<p>Fluoride has been detected in groundwater in many places throughout the world and its concentration is often higher than the WHO standard of 1.5 mg/L. Too much fluoride can cause teeth and skeletal issues in the body and inhibit local economic growth. Fluoride concentration in the local groundwater in the Rajasthan region of India is above 5 mg/L and poses significant health risks to local people. Electrocoagulation and electrodialysis have been used for fluoride removal but information on their application for cost-effective removal of fluoride in groundwater is still limited. The aim of this study was to develop and evaluate cost-effective defluoridation systems to remove fluoride from 5 mg/L to below 1 mg/L in the groundwater. Multiple electrocoagulation reactors were fabricated with an aluminum anode and copper/steel cathode. Fluoride concentrations decreased from 5 mg/L to below 1 mg/L within 2 hours of electrocoagulation under an applied potential of 8 V. Under a lower applied potential of 5 V, fluoride concentration was reduced to below 1 mg/L after 6 hours 30 minutes and further reduced to 0.191 mg/L after 9 hours 30 minutes. Our results showed that higher voltage led to higher removal efficiency at a cost of higher energy consumption. The results showed that aluminum alloy used as the anode released impurities into the water during electrocoagulation and could affect fluoride removal efficiency. In addition, synthesized groundwater with different hardness levels was prepared to simulate water quality in the groundwater in the Rajasthan region of India. The results showed that high hardness inhibited fluoride removal efficiency. An electrodialysis reactor was tested as well on the removal performance of anions, including fluoride and chloride. Fluoride concentration after one hour of electrodialysis did not decrease below 1 mg/L but showed a promising trend for effective fluoride removal. However, cation permeable membrane and anion permeable membrane are relatively expensive and could affect the overall cost-effectiveness of fluoride removal with electrodialysis. These results showed that both electrocoagulation and electrodialysis were effective in removing fluoride from groundwater. Their long-term performance and overall cost-effectiveness need further investigation.  </p>

Fluoride naturally occurs in some ground and surface waters at high concentrations all around the world. Due to increasing health concerns about over-exposure to fluoride in drinking water, the United States Environmental Protection Agency (USEPA) has begun to review fluoride as a drinking water contaminant. Should the USEPA decide to lower the fluoride maximum contaminant limit (MCL), many water systems in addition to those already struggling to meet the fluoride MCL will require defluoridation as part of their drinking water treatment process. Alum coagulation was investigated as a defluoridation treatment strategy in this research project. Surface and blended (ground/surface) drinking water sources with high fluoride concentrations pose a unique challenge to defluoridation by alum coagulation because of the presence of both natural organic matter (NOM) and fluoride. Defluoridation of synthetic and natural waters using jar tests elucidated interactions of fluoride, NOM, and aluminum during alum coagulation. Alum coagulation was able to remove 80% of fluoride from natural waters with a 500 mg/L alum dose; however, 50% fluoride removal was observed to be possible with an alum dose of 150-170 mg/L. The optimum pH for fluoride removal in synthetic and natural waters was observed to be approximately 6.5 and was found to be an important factor in determining the overall performance of alum coagulation. The presence of fluoride during alum coagulation was found to reduce the removal of three low molecular weight (LMW) organics, acting as surrogates for NOM, to different extents depending on their functionality. The presence of LMW organic acids in synthetic waters did not impact the removal of fluoride; however, increasing