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English
Inhoud:
- Effect
van Ultraviolet licht
- UV-C Productie
- Ultraviolette dosering
- Dosering/Vernietiging Relatie
- Toepassingen
- Medium en Hoge druk Boog Buizen
- Lage druk lampen
- Irradiatie Kamers
- Enkelvoudige BoogBuis Configuratie
- UV Intensiteit Monitoring
- Systeem Grootte
De afgelopen 100 jaar heeft de wetenschap de bactericidale effecten van het ultraviolette gebied van het electromagnetsich spectrum onderkend.
De specifieke golflengtes die verantwoordelijk zijn voor deze reactie liggen tussen 240 - 280 nanometer (hier nm genoemd) met een piek golflengte van 265 nm, en staan bekend als UV-C,
Figuur (1): UV-C in het spectrum van de electromagnetische straling
Fig (2): De spectrale energie distributie curve voor germicidale actie en de spectrale krachtdistributie voor lage en medium druk UVlampen
Effect van Ultraviolet licht
Wanneer een micro-organisme wordt bloogtgesteld aan LTV-C, zal de celkern als gevolg van fotolytische processen zo veranderen, dat er geen celsplitsing en dus ook geen reproductie meer kan plaatsvinden.
UV-C productie
De bron van UV licht die gebruikt wordt is doorgaans een samengesmolten buis van siliciumkwarts, met een diameter van 15mm tot 25mm en een lengte van 100mm-1200mm. Het inerte gas waarmee de buis wordt gevuld, zorgt voor de eerste uitstoot en de benodigde actie om kleine afzettingen kwik te prikkelen en te verdampen.
De lage druk UV lamp kan slechts 185nm en 254 nm produceren. Een toename van de aangevoerde stroom, zorgt er voor dat de UV lamp snel opwarmt. Hierdoor neet de kwikdruk toe, waardoor er sprake is van een medium druk spectrum output (Diagram 2).
Ultraviolette dosering
De UV dosering is een product van de UV intensiteit (uitgedrukt als energie per eenheid oppervlak) en de verblijfstijd.
Dus:- Dsering = I x T
Dit wordt doorgaans uitgedrukt als 1mJ/cm2=1000 micro Watt seconde/cm2
De minimum randdosering uitgedrukt door Willand geeft de gebruiker de garantie van succes. Gemiddelde en cumulatieve doseringen die door anderen worden gebruikt zijn afhankelijk van turbulente flow karakteristieken die verdwijnen als de flow variabel is.
Willand will recommend the appropriate UV dose for each application taking into account water quality, arc tube ageing, industry standards and microbiological challenge.
DOSE / DESTRUCTION RELATIONSHIP
The relationship between the dose and the destruction achieved of a target micro-organism can be summarized as follows:
Where:
N = Initial Number of target organisms
No = Number of target organisms after treatment
K = Constant associated with target organisms
D = Dose
From the above relationship doubling of the dose applied will increase the destruction by a factor of 10. Therefore doubling the dose required for 90% destruction will produce 99% destruction of the target organism. tripling the dose will produce a 99.9% destruction of the target organism and so on.
Some 90% destruction values are shown in Fig. 3 and the relationship between UV dose and destruction are shown in Fig. 4
FIG. 3.- DOSE REQUIREMENTS - COMMON MICRO-ORGANISMS
|
Species |
Dose (mJ/cm2) |
| Bacillus subtilis (spore) | 12.0 |
| Clostridium tetani | 4.9 |
| Legionella Pneumophilla | 2.04 |
| Pseudonomas aeruginosa | 5.5 |
| Streptococcus feacalis | 4.5 |
| Hepatitis A virus | 11.0 |
| Hepatitis Poliovirus | 12.0 |
| Saccharomyces cervisiae | 6.0 |
| Infectious pancreatic necrosis | 60.0 |
FIG. 4. -E.coli (Waterborne indicator Pathogen) DOSE = 5.4 mJ/cm2
| Dose mJ/cm2 | Reduction in number of live microorganisms |
| 5.4 | 90.0% |
| 10.8 | 99.0% |
| 16.2 | 99.9% |
| 21.6 | 99.99% |
| 27.0 | 99.999% |
APPLICATIONS
DISINFECTION
- LIQUIDS :- Water, Syrups, Emulsions, Brines.
- SURFACES :- Packaging, Conveyors, Food, Working Surfaces.
- GASES/AIR :- Food preparation, Clean rooms, Air conditioning.
PHOTOCHEMICAL REACTIONS
- OXIDATION :- TOC reduction, Ozone destruction, Chlorine removal.
- CATALYSIS :- Pesticide removal, Effluent treatment, Ground Recovery.
- DEODORISATION :- Sewage and Industrial emissions.
MEDIUM AND HIGH PRESSURE ARC TUBES
Power ratings are from 0.4kW to 7.0kW with a maximum treatment capacity of 600 m3/hour with a single lamp.
The high energy output is equally effective on both hot and cold fluids.
The broad spectrum output performs more efficiently than low pressure lamps on flows > 13 m3/hour. Conversion of power input to biocidal output is > 15%.
Useful arc tube life between 4000 - 8000 hours depending on operating conditions.
Full spectrum output 185 - 480 nm available for photochemical reactions.
LOW PRESSURE LAMPS
Ideal for low flow situations with power ratings from 15w to 200w.
Single wavelength output at 254 nm.
Conversion to UV-C typically 30% - 35%.
120 - 200 watt lamps unaffected by water temperatures.
IRRADIATION CHAMBERS
The disinfection process involves the exposure of fluids with microbiological contamination to a UV energy source which is mounted centrally in an irradiation chamber.
Lenntech have always believed that correct chamber design is a significant part of effective disinfection and to this end computer modeling is used to establish turbulent flow, which ensures good mixing and balanced exposure at high and low flows and residence time characteristics.
Lenntech UV Systems design equipments so that the dose is AT THE WALL, AT THE END OF LAMP LIFE. This protects the process from possible inadequate treatment which may occur through short circuiting when average and cumulative doses are is used.
High quality internal finishing avoids shadowing and other bacterial traps.
Chambers have integrally fabricated sample ports, drain and air vents as standard.
The inlet and outlet orientation, size and end termination are to customers specification to aid installation.
SINGLE ARC TUBE CONFIGURATION
Single arc tube configuration greatly enhances performance. One high intensity lamp is capable of disinfecting up to 600m3/hour. UV intensity monitoring is positive, simple, effective and proven.
Multi-tube designs utilizing quantities of low pressure lamps housed in one chamber present both hydraulic and mechanical problems. Maintenance is time consuming and expensive. Baffles are required to introduce turbulence and through the shadowing effect of these it is possible for untreated water to pass through the chamber shielded from the monitor.
UV INTENSITY MONITORING
Willand intensity monitors respond to UV-C. The monitor is the customer's safeguard the unit is operating at efficient output. When low UV-C output threshold is reached an alarm is initiated. Monitor output can be linked to BEM or PLC units to ensure optimum plant operation.
SYSTEM SIZING
To ensure customers are supplied with the correct unit for the intended application we recommend they contact Lenntech UV to arrange an appointment with a trained Lenntech consultant.
Information necessary to correctly size a Lenntech unit includes, but is not limited to:
1. Peak flow (liters per second or gallons per minute). 2. Fluid sample for free transmission test.
3. Microbiological challenge.
4. Required standard after UV treatment.
All information supplied is in the strictest confidence.