Groundwater Defluoridation with Raw Bauxite,Gypsum, Magnesite,and Their Composites

Breakthrough characteristics, kinetics, and dose‐effect in defluoridation with bauxite, gypsum, magnesite, and their composites were determined. The aim was to identify optimum filter and configuration viable for groundwater defluoridation. Bed depth service time (BDST) design model and empty bed residence time (EBRT) optimization model were employed to characterize breakthrough. Higher doses obtained lower loading capacities but higher sorption percentages and breakthrough times. Breakthrough times obtained were 50 400, 32 400, 25 200, and 19 800 s for 150, 120, 75, and 45 g, respectively. The equation ? = 1.0 × 10^?4 δ² ?0.022 δ + 1.5053 defined the operating line with ?, adsorbent exhaustion rate, in g L^?1 and δ, EBRT, in seconds. A critical bed depth (Z_o) of 6.56 cm was obtained. Second order kinetic rate constants were 0.73, 1.17, and 1.81 g mg^?1 s^?1 for magnesite, gypsum, and bauxite, respectively. The composite, gypsum and bauxite decreased water pH but magnesite increased pH in water defluoridation. Experimental data did not fit the two‐parameter logistics model; model values were significantly different from experimental values. Optimum defluoridation characteristics were obtained in fixed bed. Despite high residual sulphates and apparent color, fixed‐bed defluoridation with raw composites of these materials, treated in this manner, is viable.     

Electrodialytic Defluoridation of Brackish Water: Effect of Process Parameters and Water Characteristics

The aim of this work is to study the removal of fluoride from brackish polluted water using electrodialysis. The influence of several parameters such as flow rate, initial feed concentration, co‐existing ions, and initial pH on process efficiency were studied. This efficiency is evaluated by the removal rate, demineralization rate, and power consumption. The defluoridation process showed to be independent of pH of feed solution. Although the remained studied parameters plays a significant role on the defluoridation efficiency and mainly on the specific power consumption. The defluoridation of a contaminated real water sample was investigated so as to improve the efficiency of the process. The fluoride concentration could be reduced from 2.9 to 0.4 mg L⁻¹ which was lower than World Health Organization (WHO) standard (1.5 mg L⁻¹). Moreover the concentrations of different species in the obtained treated water are below the amounts recommended by WHO for drinking water.     

A Study of the Thermodynamics and Kinetics of Copper Adsorption Using Chemically Modified Rice Husk

The use of rice husk as a low cost adsorbent for the removal of copper from wastewater has been explored in a laboratory scale experiment. The rice husk used for the study was treated with alkali to increase the sorption properties. The influence of metal ion concentration, weight of biosorbent, stirring rates, temperature and pH were also evaluated, and the results are fitted using adsorption isotherm models. From the experimental results it was observed that almost 90–98% of the copper could be removed using treated rice husk. The Langmuir adsorption isotherm, Freundlich isotherm and Tempkin isotherm models were used to describe the distribution of copper between the liquid and solid phases in batch studies, and it was observed that the Langmuir isotherm better represented the adsorption phenomenon. The experimental rate constant, activation energy, Gibbs free energy, enthalpy and entropy of the reaction were calculated in order to determine the mechanism of the sorption process.     

The Impact of Geology of Recharge Areas on Groundwater Quality: A Case Study of Zhob River Basin,Pakistan

