justin hess, harini kadambi, xun zhou, taisha venort march 2012
TRANSCRIPT
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Precipitation Methods and the Nalgonda Technique
Justin Hess, Harini Kadambi, Xun Zhou, Taisha VenortMarch 2012
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Problem StatementRemove Fluoride from Groundwater in
Odisha Human Health: detrimental when exposure is
excessive for long-term; accumulation in bones causes skeletal fluorosis
Plant health: Fluoride can be easily taken up by plants through water uptake, has been shown to slow plant growth
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Defluoridation TechniquesPrecipitation using AlumActivated AluminaBone Charcoal (Calcium Phosphate
Exchange)Nalgonda Technique
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Precipitation BackgroundAddition of chemicals (precipitants) to induce
formation of floc. Precipitants performance based on rapid
ability to disperse/ separate fluoride in water.Most common method : adding calcium salts
to water leading to the precipitation of caF2. Fluoride concentration can be still be
relatively high due to rest and flocculation. Further treatment is usually done (activated
alumn adsorption / ion exchange) for more effective removal.
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Precipitation Using AlumEfficient method of flocculation (~77%
removal rate)Alum: Aluminum Sulfate Al2(SO4)3
Used extensively in water treatment in industry
Alum dissolution:Al2 (SO4)3 + 18H2O = 2Al3+ + 3SO4
2– + 18H2O
Aluminium precipitation (Acidic):2Al3+ + 6H2O = 2Al(OH)3 + 6H+
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Advantages/DisadvantagesAdvantages DisadvantagesHigh Pollutant Removal
AbilityCan be used on
community level
Optimization of treatment can be difficult pH of water is imperative
(must be between pH 7.0-7.2) to work effectively
High Maintenance Frequent maintenance
required Generally not cost
effective for small sites Remove floc build-up
from settling pond
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Activated AluminaDehydration of Aluminum Hydroxide to
produce Aluminum OxideUsed widely in industry for many applications
including arsenic, fluoride and sulfur removal from gas streams
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Advantages/DisadvantagesAdvantages
Very effective (80-90% removal of Fluoride)High mechanical strength and thermal stability
DisadvantagesEffectiveness dependent upon pHMany factors which may inhibit removal
(hardness, high level of silica or boron)Maintenance is required and is expensive
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Bone CharcoalCalcium Phosphate Exchange
Ion Exchange CaCo3 replaced by fluoride to form insoluble fluorapatite
Bones are heated to high temperatures Quality controlled by amount of oxygen present
in atmosphere while charringBone char has low Ksp
(1.3E-32) at 25°CInexpensive and largest resorvoir of carbonFiltration is easy because it does not clump when
exposed to waterRemoval capacity 1000mg/L
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Bone Char Removal
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DisadvantageCulturally Acceptable?
Religious beliefs may constrain use of animal bones
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The Nalgonda TechniqueConsists of several steps to treat water
Alum is added to water to start flocculation Al2 (SO4)3 + 18H2O = 2Al3+ + 3SO4
2– + 18H2O 2Al3+ + 6H2O = 2Al(OH)3 + 6H+
F- + Al(OH)3 = Al-F complex + undefined product
Lime is added to neutralize pH 6Ca(OH)2 + 12H+ = 6Ca2+ + 12H2O
SedimentationFiltrationDisinfection
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When should the Nalgonda process be used?“Absence of acceptable, alternate low fluoride source within
transportable distance.”“Total dissolved solids below 1500 mg/l; desalination may be
necessary when the total dissolved solids exceed 1500 mg/l.”“Total hardness is below 600 mg/l.”“Hardness >200 mg/l and <600 mg/l require precipitation
softening, and > 600 mg/l becomes a cause for rejection or adoption of desalination.”
“Alkalinity of the water to be treated must be sufficient to ensure complete hydrolysis of alum added to it and to retain a minimum residual alkalinity of 1 to 2 meq/l in the treated water to achieve pH between 6.5 to 8.5. in treated water.”
“Raw water fluorides ranging from 1.5 to 20 mgF/l.” (Water Resources Research Foundation)
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Why choose the Nalgonda Technique? (continued)
(taken from Feenstra, et al., 2007, p. ii)
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Approximated does of alum (mg/L) to obtain levels of Fluoride at less than 1 mg/L
(taken from Water Resources Research Foundation)
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Varying the Nalgonda Technique
Fluoride levels before and after treating tap water and drinking water with different concentrations of alum and lime (taken from Suneetha et al., 2008)
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Mechanism of Nalgonda Technique Material Needed: lime and aluminum salts Process:
rapid mixing flocculation sedimentation filtration disinfection and distribution
Used in large residential scale
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Mechanism of Nalgonda Technique
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Advantages of the Nalgonda TechniqueIt is adoptable by local people and they can be
easily taught to use it Energy cost is lowHas been implemented in IndiaLow cost: annual cost at 0.04 cubic meters per
capita per day works out to be Rs.15/ for domestic treatment & Rs.30/- for community treatment based on 5000 population for water with 5mg / l F and 400 mg/l alkalinity with requires 600 mg / l of alum (Central Pollution Control Board, p. 48)
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Disadvantages of the Nalgonda Technique Alum will increase the sulfate concentration of
water. In case of improper treatment, it is possible that the concentration of aluminum ion will exceed 0.2 mg/l in the treated water. This may raise the possibility of other diseases. (Central Pollution Control Board, p. 49)
Sludge as a byproduct – what to do with it?Treatment efficiency is limited to about 70% --
is this enough?Skills necessary to operate the Nalgonda
process, as well as a long time commitment
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ReferencesBrunt, R., Vasak, L., & Griffioen, J. (2004). Fluoride in Groundwater:
Probability of occurence of excessive concentration on global scale. Utrecht.
Central Pollution Control Board. Status of Water Treatment Plants in India.
Fawell, J., Bailey, K., Chilton, J., Dahi, E., Fewtrell, L., & Magara, Y. (2006). Fluoride in Drinking-water
Feenstra, L., Vasak, L., & Griffioen, J. (2007). Fluoride in groundwater: Overview and evaluation of removal methods. Utrecht.
Reardon, E. J., & Wang, Y. (2000). A Limestone Reactor for Fluoride Removal from Wastewaters. ENVIRONMENTAL SCIENCE AND TECHNOLOGY, 34, 3247-3253.
Retail Market Price Trends (Industrial Chemicals). from www.indian-chemicals.com/chemiprices.htm
Suneetha, N., Rupa, K. P., Sabitha, V., Kumar, K. K., Mohanty, S., Kanagasabapathy, A. S., et al. (2008). Defluoridation of water by a one-step modification of the Nalgonda technique. Ann Trop Med Public Health, 1(2), 56-58.
Water Resources Research Foundation. Chapter 6. from http://www.globenet.org/preceup/pages/ang/chapitre/capitali/cas/indme_g.htm