Displaying all 11 publications

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  1. Mohajeri L, Aziz HA, Isa MH, Zahed MA, Mohajeri S
    Bull Environ Contam Toxicol, 2010 Jul;85(1):54-8.
    PMID: 20577869 DOI: 10.1007/s00128-010-0058-1
    Weathered crude oil (WCO) removals in shoreline sediment samples were monitored for 60 days in bioremediation experimentation. Experimental modeling was carried out using statistical design of experiments. At optimum conditions maximum of 83.13, 78.06 and 69.92% WCO removals were observed for 2, 16 and 30 g/kg initial oil concentrations, respectively. Significant variations in the crude oil degradation pattern were observed with respect to oil, nutrient and microorganism contents. Crude oil bioremediation were successfully described by a first-order kinetic model. The study indicated that the rate of hydrocarbon biodegradation increased with decrease of crude oil concentrations.
  2. Zahed MA, Aziz HA, Isa MH, Mohajeri L, Mohajeri S
    Bioresour Technol, 2010 Dec;101(24):9455-60.
    PMID: 20705460 DOI: 10.1016/j.biortech.2010.07.077
    To determine the influence of nutrients on the rate of biodegradation, a five-level, three-factor central composite design (CCD) was employed for bioremediation of seawater artificially contaminated with crude oil. Removal of total petroleum hydrocarbons (TPH) was the dependent variable. Samples were extracted and analyzed according to US-EPA protocols. A significant (R(2)=0.9645, P<0.0001) quadratic polynomial mathematical model was generated. Removal from samples not subjected to optimization and removal by natural attenuation were 53.3% and 22.6%, respectively. Numerical optimization was carried out based on desirability functions for maximum TPH removal. For an initial crude oil concentration of 1g/L supplemented with 190.21 mg/L nitrogen and 12.71 mg/L phosphorus, the Design-Expert software predicted 60.9% hydrocarbon removal; 58.6% removal was observed in a 28-day experiment.
  3. Zahed MA, Nabi Bidhendi G, Pardakhti A, Esmaili-Sari A, Mohajeri S
    Bull Environ Contam Toxicol, 2009 Dec;83(6):899-902.
    PMID: 19760353 DOI: 10.1007/s00128-009-9874-6
    Polychlorinated biphenyl (PCB) was detected as isomer groups (congener numbers 28, 52, 101, 118, 138, 153 and 180) in the coastal water and sediment of four stations around Shadegan wetland protected area in the northwestern part of the Persian Gulf. Total PCB concentration range was 8-375 ng/L in water and 3.4-50.2 μg/g in sediment. Concentration of different congeners and chromatogram indicates that the source of PCB in this area can be Clophen A60; it used for long time in Iranian electronic industries. Other chlorinated hydrocarbons such as lindane, DDT and their metabolites were also present in the samples.
  4. Zahed MA, Aziz HA, Isa MH, Mohajeri L
    Bull Environ Contam Toxicol, 2010 Apr;84(4):438-42.
    PMID: 20224975 DOI: 10.1007/s00128-010-9954-7
    The effects of initial oil concentration and the Corexit 9500 dispersant on the rate of bioremediation of petroleum hydrocarbons were investigated with a series of ex-situ seawater samples. With initial oil concentrations of 100, 500, 1,000 and 2,000 mg/L, removal of total petroleum hydrocarbons (TPHs) with dispersant were 67.3%, 62.5%, 56.5% and 44.7%, respectively, and were 64.2%, 55.7%, 48.8% and 37.6% without dispersant. The results clearly indicate that the presence of dispersant enhanced crude oil biodegradation. Lower concentrations of crude oil demonstrated more efficient hydrocarbon removal. Based on these findings, bioremediation is not recommended for crude oil concentrations of 2,000 mg/L or higher.
  5. Mohajeri L, Aziz HA, Isa MH, Zahed MA
    Bioresour Technol, 2010 Feb;101(3):893-900.
