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Removal of arsenic(III) from water by magnetic binary oxide particles (MBOP): Experimental studies on fixed bed column
Accepted Manuscript Title: Removal of arsenic (III) from water by magnetic binary oxide particles (MBOP): Experimental studies on fixed bed column Author: Rajesh M. Dhoble Pratap Reddy Maddigapu Sadhana S. Rayalu A.G. Bhole Ashwinkumar S. Dhoble Shubham R. Dhoble PII: DOI: Reference:
S0304-3894(16)30897-4 http://dx.doi.org/doi:10.1016/j.jhazmat.2016.09.075 HAZMAT 18081
To appear in:
Journal of Hazardous Materials
Received date: Revised date: Accepted date:
19-7-2016 29-9-2016 30-9-2016
Please cite this article as: Rajesh M.Dhoble, Pratap Reddy Maddigapu, Sadhana S.Rayalu, A.G.Bhole, Ashwinkumar S.Dhoble, Shubham R.Dhoble, Removal of arsenic (III) from water by magnetic binary oxide particles (MBOP): Experimental studies on fixed bed column, Journal of Hazardous Materials http://dx.doi.org/10.1016/j.jhazmat.2016.09.075 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Removal of arsenic (III) from water by magnetic binary oxide particles (MBOP): Experimental studies on fixed bed column Rajesh M. Dhoblea, Pratap Reddy Maddigapub, Sadhana S. Rayalub*A.G. Bholec, Ashwinkumar S. Dhobled, Shubham R. Dhoblee a
Civil Engineering Department, G.H. Raisoni Academy of Engineering and Technology, Nagpur, M.S., India. E-mail: [email protected]
b
Environmental Materials Division, National Environmental Engineering Research Institute, Nagpur (CSIR-NEERI) M.S., India. E-mail: [email protected]
b*
Environmental Materials Division, National Environmental Engineering Research Institute, Nagpur (CSIR-NEERI) M.S., India. E-mail: [email protected]
c
d
e
*
Department of Civil Engineering, Visvesvaraya National Institute of Technology, Nagpur, M.S., India. E-mail: [email protected] Department of Mechanical Engineering, Visvesvaraya National Institute of Technology, Nagpur, M.S., India. E-mail: [email protected] Electronics and Instrumentation Engineering, Birla Institute of Technology, Pilani, Rajashtan, India. E-mail: [email protected]
To whom correspondence should be addressed: Phone: +91-9890367588; Fax: 0712 – 2247828; E-mail: [email protected]
1
Graphical abstract
Schematic diagram of MBOP column study for the removal of As(III) from water
2
Highlights As(III) removal was performed on magnetic binary oxide particles in column study Fresh MBOP has higher breakthrough time and capacity than regenerated MBOP The filtrate of column study maintained drinking water quality parameters TCLP and semi dynamic tests confirmed As(III) concentration were within limit
3
Abstract Magnetic binary oxide particles (MBOP) were prepared by template method using chitosan in the laboratory for the removal of As(III) from water. The prepared MBOP has super paramagnetic
property which is sufficient for magnetic separation. Column study was performed at two different flow rates of 2.0 ml/min. and 5.0 ml/min and comparison was made with regenerated MBOP, commercial activated carbon and commercial activated alumina. It is observed that fresh MBOP has higher breakthrough time and capacity than regenerated MBOP by a factor of 1.25 and 1.37 respectively. In Logit method, the values of K (adsorption rate constant) and N (adsorption capacity coefficient) were obtained as 0.2066 (L/mg h) and 1014 (mg/L) for 5.0 ml/min. flow rate. All the drinking water parameters are within the limit of BIS 10500-2012. Toxicity characteristic leaching procedure (TCLP) and semi dynamic tests were performed for the mix ratios of 01:02:01, 01:02:05 and 01:02:10 and were found safe for the disposal.
Keyword: MBOP, Arsenic, Column study, Logit model, TCLP 1. Introduction The global occurrence of arsenic in groundwater is a major and serious threat. Arsenic is generally found in rock, soil, water, air, plant, animal tissues and can exist in four valency states: –3, 0, +3 and +5. As(III) exists primarily as nonionic H3AsO3 in natural waters at low oxygen level, which is more difficult to remove when compared to As(V) species [1,2]. Several researchers reported that many countries groundwater and surface waters are affected by arsenic contamination of more than 10 μg/L [3]. The entry of arsenic in groundwater is mainly due to natural occurrences and from man-made activities. The natural arsenic sources are larger than the anthropogenic sources and their ratio is 60 to 40 [4]. The toxicity of As(III) is about 60 times more than As(V) due to its cellular uptake [5]. Arsenic might cause neurological damage to those
4
who drink arsenic contaminated water with slightly higher concentration than 0.1 mg/L and producing dermatosis at 0.2 mg/L [6]. The main objective for setting regulation of arsenic is to reduce the level as close to zero as possible, taking into consideration of occurrence, human exposure, toxicology, availability and cost of technology. Based on the above considerations, different countries have suggested permissible level of arsenic in drinking water. World health organization (WHO) suggested 10 µg/L based on the potential health risk and the practical quantitation limit [7]. In USEPA, Maximum Contamination Limit (MCL) of arsenic is 2-20 µg/L by considering the risk of skin cancer ranging from 1:10000 to 1:1000000. The arsenic standards are, in Australia (7 µg/L), France (15 µg/L), Vietnam and Mexico (50 µg/L) [8]. MCL of arsenic in drinking water is 10 µg/L, 25 µg/L, 5 µg/L, 3 µg/L and 50 µg/L in Japan, Canada, New Jersey, American Natural Resources Defense Council and China respectively [9, 10]. In India now the permissible limit for arsenic is reduced from 50 to 10 µg/L [11]. In many research papers batch studies have been reported and are difficult to apply directly to fixed bed column because isotherm cannot give accurate data to scale up [12]. Here in this research work we run column experiments for the removal of As(III). The most important aim to study the column experiments was to predict the breakthrough point, which allows further the determination of operation period and regeneration time. Several researchers reported on various adsorbents to remove As(III) from water in column study [13 and references there in]. Recently studies on various parameters which effects on synthesis of magnetic adsorbents were carried out [14-18]. In this research manuscript, the Magnetic Binary Oxide Particle (MBOP) beads
were
prepared
using
aluminium
nitrate
(Al(NO3)3.9H2O)
and
ferric
nitrate
(Fe(NO3)3.9H2O) by template method using chitosan and is used for the first time in column experiments for the removal of As(III). MBOP has sufficient super magnetic property which 5
removes the exhausted arsenic loaded MBOP from water by conventional magnet. The exhausted MBOP were found safe for disposal in secured landfill. The present study was carried out to evaluate the performances of fresh MBOP, regenerated MBOP, commercial activated alumina and commercial activated carbon for the removal of As(III) in fixed bed mode. Further fresh MBOP was compared with regenerated MBOP, commercial activated alumina and activated carbon in fixed bed mode for the same flow conditions. The effect of flow rate on adsorption was monitored in the column. For stabilization of arsenic waste, Toxicity characteristic leaching procedure (TCLP) and semi dynamic tests were conducted to know the safe disposal of arsenic loaded adsorbent in nature. 2. Materials and Methods 2.1. Reagents Reagents and chemicals used for the study were given separately in supplementary material S1. 2.2. Synthesis of MBOP Adsorption material (MBOP) was synthesized using template method. Chitosan (27 g) was dissolved in 900 mL of 5% acetic acid with constant stirring on mechanical stirrer for 1h. 84.78 g of aluminium nitrate (Al(NO3)3.9H2O) was dissolved in 100 mL of distilled water in a beaker and 97.89 g of ferric nitrate (Fe(NO3)3.9H2O) was dissolved in 100 mL of distilled water in another beaker. Solutions of aluminium nitrate and ferric nitrate were added simultaneously to the chitosan gel under continuous stirring for 180 min. The resulted Al-Fe-chitosan gel slurry was added drop by drop to NH4OH solution (50% v/v), under vigorous stirring, using a syringe pump. The gel macro spheres were allowed to stabilize in NH4OH solution for 60 min. The beads were separated from the NH4OH solution and washed using deionised water and dried at 70 oC for 24 h in oven. The dried beads were calcined at 450 oC for 6 h in muffle furnace. 6
Finally, the calcined product was subjected to multiple washings with deionised water and dried at 80 oC [19]. The mechanism of MBOP (Fig. S1) formation is shown in supplementary material S1. 2.3. Characterization of MBOP prepared by template method using chitosan Characterisation techniques used for MBOP prepared by template method using chitosan was given in supplementary material S1. 2.4. Fixed bed column study Experiments were conducted in continuous-flow system to evaluate empty bed contact time (EBCT), breakthrough time and breakthrough capacity for the reduction of As(III) concentration from aqueous solution on fresh MBOP, regenerated MBOP, commercial activated alumina and activated carbon in a fixed bed column reactor. In a column of 1.0 cm of internal diameter and 25 cm total height, the flow was controlled at the feed reservoir from the bottom side using a peristaltic pump. The column was packed with the adsorbent and glass wool at both the ends to prevent the flow of adsorbent particles into the outlet. The column was then fed continuously with As(III) containing water of 1.0 mg/L concentration at desired volumetric flow rate (2.0 ml/min. & 5.0 ml/min.) using peristaltic pump (Electro Lab, Mumbai, India) from bottom side of the tube (upflow) for uniform distribution, to avoid channeling, fouling of adsorbent and increasing the time of contact. The effluent was collected at the top at definite interval of time and examined for As(III) concentration. The schematic representation of the experimental setup and study was illustrated in Fig.1. Exhausted bed was regenerated insitu using optimal regeneration media and regeneration conditions as done in batch studies [19]. For the regenerated adsorbent, same procedure and conditions were adopted as the fresh adsorbent column study and the empty bed contact time (EBCT), breakthrough point, breakthrough capacity and saturation capacity in fresh and regenerated adsorbents were determined. For 7
