Microbial disinfection utilizing ultraviolet radiation is a universe broad engineering for imbibing H2O purification. The effectivity of this engineering depends on certain of import parametric quantities like the UV strength, the exposure clip, the country, lucidity of the H2O etc. This engineering is really convenient and fast, does n’t change the gustatory sensation of the H2O or adding chemicals into the H2O. The choice of UV wavelength is really of import for the efficient disinfection procedure. The optimal microbic killing efficiency ranges from 254 to 260 nanometers wavelength likely varies with the type of being. Viruss and bacteriums in vegetive signifiers are most sensitive to UV radiation. It gives in-depth reappraisal of UV ( UV ) visible radiation for utilizing as a disinfection engineering in drinkable H2O supplies. This paper is intended to help the reader in measuring the disinfection capablenesss of UV visible radiation to demobilize disease-causing bacteriums, viruses, and cysts.
Water borne disease has been a concern to human being of all time since its cause had discovered and the most appropriate intervention procedure adopted is microbic disinfection. Disinfection is necessary to destruct infective ( disease doing ) bacteriums and other harmful micro-organisms that are present in H2O due to taint. Over several old ages, Ultraviolet ( UV ) disinfection has developed into a feasible engineering for imbibing H2O disinfection. UV disinfection systems inactivate Protozoa, bacteriums and viruses. Through across-the-board research and punctilious field experiences, UV disinfection has proven to be safe, dependable, and cheap and accepted this as a universe broad engineering for imbibing H2O disinfection.
UV disinfects H2O without adding chemicals. It does non make any new chemical composites, does non alter the gustatory sensation or smell of the H2O and does non take good minerals from the H2O. UV devices are the most effectual when the H2O has already been partly treated for deposits and organic chemicals. Therefore UV disinfection devices are frequently combined with other intervention devices such as sediment filters and C filters.
The cardinal factor of a UV intervention system is the UV dose which can be measured from the known UV strength, exposure clip and H2O flow rate. The dose is really of import to disinfect the micro-organism. This is once more based on many factors like H2O lucidity, H2O flow, flow form, UV strength and quality of the vitreous silica arm. The H2O quality of India is a existent challenge to all H2O purifier makers. There is a broad differentiation in H2O quality from topographic point to topographic point like high turbidness, heavy microbic taint, Fe content, presence of other toxic chemicals etc. Surface H2O in river is the chief imbibing H2O beginning for urban and semi urban countries of India. Open Wells and dullard Wellss besides provides imbibing H2O to the human community every bit good.
Historical record of UV
The germicidal belongingss of UV visible radiation were discovered in 1887. The first application of UV visible radiation in imbibing H2O occurred in 1910 at Marselles, France. Since so, UV visible radiation is used in imbibing H2O systems worldwide chiefly for disinfection. Till 2006 there is merely one Commercial H2O purification device utilizing UV visible radiation for disinfection. Presently, several provinces have developed ordinances that allow systems to disinfect their imbibing H2O supplies with UV visible radiation. However, as UV research continues for conveying up more devices integrating UV engineering for its proposed germicidal consequence. At present largest UV disinfection system is being constructed in the New York City. A sum of 56 energy-efficient UV reactors will be installed to handle 2.2 billion gallons of H2O a twenty-four hours ( 8,300,000 m3/d ) to function New York City.
UV Light Description
In imbibing H2O, UV visible radiation is used for disinfection. The usage of UV for disinfection involves: ( 1 ) The coevals of UV visible radiation with the desired germicidal belongingss, and ( 2 ) The bringing ( or transmittal ) of that visible radiation to microbic pathogens. As UV light prevarications between Xrays and seeable visible radiation in the electromagnetic spectrum the UV spectrum covers the wavelength scope from 100-400 nanometer ( Figure 2 ) . UV visible radiation at certain wavelengths can demobilize micro-organisms. UV visible radiation with wavelengths from 200-300 nm inactivates most micro-organisms, with the greatest sum of inactivation happening about 260 nanometers.
Figure 1. The Electromagnetic Spectrum.
