Technical Report 01 | 08 – Revised Version of Technical Report No. 20/98

Ultraviolet Disinfection in Water Treatment figawa-Working Group on „UV Water Treatment“

Table of Contents

1. Terms and Definition 3

2. Basic Principles 5

3. Plant and Equipment 8

4. Fields of Application 104.1 Drinking Water 104.2 Heated Water 114.3 Food and Beverage Industry 114.4 Ventilation and Air-treatment Systems 114.5 Pharmaceutical and Cosmetic Industry 124.6 Private Water Supply Systems 134.7 Microelectronic and Optical Industries 134.8 Wastewater and Utility Water 13

5. Laws – Directives - Regulations - Technical Codes and Standards 14

6. References 15

7. Authors / figawa e.V. 16

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Preface

This Technical Report by the figawa-Working Group „UV Water Treatment“ is intended for and addressed to profes-sionals and practitioners. It was generated by experts in the practical application of UV water disinfection. It offers practical examples of UV disinfection in order to awake interest in UV disinfection while providing information on the application potentials and limitations of UV disinfection. In practice, the thusly provided information can serve as applicational and decision-making aids. The figawa executive team cordially invites pertinent suggestions and additions to this Technical Report.

The safe and reliable application of UV disinfection is only possible with qualified technology and qualified partners representing current best practice. The results of this input-intensive, publicly promoted research-alliance project document, inter alia, the suitability of UV disinfection for application to drinking water. One of the essential findings of this research-alliance project is its demonstration of equivalency between UV disinfection at water works and chemical disinfection of decentralized water supplies. The research project also produced proof that UV disinfection is ecologically viable and that no by-products are produced as long as the pertinent technical rules are adhered to.

UV disinfection is the process of choice for numerous applications involving the disinfection of water:

- drinking water,- product and utility water,- food and beverage industry,- pharmaceutical, cosmetic and electronic industry,- gardening / horticulture and irrigation,- wastewater (municipal and industrial)

Due to variance in the requirements to be met for disinfection in sundry different applications, the respectively applicable technical rules and specifications vary from case to case. The pertinent codes and standards are cited in the respective chapters of this Technical Report.

1. Definition of Terms

DisinfectionInactivation (destruction) of microorganisms, including pathogenic organisms. Following hygienically proper disin-fection, no pathogens remain detectable within defined volumes examined according to specified methods, and the number of unspecified microorganisms is situated below a specified level.

Colony count [cfu / ml]Number of microbial colonies to be found on a defined culture medium after a certain incubation time following application of a water sample (cf. German standard methods [DEV = Deutsche Einheitsverfahren] for the examination of water, wastewater and sludge K5 (ISO 6222) or respective applicable German-state standards and EU directives).

Spectral absorption coefficientWhen UV-C radiation (see Fig. 1) penetrates water, it is attenuated (= weakened) due to absorption by solute sub-stances (e.g., ferro-manganese compounds and humic acids). The level of attenuation is indicated by the spectral absorption coefficient SAC- [1/m]. Since the absorption of typical ingredients in water is pronouncedly wavelength-dependent, and SAC of 254 nm is of relevance to UV disinfection. The determination of SAC-254 is performed with a suitable photometer applied to a filtered sample of water.

Spectral attenuation coefficientThe spectral attenuation coefficient (or total absorption coefficient ) SSK [1/m], also accounts for (in addition to the extinction coefficient) the scattering of light (diffusion) due to suspended material. It is determined for unfilte-red samples of water. The degree of scatter can only be determined photometrically by differentiation between the filtered and unfiltered specimens. SSK-254 is the essential parameter for the design of UV disinfection equipment.

UV TransmissionThe practical term UV transmission is a percentage measure of the spectral transmissivity observed for a particular layer thickness. The latter has an exponential effect on the level of UV transmission. Consequently, knowledge of the layer thickness (cuvette size) is essential (cf. DIN 5036, part 1). Frequently, the design of UV disinfection equipment is based on UV transmission at 254 nm instead of on the SSK 254. The UV transmission rate is determined by means of a suitable photometer.3

Table 1 illustrates the link between SSK and UV transmission for various layer thicknesses.