comparison with fresh MBOP, commercial activated alumina and commercial activated carbon were used at a flow rate of 5.0 ml/min. 2.5. Logit method The fixed bed column was designed by Logit method [20, 21]. In this method the curve is plotted between ln [Co/(Co-C)] verses t. The Logit equation can be written as Co
ln (Co−C) = −
(KNX) 𝑉
+ K Co t
(1)
where C is the concentration of solute (mg/L) at any time t, Co is the initial concentration of solute (mg/L), V is the approach velocity of flow (cm/h), K adsorption rate constant (L/mg h), X is the depth of bed and N is the adsorption capacity coefficient (mg/L). Logit method is applied to experimental data of fresh MBOP and regenerated MBOP. 2.6. Solidification and stabilization of arsenic waste Many researchers reported various methods to incorporate arsenic bearing waste into polymeric matrices [22], concrete [23], soils [24], in landfills [25, 26], and in bricks [27] to dispose safely. Toxicity characteristic leaching procedure (TCLP) and semi dynamic tests were conducted to know the safe disposal of arsenic loaded adsorbent in nature. 2.6.1. Toxicity characteristic leaching procedure (TCLP) test The purpose of this test is to know whether the exhausted MBOP is hazardous or nonhazardous which helps for disposal consideration. As per USEPA 1992, when the leachate concentration of arsenic waste is less than 5.0 mg/L, the waste is classified as non-hazardous and suitable for disposal in a municipal solid waste landfill and if more than 5.0 mg/L then waste is suitable for disposal in a hazardous waste landfill. In the TCLP study, the binder material (cement) and fine aggregate (sand) were mixed with arsenic loaded MBOP solid waste in a definite ratio as cement: fine aggregates: arsenic
8
loaded MBOP solid waste (01:02:01, 01:02:05 and 01:02:10). Three different solidified waste matrices were prepared by mixing different compositions of binder materials. Water was added in a proportion to make slurry of these binders and arsenic rich waste materials. Complete preparation of solid matrices [28] for the test is mentioned in the supplementary material S1. 2.6.2. Semi dynamic test Semi-dynamic leach tests are generally used to determine the leachability of contaminants from monolithic solidified waste forms. The term ‘semi-dynamic’ means that the leachate is replaced periodically after intervals of static leaching. In this study, the stabilized/solidified waste samples were leached in a closed vessel without agitation using distilled water at a leachant to solid mass ratio of 10:1 which help to minimize leachant composition changes and extract more species for analysis. Leachate was collected after a fixed duration of 2 h, 7 h, 24 h, 48 h, 72 h, 96 h, 120 h, 456 h, 1128 h and 2160 h (90days) as per ANSI/ANS 16.1 standard [28]. 3. Results and discussion 3.1. Characterization of MBOP The X-ray diffraction analysis of fresh MBOP does not showed any peaks relevant to chitosan, as it was eliminated in the calcination step at 450 oC, whereas peaks at 2θ = 31.0 and 36.0 indicates the presence of γ-alumina phase. No specific crystalline iron oxide peaks were observed in XRD. The absence of iron oxide peaks was attributed to the higher dispersion of supported iron oxide phase. Further, the XRD pattern remained almost the same after As(III) adsorption over MBOP, indicating the structural integrity (Fig. S2a and b). It has been reported that the adsorption of arsenic on amorphous metal oxide is through the formation of inner sphere surface complexes which are mainly attached as bidentate linkages with some monodentate linkages [19, 29]. The FTIR spectrum of fresh MBOP (Fig. S2c) indicates the presence of 9
predominant peaks at 3512.38 cm-1 and 3321.24 cm-1 (-OH and -NH stretching vibrations), 2900.67 cm-1 and 2342.24 cm-1 (-CH stretching vibration), 1648.20 cm-1 (-NH bending vibration in -NH2), 1378.91cm-1 (-NH deformation vibration in -NH2). The low intensity band at 1062.40 cm-1 is ascribed to Fe–OH structural vibration. The band between 400 cm-1 and 450 cm-1 could be due to the superposition of the characteristic stretching bands of aluminum oxide. The bands observed between 1100 cm-1 and 500 cm-1 could be characteristic vibrations of aluminum oxide. FTIR spectrum of As(III) loaded MBOP is shown in (Fig. S2d). The predominant peaks due to OH and -NH stretching vibrations of hydroxyl and amine groups sharpen and shifted to 3640cm-1 and 3063cm-1 indicating interaction of arsenic at hydroxyl and amine sight through hydrogen bonding. FTIR peaks corresponding of Fe-OH structural vibration and stretching bands of aluminium oxide becomes broad and overlapped due to arsenic adsorption. The surface morphology of MBOP before and after As(III) adsorption was studied by SEM (Fig. S2e and f) analysis and observed porous in nature which implies that the adsorbent may have reasonable high surface area and adsorption capacity. The large pores are developed by the elimination of chitosan template during calcination step of synthesis. Pore size of MBOP is much larger than the radius of arsenite (0.58Ao) which may facilitate dispersion of arsenite in the inner layer of granular MBOP. It was found that after adsorption of arsenic, the surface morphology of MBOP not changed much, suggesting physical adsorption of arsenic occurred. From the XRD, SEM and FTIR analysis of MBOP, it is observed that no variation in the core structural properties of MBOP before and after the adsorption of As(III), which reveals that the MBOP retains its stability. The physical properties like BET surface area, average pore size etc., given in Table 1. The chemical composition of MBOP was analyzed by Wave length Dispersive X-Ray Fluorescence Spectrophotometer (WDXRFS) and the percentage of Fe, Al, O, Ca, P, Mg, Mn 10
and S are shown in Table 1. The special feature of MBOP is that it has super paramagnetic property. The saturation magnetization value (18.78 emu/g) achieved with MBOP was sufficient for magnetic separation (Table 1; Fig. 2) which is more than the saturation value of 16.3 emu/g for magnetic separation with a conventional magnet [30]. Hence MBOP can be easily isolated from solution by application of external magnetic bar. MBOP is attracted by the magnet before adsorption of As(III) in dry condition and after adsorption of As(III) in water as shown in Fig.2. This further confirms that MBOP has magnetic nature after adsorption of As(III) in wet condition. In the XPS spectra, Fe 2p electron binding energies are shown in Fig.3. The spectra indicates the presence of carbon, oxygen, iron and alumina on the surface of MBOP as indicated by the peaks corresponding to the binding energies at 288.2eV (C1s), 530eV (O1s), 724.5eV (Fe 2 p1/2) and 710.4eV (Fe 2p3/2), 74.2eV (Al 2p) (Fig.3 a-d). It is indicated that the relative intensity of the Fe 2p1/2 and Fe 2p3/2 peak positions (724.5eV and 710.4eV) and the shape are the characteristic presence of Fe(III). These observations confirm the presence of Fe2O3 phase of iron and Al2O3 phase of aluminium and some organic/carbonaceous chitosan residue in MBOP. 3.2. Fixed bed column study 3.2.1. Column study on fresh MBOP at flow rate of 2.0 ml/min. and 5.0 ml/min. To investigate the influence of flow rate chosen at 2.0 ml/min. and 5.0 ml/min., MBOP was used in continuous flow in column of 1.0 cm diameter and 18.0 cm media height. The schematic diagram of experimental column study is shown in Fig. 1. Comparison of empty bed contact time (EBCT), breakthrough time and breakthrough capacity of MBOP were conducted at flow rates of 2.0 ml/min. & 5.0 ml/min. and is shown in Table 2. EBCT is a significant parameter which determines the residence time when the solution is in contact with the adsorbent and the removal efficiency is strongly depends on the contact time between the adsorbate (arsenic) and the adsorbent coated with iron hydroxide [31]. From experiments, at flow rate of 11
5.0 ml/min. and 2.0 ml/min., it was observed that EBCT was 3.0 min. and 7.1 min.; breakthrough time was 26.15 h and 72 h; volume of water treated was 7.845 liters and 8.64 liters and breakthrough capacity was 0.436 mg/g and 0.477 mg/g respectively. Due to decrease of flow rate, increase in EBCT, breakthrough time, volume of water treated and breakthrough capacity were observed and the percentages were 136.66, 175.33, 10.20 and 9.40 respectively (Table 2). This trend may be due to the availability of more adsorption sites to capture arsenic ions around or within MBOP, which results the more diffusion of solute into the pores of adsorbent. An increase flow rate reduces the volume of water treated until breakthrough and this is due to the decrease in the residence time of the As(III) ions within the bed or this may be because of reduced contact time, which causes a weak distribution of the liquid inside the column that in turn leads to a lower diffusivity of the solute into MBOP indicating that adsorption of As(III) may be slightly depends on diffusion. It is also reported that at higher flow velocities, the film surrounded by adsorbent particle breaks thus reducing the adhesion of adsorbate to the adsorbent particle [12]. MBOP at 2.0 ml/min. flow rate has higher breakthrough time and breakthrough capacity by a factor of 2.75 and 1.1 than 5.0 ml/min flow rate respectively. The shape of the breakthrough curve is affected by fluid viscosity, concentration of solute in feed, pH of adsorbate and bed height. Steep slopes of breakthrough curves in column exhibiting high film transfer coefficients and high internal diffusion [12]. At 5.0 ml/min. flow rate, the breakthrough time curve is very steep compared to 2.0 ml/min. flow rate indicating high film transfer coefficient and high internal diffusion coefficient (Fig.4). Hence the time required to reach breakthrough time at 5.0 ml/min. flow rate is less than 2.0 ml/min. flow rate. As per IS 1172-1993, drinking water requirement is 5.0 liter/capita/day and it was observed that at 5.0 ml/min flow rate, the volume of water treated by single column was 7.845 liters in 26.15 h (Table 2) which is more than 5.0 liters/capita/day and hence in this study, all the experiments were conducted at 5.0 12
