammonium, consequently forming less AOX. Chlorine dioxide is also occasionally
used in the cooling water field, whereby it is usually generated on location through
the reaction of chlorine gas with sodium chlorite (NaClO2). Organic chlorine and
bromine release agents are used especially in open recirculation cooling systems.
Here, above all, the rapidly hydrolyzing biocide 1-bromo-3-chloro-5,5-
dimethylhydantoin (BCDMH) should be mentioned. Related compounds like 1,3-
dichloro-5,5-dimethylhydantoin or 1,3-dichloro-5-ethyl-5-methylhydantoin are also
occasionally used.
Ozone is a highly effective oxidatively acting biocide. Usually, ozone is continuously
added to the cooling water in very low concentrations of 0.1 to 0.3 mg/l (Wasel-
Nielen and Baresel 1997, Viera et al. 1999). Production is achieved directly on
location using high voltage, In comparison with the other oxidative biocides,
hydrogen peroxide is only effective at higher concentrations (> 15 mg/l; cf., van Donk
and Jenner 1996) and has a short half-life. Rarely, peracetic acid is also used as an
organic oxygen release agent in cooling systems. Under unfavorable conditions,
peracetic acid is corrosive. This chemical is readily bio-degradable.
2.5.3.3 Non-oxidative biocides
Non-oxidative biocides are used nearly exclusively in open recirculation cooling
systems, where the contact time of the cooling water with the biocide suffices for a
satisfactory effect. As a rule, here the biocide is added batchwise in a shock
treatment.
One of the most important non-oxidative cooling water biocides, a mixture consisting
of a chemical belonging to the isothiazolinone family, 5-chlorine-2-methyl-4-
isothiazolin-3-one, together with 2-methyl-4-isothiazolin-3-one, is already effective at
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16
concentrations below 1 mg/l. Isothiazolinones hydrolyze slowly (t1/2 = 7 d at 30C and
pH 8) and are not readily bio-degradable. Quarternary ammonium compounds (QAV)
act through their binding to the cell membrane and are also not readily bio-
degradable. During passage through the sewage treatment plant they are largely
eliminated by adsorption on the activated sludge. The most important representative
in the cooling water area is alkyldimethylbenzylammonium chloride.
The addition of dibromonitrilopropionamide (DBNPA) is also widespread in the
treatment of cooling water. This compound hydrolyzes rapidly to the still partially
biocidally active compounds dibromoacetonitrile, dibromoacetamide, monobromo-
nitrilopropionamide and cyanoacetamide. Further members of the organic bromine
compound group include 2-bromo-2-nitropropan-1,3-diol (Bronopol) and beta-bromo-
beta-nitrostyrene.
Glutardialdehyde is also rather frequently used in the cooling water field. The
mechanism of action is based on the denaturation of proteins. Glutardialdehyde is
less toxic for aquatic life forms as compared to the other biocides, and the
concentration added is correspondingly higher. This compound is readily bio-
degradable. Specifically for the control of algal growth additional biocides are used,
such as copper sulfate, as well as photosynthesis inhibitors based on triazine-
derivatives.
To reduce the risk of the appearance of microorganisms resistant to the added
biocides combination products containing several biocides are used.
2.5.3.4 Elimination of the biocidal effects
A basic requirement for cooling water biocides is that their damaging action or
biocidal effects must diminish in a relatively short time, since otherwise there might
be toxic effects on the surface waters, especially after the direct discharge of cooling
water. This calls for a rapid hydrolysis and/or biological degradability of the biocides.
For indirect emissions via municipal sewage treatment plants it has to be proven that
the biological wastewater treatment is not inhibited and that the biocides are retained
in the treatment plant. Preferably, the biocides should be biologically degraded.
While elimination through adsorption on the activated sludge (cf., QAV) protects the
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17
receiving water, this merely shifts the problem, when the collected sludge is spread
on the land for agricultural or forestry use.
The elimination of the biocidal effects can be assayed either in the laboratory or on
site at the actual treatment plant. For the completion of such so-called elimination
curves in the laboratory there are, however, no generally acceptable specifications
to date. Here the manufacturers have proposed static experiments with relatively
high concentrations of activated sludge (0.5 g d.s./l), in order to simulate the
influence of a hypothetical biofilm in the cooling system circulation (Scheidel et al.
1996). Other authors, on the other hand, determine an elimination curve without
adding any inoculum (Gartiser and Scharmann 1993, Gellert and Stommel 1995,
Baltus et al. 1999).
