PROF. A.B. GUPTADepartment OF Civil Engineering
MALAVIYA NATIONAL INSTITUTE OF TECHNOLOGY, JAIPUR
Delivered atIIT Kanpur, February 2, 2015
Disinfection of water using Chlorine, U.V., or Ozone or combinations
thereof- directions for future
Water Health Water as direct vehicle for transmission of disease- water borne diseases
Water as habitat for vectors of disease- Malaria
Water transmitting toxic chemicals- As, F, NO3, pesticides.
Beneficial effects2
ORGANISMEXCRETED LOAD(no/g)
Champhylobacter spp. 1.00E+07Giardia lamblia 1.00E+08Entamoeba histolytica 1.00E+08Shigella spp. 1.00E+07Vibrio cholerae 1.00E+07Salmonella typhi 1.00E+08Salmonella spp. 1.00E+08E. coli (path) 1.00E+08Enteroviruses 1.00E+07Hepatitis A virus 1.00E+06Ancylostoma duodenale 1.00E+02Trichuris trichura 1.00E+03Taenia Saginata 1.00E+04Ascaris lunbricoides 1.00E+04
Human Being is
the Biggest
of Human Being3
Testing of microbiological quality of water
Routine MPN testing involves standard plating or multiple dilution tubes tests, which are time consuming and elaborate
UNICEF has supplied some quick assessment kits, which were analyzed for sensitivity in our laboratory and corroborated with “Colialert” results
Developing a kit to detect emerging pathogens
4
Colilert18
Quanti try sealer Quanti tray
5
Bacteriological H2S Strip Test medium provided by PHED
Rajasthan.
Principle Dilution preparation
9+1
Salmonella& Citrobacter
OthersSafe for drinkingNote safe for drinking 6
Bacteriological H2S Strip Test Kit provided by PHED
Rajasthan.
Principle Preparation of very close dilutions
7
Sensitivity Performance (Colilert)
Dilution Factor Table MPN value Total Coliform
count/100ml
100X Uncountable Uncountable
1000X 483.3 483000
10000X 51.9 520000
100000X 5.0 500000
1000000X <1 0
Average=501000
(Dinesh seminar 2009)
Bacteriological H2S Strip Test medium provided by PHED
Rajasthan.
Principle Dilution preparation
9+1
Salmonella& Citrobacter
OthersSafe for drinkingNote safe for drinking
Sensitivity ResultsTotalColiform count/100ml Sensitivity within 24 Hrs Sensitivity within 48Hrs
Salmonella& Citrobacter Others Salmonella& Citrobacter Others
6000 yes Yes yes yes
4800 yes Yes yes yes
3600 yes yes yes yes
2400 yes yes yes yes
1200 yes yes yes yes
600 yes yes yes yes
480 yes yes Yes yes
360 Yes yes Yes yes
240 Yes yes yes yes
120 Yes yes yes yes
60 No yes yes yes
48 No yes yes yes
36 No yes yes yes
24 No yes N.C yes
(Dinesh seminar 2009)
Cont…12 no yes no yes
6 no yes no yes
4-5 no yes no yes
3-4 no yes no yes
2-3 no no no N.C
1 no no no N.C
0 no no no N.C
0 no no no N.C
0 no no no N.C
0 no no no N.C
0 no no no N.C
0 no no no N.C
0 no no no N.C
0 no no no N.C
0 no no no N.C
0 no no no N.C
(Dinesh seminar 2009)
Bacteriological H2S Strip Test Kit provided by PHED
Rajasthan.
Principle Preparation of very close dilutions
Sensitivity Results
Total Coliform count/100ml Sensitivity within 24 Hrs Sensitivity within 48 Hrs
5000 yes yes
4000 yes yes
3000 yes yes
2000 yes yes
1000 yes yes
500 no yes
400 no yes
300 no yes
200 no yes
100 no yes
50 no yes
40 no no
(Dinesh seminar 2009)
Microbiological Analysis
Cultivation & Isolation of microbial species from water and waste water.
1. Media Preparation – Plate count agar (PCA), Potato Dextrose Agar (PDA) and Xylose desoxycholate Agar ( XLD).
2. Sterilization of media.3. Pouring plating after serial dilutions and incubating for 24
h.4. Morpho-type quantification conforming via microscopy
and gram test..