ml/min. flow rate. The saturation time and saturation capacity of MBOP was found to be 515 h and 4.67 mg/g respectively at flow rate of 5.0 ml/min. (Table 3). Compared with other adsorbents reported in literature [13 and references there in], MBOP showed higher breakthrough capacity of 0.436 mg/g and 0.477 mg/g at a flow rate of 5.0 ml/min. and 2.0 ml/min. respectively. 3.2.2. Regeneration study Due to regeneration, the replacement of new adsorbent and disposal problem can be reduced considerably. Economic viability of any adsorbent depends on its regeneration and reuse for many cycles of operation. Once the adsorbent exhausted, then adsorbate which is adsorbed must be recovered and then regenerated. Selection of regeneration solution is depending upon the arsenic adsorption mechanism and the nature of adsorbent. During the first cycle of regeneration study, 1% of 1N NaOH was passed through the exhausted MBOB column for 1h at the rate of 5.0 ml/min. in upflow condition and then the column was washed with double distilled water with a flow rate of 5.0 ml/min. till the effluent pH comes to neutral. The regenerated adsorbent was then reused for adsorption of As(III) in the column. The nature of curves for fresh and regenerated MBOP is shown in Fig.5. The regenerated MBOP at 5.0 ml/min. flow rate showed, breakthrough time, saturated time, breakthrough capacity and saturation capacity of 21 h, 314 h (13.08 days), 0.318 mg/g and 2.05 mg/g respectively (Table 3). When compared with fresh MBOP, it was observed that fresh MBOP has higher breakthrough time and breakthrough capacity than regenerated MBOP by a factor of 1.25 and 1.37 respectively (Table 3). Thus the percentage decrease in EBCT, breakthrough time, saturation time, breakthrough capacity and saturation capacity of regenerated MBOP were 6.66, 19.69, 39.03, 27.21 and 56.10 respectively (Table 3) indicating that few adsorption sites were still occupied by As(III) ions even after regeneration of MBOP. 13
3.2.3. Arsenic removal by commercial activated alumina and activated carbon To compare the MBOP with the commercial activated alumina and commercial activated carbon, column experiments for activated alumina and activated carbon were conducted at the flow rate of 5.0 ml/min. The surface area (m2/g), total pore volume (cm3/g) and average pore diameter (Ao) of bare alumina was 189.12, 0.4691 and 98.33 respectively. Pore diameter of bare activated alumina is more than the diameter of arsenite (0.58 Ao) which helps to insert arsenite into activated alumina. Column study upto breakthrough capacity on commercial activated alumina and commercial activated carbon is shown in Fig.6. In commercial activated alumina column study, EBCT, breakthrough time, breakthrough capacity and saturation capacity were found to be 2.42 min., 5.0 h, 0.126 mg/g and 0.35 mg/g respectively whereas on commercial activated carbon column study the results were observed as 2.98 min., 3.75 h, 0.109 mg/g and 0.29 mg/g respectively (Table 4). The saturation time on activated alumina and activated carbon was found to be 55.45 h and 36.56 h respectively. 3.2.4. Comparison of fresh MBOP with commercial activated alumina and activated carbon From the Table 4, it is observed that at 5.0 ml/min. flow rate, percentage increase in EBCT, breakthrough time, breakthrough capacity and saturation capacity of fresh MBOP were 23.97, 423, 246 and 1234 respectively when compared with commercial activated alumina. Similarly on commercial activated carbon were also found to be higher by 0.67%, 596%, 300% and 1510% respectively. Breakthrough capacity of fresh MBOP was observed much higher by a factor of 3.46 and 4.0 compared to commercial activated alumina and commercial activated carbon respectively. These observations reveals that MBOP had significant enhancement of adsorption capacity for As(III) removal than commercial activated alumina and commercial activated carbon in water. 3.2.5. Logit method
14
From Logit method (Fig.7), the values of K and N on fresh MBOP were found to be 0.2076 (L/mg h) and 1015 (mg/L) respectively. These K and N values might be used for the design of adsorption column. After regeneration of MBOP with 1N NaOH, the value of K and N were obtained as 0.2032 (L/mg h) and 756 (mg/L) respectively. This shows that the adsorption capacity coefficient (N) was reduced by 25.51% due to regeneration of first cycle, which is nearly same as the percentage decrease of 27.21 for the regenerated MBOP (Table 3). 3.2.6. Effluent water quality parameter To understand the effect of using MBOP to remove As(III) from drinking water, water quality parameters of effluent after column adsorption were determined. From Table 5, it is observed that pH of the treated water remained within permissible limit and was closed to the pH of the water before treatment, suggesting that no post treatment is required. After treatment, As(III) concentration was less than permissible limit of 10 µg/L [11]. It is also observed that the conductivity was reduced significantly from 306 µS/cm to 214 µS/cm, indicating that there is significant removal of dissolved solids. Aluminum (Al3+) concentration was below the permissible limit of BIS 10500-2012, indicating that the MBOP can be used for treatment of As(III) in groundwater. All the parameters are within in the prescribed standard limit [11]. 4. Solidification and stabilization of arsenic waste 4.1. Toxicity characteristic leaching procedure (TCLP) test From the TCLP test as per the procedure mentioned in the supplementary material S1, it is observed that the maximum As(III) concentration in leachate was 0.0167 mg/L, 0.0186 mg/L and 0.0722 mg/L for the mix of cement: fine aggregates: arsenic loaded MBOP solid waste ratios of 01:02:01, 01:02:05 and 01:02:10 respectively (Fig.8). The leachates from all the mix proportions showed much less than 1.0 mg/L as per the limit [32]. Hence the above said mixed proportions of combination are safe for disposal in secured landfill. 15
4.2. Semi dynamic test Semi dynamic test was carried out on exhausted As(III) loaded MBOP before disposal. From Fig.9, it is observed that the maximum concentration of As(III) in leachate was 0.813 mg/L, 0.915 mg/L and 0.989 mg/L for the mix proportion of 01:02:01, 01:02:05 and 01:02:10 after 72 h, 72 h and 96 h respectively which is less than the permissible limit of 5.0 mg/L [3235]. This shows that all mix proportions are safe for disposal in landfill. 5. Conclusion In the present study, removal of As(III) from groundwater was achieved using MBOP which is cost effective and can be developed with the help of locally available materials. The most significant feature of MBOP is that it has magnetic property before and after adsorption of As(III) and is easy to separate from the effluent using magnet. The breakthrough time of MBOP at a flow rate of 2.0 ml/min. and 5.0 ml/min. was observed to be 72 h and 26.15 h respectively. The percent increase of breakthrough capacity was observed 9.4 as the flow rate decreased from 5.0 ml/min. to 2.0 ml/min. Fresh MBOP has higher breakthrough time and capacity than regenerated MBOP by a factor of 1.25 and 1.37 respectively. In Logit method, the values of K (adsorption rate constant) and N (adsorption capacity coefficient) were obtained as 0.2076 (L/mg h) and 1015 (mg/L) for 5.0 ml/min. flow rate. These K and N values might be used for the design of adsorption column. Breakthrough capacity of fresh MBOP was higher by a factor of 3.46 and 4.0 than the commercial activated alumina and commercial activated carbon respectively; indicating MBOP is much better adsorbent. The effluent water quality parameters after adsorption was within the permissible limit of drinking water standards BIS 10500-2012; indicating that the MBOP can be used for treatment of As(III) from groundwater. TCLP and semi dynamic tests were performed on stabilized MBOP which are proving to be non-hazardous mode of disposal consideration. Concentration of As(III) in leachates from all 16
the mix proportions (01:02:01, 01:02:05 and 01:02:10 for cement: fine aggregates: arsenic loaded waste) showed much less than 1.0 mg/L as per the limit hence safe for disposal. In semi dynamic test, the As(III) concentration in leachates were less than the permissible limit (5.0 mg/L) for all mix proportions hence it is safe for disposal in secured landfill. Acknowledgement We thank Director of CSIR- National Environmental Research Institute (NEERI) Nagpur for providing research facilities. Dr. M.P. Reddy thanks CSIR, New Delhi in granting the Pool Scientist award.
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http://dx.doi.org/10.1016/j.jaap.2016.06.026. [15] M.N. Noraini, E.C. Abdullah, R. Othman, N.M. Mubarak, Single-route synthesis of magnetic biochar from sugarcane bagasse by microwave-assisted pyrolysis, Mater. lett. (2016), http://dx.doi.org/10.1016/j.matlet.2016.08.064. [16] N.M. Mubarak, A. Kundu, J.N. Sahu, E.C. Abdullah, N.S. Jayakumar, Synthesis of palm oil empty fruit bunch magnetic pyrolytic char impregnating with FeCl 3 by microwave heating technique, Biomass bioenergy 61 (2014) 265-275. [17] K.R. Thines, E.C. Abdullah, M. Ruthiraan, N.M. Mubarak, M. Tripathi, A new route of magnetic biochar based polyaniline composites for supercapacitor electrode materials, J. Anal. Appl. Pyrolysis (2016), http://dx.doi.org/10.1016/j.jaap.2016.08.004 [18] A. Kundu, B.S. Gupta, M.A. Hashim, J.N. Sahu, M. Mubarak, G. Redzwan, Optimisation of the process variables in production of activated carbon by microwave heating, RSC advances 5 (2015) 35899–35908. [19] R.M. Dhoble, S. Lunge, A.G. Bhole, S. Rayalu, Magnetic binary oxide particles (MBOP): a promising adsorbent for removal of As(III) in water, Water Res. 45 (2011) 4769–4781. [20] S.K. Maji, A. Pal, T. Pal, Arsenic removal from real-life groundwater by adsorption on laterite soil, J. Hazard. Mater. 151 (2008) 811-820.
