WELCOME

SEMINAR ON WATER TREATMENT PROCESS-OZONISATION AND UV APPLICATION

PRESENTED BY GOWRI V PRABHU 2nd MSc EVS

•Water treatment describes those processes used to make water more acceptable for a desired purpose.

•It is the process of removing undesirable chemicals, biological contaminants, suspended solids and gases from contaminated water.

• In general the methods used include physical processes such as filtration and sedimentation, chemical processes like flocculation and chlorination and the use of electromagnetic radiation such as ultraviolet light, biological processes such as slow sand filters and activated sludge.

• The Purification process of water reduce the concentration of particulate matter including suspended particles,parasites,bacteria,virus,fungi,and a range of dissolved and particulate matter derived from surfaces that water have made contact after rain.

• Ozone [O3 ] is a molecule composed of three oxygen atoms temporarily existing in a very unstable and reactive state.

•Ozone is very strong disinfectant and oxidizer

•Any pathogen or contaminant that can be disinfected,alterd,or removed through an oxidation process will be affected by ozone.

•The oxidizing properties of ozone can reduce the concentration of iron,manganese,sulfur and help eliminate taste and odour problem.

OZONISATION IN WATER TREATMENT

CONCEPT OF GENERATING OZONE

The primary process used commercially today to make ozone is called electrical discharge or corona discharge.

Inside the machine, a high voltage electrical spark is fired to turn oxygen into ozone.

•The formation of oxygen into ozone occurs with the use of energy. This process is carried out by an electric discharge field as in the CD-type ozone generators (corona discharge simulation of the lightning), or by ultraviolet radiation as in UV-type ozone generators (simulation of the ultraviolet rays from the sun). •In general, an ozonation system includes passing dry, clean air through a high voltage electric discharge, i.e., corona discharge, which creates and ozone concentration of approximately 1% or 10,000 mg/L. • In treating small quantities of waste, the UV ozonators are the most common, while large-scale systems use either corona discharge or other bulk ozone-producing methods

OZONISATION IN WATER TREATMENT

OZONATION PROCESS

Air Preparation•The key to an efficient, reliable CD ozone generator is making sure that the feed gas is dried to a dew point of at least -60° F.• This is important because as the electrical discharge splits the oxygen molecules, nitrogen molecules are also being split, forming several species of nitrogen oxides. •They are normally benign, but if combined with moisture (ordinary humidity), these oxides form a very corrosive substance called nitric acid. Consequently, proper air preparation is critical.

Ozone Injection•The raw water is then passed through a venturi injector which creates a vacuum and the air is then bubbled up through the water being treated. Since the ozone will react with metals to create insoluble metal oxides, post filtration is required.

Ozone Contact•After injection, the ozone must have time to do its work. This time is known as contact time.• Contact time is the time ozone has to oxidize and disinfect, or the time the water is allowed to hold the disinfectant.•For ozone, contact time is measured from the point of injection to the filter. All gasses inducted through the venturi must be properly disposed of or “off-gassed.” At a bare minimum, this is accomplished by simply venting the contact tank to the outside.

Filtration of Oxidized Particles•In most cases, a properly sized multi-media depth filter is very well suited to filtering objectionable oxidized contaminants and will give years of operation with little maintenance required.

1. Ozone is effect over a wide pH range and rapidly reacts with bacteria, viruses, and protozoan's and has stronger germicidal properties then chlorination. Has a very strong oxidizing power with a short reaction time.

2. The treatment process does not add chemicals to the water.

3. Ozone can eliminate a wide variety of inorganic, organic and microbiological problems and taste and odor problems.

4. Ozone’s ability to kill algae [Planktons] with low doses makes it a popular treatment method for ponds and water features.

ADVANTAGES TO OZONATION

1. There is a higher equipment and operational cost and it may be more difficult to find professional proficient in ozone treatment and system maintenance.

2. Ozonation provides no germicidal or disinfection residual to inhibit or prevent regrowth.

3. Ozonation by-products are still being evaluated and it is possible that some by-products may be carcinogenic. These may include brominated by-products, aldehydes, ketones, and carboxylic acids. This is one reason that the post filtration system may include an activate carbon filter.

4. The system may require pretreatment for hardness reduction.

5. Ozone is less soluble in water, compared to chlorine, and therefore special mixing techniques are needed.

6. Potential fire hazards and toxicity issues associated with ozone generation.

DISADVANTAGES TO OZONATION

ULTRAVIOLET APPLICATION IN WATER TREATMENT

•Ultraviolet disinfection systems are used in many water purification systems to control bacteria.

•Ultraviolet or UV energy is found in the electromagnetic spectrum between visible light and x-rays and can best be described as invisible radiation.

•UV light occurs with a wavelength ranging from 200 to 390 nanometers (nm). The most effective wavelength frequency, from the point-of-view of microbiological disinfection, is 254 nm as this is where the optimum energy intensity is found. 

WORKING OF UV IN WATER TREATMENT•Typical UV disinfection systems involve the flow of water through a vessel containing a UV lamp .

•As the water passes through this vessel, microorganisms are exposed to intense ultraviolet light energy which causes damage to genetic molecules (i.e. nucleic acids: DNA or RNA) needed for reproductive functions.  

•In order to kill microorganisms, the UV rays must actually strike the cell. UV energy penetrates the outer cell membrane, passes through the cell body and disrupts its DNA preventing reproduction

•This damage prevents the microorganism from multiplying or replicating in a human or animal host. Because the microorganism cannot multiply, no infection can occur. Disinfection of water is achieved when UV light causes microbial inactivation.

ADVANTAGES TO UV TREATMENT•UV disinfection does not add chemicals to the water. • UV is effective against bacteria and viruses. Cryptosporidium, giardia and other biological pathogens get inactivated, and bacterial regrowth is arrested.•Most UV device have audible UV emission detector to notify user when lamp intensity is inadequate.

DISADVANTAGES TO UV TREATMENT• Regular maintenance and lamp replacement is essential.

• Point” Disinfection UV units only kill bacteria at one point in a watering system and do not provide any residual germicidal effect downstream.

• The piping in a watering system treated by UV disinfection will need to be periodically sanitized with a chemical disinfectant.

•Water being treated must not be turbid or cloudy. Any level of colour present in water will hinder the ability of UV radiation to penetrate it and destroy the microorganisms within.

CONCLUSION

Disinfection is generally final treatment process in Water Treatment. The objective of Disinfection is to destroy pathogens in water and provide additional protection against subsequent contamination.

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