Air exposed Petri plate (PDA) INLET AREA
Air exposed Petri plate (PCA) INLET AREA
Air exposed Petri plate (PDA) near PRIMARY CLARIFIER
Air exposed Petri plate (XLD) near PRIMARY CLARIFIER
1. Introduction2. Factors Influencing Disinfection3. Common Disinfectants:4. Chlorine Disinfection5. Recent Research on chlorination6. Scope for Future
Disinfection
Disinfection is a process designed for the deliberate reduction of the number of pathogenic microorganisms. Microorganisms are destroyed or deactivated, resulting in termination of growth and reproduction
The effectiveness of disinfection is judged by analyzing for an indicator organism (total coliform bacteria)
Major factors affecting disinfection efficiency are- Kind and concentration of microorganisms in the water; presence of other constituents may impede disinfection; Temperature; Contact time; Type of disinfectant; and chemical and physical interference e.g. clumping of cells or adsorption to larger particles
Introduction
Disinfectant methods Chemical agentsIt includes:Chlorine and its compound, bromine, iodine,ozone, alcohols, dyes, soaps and manymore. Physical agentsThat can use heat, sound waves and light (UV
radiations) Mechanical meansLike chemical precipitation (New Mumbai plant),
trickling filters, activated sludge. RadiationsMajor types of radiations are electromagnetic
particle.Gamma rays can sterlize both water and wastewater.
Ozone
Ultraviolet Radiations
Chlorine
Chloramines
Chlorine Dioxide
Common Disinfectants
Comparison of common disinfectantsCharacteristic Chlorine Ozone UV radiation
Availability Low cost Moderately high cost
Moderately high cost
Homogeneity Homogenous
Homogenous No
Noncorrosive and nonstaining
Highly corrosive
Highly corrosive
No
Nontoxic to higher forms of life
Highly toxic to higher life forms
Toxic Toxic
Safety concern High Moderate Low
Solubility Stable Unstable, must be generated as used
No
CHLORINE DISINFECTION
Chlorine is the most widely used disinfectant for municipal wastewater
It destroys target organisms by oxidizing cellular material
Chlorine can be supplied in many forms, e.g. chlorine gas, hypochlorite solutions, and other chlorine compounds in solid or liquid form
Water is chlorinated by the bubbling of chlorine gas or the dissolving of chlorine compounds and their subsequent doses
Cl2 + H2O = H + Cl- + HOCl
HOCl = H+ +OCl-
Both segments of the agent are microbicides and operate by inhibiting enzymatic activity and inactivating bacteria and viruses
Chlorine Disinfection
HOCl efficiency is at least 80% greater than that of OCl-
WHO recommends a pH< 8 for appropriate disinfection
The required degree of disinfection can be achieved by varying the dose and the contact time for any chlorine disinfection system
The dose usually ranges from 5 to 20 milligrams per liter
Contd…
The effect of disinfection is determined by the pH of the water
Contd…
Reactions of chlorinewith ammonia : Ammonium ion is in equilibrium with ammonia and
hydrogen ion.NH4 + ↔ NH3 + H+
NH3 react with Cl2 or HOCl (hypochlorous acid)
NH3 + HOCl → NH2Cl (monochloramine) + H2O
NH2Cl + HOCl → NHCl2 (dichloramine) + H2O
NHCl2+ HOCl → NCl3 (Nitrogen Trichloride) + H2O
Rxns are dependent on pH , temperature , contact time , and Cl2 / NH3 ratio . Cl2 / NH3 ratio 1:1 for the formation of Monochloramine (NH2Cl) and Dichloramine (NHCl2). Further increase in mole ratio trichloramine, oxidation of part of ammonia to N2 or NO3 -.
Break Point Chlorination
More cost-effective Chlorine residual plays a important role in
disinfection Chlorine disinfection is reliable and
effective against a wide spectrum of microorganisms
Chlorine can eliminate noxious odors while disinfecting
Cont…Advantages of Chlorine
Liquid chlorine Amber in colour 1.44 times heavy as water Moderately soluble in water Use of chlorine for disinfection has been of great
importance, but important concern are also there with it.
Chlorine reaction in water
Cl2 + H2O HOCl + H+ + Cl
HOCl H+ + OCl-
Typical supply and storage of chlorine
Sodium hypochlorite (NaOCl) Solves various concerns of safety, transport,
handling Contain 12.5 to 17% available chlorine at the
time it is manufactured Cost 150 to 200% the cost of liquid chlorine Require special design consideration
Hypochlorite reaction in water
Ca(OCl)2 + 2H2O 2HOCl + Ca(OH)2
NaOCl +H2O HOCl + NaOH
Tablet Chlorinator
Calcium Hypochlorite
Sodium Hypochlorite
It depend upon the inorganic and organic impurities present in it
Excess chlorine after it reacts with ammonia forms chloramines and rest appears as free chlorine
Dose which leaves a residual of about 0.2mg/l after 10 minutes of contact period is chlorine demand of water
Cont…Doses of Chlorine
Chlorine Dose
CHLORINE DISINFECTION
ADVANTAGES• They have broad-spectrum
germicidal potency.• They show a good degree
of persistence in water distribution systems.