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[21] P.B. Bhatkar, A.K. Gupta, S. Ayoob, S. Kundu, Investigation on arsenic (V) removal by modified calcined bauxite, Colloids and surf., A 281 (2006) 237-245. [22] J.K. Shaw, S.B. Fathordoobadi, J. Zelinski, W.P. Ela, A.E. Sáez, Stabilization of arsenicbearing solid residuals in polymeric matrices, J. Hazard. Mater. 152 (3) (2008) 1115-1121. [23] W.H. Choi, S.R. Lee, J.Y. Park, Cement based solidification/stabilization of arseniccontaminated mine tailings, Waste Manage. 29 (5) (2009) 1766-1771. [24] J. Kumpiene, A. Lagerkvist, C. Maurice, Stabilization of As, Cr, Cu, Pb and Zn in soil using amendments-a review, Waste Manage. 28 (1) (2008) 215-225. [25] K.S.B. Kameswari, A.G. Bhole, R. Paramasivam, Evaluation of solidification/stabilization (S/S) process for the disposal of arsenic-bearing sludges in landfill sites, Environ. Eng. Sci. 18 (3) (2001) 167-176. [26] C. Sullivan, M. Tyrer, C.R. Cheeseman, N.J.D. Graham, Disposal of water treatment wastes containing arsenic - a review, Sci. Total Environ. 408 (8) (2010) 1770-1778. [27] H.M.A. Mahzuz, R. Alam, M. Alam, N.R. Basak, M.S. Islam, Use of arsenic contaminated sludge in making ornamental bricks, Int. J. Environ. Sci. Tech. 6 (2) (2009) 291-298. [28] T.S. Singh, K.K. Pant, Solidification/stabilization of arsenic containing solid wastes using Portland cement, fly ash and polymeric materials, J. Hazard. Mater. B 131 (2006) 29–36. [29] S.M. Maliyekkala, L. Philip, T. Pradeep, As(III) removal from drinking water using manganese oxide-coated-alumina: Performance evaluation and mechanistic details of surface binding, Chem. Eng. J. 153 (2009) 101–107.
20
[30] Z.Y. Ma, Y.P. Guan, H.Z. Liu, Synthesis and characterization of micron-sized monodisperse supermagnetic polymer particles with amino groups, J. Polym. Sci. Pol. Chem. 43 (2005) 3433-3439. [31] I.A. Katsoyiannis, A.I. Zouboulis, Removal of arsenic from contaminated water sources by sorption onto iron-oxide-coated polymeric materials, Water Res. 36 (2002) 5141-5155. [32] B. Sengupta, D.B. Boralkar, T. Chatterjee, Identification/characterisation of hazardous wastes, in: B. Sengupta, S.P. Chakrabarthi, N.K. Varma, J.C. Babu (Eds.), Management of hazardous wastes: Guideline for proper functioning and upkeep of disposal sites, NISCIRCSIR, New Delhi, 2005, pp. 2-6. [33] Hazardous Waste (Management, Handling & Transboundary Movement) Rules, CPCB, New Delhi, India. http://www.cpcb.nic.in/divisionsofheadoffice/hwmd/mhtrules2008.pdf, 2008 (accessed 05.09.16). [34] T.M. Clancy, F.K. Hayes, L. Raskin, Arsenic waste management: A critical review of testing and disposal of arsenic-bearing solid wastes generated during arsenic removal from drinking water, Environ. Sci. Technol. 47 (2013) 1079 -1081. [35] U.S. Environmental Protection Agency, Hazardous waste test methods/SW-846 test method
1311:
Toxicity
characteristic
leaching
procedure.
https://www.epa.gov/sites/production/files/2015-12/documents/1311.pdf, 1992 (accessed 05.09.16).
21
List of figures Figure number Fig. 1.
Figure caption Schematic diagram of MBOP column study for the removal of As(III) from water
Fig. 2.
VSM Magnetization curve of MBOP (insight MBOP attracted by magnet: (a) Before adsorption (dry condition) (b) After adsorption (in water)).
Fig. 3.
XPS spectrum of
Fig. 4.
a) Carbon 1s b) Oxygen 1s c) Fe2O3 - Fe 2p3/2 & 2p1/2 d) Al2O3 - Al 2p Column study on fresh MBOP upto breakthrough time at flow rate of 2.0 & 5.0ml/min.
Fig. 5.
Column study on fresh MBOP and regenerated MBOP with 1% of 1N NaOH.
Fig. 6.
Column study on commercial activated alumina and commercial activated carbon upto breakthrough capacity.
Fig. 7.
Linearized form of Logit model.
Fig. 8.
TCLP on exhausted MBOP.
Fig. 9.
Semi dynamic test for leaching of As(III) on exhausted MBOP.
22
List of tables Table number Table 1
Table caption Physical property, chemical composition and magnetic property of MBOP.
Table 2
Comparison of EBCT, breakthrough time and breakthrough capacity of MBOP at flow rate of 2.0 ml/min. & 5.0 ml/min.
Table 3
Comparison of fresh MBOP and regenerated MBOP with 1% of 1N NaOH at flow rate of 5.0 ml/min.
Table 4
Comparison of breakthrough and saturation capacity of commercial activated carbon, commercial activated alumina with fresh MBOP.
Table 5
Physico-chemical properties of field water before and after treatment by MBOP.
23
Table 1 Physical property, chemical composition and magnetic property of MBOP. Physical property (MBOP) BET surface area (m2/g)
123.28
Average pore size (Ao)
61.59
Total pore volume (cm3/g)
0.1732
Average diameter of particle (micron)
230.87
Chemical Composition (%) Fe
42.6
O
34.21
Al
16.69
Ca
0.65
P
0.18
Mg
0.16
Mn
0.07
S
0.02
Magnetic property of MBOP Saturation magnetization value (emu/g)
18.78
Table 2 Comparison of EBCT, breakthrough time and breakthrough capacity of MBOP at flow rate of 2.0 ml/min. & 5.0 ml/min. Flow rate (ml/min.)
EBCT (min.)
Break through time (h)
Vol. of water treated (L)
Breakthrough capacity, qe (mg/g)
5.0
3.0
26.15
7.845
0.436
2.0
7.1
72.0
8.64
0.477
Percentage increase of EBCT (decreasing flow rate from 5.0ml/min. to 2.0ml/min.)
136.66
Percentage increase of breakthroug h time (decreasing flow rate from 5.0ml/min. to 2.0ml/min.)
Percentage increase of volume of treated water (decreasing flow rate from 5.0ml/min. to 2.0ml/min.)
Percentage increase of breakthrough capacity (decreasing flow rate from 5.0ml/min. to 2.0ml/min.)
175.33
10.20
9.40
EBCT= Empty bed contact time
24
Table 3 Comparison of fresh MBOP and regenerated MBOP with 1% of 1NNaOH at flow rate of 5.0 ml/min. Condition
Flow rate EBCT (ml/min.) (min.)
Fresh MBOP
5.0
Regenerated MBOP
5.0
Percentage decrease of EBCT after regeneration
3.0
Breakthrough time (h)
Saturated time (h)
Breakthrough capacity, qb (mg/g)
Saturation capacity, qs (mg/g)
26.15
515
0.436
4.67
2.8
21.0
314
0.318
2.05
--
6.66
--
--
--
--
Percentage decrease of breakthrough time after regeneration
--
--
19.69
--
--
Percentage decrease of saturation time after regeneration
--
Percentage decrease of breakthrough capacity after regeneration
--
Percentage decrease of saturation capacity after regeneration
--
--
--
--
39.03
----
--
--
--
27.21 --
--
--
--
--
56.10
25
Table 4 Comparison of breakthrough and saturation capacity of commercial activated carbon, commercial activated alumina with fresh MBOP. Adsorbent
Flow rate (ml/ min.)
EBCT (min.)
Break through time (h)
Break through capacity, qe (mg g-1)
Saturation capacity, qS (mg/g)
Commercial activated alumina
5.0
2.42
5.0
0.126
0.35
Commercial activated carbon
5.0
2.98
3.75
0.109
Fresh MBOP
5.0
3.0
26.15
0.436
Percentage increase of EBCT of fresh MBOP compared with
Percentage increase of break through capacity of fresh MBOP compared with
Percentage increase of saturation capacity of fresh MBOP compared with
23.97
Percentage increase of break through time of fresh MBOP compared with 423
246
1234
0.29
0.67
596
300
1510
4.67
--
--
--
--
Table 5 Physico-chemical properties of field water before and after treatment by MBOP. Parameter
Unit
Before treatment
After treatment
pH
-
7.23
6.89
Desirable limits as per Indian Drinking Water Standard ( BIS :10500-2012)* 6.5-8.5
Colour
-
colourless
colourless
colourless
Odour
-
odourless
odourless
Unobjectionable
mg/L
129
118
200
Total hardness
CaCO3
109
102
200
Conductivity
µS/cm
306
214
--
Chloride
mg/L
154
29
250
Sulphate
mg/L
21
17
200
Nitrate
mg/L
1.514
1.213
45
TDS
mg/L
397
149
500
2+
mg/L
42
36
75
Mg
mg/L
18.2
13.56
30
Fe3+
mg/L
0.216
0.241
0.3
As(III)
µg/l
992.6
9.81
10
Aluminium
mg/L
<0.002
<0.002
<0.003
Alkalinity
Ca
2+
26
*Bureau of Indian standard specifications for drinking water (IS:10500-2012) second Revision.
27
Fig. 1. Schematic diagram of MBOP column study for the removal of As(III) from water
Fig. 2. VSM Magnetization curve of MBOP (insight MBOP attracted by magnet (a). Before adsorption (dry condition) (b) After adsorption (in water)).