Groundwater is a major source of water supply for domestic and irrigation uses in semiarid, remote but rapidly developing Kilasaifullah district part of Zhob River Basin, located at Pakistan–Afghanistan Border. Zhob River is among few major rivers of perennial nature in Balochistan, which flows from WSW to ENE and falls in Gomal River, a tributary of Indus River. Keeping in view the important geopolitical position and rapid development of the region, this study is primarily focused on groundwater chemistry for contamination sources as well as agriculture development. Water samples from open and tube wells are analyzed and calculated for electrical conductivity (EC), total dissolved solids (TDS), turbidity, pH, K⁺, Na⁺, Ca²⁺, Mg²⁺, HCO, Cl^?, NO, SO, PO, sodium percent (Na%), sodium adsorption ratio (SAR), Kelly's index (KI), and heavy metals (Fe, Cu, Cr, Zn, Pb, and Mn). On the basis of the chemical constituents two zones within the study area are identified and possible causes of the contaminants are pointed out. Two recharge areas were responsible for the different chemical results in groundwater, e.g., zone A was recharged from NNW saline geological formations (Nisai, Khojak, Multana, Bostan formations, and Muslim Bagh ophiolites), which are concentrated with high sodium and chloride. On the other hand Zone B was sourced from SSW from carbonate rich rocks (Alozai, Loralai, Parh formations, and Muslim Bagh ophiolites). The groundwater is classified as C2–S1, C3–S1, C3–S2, C4–S2 on the basis of EC and SAR values which indicate that most of the water of both zones can be used for irrigation safely except the samples plotted in C3–S2 and C4–S2 categories which could be dangerous for soil and crops. Groundwater samples are plotted in good to permissible limits with some samples excellent to good and few samples belong to doubtful category based on sodium percent. Groundwater of zone A is unsuitable for irrigation use due to higher values of KI (more than one) but water of zone B are good for irrigation based on KI. In general, water of both zones is suitable for irrigation but care should be taken during the selection of crops which are sensitive to alkalinity or sodium hazards particularly in zone A.     

Removal of Bromate from Water Using De‐Acidite FF‐IP Resin and Determination by Ultra‐Performance Liquid Chromatography‐Tandem Mass Spectrometry

Contamination of water due to bromate is a severe health hazard. The aim of the present study was to remove bromate from water using a crosslinked polystyrene based strongly basic anion exchange resin De‐Acidite FF‐IP. Batch experiments were performed to study the influence of various experimental parameters such as effect of pH, contact time, temperature, and effect of competing anions on bromate removal by De‐Acidite FF‐IP resin. At optimum parameters, the removal rate of bromate was very fast and 90% removal took place in 5 min and equilibrium was established within 10 min. The presence of competitive anions reduced the bromate adsorption in the order of Cl^? > F^? > CO > SO > NO > PO. The practical utility of this resin has been demonstrated by removing bromate in some of the commercial bottled water from Saudi Arabia. The level of bromate was determined using a very sensitive, precise and rapid method based on ultra‐performance liquid chromatography‐tendem mass spectrometry (UPLC‐MS/MS).     

Removal of Arsenic from Simulated Groundwater Using GAC‐Ca in Batch Reactor: Kinetics and Equilibrium Studies

This paper deals with kinetics and equilibrium studies on the adsorption of arsenic species from simulated groundwater containing arsenic (As(III)/As(V), 1:1), Fe, and Mn in concentrations of 0.188, 2.8, and 0.6 mg/L, respectively, by Ca²⁺ impregnated granular activated charcoal (GAC‐Ca). Effects of agitation period and initial arsenic concentration on the removal of arsenic species have also been described. Although, most of the arsenic species are adsorbed within 10 h of agitation, equilibrium reaches after ～24 h. Amongst various kinetic models investigated, the pseudo second order model is more adequate to explain the adsorption kinetics and film diffusion is found to be the rate controlling step for the adsorption of arsenic species on GAC‐Ca. Freundlich isotherm is adequate to explain the adsorption equilibrium. However, empirical polynomial isotherm gives more accurate prediction on equilibrium specific uptakes of arsenic species. Maximum specific uptake (q_max) for the adsorption of As(T) as obtained from Langmuir isotherm is 135 µg/g.     

Adsorption of Zinc using Tea Factory Waste: Kinetics,Equilibrium and Thermodynamics

