Justin Hess, Harini Kadambi, Xun Zhou, Taisha Venort March 2012.

Precipitation Methods and the Nalgonda Technique

Justin Hess, Harini Kadambi, Xun Zhou, Taisha VenortMarch 2012

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

Defluoridation TechniquesPrecipitation using AlumActivated AluminaBone Charcoal (Calcium Phosphate

Exchange)Nalgonda Technique

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.

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+

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

Activated AluminaDehydration of Aluminum Hydroxide to

produce Aluminum OxideUsed widely in industry for many applications

including arsenic, fluoride and sulfur removal from gas streams

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

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

Bone Char Removal

DisadvantageCulturally Acceptable?

Religious beliefs may constrain use of animal bones

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

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)

Why choose the Nalgonda Technique? (continued)

(taken from Feenstra, et al., 2007, p. ii)

Approximated does of alum (mg/L) to obtain levels of Fluoride at less than 1 mg/L

(taken from Water Resources Research Foundation)

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)

Mechanism of Nalgonda Technique Material Needed: lime and aluminum salts Process:

rapid mixing flocculation sedimentation filtration disinfection and distribution

Used in large residential scale

Mechanism of Nalgonda Technique

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)

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

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