1
(a)
(b)
(c)
Fig. 3. XPS spectrum of
(d)
a) Carbon 1s
b) Oxygen 1s
c) Fe2O3 - Fe 2p3/2 & 2p1/2
d) Al2O3 - Al 2p
2
0.012 Flow rate : 5.0 ml/min Flow rate : 2.0 ml/min
Ct/Co
0.01 0.008 0.006 0.004 0.002 0 0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
Time (h) Fig. 4. Column study on fresh MBOP upto breakthrough time at flow rate of 2.0 & 5.0ml/min.
1.2
Fresh MBOP at 5.0 ml/min Regenerated MBOP with 1%NaOH
1
Ct/Co
0.8 0.6 0.4
0.2 0 0
50
100
150
200
250
300
350
400
450
500
550
Time (h) Fig. 5. Column study on fresh MBOP and regenerated MBOP with 1% of 1N NaOH.
3
0.016 Commercial activated alumina Commercial activated carbon
0.014 0.012
Ct/Co
0.01 0.008 0.006 0.004 0.002 0 0
1
2
3
4
5
6
Time (h) Fig. 6. Column study on commercial activated alumina and commercial activated carbon upto breakthrough capacity. 0 Regenerated MBOP Fresh MBOP
-1
Ln Ct/( Co- Ct)
-2
y = 0.2032x - 7.3355 R² = 0.8675
-3 -4 -5
y = 0.2066x - 9.9955 R² = 0.9231
-6 -7 0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
Time (h) Fig. 7. Linearized form of Logit model.
4
Concentration of As(III) in leachate (mg/L)
0.08 0.0722 0.07 0.06 0.05 0.04 0.03 0.0186
0.02
0.0167
0.01 0 1:02:01
1:02:05
1:02:10
Cement: Sand : Waste material (MBOP) Fig. 8. TCLP on exhausted MBOP.
1.2
As(III) conecntration in Leachate (mg/L)
01:2:01 mix proportion 01:02:05 mix proportion
1
01:02:10 mix proportion 0.8 0.6 0.4 0.2 0
Time in days Fig. 9. Semi dynamic test for leaching of As(III) on exhausted MBOP.
5
S0304-3894(16)30897-4 http://dx.doi.org/doi:10.1016/j.jhazmat.2016.09.075 HAZMAT 18081
To appear in:
Journal of Hazardous Materials
Received date: Revised date: Accepted date:
19-7-2016 29-9-2016 30-9-2016
Please cite this article as: Rajesh M.Dhoble, Pratap Reddy Maddigapu, Sadhana S.Rayalu, A.G.Bhole, Ashwinkumar S.Dhoble, Shubham R.Dhoble, Removal of arsenic (III) from water by magnetic binary oxide particles (MBOP): Experimental studies on fixed bed column, Journal of Hazardous Materials http://dx.doi.org/10.1016/j.jhazmat.2016.09.075 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Removal of arsenic (III) from water by magnetic binary oxide particles (MBOP): Experimental studies on fixed bed column Rajesh M. Dhoblea, Pratap Reddy Maddigapub, Sadhana S. Rayalub*A.G. Bholec, Ashwinkumar S. Dhobled, Shubham R. Dhoblee a
Civil Engineering Department, G.H. Raisoni Academy of Engineering and Technology, Nagpur, M.S., India. E-mail: [email protected]
b
Environmental Materials Division, National Environmental Engineering Research Institute, Nagpur (CSIR-NEERI) M.S., India. E-mail: [email protected]
b*
Environmental Materials Division, National Environmental Engineering Research Institute, Nagpur (CSIR-NEERI) M.S., India. E-mail: [email protected]
c
d
e
*
Department of Civil Engineering, Visvesvaraya National Institute of Technology, Nagpur, M.S., India. E-mail: [email protected] Department of Mechanical Engineering, Visvesvaraya National Institute of Technology, Nagpur, M.S., India. E-mail: [email protected] Electronics and Instrumentation Engineering, Birla Institute of Technology, Pilani, Rajashtan, India. E-mail: [email protected]
To whom correspondence should be addressed: Phone: +91-9890367588; Fax: 0712 – 2247828; E-mail: [email protected]
1
Graphical abstract
Schematic diagram of MBOP column study for the removal of As(III) from water
2
Highlights As(III) removal was performed on magnetic binary oxide particles in column study Fresh MBOP has higher breakthrough time and capacity than regenerated MBOP The filtrate of column study maintained drinking water quality parameters TCLP and semi dynamic tests confirmed As(III) concentration were within limit
3
Abstract Magnetic binary oxide particles (MBOP) were prepared by template method using chitosan in the laboratory for the removal of As(III) from water. The prepared MBOP has super paramagnetic
property which is sufficient for magnetic separation. Column study was performed at two different flow rates of 2.0 ml/min. and 5.0 ml/min and comparison was made with regenerated MBOP, commercial activated carbon and commercial activated alumina. It is observed that fresh MBOP has higher breakthrough time and capacity than regenerated MBOP by a factor of 1.25 and 1.37 respectively. In Logit method, the values of K (adsorption rate constant) and N (adsorption capacity coefficient) were obtained as 0.2066 (L/mg h) and 1014 (mg/L) for 5.0 ml/min. flow rate. All the drinking water parameters are within the limit of BIS 10500-2012. Toxicity characteristic leaching procedure (TCLP) and semi dynamic tests were performed for the mix ratios of 01:02:01, 01:02:05 and 01:02:10 and were found safe for the disposal.
Keyword: MBOP, Arsenic, Column study, Logit model, TCLP 1. Introduction The global occurrence of arsenic in groundwater is a major and serious threat. Arsenic is generally found in rock, soil, water, air, plant, animal tissues and can exist in four valency states: –3, 0, +3 and +5. As(III) exists primarily as nonionic H3AsO3 in natural waters at low oxygen level, which is more difficult to remove when compared to As(V) species [1,2]. Several researchers reported that many countries groundwater and surface waters are affected by arsenic contamination of more than 10 μg/L [3]. The entry of arsenic in groundwater is mainly due to natural occurrences and from man-made activities. The natural arsenic sources are larger than the anthropogenic sources and their ratio is 60 to 40 [4]. The toxicity of As(III) is about 60 times more than As(V) due to its cellular uptake [5]. Arsenic might cause neurological damage to those
4
who drink arsenic contaminated water with slightly higher concentration than 0.1 mg/L and producing dermatosis at 0.2 mg/L [6]. The main objective for setting regulation of arsenic is to reduce the level as close to zero as possible, taking into consideration of occurrence, human exposure, toxicology, availability and cost of technology. Based on the above considerations, different countries have suggested permissible level of arsenic in drinking water. World health organization (WHO) suggested 10 µg/L based on the potential health risk and the practical quantitation limit [7]. In USEPA, Maximum Contamination Limit (MCL) of arsenic is 2-20 µg/L by considering the risk of skin cancer ranging from 1:10000 to 1:1000000. The arsenic standards are, in Australia (7 µg/L), France (15 µg/L), Vietnam and Mexico (50 µg/L) [8]. MCL of arsenic in drinking water is 10 µg/L, 25 µg/L, 5 µg/L, 3 µg/L and 50 µg/L in Japan, Canada, New Jersey, American Natural Resources Defense Council and China respectively [9, 10]. In India now the permissible limit for arsenic is reduced from 50 to 10 µg/L [11]. In many research papers batch studies have been reported and are difficult to apply directly to fixed bed column because isotherm cannot give accurate data to scale up [12]. Here in this research work we run column experiments for the removal of As(III). The most important aim to study the column experiments was to predict the breakthrough point, which allows further the determination of operation period and regeneration time. Several researchers reported on various adsorbents to remove As(III) from water in column study [13 and references there in]. Recently studies on various parameters which effects on synthesis of magnetic adsorbents were carried out [14-18]. In this research manuscript, the Magnetic Binary Oxide Particle (MBOP) beads
were
prepared
using
aluminium
nitrate
(Al(NO3)3.9H2O)
and
ferric
nitrate
(Fe(NO3)3.9H2O) by template method using chitosan and is used for the first time in column experiments for the removal of As(III). MBOP has sufficient super magnetic property which 5
removes the exhausted arsenic loaded MBOP from water by conventional magnet. The exhausted MBOP were found safe for disposal in secured landfill. The present study was carried out to evaluate the performances of fresh MBOP, regenerated MBOP, commercial activated alumina and commercial activated carbon for the removal of As(III) in fixed bed mode. Further fresh MBOP was compared with regenerated MBOP, commercial activated alumina and activated carbon in fixed bed mode for the same flow conditions. The effect of flow rate on adsorption was monitored in the column. For stabilization of arsenic waste, Toxicity characteristic leaching procedure (TCLP) and semi dynamic tests were conducted to know the safe disposal of arsenic loaded adsorbent in nature. 2. Materials and Methods 2.1. Reagents Reagents and chemicals used for the study were given separately in supplementary material S1. 2.2. Synthesis of MBOP Adsorption material (MBOP) was synthesized using template method. Chitosan (27 g) was dissolved in 900 mL of 5% acetic acid with constant stirring on mechanical stirrer for 1h. 84.78 g of aluminium nitrate (Al(NO3)3.9H2O) was dissolved in 100 mL of distilled water in a beaker and 97.89 g of ferric nitrate (Fe(NO3)3.9H2O) was dissolved in 100 mL of distilled water in another beaker. Solutions of aluminium nitrate and ferric nitrate were added simultaneously to the chitosan gel under continuous stirring for 180 min. The resulted Al-Fe-chitosan gel slurry was added drop by drop to NH4OH solution (50% v/v), under vigorous stirring, using a syringe pump. The gel macro spheres were allowed to stabilize in NH4OH solution for 60 min. The beads were separated from the NH4OH solution and washed using deionised water and dried at 70 oC for 24 h in oven. The dried beads were calcined at 450 oC for 6 h in muffle furnace. 6
