DSpace at VNU: Investigation of As, Mn and Fe fixation inside the aquifer during groundwater exploitation in the experimental system imitated natural conditions

Environ Geochem Health (2012) 34:349–354 DOI 10.1007/s10653-011-9401-7 ORIGINAL PAPER Investigation of As, Mn and Fe fixation inside the aquifer during groundwater exploitation in the experimental system imitated natural conditions Nguyen Thi Kim Dung • Tran Hong Con Bui Duy Cam • Yumei Kang • Received: 21 March 2011 / Accepted: 13 July 2011 / Published online: August 2011 Ó Springer Science+Business Media B.V 2011 Abstract Water-dissolved oxygen was supplied into anaerobic aquifer , which oxidized Fe(II), Mn(II) and trivalent arsenic and changed them into undissolved solid matter through hydrolysis, precipitation, co-precipitation and adsorption processes The experiment was carried out on the column imitated a bore core of anaerobic aquifer with water phase containing Fe(II), Mn(II), As(III) concentration of 45.12 mg/L, 14.52 mg/L, 219.4 lg/L, respectively and other ions similarly composition in groundwater After days of air supply, concentration of iron reduced to 0.38 mg/L, manganese to 0.4 mg/L, arsenic to 9.8 lg/L (equivalent 99.16% of iron, 97.25% of manganese and 95.53% of arsenic fixed), and for other ions, the concentration changed almost according to general principles Ion phosphate and silicate strongly influenced on arsenic removal but supported iron and N T K Dung (&) Haiphong Private University, 36 Dan Lap Street, Le Chan District, Hai Phong, Vietnam e-mail: dungntk10@gmail.com T H Con Á B D Cam Hanoi University of Science, Vietnam National University, 334 Nguyen Trai Street, Thanh Xuan, Hanoi, Vietnam Y Kang Laboratory of Soil Environmental Science, Faculty of Agriculture, Kochi University, Monobe B200, Nankoku City, Kochi 783-8502, Japan manganese precipitation from water phase Based on the experimental results, new model of groundwater exploitation was proposed Keywords Arsenic Á Exploitation Á Groundwater manganese Á Iron fixation Introduction In recent years, arsenic contamination in groundwater and drinking water in Vietnam has received considerable attention Elevated levels of As were found in groundwater in the upper aquifers in several areas in Red River Delta (Berg et al 2001; Agusa et al 2006, 2009) Residents living in high As-contaminated groundwater area are exposed to As through consumption of rice and groundwater, suggesting potential health risk of As exposure (Agusa et al 2009) Symptoms for chronic exposure to As have not yet observed, but the continuous usage of tube wells might cause health effects of the residents Given high degree of exposure to As in a large area of Red River and Mekong River in Vietnam, investigations on the mechanisms of arsenic releases into groundwater, as well as model for reduction in As in groundwater, are critically important to develop a simple and effective technology for arsenic removal in groundwater and thus reduce health risk due to elevated and chronic exposure 123 350 In the aquifer, under anaerobic conditions, iron and manganese exist as divalent species and arsenic as almost nondissociated trivalent arsenious acid (Con et al 2002; Nriagu 1994; Saha et al 1999) In order to remove iron from underground water, traditional technology used aeration technique to oxidize Fe(II) to Fe(III) and then separated it from water in the form of insoluble Fe(III) For manganese removal, normally use filtration through sand-coated MnO2 (Chang et al 2010) For groundwater contaminated by arsenic, there were many methods and technologies for arsenic treatment, especially since ‘‘largest poisoning in the World’’ at Bangladesh revealed in 1993 (Chang et al 2010; Chakraborti et al 2010) Our recent study has showed that during and after oxidation of Fe(II) to Fe(III), Fe(III) immediately hydrolyzed to form almost insoluble Fe(OH)3 and the iron hydroxide species strongly adsorbed arsenate anions and partly co-precipitated with manganese (Dung et al 2009) We investigated fixation capabilities of iron, manganese and arsenic on equipment imitated natural conditions of the aquifer During the fixation of iron, manganese and arsenic, the expected influencing factors such as phosphate, silicate, NO3-, NH4? and SO42- concentrations were also investigated Experiment result of this study was applied for fixation of iron, manganese, arsenic inside aquifer and reduction in ammonium concentration in exploited water The underground water exploitation model was established based on the idea that underground water after pumped up was saturated by air oxygen Part of the oxygen-saturated water