SAC (1/m) T10 mm (%) T50 mm (%) T100 mm (%)0.44 99 95 900.88 98 90 821.32 97 86 741.77 96 82 672.23 95 77 602.69 94 73 543.15 93 70 483.62 92 66 434.10 91 62 394.58 90 59 355.55 88 53 286.55 86 47 227.57 84 42 178.62 82 37 149.69 80 33 1112.49 75 24 5.615.49 70 17 2.822.18 60 7.8 0.630.10 50 3.1 0.1

SSK = spectral attenuation coefficient at 254 nm T 10 mm = transmission through 10-mm layerT 50 mm = transmission through a 50-mm layerT 100 mm = transmission through a 100-mm layer

Tab 1: Conversion table for radiation-physical terms

Conversion formula: SSK = [-Log(T1cm/100)] x 100 T1 cm = 100 x 10 –(SSK/100) T10 cm = 100 x 10 –(SSK/10)

Reduction rateReduction in colony count via a disinfection process. Expressed either as a percentage or as a common logarithm (log stage), based on the initial count.

UV lamp ageingDecline in UV intensity of a UV lamp as a function of time in service and operating conditions.

UV lamp lifeThe number of operating hours a UV lamp can complete before the required UV intensity can no longer be guaran-teed (as stated by the manufacturer of the UV disinfection unit), and replacement of the UV lamp becomes necessa-ry.

Emission performance of a UV disinfection UV lampRadiant output (emission) within the disinfection-relevant spectral range of 240 - 290 nm.

TurbidityReduction in the transparency of water due to the presence of fine-particle suspended solids. Turbidity is determin-ed in accordance with DIN EN 27027 and stated either in terms of formazine attenuation units (FAU) for transmitted-light measurements or in formazine nephelometric units (FNU) for 90° scattered-light measurements (tyndallo-metry) at a wavelength of 860 nm.

UV sensorA spectral-selective physical measuring device for radiation in the disinfection-relevant spectral range of 240 - 290 nm. The UV irradiance (flux density) at the monitoring position in a UV unit is permanently monitored by a UV sensor to ensure that the disinfection performance remains adequate. UV dose; fluence rateTime-integrated radiant flux impinging on a small spherical surface, divided by the area of the spherical surface. 4

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The UV dose is stated in units of J/m2.2. Basic Principles

Invisible ultraviolet radiation was first documented in 1901. Since then, numerous phototechnical and photobiological processes have been discovered and investigated, and a host of chemical and biological applications have emerged as a result. High-intensity UV lamps optimized for their respective applications are available on the market.

Characterization of UV radiation

Ultraviolet (UV) radiation - like visible light - is a form of electromagnetic radiation, but does not count among the high-energy, ionizing forms of radiation. Figure 1 illustrates the position of invisible „UV light“ within the overall electromagnetic spectrum.

X-ray Ultraviolet Visible light Infrared

Figure 1: Electromagnetic radiation spectrum

UV radiation, again like visible light, can be described as waves or energy particles (photons). The same basic laws of optical conformity (reflection, absorption, transmission, scatter, refraction) apply.

With regard to biological effect, UV radiation is divided into three spectral ranges. The following breakdown is com-monly employed: UV-A: 315 - 380 nm, UV-B: 280 - 315 nm, UV-C: 200 - 280 nm. The spectral range below 200 nm has pronounced photochemical effects and is therefore unsuitable for UV-disinfection applications.

Figure 2: Absorption maxima vs. wavelength

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Action mechanismThe inactivation of pathogens by UV radiation is essentially due to a photochemical reaction in the pathogens‘ infor-mation and replication centre without addition of extraneous substances. Ultraviolet rays (photons) impact upon the deoxy ribonucleic acid (DNA) of the pathogen and deactivate the corresponding genetic information within a fraction of a second. The absorption spectrum of the DNA and the effective germicidal action spectrum therefore display mutually similar profiles and are characterized by broad absorption maxima at 260 nm (cf. Fig. 2). Consequently, radiation sources (UV lamps) covering the UV spectral range between 240 and 290 nm are suitable for deactivation applications. Mercury vapour lamps in particular satisfy that criterion very well.

Figure 3: Effect of a UV photon on a pair of thymine bases

UV lampsAll UV radiation sources now in use for UV disinfection are of the gas-discharge type. Made of UV transmitting material, such UV lamps contain a gas / steam mixture that, in the excited state, emits intensive UV-C radiation (stimulated emission).