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18
3 Goals and investigative strategy
In accordance with the project description, the following goals have been set:
Estimation of the emission of cooling water conditioners in flowing surface waters
of the Federal Republic of Germany
Determination of the introduced cooling water chemicals and investigation with
respect to their ecotoxicity, genotoxicity, bioaccumulation and degradability
Determination of current practices of the governmental control agencies in the
individual Bundeslnder
Extension of the data status on ecotoxicity, genotoxicity and biological
degradability of the cooling water chemicals in use through measurements of our
own
Develop suggestions/proposals for the reduction and optimization of the addition
of cooling water chemicals
Develop a recommendation for the selection of cooling water chemicals based on
the present technical state of the art
The investigative strategy is based on three pillars (see Fig. 1):
Literature and database research on the active ingredients/substances of the
standard commercially used cooling water conditioners
Drawing up of an overall accounting balance sheet of the loads and
concentrations of cooling water conditioners in treatment systems
Direct testing of cooling water samples, products and active ingredients with
respect to their ecotoxicity and genotoxicity, as well as determining the rate of
elimination of biocides (elimination curves)
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19
Figure 1: Investigative strategy
- Products- Active substances- Elimination of biocides- Ecotoxicity, Biodegradability Genotoxicity
- Consumption data of plants- Wastewater concentration- Total volume loads in BRD- Total loads of active Subst.
Cooling water
Active substances/Products
Comparision of data
Elimination of biocides/
Products
Research Overall Balance
Tests
Practice of regulatorycontrol
State of the art
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20
4 Methods
4.1 Laboratory investigations
4.1.1 Cooling water samples
Cooling water samples from 7 treatment plants in Southern and Northern Baden
were investigated. All these plants have open recirculation cooling systems.
Collection of the samples was as qualified test samples direct from the investigated
cooling vessel or from the return flow of the circulation (DIN 38402 1991). The
descriptive data of the investigated cooling water with respect to water consumption
and the products added are presented in Table 4.
a) Plant 1, Electroindustry
The operation of a semi-conductor manufacturer has six cooling towers with a total
cooling capacity of 2.5-3 MW. The cooling tower investigated has a cooling capacity
of 1.2 MW and removes the heat produced by a refrigeration system. As a special
feature, the concentrate of the water treatment (reverse-osmosis system with a
capacity of 700 S/cm) is used as cooling water. For hardness stabilization and
corrosion inhibition a product based on sodium phosphonates, sodium molybdate,
sodium polycarboxylates and triazoles is added continuously. As a biocide,
isothiazolinone is added in summer as needed. Through regular mechanical cleaning
of the cooling vessel and an adequate shading of the cooling tower the amount of
this chemical added was reduced by more than 90% compared to the previous
years. The yearly consumption of isothiazolinones in the year 2000 was ca. 0.4 kg/a
of active substance. At the time of sampling no biocides were being added.
b) Plant 2, Plastics manufacturing industry
The company manufactures molded plastic parts for the automobile industry and has
several cooling towers with a total capacity of 6700 kW, which are fed with ground
water. As biocide a quarternary ammonium compound is added batchwise as
needed and then the outflow is closed for the next three days. The time of addition is
decided upon by visual examination of the algal growth. In addition, corrosion
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21
inhibitors and hardness stabilizers based on phosphonic acids, zincchloride and
dispersants are continuously added.
The first sample collection on 19.07.00 took place two months after a shock
treatment with biocides, and the second and third samples were taken either directly
after the biocide was added and after an elimination time of three days resp. Besides
the cooling water, the wastewater produced from the released steam, to which
hydrazine was added, was also examined.
c) Plant 3, Plastics manufacturing industry
The plant manufactures PVC-foils and has a cooling tower with a capacity of 2.3-9.2
MW. Ca. 250 m3 of completely desalted cooling water are added weekly. In the non-
shaded cooling tower problems with algae arise. In this event, a "heterocyclic
sulfur/nitrogen-compound" (Isothiazolinone) is added batchwise in a shock treatment
(total load 0.8 kg/a active ingredient).
d) Plant 4, Plastics industry
The plant of a manufacturer of adhesive foils has four cooling towers, whose function
is to thermally reclaim solvents from activated charcoal filters. About four times a
year a preparation based on isothiazolinones is added batchwise (ca. 30 liters of
product/a). After a retention time of 24 h according to statements from the operator,
the GL-value is ascertained to be below 12. As hardness stabilizers polycarboxylates
and phosphonocarboxylates are added continuously. At the time of the collection of
the first sample, there was no addition of biocide, and the second sample was taken
24 h after a biocide treatment just after the outflow was reopened.