UV Light Generation
Coevals of UV visible radiation is similar to the coevals of visible radiation in a fluorescent lamp. In general, a UV lamp contains an inert gas ( e.g. , Ar ) and a little sum of liquid quicksilver. When a electromotive force is applied to the lamp, some of the liquid quicksilver vaporizes. Free negatrons and ions so collide with the gaseous quicksilver atoms, “ exciting ” the quicksilver atoms into a higher energy province. Aroused quicksilver atoms have a inclination to return to their land, or normal, energy province by dispatching energy. The energy discharged is in the signifier of UV visible radiation. Mercury is advantageous for UV disinfection applications because it emits visible radiation in the germicidal wavelength scope ( 200 – 300 nanometer ) . The UV visible radiation produced depends on the concentration of quicksilver atoms in the UV lamp, which is straight related to the quicksilver vapour force per unit area. Low force per unit area quicksilver vapour produces monochromatic ( light at chiefly one wavelength ) UV visible radiation at a wavelength of 253.7 nanometers. Higher force per unit area quicksilver vapour produces UV visible radiation at several wavelengths ( polychromatic ) .
UV Lamps and its types
For H2O intervention systems, there are three general types of UV lamps typically used ; low force per unit area ( LP ) , low-pressure high-output ( LPHO ) , and medium-pressure ( MP ) . These footings are based on the vapor force per unit area of quicksilver when the lamps are runing.
LP and LPHO lamps operate at quicksilver vapour force per unit areas of 2×10-3 – 2×10-5 lbs per square inch ( pounds per square inch ) , thereby bring forthing monochromatic UV visible radiation at 253.7 nanometer. MP lamps operate at much higher quicksilver vapour force per unit areas of 2- 200 pounds per square inchs and bring forth polychromatic UV visible radiation at a higher strength. LP and LPHO lamps operate at temperatures of 40 – 200A° C, while MP lamps operate at a much higher temperature scope of 600-900A° C. LP lamps have the lowest power demands, while LPHO and MP lamps have higher power demands. Subsequently, LP lamps have the lowest germicidal end product ( 0.2 W/cm ) , while LPHO and MP lamps have higher germicidal end products ( 0.5 – 3.5 W/cm and 5 – 30 W/cm, severally ) . Figure 2 shows drawings of LP, LPHO, and MP lamps. There is by and large no difference in disinfection capableness between these lamps. But there are advantages and disadvantages to each. For illustration, compared to LP lamps, MP lamps have a higher germicidal end product, typically require fewer lamps for a given applications, and would probably be a smaller reactor.
There are other types of lamps that can bring forth UV visible radiation such as metal halide lamps, electrode-less quicksilver vapour lamps, and eximer lamps. Most UV H2O purification devices use LP lamps due to take down operating temperatures and lower power demands.
Figure 2. LP, LPHO and MP Lamp Drawings.
In imbibing H2O systems, UV lamps are contained in a UV reactor. UV reactors operate as either batch or uninterrupted flow reactors. Several features must be taken into history when designing, installation, and runing a UV reactor. Among them are H2O quality features, distance between the lamp and the reactor wall, and the distribution of UV visible radiation. Additionally, uninterrupted flow reactors must take into history hydraulic features of H2O fluxing through the reactor. Due to all these features, all micro-organisms will non have the same UV dosage. For illustration, UV lamp arrangement in a reactor influences UV dose bringing. If the distance between the lamp and the reactor wall is excessively big ( i.e. , a big sum of H2O between the lamp and the reactor wall ) , microorganisms furthest from the lamp will have less UV strength and later a lower UV dosage. Most UV-using H2O purification devices use a batch reactor system.
UV Dose and its appraisal
In imbibing H2O applications, disinfection utilizing UV visible radiation follows the familiar CT construct ( bactericidal concentration times contact clip ) . However, alternatively of utilizing CT to depict UV disinfection, UV dosage is used alternatively. UV dosage is defined as the measuring of the energy per unit country that falls upon a surface. UV dosage is the merchandise of UV strength, I, and exposure clip, T ( IT ) , similar to the CT construct. UV strength is normally expressed as mW/cm2 and exposure clip is measured in seconds ( s ) . So UV dosage is reported as mWs/cm2. However, UV dosage is normally expressed as millijoules per square centimetre ( mJ/cm2 ) , because 1 mWs = 1 mJ.