Practically all intensive UV-C radiation for disinfection purposes is generated by means of mercury vapour (Hg) UV lamps. A distinction is drawn between low-pressure and medium-pressure UV lamps, both of which, however, emit intensively across the 240 – 290nm range and are therefore quite suitable for UV disinfection applications. Their typical emission spectra are shown in Figures 4 and 5, and Table 2 surveys their characteristics and properties.

Figure 4: Typical spectrum of a low-pressure mercury lamp

UV-Licht h-v = UV light h-vEnzym = EnzymeAdenin = adenineCytosin = cytosineGuanin = guanineThymin = thymineDimer = dimer

Wavelength [nm]

Spec

tral

irra

dian

ce [r

el. u

nits

]

Figure 5: Typical spectrum of a medium pressure mercury lamp

Characteristics and properties Low-pressure UV lamps Medium-pressure UV lamps

Mercury vapour pressure approx. 0.01 hPa 1,000 - 10,000 hPa

Spectrum line spectrum broad beam

Wavelength, UV-C range 254 nm 240 - 280 nm

Typical power input 10 – 600 W 1,000 – 30,000 W Power density specific to arc length 1 – 4 W/cm 100 - 200 W/cm UV-C output (254 nm) [%] specific to approx. 20 – 35 % approx. 8 – 15 %electr. input power for a new UV lamp Surface temperature of UV lamp 40 - 120°C 600 - 950°C

Average useful life 8,000 h - 16,000 h 4,000 - 12,000 h

Advantages - height efficiency - high power density - high longevity - easily controllable - low surface temperature - compact design - little dependence on water - no dependence on water temperature (amalgam tubes) temperature

Table 2: Characteristics and properties of low- and medium-pressure UV lamps

Note: Radiation situated below 240 nm has a pronounced photochemical effect and is therefore prohibited from use in UV radiation sources for drinking-water disinfection according to DVGW Technical Standard W 294 or OENORM M5873-1.

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Wavelength [nm]

Spec

tral

irra

dian

ce [r

el. u

nits

]

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3. Plant and Equipment

UV irradiation chamberThe UV irradiation chamber of a typical UV disinfection unit consists of an interior irradiation chamber and its con-necting branches and is usually made of stainless steel. Depending on the application and on the type and quantity of employed UV lamps, irradiation chambers can be of various design, the main distinguishing feature being the arrangement of UV lamps within the irradiation chamber. A selection of typical arrangements is shown below.

Figure 6: Some typical UV lamp arrangements (from left): axial, cross flow, exterior, open race

In some applications, e.g., for the disinfection of municipal wastewater, open races are employed instead of actual chambers, so the water can flow past the UV lamp unpressurized.

Submersible UV lampsThis type is used for disinfecting liquids (e.g., water, sugar syrup, …) in tanks and troughs. Submersible UV lamps are UV radiation sources with protection that enables their direct installation in existing tanks and troughs. Prior to installation, however, all materials within the radiation area must be checked for UV resistance. Since submersible UV lamps are normally installed in existing systems, the UV safety provisions are of special importance (cf. pertinent guidelines for workplace safety issued by the relevant employers‘ liability insurance association).

Monitoring equipmentUV units must be monitored to ensure that proper disinfection is always guaranteed. The monitoring function of the UV sensor is just as important as that of the concentration sensor in a chemical disinfection system.

Requisite monitoring elements• UV sensor• elapsed-time indicator • UV lamp-function monitor• UV lamp-switching counter

Figure 7: DVGW sensor with analysis window

Optional monitoring elements • flow monitor • temperature monitor• turbidity monitor

Figure 8: Turbidity monitor

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Factors with possible impacts on the values displayed by a UV sensor

• soiling of the analysis window

• ageing of the UV sensor

• absorption of UV radiation in water by - solutes (iron and manganese compounds, humic material) - suspended particles

• soiling of UV lamp cladding tube

• ageing of UV UV lamp

Figure 9: Schematic diagram of a UV unit

Flow rateDue to the fact that UV disinfection units can only be expected to work properly up to a certain maximum, system- and transmission-dependent flow rate, transgression of the permissible flow rate must be prevented, either by limi-ting the output of the feed pump or by way of flow limitation / regulation. Such a setup is particularly advantageous when several UV units are installed in parallel.If automatic interruption of flow is required in case of a malfunction, a signal from the UV-unit‘s monitoring system can be used to stop the feed pump and/or to close an isolating valve. Sizing of UV equipmentThe sizing of UV units is essentially based on the following parameters:

