NALGONDA TECHNIQUE
• The process removes only a smaller portion of fluoride (18-33%) in the form of precipitant and converts a greater portion of ionic fluoride into soluble aluminium fluoride complex ion. • Due to use of aluminium sulfate as coagulant, the sulfate ion concentration increases tremendously and in few cases, it crosses maximum permissible limit of 400 mg/l, which causes cathartic effect on human beings. • The residual aluminium in excess of 0.2 mg/l in treated water causes dangerous dementia disease. • Sludge disposal is a problem. • Regular analysis of feed and treated water is required to calculate the correct dose of chemicals to be added, because water matrix keeps on changing with time and season as evident from our earlier studies conducted in laboratory.
ADSORPTION
• The process is highly dependent on pH and works best only in a narrow pH range (5-6). High concentration of total dissolved salts (TDS) can result in fouling of the alumina bed. Presence of sulfate, phosphate or carbonate can result in ionic competition. Disposal of fluoride laden sludge The regeneration is required after every 4-5 months and effectiveness of adsorbent for fluoride removal reduces after each regeneration.
ADVERSE EFFECTS OF ARSENIC
General muscular weakness, loss of appetite, nausea, inflammation of mucous membranes in the eyes, nose and larynx. Skin lesions (often confused with leprosy), gastrointestinal injuries, kidney damage, circulatory collapse, respiratory failure and neurological disorders. Unusual pigmentation. Vascular system damage, gangrene. Skin, lung, bladder, lymph glands, kidney & liver cancers. It builds up in the tissues- skin, hair etc.
ADVERSE EFFECTS OF FLUORIDE
Fluoride conc. (mg/l) < 1.0 1.0 to 3.0 3.0 to 4.0 4.0 to 6.0 and above Effects Safe limit Dental fluorosis (Discoloration, mottling and pitting of teeth) Stiffened and brittle bones and joints Deformities in knee and hip bones and finally paralysis making the person unable to walk or stand in straight posture, Crippling fluorosis
Source:
TREATMENT
TECHNIQUES AVAILABLE FOR FLUORIDE REMOVAL
Nalgonda technique (Coagulation-precipation) Adsorption Ion – exchange Membrane process
FLUOeactive, so never found in free state Permissible limit: 1-1.5 mg/l Excessive concentrations reported in more than 20 countries including India 150 districts of 17 states of India are affected Highly electronegative, therefore strong affinity for calcium Affects teeth and bones Persons affected by skeletal fluorosis in India are ≈ 60 lacs (90% of total affected world population)
VARIOUS STAGES OF DENTAL FLUOROSIS
SKELETAL FLUOROSIS
SKELETAL FLUOROSIS
ARSENIC: AN OVERVIEW
Permissible limit: 10 ppb Well known poison and carcinogen Bangladesh, West Bengal region of India, inner Mangolia region in China, Thailand, Argentina, Ghana, Japan, Chile, Mexico, Hungary, Romania, U.S.A. and Taiwan etc. Upto 3.0 mg/l arsenic has been reported. In 8 districts of West Bengal (India) almost all underground water sources have excess arsenic, so millions of people are suffering from ill effects.
FLUORIDE AND ARSENIC REMOVAL FROM UNDERGROUND WATER FOR POTABLE USE
MEENAKSHI ARORA TERI UNIVERSITY, NEW DELHI INDIA
MINERALOGICAL WATER POLLUTION Fluoride Arsenic Nitrate
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ION EXCHANGE
Lower capacity of removal of fluoride in presence of other ions like NO3 and SO4. Regeneration of resin is a problem. Disposal of waste stream.
Chemical tolerance Mechanical suitability Cleanability Operating pH range Separation performance Cost
Separation Performance
Performance of membrane is determined by the Pore size of the membrane. Pore size of NF membrane: 1-10 nm Pore size of RO membrane: <1.0 nm Particle size of Na+: 0.102 nm Particle size of F- : 0.133 nm Particle size of Ca2+ : 0.10
ARSENIC CHEMISTRY
Arsenic exists primarily in two valence states As (III) H3AsO3 (upto pH 9) H2AsO3-1 (at pH 9-12) HAsO3-2 (at pH 12-14) As (V): Less toxic and easy to be removed H3AsO4 (upto pH 2) H2AsO4-1 (at pH 2-7) HAsO4-2 (at pH 7-11) AsO4-3 (at pH 11-14)
BRINE DISPOSAL
Deep well injection Sea disposal Concentration and substance extraction Fluoride resistant plants Fluoride combines with the calcium to form a very insoluble calcium fluoride complex and is no longer available to plants, thus it can be used for irrigation