When disinfection trial informations is non available theoretical accounts can be used to derive an apprehension of disinfection capablenesss of UV purification devices. Several complex theoretical accounts have been developed to gauge UV strength delivered to a micro-organism. With the estimated UV strength, the UV dosage can be calculated based on assorted exposure times and compared to UV doses determined in scientific literature. The simplest theoretical account used to gauge UV strength is the radial theoretical account:
I ( R ) = ( PL / 2Iˆr ) ten ( e-aer )
Where: PL = UV power emitted per unit arc length of the lamp ( mW/cm ) ; R = Radial distance from the lamp ( centimeter ) ; ae = Base soaking up coefficient of the H2O ( 1/cm ) . ae = 2.303*A254 ; I ( R ) = UV strength ( mW/cm2 ) at a distance R from the lamp.
Using informations provided by the maker on UV power emitted ( PL ) , dimensions of the purification device, UV reactor, and presuming H2O quality variables to develop an soaking up coefficient ( ae ) , UV strength can be calculated. In the absence of good quality specific proving information, this radial theoretical account can be used to supply a unsmooth rating of disinfection capableness.
Mechanism of UV Disinfection
When discoursing UV light disinfection capablenesss, a differentiation must be made between demobilizing and killing micro-organisms. For chemical germicides ( e.g. , Cl, Cl dioxide, I ) , demobilizing and killing can be considered synonymous footings since chemical germicides destroy and harm cellular constructions which interferes with metamorphosis, biogenesis, and growing. In contrast, UV visible radiation does non destruct or damage cellular constructions. Rather, UV light prevents micro-organisms from reproducing. Microorganisms that can non reproduce can non infect and are thereby inactivated. Subsequently, when measuring UV disinfection capableness, Giardia cyst and Cryptosporidium oocyst assays that step infectivity, non viability must be used. Excystation assays mensurating viability are non accurate indexs of UV disinfection capableness.
UV visible radiation inactivates micro-organisms by damaging deoxyribonucleic acid ( DNA ) and ribonucleic acid ( RNA ) . When Deoxyribonucleic acid and RNA absorb UV visible radiation, dimers ( covalent bonds between the same nucleic acids ) are formed ensuing in harm. Dimers cause mistakes in the written text of information from Deoxyribonucleic acid to RNA, which in bend consequences in break of micro-organism reproduction. The micro-organism continues to populate, but it ca n’t reproduce and therefore is non morbific. A micro-organism that can non retroflex can non infect a host. Microorganisms developed two mechanisms to mend harm caused by UV visible radiation. These mechanisms are termed light and dark fix.
It is possible for micro-organisms to mend themselves to the extent where they will go morbific once more after exposure to UV visible radiation. Fortunately, nevertheless, most informations indicates UV doses typically used in H2O intervention prevent most fixs. In general, micro-organism inactivation by UV visible radiation follows first order reaction rates. However, inactivation rates can change depending on micro-organism type, and H2O quality conditions ( e.g. , turbidness, particulate affair, and clip-clop of micro-organisms ) . Last, similar to chemical germicides and the CT attack to disinfection rating, information has shown that UV disinfection follows the jurisprudence of reciprocality over an strength scope of 1-200mW/cm2. For illustration, a UV dosage of 1 mW/cm2 for 200 sec ( i.e. , 200 mJ/cm2 ) achieves the same degree of inactivation as a UV dosage of 200mW/cm2 for 1 sec ( i.e. , 200 mJ/cm2 ) .
