Modeling in situ benzene bioremediation in the contaminated Liwa aquifer (UAE) using the slow-release oxygen source technique

Irrigation and Hydraulics Department, Faculty of Engineering, Cairo University, Giza, Egypt
Environmental Earth Sciences (Impact Factor: 1.77). 10/2010; 61(7):1385-1399. DOI: 10.1007/s12665-010-0456-z


Dissolved benzene was detected in the shallow unconfined Liwa aquifer, UAE, which represents the main freshwater source for
the nearby residence Bu Hasa camp area. The main source of this contamination is believed to be the rejected water released
from Bu Hasa liquid recovery plant. In this paper, a finite element model (METABIOTRANS) is used to simulate the fate and
transport of the dissolved benzene plume in Liwa aquifer. Different remediation scenarios were simulated in which the slow-release
oxygen source (SOS) technique is utilized to minimize benzene concentrations at the nearest camp supply wells downstream of
the contamination zone. Results of the remediation scenarios show that the highest biodegradation rates occur when the oxygen
source is placed near the plume center; where higher benzene concentrations exist. The nearest oxygen release source to the
contamination zone caused higher stimulation to bacterial growth than further down-gradient oxygen sources. It also exhibited
longer resident time of oxygen in the aquifer; and therefore, yielded higher reductions in benzene concentrations. However,
using one central SOS proved to be insufficient as contaminant escaped laterally. Additional four transverse oxygen sources
were necessary to capture benzene that laterally spread away from the contamination zone. These lateral SOSs were essential
to reduce benzene concentrations at the supply wells that are located at the plume fringes. Finally, it was found that increasing
oxygen release from one source did not always improve remediation; and that using several SOSs with lower release rates could
be a more practical approach to enhance benzene biodegradation in the aquifer.

KeywordsBenzene-Biodegradation-Slow-release oxygen source-Modeling-UAE

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    • "Approximately , 10% of this amount annually recharges the shallow and deep aquifers (UAE 1993; Sherif et al. 2011). The groundwater aquifers can be divided into two groups: the upper 5 m unconfined of the friable (uncemented) alluvial deposits and the lower confined fractured carbonate rocks (Mohamed et al. 2010a, 2010b). In the Wadi Bih, approximately 9% or 6.7 × 106 m 3 of the total annual precipitation (74 × 106 m 3 ) becomes groundwater in the catchment (Al Wahedi 1997; Sherif et al. 2010). "
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    ABSTRACT: Monod expressions are preferred over zero- and first-order decay expressions in modeling contaminants biotransformation in groundwater because they better represent complex conditions. However, the wide-range of values reported for Monod parameters suggests each case-study is unique. Such uniqueness restricts the usefulness of modeling, complicates an interpretation of natural attenuation and limits the utility of a bioattenuation assessment to a small number of similar cases. In this paper, four Monod-based dimensionless parameters are developed that summarize the effects of microbial growth and inhibition on groundwater contaminants. The four parameters represent the normalized effective microbial growth rate (η), the normalized critical contaminant/substrate concentration (S*), the critical contaminant/substrate inhibition factor (N), and the bioremediation efficacy (η*). These parameters enable contaminated site managers to assess natural attenuation or augmented bioremediation at multiple sites and then draw comparisons between disparate remediation activities, sites and target contaminants. Simulations results are presented that reveal the sensitivity of these dimensionless parameters to Monod parameters and varying electron donor/acceptor loads. These simulations also show the efficacy of attenuation (η*) varying over space and time. Results suggest electron donor/acceptor amendments maintained at relative concentrations S* between 0.5 and 1.5 produce the highest remediation efficiencies. Implementation of the developed parameters in a case study proves their usefulness.
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    ABSTRACT: Groundwater contamination caused by petroleum products has become a common problem. These hazardous chemicals themselves soak down into groundwater through the soil or rock and cause significant health risk. Benzene, one species of chemicals, gives rise to specific concerns due to its relatively high water solubility and toxicity. For the removal of benzene in aquifer, natural biodegradation has indicated its limited ability because of the lack of dissolved oxygen (DO) in groundwater. A new method, namely the slow-release oxygen source (SOS) technique, could increase concentration of dissolved oxygen in groundwater and accelerate biodegradation processes. Therefore, the paper first built a transport model including benzene, DO and microbial species. Relevant program codes were developed on the basis of MODFLOW/MT3DMS. Then, a two-dimensional synthetic aquifer with a point source of benzene was simulated by the modified model to analyze the treatment efficiency of SOS. There were seven schemes designed by using different locations of well and oxygen release rates. Their treatment efficiencies were analyzed. The results showed that the modified model can be used to simulate benzene transport under SOS technique where Monod kinetic reactions occur. It was more efficient when placing release oxygen well was close to contamination sources of groundwater. For the same location of well, higher release rate of oxygen would enhance the effect of bioremediation. Enough dissolved oxygen maybe accelerates the growth of microbial species, and more benzene could be consumed by increasing microbial mass.
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