An anaerobic two-layer permeable reactive biobarrier for the remediation of nitrate-contaminated groundwater

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<ul><li><p>of nitrate-contaminated groun</p><p>She-Jiang Liu*, Zhi-Yuan Zha</p><p>School of Environmental Science &amp; Engineerin</p><p>a r t i c l e i n f o</p><p>Article history:</p><p>duct. Results showed</p><p>mediate, nitrite, could</p><p>necessary in order to</p><p>evaluate performance of its field application.</p><p>td. All rights reserved.</p><p>In the last decade, there has been an explosion of activities</p><p>directed at the development and implementation of a most</p><p>promising remediation technology-permeable reactive barrier</p><p>(PRB) (Bartzas et al., 2006; Basu and Johnson, 2012; Ebert et al.,</p><p>2006; Flury et al., 2009; Ludwig et al., 2009; Mak and Lo, 2011;</p><p>006). A PRB consist-</p><p>e media is placed in</p><p>the subsurface across the flow path of contaminated</p><p>groundwater, which must move through it as it flows, typi-</p><p>cally under its natural gradient, thereby creating a passive</p><p>treatment system. PRB is not a barrier to the groundwater, but</p><p>a barrier to the contaminants (Nooten et al., 2008; Phillips</p><p>* Corresponding author. Tel.: 86 22 27890017; fax: 86 22 27891291.</p><p>Available online at</p><p>.e ls</p><p>wat e r r e s e a r c h x x x ( 2 0 1 3 ) 1e9E-mail address: (S.-J. Liu). 2013 Elsevier L</p><p>1. Introduction Michalsen et al., 2006; Morrison et al., 2ing of permanent or replaceable reactivcolumn were analyzed for nitrate and its major degradation bypro</p><p>that nitrate could be removed more than 94%, and its metabolic inter</p><p>also be biodegraded further in this passive system. Further study isSimulated nitrate-contaminated groundwater (40 mg NO3eN/L, pH 7.0) with 6 mg/L of DO</p><p>content was pumped into this system at a flow rate of 235 mL/d. Samples from the secondReceived 4 March 2013</p><p>Received in revised form</p><p>4 June 2013</p><p>Accepted 16 June 2013</p><p>Available online xxx</p><p>Keywords:</p><p>Nitrate</p><p>Remediation</p><p>Groundwater</p><p>Permeable reactive barrier</p><p>DenitrificationPlease cite this article in press as: Liu, S.-nitrate-contaminated groundwater, Wat</p><p>0043-1354/$ e see front matter 2013 Elsev</p><p>o, Jie Li, Juan Wang, Yun Qi</p><p>g, Tianjin University, Tianjin 300072, China</p><p>a b s t r a c t</p><p>In this paper, an anaerobic two-layer permeable reactive biobarrier system consisting of an</p><p>oxygen-capturing layer followed by a biodegradation layer was designed firstly for evalu-</p><p>ating the remediation effectiveness of nitrate-contaminated groundwater. The first layer</p><p>filling with granular oxygen-capturing materials is used to capture dissolved oxygen (DO)</p><p>in groundwater in order to create an anaerobic condition for the microbial denitrification.</p><p>Furthermore, it can also provide nutrition, such as carbon and phosphorus, for the normal</p><p>metabolism of immobilized denitrifying bacteria filled in the second layer. The second</p><p>layer using granular activated carbon as microbial carrier is able to biodegrade nitrate</p><p>entering the barrier system. Batch experiments were conducted to identify the effect of DO</p><p>on microbial denitrification, oxygen-capturing performance of zero valent iron (ZVI)</p><p>powder and the characteristics of the prepared oxygen-capturing materials used to stim-</p><p>ulate growth of denitrifying bacteria. A laboratory-scale experiment using two continuous</p><p>upflow stainless-steel columns was then performed to evaluate the feasibility of this</p><p>designed system. The first column was filled with granular oxygen-capturing materials</p><p>prepared by ZVI powder, sodium citrate as well as other inorganic salts, etc. The second</p><p>column was filled with activated carbon immobilizing denitrifying microbial consortium.biobarrier for the remediation</p><p>An anaerobic two-layer permeable reactivejournal homepage: wwwJ., et al., An anaerobic twer Research (2013), http:</p><p>ier Ltd. All rights reservedevier .com/locate/watreso-layer permeable reactive biobarrier for the remediation of//</p><p>.