was pumped back to exploited layer to fixation of iron, arsenic and manganese, and other part was filtrated to supply Experiment The experimental system was installed as described in Fig The research column was filled 50-mm layer of weathering gravel in bottom, next was 600-mm layer of sand mixed with 0.001% of As in the form of arsenate, 0.01% of Mn in the form of MnO2 and 0.1% of Fe in the form of Fe(OH)3 (w/w percentage) The main components in water phase are listed in Table Before fixation investigation, the experimental system (Fig 1) was running with circulation of water 123 Environ Geochem Health (2012) 34:349–354 10 (6) (5) (4) (3) (2) (1) Fig Schematic diagram of the research system, Column head, Thermoisolation cover, Layer of sand, MnO2, Fe(OH)3, undissolved As(V) and other components, Weathering gravel layer, Porous membrane, (1)-(6) Sampling valves, Peristaltic pump, Regulation tank, Thermostat, 10 Air supply device Table Main composition of water phase (Berg et al 2001) Component Concentration (M) Ca2? 1.0 10-3 - HCO3 2.4 10-3 - NO3 SO42- 3.0 10-4 5.2 10-4 PO43- 3.0 10-5 Mg2? 6.0 10-5 Digestible organic matter 1.2 10-3 (glucose) phase and air tightening for 50 days in order to create anaerobic condition in inner system similar to condition in natural aquifer The investigation started when air was continually supplied to the regulation tank with a rate of 0.5 L/min Samples were taken daily at fixed time from valve (6) Environ Geochem Health (2012) 34:349–354 351 Table Analysis methods APHA, AWWA, WEF (1995) Parameter Analysis method As AAS-HVG method Fe, Mn F-AAS method NO3-, Phosphate Cadmium reduction method Stannous chloride method Silicate Molybdosilicate method SO42- Methylthymol blue method NH4? Phenate method at the experimental column, and parameters were analyzed triplicate by the methods listed in Table Fig Variation in Fe, Mn, As concentrations, ORP and DO versus air supply time (sampling from valve 6) When air oxygen was supplied into system, dissolved oxygen concentration (DO) increased along with bubbling time and reached near mg/L after 10 days (the system changed into almost aerobic condition) Changing nature of the system from anaerobic to aerobic caused variation in almost all constituents in the system (Fig 2) Together with increasing in DO, ORP of water phase also increased regularly It was inevitable dissolved forms of iron(II) and arsenic(III) from fresh and unstable precipitate species of iron arsenide and sulfide (Dung et al 2010) In the following days, the system was in oxygen-rich condition, iron(II) oxidized into iron(III) This species started to hydrolyzed and precipitated as undissolved Fe(OH)3 That is why iron concentration decreased In this condition, arsenite species also slowly oxidized into arsenate in the form of anions hydoarsenate and started to coprecipitate with iron(III) hydroxide or to adsorb onto surface of iron(III) hydroxide particles So total arsenic concentration in the system also decreased (Dung et al 2009) When system was almost in the aerobic condition, the concentrations of iron as well as arsenic decreased to meet limited concentrations of 0.50 mg/L and 0.010 lg/L, respectively The results of samples collected from valves 1–5 showed the similar law of elements’ concentration variation and transformation but the time to reach aerobic condition was earlier from valves 1–5 In case of arsenic and iron, the variations were different In the beginning hours of oxygen supply (about first day), the concentrations of both elements increased The reason of this phenomenon could be oxidation by DO yielding For manganese(II) ion, its concentration was decreased continuously from beginning to the end The reason could be that slow oxidation of Mn(II) to Mn(IV) by DO in neutral environment formed undissolved MnO2 This process was less influenced Results and discussion Composition of water phase in anaerobic state The composition and main parameters of water phase in anaerobic system (after 50 days air absent running) are analyzed (samples were taken from valve number (6) at the experimental column and result is shown in Table 3) The variation in Fe, Mn and As concentrations under influence of oxygen present Table Composition of water phase in anaerobic state Parameters DO (mg/L) ROP (mV) Fe (mg/L) Mn (mg/L) As (lg/L) NO2(mg/L) NH4? (mg/L) SO42(mg/L) PO43(mg/L) SiO32(mg/L) Value 0.8 -45 45.12 1.45 219.4 1.24 48.20 13.76 0.95 2.82 123 352 Fig Variations in sulfate, phosphate and silicate concentrations Environ Geochem Health (2012) 34:349–354 Fig Variations in NH4?, NO2- and NO3- concentrations by chemical and physicochemical processes