In India, the annual production of tea is ca. 857,000 tonnes, which is 27.4% of the total world production. The amount of tea factory waste (TFW) produced per annum after processing is ca. 190,400 tonnes. TFW can be used as a low cost adsorbent for the removal of toxic metals from the aqueous phase. An investigation was carried out to study the feasibility of the use of TFW as an adsorbent for the removal of the heavy metal, zinc. Equilibrium, kinetic and thermodynamic studies were reported. The straight line plot of log (q_e–q) versus time t for the adsorption of zinc shows the validity of the Lagergren equation. The various steps involved in adsorbate transport from the solution to the surface of the adsorbent particles were dealt with by using a Weber‐Morris plot, q_e versus t^0.5 for the TFW. The rate controlling parameters, k_id,1 and k_id,2, were determined and it was found that the macro‐pore diffusion rate was much larger than micro‐pore diffusion rate. A batch sorption model, which assumes the pseudo‐second‐order mechanism, was used to predict the rate constant of sorption, the equilibrium sorption capacity and the initial sorption rate with the effect of initial zinc (II) ion concentration. Equilibrium data obtained from the experiments were analyzed with various isotherms, i. e., Freundlich, Langmuir, Redlich‐Peterson and Tempkin. The adsorption equilibrium was reached in 30 min and the adsorption data fitted well to all models. The maximum adsorption capacity of TFW for zinc (II) ions was determined to be 14.2 mg/g. The capacity of adsorption on Zn(II) increased with increasing temperatures and pH. The maximum uptake level of zinc was observed at pH of 4.2. The various thermodynamic parameters, i. e., ΔG°, ΔH° and ΔS°, were estimated. The thermodynamics of the zinc ion/TFW system indicated a spontaneous, endothermic and random nature of the process. The results showed that the TFW, which has low economical value, is a suitable adsorbent for the removal of zinc (II) ions from aqueous solutions.     

Copper Biosorption by Spent Coffee Ground: Equilibrium,Kinetics, and Mechanism

The potential use of spent coffee ground (SCG) for the removal of copper has been investigated as a low‐cost adsorbent for the biosorption of heavy metals. Adsorption batch experiments were conducted to determine isotherms and kinetics. The biosorption equilibrium data were found to fit well the Freundlich model and an experimental maximum biosorption capacity of copper ions 0.214 mmol/g was achieved. The biosorption kinetics of SCG was studied at different adsorbate concentrations (0.1–1.0 mM) and stirring speeds (100–400/min). The results showed an increase in the copper ion uptake with raising the initial metal concentration and the kinetic data followed the pseudo‐second order rate expression. The effect of stirring speed was a significant factor for the external mass transfer resistance at 100/min and coefficients were estimated by the Mathews and Weber model. Biosorption of copper ions onto SCG was observed to be related mainly with the release of calcium and hydrogen ions suggesting that biosorption performance by SCG can be attributed to ion‐exchange mechanism with calcium and hydrogen ions neutralizing the carboxyl and hydroxyl groups of the biomass.     

Kinetics,Mechanistic and Thermodynamics of Zn(II) Ion Sorption: A Modeling Approach

Biosorption potential of Cedrus deodara sawdust (CDS) in terms of sorption of Zn(II) ion across liquid phase has been evaluated in the present investigation. The surface of the CDS biomass before the sorption of Zn(II) ions seemed to be more porous, non‐crystalline and heterogeneous. The maximum uptake capacity of CDS was 97.39 mg g^?1. Sorption of Zn(II) ion on the surface of CDS sawdust was maximum at pH 5, temperature 45°C, initial concentration of Zn(II) ion 100 mg L^?1, biomass dose 1 g L^?1, contact time 150 min, and agitation rate 160 rpm. Pseudo second‐order kinetics with the highest linear regression coefficient (R² = 0.99), and lowest values of error functions, i.e., chi (χ²) and sum of square errors (SSE) against pseudo first‐order rate kinetics showed that the sorption of Zn(II) ion on the surface of CDS was mediated by chemosoprtive forces of attraction rather than physical adsorption. Mechanistically, relatively higher proportion of sorption of Zn(II) ion in early phase of contact time was profoundly explained by Bangham's equation and film diffusivity (D^f). Intraparticle or pore diffusion (D_p) of Zn(II) ion inside the pores of CDS was rate limiting step at the later stage of contact time. Furthermore, the thermodynamic study on sorption of metal ion delineated the fact that the Zn(II) sorption on the surface of CDS was spontaneous, endothermic together with increased entropy at solid liquid interface.     