NOM concentrations in the natural waters likely accounted for decreasing fluoride removals observed in the natural waters. Additional jar tests with natural waters revealed that pH adjustment was unnecessary for defluoridation of high pH and high alkalinity waters and that an enhanced precipitation effect occurred at low alum doses when no pH adjustment was made during alum coagulation. The enhanced precipitation effect caused comparable or enhanced removals of fluoride and NOM to be observed despite system pH values being higher than the optimal defluoridation pH of 6.5. Lower aluminum residuals were also observed as part of the enhanced precipitation effect, suggesting that when precipitation begins under high pH conditions, fluoride interference does not occur and therefore promotes more precipitate formation with greater available surface area for adsorption. However, as precipitation occurs, pH drops, and fluoride increasingly interacts with the aluminum precipitate resulting in greater overall fluoride removals. / text

Excess fluoride (F-) in drinking water poses a health threat to millions of people around the world. In the present work, activated alumina (AA) has been used as an adsorbent. Data obtained from batch experiments were fitted to the (i) pseudo-first order, (ii) pseudo-second order, and (iii) Langmuir kinetic model. Model (ii) performed better than model (i), and fitted the data well. However, the rate constant for adsorption ka had to be varied as a function of the initial concentration of F- in the liquid phase c0. A more satisfactory approach is provided by Langmuir model, which fitted the data reasonably even though ka was independent of c0. Shreyas (2008) developed a model for the batch adsorption of F- onto porous pellets of AA. Some errors were detected in his computer program were corrected. The parameters of the model were estimated by fitting predictions to data. The parameter values suggest that the adsorption process is likely to be diffusion limited. Column experiments were conducted as follows. The pellets were soaked in deionized water for a time ts before they were loaded into columns. A feed solution having a fluoride concentration cf = 3 mg/L was fed to column and the concentration of F- in the exit stream ce was measured at regular intervals. Breakthrough was deemed to have occurred when ce exceeded the permissible limit (= 1 mg/L). Constant values of the bed height H, and the empty bed contact time tc were used in the experiments. The volume of treated water V, scaled by the volume of the bed Vb, varied strongly with the soaking time ts, with a maximum at ts = 24 h. To understand the possible reasons for this behaviour, XRD, FESEM, and FTIR were used to characterize the surface of AA. Though the concentrations of the surface hydroxyl groups may influence the adsorption of F-, FTIR studies show there is no direct correlation between V/Vb and the concentrations of these groups. The FESEM and XRD studies indicate that fresh AA consists mainly of boehmite, which gradually converted to gibbsite during soaking. For fixed values of H and tc, the dimensionless volume of treated water V/Vb was a maximum at D = 45 mm. This behaviour may be caused by wall effects for small values of D and by occurrence of quasi-static regions near the wall for large values of D. The cost of treated of water was Rs. 0.42/L. It decreased slightly to Rs. 0.37/L after one regeneration cycle, but increased to Rs. 0.41/L after two cycles. The volume of treated water after two regeneration cycles was 595 L/kg. The concentration of Al3+ ions ca in the treated water increased and exceeded the permissible limit of 0.2 mg/L as the number of regeneration cycles increased. The concentration of F- in regeneration effluent cre was in the range 32-70 mg/L. The effluent was subjected to solar distillation, leading to a distillate whose fluoride concentration F- was in the range 9-12 mg/L. The distillate can be discharged into the public sewers, as the permissible limit is 15 mg/L.