of iron and arsenic species in the system The variation in sulfate, phosphate and silicate concentrations For investigation of sulfate, phosphate and silicate variations, samples were taken after interval of days each other The result for 20-day survey is shown in Fig There were different variations in concentrations between ions While concentrations of phosphate and silicate were almost unchanged, concentration of sulfate increased during survey time However, in beginning days, the increase rate was low in comparison with the following time Increasing in sulfate ion in the system was result of oxidation process of sulfide together with arsenide in the precipitate created before in anaerobic period The low increasing rate of sulfate concentration in the system at beginning days could be consequence of competitive oxidation reactions of iron(II), arsenic(III) and other easier oxidation species present in the system The variations in NH4?, NO2-, NO3concentrations When system in anaerobic condition, concentration of nitrate was almost limited to analyze, nitrite was 1.28 mg/L and ammonium was 48.20 mg/L Supplying oxygen from air supplied changed concentration of all those nitrogen formations Ammonium concentration slowly decreased, nitrite concentration decreased to detection limit and nitrate concentration increased (Fig 4) 123 Fig Influence of phosphate concentration on fixation of As, Fe and Mn Influence of phosphate concentration For investigation of influence of phosphate concentration on immobilization of arsenic, iron and manganese, phosphate solution was putted on into the system to meet designed concentration range The samples were collected h each after other, and arsenic, manganese, iron were analyzed Based on the results presented in Fig 5, we can see that increasing phosphate concentration only lightly influenced on dissolved iron and manganese With concentration of 20 mg/L phosphate, concentration of total iron dropped from 0.80 to 0.54 mg/L and manganese from 1.38 to 1.12 mg/L The lightly decreasing concentration of iron and manganese could be the result of precipitation of iron and manganese phosphate in the system For arsenic, this was different Phosphate ion strongly influenced on arsenic immobilization With the concentration of phosphate lower than 10 mg/L, the concentration of arsenic was almost uninfluenced; but when phosphate concentration was higher than 10 mg/L, the adsorptive competition Environ Geochem Health (2012) 34:349–354 353 between phosphate and arsenate ions on solid phase appeared; therefore, concentration of arsenic sharply increased Influence of silicate concentration Investigation of influence of silicate concentration on immobilization of arsenic, iron and manganese was implemented similarly as case of phosphate The result presented in Fig showed that soluble species of iron and manganese in the system were almost uninfluenced by concentration of silicate But for arsenate ion, the situation was similar to phosphate interaction However, the competitive power was weaker than phosphate Those expressed by affected concentration of silicate was higher than phosphate (15 mg/L vs 10 mg/L), and angular coefficient of line segment slope in the graph of silicate was less than phosphate (2.150 vs 5.342) So, in any case, the presence of phosphate or silicate or both with high enough concentration raised difficulties for immobilization of arsenic, iron and manganese in oxygen-rich (aerobic) condition Proposal model of fixation of As, Fe and Mn in the aquifer during groundwater exploitation The aquifer is a water-saturated layer of sand and gravel Horizontal water flow rate in the aquifer is normally 10–15 m per day So the aquifer is underground water resource and also can play as a good water filter Based on our results presented above together with exploitability of the aquifer, we have had idea to bring some stages of groundwater treatment process down to the aquifer These are aeration, iron precipitation, filtration, arsenic and Treatment system/Oxygenation Supply water O2 rich current back Ground water flow direction Groundwater current up Oxidation zone Fit-back well Exploitation well Fig The schema of underground water exploitation manganese treatment stages The oxygenation and sterilization stages are kept on ground The schema of underground water exploitation is described in Fig The production process could be that: Groundwater firstly was pumped up from first tube well to oxygenation basin A portion of oxygen saturation water was pumped back to the aquifer though second tube well Where second well is located in front of first well along to groundwater