Terms and definitions
Liquid or solid alloys of mercury with other metals. The mercury in the alloys is not dangerous to humans or the environment. Amalgam is used in the manufacture of mirrors, as a filling material in dentistry and other applications. Amalgam based on an alloy of mercury with bismuth, indium and lead is used in the production of UV light sources.
Low-pressure UV lamps that use amalgam instead of mercury. These lamps have a higher intensity than conventional mercury lamps, while retaining the advantages of low-pressure lamps such as long life and high efficiency. If an amalgam UV lamp breaks, there is no need to demercurise (clean up mercury contamination) the premises. The amalgam bactericidal lamps that have expired (lost their consumer properties) are hazard class III waste in accordance with the Federal Classification Catalogue of Wastes.
The relative inactivation efficiency for each wavelength of the emission spectrum. This value is conditionally dependent on the absorption by nucleic acids of each wavelength.
Electromagnetic radiation of the UV range with wavelengths of 205-315 nm. The maximum efficiency of inactivation of microorganisms is observed in the wavelength range 250-270 nm, this part of the spectrum is the wavelength generated by low-pressure UV lamps - 254 nm.
A UV lamp whose emission spectrum contains bactericidal wavelengths (one or more) in the range from 205 to 315 nm.
Experimental verification of the provision of the required UV dose by the equipment under the conditions declared by the manufacturer. There are regulations governing the validation of UV equipment: ÖNORM M 5873-1 (2001) ‘Plants for the Disinfection of Water using Ultraviolet Radiation: Requirements and Testing Low Pressure Mercury Lamp Plants’, ÖNORM M5873-2 (2003) “Plants for the Disinfection of Water using Ultraviolet Radiation: Requirements and Testing Medium Pressure Mercury Lamp Plants” (Austria), DVGW W294-3 (2003) “UV Disinfection Devices for Drinking Water Supply - Requirements and Testing” (Germany), USEPA UVDGM, NWRI, NSF 55 (USA).
UV equipment of open type, consists of modules grouped in sections, which are placed in a non-pressurised channel (tray). A UV disinfection station may consist of one or more trays. The number of modules in a tray is selected individually for each station. Channel equipment is used only in non-pressurised systems, mainly in wastewater disinfection.
A process of cleaning lamp covers that uses reagents to remove contaminants. Usually, weak solutions of citric acid or oxalic acid are used. During the flushing process, the case equipment is taken out of operation and isolated from the main flow. Washing is performed by circulating the washing solution inside the disinfection chamber for 1.5-3 hours. To flush flume equipment, modules are removed from the channel one by one and immersed in a pit or tank with flushing solution. Chemical cleaning effectively removes most of the contaminants formed during operation of the equipment in natural and waste water: iron salts, calcium salts, etc. The contamination reserve of quartz covers is usually selected so that the need for flushing occurs about once a month. If mechanical cleaning is available, chemical flushing is used much less frequently (once a year) or not at all.
The UV lamps in the equipment are separated from water by a quartz cover, which is also necessary to maintain the temperature of the lamps. In the process of operation on the outer side of the quartz covers, which is in contact with water, forms a deposit, which reduces the transparency of the covers and the output of UV radiation. The speed of formation of the contamination and its characteristics depend on the quality of water. Mechanical cleaning and/or chemical washing is used to remove contamination and is carried out when a certain level of contamination is reached. When designing a UV disinfection unit, a reserve for contamination of quartz covers of 5 to 30% is included, depending on water properties and type of treatment. The level of contamination is monitored by a UV sensor.
The unit that monitors and controls the UV equipment.
An electrical cabinet that includes the required number of lamp control gear (‘control gear’, sometimes called ballasts), safety automation and switching equipment to supply ballasts with mains voltage.
A tank or chamber subjected to UV radiation. It necessarily consists of a housing and UV lamps, but may also include quartz covers, UV sensors, cover cleaning systems, levelling grids and other components.
Enclosed type UV equipment in which the lamps are inside the disinfection chamber. Except for special applications the disinfection chambers are made of stainless steel. Can be used in both pressurised and non-pressurised systems.
In the context of disinfection, an action that deprives microorganisms of their ability to multiply and thus cause disease.
This is the ratio of the flux of irradiation to the surface area on which that irradiation falls.
A quartz tube or nozzle that surrounds and protects the UV lamp. The outside of the cover is in contact with water. There is usually a gap (about 1cm) between the bulb of the lamp and the quartz cover.
Quartz or glass tube, the main structural element of a UV lamp.