• Maximum flow rate [m3/h]• UV absorption by the treated water at 254 nm; stated either as SSK-254 nm (1/m) or as UV transmission specific to a defined layer thickness (e.g., %/cm).• Legal regulations and code and standards, e.g., Drinking Water Ordinance and DVGW Technical Standards• Certain microbiological requirements, e.g., for the food and beverage sector and ultrapure water

Furthermore, the respective application- and customer-specific circumstances must be allowed for.

Figure 10 exemplifies the causal relationship between SSK-value and flow rate for a typical UV disinfection unit.

53 61 70 88 Flow rate [m /h]

SAC [m-1] 3.6

2.7

1.8

0.9

Range of suitability

SSK

Flow rate [m3/h]

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4. Fields of Application 4.1 Drinking Water If the bacteriological innocuousness of supplied drinking water cannot be permanently and uninterruptedly assured, the water must be disinfected. For a long time now, the UV disinfection of drinking water has been in application around the world as a safe and reliable solution to the problem. Even such parasites as cryptosporides and giardia are reliably inactivated. Especially during the past decade, more and more public water utilities have adopted UV technology for the nonchemical disinfection of drinking water. Indeed, low-maintenance, user-friendly UV disinfec-tion is now the process of preference for private water supply systems, too. Used properly, UV equipment generates no by-products. Of particular importance is the fact that the process does not alter the natural odour or taste of drinking water. The limit values of the microbiological parameters listed in Appendix 1, part I, of Germany‘s 2001 Drinking Water Ordinance must not be surpassed in water for human consumption. With regard to the parameters Escherichia coli (E. coli), enterococci and coliform bacteria, no such pathogens must be detectable in 100 ml.

Legal basisThe regulation entitled Verordnung über die Qualität von Wasser für den menschlichen Gebrauch, Trinkwasserver-ordnung – TrinkwV 2001 (ordinance governing the quality of water for human consumption); article 1 of Verordnung zur Novellierung der Trinkwasserverordnung vom 21. Mai 2001 (administrative provision amending the drinking water ordinance dated May 21, 2001), Bundesgesetzblatt I (BGBI. I, German Federal Law Gazette I), pp. 959 - 980, together with the list of treatment substances and disinfection processes defined in article 11 of Germany‘s 2001 Drinking Water Ordinance, serves as the pertinent legal basis. That list is generated, updated and published (in German only)at regular intervals via internet at http://www.umweltbundesamt.de/wasser/themen/trinkwasser/empfehlungen.htm by the Trink- und Badebeckenwasserhygiene (~drinking and swimming-pool water hygiene) department of the German Federal environment agency.

Generally accepted rules of engineering practiceAccording to art. 11 of Germany‘s 2001 Drinking Water Ordinance, UV equipment must be certified in accordance with DVGW Technical Standard W 294. UV equipment tested on the basis of other codes or standards can be employed in Germany if its equivalent compliance with DVGW Technical Standard W 294 has been confirmed by an accredited certification body – such as DVGW Cert GmbH - within the scope of a certification process.

Water quality criteriaThe use of UV disinfection is contingent on compliance with the requirements of the Drinking Water Ordinance, and/or on their fulfilment by upstream water treatment facilities (DVGW Technical Standard W 290, Feb. 2005, dealing with drinking water disinfection: applications and criteria).Solute iron and manganese present in concentrations allowed by the Drinking Water Ordinance absorb little UV radi-ation and therefore contribute accordingly little to the water‘s SSK 254. However, even at low concentration levels, iron and manganese can collect and form deposit layers that do absorb UV radiation. Hence, the quartz sleeves of UV lamps require regular cleaning, the frequency of which depends on numerous different water-quality factors. In most cases, however, between one and four cleanings a year is considered adequate. Progressive soiling of quartz sleeves is indicated by gradual weakening of the UV-irradiance signal, so that the need for prophylactic cleansing of the sleeve is both recognizable and plannable.