flow direction Other portion of oxygen-saturated water was used for supply The proportion of supply and fit-back water portions depends on iron concentration in groundwater and oxygen saturation possibility The distance between exploitation and fit-back wells depends on groundwater flow rate and exploitation capacity Based on the result of our study, when iron concentration in water phase C10 mg/L, more than 98% arsenic was remained in solid phase despite total arsenic concentration was up to 0.3 mg/L and the part of it was oxidized from arsenide formation and dissolved into water phase Conclusion Fig Influence of silicate concentration Supplying oxygen in the form of dissolved oxygen in water into anaerobic system imitated natural aquifer oxidized almost Fe(II) into Fe(III), partly Mn(II) into Mn(IV) and arsenite into arsenate Hydrolysis of Fe(III) and Mn(IV) helped co-precipitation and adsorption process of arsenate together with iron hydroxide and manganese dioxide The result of these processes reduced concentration of iron, manganese 123 354 and arsenic in water phase and retained them among sand/gravel layer in the system Fixation of the elements, especially arsenic, influenced by phosphate and silicate concentrations in water phase However, ammonia, nitrite, nitrate and sulfate showed almost no affect Other oxidation processes of sulfide, ammonia even organic mater increased supplied water quality Acknowledgments The authors acknowledge the financial support from the sub-project TRIG A from Hanoi University of Science and Dr Michael Berg, ESTNV Manager & Scientific Advisor Department of Water Resources and Drinking Water to facilitate the implementation process References Agusa, T., Kunito, T., Minh, T B., Trang, P T K., Iwata, H., Viet, P H., et al (2009) Relationship of urinary arsenic metabolites to intake estimates in residents of the Red River Delta, Vietnam Environmental Pollution, 157, 396–403 Agusa, T., Kunito, T., Minh, T B., Trang, P T K., Iwata, H., Viet, P H., et al (2006) Contamination by arsenic and other trace elements to humans in Hanoi, Vietnam Environmental Pollution, 139, 95–106 American Water Works Association (1999) Water quality and treatment—A handbook of community water supplies (5th ed.) New York: McGraw-Hill Publishing Company APHA, AWWA, WEF (1995) Standard methods for the examination of water and wastewater, 19th Edn Washington, DC: APHA 123 Environ Geochem Health (2012) 34:349–354 Berg, M., Con, T H., et al (2001) Arsenic contamination of groundwater and drinking water in Vietnam: A human health threat Environmental Science and Technology, 35, 2621–2626 Chakraborti, D., Rahman, M M., Das, B., Murrill, M., Dey, S., Mukherjee, S C., et al (2010) Status of groundwater arsenic contamination in Bangladesh A 14-year study report Water Research, 44, 5789–5802 Chang, F., Qui, J., Liu, R., Zhao, X., & Lei, P (2010) Practical performance and its efficiency of arsenic removal from groundwater using Fe–Mn binary oxide Journal of Environmental Sciences, 22, 1–6 Con, H T., Hanh, T N., et al (2002) Investigation of arsenic releasing from solid phase into water in the earth’s crust In The proceeding of the 5th international conference on arsenic exposure and health effects, San Diego, CA Dung, N T K., Cam, B D., & Con, T H (2009) Investigation of influence of basic parameters in groundwater on coprecipitation–adsorption of arsenic, manganese and fresh iron(III) hydroxide Journal of Analytical Science, 14, 40–45 (in Vietnamese) Dung, N T K., Cam, B D., Con, T H., & Cuong, L M (2010) Investigation and evaluation of factors influencing on arsenic, manganese and iron releasing into groundwater in experimental system imitated natural anearobic conditions Journal of Chemistry, 8, 390–395 (in Vietnamese) Nriagu, J O (1994) Arsenic in environment Part I: Cycling and characterization New York: Wiley Saha, J C., Diskshit, A K M., & Saha, K C (1999) A review of arsenic poisoning and its effects on human health Critical Review of Environmental Science and Technology, 29, 281–313  ... model of fixation of As, Fe and Mn in the aquifer during groundwater exploitation The aquifer is a water-saturated layer of sand and gravel Horizontal water flow rate in the aquifer is normally... limit and nitrate concentration increased (Fig 4) 123 Fig Influence of phosphate concentration on fixation of As, Fe and Mn Influence of phosphate concentration For investigation of influence of. .. 50-mm layer of weathering gravel in bottom, next was 600-mm layer of sand mixed with 0.001% of As in the form of arsenate, 0.01% of Mn in the form of MnO2 and 0.1% of Fe in the form of Fe( OH)3 (w/w