• Their easily measurable residual properties can be monitored in water networks after treatment and/or delivery to users
• This method is economic and cost-effective
DISADVANTAGES• The chlorine residual, even
at low concentrations, is toxic to aquatic life and may require dechlorination
• All forms of chlorine are highly corrosive and toxic. Thus, storage, shipping, and handling pose a risk
• Chlorine oxidizes certain types of organic matter, creating more hazardous compounds DPBs
Dechlorination
Chlorination used for destruction of harmful organisms
But many organic constituents in waste water interfere with chlorine to form toxic compounds…THMs and HAAs
So to minimize this effect dechlorination is required
During spread of diseases or ceertain specific conditions super chlorination may be practiced requiring dechlorination before supplying water (UK example…algal cells)
ULTRAVIOLET (UV) DISINFECTION
An Ultraviolet (UV) disinfection system transfers electromagnetic energy from a mercury arc lamp to an organism's genetic material (DNA and RNA)
When UV radiation penetrates the cell wall of an organism, it destroys the cell's ability to reproduce
The effectiveness of a UV disinfection system depends on the characteristics of the wastewater, the intensity of UV radiation, the amount of time the microorganisms are exposed to the radiation, and the reactor configuration
UV DISINFECTION UNIT
UV DISINFECTION
UV Disinfection
UV DISINFECTION
ADVANTAGES
Effective at inactivating most viruses, spores, cysts
It is a physical process rather chemical hence eliminates the need to handle, transport, or store toxic/ corrosive chemicals.
No residual that can be harmful to humans or aquatic life.
shorter contact time compared to other disinfectants
DISADVANTAGES Low dosage may not
effectively inactivate some viruses, spores, and cysts.
Re-vegetation of microbes in case of partial exposure
Preventive maintenance important to control fouling of tubes.
Turbidity and TSS in the wastewater can render UV disinfection ineffective
Ozone Disinfection
O3 a gas, must be generated on-site
Bubbled into a basin (or pipeline) with treated effluent
Great disinfectant!
No residual…ozone degrades to oxygen, O2
Costs More, Need equipment and electricity
Ozone chemistry
O3 + H2O HO3+ + OH-
HO3+ + OH- 2HO2
O3 + HO2 HO + 2O2
HO + HO2 H2O + O2
Free radicals HO and HO2 have greatoxidizing power and are activeforms in disinfection process.
Ozone Disinfection
Flow DiagramOzone Generation
Ozonation: +/-
Advantages: rapid reaction rate,
dissolved ozone half-life only 0-15 sec (Bullock et al., 1997);
few harmful reaction by-products in freshwater; oxygen is produced as a reaction end-product.
Disadvantages: ozone is dangerous to humans and fish.
Ozone Supports Water Treatment
directly oxidizes NO2- to NO3
- ; helps remove color & dissolved organic matter:
breaks non-biodegradable compounds into smaller & more biodegradable compounds;
helps remove dissolved & fine particulate matter precipitates dissolved organic molecules, micro-flocculates fine particulate matter, improving solids removal by settling, filtration, or
flotation.
Maintaining Ozone Residual
Sometimes difficult to maintain ozone residual for a given contact time due to ozone demand of water. dissolved ozone has a half-life of only 0-15 sec in
recirc systems (Bullock et al., 1997); Ozone demand of relatively clean surface water
supplies can range from 2-10 mg/L!
During disinfection, chlorine may react with NOM in the raw water, resulting in the formation of various DBPs such as THMs & HAAs. These THMs have some adverse health effects, in particular cancer & reproductive disorder.
Hence, disinfection methods using only chlorine are not totally safe and have some environmental consequences.
Application of a single technology is not recommended and a hybrid system such as using U.V. or Ozone after chlorination can be beneficial to carry out disinfection studies in better ways by reducing the chances of formation of carcinogenic compounds and reducing the use of high doses of chlorine against the remaining resistant bacteria
Disinfection…
Pathogenic bacteria count (per100ml) removal profile for chlorine dose of 20 ppm (Dinesh et al., 2011)
Contd…Efficacy of chlorine against different pathogens
present in sewage
Chlorine Disinfection limitation…
Figure 1: Total Coliform count (per 100ml) removal profile for chlorine dose of 5 ppm & 17.5 ppm (Dinesh et al., 2011)
Thank You
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