Figure 11: Disinfection of drinking water at an approx. rate of 300 m3/h

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4.2 Heated Water The most frequently encountered microbiological problem with heated water is the proliferation of legionella bac-teria. These thermophilic pathogens are able to enter building plumbing systems by way of the public water supply grid. The most well-known legionella bacter is legionella pneumophilia. Infection occurs via inhalation or, less so, via contact between legionella-infected water and mucous membranes or open wounds. Infection via the gastro-intestinal tract is unknown.

The propagation of legionella in water is encouraged by water temperatures between 25°C and 50°C and by the accumulation of sludge in tanks and vessels, incrustation in pipes and valves, biofilms, dead zones and the presence of protozoa, e.g., amoebae, which serve as host organisms for legionella in water.

Legal basisThe Drinking Water Ordinance applies without limitation to heated drinking water. It requires that drinking water be totally free of pathogenic organisms.

Generally accepted engineering practiceIn addition to the requirements stated in the section entitled „Sizing of UV equipment“, numerous other factors are of importance for the control of legionella with UV equipment: supplementary structural measures, operation of UV lamps in water at elevated temperatures, and the propagation of legionella in protective enclosures (biofilms, amoebae, solid conglomerates). The technical assistance of a specialist contractor is essential. Operational, struc-tural and process-related measures are out-lined in DVGW Technical Rule W 551 Technische Maßnahmen zur Vermin-derung des Legionellenwachstums (technical measures for the control of legionella growth). Concomitant codes and standards include DVGW Technical Rule W 553 Dimensioning of Circulation Systems in Central Drinking Water Heating Systems) and VDI 6023 Hygiene for Drinking Water Supply Systems).

4.3 Food and Beverage Industry

In the good and beverage industry, water is needed for the product itself (e.g., table water, beer, sweetened beve-rages) as well as for cooling and washing. In the course of production, there is direct or indirect contact between water and food. Hence, the quality of the water has a major impact on the quality and microbiological stability of the product. One of the main advantages of UV disinfection is that it requires no addition of chemical substances that could undesirably alter the beverage / food.

Legal basisOn the grounds of the German Food Law, the treatment of food with ultraviolet radiation is governed by the German Food Irradiation Ordinance (Ordinance on Food and Food Ingredients Treated with Ionizing Radiation - LMBestrV). According to art. 1 (4) of that ordinance, the direct application of UV disinfection is permitted subject to limitations. According to art. 3 of the ordinance, special labelling is not obligatory.

In Germany, the Mineral- and Table-water Ordinance prohibits the use of disinfection processes per se on »natural mineral water« and »spring water«. Hence, the UV treatment of such water is likewise prohibited. Water marketed as »table water«, however, may be disinfected in compliance with this ordinance.

Generally accepted rules of engineering practiceWith reference to the strict requirements concerning disinfection safety in the food and beverage industry, the use of certified UV equipment for water disinfection is recommended.

4.4 Ventilation and Air-treatment Systems

Due to the design and function of rotary spray humidifiers (air scrubbers) and recooling plants in ventilation and air-conditioning systems, the circulating water is subject to a high rate of soiling. Such soiling causes biological contamination of the water. The use of UV disinfecting equipment enables limitation of the water‘s colony count to less than the respective guideline level. One of the main advantages of disinfection with UV equipment is that no substances with a sensitizing effect on humans are generated in the water, and supplementary disinfectants are rarely needed. Thanks to the absence of disinfectants, the cooling water can be discharged without fear of problems concerning the legal aspects of disinfectant disposal.

Legal basisThe quality of circulating water for rotary spray humidifiers in normal operation is subject to VDI 6022. The guideline levels stated therein (< 103 cfu/ml or, if possible, < 104 cfu/ml) are binding for recooling plants.

Best available technologyUV disinfection units are placed either in the main flow of medium or in a separate loop, or installed as submersible UV lamps in the air washers. In addition to the requirements stated in the section on »Sizing of UV equipment«, it must be kept in mind that the quality of water is subject to pronounced seasonal fluctuation (e.g., temperature and contamination), and that the accumulation of substances in water can lead to precipitation. When the use of biocides is necessary to achieve single-dose disinfection, it must be kept in mind that such agents are liable to absorb UV light.

