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  • of nitrate-contaminated groun

    She-Jiang Liu*, Zhi-Yuan Zha

    School of Environmental Science & Engineerin

    a r t i c l e i n f o

    Article history:

    duct. Results showed

    mediate, nitrite, could

    necessary in order to

    evaluate performance of its field application.

    td. All rights reserved.

    In the last decade, there has been an explosion of activities

    directed at the development and implementation of a most

    promising remediation technology-permeable reactive barrier

    (PRB) (Bartzas et al., 2006; Basu and Johnson, 2012; Ebert et al.,

    2006; Flury et al., 2009; Ludwig et al., 2009; Mak and Lo, 2011;

    006). A PRB consist-

    e media is placed in

    the subsurface across the flow path of contaminated

    groundwater, which must move through it as it flows, typi-

    cally under its natural gradient, thereby creating a passive

    treatment system. PRB is not a barrier to the groundwater, but

    a barrier to the contaminants (Nooten et al., 2008; Phillips

    * Corresponding author. Tel.: 86 22 27890017; fax: 86 22 27891291.

    Available online at www.sciencedirect.com

    .e ls

    wat e r r e s e a r c h x x x ( 2 0 1 3 ) 1e9E-mail address: liushejiang@tju.edu.cn (S.-J. Liu). 2013 Elsevier L

    1. Introduction Michalsen et al., 2006; Morrison et al., 2ing of permanent or replaceable reactivcolumn were analyzed for nitrate and its major degradation bypro

    that nitrate could be removed more than 94%, and its metabolic inter

    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

    content was pumped into this system at a flow rate of 235 mL/d. Samples from the secondReceived 4 March 2013

    Received in revised form

    4 June 2013

    Accepted 16 June 2013

    Available online xxx

    Keywords:

    Nitrate

    Remediation

    Groundwater

    Permeable reactive barrier

    DenitrificationPlease cite this article in press as: Liu, S.-nitrate-contaminated groundwater, Wat

    0043-1354/$ e see front matter 2013 Elsevhttp://dx.doi.org/10.1016/j.watres.2013.06.028dwater

    o, Jie Li, Juan Wang, Yun Qi

    g, Tianjin University, Tianjin 300072, China

    a b s t r a c t

    In this paper, an anaerobic two-layer permeable reactive biobarrier system consisting of an

    oxygen-capturing layer followed by a biodegradation layer was designed firstly for evalu-

    ating the remediation effectiveness of nitrate-contaminated groundwater. The first layer

    filling with granular oxygen-capturing materials is used to capture dissolved oxygen (DO)

    in groundwater in order to create an anaerobic condition for the microbial denitrification.

    Furthermore, it can also provide nutrition, such as carbon and phosphorus, for the normal

    metabolism of immobilized denitrifying bacteria filled in the second layer. The second

    layer using granular activated carbon as microbial carrier is able to biodegrade nitrate

    entering the barrier system. Batch experiments were conducted to identify the effect of DO

    on microbial denitrification, oxygen-capturing performance of zero valent iron (ZVI)

    powder and the characteristics of the prepared oxygen-capturing materials used to stim-

    ulate growth of denitrifying bacteria. A laboratory-scale experiment using two continuous

    upflow stainless-steel columns was then performed to evaluate the feasibility of this

    designed system. The first column was filled with granular oxygen-capturing materials

    prepared by ZVI powder, sodium citrate as well as other inorganic salts, etc. The second

    column was filled with activated carbon immobilizing denitrifying microbial consortium.biobarrier for the remediation

    An anaerobic two-layer permeable reactivejournal homepage: wwwJ., et al., An anaerobic twer Research (2013), http:

    ier Ltd. All rights reservedevier .com/locate/watreso-layer permeable reactive biobarrier for the remediation of//dx.doi.org/10.1016/j.watres.2013.06.028

    .

  • 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.,

    2007). The main advantage of permeable reactive barrier is

    the lower cost. Once installed, PRB does not need above

    ground facilities or energy inputs, and it can take advantage of

    the in situ groundwater flow to bring the contaminants in

    contact with the reactive materials (Liu et al., 2006).

