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The objective of this study was to assess the potential of applying enhanced bioremediation on the treatment of petroleumhydrocarbon contaminated soils. Microcosm experiments were conducted to determine the optimal biodegradation conditions. The control factors included oxygen content, nutrient addition, addition of commercially available mixed microbial inocula, addition of wood chip and rice husk mixtures (volume ratio = 1 : 1) as bulking agents, and addition of organic amendments (chicken manures). Results indicate that the supplement of microbial inocula or chicken manures could significantly increase the microbial populations in soils, and thus enhance the efficiency of total petroleum hydrocarbon (TPH) removal (initial TPH=5,500 mg/kg). The highest first-order TPH decay rate and removal ratio were approximately 0.015 [day.sup.-1] and 85%, respectively, observed in microcosms containing microbial inocula (mass ratio of soil to inocula=50:1), nutrient, and bulking agent (volume ratio of soil to bulking agent= 10 to 1) during 155 days of incubation. Results indicate that the first-order TPH decay rates of 0.015 and 0.0142 [day.sup.-1] can be obtained with the addition of microbial inocula and chicken manures, respectively, compared with the decay rate of 0.0069 [day.sup.-1] under intrinsic conditions. Thus, chicken manures have the potential to be used as substitutes of commercial microbial inocula. The decay rate and removal ratio can be further enhanced to 0.0196 [day.sup.-1] and 87%, respectively, with frequent soil shaking and air replacement. Results will be useful in designing an ex situ soil bioremediation systems (e.g., biopile and land farming) for practical application. DOI: 10.1061/(ASCE)EE.1943-7870.0000166 CE Database subject headings: Soil pollution; Hydrocarbons; Biological processes; Soil treatment; Laboratory tests. Author keywords: Soil contamination; Total petroleum hydrocarbon; Enhanced bioremediation.

Natural attenuation is a passive remedial approach that depends upon natural processes to degrade and dissipate contaminants in soil and groundwater. Intrinsic bioremediation is believed to be the major process among the natural attenuation mechanisms that account for the reduction of contaminant concentrations. In this study, a mass flux approach was used to calculate the contaminant mass reduction at a petroleum-hydrocarbon spill site. The mass flux technique is a simplified mass balance procedure, which is accomplished using the differences in total contaminant mass flux across two cross sections of the contaminant plume. The mass flux calculation results show that up to 86% of the dissolved total benzene, toluene, ethylbenzene, and xylene (BTEX) isomers removal was observed via natural attenuation at this site. Evidence for the occurrence of natural attenuation was the decreased contaminant mass flux through the plume cross sections along the transport path and limited spreading of the BTEX plume. Evidences for the BTEX biodegradation include: (1) decreased BTEX concentrations along the transport path: (2) depletion of dissolved oxygen, nitrate, and sulfate: (3) production of dissolved ferrous iron, sulfide, methane, and C[O.sub.2]; (4) deceased pH in the spill source area and increased pH in iron-reducing area; (5) increased alkalinity and microbial populations: and (6) preferential removal of certain BTEX components along the transport path. The effectiveness of intrinsic bioremediation on BTEX removal was evaluated by the in situ tracer method. Results reveal that approximately 74% of the BTEX removal was due to the intrinsic biodegradation process. The first-order decay model was applied for the natural attenuation and intrinsic bioremediation rates calculation. Results show that the biodegradation capacity (34.5 mg/L) for BTEX was much higher than the detected contaminants within the plume. The calculated total BTEX first-order natural attenuation and intrinsic bioremediation rates were 0.025 and 0.017% l/day, respectively. Results of polymerase chain reaction, denaturing gradient gel electrophoresis. and nucleotide sequence analysis reveal that some petroleum-hydrocarbon degraders (Flavobacterium capsulatum, Xanthobacter sp., Xanthobacter flavus, Xanthomonas codiaei, Pseudomonas boreopolis, Methvlobacterium sp., Reichenonwia pictae) might exist at this site. which might contribute to the BTEX biodegradation. Results suggest that the natural attenuation mechanisms can effectively contain the plume, and the mass flux method is useful in assessing the occurrence and efficiency of the natural attenuation and intrinsic biorelnediation processes. CE Database subject headings: Attenuation: Groundwater pollution; Biological processes: Hydrocarbons; Laboratory tests; Field tests. Author keywords: Natural attenuation: Groundwater contamination: Intrinsic bioremediation; Mass flux. DOI: 10.1061/(ASCE)EE.1943-7870.0000122