</p></li><li><p>wa t e r r e s e a r c h x x x ( 2 0 1 3 ) 1e92et al., 2010; Thiruvenkatachari et al., 2008; Van Nooten et al.,</p><p>2007). The main advantage of permeable reactive barrier is</p><p>the lower cost. Once installed, PRB does not need above</p><p>ground facilities or energy inputs, and it can take advantage of</p><p>the in situ groundwater flow to bring the contaminants in</p><p>contact with the reactive materials (Liu et al., 2006).</p><p>Agricultural runoff has been identified as the principal</p><p>source of groundwater contamination by nitrate. Additional</p><p>sources of nitrates contamination include landfill leachate,</p><p>leaking septic tanks, treated wastewater discharged to rivers,</p><p>and municipal storm water runoff (Savard et al., 2010; Suthar</p><p>et al., 2009; Tarkalson et al., 2006; Wick et al., 2012). In addi-</p><p>tion, climate changes such as changes in temperature, pre-</p><p>cipitation amounts and distribution, and the underlying</p><p>increases in atmospheric CO2 concentrations will impact on</p><p>both soil processes and agricultural productivity. Studies of soil</p><p>processes suggest climate change is likely to lead to increased</p><p>nitrate leaching from the soil. Climate change will also affect</p><p>the hydrological cycle with changes to recharge, groundwater</p><p>levels and resources and flowprocesses. The predicted impacts</p><p>are variable but many predictions suggest an overall decrease</p><p>in recharge and a fall in water levels and almost all predict an</p><p>enhanced seasonal variation in water levels. This will impact</p><p>on concentrations of nitrate in abstracted water and other</p><p>possibly more-sensitive receptors such as groundwater</p><p>dependent wetlands on an annual timescale (Stuart et al.,</p><p>2011). In recent decades, a lot of projects succeeded on</p><p>reducing nitrate pollution, nevertheless in most places nitrate</p><p>concentration in groundwater is still on the rise in varying</p><p>degrees (Chen et al., 2010; Fenech et al., 2012; Majumder et al.,</p><p>2008; Rivett et al., 2008). The EuropeanUnion andWorld Health</p><p>Organization (WHO) have both set the standard for nitrate in</p><p>potable water at 11.3 mg N/L (50 mg-NO3/L) (WHO, 2004).</p><p>Excessive ingested nitrites and nitrates from polluted drinking</p><p>waters can induce methemoglobinemia in humans, and also</p><p>have a potential role in developing cancers (Camargo and</p><p>Alonso, 2006; Fewtrell, 2004; Suthar et al., 2009). Many tech-</p><p>nologies are available for treating nitrate from groundwater,</p><p>such as reverse osmosis; ion exchange; chemical denitrifica-</p><p>tion; electrodialysis and distillation (McAdam and Judd, 2007;</p><p>Ricardo et al., 2012; Schnobrich et al., 2007). Although these</p><p>techniques are effective in moving nitrate from water, most of</p><p>them are limited in factual application for the remediation.</p><p>Themain products of such chemical reduction are ammonium</p><p>ions that are potential toxic to aquatic organisms at high</p><p>concentrations (Hwang et al., 2011; Li et al., 2010; Shin and Cha,</p><p>2008; Suzuki et al., 2012). Research is carried out toward nitrate</p><p>removal from water resources, whereas the most promising</p><p>approach being studied is biological denitrification. Microcosm</p><p>studies demonstrated that nitrate may be biodegrable with</p><p>special bacterial strains on natural isolates under aerobic and</p><p>anaerobic condition (Aslan and Cakici, 2007; Liu et al., 2009;</p><p>Wang et al., 2009; Zhou et al., 2011). The pathway for nitrate</p><p>reduction is</p><p>NO3/NO2/NO/N2O/N2 (1)</p><p>The reaction of complete microbial denitrification is</p><p>commonly shown in general equation (reaction 2) wheremicrobially available carbon is simplified as carbohydrate</p><p>(Rivett et al., 2008).</p><p>Please cite this article in press as: Liu, S.-J., et al., An anaerobic twnitrate-contaminated groundwater, Water Research (2013), http:matic diagram of this designed system is shown in Fig. 1.