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UV Disinfection VS Chemical Chlorine Disinfection ???

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UV Disinfection VS Chemical Chlorine Disinfection

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UV DisinfectionVS Chemical Chlorine Disinfection

By: Ummi Nuraihan Binti Mohamad Rizal55102215038

Ultraviolet (UV) Disinfection for Wastewater Treatment

Physical process that instantaneously neutralizes microorganisms as they pass by ultraviolet lamps submerged in the effluent. Adds nothing to the water but UV lightHas no impact on the chemical composition or the dissolved oxygen content of the water.UV Disinfection ?

Consists of one or more UV lamps and a conduit or duct in which the water or wastewater to be irradiated flows.Transparent material separates the lamps from the wastewater generally enclosed in a cylindrical quartz sleeve

Number of UV lamps are required to give the required UV dose. The energy required to inactivate a microorganism is termed the UV dose and is measured in mJ.cm-2, or mW.s.cm-2, or J.m-2.

Dose = Average intensity (eg. mW.cm-2) x contact time (eg. seconds)Inactivation of bacteria and viruses depends on temperature and pH.

Temperatures: between 5 and 35 CpH: between pH 6 and 9.Iron and Aluminium PrecipitatesActivated Sludge SolidsAlgaeOil and GreaseCleaningBrushingScrapingHosing

Suitable for inactivating; bacteria (eg. coliforms, salmonella spp.)viruses (eg. poliovirus, rotavirus, enterovirus, adenovirus and bacteriophages)protozoan parasites (eg. Cryptosporidium and Giardia species)

It damages the DNA or RNA of the organism. The organism is still able to function, however cannot use its DNA/RNA to reproduce and so the population of the organism dies out. It is difficult to inactivate Ascaris eggs with ultraviolet radiation because the ultraviolet light cannot easily penetrate the outer two layers of skin of the Ascaris egg.

Practicalities health, safety & eNvironmentInclude provision of ground fault interrupt or other electrical protection devices, in addition to the usual circuit breakers, etc.Install lockable UV opaque covers over open channel UVdisinfectionunits, to prevent access by the public. Place signs WARNING - UV RADIATION - WILL BURN EXPOSED SKIN AND EYES around the unit.Do not open closed in-pipe UV units whilst the lamps are on, unless exposure precautions are taken. When working around open UV channels with automatic level control, and covers are removed, wear a pair of UV absorbing clear plastic glasses or UV absorbing dark glasses. This will protect your eyes if the automatic level control fails and the lamps are exposed.If exposure occurs, obtain medical advice as soon as practicable.Lamps and sleeves produce sharp edges when broken. Conventional LP UV lamps contain mercury (wear rubber gloves when handling broken lamps).Disposing lamps to landfill will contaminate the landfill. Please return your used lamps and sleeves to the lamp or sleeve supplier or a recycler, for recycling of the quartz and mercury.

Cost-effective Safe Environmentally-friendly

Thank you.

Iron phosphate and/or hydroxides particles can settle out on sleeves and tubes, at low flowrates, in a similar manner to activatedsludgesolids. It is expected that iron (III) precipitates are high UV absorbers.Excess aluminium and iron ions, as carbonate, phosphate or hydroxide (if used in the process) can be precipitated on the surfaces of quartz sleeves.It is suggested that you seek the services of a chemical laboratory to trial various solvents to deal with fouling.

Activatedsludgesolids, such as fine particulate solids can settle out on the tops of sleeves or inside fluoropolymer tubes at low or zero flowrates. Optimisation of the activatedsludgeprocess may reduce entrained solids.Fluoropolymer tubes can readily be flushed or brushed to eliminate accumulated solids. A jet nozzle is the best manner to clean these tubes. Quartz sleeves tend to get warmer and this may encourage the deposits to stick to the sleeve.If these deposits, are present on quartz sleeves, they will tend to be associated with carbonate deposits and so acid is the preferred cleaning method (see above). Otherwise brushing will be necessary to remove solids deposits.

Algae tends to build-up inside and around the outside walls of clarifier launders, clarifier walls and effluent transfer channels. It is encouraged by warmer temperatures and increased sunlight. The best method of eliminating algae build-up is to keep the launder inside and outside walls clear of algae, by brushing, scraping or hosing, or by covering the areas where the algae to grow, thus preventing visible light getting to the water column.Strands of algae may wrap around the UV unit and accumulate, inhibiting transmission of UV light to the water. Algae particles can stick to quartz sleeves at low flowrates and higher temperatures. This is not such a problem for fluoropolymer tube units.Brushing and hosing the sleeves and supports is best for removal of strands of algae and algae accumulation. Otherwise try acid cleaning the sleeves, if associated with carbonate deposits.

Oil and grease may arise from carryover of foaming organisms. The lamps may need frequent cleaning with detergent if there is significant solids accumulation on the lamps. Frequency would depend on the rate of solids build-up, remembering the usual fouling design factor is of the order of 0.7 to 0.8.

As ultraviolet light is absorbed by ordinary glass, usually a pure quartz is used as the separating material. It is important to have minimal backmixing from the waters inlet to outlet. Having some mixing perpendicular to the axis of flow, ensures that all parcels of fluid receive a broad range of UV intensities through their travel through the reactor. Parcels of fluid that move through the reactor solely a large distance from the UV lamp, and receive minimaldisinfection, are thus eliminated.

Proven Technology, Environmentally-Friendly, SafeThe adoption of ultraviolet light for wastewater disinfection has grown significantly over the past few decades. Today, over 20% of wastewater treatment plants in North America employ thisenvironmentally-friendlytechnology. Thousands of municipalities have converted from chemical-based disinfection, such as chlorine gas, to UV due to the significantsafety advantagesfor their communities, plant employees and local water bodies.Cost-EffectiveAs new wastewater treatment plants are constructed around the world, UV is most often selected for disinfection because of the cost savings in both initial construction and long term operation.Disinfectionby ultraviolet irradiation is a relatively cost effective method for disinfecting water andwastewater. It has a similar cost to the combinedchlorinationand dechlorination processes.

Works AgainstCryptosporidiumandGiardia, Field-TestedUV is the only disinfection alternative that does not have the potential to create or release carcinogenic by-products into the environment. In addition, UV is an effective disinfectant for chlorine-resistant protozoa likeCryptosporidiumandGiardia.While unregulated in wastewater, these harmful protozoa, if left untreated, can find their way into drinking water intakes located downstream of the wastewater treatment plant. Our UV disinfection systems have undergone field-testing and third-party witnessedbioassay validationtesting to ensure the UV system will meet regulatory requirements.

Ultraviolet light in the UV-C band is responsible for this damage. Specifically damage by ultraviolet radiation in the range of 230 to 290 nm is responsible for the damage to DNA/RNA.There are mechanisms in cells which repair damage to the DNA/RNA. These can be divided into light-catalysed repair, called photoreactivation, and dark space repair mechanisms. Photoreactivation is the cleavage of the Thymine-Thymine (Cytosine or Uracil) double bonds, initiated by enzymes and (blue to UV - 350 to 450 nm) light wavelengths, and in the case ofE. colican account for repair of the order of 1% of original viable organisms. The lower the UV dose administered to the organisms (the less the DNA damage) and the higher the visible light irradiation time the greater is the repair effect of photoreactivation. Dark space repair accounts for a much lower fractional repair of organisms (E.colior thermotolerant coliforms typically of the order of 0.05% of original viable organisms). Enzymatic mechanisms such as excision and SOS repair account for this repair.