Nitrate Removal by Chemical Reduction using Nano Zero-Valent Iron in a CO 2 -bubbled Recirculated System

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1 Nitrate Removal by Chemical Reduction using Nano Zero-Valent Iron in a CO 2 -bubbled Recirculated System Erickson C. Roque, Asst. Professor Department of Chemical Engineering Adamson University, Manila Dr. Ma. Lourdes P. Dalida Professor Department of Chemical Engineering University of the Philippines-Diliman Dr. Chih-Hsiang Liao Professor Department of Environment and Resources Management Director, Innovation and Incubation Center Chia Nan University of Pharmacy and Science Taiwan

2 Nitrate primary form of nitrogen beneath agricultural lands It is soluble in water and can easily pass through the soil and to the groundwater table due to its high mobility can persist in ground water for decades and accumulate to high levels as more nitrogen is applied to the land surface every year. Introduction Unfortunately, shallow groundwater is susceptible to contamination by chemicals derived from the land surface.

3 What are the concerns about nitrate in ground water? Human health Livestock health Aquatic Life Surface Water Note the chocolate brown color of methemoglobinemia. Tube 1 and tube 2 have a methemoglobin concentration of 70%; tube 3, a concentration of 20%; and tube 4, a normal concentration. Although nitrate generally is not an adult public-health threat, ingestion in drinking water by infants can cause low oxygen levels in the blood, a potentially fatal condition known as methemoglobinemiaor "blue baby" disorder. Hemoglobin( Fe + ( cancombinew / 2 2 ) ( can' tcombinewitho 2 U.S. Environmental Protection Agency (EPA) has established a drinking-water standard of 10 milligrams per liter (mg/l NO 3 -N) nitrate as nitrogen (USEPA, 1995). O NO Methaemoglobin ) 2 )

4 What are the concerns about nitrate in ground water? Human health Livestock health Aquatic Life Surface Water Although nitrate generally is not an adult public-health threat, ingestion in drinking water by infants can cause low oxygen levels in the blood, a potentially fatal condition known as methemoglobinemiaor "blue baby" disorder. U.S. Environmental Protection Agency (EPA) has established a drinking-water standard of 10 milligrams per liter (mg/l NO 3 -N) nitrate as nitrogen (USEPA, 1995). Note the chocolate brown color of methemoglobinemia. Tube 1 and tube 2 have a methemoglobin concentration of 70%; tube 3, a concentration of 20%; and tube 4, a normal concentration. Health Issues

5 Aquatic Life Nitrate does not appear to be acutely toxic to adult fish except at extremely high concentrations where mortality is due to salinity effects (USEPA, 1977). However, available research indicates that nitrate concentrations lower than the drinking water standard cause substantial egg and fry mortality in some salmonid fish species (Kincheloe et. al., 1979). Tadpoles exposed to nitrate at the drinking water standard show decreased appetite, sluggishness and paralysis prior to death (Hecnar, 1995). Surface Water Ground water can carry nitrogen (in the form of nitrate) into surface water bodies through recharge and spring discharges. Plant-available nitrogen and phosphorus in surface water promotes excessive growth of weeds and algae in a process called "eutrophication." Nitrate supplied by ground water discharge may cause increases in rooted aquatic plants (Lillie and Barko, 1990, Rodgers, et. al., 1995). Livestock Health According to research conducted on dairy cattle (Crowley et. al., 1974), nitratenitrogen in drinking water at levels under 10 mg/l is safe for animals. Between mg/l nitrate-nitrogen, water is safe for livestock unless their feed has high nitrate levels. Problems can occur between mg/l nitrate-nitrogen if feed contains more than 1,000 ppm. If well water is between mg/l nitratenitrogen, feed should be low in nitrate, well balanced and fortified with vitamin A. At levels between mg/l nitratenitrogen in water, studies report decreased appetite (Mahler, et. al, 1990, Taylor, et. al., 1990).