The period of operation of a UV lamp during which the intensity of radiation in the UV spectrum corresponds to the minimum declared in the lamp specification. Lamp lifespan depends on the type of lamp, manufacturing technology, and operating conditions. The lifespan of medium-pressure lamps is 6000-8000 hours, low-pressure lamps 12 000-16 000. If the UV unit is not equipped with a UV sensor, then after the expiry of the manufacturer's specified service life, the lamps should be replaced: despite the fact that they continue to ‘burn’, the intensity of UV radiation decreases and the required dose of irradiation is not provided. If a UV sensor is available, the lamp can continue to be used, but a spare lamp should be kept in stock, as at the end of its lifespan there may be a sudden drop in UV intensity which will require urgent replacement of the lamp.
For normal operation of the channel equipment it is necessary to maintain a certain level of water in the channel. For this purpose, level control systems are used, which are static (branched weir) and dynamic (automatic gate). A dynamic level control system works automatically by adjusting the position of the gate at the canal outlet based on the readings of level gauges. The best way to maintain the level is to use gates with a top overflow.
A mercury lamp that operates at an internal pressure of 0.13 to 1.3 Pa and with a specific power of 0.4-2.5 W/cm. The result is the generation of biocidal monochromatic radiation with a wavelength of 254 nm.
The process of cleaning the outer surface of quartz covers by a mechanical device (e.g. a cleaning scraper), which operates at a predetermined frequency in automatic mode (but manual mechanical cleaning is also possible).
A mercury lamp operating at an internal pressure of 1.3 to 13,000 Pa and a specific electrical power of 50 to 150 W/cm. It has a wide spectrum of radiation, including wavelengths in the bactericidal range.
The emission of light of only one wavelength. Such light is generated by low-pressure lamps, including high-efficiency amalgam lamps.
The UV dose required to achieve a certain degree of disinfection. Data on the required doses to inactivate different microorganisms are obtained by summarising the results of experiments.
This is a combination of one or more UV modules overlapping a channel section. It is the minimum technological unit of a tray UV station. Several UF sections can be placed in series in one canal.
An instrument (photometer) used to measure the transmittance of water. For UV disinfection systems, it usually operates at a wavelength of 254 nm. Taumeter can be of laboratory type for one-time measurements of transmittance in selected water samples, and can be of flow-through type, when the instrument is installed in a canal or pipe with treated water and continuously monitors water quality.
UV lamp that does not generate ozone during operation. Blocking of ozone generating wavelengths (100-220 nm) is due to the use of special, doped quartz glass in the UV lamp design.
For UV disinfection, this is the tray or channel that houses the UV modules and auxiliary equipment. For small capacity stations, the tray can be made of stainless steel and delivered to the site ready-made. For medium and large capacity plants, the channels are constructed of reinforced concrete on site. The channel must have certain geometric dimensions, which are determined by the project.
A measure of bactericidal energy per unit area. Usually measured in mJ/cm² or J/m². 1 mJ/cm² = 10 J/m². In general, the dose is equal to the product of the UV intensity by the irradiation time. In the case of UV equipment for disinfection of e.g. water, the dose is calculated on the basis of the UV lamp power, the number of UV lamps, the distance between the lamps, the lifetime of the UV lamps, the UV transmittance factor, the contamination of the quartz covers, the water flow rate through the UV reactor, the geometric dimensions of the disinfection chamber and the calculated water distribution in the chamber.
Although the UV dose is the main technological parameter of the UV equipment, it cannot be directly measured, only calculated from the UV sensor readings. The only practical way to confirm the UV dose is to have the UV equipment biotested or certified by a specialised centre.
This is an electrotechnical device that provides disinfection by ultraviolet light. Enclosure equipment includes: disinfection chamber, UV lamps, UV sensor, UV control unit, control unit, chemical washing system. Channel equipment consists of modules, UV sensors, water level sensors, channel or tray, water level control system, mechanical cleaning system, junction boxes, gear boxes and control units.
The efficiency of a UV lamp is a coefficient that characterises what percentage of the electricity consumed is converted into useful bactericidal radiation.
An artificial source of UV radiation.
A unitised piece of channel equipment consisting of cassettes with lamps. Several UV modules overlapping the channel cross-section form a section.
Electromagnetic radiation occupying a range between X-rays and visible radiation (wavelength range 100 to 400 nm).
A photosensitive detector used to measure UV intensity at a given point in a UV reactor, converting the input signal into milliamperes (mA) or a digital signal. The UV sensor is a process monitoring instrument for UV intensity.
This is the amount (magnitude) of UV radiation transmitted by a substance or medium (most commonly water) at a wavelength of 254 nm. The transmittance shows the percentage of UV radiation at 254 nm that has passed through a layer of water of a certain thickness (typically a 10 mm thick layer is used, but for very clear and clean water it can be 100 mm). The purer the medium (e.g. water), the higher the transmittance. Inverse of the UV absorption coefficient.