Finally, the calcined product was subjected to multiple washings with deionised water and dried at 80 oC [19]. The mechanism of MBOP (Fig. S1) formation is shown in supplementary material S1. 2.3. Characterization of MBOP prepared by template method using chitosan Characterisation techniques used for MBOP prepared by template method using chitosan was given in supplementary material S1. 2.4. Fixed bed column study Experiments were conducted in continuous-flow system to evaluate empty bed contact time (EBCT), breakthrough time and breakthrough capacity for the reduction of As(III) concentration from aqueous solution on fresh MBOP, regenerated MBOP, commercial activated alumina and activated carbon in a fixed bed column reactor. In a column of 1.0 cm of internal diameter and 25 cm total height, the flow was controlled at the feed reservoir from the bottom side using a peristaltic pump. The column was packed with the adsorbent and glass wool at both the ends to prevent the flow of adsorbent particles into the outlet. The column was then fed continuously with As(III) containing water of 1.0 mg/L concentration at desired volumetric flow rate (2.0 ml/min. & 5.0 ml/min.) using peristaltic pump (Electro Lab, Mumbai, India) from bottom side of the tube (upflow) for uniform distribution, to avoid channeling, fouling of adsorbent and increasing the time of contact. The effluent was collected at the top at definite interval of time and examined for As(III) concentration. The schematic representation of the experimental setup and study was illustrated in Fig.1. Exhausted bed was regenerated insitu using optimal regeneration media and regeneration conditions as done in batch studies [19]. For the regenerated adsorbent, same procedure and conditions were adopted as the fresh adsorbent column study and the empty bed contact time (EBCT), breakthrough point, breakthrough capacity and saturation capacity in fresh and regenerated adsorbents were determined. For 7
comparison with fresh MBOP, commercial activated alumina and commercial activated carbon were used at a flow rate of 5.0 ml/min. 2.5. Logit method The fixed bed column was designed by Logit method [20, 21]. In this method the curve is plotted between ln [Co/(Co-C)] verses t. The Logit equation can be written as Co
ln (Co−C) = −
(KNX) 𝑉
+ K Co t
(1)
where C is the concentration of solute (mg/L) at any time t, Co is the initial concentration of solute (mg/L), V is the approach velocity of flow (cm/h), K adsorption rate constant (L/mg h), X is the depth of bed and N is the adsorption capacity coefficient (mg/L). Logit method is applied to experimental data of fresh MBOP and regenerated MBOP. 2.6. Solidification and stabilization of arsenic waste Many researchers reported various methods to incorporate arsenic bearing waste into polymeric matrices [22], concrete [23], soils [24], in landfills [25, 26], and in bricks [27] to dispose safely. Toxicity characteristic leaching procedure (TCLP) and semi dynamic tests were conducted to know the safe disposal of arsenic loaded adsorbent in nature. 2.6.1. Toxicity characteristic leaching procedure (TCLP) test The purpose of this test is to know whether the exhausted MBOP is hazardous or nonhazardous which helps for disposal consideration. As per USEPA 1992, when the leachate concentration of arsenic waste is less than 5.0 mg/L, the waste is classified as non-hazardous and suitable for disposal in a municipal solid waste landfill and if more than 5.0 mg/L then waste is suitable for disposal in a hazardous waste landfill. In the TCLP study, the binder material (cement) and fine aggregate (sand) were mixed with arsenic loaded MBOP solid waste in a definite ratio as cement: fine aggregates: arsenic
8
loaded MBOP solid waste (01:02:01, 01:02:05 and 01:02:10). Three different solidified waste matrices were prepared by mixing different compositions of binder materials. Water was added in a proportion to make slurry of these binders and arsenic rich waste materials. Complete preparation of solid matrices [28] for the test is mentioned in the supplementary material S1. 2.6.2. Semi dynamic test Semi-dynamic leach tests are generally used to determine the leachability of contaminants from monolithic solidified waste forms. The term ‘semi-dynamic’ means that the leachate is replaced periodically after intervals of static leaching. In this study, the stabilized/solidified waste samples were leached in a closed vessel without agitation using distilled water at a leachant to solid mass ratio of 10:1 which help to minimize leachant composition changes and extract more species for analysis. Leachate was collected after a fixed duration of 2 h, 7 h, 24 h, 48 h, 72 h, 96 h, 120 h, 456 h, 1128 h and 2160 h (90days) as per ANSI/ANS 16.1 standard [28]. 3. Results and discussion 3.1. Characterization of MBOP The X-ray diffraction analysis of fresh MBOP does not showed any peaks relevant to chitosan, as it was eliminated in the calcination step at 450 oC, whereas peaks at 2θ = 31.0 and 36.0 indicates the presence of γ-alumina phase. No specific crystalline iron oxide peaks were observed in XRD. The absence of iron oxide peaks was attributed to the higher dispersion of supported iron oxide phase. Further, the XRD pattern remained almost the same after As(III) adsorption over MBOP, indicating the structural integrity (Fig. S2a and b). It has been reported that the adsorption of arsenic on amorphous metal oxide is through the formation of inner sphere surface complexes which are mainly attached as bidentate linkages with some monodentate linkages [19, 29]. The FTIR spectrum of fresh MBOP (Fig. S2c) indicates the presence of 9
predominant peaks at 3512.38 cm-1 and 3321.24 cm-1 (-OH and -NH stretching vibrations), 2900.67 cm-1 and 2342.24 cm-1 (-CH stretching vibration), 1648.20 cm-1 (-NH bending vibration in -NH2), 1378.91cm-1 (-NH deformation vibration in -NH2). The low intensity band at 1062.40 cm-1 is ascribed to Fe–OH structural vibration. The band between 400 cm-1 and 450 cm-1 could be due to the superposition of the characteristic stretching bands of aluminum oxide. The bands observed between 1100 cm-1 and 500 cm-1 could be characteristic vibrations of aluminum oxide. FTIR spectrum of As(III) loaded MBOP is shown in (Fig. S2d). The predominant peaks due to OH and -NH stretching vibrations of hydroxyl and amine groups sharpen and shifted to 3640cm-1 and 3063cm-1 indicating interaction of arsenic at hydroxyl and amine sight through hydrogen bonding. FTIR peaks corresponding of Fe-OH structural vibration and stretching bands of aluminium oxide becomes broad and overlapped due to arsenic adsorption. The surface morphology of MBOP before and after As(III) adsorption was studied by SEM (Fig. S2e and f) analysis and observed porous in nature which implies that the adsorbent may have reasonable high surface area and adsorption capacity. The large pores are developed by the elimination of chitosan template during calcination step of synthesis. Pore size of MBOP is much larger than the radius of arsenite (0.58Ao) which may facilitate dispersion of arsenite in the inner layer of granular MBOP. It was found that after adsorption of arsenic, the surface morphology of MBOP not changed much, suggesting physical adsorption of arsenic occurred. From the XRD, SEM and FTIR analysis of MBOP, it is observed that no variation in the core structural properties of MBOP before and after the adsorption of As(III), which reveals that the MBOP retains its stability. The physical properties like BET surface area, average pore size etc., given in Table 1. The chemical composition of MBOP was analyzed by Wave length Dispersive X-Ray Fluorescence Spectrophotometer (WDXRFS) and the percentage of Fe, Al, O, Ca, P, Mg, Mn 10
and S are shown in Table 1. The special feature of MBOP is that it has super paramagnetic property. The saturation magnetization value (18.78 emu/g) achieved with MBOP was sufficient for magnetic separation (Table 1; Fig. 2) which is more than the saturation value of 16.3 emu/g for magnetic separation with a conventional magnet [30]. Hence MBOP can be easily isolated from solution by application of external magnetic bar. MBOP is attracted by the magnet before adsorption of As(III) in dry condition and after adsorption of As(III) in water as shown in Fig.2. This further confirms that MBOP has magnetic nature after adsorption of As(III) in wet condition. In the XPS spectra, Fe 2p electron binding energies are shown in Fig.3. The spectra indicates the presence of carbon, oxygen, iron and alumina on the surface of MBOP as indicated by the peaks corresponding to the binding energies at 288.2eV (C1s), 530eV (O1s), 724.5eV (Fe 2 p1/2) and 710.4eV (Fe 2p3/2), 74.2eV (Al 2p) (Fig.3 a-d). It is indicated that the relative intensity of the Fe 2p1/2 and Fe 2p3/2 peak positions (724.5eV and 710.4eV) and the shape are the characteristic presence of Fe(III). These observations confirm the presence of Fe2O3 phase of iron and Al2O3 phase of aluminium and some organic/carbonaceous chitosan residue in MBOP. 3.2. Fixed bed column study 3.2.1. Column study on fresh MBOP at flow rate of 2.0 ml/min. and 5.0 ml/min. To investigate the influence of flow rate chosen at 2.0 ml/min. and 5.0 ml/min., MBOP was used in continuous flow in column of 1.0 cm diameter and 18.0 cm media height. The schematic diagram of experimental column study is shown in Fig. 1. Comparison of empty bed contact time (EBCT), breakthrough time and breakthrough capacity of MBOP were conducted at flow rates of 2.0 ml/min. & 5.0 ml/min. and is shown in Table 2. EBCT is a significant parameter which determines the residence time when the solution is in contact with the adsorbent and the removal efficiency is strongly depends on the contact time between the adsorbate (arsenic) and the adsorbent coated with iron hydroxide [31]. From experiments, at flow rate of 11