Groundwater is a major and sometimes lone source of drinking water worldwide. The chemical composition of groundwater is a combined product of the composition of water that enters the aquifer and its reaction with various minerals present in the soil and rock mass, which alter the water composition with time and space. Some important factors influencing groundwater quality are (1) physiochemical characteristics o the rocks through which the water circulates; (2) geology of the location; (3) climate of the area; (4) role of microorganisms, which includes oxidative and reductive biodegradation of organic matter; (5)chemical, physical, and mineralogical characteristics of the overburden soils through which the rainwater percolates; and (6) human intrusion affecting the hydrological cycle and degradation in water quality through utilization of water for agricultural and industrial activities. By far the most serious naturally occurring groundwater-quality problem in India derives from high fluoride, arsenic and iron concentrations which are dissolved from the bedrocks by geochemical processes. Presence of excess fluoride in groundwater is identified as a naturally occurring health hazard by the World Health Organization (WHO). Prolonged ingestion of fluoride beyond certain permissible limit leads to ffluorosis, one of the common water-related diseases recognized by the WHO and the United Nations Children's Fund (UNICEF). Endemic fluorosis is now known to be global in scope, occurring on all continents and affecting many millions of people. According to estimates made in the early 1980s, around 260 million people in 30 countries worldwide were drinking water with more than 1 ppm of fluoride. The ultimate source of fluoride in water, soil or biosphere is associated with its distribution in rocks and its dispersion in groundwater. The three most important minerals of fluoride are fluorite (CaF2), cryolite (Na3AlF6) and fluorapatite (Ca5(PO4)3F); cryolite is a rare mineral where as by far the largest amount of fluorine in the earth's crust is in the form of fluorapatite (about 3.5% by weight of fluorine) which is processed almost exclusively for its phosphate content. Fluoride substitutes readily in hydroxyl positions in late-formed minerals in igneous rocks, and in primary minerals especially micas (such as biotites) and amphiboles (such as hornblende). The most important controlling factors influencing fluoride presence in groundwater include: distribution of easily weathered fluoride-bearing minerals, the accessibility of circulating water to these minerals, pH of the percolating water, calcium content of the leaching water, temperature of the percolating water and the soil, exchangeable ions in the percolating water, extent of fresh water exchange in an aquifer, evaporation and evapotranspiration, complexing of fluoride ions with other ions, presence of CO2 and other chemicals in draining water and residence time of the percolating water in soil. High fluoride levels are observed in the groundwater in 19 states of the country. Fluorite, apatite, rock phosphate, phosphorites, phosphatic nodules and topaz are major fluoride bearing minerals in India with varying levels of fluoride content. There are three major fluoride bearing areas in India :1) Gujarat-Rajasthan in the north-west and 2) Chandidongri-Raipur in central India 3) Tamil Nadu-Andhra Pradesh in the south; besides other areas in Karnataka, Bihar, Punjab and in the North-west Himalayas. The total mineral reserves of fluorite, rock phosphate and apatite in the country are estimated at 11.6, 71 and 2.82 million tonnes respectively. The distribution of areas with excess fluoride in groundwater concurs with that of fluorine-bearing minerals. Further high fluoride concentrations are observed from arid and semi arid regions of the country and the areas with advanced stage of groundwater development. An estimated 62 million people, including 6 million children suffer from fluorosis in India because of consuming fluoride-contaminated water. Endemic fluorosis is found to practically exist only in the villages due to lack of piped water supply. The Indian Drinking Water Standard specifies the desirable and permissible limits for fluoride in drinking water as 1.0 and 1.5ppm respectively. De-fluoridation of groundwater is the only alternative to prevent fluorosis in the absence of alternate water source especially for immediate and/or interim relief. De-fluoridation of drinking water in India is usually achieved by the Nalgonda technique or activated alumina process. The Nalgonda method involves addition of aluminum salts (aluminium sulphate and/or aluminium chloride), lime and bleaching powder to water, followed by rapid mixing, flocculation, sedimentation, filtration and disinfection. Only aluminum salt is responsible for removal of fluoride from water .Fluoride removal is achieved in a combination of complexation with polyhydroxy aluminium species and adsorption on polymeric alumino hydroxides (floc). Activated alumina(Al2O3) was proposed for de-fluoridation of water for domestic use in 1930’s and since then it has become one of the most advocated de-fluoridation methods. Activated alumina is a semi crystalline porous inorganic adsorbent and an excellent medium for fluoride removal. When the source water passes through the packed column of activated alumina, fluoride (and other components in the water) is removed via exchange reaction with surface hydroxides on alumina; this mechanism is generally called adsorption although ligand exchange is a more appropriate term for the highly specific surface reactions involved. The fluoride removal capacity of alumina is highly sensitive to pH, the optimum being about pH5.5-6. Significant reduction in fluoride removal by activated alumina is also observed in presence of sulfate and silicate ions. The column needs periodic regeneration once break point(where the effluent concentration is, for example, 2ppm at normal saturation) is reached. For regeneration, the medium is backwashed for 5-10 min and then subjected to two step regeneration with base (NaOH) followed by acid(H2SO4). A major cause for concern with the Nalgonda method is the possibility of formation of residual aluminum