e) Plant 5, Plastics manufacturing industry
The plant manufactures foamed polystyrene- and polypropylene-packaging and has
three cooling towers. For the foaming of the plastics 10-12 t/h of desalted boiler
feeder water (steam) is needed. The boiler feeder water is treated with a corrective
material and the condensed steam (condensate) enters the open cooling system
during the production process. Thereby solid materials from the production process
are also carried over and are removed from the cooling water circulation with bag
filters (towel filters). These filters are cleaned daily. Twice weekly 60 liters of a
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22
biocidal product based on hydrogen peroxide and quarternary ammonium
compounds are added. The cooling water sample was taken in the filter outflow 7 h
after a batch treatment.
f) Plant 6, Chemical industry
The plant has two cooling water systems, which were both sampled. The plant
cicrculation (KW1) has four forced-aeration cooling towers and is operated with a low
compression ratio of 1.1. The second circulation (KW2) handles the central cooling
system and is run at a high cycle of concentration of 3.0. Both circulations are
treated continuously with the biocide 1-bromo-3-chloro-5,5-dimethylhydantoin. As
needed, a product based on 2-bromo-2-nitropropan-1,3-diol and isothiazolinones is
added. For corrosion inhibition phosphonic acids and tolyltriazole are continuously
added.
g) Plant 7, Chemical industry
This pharmaceuticals producing operation set up a new cooling system for the
expansion of the refrigeration plant. A portion of the drinking water needed for
feeding this system is completely desalted by an ion-exchanger. The cooling water is
treated twice weekly for several h with the biocide 1-bromo-3-chloro-5,5-
dimethylhydantoin. To inhibit corrosion phosphonic acids and triazoles are added
continuously. The sample was collected 24 h after the last biocide treatment after
opening the outflow.
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23
Table 4: Charateristic data for the investigated systemsFirm Water consumption Principle Products Active
ingredient 1
Active
ingredient 2
Active
ingredient 3
Active
ingredient 4
Branch [kW] [m3/a]
[m3/(a*KW)]
Concentrationratio
Pro-ducts
Biocide-addition
Pro-duct[kg/a]
Discharge
Conc.[%]
Load[kg]
Conc.[%]
Load[kg]
Conc.[%]
Load[kg]
Nr. 1 2.500 14.402 5,8 RO OK Biocide 1 10 KA CMI 2,4 0,2 MI 2,4 0,2Electro- TW Product S 457 Triazoles 2,5 11,4 NaOH 2,5 11,4 Phosphonate Na.molybdateindustry Product 90 HCl 21,0 18,9 (without conc.)Nr. 2 6.700 1.761 0,3 G OK Biocide 3 S 660 KA QAVPlastics manufacturing 1,8 Product 2250 HEDP 15,1 339,8 ATMP 20,1 452,3 Polyoxy-
carbonacid10,1 227,3 Zinc chloride
(without conc.)Product 4145 HCl 30,0 1243,4 HEDP 9,9 1,4-Butindiol 9,9 410,3
Nr. 3 3.000 13.000 4,3 VE OK Biocide 4 S 40 KA CMI 0,9 0,4 MI 0,9 0,4Plastics manufacturing ? PO43- 24 Ortho-
phosphate100,0 24,0
Nr. 4 18.710 23.579 1,3 G OK Product 900 O Poly-carbonates
Phosphon-carbonate
Foil production 3,0 Biocide 2 S 30 CMI/MINr. 5 4.000 2.600 TW OK Biocide 5 S 6240 KA H2O2 QAVPlastics manufacturing NaOH 3120 NaOH 25,0 780,0
Product 1200 Polyethoxylate Non-ion.Tenside
Nr. 6 Chemical Industry 7020 NaOH 3,5 245,7 Tolyltriazole 3,0 210,6 Phosphonicacid
7,5 526,5
Circulation1
6.300 720.000 114,3
G OK/1,1 1600 Phosphonicacids
Biocide 6 K 644 O and BCDMH 25,1 161,6Biocide 7 S 125 KA Bronopol 9,0 11,3 MI 1,8 2,3 CMI 1,8 2,3NaOCl 2000 Sodium-
hypochlorite13,0 260,0
Circulation2
43.500 120.000 G OK/3,0 Product 7350 NaOH 3,5 257,3 Tolyltriazole 3,0 220,5 Phosphonicacid
7,5 551,3
Product 1000 Phosphonicacids
Biocide 6 K 2323 KA BCDMH 25,1 583,1Biocide 7 S 25 Bronopol 9,0 2,3 MI 1,8 0,5 CMI 1,8
Nr. 7 6.000 58.000 9,7 TW OK Product Planning KA Polycarbonicacid
17,5 Phosphonicacid
6,3 Triazole 2,5
Chemical Industry max. 4.0 Biocide 8 S stage BCDMH 75,0Water consumption: G=Ground water; RO=Reverse osmosis; VE=completely desalted water; TW=Drinking water; Biocide added: K= continuous; S=Batch treatment; Source: O=surface water; KA=municipal waterpurification plant; ingredients: CMI: 5-chloro-2-methyl-2H-isothiazolin-3-one; MI: 2-methyl-2H-isothiazolin-3-one; BCDMH: 1-bromo-3-chloro-5,5-dimethylhydantoin; Bronopol: 2-bromo-2-nitropropan-1,3-diol; HEDP: 1-Hydroxyethan-1,1-diphosphonic acid; ATMP: Aminotrimethylphosphonic acid
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24
4.1.2 Product investigations
Altogether five biocides and one corrosion inhibitor were tested. All of these active
substances are used in the plants investigated. They were tested with respect to
their mutagenicity, genotoxicity and ecotoxicity. At a later time four more products as
well as the biocide Bronopol were investigated in the umu test, in order to to
determine the source of the genotoxicity in the wastewater of one plant by systematic
"backtracking". An additional emphasis was the determination of the elimination
behavior of the most important biocides applied in the cooling water field, using the
fluorescent bacteria test (cf., sect. 4.1.9).