5.0 ml/min. and 2.0 ml/min., it was observed that EBCT was 3.0 min. and 7.1 min.; breakthrough time was 26.15 h and 72 h; volume of water treated was 7.845 liters and 8.64 liters and breakthrough capacity was 0.436 mg/g and 0.477 mg/g respectively. Due to decrease of flow rate, increase in EBCT, breakthrough time, volume of water treated and breakthrough capacity were observed and the percentages were 136.66, 175.33, 10.20 and 9.40 respectively (Table 2). This trend may be due to the availability of more adsorption sites to capture arsenic ions around or within MBOP, which results the more diffusion of solute into the pores of adsorbent. An increase flow rate reduces the volume of water treated until breakthrough and this is due to the decrease in the residence time of the As(III) ions within the bed or this may be because of reduced contact time, which causes a weak distribution of the liquid inside the column that in turn leads to a lower diffusivity of the solute into MBOP indicating that adsorption of As(III) may be slightly depends on diffusion. It is also reported that at higher flow velocities, the film surrounded by adsorbent particle breaks thus reducing the adhesion of adsorbate to the adsorbent particle [12]. MBOP at 2.0 ml/min. flow rate has higher breakthrough time and breakthrough capacity by a factor of 2.75 and 1.1 than 5.0 ml/min flow rate respectively. The shape of the breakthrough curve is affected by fluid viscosity, concentration of solute in feed, pH of adsorbate and bed height. Steep slopes of breakthrough curves in column exhibiting high film transfer coefficients and high internal diffusion [12]. At 5.0 ml/min. flow rate, the breakthrough time curve is very steep compared to 2.0 ml/min. flow rate indicating high film transfer coefficient and high internal diffusion coefficient (Fig.4). Hence the time required to reach breakthrough time at 5.0 ml/min. flow rate is less than 2.0 ml/min. flow rate. As per IS 1172-1993, drinking water requirement is 5.0 liter/capita/day and it was observed that at 5.0 ml/min flow rate, the volume of water treated by single column was 7.845 liters in 26.15 h (Table 2) which is more than 5.0 liters/capita/day and hence in this study, all the experiments were conducted at 5.0 12
ml/min. flow rate. The saturation time and saturation capacity of MBOP was found to be 515 h and 4.67 mg/g respectively at flow rate of 5.0 ml/min. (Table 3). Compared with other adsorbents reported in literature [13 and references there in], MBOP showed higher breakthrough capacity of 0.436 mg/g and 0.477 mg/g at a flow rate of 5.0 ml/min. and 2.0 ml/min. respectively. 3.2.2. Regeneration study Due to regeneration, the replacement of new adsorbent and disposal problem can be reduced considerably. Economic viability of any adsorbent depends on its regeneration and reuse for many cycles of operation. Once the adsorbent exhausted, then adsorbate which is adsorbed must be recovered and then regenerated. Selection of regeneration solution is depending upon the arsenic adsorption mechanism and the nature of adsorbent. During the first cycle of regeneration study, 1% of 1N NaOH was passed through the exhausted MBOB column for 1h at the rate of 5.0 ml/min. in upflow condition and then the column was washed with double distilled water with a flow rate of 5.0 ml/min. till the effluent pH comes to neutral. The regenerated adsorbent was then reused for adsorption of As(III) in the column. The nature of curves for fresh and regenerated MBOP is shown in Fig.5. The regenerated MBOP at 5.0 ml/min. flow rate showed, breakthrough time, saturated time, breakthrough capacity and saturation capacity of 21 h, 314 h (13.08 days), 0.318 mg/g and 2.05 mg/g respectively (Table 3). When compared with fresh MBOP, it was observed that fresh MBOP has higher breakthrough time and breakthrough capacity than regenerated MBOP by a factor of 1.25 and 1.37 respectively (Table 3). Thus the percentage decrease in EBCT, breakthrough time, saturation time, breakthrough capacity and saturation capacity of regenerated MBOP were 6.66, 19.69, 39.03, 27.21 and 56.10 respectively (Table 3) indicating that few adsorption sites were still occupied by As(III) ions even after regeneration of MBOP. 13
3.2.3. Arsenic removal by commercial activated alumina and activated carbon To compare the MBOP with the commercial activated alumina and commercial activated carbon, column experiments for activated alumina and activated carbon were conducted at the flow rate of 5.0 ml/min. The surface area (m2/g), total pore volume (cm3/g) and average pore diameter (Ao) of bare alumina was 189.12, 0.4691 and 98.33 respectively. Pore diameter of bare activated alumina is more than the diameter of arsenite (0.58 Ao) which helps to insert arsenite into activated alumina. Column study upto breakthrough capacity on commercial activated alumina and commercial activated carbon is shown in Fig.6. In commercial activated alumina column study, EBCT, breakthrough time, breakthrough capacity and saturation capacity were found to be 2.42 min., 5.0 h, 0.126 mg/g and 0.35 mg/g respectively whereas on commercial activated carbon column study the results were observed as 2.98 min., 3.75 h, 0.109 mg/g and 0.29 mg/g respectively (Table 4). The saturation time on activated alumina and activated carbon was found to be 55.45 h and 36.56 h respectively. 3.2.4. Comparison of fresh MBOP with commercial activated alumina and activated carbon From the Table 4, it is observed that at 5.0 ml/min. flow rate, percentage increase in EBCT, breakthrough time, breakthrough capacity and saturation capacity of fresh MBOP were 23.97, 423, 246 and 1234 respectively when compared with commercial activated alumina. Similarly on commercial activated carbon were also found to be higher by 0.67%, 596%, 300% and 1510% respectively. Breakthrough capacity of fresh MBOP was observed much higher by a factor of 3.46 and 4.0 compared to commercial activated alumina and commercial activated carbon respectively. These observations reveals that MBOP had significant enhancement of adsorption capacity for As(III) removal than commercial activated alumina and commercial activated carbon in water. 3.2.5. Logit method
14
From Logit method (Fig.7), the values of K and N on fresh MBOP were found to be 0.2076 (L/mg h) and 1015 (mg/L) respectively. These K and N values might be used for the design of adsorption column. After regeneration of MBOP with 1N NaOH, the value of K and N were obtained as 0.2032 (L/mg h) and 756 (mg/L) respectively. This shows that the adsorption capacity coefficient (N) was reduced by 25.51% due to regeneration of first cycle, which is nearly same as the percentage decrease of 27.21 for the regenerated MBOP (Table 3). 3.2.6. Effluent water quality parameter To understand the effect of using MBOP to remove As(III) from drinking water, water quality parameters of effluent after column adsorption were determined. From Table 5, it is observed that pH of the treated water remained within permissible limit and was closed to the pH of the water before treatment, suggesting that no post treatment is required. After treatment, As(III) concentration was less than permissible limit of 10 µg/L [11]. It is also observed that the conductivity was reduced significantly from 306 µS/cm to 214 µS/cm, indicating that there is significant removal of dissolved solids. Aluminum (Al3+) concentration was below the permissible limit of BIS 10500-2012, indicating that the MBOP can be used for treatment of As(III) in groundwater. All the parameters are within in the prescribed standard limit [11]. 4. Solidification and stabilization of arsenic waste 4.1. Toxicity characteristic leaching procedure (TCLP) test From the TCLP test as per the procedure mentioned in the supplementary material S1, it is observed that the maximum As(III) concentration in leachate was 0.0167 mg/L, 0.0186 mg/L and 0.0722 mg/L for the mix of cement: fine aggregates: arsenic loaded MBOP solid waste ratios of 01:02:01, 01:02:05 and 01:02:10 respectively (Fig.8). The leachates from all the mix proportions showed much less than 1.0 mg/L as per the limit [32]. Hence the above said mixed proportions of combination are safe for disposal in secured landfill. 15
4.2. Semi dynamic test Semi dynamic test was carried out on exhausted As(III) loaded MBOP before disposal. From Fig.9, it is observed that the maximum concentration of As(III) in leachate was 0.813 mg/L, 0.915 mg/L and 0.989 mg/L for the mix proportion of 01:02:01, 01:02:05 and 01:02:10 after 72 h, 72 h and 96 h respectively which is less than the permissible limit of 5.0 mg/L [3235]. This shows that all mix proportions are safe for disposal in landfill. 5. Conclusion In the present study, removal of As(III) from groundwater was achieved using MBOP which is cost effective and can be developed with the help of locally available materials. The most significant feature of MBOP is that it has magnetic property before and after adsorption of As(III) and is easy to separate from the effluent using magnet. The breakthrough time of MBOP at a flow rate of 2.0 ml/min. and 5.0 ml/min. was observed to be 72 h and 26.15 h respectively. The percent increase of breakthrough capacity was observed 9.4 as the flow rate decreased from 5.0 ml/min. to 2.0 ml/min. Fresh MBOP has higher breakthrough time and capacity than regenerated MBOP by a factor of 1.25 and 1.37 respectively. In Logit method, the values of K (adsorption rate constant) and N (adsorption capacity coefficient) were obtained as 0.2076 (L/mg h) and 1015 (mg/L) for 5.0 ml/min. flow rate. These K and N values might be used for the design of adsorption column. Breakthrough capacity of fresh MBOP was higher by a factor of 3.46 and 4.0 than the commercial activated alumina and commercial activated carbon respectively; indicating MBOP is much better adsorbent. The effluent water quality parameters after adsorption was within the permissible limit of drinking water standards BIS 10500-2012; indicating that the MBOP can be used for treatment of As(III) from groundwater. TCLP and semi dynamic tests were performed on stabilized MBOP which are proving to be non-hazardous mode of disposal consideration. Concentration of As(III) in leachates from all 16
the mix proportions (01:02:01, 01:02:05 and 01:02:10 for cement: fine aggregates: arsenic loaded waste) showed much less than 1.0 mg/L as per the limit hence safe for disposal. In semi dynamic test, the As(III) concentration in leachates were less than the permissible limit (5.0 mg/L) for all mix proportions hence it is safe for disposal in secured landfill. Acknowledgement We thank Director of CSIR- National Environmental Research Institute (NEERI) Nagpur for providing research facilities. Dr. M.P. Reddy thanks CSIR, New Delhi in granting the Pool Scientist award.