and soluble aluminum fluoride complexes in the treated water and a potential breach of the 0.2ppm Indian drinking water standard for aluminium. Concerns with the activated alumina filter method are that the process is pH dependent, with an optimum (pH) working range of 5-6. Further, the activated alumina column requires periodic recharge using caustic soda and acid solutions to rejuvenate the fluoride retention capacity of the column. After 3-4 regenerations the medium has to be replaced. If the pH is not readjusted to normal following the regeneration process, there is a possibility that the aluminum concentration in the treated water may exceed the 0.2ppm standard. Due to the aforementioned drawbacks of the currentde-fluoridation technologies in India that chiefly rely on aluminum based compounds, magnesia(magnesium oxide, MgO) is selected to develop an alternate sustainable de-fluoridation method. The potential of MgO for de-fluoridation has been examined owing to its very limited solubility(6.2mg/L), non-toxicity and excellent fluoride retention capacity. A review of the previous studies on fluoride removal using MgO reveals that the relevant information is essentially scattered. Though studies demonstrated the fluoride removing ability of MgO and brought into focus certain aspects of the fluoride removal mechanism and change in water quality upon MgO addition, vital issues necessary for efficient design and successful field implementation of the de-fluoridation processusing MgO were not addressed. The significant limitations in the earlier works include: influence of process variables(such as MgO dosage, initial fluoride concentration, contact time, temperature, initial solution pH, presence of co-ions and ionic strength) on fluoride retention characteristics (such as removal rate, equilibrium time, capacity) of MgO were not systematically determined, optimum operating parameters/conditions (such as MgO dosage, stirring and settling time) for effective de-fluoridation process applicable to a wide range of groundwater chemical composition and fluoride concentrations were not defined, mechanism of fluoride retention by MgO was not fully understood, issue of lowering the pH of MgO treated water within potable water limits was not comprehensively addressed, safe disposal methods of fluoride bearing sludge were not explored. Failure to address the above issues has impeded the adoption of the MgO treatment method for fluoride removal from water. Scope of the study Present study aims to develop a new sustainable de-fluoridation method, applicable to a wide range of groundwater chemical compositions and fluoride concentrations, based on co-precipitation/precipitation-sedimentation-filtration processes using light MgO. Efforts are made to implement the method at domestic level in a rural area with incidence of high fluoride concentration in groundwater and to understand the status and geochemistry of fluoride contamination in the area. The main objectives of the study include: To determine the fluoride retention characteristics of MgO viz.,rate, equilibrium time and capacity of fluoride retention. To examine the influence of process variables on fluoride retention characteristics of MgO and to determine the optimum operating parameters for effective de-fluoridation process. To understand the mechanism and rate limiting step of MgO de-fluoridation process. To propose methods and specifications to lower the pH of MgO treated water within permissible limits to ensure its potability. To design a simple to use, single-stage domestic de-fluoridation unit. To propose procedures for implementation of the new de-fluoridation method in field. To evaluate the efficiency of the new de-fluoridation method as a useful remedial measure in the fluoride affected areas. To understand the geochemical factors governing the quality of the fluoride rich groundwater and to ascertain the status and geochemistry of fluoride contamination in the area where felid implementation of de-fluoridation method is planned. To characterize the fluoride bearing sludge and propose methods for safe disposal and reuse of fluoride bearing sludge. Organization of the thesis Chapter1 presents an overview of the various aspects of excess fluoride presence in groundwater, remedial measures, and emphasizes the need for a new sustainable de-fluoridation method and defines the scope of present study. Chapter 2 performs a detailed investigation to determine the fluoride retention characteristics of MgO under the influence of various process variables at transient and equilibrium conditions using batch studies. The process variables that have been considered are, contact time, initial fluoride concentration, dosage of MgO, temperature, initial pH, presence of co-ions and ionic strength. Studies to determine the optimum operating parameters for efficient de-fluoridation and to understand some basics of reaction mechanisms involved are also part of this chapter. Chapter 3 examines the true nature of the reaction mechanism between fluoride ions and MgO in aqueous media and the rate-limiting step of the de-fluoridation process by investigating the hydration process of MgO and its influence/relation on fluoride removal. Chapter 4 addresses issues that will assist applying the MgO treatment method for fluoride removal in field such as 1)methods and specifications for lowering the pH of the MgO treated water within permissible limits, 2)design of a simple to use, single-stage de-fluoridation unit, and 3)characterization of the resultant fluoride bearing sludge. Chapter 5 performs a detailed investigation to evaluate the efficiency of the new de-fluoridation method in laboratory and field, and to understand the origin and the geochemicall mechanisms driving the groundwater fluorine enrichment in the area where field implementation of the de-fluoridation unit was planned. Chapter 6 explores an environmentally safe route for the disposal and re-use of fluoride bearing sludge in soil based building materials such as, stabilized soil blocks (produced by cement stabilization of densely compacted soil mass) which are alternative to burnt bricks. Chapter 7 summarizes the major results, observations and contributions from the study.