4.5 Pharmaceutical and Cosmetic Industry

Water of various quality is needed for pharmaceutical production processes. Aqua purificata (purified water, demi-neralised water) is used for salves and other externally applied medicinal products, as well as for most cleaning operations. As a rule, such water is obtained by rough filtration, softening, reverse osmosis and, in some cases, elec-trodialysis and then stored at room temperature in clean-water tanks, from where a ring-line arrangement circulates the water to the water taps and returns the rest to the tank (Figure 13).

Figure 13: Typical configuration of an ultrapure water system with UV unit for removing residual ozone

In most modern setups, the possible formation of biofilms in storage vessels and piping is prevented by injecting ozone into the return line to the tank at a concentration of approx. 0.02 – 0.04 mg/l. To keep the pharmaceutical product from coming into contact with ozoniferous water at any point of the production process, all of the ozone is broken down by a UV unit in the supply section of the ring line. Outside of production time, the ozonized water is left to circulate at a higher concentration past the off-state UV unit around the ring. Just before production is resumed, the UV unit cuts in and lowers the ozone concentration back down to below the detection threshold of 0.005 mg/l.

AP water for use in internally administered products undergoes further treatment (to become highly purified water) and is often distilled and subsequently stored at approx. 80°C (water for injection - WFI).

Legal basisThe quality of water is defined in diverse dispensatories (American/European pharmacopeia). The universally applied and accepted Good Manufacturing Practice (GMP) Guidelines contain additional requirements for the planning, cons-truction and operation of pharmaceutical production facilities. Also listed are far-reaching criteria for the design of UV units (as little dead space as possible, material certification according to EN 1082 3.1b, UV lamp testing, pressure testing, …) and for quality assurance of in-process UV irradiation, e.g., by use of a certified sensing system.

The output of UV units is defined on the one hand by the need to lyse roughly 0.1 mg/l solute ozone to below the detection threshold and, on the other, to target a residual colony count of between <10 and <100 cfu/100 ml. That can

Distillation

A P storage

Hot storage

WF I r ing

A P ring Ozone

UV Residual-ozone -

removal

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Ozone AP ring

WFI ring

AP storage

Destillation Hot storage

Residual-ozoneremoval

be achieved with a minimum dose rate of 800 – 1200 J/m2. The level of water deozonization downstream of the UV unit can be directly monitored by means of a special-purpose residual ozone meter or, alternatively, by way of the UV unit‘s sensor. Continuous registration of the intensity levels is therefore advisable.

CosmeticsMuch like the water used in the pharmaceutical sector, water used in the production of cosmetics occupies a wide range of qualities, from normal drinking water to demineralised water. The UV-equipment requirements range bet-ween 400 J/m2 and 1200 J/m2. Increasingly, the GMP Guidelines are being adopted.

4.6 Private Water Supply Systems

Basically, the criteria for both the UV equipment and the water itself in private systems are the same as those discussed above for the disinfection of drinking water. In connection with private water supply systems, however, there is greater likelihood of encountering humic acids and undesirable inclusions, either from surface runoff and rainwater or due to unsound wells. Legal basisPrivate water supply systems are governed by the new DIN 2001 „Drinking Water Supply from Small Units and Non stationary Plants.“ Part 1 of that standard - „Small Units“ - lists irradiation with ultraviolet light (UV disinfection) with continuous monitoring of the disinfectant effect as the process of preference for disinfection. Again, art. 11 of the German Drinking Water Ordinance prescribes that, for new installations in Germany, only UV equipment certified in accordance with DVGW Technical Standard W 294 is permitted.

4.7 Microelectronic and Optical Industries

Thanks to technical progress, the distance between individual tracks on microchips is becoming narrower all the time. In the microelectronic and optical industries, the separation of mechanical particles is being improved by ever-finer filters. Bacteria, however, are able to quickly pass (= grow) through filters with a mesh size of only 0.2 m, and such microorganisms cause damage to microchips because of the tight-and-narrow track structures.

Consequently, ultrapure water is required to have a colony count of less than 10 cfu/100 ml in general and at times even below 1 cfu/l. That stringent requirement is generally met, i.e., such a low colony achieved, by applying an irradiation dose rate of 1200 - 1600 J/m2. The TOC (total organic carbon) content of ultrapure water is potentially disruptive, because it promotes deposits that in some processes can cause „hot spots“. However, the perturbing hydrocarbons can be oxidized to carbon dioxide by use of special-purpose UV lamps offering both UV-C and 185-nm V-UV radiation. The irradiation dose, which is significantly higher than for normal disinfection, typically amounts to some 4000 - 6000 J/m2 (referred to UV-C).

