UV water treatment
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Technical Report 01 | 08 Revised Version of Technical Report No. 20/98
Ultraviolet Disinfection in Water Treatmentfigawa-Working Group on UV Water Treatment
Table of Contents1. 2. 3. 4. 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 5. 6. 7. Terms and Definition Basic Principles Plant and Equipment Fields of Application Drinking Water Heated Water Food and Beverage Industry Ventilation and Air-treatment Systems Pharmaceutical and Cosmetic Industry Private Water Supply Systems Microelectronic and Optical Industries Wastewater and Utility Water Laws Directives - Regulations - Technical Codes and Standards References Authors / figawa e.V. 3 5 8 10 10 11 11 11 12 13 13 13
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PrefaceThis Technical Report by the figawa-Working Group UV Water Treatment is intended for and addressed to professionals 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 TermsDisinfection Inactivation (destruction) of microorganisms, including pathogenic organisms. Following hygienically proper disinfection, 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 coefficient When UV-C radiation (see Fig. 1) penetrates water, it is attenuated (= weakened) due to absorption by solute substances (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 wavelengthdependent, 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 coefficient The 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 unfiltered 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 Transmission The 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.
Table 1 illustrates the link between SSK and UV transmission for various layer thicknesses. SAC (1/m) 0.44 0.88 1.32 1.77 2.23 2.69 3.15 3.62 4.10 4.58 5.55 6.55 7.57 8.62 9.69 12.49 15.49 22.18 30.10 T10 mm (%) 99 98 97 96 95 94 93 92 91 90 88 86 84 82 80 75 70 60 50 T50 mm (%) 95 90 86 82 77 73 70 66 62 59 53 47 42 37 33 24 17 7.8 3.1 T100 mm (%) 90 82 74 67 60 54 48 43 39 35 28 22 17 14 11 5.6 2.8 0.6 0.1
SSK T 10 mm T 50 mm T 100 mm
= = = =
spectral attenuation coefficient at 254 nm transmission through 10-mm layer transmission through a 50-mm layer 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 rate Reduction 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 ageing Decline in UV intensity of a UV lamp as a function of time in service and operating conditions. UV lamp life The number of operating hours a UV lamp can complete before the required UV intensity can no longer be guaranteed (as stated by the manufacturer of the UV disinfection unit), and replacement of the UV lamp becomes necessary. Emission performance of a UV disinfection UV lamp Radiant output (emission) within the disinfection-relevant spectral range of 240 - 290 nm. Turbidity Reduction in the transparency of water due to the presence of fine-particle suspended solids. Turbidity is determined in accordance with DIN EN 27027 and stated either in terms of formazine attenuation units (FAU) for transmittedlight measurements or in formazine nephelometric units (FNU) for 90 scattered-light measurements (tyndallometry) at a wavelength of 860 nm. UV sensor A 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 rate Time-integrated radiant flux impinging on a small spherical surface, divided by the area of the spherical surface.
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 commonly 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
Action mechanism The inactivation of pathogens by UV radiation is essentially due to a photochemical reaction in the pathogens information 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) cove