No description available.

Made available in DSpace on 2015-04-01T12:09:00Z (GMT). No. of bitstreams: 1 parte1.pdf: 5912827 bytes, checksum: 8aa051b3bbcd467b255123e71e4dea47 (MD5) Previous issue date: 2012-02-15 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This research was undertaken to evaluate, implement and compare the effectiveness of two water defluoridation systems in two locations with endemic fluorosis problem in the countryside of São João do Rio do Peixe, Paraiba. The systems investigated were the Water Treatment Resort (ETA) and Defluoridation Regenerable Filter (DRF). The study was divided into two parts, namely: Part I (risk assessment: mapping of residual levels of fluoride in groundwater and perception of dental fluorosis) and Part II (reduction of injuries: defluoridation systems). The sample consisted of 59 individuals of both sexes and different age groups, being 29 for the study of ETA (artesian well with 5.3 mg/L fluoride) and 30 for the FDR (artesian well with 2.6 mg/L fluoride). To investigate the estimation of fluoride intake were collecting water, other liquids, by food duplicate plate methodology. For children the estimated intakes of fluoride dentifrice was performed with a simulated toothbrushing. The excretion values of fluoride were estimated by collecting 24-hour urine. All samples were stored under refrigeration and analyzed for fluoride ion-selective electrode through direct and indirect method for diffusion hexamethyldisiloxane as appropriate. Evaluations were performed at two different times D1 (baseline) and D2 (1 to 2 months after defluoridation) for both defluoridation models (ETA and DRF). It was observed that the total fluoride intake and excretion decreased after installation of the two defluoridation models, both communitarian model (ETA) as the domiciliary model (FDR), thus indicating the effectiveness of these models to control optimal levels of fluoride in drinking water. The map of fluoride concentration in water from artesian wells in rural areas of São João do Rio do Peixe PB, confirmed the risk of dental fluorosis in that municipality. 63.9% of samples analyzed had [F] above the ideal value of 0.7 mg / L and 35% had values above 1.5 mg / L. It was estimated that about 2,465 people are at risk of developing dental fluorosis and 1,057 individuals can be affected by skeletal fluorosis. The water component of the diet was the largest contributor to total daily fluoride ingestion (50%) in two locations. It was observed that there was significant reduction in total fluoride intake in the group of children between periods D1-ETA (0.10 mg F / kg / day) for D2-ETA (0.04 mg F / kg / day) and D1-F (0.07 mg F / kg / day) for D2-F (0.03 mg F / kg / day) as well as for adult groups of ETA and the DRF. The period of regeneration in the ETA system was superior to DRF suggesting the application of the ETA system in locations with high concentrations of fluoride where FDR would not be effective (> 3.0 mg / L). It is concluded that the two defluoridation models were effective in reducing the intake of fluoride and therefore reducing the risk of dental fluorosis. Although both systems are effective in reducing the bioavailability of fluoride among users, only communitarian defluoridation system (ETA) has