In this study, microcosm experiments were conducted to evaluate the effectiveness of (1) nutrients, hydrogen peroxide ([H.sub.2][O.sub.2]), and cane molasses addition; (2) soil washing by biodegradable surfactant [Simple Green (SG)]; and (3) soil pretreatment by Fenton-like oxidation on the bioremediation of fuel-oil contaminated soils. The dominant native microorganisms in the fuel-oil contaminated soils after each treatment process were determined via polymerase chain reaction, denaturing gradient gel electrophoresis, and nucleotide sequence analysis. Results show that approximately 32 and 56% of total petroleum hydrocarbon (TPH) removal (initial concentration of 5,000 mg [kg.sup.-1]) were observed in microcosms with the addition of nutrient and cane molasses (1,000 mg [L.sup.- 1]), respectively, compared to only 9% of TPH removal in live control microcosms under intrinsic conditions (without amendment) after 120 days of incubation. Addition of cane molasses would cause the increase in microbial population and thus enhance the TPH degradation rate. Results also show that approximately 61% of TPH removal was observed in microcosms with the addition of [H.sub.2][O.sub.2](100 mg [L.sup.-1]) and nutrient after 120 days of incubation. This indicates that the addition of low concentration of [H.sub.2][O.sub.2](100 mg [L.sup.-1]) would cause the desorption of TPH from soil particles and increase the dissolved oxygen and subsequent bioremediation efficiency in microcosms. Approximately 95 and 69% of TPH removal were observed in microcosms with SG (100 mg [L.sup.-l]) and higher dose of [H.sub.2][O.sub.2](900 mg [L.sup.- 1]) addition, respectively. Moreover, significant increases in microbial populations were observed and two TPH biodegraders (Pseudomonas sp. and Shewanella sp.) might exist in microcosms with SG or [H.sub.2][O.sub.2] addition. This indicates that the commonly used soil remedial techniques, biodegradable surfactant flushing, and Fenton-like oxidation would improve the TPH removal efficiency and would not cause adverse effects on the following bioremediation process. DOI: 10.1061/(ASCE)EE.1943-7870.0000049 CE Database subject headings: Soil pollution; Oils; Petroleum; Biological treatment; Soil treatment.

Abstract: The objectives of this bench-scale study were to (1) determine the optimal operational parameters and kinetics when potassium permanganate (KMnO4) was applied to in situ oxidize and remediate trichloroethylene (TCE)-contaminated groundwater and (2) evaluate the effects of manganese dioxide (MnO2) on the efficiency of TCE oxidation. The major controlling factors in the TCE oxidation experiments included molar ratios of KMnO4 to TCE (P value) and molar ratios of Na2HPO4 to Mn2+ (D value). Results show that the second-order decay model can be used to describe the oxidation when P value was less than 20, and the observed TCE decay rate was 0.8M−1 s−1. Results also reveal that (1) higher P value corresponded with higher TCE oxidation rate under the same initial TCE concentration condition and (2) higher TCE concentration corresponded with higher TCE oxidation rate under the same P value condition. Results reveal that significant MnO2 production and inhibition of TCE oxidation were not observed under acidic (pH 2.1) or slightly acidic conditions (pH 6.3). However, significant reduction of KMnO4 to MnO2 would occur under alkaline condition (pH 12.5), and this caused the decrease in TCE oxidation rate. Results from the MnO2 production experiments show that MnO2 was produced from three major routes: (1) oxidation of TCE by KMnO4, (2) further oxidation of Mn2+, which was produced during the oxidation of TCE by KMnO4, and (3) reduction of MnO4 −1 to MnO2 under alkaline conditions. Up to 81.5% of MnO2 production can be effectively inhibited with the addition of Na2HPO4. Moreover, the addition of Na2HPO4 would not decrease the TCE oxidation rate. [Copyright &y& Elsevier]