4.1.3 Chemical parameters
pH-value: pH 196 pH-meter from WTW GmbH in Weilheim.
Conductivity: Measuring instrument pH-LF 3001 from Neukumelektronik GmbH in
Straubenhardt.
CSB: Round cuvette test (Dr. Lange Co.): Two-hour oxidation with potassium
dichromate, sulfuric acid, silver- and mercury sulfate at 148 C in conformance with
DIN 38409 H41.
Chlorine (free and total): Round cuvette test (Dr. Lange Co.): reaction with diphenyl-
p-phenylendiamine (DPD) witih the formation of a colored substance; total chlorine
determined after addition of potassium iodide.
4.1.4 Fluorescent bacteria test according to DIN 38412-34 and Nr. 404 of theAbwV
The toxicity of wastewater contaminants is detected on the marine bacteria of the
species Vibrio fischeri, which show a natural light production (bioluminescence) that
is closely coupled with their metabolic activity. The decrease of the light intensity
provides a quantitative measure of the toxic effect on the bacteria. The test is
performed with the LUMIS-tox system of the company Dr. Lange, Dsseldorf. The
lyophilized bacteria of the strain Vibrio fischeri NRRL-B-11177 were obtained from
the same company (LCK 482). The wastewater samples were tested without further
pre-treatment after salinizing with sufficient sodium chloride to give a 2% solution
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25
and adjusting the pH-value to 7.0 +/- 0.2. The test result is given as the least
stepwise dilution (GL-value), for which the light emission is inhibited less than 20%.
4.1.5 Alga test according to DIN 38412-33 and Nr. 403 of the AbwV
The chronic inhibitory effect of the cooling water samples on the growth of
Scenedesmus subspicatus, a planktonic fresh-water alga, was determined. For this
purpose, a dilution series of the cooling water sample was made, without any further
preparation, but adding an algal nutrient solution inoculated with a defined algae
suspension (corresponding to 104 cells/ml) and incubating under defined light and
temperature conditions. After 72 h, the number of cells was determined
microscopically as a measure for the biomass. The result given is the least dilution
step (GA-value), after which the measured inhibitory effect on biomass production is
less than 20%.
4.1.6 Daphnia test according to DIN 38412-30 and Nr. 402 of the AbwV
The acute toxic effect of wastewater on Daphnia magna STRAUS (Crustacea, clone
5 of the German Federal Health Agency) was determined. The value measured is
the dilution factor GD beyond which no acute toxicity for Daphnia is detected within
24 h. The GD-value corresponds to the least dilution factor by which a wastewater
sample must be diluted in order for 90% of the Daphnia to maintain their ability to
swim. The pH-value of the sample was adjusted with hydrochloric acid or sodium
hydroxide solution to 7.0 7.5. No other pre-treatment was performed.