proved suitable for locations with high concentrations of fluoride at risk for skeletal fluorosis. / O presente estudo objetivou implantar, avaliar e comparar a eficácia de dois sistemas de desfluoretação de águas em duas localidades com problema de fluorose endêmica na zona rural de São João do Rio do Peixe, Paraíba. Os sistemas investigados foram Estação de Tratamento de Águas (ETA) e Filtro Desfluoretador Regenerável (FDR). O estudo foi dividido em duas partes, quais sejam: Parte I (avaliação de riscos: mapeamento dos teores residuais de flúor nas águas subterrâneas e percepção de fluorose dentária) e Parte II (redução de agravos: sistemas de desfluoretação). A amostra consistiu de 59 indivíduos de ambos os sexos e variadas faixas etárias; sendo 29 para o estudo da ETA (poço com 5,3 mg/L de flúor) e 30 para o do FDR (poço com 2,6 mg/L de flúor). Para investigar a estimativa de ingestão de flúor foi realizada a coleta de água, outros líquidos, alimentos pela metodologia do prato duplicado. Para crianças a estimativa de ingestão de flúor por dentifrício foi realizada com escovação simulada. Os valores de excreção de flúor foram estimados por coleta de urina de 24 horas. Todas as amostras coletadas foram armazenadas sob refrigeração e analisadas por eletrodo específico para flúor através de método direto e indireto por difusão com hexametildisiloxano quando apropriado. As avaliações foram realizadas em dois momentos distintos D1 (baseline) e D2 (1 a 2 meses após a desfluoretação), para ambos os modelos de desfluoretação (-ETA e -F). Observou-se que a ingestão total de flúor bem como sua excreção diminuiu após a instalação dos dois modelos de desfluoretação, tanto o de base comunitária (ETA) como o de base domiciliar (FDR), indicando assim a eficácia desses modelos quanto ao controle de níveis ideais de flúor na água destinada ao consumo humano. O mapeamento da concentração de flúor na água proveniente dos poços artesianos da zona rural de São João do Rio do Peixe PB confirmou o risco de fluorose dentária naquele município. Das amostras analisadas, 63,9% apresentaram [F] acima do valor ideal de 0,7 mg/L e 35% apresentaram valores acima de 1,5 mg/L. Estimou-se que cerca de 2.465 pessoas tem o risco de desenvolver fluorose dentária e 1.057 indivíduos podem ser portadores de fluorose óssea. A água foi o componente da dieta que mais contribuiu para a ingestão diária total de fluoreto (50%) nas duas localidades. Houve redução significativa na ingestão total de flúor no grupo de crianças entre os períodos de D1-ETA (0,10 mgF/kg/dia) para D2-ETA (0,04 mgF/kg/dia); e D1-F (0,07 mgF/kg/dia) para D2-F (0,03 mgF/kg/dia), bem como para os grupos de adultos da ETA e do FDR. O período de regeneração na ETA foi superior ao do sistema FDR sugerindo a aplicação do sistema ETA em localidades com elevadas concentrações de flúor onde o FDR não seria eficaz (>3,0 mg/L). Conclui-se que os dois modelos de desfluoretação foram eficazes em reduzir a ingestão de flúor e, por conseguinte reduzir o risco de fluorose dentária. Apesar de ambos os sistemas serem eficientes em reduzir a biodisponibilidade de flúor entre os usuários, apenas o sistema de base comunitária (ETA) se mostrou indicado para localidades com elevadas concentrações de flúor com risco de fluorose óssea.