    Agricultural runoff has been identified as the principal

    source of groundwater contamination by nitrate. Additional

    sources of nitrates contamination include landfill leachate,

    leaking septic tanks, treated wastewater discharged to rivers,

    and municipal storm water runoff (Savard et al., 2010; Suthar

    et al., 2009; Tarkalson et al., 2006; Wick et al., 2012). In addi-

    tion, climate changes such as changes in temperature, pre-

    cipitation amounts and distribution, and the underlying

    increases in atmospheric CO2 concentrations will impact on

    both soil processes and agricultural productivity. Studies of soil

    processes suggest climate change is likely to lead to increased

    nitrate leaching from the soil. Climate change will also affect

    the hydrological cycle with changes to recharge, groundwater

    levels and resources and flowprocesses. The predicted impacts

    are variable but many predictions suggest an overall decrease

    in recharge and a fall in water levels and almost all predict an

    enhanced seasonal variation in water levels. This will impact

    on concentrations of nitrate in abstracted water and other

    possibly more-sensitive receptors such as groundwater

    dependent wetlands on an annual timescale (Stuart et al.,

    2011). In recent decades, a lot of projects succeeded on

    reducing nitrate pollution, nevertheless in most places nitrate

    concentration in groundwater is still on the rise in varying

    degrees (Chen et al., 2010; Fenech et al., 2012; Majumder et al.,

    2008; Rivett et al., 2008). The EuropeanUnion andWorld Health

    Organization (WHO) have both set the standard for nitrate in

    potable water at 11.3 mg N/L (50 mg-NO3/L) (WHO, 2004).

    Excessive ingested nitrites and nitrates from polluted drinking

    waters can induce methemoglobinemia in humans, and also

    have a potential role in developing cancers (Camargo and

    Alonso, 2006; Fewtrell, 2004; Suthar et al., 2009). Many tech-

    nologies are available for treating nitrate from groundwater,

    such as reverse osmosis; ion exchange; chemical denitrifica-

    tion; electrodialysis and distillation (McAdam and Judd, 2007;

    Ricardo et al., 2012; Schnobrich et al., 2007). Although these

    techniques are effective in moving nitrate from water, most of

    them are limited in factual application for the remediation.

    Themain products of such chemical reduction are ammonium

    ions that are potential toxic to aquatic organisms at high

    concentrations (Hwang et al., 2011; Li et al., 2010; Shin and Cha,

    2008; Suzuki et al., 2012). Research is carried out toward nitrate

    removal from water resources, whereas the most promising

    approach being studied is biological denitrification. Microcosm

    studies demonstrated that nitrate may be biodegrable with

    special bacterial strains on natural isolates under aerobic and

    anaerobic condition (Aslan and Cakici, 2007; Liu et al., 2009;

    Wang et al., 2009; Zhou et al., 2011). The pathway for nitrate

    reduction is

    NO3/NO2/NO/N2O/N2 (1)

    The reaction of complete microbial denitrification is

    commonly shown in general equation (reaction 2) wheremicrobially available carbon is simplified as carbohydrate

    (Rivett et al., 2008).

    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.

    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

    economical strategy among other conventional techniques

    like physicochemical. The denitrifying bacteria using nitrate

    as sole source of nitrogen under anaerobic conditions grow

    slowly with low yields of biomass and are sometimes unsta-

    ble. As a result, an effective bioremediation process for nitrate

    from groundwater has not been fully developed so far.

    The aim of the recent studies was to select a suitable nat-

    ural organic substrate as a potential carbon source for use in a

    denitrification PRB (Gibert et al., 2008). However, few re-

    searchers focus their attention on the negative influence of

    microbial denitrification caused by dissolved oxygen (DO) level

    in the groundwater so far. In generally, DO content is not low

    enough in the groundwater (Schnobrich et al., 2007). As a

    result, an anaerobic condition is difficult to achieve for deni-

    trifying bacteria used in the bioremediation of nitrate-

    contaminated groundwater. This paper attempted to treat

    groundwater contaminated by nitrate using a two-stage

    removal system. The first is to capture DO in order to create

    artificially an anaerobic environment in groundwater, and the

    second is to degrade nitrate using the denitrifying bacteria.

    Studies demonstrated that zero valent iron (ZVI) has a chem-

    ical reaction with O2 dissolved in the water (Su and Puls, 2007).

    2Fe0 2H2OO2/2Fe2 4OH (3)

    2Fe0 4H O2/2Fe2 2H2O (4)Therefore, ZVI was selected as the potential oxygen-