4.1.7 Ames test in conformance with DIN 38415-4
The Ames test is a bacterial mutagenicity test with Salmonella typhimurium. The
Salmonella-bacterial strains used are deficient mutants, which are unable to grow in
histidine-free medium. These histidine-requiring mutants can back-mutate (reversion)
and then are able to form colonies on minimal-agar plates. Each of the Salmonella-
strains has a specific spontaneous mutation rate. The number of back-mutated
bacteria (revertants) above this level provides a measure of the mutagenic potential
of a substance or a sample. Certain mutagens in higher organisms are first activated
by being metabolized (promutagens) or are thereby inactivated. Therefore, to the
bacterial system the needed enzymes are added in the form of rat liver extract S9
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26
(Moltox Co.). The test version used is based on a simplified version of the OECD-
Guideline 471 with the test strains TA98 and TA100. The strain TA98 detects
frameshift mutagens; strain TA100 in contrast is for base pair substitution mutagens
(point mutations). The cooling water samples were sterilized over a membrane filter
(0.45 m). Up to 1 ml of cooling water per Petri dish could be added. Because of the
substantial effort involved, the samples were initially investigated in the Screening-
Test at only one test concentration. A sample is then classified as mutagenic
according to DIN 38415-4 if in one of the strains with or without S9 an induction
difference compared to the control (solvent alone) of 80 (for TA100) or 20 revertants
(for TA98) is induced and a dose-effect relationship is found. The GEA-value
corresponds to the last dilution step at which the induction difference established for
that strain is not exceeded. Since the wastewater sample in the test is diluted by a
factor of 3 with medium/inoculum, the lowest possible GEA-value = 3 (non-
mutagenic). The number of revertants of the negative controls should be: for TA100
in the range of 80-180 and for TA98 in the range of 15-40 revertants per plate.
In testing substances or products a sample was evaluated as being mutagenic in
accordance with the relevant OECD-guideline if the induction rate (ratio of the
number of revertants in the test plates to the negative controls) exceeded a factor of
2 and a dose-effect relationship existed.
4.1.8 umu test according to DIN 38415-3 and Nr. 410 of the AbwV
The umu test is a genotoxicity test with the gene-technologically modified bacterium
Salmonella typhimurium strain TA1535/pSK 1002. The bacteria are exposed to
various concentrations of the cooling water. Here gene toxins induce the so-called
umuC-gene, which belongs to the SOS-repair system of the cell and which acts to
prevent damage to bacterial genetic material. Through the coupling of the umuC-
gene promoter with the lacZ-gene for -galactosidase the activation of the umuC-
gene can be indirectly measured spectrophotometrically at 420 nm through the
formation of a colored product from the -galactosidase substrate o-nitrophenyl-
galactopyranoside (ONPG). The induction rate (IR) corresponds to the increase of
the extinction at 420 nm relative to the negative control. In calculating the induction
rates one must take into account the growth factor, which is determined
turbidometrically from the optical density at 600 nm. An inhibition of bacterial growth
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27
is expressed as a reduced growth factor ("Wachstumsfaktor" or WF) compared to the
controls. For growth factors below 0.5 (50% growth inhibition) the results are not
evaluated. The result given is the smallest dilution step G (GEU-value), at which an
induction rate < 1.5 is measured. If a different induction rate is seen upon addition of
S9, the higher of the two values is taken (=GEU-value).
4.1.9 Elimination of biocides
Until now there have been no generally accepted specifications for a procedure to
determine elimination curves in the laboratory. On the part of the producing
companies there have been proposals for static experiments with a relatively high
concentration of activated sludge (0.5 g d.s./l), in order to simulate the influence of a
hypothetical biofilm in the cooling circulation (Scheidel et al. 1996). However, at an
UBA-Workshop on the present project the consensus was arrived at that such high
biomass concentrations in cooling circulation are not usual (cf., table 5, (Gartiser and
Urich 2001).
In order to determine the effect of the inoculum concentration on the elimination
behavior of biocides, various inocula were introduced. As a test-system the Zahn-
Wellens test according to DIN EN 29888 or Nr. 408 of the AbwV was
correspondingly adapted. The tests with activated sludge were supplemented with an
inorganic nutrient solution according to DIN EN 29888; all tests were continuously
stirred and aerated with an aquarium pump.
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28
Table 5: Determination of the elimination of cooling water biocides
Inoculum Concentration Comments
Activated sludge 1 g d.s./l Upper conc. Zahn-Wellens test
" 0.5 g d.s./l Proposal by VCI AG"Microbiocides in Annex 31"
" 0.2 g d.s.//l Lower conc. Zahn-Wellens test
" 0.03 g d.s./l OECD 301 A, B, C and F"ready bio-degradation"
Outflow final-clarifier
- Model for microbiologically activeinoculum with low d.s.-content
Tap water - predominantly abiotic hydrolysis
The starting concentrations of the biocides were selected on the basis of various
information provided on the effective concentrations of the active ingredients in the
cooling water (Baltus and Berbee 1996; Anonymous 1994, Fielden and Iddon 1997)
and in part reduced further according to updated information from the manufacturers
(Klautke 2001) (Table 9). As the end point, after filtration through a folded paper filter
a bacterial fluorescence toxicity test was performed at dilution step 12 (based on
Annex 31 to the AbwV). For low toxicity, dilution step 2 was also tested.
