Fereshteh Naeimpoor

Carbon content reduction in a model reluctant clayey soil: Slurry phase n-hexadecane bioremediation

Clayey soils contaminated with organic pollutants are nowadays one of the important environmental issues as they are highly reluctant to conventional bioremediation techniques. In this study, biodegradability of n-hexadecane as a model contaminant in oil polluted clayey soil by an indigenous bacterium was investigated. Maximal bacterial growth was achieved at 8% (v/v) n-hexadecane as sole carbon and energy sources in aqueous phase. The predominant n-hexadecane uptake mechanism was identified to be biosurfactant-mediated using bacterial adhesion to hydrocarbon (BATH) test and surface tension measurements. The effect of n-hexadecane concentration, soil to water ratio, inoculum concentration and pH on total organic carbon (TOC) reduction from kaolin soil in slurry phase was investigated at two levels in shake flasks using full factorial experimental design method where 10,000 (mg n-hexadecane)(kg soil)(-1), soil-water ratio of 1:3, 10% (v/w) inoculum and pH of 7 resulted in the highest TOC reduction of 70% within 20 days. Additionally, slurry bioreactor experiments were performed to study the effect of various aeration rates on n-hexadecane biodegradation during 9 days where 2.5 vvm was found as an appropriate aeration rate leading to 54% TOC reduction. Slurry phase bioremediation is shown to be a successful method for remediation of clayey reluctant soils.

Statistical factor-screening and optimization in slurry phase bioremediation of 2,4,6-trinitrotoluene contaminated soil

Since slurry phase bioremediation is a promising treatment for recalcitrant compounds such as 2,4,6-trinitrotoluene (TNT), a statistical study was conducted for the first time to optimize TNT removal (TR) in slurry phase. Fractional factorial design method, 2(IV)(7-3), was firstly adopted and four out of the seven examined factors were screened as effective. Subsequently, central composite design and response surface methodology were employed to model and optimize TR within 15 days. A quadratic model (R(2) = 0.9415) was obtained, by which the optimal values of 6.25 g/L glucose, 4.92 g/L Tween 80, 20.23% (w/v) slurry concentration and 5.75% (v/v) inoculum size were estimated. Validation experiments at optimal factor levels resulted in 95.2% TR, showing a good agreement with model prediction of 96.1%. Additionally, the effect of aeration rate (0-4 vvm) on TR was investigated in a 1-liter bioreactor. Maximum TR of 95% was achieved at 3 vvm within 9 days, while reaching the same removal level in flasks needed 15 days. This reveals that improved oxygen supply in bioreactor significantly reduces bioremediation time in comparison with shake flasks.

Effect of hydraulic retention time and temperature on submerged membrane bioreactor (SMBR) performance

Water shortages and strict environmental provisions necessitate wastewater renovation using various wastewater treatment methods, among which applications of submerged membrane bioreactors (SMBRs) are rapidly increasing due to their advantages such as high loading capacity and quality of effluent. In this work, the effect of hydraulic retention time (HRT 8, 10 and 12 h) and temperature (25, 30 and 35°C) on membrane fouling and sludge production was investigated in a 5-Liter SMBR equipped with immersed PVDF hollow fiber membrane module. Phenolic synthetic wastewater and acclimatized activated sludge with phenol during a 2-month period were used as toxic and microbial sources, respectively. Results showed that by increasing HRT membrane fouling decreases, while excellent treatment performance of over 99.5% phenol and 95% COD removals was achieved at all HRTs. Therefore, HRT=8 h corresponding to the highest effluent flow rate of 12 L/m2·h was used to investigate the effect of temperature, resulting in phenol and COD removals of higher than 99 and 96%, respectively, at all temperatures. Membrane fouling occurred at 12, 5 and 3 days for 25, 30 and 35 °C, respectively. Additionally, the effect of HRT and temperature on mixed liquor volatile suspended solid (MLVSS) as a measure of biomass was examined. MLVSS concentration showed decreases with increasing HRT and temperature. Overall, it was shown that SMBR can be used to efficiently treat phenolic wastewater at a range of flow rates and temperatures, among which HRT=8 h and T=25 °C are the preferred operating conditions, resulting in high flow rate and low membrane fouling.

LAMOS: A linear algorithm to identify the origin of multiple optimal flux distributions in metabolic networks

Abstract In flux balance analysis, where flux distribution within a cell metabolic network is estimated by optimizing an objective function, there commonly exist multiple optimal flux distributions. Although finding all optimal solutions is possible, their interpretation is a challenge. A new four-phase algorithm (LAMOS) is therefore proposed in this work to efficiently enumerate all of these solutions based on iterative substitution of a current non-basic variable with a basic variable. These basic and non-basic variables are called key reaction pairs that their successive activity or inactivity causes alternate optimal solutions. LAMOS was implemented on E. coli metabolic models and the results proved it as a simple and fast method capable of finding the key reactions as well as reactions participating in the futile cycles. Key reactions were 1–3% of all reactions for the large-scale models and these reactions were identified using only 1% of optimal solutions.