</p><p>The principle of this work was to design a passive treat-4NO3 5CH2O/2N2 CO2 4HCO3 3H2O (2)Biological denitrification is considered to be the most</p><p>economical strategy among other conventional techniques</p><p>like physicochemical. The denitrifying bacteria using nitrate</p><p>as sole source of nitrogen under anaerobic conditions grow</p><p>slowly with low yields of biomass and are sometimes unsta-</p><p>ble. As a result, an effective bioremediation process for nitrate</p><p>from groundwater has not been fully developed so far.</p><p>The aim of the recent studies was to select a suitable nat-</p><p>ural organic substrate as a potential carbon source for use in a</p><p>denitrification PRB (Gibert et al., 2008). However, few re-</p><p>searchers focus their attention on the negative influence of</p><p>microbial denitrification caused by dissolved oxygen (DO) level</p><p>in the groundwater so far. In generally, DO content is not low</p><p>enough in the groundwater (Schnobrich et al., 2007). As a</p><p>result, an anaerobic condition is difficult to achieve for deni-</p><p>trifying bacteria used in the bioremediation of nitrate-</p><p>contaminated groundwater. This paper attempted to treat</p><p>groundwater contaminated by nitrate using a two-stage</p><p>removal system. The first is to capture DO in order to create</p><p>artificially an anaerobic environment in groundwater, and the</p><p>second is to degrade nitrate using the denitrifying bacteria.</p><p>Studies demonstrated that zero valent iron (ZVI) has a chem-</p><p>ical reaction with O2 dissolved in the water (Su and Puls, 2007).</p><p>2Fe0 2H2OO2/2Fe2 4OH (3)</p><p>2Fe0 4H O2/2Fe2 2H2O (4)Therefore, ZVI was selected as the potential oxygen-</p><p>capturing reagent in this paper. In addition, the following</p><p>reasons also make it good candidate for this study: (1) It is</p><p>nontoxic to aquatic organisms; (2) Nitrate can be degraded</p><p>chemically by ZVI; (3) It is available and cheap.</p><p>Besides indigenous microbe, injection of special bacterial</p><p>strains as well as nutrient salts is usual measure for</p><p>enhancing remediation efficiency of groundwater (Ito et al.,</p><p>2012). For preventing special microorganism injected into</p><p>the aquifer from losing with groundwater flow, it may be</p><p>necessary to immobilize bacteria in the barrier (Ha et al., 2009).</p><p>In this paper, activated carbon was selected as microbial</p><p>carrier because of the following reasons: (1) the surface of</p><p>activated carbon is porous and coarse, which helpsmicrobe to</p><p>adsorb and immobilize; (2) activated carbon doesnt bring any</p><p>new contaminant into groundwater when it is placed in the</p><p>barrier; (3) activated carbon is relatively inexpensive.</p><p>Based on the above discussions, we designed an anaerobic</p><p>two-layer permeable reactive biobarrier system containing</p><p>oxygen-capturing and biodegradation layers to evaluate the</p><p>remediation effectiveness of nitrate-contaminated ground-</p><p>water. The first layer that filled with granular oxygen-</p><p>capturing materials can capture oxygen dissolved in ground-</p><p>water, and provide carbon source as well as other nutrition for</p><p>the metabolism of denitrifying bacteria. The second layer that</p><p>filled with immobilized denitrifying bacteria can enhance the</p><p>removal efficiency of nitrate in the groundwater. The sche-ment system to bioremediate groundwater contaminated by</p><p>nitrate. Experiments were conducted as follows:</p><p>o-layer permeable reactive biobarrier for the remediation of//</p></li><li><p>2.1. Denitrifying Bacterias collection, enrichment and</p><p>wat e r r e s e a r c h x x x ( 2 0 1 3 ) 1e9 3acclimation</p><p>The original experimental microbes were collected from a</p><p>cornfield soil located 25e40 cm deep at Xiqing District, Tianjin</p><p>city, China. Microbes were enriched and acclimated in a bio-</p><p>chemical culture bottle for the next experiments. The com-(1) Effects of DO on biodegradation efficiency of nitrate;</p><p>(2) Oxygen-capturing performance of ZVI;</p><p>(3) Preparation and characteristics of oxygen-capturing</p><p>materials;</p><p>(4) A column experiment for evaluating the feasibility and</p><p>potential by using this designed barrier system.