MENVSC / Department of Hydrology and Water Resources / See the attached abstract below

Excess Fluoride in drinking water is a cause for concern in several countries in the world. Various techniques have been developed to mitigate the harmful effects of fluoride. In the present work, a combined alum and activated alumina (AA) process has been investigated. Tap water with sodium fluoride dissolved in it to produce a solution having a fluoride concentration of 5 mg/L was used as the feed. It was found that pretreatment with alum extends the time required for the regeneration of the AA column. The volume of water treated increased by 89% compared to AA process alone. Though the regeneration of the AA column has been well documented, subtle issues have ot been reported. The disposal of regeneration effluent is a concern in adsorption-based processes. This study aims to examine some of the issues involved in the regeneration of the AA column such as disposal of effluent, and the quantity of acid and alkali required. The regeneration effluent from the combined process, which had a fluoride concentration of 10-16 mg/L was treated in a solar still. The distillate from the still had a fluoride concentration of 2-3 mg/L, which is much lower than the concentration of the regeneration effluent. The cost of treatment decreased with each regeneration cycle and after four regenerations the cost was Rs 0.5/L of treated water. The volume of water treated after four regenerations was 307 L/Kg of AA. Studies were also done using field water from Banavara, Hassan district, Karnataka, which had a fluoride concentration of 3,0-3.5 mg/L. The combined process successfully produced treated water having an acceptable fluoride concentration. After one regeneration cycle, the operating cost was Rs. 1/L of treated water. Studies have also been conducted on a point-of-use water filter containing a bed of AA pellets. The filter was provided by an organization called TIDE. The present results appear to suggest that a column with a smaller diameter than the TIDE filter has a better removal capacity. Ceramic candles are widely used for water filtration as they are readily available and inexpensive. Hence they are suitable for household water treatment purposes. In the present work, ceramic candles have been impregnated with nano-size alumina and nano-size magnesium oxide and tested for their defluoridation capacity. The nanoparticles were generated in situ in the pores of the candle by solution combustion synthesis. It has been found the candle impregnated with nano-size magnesium oxide has a higher defluoridation capacity than nano-size alumina. Estimation of the particle size in the samples of treated water did not give conclusive evidence for the presence or absence of nanoparticles. The volume of water treated was low and the cost of treatment was high (Rs. 12/L for the candle impregnated with MgO). Hence such candles are unsuitable for defluoridation. Batch adsorption has been employed to measure the adsorption capacity of adsorbents. A model to capture the overall picture of the batch adsorption process, obtaining the kinetic and transport parameters involved has been developed. The mathematical model takes into account external mass transfer resistance, intraparticle diffusion, adsorption, and desorption. The equilibrium adsorption data was fitted using the Langmuir isotherm. The governing equations were solved using a finite difference technique known as the Laasonen method. The parameters were estimated by fitting two sets of data using a MATLAB function. The values estimated suggest that the adsorption process may not be diffusion-limited, in contrast to the assumption commonly used in the literature. The estimated parameter values were used to predict the concentration profiles for the other data sets. It was found that predicted and measured profiles agreed reasonably well.

MENVM / Department of Ecology and Resource Management / See the attached abstract below

Fluoride in drinking water can lead to a crippling disease called fluorosis. As there is no cure for fluorosis, prevention is the only means of controlling the disease and research into fluoride remediation is critical. This work begins by providing a new approach to assessing fluoride remediation strategies using a combination of groundwater chemistry, saturation indices, and multivariate statistics based on the results of a large groundwater survey performed in a fluoride-contaminated region of India. From the Indian groundwater study, it was noted that one technique recommended for defluoridation involved using hydrous ferric oxide (HFO) as a solid phase sorbent for fluoride. This prompted investigation of bacteriogenic iron oxides (BIOS), a biogenic form of HFO, as a means of approaching bioremediation of fluoride. Batch sorption experiments at ionic strengths ranging from 0.001 to 0.1 M KNO3 and time course kinetic studies with BIOS and synthetic HFO were conducted to ascertain total sorption capacities (ST), sorption constants (Ks), and orders of reaction (n), as well as forward (kf) and reverse (kr) rate constants. Microcosm titration experiments were also conducted with BIOS and HFO in natural spring water from a groundwater discharge zone to evaluate fluoride sorption under field conditions. This thesis contributes significant, new information regarding the interaction between fluoride and BIOS, advancing knowledge of fluoride remediation and covering new ground in the uncharted field of fluoride bioremediation.