4.2 Drawing up an overall balance sheet
4.2.1 Compilation of production information materials
Letters were sent to a total of more than 100 firms in the chemical industry that also
offer product groups used in the cooling water field (including algicides, antifouling
agents, bactericides, corrosion inhibitors, dispersants, biocides, inhibitors, and water
chemicals). Addresses were obtained in some cases from the relevant handbooks
but also to a large extent through information provided by the operators of the
cooling plants. Altogether, 49 firms replied that they were not engaged in the cooling
water field. Product information was sent by 22 firms. These materials were of
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29
varying quality (from safety data sheets with little useful information to detailed
product descriptions with ecological evaluations). In order to learn more about the
substances in the products investigated in the context of preparing the balance (cf.,
sect. 4.2.2) the operators of ca. 50 cooling plants were requested to provide the
corresponding safety data sheets. In this way information on 418 products from 35
manufacturers was obtained and evaluated. The active substances documented in
these materials served as the basis for our literature- and database-research (cf., sect.
4.3).
4.2.2 Making a balance sheet of the emissions of cooling water chemicals
The yearly emissions of cooling-water chemicals by the firms considered in the
cooling water sampling were determined on site. In order to extend the data base a
questionnaire was prepared for the operators of the cooling plants, including
questions about the cooling system used, the cooling capacity, the source of the
water, the annual consumption of cooling water chemicals (on a product basis), the
mode of addition of biocides and the parameters controlled. Initially, this was sent to
all business-controlling governmental agencies in Baden-Wrttemberg and then to
the environmental agencies in all the Bundeslnder (usually to the Environmental
Ministry). After the questionnaires had been passed on to the local sub-authorities
and/or the operators of the cooling plants, they were then returned to us either
directly or through the authorities. In some cases, Hydrotox was also provided by the
authorities with lists of addresses of operators of cooling plants, and we then
contacted them directly. Ultimately, 182 questionnaires from 176 operators were
evaluated. Because of incorrect or incomplete data, ca. 1/3 of the firms had to be
contacted again by telephone or by e-mail. In most cases, we ultimately succeeded
in obtaining consistent data sets.
We did not ask about and consequently did not make any systematic balance sheet
for chemicals added in treating the water (decarbonizing, flocculation, production of
VE-water, regeneration of the ion-exchanger). Nonetheless, such consumption data
were provided by some of the operators and were evaluated.
Based on the annual consumption data for cooling water conditioners (on a product-
basis) and the recipes for preparation in product information sheets, the loads of
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30
defined ingredients and chemicals could be estimated. In cases where only an order
of magnitude of the substance concentrations was documented, the following
procedure was followed. Where less than or more than was given, the next lower
or higher concentration after the decimal was used for the balance. Where
concentration ranges were given, the mean was used. Example:
Given in the production information Assumed for the balance
< 10% 9.9%
> 10% 10.1%
10% - 20% 15%
When no concentration was given, and only the product group was listed in the
product information, typical concentrations from the literature or the available additive
concentrations and product recipes were used. For example, for quarternary
ammonium compounds and polycarboxylates no concentration could be obtained
from the product information sheets.
All data were subjected to a plausibility control. Thereby the annual water
consumption per installed kW of cooling capacity was calculated as a basic
parameter and the following classification was made:
Cooling system spec. water consumption [m3/(kW*a)]
Once-through cooling system 100 - 1000
Open recirculation cooling system 1 - 100
Closed cooling system 0 - 1
Deviations from this rule of thumb classification indicated incorrect data or special
features such as the use of hybrid cooling towers, a limited running time during the
year or the like. In addition, the calculated concentrations of introduced substances
in the wastewater of the individual plants were compared with the concentrations to
be added as given in the literature (Anonymous 1994, Baltus and Berbee 1996,
Fielden and Iddon 1997). For implausible concentrations the operators of the plants
were contacted.
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31
Estimating the annual loads for Germany:
In order to calculate to an order of magnitude the total consumption of cooling water
chemicals for Germany the questionnaires of the 176 plants were evaluated in
separate categories of once-through, open recirculation, and closed cooling systems.
The addition of chemicals in closed cooling systems was assumed to be irrelevant
for the wastewater since the amounts added at the time of initial filling can only with
some reservation be assigned to any years consumption (instead usually being
disposed of as a concentrate in the garbage when the water is changed). Because of
fundamental differences between industrial cooling systems and power plants (cf.,
sect. 5.4.4.1), the two categories were calculated separately. For the remaining
cooling plants the percentage of plants that used a particular substance or a
substance group was determined. Then the means and medians of the
concentrations (on a substance basis rather than a product basis) were calculated
from the annual water- and substance-consumption. Here the relationship of the
amounts consumed to the added water volumes is a parameter which makes it
possible to take into account the temporal components. (In principle, the substance
consumption could also be derived from the wastewater volumes, but usually these
were not known). For substances which were not continuously added, the calculated
mean concentration generally lies well below the actual concentrations in practice.