6 Current technologies In dealing with the nitrate problem in subsurface waters, there are two options for achieving safe nitrate levels. non-treatment techniques blending drinking waters or changing water sources. treatment processes ion exchange, reverse osmosis, biological denitrification and chemical reduction

7 Zero-valent metal reduction is a process in which a metal such as iron, platinum, or other zerovalent metals are used to refine polluted waters. These metals are placed in the flow of water, where they begin oxidizing, causing other chain reactions to purify the water. Chemical Reduction

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9 Zero-Valent Iron (ZVI), Feo

10 Nitrate Reduction by ZVI Fe isoxidizedtofe NO isreducedtonh orn gas NO + 4Fe + 10H 4Fe + NH + 3H O NO + 5Fe + 12H 5Fe + N + 6HO

11 Why CO 2 bubbling? Nitrate removal is enhanced by lowering the ph (Cheng et al, 1997; Huang et al., 1998; Zawaideh and Zhang, 1998; Alowitz and Scherer, 2002; Huang and Xhang, 2004) System with ph control by addition of acidic solution is better than adding buffer (Zawaideh and Zhang, 1998; Choe et al., 2000; Alowitz and Scherer, 2002; Su and Puls, 2007). Addition of acidic solution like sulfuric acid (Huang, et al., 1998), hydrochloric acid and acetic acid (Cheng et al., 1997; Su and Puls, 2004) maybe effective in lowering the ph but it also introduces species that has adverse impact on the quality of the drinking water. An alternative procedure to lower the ph is through the use of carbon dioxide bubbling(ruangchainikom et al, 2006; Li et al, 2007) since it can create an acidic environment (Hsu et al., 2004) by supplying the system with hydrogen ion.

12 Objective The study aimed to remove nitrate by chemical reduction using nano zero-valent iron (nzvi) with CO 2 bubbling in a recirculated system. Specifically, it aimed to: Determine the effect of CO 2 bubbling rate to ph, DO and ORP of pure water Determine the effect of CO 2 bubbling to ph, DO and ORP of H 2 O/nZVI H 2 O/nZVI/NO - 3 Determine the nitrate removal efficiency of nzvi/co 2 system in a nitrate spiked water Determine the effect of initial nitrate concentration in terms of nitrate removal efficiency Determine the effect of recirculation rate in in terms of nitrate removal efficiency

13 Experimental Methods

14 NZVI Synthesis 0.25 M NaBH rpm (Pump) Feedingrate 10 ml/min /min M FeCl 3 6H 2 O

15 NZVI Synthesis Use of strong reducing agent NaBH 4 to reduce ferric ion to NZVI: Fe(H2O) + 3BH4 +3H2O Fe B(OH) +10.5H 3 2

16 Experimental Setup Ion Chromatography (IC) Residual nitrate Nitrite formation UV-Spectrophotometer Ammonium formation Ferrous AAS Fe total in solution

17 Results and Discussions I Effect of CO 2 bubbling on ph, DO and ORP of a) pureh 2 O b) Fe o /H 2 O c) Fe o /H 2 O/NO - 3 II Nitrate removal Efficiency III Effect of Initial Nitrate Concentration IV Effect of Recirculation rate

18 CO 2 /H 2 O System DO initially increase then decrease DO is purged from bottom of the reactor to the top where the DO probe is located The higher the CO 2 bubbling rate, the faster the DO is stripped

19 CO 2 /H 2 O System Bubbling the reactor system with CO 2 resulted in ph lowering

20 Effect of CO 2 bubbling on Pure Water Statistical treatment of data showed there is no significant difference in terms of ph lowering and DO stripping among the bubbling rates used any CO 2 bubbling rate can be chosen

21 Fe o /CO 2 /H 2 O System [0.25 g/l nzvi, 200 ml/min CO2 bubbling rate, 200 ml/min recirculation rate] DO is stripped and the system remained anoxic ph decreased then increase The ORP decreased up to -455 mv, The negative ORP indicated the system is a reducing environment