Legal basisThere is no legal basis for ultraviolet disinfection and TOC reduction for ultra-pure water.

Best available technologyCustomer-specific requirements in the microelectronic and optical industry must be heeded. A typical requirement: residual colony count on admission to the ring line < 5 cfu/100 ml and/or residual colony count at the end of the ring line < 10 cfu/100 ml and, in certain cases, even less than 1 cfu/1000 ml; for UV oxidation: post-TOC oxidation < 1 - 3 ppb.

4.8 Wastewater and Utility Water

In view of the increasing scarcity of potable drinking water resources all around the world, the disinfection of was-tewater for use as utility water, i.e., for such applications as irrigation, reinfiltration and drinking-water supplemen-tation, is becoming increasingly important. Disinfection with UV light is employed as the last stage of wastewater treatment prior to discharge or reuse. The process can be applied both to free flowing water in clarifier discharge channels for disinfecting utility water in and with enclosed UV units in closed pressure pipes.Since the organic content of residue-laden wastewater increases the water‘s UV absorption at 254 nm to a much higher level than that of drinking water, the specific power input required for disinfecting a certain volumetric flow is higher by a factor of 3 to 10. Accordingly, UV units for wastewater disinfection contain more UV lamps than those used in drinking water systems, and the lamps are arranged closer together. The flow-handling equipment is designed for accordingly low velocities of flow. Typical dose rates are geared to the reduction of faecal bacteria and viruses, hence amounting to 400 – 800 J/m2, depending on the application.13

The microbiological criteria for the direct discharge of sewage-works effluent into bathing waters range between 100 and 200 faecal coliforms per 100 ml.

Figure 14: Disinfection of utility water / sewage

Legal basisThroughout Europe, the introduction / discharge of sewage-works effluent and the use of utility water from sewage treatment facilities is governed by the EC directive on bathing water quality.In the United States of America, the legal basis comprises pertinent regulations issued by the US Environmental Protection Agency (EPA) in combination with such regional directives as the California Wastewater Reclamation Title.

5. Laws – Directives - Regulations - Technical Codes and Standards

Effective 2001-01-01, the Bundesseuchengesetz (German Federal Act on the Prevention of Contagious Diseases) was superseded by the Infektionsschutzgesetz (Infection Prevention Act), i.e., by the Gesetz zur Verhütung und Bekämpfung von Infektionskrankheiten beim Menschen (German Federal Act on the Prevention of Infectious Diseases in Humans), dated 2000-07-20 (see Bundesgesetzblatt / BGBl. [Federal Law Gazette] I, p. 1045), last revised per communication dated 2007-10-01 (see Bundesgesetzblatt / BGBl. [Federal Law Gazette] II, p. 1528).

Verordnung über die Qualität von Wasser für den menschlichen Gebrauch TrinkwV 2001 - Trinkwasserverordnung (Ordinance on the Quality of Water for Human Consumption - Drinking Water Ordinance) dated 2001-05-21; (see Bun-desgesetzblatt / BGBl. [Federal Law Gazette] I, No. 24, dated 2001-05-28, p. 959; 2003-11-25, p. 2304; 2006-10-31, p. 2407 06). For a list of treatment substances und disinfection processes, see Art. 11, Drinking Water Ordinance 2001.

http://www.umweltbundesamt.de/wasser/themen/downloads/trinkwasser/trink11.pdf

Food Radiation Ordinance; Long Title: Ordinance on Food and Food Ingredients Treated with Ionising Radiation, dated 2000-12-14, last revised by the Neunte Zuständigkeitsanpassungsverordnung (Ninth Ordinance on the Adjustment of Responsibilities), dated 2006-10-31.