UV radiation and its bactericidal consequence
UV radiation really destroys the familial construction of micro-organisms and inhibits its ability to reproduce and finally doing its decease. UV radiation ranges from 200 nanometers to 400 nanometers. The radiation from 200 nm – 285 nanometer is called as UV C radiation and it is bactericidal. In nature bactericidal UV is a portion of the Sun ‘s radiation nevertheless, most bactericidal radiation ( UV-C ) does non make on Earth. State-of-the-art engineerings can be used to change over electrical power into bactericidal UV radiation in an effectual manner. One of these engineerings is a low force per unit area quicksilver vapour discharge lamp that generates UV-C radiation, which can be used to demobilize micro-organisms by destructing its familial stuff, DNA.
UV-C efficaciously kills airborne pathogens, surface and H2O life bacteriums, viruses and cysts signifiers. Low doses of radiation may non bring forth any inauspicious affects on cells. If one lengthens the exposure clip, or increases the strength of the UV visible radiation, an addition in the figure of unrepaired dimers and an addition in mutants likely occur. If a mutant occurs in an indispensable cistron, the cell may decease and is said to incorporate a deadly mutant.
Some viruses are immune to conventional chlorination, which can be efficaciously destroyed by UV radiation. The choice of UV wavelength is really of import for the efficient disinfection procedure. The optimal microbic killing efficiency ranges from 254 to 260 nm wavelength. Bactericidal UV does non alter the chemical composing and gustatory sensation of H2O in contrast to reagent methods of disinfection ( chlorination, ozonation ) . Viruss and bacteriums in vegetive signifiers are most sensitive to UV radiation, for illustration, good known micro-organisms such as Salmonella typhi, Vibrio cholerae, Shigella dysenteriae, Hepatitis virus, Mycobacterium TB etc.
More UV dosage is required to demobilize cysts, while the largest Ultraviolet dosage is necessary to destruct spores. Since there is no negative o.d.ing consequence, it is ever possible to take a UV dosage that provides proper disinfection in any peculiar instance.
Figure 3. Germicidal effectivity of UV lamp
Bacteria, Virus, and Protozoa Inactivation Capability
The effectivity of UV visible radiation on micro-organism inactivation varies with different types of micro-organism. Generally, UV visible radiation is most effectual at demobilizing Cryptosporidium and Giardia, followed by bacteriums and so viruses:
Cryptosporidium and Giardia & gt ; Bacteria & gt ; Viruss
Interestingly, UV opposition appears to follow micro-organism size, with the smallest micro-organisms being most immune. The ground for this may be due to the sum of UV light soaking up per cell. With micro-organisms larger than 1 micrometer, the soaking up of UV visible radiation by the cell can be important, efficaciously cut downing opposition to UV disinfection. The most UV immune viruses of concern in imbibing H2O are adenovirus Type 40 and 41. Because viruses are the most immune to UV disinfection, dosing is controlled by log inactivation demands for viruses, non protozoal cysts.
Table 1. Describe the UV dose required to destruct the micro-organisms.
Dose of Ultraviolet radiation ( UV dose ) in mW sec/cm2needed to kill the selected micro being.
( 1 log decrease )
( 2 log decrease )
Salmonela paratyphi- Enteric febrility
Salmonella typhosa- Typhoid febrility
Shigella dysenteriae- Dysentery
Shigella flexneri- Dysentery
Vibrio comma – Cholera
Bacteriophage – E. Coli
Poliovirus – Poliomyelitis
A chief chronic wellness concern with chemical germicides is the formation of disinfection by-products. Trihalomethanes and haloacetic acids, the merely regulated by-products are non formed during UV disinfection. However, there are surveies that show low-level ( i.e. , ug/L ) formation of non-regulated disinfection by-products ( e.g. , aldehydes ) . The wellness effects of non-regulated disinfection by-products at the degrees formed during UV disinfection has non been widely researched.
Factors impacting the UV disinfection efficiency
The effectual UV disinfection procedure depends upon by several parametric quantities. Prior to the UV disinfection, stairss have to be taken to cut down the physical burden like dust, soil and clay atoms from the H2O ( sediment Filters ) . Besides guarantee and utilizes necessary intervention systems ( activated C filter ) to cut down the organic burden from the H2O. Furthermore UV strength, H2O lucidity, contact clip, flow rate, surface country of the disinfection chamber, quality of the quartz glass etc. , are really of import to supply the equal UV dose for the microbic disinfection.