</p><p>2. Material and methods</p><p>Fig. 1 e Schematic diagram of the designed biological</p><p>barrier system.ponents of liquid mineral salts mediumwere as follows (units</p><p>are in mg/L of water): sodium citrate, 5000; KNO3, 2000;</p><p>KH2PO4, 1000; K2HPO4, 1000; CaCl2, 180; MgSO4, 100. KNO3 was</p><p>used as the sole nitrogen source in themedium. It is sufficient</p><p>to mention that the DO was removed from the medium by</p><p>sparging nitrogen in this present work. A previous study has</p><p>reported that the optimum pH for microbial denitrification</p><p>should be keep in the range of 7.0e9.0 (Tang et al., 2011).</p><p>Thereby, the pH of cultures was checked every 3 day, and it</p><p>was regulate to about 7.5 using KH2PO4 and K2HPO4 when the</p><p>pH value changed. Microbes were enriched and acclimated at</p><p>room temperature for 2 months. Then, the suspension of</p><p>acclimated denitrifying bacteria was used for the subsequent</p><p>experiments.</p><p>2.2. Batch experiments</p><p>2.2.1. Effects of DO on the denitrification efficiency of nitrateBecause of the effect of DO on the nitrate reductase activity</p><p>and metabolism pathways, the control of DO is crucial to the</p><p>nitrate biodegradation. In the present experiments, the effect</p><p>of DO on denitrification was investigated by varying the initial</p><p>Please cite this article in press as: Liu, S.-J., et al., An anaerobic twnitrate-contaminated groundwater, Water Research (2013), http:DO value in the medium from 0.02 mg/L to 4 mg/L. The ex-</p><p>periments were performed in four 600 mL enclosed reactors</p><p>containing 400 mL of the mineral salts medium described</p><p>above except KNO3. In order to control the DO content, ni-</p><p>trogen was sparged into the medium before the experiment.</p><p>40 mg NO3eN/L was added into the each reactor firstly, and</p><p>then, 100 mL of the suspension of acclimated denitrifying</p><p>bacteria was inoculated, respectively. The four reactors, once</p><p>inoculated, were enclosed and placed in a reciprocal shaker at</p><p>constant temperature (20 C) and rotate speed (130 r/min). Thecontrol case was also maintained with the same concentra-</p><p>tion of nitrate and abiotic denitrifying bacteria. The enclosed</p><p>reactors were incubated for 60 h with shaking. The concen-</p><p>trations of NO3eN in the reactor were analyzed at the begin-</p><p>ning and end of the experiments.</p><p>2.2.2. Oxygen-capturing performance of ZVITechnical ZVI powder was purchased from Tianjin Jiangtian</p><p>Chemical Corporation Ltd, whose main impurity was about</p><p>0.5% of sulfuric acid insoluble material by weight. ZVI can</p><p>consume oxygen upon contact with water according to the</p><p>equation (3) or (4). For evaluating oxygen-capturing perfor-</p><p>mance of ZVI, the experiments were performed by adding</p><p>1000mL of sterile deionized water into four enclosed reactors,</p><p>and then 208, 503, 804, 1000 mg of ZVI powder were also</p><p>added, respectively. Here, it is sufficient to mention that 6mg/</p><p>L of DO content in sterile deionized water was controlled by</p><p>sparging nitrogen at the beginning of experiments. In addi-</p><p>tion, the same adding weights of ZVI powder (1000 mg/L)</p><p>under the condition of different initial DO values was also</p><p>studied. All above experiments were conducted in a reciprocal</p><p>shaker at constant temperature (20 C) and rotate speed (130 r/min). A portable DO meter (HQ30D, HACH) was used to online</p><p>monitor the DO change.</p><p>2.2.3. Preparation and characteristics of oxygen-capturingmaterialsThe oxygen-capturing materials were prepared by blending</p><p>ZVI powder, sodium citrate, KH2PO4, K2HPO4, CaCl2, MgSO4,</p><p>cement, quartz sand at a ratio of 0.10:0.20:0.04:0.04:0.006:</p><p>0.004:0.30:0.31 by weight. ZVI powder was used a...</p></li></ul>


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