title: Arsenic and iron removal from groundwater by oxidation-coagulation at optimized pH: laboratory and field studies.
abstract: A three-step treatment process involving (i) mild alkaline pH-conditioning by NaHCO₃; (ii) oxidation of arsenite and ferrous ions by KMnO₄, itself precipitating as insoluble MnO₂ under the pH condition; and (iii) coagulation by FeCl₃ has been used for simultaneous removal of arsenic and iron ions from water. The treated water is filtered after a residence time of 1-2 h. Laboratory batch experiments were performed to optimize the doses. A field trial was performed with an optimized recipe at 30 households and 5 schools at some highly arsenic affected villages in Assam, India. Simultaneous removals of arsenic from initial 0.1-0.5 mg/L to about 5 μg/L and iron from initial 0.3-5.0 mg/L to less than 0.1 mg/L have been achieved along with final pH between 7.0 and 7.5 after residence time of 1h. The process also removes other heavy elements, if present, without leaving any additional toxic residue. The small quantity of solid sludge containing mainly ferrihydrite with adsorbed arsenate passes the toxicity characteristic leaching procedure (TCLP) test. The estimated recurring cost is approximately USD 0.16 per/m(3) of purified water. A high efficiency, an extremely low cost, safety, non-requirement of power and simplicity of operation make the technique potential for rural application.
authors.affiliation: Department of Chemical Sciences, Tezpur University, Napaam, Tezpur 784028, Assam, India.
authors.forename: Shreemoyee
authors.initials: S
authors.lastname: Bordoloi
authors.forename: Suresh K
authors.initials: SK
authors.lastname: Nath
authors.forename: Sweety
authors.initials: S
authors.lastname: Gogoi
authors.forename: Robin K
authors.initials: RK
authors.lastname: Dutta
mesh_terms: D001151:Arsenic / Q000032:analysis* / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D005290:Ferric Compounds / Q000737:chemistry; D060587:Groundwater / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007194:India; D007477:Ions; D007501:Iron / Q000032:analysis* / Q000737:chemistry; D017895:Manganese Compounds / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D016877:Oxidants / Q000737:chemistry; D010087:Oxides / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*; D011196:Potassium Permanganate; D015203:Reproducibility of Results; D012722:Sewage; D017550:Spectroscopy, Fourier Transform Infrared; D014865:Waste Disposal, Fluid / Q000379:methods; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry; D018508:Water Purification / Q000379:methods*; D014961:X-Ray Diffraction
chemical_list: D002712:Chlorides; D005290:Ferric Compounds; D007477:Ions; D017895:Manganese Compounds; D016877:Oxidants; D010087:Oxides; D012722:Sewage; D014874:Water Pollutants, Chemical; D011196:Potassium Permanganate; D014867:Water; C027424:manganese oxide; D007501:Iron; D001151:Arsenic; D010100:Oxygen; C024555:ferric chloride
keywords: Arsenic removal; Ferric chloride; Oxidation–coagulation; Potassium permanganate; Sodium bicarbonate