However, in individual cases, such as the shock treatment by batchwise addition of
oxidative biocides to the circulation water, higher concentrations could also be
calculated when the system volume is larger than the added water volume (cf., sect.
5.4.5). The estimation of the total loads of the non-continuously added chemicals
(biocides) for Germany was then obtained from the following formula:
Fx = Concx * AX * Qx / 1000
where
Fx Substance load [kg/a]
Concx Median of the balance concentration [mg/l]
Ax Relative proportion of the plants that use the substance
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(e.g., 0.01 represents 1%)
Qx Water consumption for cooling purposes [m3/a]
x Cooling principle (x = D for flow-through cooling and x = OK for open
circulation cooling)
This estimation is based on simplifying assumptions, which are briefly explained
below:
The classification of the plants as once-through, open recirculation, and closed
cooling systems is not always unequivocal. There are substantial overlaps so as
to give more of a continuum.
The estimation of the total loads from the proportion of the plants that use this
substance, based on the available data set provided by the operators, assumes
that the specific consumption values are independent of the size of the cooling
plant. This is only true to a certain extent. Thus, for example, larger plants tend to
use oxidative and smaller plants non-oxidative biocides. However, because of the
limited database at hand, a further sub-classification into various size classes,
going beyond the separate consideration of industrial cooling and power plants,
was not deemed appropriate.
In general, it can be assumed that in the various industry branches, different
requirements are placed on cooling water conditioning. Thus in the foodstuffs
industry, because of hygiene requirements, a tendency to higher consumption
amounts for biocides compared to other branches can be observed. However, the
limited database does not permit a separate consideration of each branch.
Although we asked the manufacturing firms to calculate the total loads on the basis
of their product sales for cooling water conditioners in combination with the
preparation recipes and the individual share of the market, we did not succeed in
obtaining the desired results (Gartiser and Urich 2001).
For continuously added conditioners (phosphonates, polycarboxylates) instead of the
balance sheet values, the concentrations to be added in normal practice, as provided
by industry, were used (cf., table 16). The annual loads of auxilliary additives (N-
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methyl-2-pyrrolidone, alcohols) as well as inorganic pH-regulators and flocculation
agents such as Fe(III)Cl3 for additional water treatment were not calculated for the
Federal Republic of Germany, because the consumption in the plants was not
systematically determined.
4.3 Literature and database-research
The cooling water chemicals for which literature- and database-research was to be
performed were determined on the basis of the product information. We did not
consider chemicals for water treatment (inorganic acids and bases, salts for
regeneration of the ion-exchanger) as well as auxilliary additives, e.g., solubilizing
aids such as alcohols, which have no specific biocidal, dispersive or corrosion
inhibiting effect. With the help of the following data banks/collections and databases,
research was carried out on the individual substances:
Substance data collections and fact databases
Roth: Wassergefhrdende Stoffe, ecomed-Verlag, Landsberg
Verschueren: Handbook of Environmental Data on Organic Chemicals, vanNostrand Reinhold (1996)
Kommission zur Bewertung wassergefhrdender Stoffe (KBwS): Dokumentationwassergefhrdender Stoffe, Hirzel-Verlag, Stuttgart
Merck Index 12th Ed. (1996)
Ash: Handbook of Water Treatment Chemicals, Gower House (1996)
Paulus: Microbicides for the Protection of Materials, Chapman & Hall (1993)
Rossmoore: Handbook of Biocide and Preservative Use, Chapman & Hall (1995)
Chemfinder, ECDIN and other Internet-Databases
Dictionary of Substances and Their Effects (DOSE)
International Uniform Chemical Information Database (IUCLID)
Hazardous Substances Data Bank (HSDB)
Data Bank of Environmental Properties of Chemicals (EnviChem)
Register of Toxic Effects of Chemical Substances (RTECS)
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Gefahrstoffinformationssystem der gewerblichen Berufsgenossenschaften(GESTIS)
PhysProp and Biolog/Biodeg (On-Line Databases of the Syracuse ResearchCooperation, SRC, http://esc.syrres.com)
Literature databases
Biological Abstracts
Current Contents
MEDLINE
The hazard risk statements (R-Phrases) in the dangerous substance regulations
were researched in the GESTIS database. Here, in addition to the official
classification according to Annex I of the Guideline 67/548/EWG, are also found self-
evaluations by the producers (http://www.hvbg.de/d/bia/fac/zesp/zesp.htm). We went
beyond this information and performed with varied success additional internet-
searches of the databases of the U.S. Environmental Protection Agency (EPA), the
U.S. National Institutes of Health (NIH) and the National Library of Medicine
(including the database GENE-TOX). The available data were compared with the
internal substance-database shared by Bund/Lnder (GSBL), which includes the
UBA-Neustoffdatenbank for new substances, the databases of the KBwS
(RIGOLETTO), the BgVV Chemis and BIG of the Feuerwehrinformationszentrum in
Geel (Belgium). Additional information so obtained substantially extended our
database.
