Mitigation and Remedy of Groundwater Arsenic Menace in India

More documents

Recommendations

Info

Mitigation and Remedy of Groundwater Arsenic Menace in India : A Vision Documentsingle pass (NSF, 2001a; NSF 2001b). As an added benefit, RO also effectively removesseveral other constituents from water including organic carbon, salts, dissolved minerals andcolor. The treatment process is relatively insensitive to pH. In order to drive water across themembrane surface against natural osmotic pressure, feed water must be sufficiently pressurizedwith a booster pump. For drinking water treatment, typical operating pressures are between 100and 350 psi. Water recovery is typically 60-80%, depending on the desired purity of the treatedwater.Most RO modules are designed for cross-flow filtration, which allows water topermeate the membrane while the retentate flow sweeps rejected salts away from themembrane surface. In many cases, pre-filtration (commonly through sand or granular activatedcarbon) is worthwhile. This minimizes the loading of salt precipitates and suspended solids on themembrane surface, thereby extending run length, improving system hydraulics and reducingO&M requirements.Some membranes, particularly those composed of polyamides, are sensitive to chlorine.In such cases, feed water should be dechlorinated. Another potential concern associated withRO treatment is the removal of alkalinity from water, which in turn could affect corrosioncontrol within the distribution system. If feasible, this problem can usually be avoided byconducting side-stream treatment for arsenic removal. Residual can be discharged either to atreatment plant or on-site sewerage system.MRT-1000 and Reid System Ltd.: M/s Jago Corporation Limited promoted a householdreverse osmosis water dispenser MRT-1000 manufactured by B & T Science Co. Limited,Taiwan. This system was tested at BUET and showed As (III) removal efficiency more than80%. A wider spectrum reverse osmosis system developed by M/s Reid System Limited wasalso promoted in Bangladesh. Experimental results showed that the system could effectivelyreduce arsenic content along with other impurities in water. However, the capital andoperational costs of the reverse osmosis system are relatively high.Reverse Osmosis and Low-pressure Nanofiltration: Oh et al. (2000) applied reverseosmosis and nanofiltration membrane processes for the treatment of arsenic contaminatedwater applying low pressure by bicycle pump. A nanofiltration membrane process coupled witha bicycle pump could be operated under condition of low recovery and low pressure range from0.2 to 0.7 MPa. Arsenite was found to have lower rejection than arsenate in ionized forms andhence water containing higher arsenite requires pre-oxidation for reduction of total arsenicacceptable level. In tube well water in Bangladesh the average ratio of arsenite to total arsenicwas found to be 0.25. However, the reverse osmosis process coupled with a bicycle pumpsystem operating at 4 Mpa can be used for arsenic removal because of its high arseniterejection. The study concluded that low-pressure nanofiltration with pre-oxidation or reverseosmosis with a bicycle pump device could be used for the treatment of arsenic contaminatedground water in rural areas (Oh et al., 2000; Rahman and Rahaman, 2000).NIH & CGWB 93
Technological Options and Arsenic Removal Technologies5.3 Innovative TechnologiesInnovative technologies, such as permeable reactive barriers, phytoremediation,biological treatment and electrokinetic treatment, are also being used to treat arsenic-contaminatedwater, waste water and soil. However, only a few applications of these technologies at fullscale are available in the literature and additional treatment data are needed to determine theirapplicability and effectiveness in field condition. These technologies may be developed at fullscale to treat arsenic contaminated aquifers. A brief description of these technologies is givenbelow.5.3.1 Permeable Reactive Barriers (PRBs)PRBs are walls containing reactive media that are installed across the path of acontaminated groundwater plume to intercept the plume. The barrier allows water to pass throughwhile the media remove the contaminants by precipitation, degradation, adsorption or ionexchange. PRBs are used to treat groundwater in-situ. This technology tends to have loweroperation and maintenance costs than ex-situ (pump and treat) technologies, and typicallyrequires a treatment time of many years.PRBs are applicable to the treatment of both organic and inorganic contaminants. Theformer usually are broken down into carbon dioxide and water, while the latter are converted tospecies that are less toxic or less mobile. The most frequent application of PRBs is the in-situtreatment of groundwater contaminated with chlorinated solvents. A number of different treatmentmedia have been used, the most common being zero valent iron (ZVI). Other media includehydrated lime, slag from steel making processes that use a basic oxygen furnace, calciumoxides, chelators (ligands selected for their specificity for a given metal), iron oxides, sorbents,substitution agents (e.g., ion exchange resins) and microbes (EPA, 1998; Smyth et al., 2000).PRBs are being used to treat arsenic in groundwater at full scale at only few sites.Although many materials for the reactive portion of the barrier have been tested at bench scale,only zero valent iron and limestone have been used at full scale. The installation techniques forPRBs are established for depths less than 30 feet, and require innovative installation techniquesfor deeper installations. The following chemicals and reactive media are used in PRBs to treatarsenic:• Zero valent iron (ZVI),• Limestone,• Basic oxygen furnace slag,• Surfactant modified zeolite, and• Ion exchange resin.As groundwater reacts with ZVI, pH increases Eh decreases and the concentration ofdissolved hydrogen increases. These basic chemical changes promote a variety of processes94NIH & CGWB
Page 5:
ACKNOWLEDGEMENTThe Government of In
Page 8 and 9:
nearly 33 villages in 4 districts i
Page 10:
(iii) Whether ex-situ removal techn
Page 14 and 15:
6.4 Experiences during Arsenic Remo
Page 16 and 17:
List of FiguresFigure no. Figure ca
Page 18 and 19:
List of TablesTable no. Table Capti
Page 20 and 21:
Mitigation and Remedy of Groundwate
Page 22 and 23:
Page 24 and 25:
Page 26 and 27:
Page 28 and 29:
Page 30 and 31:
Page 32 and 33:
Page 34 and 35:
Page 36 and 37:
Page 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 44 and 45:
Page 46 and 47:
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Page 60 and 61:
Page 62 and 63: Mitigation and Remedy of Groundwate
Page 102 and 103: 5.2.2 Co-precipitationMitigation an
Page 124 and 125: 5.8 SummaryMitigation and Remedy of
Page 162 and 163:
Page 164 and 165:
Page 166 and 167:
Page 168 and 169:
Page 170 and 171:
Page 172 and 173:
Page 174 and 175:
Page 176 and 177:
Page 178 and 179:
Page 180 and 181:
Page 182 and 183:
Page 184 and 185:
Page 186 and 187:
Page 188 and 189:
Page 190 and 191:
Page 192 and 193:
Page 194 and 195:
Page 196 and 197:
Page 198 and 199:
Page 200 and 201:
Page 202 and 203:
show all

Mitigation and Remedy of Groundwater Arsenic Menace in India

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?