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[30] Z.Y. Ma, Y.P. Guan, H.Z. Liu, Synthesis and characterization of micron-sized monodisperse supermagnetic polymer particles with amino groups, J. Polym. Sci. Pol. Chem. 43 (2005) 3433-3439. [31] I.A. Katsoyiannis, A.I. Zouboulis, Removal of arsenic from contaminated water sources by sorption onto iron-oxide-coated polymeric materials, Water Res. 36 (2002) 5141-5155. [32] B. Sengupta, D.B. Boralkar, T. Chatterjee, Identification/characterisation of hazardous wastes, in: B. Sengupta, S.P. Chakrabarthi, N.K. Varma, J.C. Babu (Eds.), Management of hazardous wastes: Guideline for proper functioning and upkeep of disposal sites, NISCIRCSIR, New Delhi, 2005, pp. 2-6. [33] Hazardous Waste (Management, Handling & Transboundary Movement) Rules, CPCB, New Delhi, India. http://www.cpcb.nic.in/divisionsofheadoffice/hwmd/mhtrules2008.pdf, 2008 (accessed 05.09.16). [34] T.M. Clancy, F.K. Hayes, L. Raskin, Arsenic waste management: A critical review of testing and disposal of arsenic-bearing solid wastes generated during arsenic removal from drinking water, Environ. Sci. Technol. 47 (2013) 1079 -1081. [35] U.S. Environmental Protection Agency, Hazardous waste test methods/SW-846 test method
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21
List of figures Figure number Fig. 1.
Figure caption Schematic diagram of MBOP column study for the removal of As(III) from water
Fig. 2.
VSM Magnetization curve of MBOP (insight MBOP attracted by magnet: (a) Before adsorption (dry condition) (b) After adsorption (in water)).
Fig. 3.
XPS spectrum of
Fig. 4.
a) Carbon 1s b) Oxygen 1s c) Fe2O3 - Fe 2p3/2 & 2p1/2 d) Al2O3 - Al 2p Column study on fresh MBOP upto breakthrough time at flow rate of 2.0 & 5.0ml/min.
Fig. 5.
Column study on fresh MBOP and regenerated MBOP with 1% of 1N NaOH.
Fig. 6.
Column study on commercial activated alumina and commercial activated carbon upto breakthrough capacity.
Fig. 7.
Linearized form of Logit model.
Fig. 8.
TCLP on exhausted MBOP.
Fig. 9.
Semi dynamic test for leaching of As(III) on exhausted MBOP.
22
List of tables Table number Table 1
Table caption Physical property, chemical composition and magnetic property of MBOP.
Table 2
Comparison of EBCT, breakthrough time and breakthrough capacity of MBOP at flow rate of 2.0 ml/min. & 5.0 ml/min.
Table 3
Comparison of fresh MBOP and regenerated MBOP with 1% of 1N NaOH at flow rate of 5.0 ml/min.
Table 4
Comparison of breakthrough and saturation capacity of commercial activated carbon, commercial activated alumina with fresh MBOP.
Table 5
Physico-chemical properties of field water before and after treatment by MBOP.
23
Table 1 Physical property, chemical composition and magnetic property of MBOP. Physical property (MBOP) BET surface area (m2/g)
123.28
Average pore size (Ao)
61.59
Total pore volume (cm3/g)
0.1732
Average diameter of particle (micron)
230.87
Chemical Composition (%) Fe
42.6
O
34.21
Al
16.69
Ca
0.65
P
0.18
Mg
0.16
Mn
0.07
S
0.02
Magnetic property of MBOP Saturation magnetization value (emu/g)
18.78
Table 2 Comparison of EBCT, breakthrough time and breakthrough capacity of MBOP at flow rate of 2.0 ml/min. & 5.0 ml/min. Flow rate (ml/min.)
EBCT (min.)
Break through time (h)
Vol. of water treated (L)
Breakthrough capacity, qe (mg/g)
5.0
3.0
26.15
7.845
0.436
2.0
7.1
72.0
8.64
0.477
Percentage increase of EBCT (decreasing flow rate from 5.0ml/min. to 2.0ml/min.)
136.66
Percentage increase of breakthroug h time (decreasing flow rate from 5.0ml/min. to 2.0ml/min.)
Percentage increase of volume of treated water (decreasing flow rate from 5.0ml/min. to 2.0ml/min.)
Percentage increase of breakthrough capacity (decreasing flow rate from 5.0ml/min. to 2.0ml/min.)
175.33
10.20
9.40
EBCT= Empty bed contact time
24
Table 3 Comparison of fresh MBOP and regenerated MBOP with 1% of 1NNaOH at flow rate of 5.0 ml/min. Condition
Flow rate EBCT (ml/min.) (min.)
Fresh MBOP
5.0
Regenerated MBOP
5.0
Percentage decrease of EBCT after regeneration
3.0
Breakthrough time (h)
Saturated time (h)
Breakthrough capacity, qb (mg/g)
Saturation capacity, qs (mg/g)
26.15
515
0.436
4.67
2.8
21.0
314
0.318
2.05
--
6.66
--
--
--
--
Percentage decrease of breakthrough time after regeneration
--
--
19.69
--
--
Percentage decrease of saturation time after regeneration
--
Percentage decrease of breakthrough capacity after regeneration
--
Percentage decrease of saturation capacity after regeneration
--
--
--
--
39.03
----
--
--
--
27.21 --
--
--
--
--
56.10
25
Table 4 Comparison of breakthrough and saturation capacity of commercial activated carbon, commercial activated alumina with fresh MBOP. Adsorbent
Flow rate (ml/ min.)
EBCT (min.)
Break through time (h)
Break through capacity, qe (mg g-1)
Saturation capacity, qS (mg/g)
Commercial activated alumina
5.0
2.42
5.0
0.126
0.35
Commercial activated carbon
5.0
2.98
3.75
0.109
Fresh MBOP
5.0
3.0
26.15
0.436
Percentage increase of EBCT of fresh MBOP compared with
Percentage increase of break through capacity of fresh MBOP compared with
Percentage increase of saturation capacity of fresh MBOP compared with
23.97
Percentage increase of break through time of fresh MBOP compared with 423
246
1234
0.29
0.67
596
300
1510
4.67
--
--
--
--
Table 5 Physico-chemical properties of field water before and after treatment by MBOP. Parameter
Unit
Before treatment
After treatment
pH
-
7.23
6.89
Desirable limits as per Indian Drinking Water Standard ( BIS :10500-2012)* 6.5-8.5
Colour
-
colourless
colourless
colourless
Odour
-
odourless
odourless
Unobjectionable
mg/L
129
118
200
Total hardness
CaCO3
109
102
200
Conductivity
µS/cm
306
214
--
Chloride
mg/L
154
29
250
Sulphate
mg/L
21
17
200
Nitrate
mg/L
1.514
1.213
45
TDS
mg/L
397
149
500
2+
mg/L
42
36
75
Mg
mg/L
18.2
13.56
30
Fe3+
mg/L
0.216
0.241
0.3
As(III)
µg/l
992.6
9.81
10
Aluminium
mg/L
<0.002
<0.002
<0.003
Alkalinity
Ca
2+
26
*Bureau of Indian standard specifications for drinking water (IS:10500-2012) second Revision.
27
Fig. 1. Schematic diagram of MBOP column study for the removal of As(III) from water
Fig. 2. VSM Magnetization curve of MBOP (insight MBOP attracted by magnet (a). Before adsorption (dry condition) (b) After adsorption (in water)).
1
(a)
(b)
(c)
Fig. 3. XPS spectrum of
(d)
a) Carbon 1s
b) Oxygen 1s
c) Fe2O3 - Fe 2p3/2 & 2p1/2
d) Al2O3 - Al 2p
2
0.012 Flow rate : 5.0 ml/min Flow rate : 2.0 ml/min
Ct/Co
0.01 0.008 0.006 0.004 0.002 0 0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
Time (h) Fig. 4. Column study on fresh MBOP upto breakthrough time at flow rate of 2.0 & 5.0ml/min.
1.2
Fresh MBOP at 5.0 ml/min Regenerated MBOP with 1%NaOH
1
Ct/Co
0.8 0.6 0.4
0.2 0 0
50
100
150
200
250
300
350
400
450
500
550
Time (h) Fig. 5. Column study on fresh MBOP and regenerated MBOP with 1% of 1N NaOH.
3
0.016 Commercial activated alumina Commercial activated carbon
0.014 0.012
Ct/Co
0.01 0.008 0.006 0.004 0.002 0 0
1
2
3
4
5
6
Time (h) Fig. 6. Column study on commercial activated alumina and commercial activated carbon upto breakthrough capacity. 0 Regenerated MBOP Fresh MBOP
-1
Ln Ct/( Co- Ct)
-2
y = 0.2032x - 7.3355 R² = 0.8675
-3 -4 -5
y = 0.2066x - 9.9955 R² = 0.9231
-6 -7 0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
Time (h) Fig. 7. Linearized form of Logit model.
4
Concentration of As(III) in leachate (mg/L)
0.08 0.0722 0.07 0.06 0.05 0.04 0.03 0.0186
0.02
0.0167
0.01 0 1:02:01
1:02:05
1:02:10
Cement: Sand : Waste material (MBOP) Fig. 8. TCLP on exhausted MBOP.
1.2
As(III) conecntration in Leachate (mg/L)
01:2:01 mix proportion 01:02:05 mix proportion
1
01:02:10 mix proportion 0.8 0.6 0.4 0.2 0
Time in days Fig. 9. Semi dynamic test for leaching of As(III) on exhausted MBOP.
5