A preliminary listing of the results of our research was distributed to participating
firms in preparation for the UBA-Workshop on the present project with the request
that they fill in any gaps in the data (Gartiser and Urich 2001). As a result, the data
pool was enlarged further. Whenever there were no citable published data available,
the product-specific entries on the safety data sheets of the manufacturers were
taken into account after consulting with them. The research results are presented in
the Annex to this report. It remains to be noted that it was not the aim of this report to
carry out a comprehensive and complete evaluation of all substances in the sense of
a Risk Assessment in accordance with the laws on chemicals or biocide-
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35
regulations. Consequently, as a standard for the selection of substance data we
relied on the wastewater relevance of the data. In addition, we looked at the oral
toxicity for mammals and the risk statements (R-Phrases), which are the prerequisite
for classification in water-hazard classes (Anonymous 2000). Those organisms that
are of importance in governmental control and are included in the list of parameters
of the wastewater regulations were given a higher significance. Hereby it was sought
to make a comparison possible with the practical investigations on wastewater
sidestreams, products and active ingredients.
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5 Results
5.1 Cooling water investigations
The results of the investigated wastewater samples are presented in Table 6. A total
of 12 cooling water samples and one condensate from steam production were
tested. The pH of the cooling water samples lay between 7.9 and 9.5; the
conductivity was between 121 s/cm (for VE-water in plant 2) and 10,130 S/cm (for
the concentrate of the reverse-osmosis system in plant 1).
The ecotoxicity of the cooling water samples in the algae, fluorescent bacteria and
Daphnia tests was in most cases low (GA/L/D -values from 1 to 3). After a shock-
treatment with quarternary ammonium compounds (plant 2) and isothiazolinones
(plant 6), values up to a dilution factor of GL=196 were determined. However, after
the elimination times of 1 to 3 days typically observed in practice, the ecotoxicity in
the cooling water of plants 4, 7 and 2 was completely eliminated. In the cooling water
of plant 5, 7 hours after the addition of QAV and hydrogen peroxide a slightly
elevated ecotoxicity was measured, but this can be largely attributed to the input of
solid materials during production. Also in the case of the continuous addition of
bromochlorodimethylhydantoin, no ecotoxicity of the cooling water was observed. In
the Ames test (screening) there was no mutagenic effect. However, one cooling
water sample was toxic after a shock treatment with isothiazolinones (plant 6). The
same sample turned out to be the only one that was genotoxic in the umu test
(GEU=6).
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Table 6: Summary of the wastewater investigations
Nr. 1 Nr. 2 Nr. 3 Nr. 4 Nr. 5 Nr. 6 Nr. 7
Company No./ BranchElectro industry Plastic manufacturing
Plastic manufacturing
Plastic manufacturing
Chemical industry
KW KWKW after
biocide shock dosage
Blow-down after inacti-
vation period
Steam condensate KW KW KW KW KW 1 KW 2 KW2 KW
Biocide (shock treatment)
(Isothia-zolinone) (QAV) QAV
(Isothia-zolinones)
(Isothia-zolinones)
24 h after shock treatment with Isothiazolinones
H2O2/QAV
BCDMH, (Bronopol, Isothia-zolinones), NaOCl
BCDMH, Bronopol, shock-dosage with Isothia-zolinones
BCDMH Isothia-zolinones
Sampling 27.06.00 19.07.00 11.10.00 14.10.00 19.07.00 19.07.00 12.07.00 17.07.01 27.07.00 11.12.00 11.12.00 16.07.01 17.07.01
pH pH 9,5 8,7 8,60 9,00 7,6 8,1 8,8 8,6 8,7 8,3 7,9 7,8 9,0
Conductivity S/cm 10130 1640 2160 121 31600 130 720 831 240 735 2170 2220 1620
COD mg/l 52 24 67 501721
(filtered) 17 14 11302 (unfilt.)
138 (filtered)
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5.2 Product investigations
5.2.1 Eco- and Genotoxicity
The results on the mutagenicity, ge