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

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

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

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

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

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

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

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

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

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

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

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.

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.

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.

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

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.)

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!

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

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

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

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.

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

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

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

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).

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)

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

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

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

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.

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

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

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

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

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.

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

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

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.

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

32

(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-

33

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)

34

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-

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.

36

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).

37

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)

38

5.2 Product investigations

5.2.1 Eco- and Genotoxicity

The results on the mutagenicity, ge