    PMID: 19773160 DOI: 10.1016/j.biortech.2009.09.013
    This work studied the bioremediation of weathered crude oil (WCO) in coastal sediment samples using central composite face centered design (CCFD) under response surface methodology (RSM). Initial oil concentration, biomass, nitrogen and phosphorus concentrations were used as independent variables (factors) and oil removal as dependent variable (response) in a 60 days trial. A statistically significant model for WCO removal was obtained. The coefficient of determination (R(2)=0.9732) and probability value (P<0.0001) demonstrated significance for the regression model. Numerical optimization based on desirability function were carried out for initial oil concentration of 2, 16 and 30 g per kg sediment and 83.13, 78.06 and 69.92 per cent removal were observed respectively, compare to 77.13, 74.17 and 69.87 per cent removal for un-optimized results.
  6. Mojiri A, Aziz HA, Zaman NQ, Aziz SQ, Zahed MA
    J Environ Manage, 2014 Jun 15;139:1-14.
    PMID: 24662109 DOI: 10.1016/j.jenvman.2014.02.017
    Sequencing batch reactor (SBR) is one of the various methods of biological treatments used for treating wastewater and landfill leachate. This study investigated the treatment of landfill leachate and domestic wastewater by adding a new adsorbent (powdered ZELIAC; PZ) to the SBR technique. ZELIAC consists of zeolite, activated carbon, lime stone, rice husk ash, and Portland cement. The response surface methodology and central composite design were used to elucidate the nature of the response surface in the experimental design and describe the optimum conditions of the independent variables, including aeration rate (L/min), contact time (h), and ratio of leachate to wastewater mixture (%; v/v), as well as their responses (dependent variables). Appropriate conditions of operating variables were also optimized to predict the best value of responses. To perform an adequate analysis of the aerobic process, four dependent parameters, namely, chemical oxygen demand (COD), color, ammonia-nitrogen (NH3-N), and phenols, were measured as responses. The results indicated that the PZ-SBR showed higher performance in removing certain pollutants compared with SBR. Given the optimal conditions of aeration rate (1.74 L/min), leachate to wastewater ratio (20%), and contact time (10.31 h) for the PZ-SBR, the removal efficiencies for color, NH3-N, COD, and phenols were 84.11%, 99.01%, 72.84%, and 61.32%, respectively.
  7. Zahed MA, Aziz HA, Isa MH, Mohajeri L, Mohajeri S, Kutty SR
    J Hazard Mater, 2011 Jan 30;185(2-3):1027-31.
    PMID: 21041026 DOI: 10.1016/j.jhazmat.2010.10.009
    Hydrocarbon pollution in marine ecosystems occurs mainly by accidental oil spills, deliberate discharge of ballast waters from oil tankers and bilge waste discharges; causing site pollution and serious adverse effects on aquatic environments as well as human health. A large number of petroleum hydrocarbons are biodegradable, thus bioremediation has become an important method for the restoration of oil polluted areas. In this research, a series of natural attenuation, crude oil (CO) and dispersed crude oil (DCO) bioremediation experiments of artificially crude oil contaminated seawater was carried out. Bacterial consortiums were identified as Acinetobacter, Alcaligenes, Bacillus, Pseudomonas and Vibrio. First order kinetics described the biodegradation of crude oil. Under abiotic conditions, oil removal was 19.9% while a maximum of 31.8% total petroleum hydrocarbons (TPH) removal was obtained in natural attenuation experiment. All DCO bioreactors demonstrated higher and faster removal than CO bioreactors. Half life times were 28, 32, 38 and 58 days for DCO and 31, 40, 50 and 75 days for CO with oil concentrations of 100, 500, 1000 and 2000 mg/L, respectively. The effectiveness of Corexit 9500 dispersant was monitored in the 45 day study; the results indicated that it improved the crude oil biodegradation rate.
  8. Zahed MA, Aziz HA, Mohajeri L, Mohajeri S, Kutty SR, Isa MH
    J Hazard Mater, 2010 Dec 15;184(1-3):350-6.