Evaluation of UV H2O purification system
There are several criterions to measure the H2O purification system ‘s microbic efficiency. Bureau Of Indian Standard – BIS 14724, covered this criterion to measure the efficiency of UV H2O purification systems.
UV purification systems efficiency can besides be tested by the undermentioned criterions set by National Sanitation foundation. i.e. NSF/ ANSI 55 – Ultraviolet Microbiological Water Treatment systems. This Standard covers ultraviolet microbiological H2O purification systems and constituents for point-of-use and point-of-entry applications. The systems are intended to be used under the undermentioned specific conditions. There are two types of categories.
1. Class A systems
Class A point-of-entry and point-of-use H2O purification systems covered by this Standard are designed to demobilize or take micro-organisms, including bacteriums, viruses, Cryptosporidium oocysts, and Giardia cysts, from contaminated H2O. It has been indicated that the H2O purification systems are intended to be installed on visually clear H2O ( non colored, cloudy, or turbid ) .
2. Class B systems or constituents
Class B point-of-entry and point-of-use H2O purification systems covered by this criterion are designed for auxiliary disinfectant intervention of disinfected public imbibing H2O or other imbibing H2O that has been tested and deemed acceptable for human ingestion by the province or local wellness bureau holding legal power. In this category, the system is designed to cut down usually happening nonpathogenic nuisance micro-organisms entirely. The Class B system is non intended for the disinfection of microbiologically insecure H2O and may non do single or general cyst claims.
Advantages of UV disinfection engineering
UV disinfection refers to disinfecting imbibing H2O with UV Radiation of 254 nm wavelength, a set of radiation located merely beyond the seeable visible radiation spectrum
UV radiation is absorbed by the cells of micro-organisms and amendss the familial stuff
UV radiation amendss the familial stuff in such a manner that the beings are no longer able to turn or retroflex, therefore finally destruct them
No chemicals are added to the H2O, therefore the H2O retains its natural gustatory sensation and smell
There are non jeopardies to wellness
The disinfection procedure is non affected by ammonium hydroxide and pH
The disinfection procedure is rapid, and hence a “ detainment clip ” is non required
Ultraviolet disinfection is a proved engineering for disinfecting imbibing H2O and is being used universe broad since long clip. UV visible radiation is most effectual against Cryptosporidium and Giardia followed by bacteriums. UV visible radiation is least effectual against viruses. It does non make any new chemical by-products, does non alter the spirit or smell of the H2O and besides does non take any good minerals. Its effectivity depends upon many factors and it is really of import to plan the H2O purifier scientifically so as to present the safe & A ; purified H2O. Turbidity, particulate affair, and natural organic affair are the most important H2O quality parametric quantities holding the greatest consequence on UV disinfection capableness. Water temperature and pH have an undistinguished consequence on UV disinfection capableness. Increasing degrees of turbidness, particulate affair, and natural organic affair absorb more UV visible radiation, doing less UV visible radiation available for disinfection. Similar to the CT construct, the IT concept [ UV strength ( mW/cm2 ) times exposure clip ( s ) ] , normally referred to as UV dosage ( mJ/cm2 ) , is used to depict UV disinfection capableness. Increasing concentrations of turbidness, particulate affair, and NOM require higher UV doses in the signifier of increased UV strength and/or longer exposure times to accomplish the same sum of inactivation. Studies measuring UV disinfection capableness indicate UV doses of 120 mJ/cm2 are equal to accomplish 4-log virus inactivation of the most immune viruses. They will guarantee a 3-log Giardia and Cryptosporidium inactivation and likely guarantee a 6-log bacterium inactivation. Most UV lamps used in imbibing H2O applications contain quicksilver. There is concern of inauspicious wellness effects to the consumer as a consequence of quicksilver exposure from UV lamp breakage during operation. It is really convenient, instant and easy to run is some of other of import advantages.