22 Low ph favors formation of Fe +2 E-pH diagram of Fe in the presence of water

23 Nitrate Removal by nzvi Thermodynamic Criterion E o << 0 for reaction to occur or G << 0

24 Fe o /CO 2 /NO 3- System [80 mg/l NO 3-, 0.25 g/l nzvi, 200 ml/min CO 2 bubbling rate, 200 ml/min recirculation rate]

25 Fe o /CO 2 /NO 3- System Around 85% nitrate removal for [NO 3- ] o = 80 mg/l concentration in 60 minutes with the reaction occurring fast for the first twenty minutes (0.25 g/l nzvi, 200 ml/min recirculation rate, 200 ml/min CO 2 bubbling rate) Ammonium dominated the reaction product with no nitrite formation observed Fe +2 determined is lower than the theoretically produced amount of nitrate reduced probably due to formation of hydroxide of iron

26 Effect of Initial [NO 3- ] 200 ml/min bubbling and recirculation rates Around 75% removal for [NO 3- ] o = 120 mg/l in 60 min Around 85% removal for [NO 3- ] o = 80 mg/l in 60 min Around 98% in just 55 minutes for [NO 3- ] o= 50 mg/l The higher the initial nitrate concentration, the higher the residual nitrate

27 Effect of Initial [NO 3- ] 1000 ml/min recirculation rate and 200 ml/min bubbling rate Around 74% removal for [NO 3- ] o = 120 mg/l in 60 min Around 85% removal for [NO 3- ] o = 80 mg/l in 60 min Around 98% in just 50 minutes for [NO 3- ] o = 50 mg/l Complete removal for [NO 3- ] o = 50 mg/l Residual nitrate is below the 45 mg/l MCL for [NO 3- ] o of 80 to 120 mg/l

28 Effect of Recirculation Rate (RR) At the same nzvi loading and bubbling rates, removal efficiency is the same for 200 ml/min and 1000 ml/min recirculation rates in 60 minutes Faster initial reaction rate at higher recirculation for moderately high to high initial nitrate concentration 53%and 38%removal in 10 min at 1000 ml/min and 200 ml/min recirculation rates, respectively for [NO 3- ] o = 120 mg/l 65%and 57%removal in 10 min for 1000 ml/min and 200 ml/min recirculation rates, respectively for [NO 3- ] o = 80 mg/l Not significant at lower initial nitrate concentration 73%and 74%removal in 10 min at 200 ml/min and 1000 ml/min recirculation rates, respectively for [NO 3- ] o = 50 mg/l

29 Conclusions Any bubbling rate can be chosen with regards to the DO removal and ph lowering of pure water The 200 ml/min CO 2 bubbling rate is sufficient to lower the ph, reduce the DO and produce a highly reducing environment for the Fe o /H 2 O system suitable for nitrate removal by chemical reduction. Fe o /CO 2 system can effectively remove nitrate by chemical reduction The higher the initial nitrate concentration, the higher the residual The residual nitrate is below the MCL for initial nitrate concentration of up to 120 mg/l Faster initial reaction rate at higher recirculation rate and has no effect on the final conversion No nitrite formation is observed while ammonium is the dominant reaction product

30 Recommendations Ammonium, as well as ferrous formed in solution, require post treatment Air aeration in a fluidized sand bed Ammonium will be stripped Ferrous will precipitate Another option is to modify the pathway to lower the formation of ammonium and shift towards nitrogen gas

31 ACKNOWLEDGEMENTS Taiwan National Science Council (NSC) Project No.: NSC E MY3 Chia Nan University of Pharmacy and Science President Gloria Macapagal- Arroyo Science and Engineering Graduate Scholarship (PGMASEGS) University of the Philippines-Diliman Adamson University

32 Thank You!

33 Questions???