    PMID: 20837377 DOI: 10.1016/j.jhazmat.2010.08.043
    Response surface methodology (RSM) was employed to optimize nitrogen and phosphorus concentrations for removal of n-alkanes from crude oil contaminated seawater samples in batch reactors. Erlenmeyer flasks were used as bioreactors; each containing 250 mL dispersed crude oil contaminated seawater, indigenous acclimatized microorganism and different amounts of nitrogen and phosphorus based on central composite design (CCD). Samples were extracted and analyzed according to US-EPA protocols using a gas chromatograph. During 28 days of bioremediation, a maximum of 95% total aliphatic hydrocarbons removal was observed. The obtained Model F-value of 267.73 and probability F<0.0001 implied the model was significant. Numerical condition optimization via a quadratic model, predicted 98% n-alkanes removal for a 20-day laboratory bioremediation trial using nitrogen and phosphorus concentrations of 13.62 and 1.39 mg/L, respectively. In actual experiments, 95% removal was observed under these conditions.
  9. Mohajeri S, Aziz HA, Isa MH, Zahed MA, Adlan MN
    J Hazard Mater, 2010 Apr 15;176(1-3):749-58.
    PMID: 20022166 DOI: 10.1016/j.jhazmat.2009.11.099
    Mature landfill leachate is typically non-biodegradable and contains high concentration of refractory organics. The aim of this research was to optimize operating parameters in electro-Fenton process, for the removal of recalcitrant organics from semi-aerobic landfill leachate using response surface methodology (RSM). Effectiveness of important process parameters H(2)O(2)/Fe(2+) molar ratio, current density, pH and reaction time were determined, optimized and modeled successfully. Significant quadratic polynomial models were obtained (R(2)=0.9972 and 0.9984 for COD and color removals, respectively). Numerical optimization based on desirability function were employed; in a 43 min trial 94.07% of COD and 95.83% of color were removed at pH 3 and H(2)O(2)/Fe(2+) molar ratio 1, while current density was 49 mA/cm(2). The results indicate that E-Fenton process was an effective technology for semi-aerobic landfill leachate treatment.
  10. Mohajeri S, Aziz HA, Isa MH, Zahed MA, Bashir MJ, Adlan MN
    Water Sci Technol, 2010;61(5):1257-66.
    PMID: 20220248 DOI: 10.2166/wst.2010.018
    In the present study, Electrochemical Oxidation was used to remove COD and color from semi-aerobic landfill leachate collected from Pulau Burung Landfill Site (PBLS), Penang, Malaysia. Experiments were conducted in a batch laboratory-scale system in the presence of NaCl as electrolyte and aluminum electrodes. Central composite design (CCD) under Response surface methodology (RSM) was applied to optimize the electrochemical oxidation process conditions using chemical oxygen demand (COD) and color removals as responses, and the electrolyte concentrations, current density and reaction time as control factors. Analysis of variance (ANOVA) showed good coefficient of determination (R(2)) values of >0.98, thus ensuring satisfactory fitting of the second-order regression model with the experimental data. In un-optimized condition, maximum removals for COD (48.77%) and color (58.21%) were achieved at current density 80 mA/cm(2), electrolyte concentration 3,000 mg/L and reaction time 240 min. While after optimization at current density 75 mA/cm(2), electrolyte concentration 2,000 mg/L and reaction time 218 min a maximum of 49.33 and 59.24% removals were observed for COD and color respectively.
  11. Mohajeri S, Aziz HA, Zahed MA, Mohajeri L, Bashir MJ, Aziz SQ, et al.
    Water Sci Technol, 2011;64(8):1652-60.
    PMID: 22335108
    Landfill leachate is one of the most recalcitrant wastes for biotreatment and can be considered a potential source of contamination to surface and groundwater ecosystems. In the present study, Fenton oxidation was employed for degradation of stabilized landfill leachate. Response surface methodology was applied to analyze, model and optimize the process parameters, i.e. pH and reaction time as well as the initial concentrations of hydrogen peroxide and ferrous ion. Analysis of variance showed that good coefficients of determination were obtained (R2 > 0.99), thus ensuring satisfactory agreement of the second-order regression model with the experimental data. The results indicated that, pH and its quadratic effects were the main factors influencing Fenton oxidation. Furthermore, antagonistic effects between pH and other variables were observed. The optimum H2O2 concentration, Fe(II) concentration, pH and reaction time were 0.033 mol/L, 0.011 mol/L, 3 and 145 min, respectively, with 58.3% COD, 79.0% color and 82.1% iron removals.
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