DIN 2001 Drinking Water Supply from Small Units and Non-stationary Plants - Part 1: Small Units

DIN 1946-4 Norm, Ventilation and Air Conditioning - Part 4: Ventilation in Buildings and Rooms of Health Care

DIN 5031 Optical Radiation Physics and Illumination engineering, various parts

DIN 5036 Radiometric and Photometric Properties of Materials, various parts

DIN EN 14897: Water Treatment Equipment Inside Buildings – Devices Using Mercury Low-pressure Ultraviolet Radia-tors - Requirements for Performance, Safety and testing

DVGW Technical Standard W 290 | 2005-02 – Drinking water disinfection – Applications and Performance criteriaAvailable in German only

DVGW Technical Standard W 294-1 | 2006-06 – UV equipment for water-supply Disinfection part 1: qualitative, functio-nal and operational requirements | Available in German only

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DVGW Technical Standard W 294-2 | 2006-06 – UV equipment for water-supply Disinfection part 2: qualitative, functional and disinfection-efficacy testingAvailable in German only

DVGW Technical Standard W 294-3 | 2006-06 – UV equipment for water-supply disinfectionpart 3: analysis window and sensors for radiometric monitoring of UV disinfection equipment;requirements, testing and calibrationAvailable in German only

Technical rule /Technical Standard W 551 | 2004-04 – heating of drinking water, drinking water piping systems;technical measures for reducing the growth of legionellae; planning, construction, operation and rehabilitation of drinking water installationsAvailable in German only

Technical Standard W 553 | 1998-12 – sizing of circulation systems in drinking water heating systems)Available in German only

OENORM M 5873-1: 2001-03-01 – Plants for the Disinfection of Water Using Ultraviolet Radiation- Requirements and Testing – Part 1: Low-pressure Mercury Lamp Plants

OENORM M 5873-2: 2003-08-01 - Plants for the Disinfection of Water Using Ultraviolet Radiation - Requirements and Testing – Part 1: Medium-pressure Mercury Lamp Plants

ATV Specification M 205 Disinfection of Wastewater, 1998-07

VDI 6023, Sheet 1 | 2006-07Hygiene in Drinking Water Installations – Planning, Construction, Operation and Maintenance Requirements

6. References

DIN EN ISO Standard specifications, OENORM; Beuth Verlag, Tel. +49 30/26 01-26 68, Fax +49 30/26 01-12 60

DVGW-Rules and Standards; WVGW Wirtschafts- und Verlagsges. mbH, Tel. +49 228/25 98-4 00, Fax +49 228/25 98-4 20

Österreichisches Normungsinstitut, Heinestraße 38, 1020 Wien, Austria, Tel. +43 1 21300-805, Fax: +43 1 21300-815

DWA Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall e.V., Theodor-Heuss-Allee 17, D-53773 Hennef, Tel. +49 2242 872 333, Fax +49 2242 872 135

Verein Deutscher Ingenieure e.V., Graf-Recke-Straße 84, D-40239 Düsseldorf, Tel. +49 211/62 14-0, Fax. +49 211/62 14-5 75

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7. Authors / figawa

This Technical Report was principally generated by members of the figawa-Working Group on UV Water Treatment with the kind assistance of the following member companies and their representatives:

Company / location RepresentativeBWT Wassertechnik GmbH, Schriesheim Dr. Ralph W. BergmannFranke Aquarotter AG, Ludwigsfelde Dipl.-Ing. Ronald Karger Grünbeck Wasseraufbereitung GmbH, Höchstädt/Donau Dr.-Ing. Heinz RötlichHeraeus Noblelight GmbH, Hanau Volker Adam, Erik RothKryschi Wasserhygiene, Kaarst Dipl.-Ing. Rainer KryschiProMinent ProMaqua GmbH, Heidelberg Dr. Wolfgang Weibler (WG convenor)Siemens Water Technologies, Wallace & Tiernan GmbH Rob van EschTrojan Technologies Deutschland GmbH, Schöllkrippen Hans-Reiner GoworUMEX GmbH, Kirchheim Dipl.-Chem. Rüdiger NoackUV-EL GmbH, Dresden Steffen JohneITT WEDECO AG, Herford Dipl.-Ing. Robert Rongen

Comments and helpful suggestions concerning this Technical Report are welcomed by the figawa executive team. Contact: figawa project manager Dipl.-Ing. Mario Jahn.

Since 1926, producers and service providers in the gas and hydraulic engineering sector have been organized within a technoscientific federation called figawa e. V. - Federal Association of the Companies in the Gas and Water indus-tries. Since its inception, the purpose of this association has been to provide codes and standards regarding the safety, hygiene, environmental impact and economic viability of relevant products and processes. In all, more than one thousand companies are figawa members. For a current survey, please go to www.figawa.de.