Geomorphological Impact Assessment on Groundwater Quality and Fluoride Genesis along the Bay of Bengal of Visakhapatnam District,Andhra Pradesh,India

Geomorphological effects might not be the mere natural topographical changes but, their impact on groundwater quantity/quality would be an aspect of great concern. Especially the qualitative fluctuations in coastal region would suffer more than those observed in the elevated or the plains. The ease and severity would magnify from the anthropogenic activities and from the effects carried over from the uplands. To evaluate this, a study was conducted by collecting 44 water samples of bore and open well origin along the Bay of Bengal coast of Visakhapatnam district. Geochemical assessment was carried from the results of all major chemical constituents and geological data of the sampling stations. The expansive and correlative interpretation of the results yielded the mechanisms control the genesis of principle chemical species, present status, reserves, drainage pattern and the recent intrusion zones in the study area. The genesis and spatial distribution of fluoride was assessed due to sporadic reports of fluorosis in the district. Upon receiving the findings with suitable recommendations, the Groundwater Board and the civil society organizations widely published and the displayed the results for further action made the study a purposeful.     

Mineral Content of Bottled and Desalinated Household Drinking Water in Kuwait

Three hundred and twenty‐two samples of desalinated household water were collected from 99 sampling locations that covered 95% of Kuwaiti's residential areas. Seventy‐one brands of bottled water were collected from Kuwaiti markets. The water quality parameters that were studied included pH, electrical conductivity (EC), total dissolved solids (TDS), F^?, Cl^?, Br^?, , , , , , , , and the major macronutrients Na⁺, K⁺, Ca²⁺, and Mg²⁺. The analysis yielded a large range of results for most of these parameters, with differences in some cases exceeding 10‐fold. With a few exceptions, the results were found to comply with US‐EPA and WHO standards. Only the water in two brands of bottled water was acidic (pH < 6.5). The TDS was found to be higher than the US‐EPA regulated value in 4 and 3% of the household samples and bottled water brands, respectively. The fluoride levels were generally higher in bottled water than in household water. However, the household water that was produced by the Doha desalination plant and some of the European brands of bottled water were the best samples studied in terms of their quantity of Ca²⁺, Mg²⁺, and Na⁺ compared with the DRI values for those substances. EC and TDS were positively correlated with , , Na⁺, K⁺, Ca²⁺, and Mg²⁺ for household water but only with Ca²⁺ and Mg²⁺ for bottled water.     

Dense water formation in the Gulf of Lions shelf: Impact of atmospheric interannual variability and climate change

Dense water formed over the continental shelf and cascading down the slope is responsible for shelf-slope exchanges in many parts of the world ocean, and transports large amounts of sediment and organic matter into the deep ocean. Here we perform numerical modeling experiments to investigate the impact of atmospheric interannual variability and climate change on dense water formation over the Gulf of Lions shelf, in the Northwestern Mediterranean Sea. Results obtained for a 140 years eddy-permitting simulation (1960–2100) performed over the whole Mediterranean Sea under IPCC A2 scenario forcings are used to force a regional eddy-resolving model of the Northwestern Mediterranean Sea.     

Modeling and Optimization of Fluoride and Cadmium Trapping in Phosphogypsum Using Design Methodology

The manufacturing of phosphoric acid from natural calcium phosphate generates a solid residue containing 25–30% humidity. This solid residue (phosphogypsum) generates acidic solution (pH ≈ 2.5) containing several toxic ionic species, that coat its grains. Fluorides and heavy metals such as cadmium are considered the most harmful species contained in the released solution from phosphogypsum. The purpose of this work is to study the trapping of fluorides and cadmium in phosphogypsum as well as effluent neutralization before its discharge into natural recipient. Therefore, calcium carbonate finely ground was added and fully mixed with wet phosphogypsum. A four factors central composite design was used to model and to optimize the operating parameters that govern the process. The studied factors were temperature, reaction time, mass, and grains size of CaCO₃. Considered responses were pH, F⁻, and Cd²⁺ concentrations in the released solution after reaction with CaCO₃. The optimum operating conditions were quite efficient to trap, respectively, 99% Cd²⁺ and 97% of F⁻ with a final pH of 6.66. So an original, easy, simple, and cost effective method to trap some toxic species on phosphogypsum through CaCO₃ addition would likely to be integrated in phosphoric acid manufacturing plant.