At military bases and munitions factories, 2,4,6-trinitrotoluene (TNT) is a common soil and groundwater contaminant. Although the reduction of nitro groups in TNT and related nitroarenes has been extensively investigated, few researchers have studied the link between reduction rates and the electrochemical properties of these compounds. In this work, the standard one-electron redox potentials at pH 7 (E 1 °‘) for six important nitroarenes have been measured by pulse radiolysis. The internally consistent values were −0.253 V for TNT, −0.417 V for 2-amino-4,6-dinitrotoluene, −0.449 V for 4-amino-2,6-dinitrotoluene, −0.397 V for 2,4-dinitrotoluene, −0.402 V for 2,6-dinitrotoluene, and −0.502 V for 2,4-diamino-6-nitrotoluene. The reduction kinetics of these nitroarenes was investigated using a bacterial nitroreductase, NAD(P)H:FMN oxidoreductase that uses NADH·H+ as a cosubstrate. A log-linear relationship was observed between the E 1 °‘ values and the enzymatic reduction rates for five nitroarenes, suggesting that transfer of the first electron is the rate-limiting step in nitroreduction.

Currently, no fast and accurate methods exist for measuring extant biokinetic parameters for biofilm systems. This article presents a new approach to measure extant biokinetic parameters of biofilms and examines the numerical feasibility of such a method. A completely mixed attached growth bioreactor is subjected to a pulse of substrate, and oxygen consumption is monitored by on-line measurement of dissolved oxygen concentration in the bulk liquid. The oxygen concentration profile is then fit with a mechanistic mathematical model for the biofilm to estimate biokinetic parameters. In this study a transient biofilm model is developed and solved to generate dissolved oxygen profiles in the bulk liquid. Sensitivity analysis of the model reveals that the dissolved oxygen profiles are sufficiently sensitive to the biokinetic parameters-the maximum specific growth rate coefficient (µ ˆ) and the half-saturation coefficient (K s )-to support parameter estimation if accurate estimates of other model parameters can be obtained. Monte Carlo simulations are conducted with the model to add typical measurement error to the generated dissolved oxygen profiles. Even with measurement error in the dissolved oxygen profile, a pair of biokinetic parameters is always retrievable. The geometric mean of the parameter estimates from the Monte Carlo simulations prove to be an accurate estimator for the true biokinetic values. Higher precision is obtained for µ êstimates than for K s estimates. In summary, this theoretical analysis reveals that an on-line respirometric assay holds promise for measuring extant biofilm kinetic parameters.

9The purpose of the present study was to develop enhanced membrane technologies that 10 can avoid fatal fouling problems, thus making it possible to concentrate microalgae 11 solutions efficiently. A conductive filter called 'electro-membrane' was manufactured 12 and then tested in a cross-flow electro-filtration system. In continuous mode, the applied 13 electric field enhanced the harvesting performance by 150% compared with using a 14 commercial membrane, demonstrating the anti-fouling property of the synthesized 15 electro-membrane. In discrete mode, the membrane surface, in which microalgae cells 16 were clogged, was almost completely cleansed by the use of a periodic powerful 17 repulsive force, resulting in flux recovery to the initial high level. 18

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We previously reported on the mineralization of 2,4‐dinitrotoluene (2,4‐DNT) and 2,6‐dinitrotoluene (2,6‐DNT) in an aerobic fluidized‐bed bioreactor (FBBR) (Lendenmann et al. 1998 Environ Sci Technol 32:82–87). The current study examines the kinetics of 2,4‐DNT and 2,6‐DNT mineralization at increasing loading rates in the FBBR with the goal of obtaining system‐independent kinetic parameters. At each steady state, the FBBR was subjected to a set of transient load experiments in which substrate flux in the biofilm and bulk substrate concentrations were measured. The pseudo‐steady‐state data were used to estimate the biokinetic parameters for 2,4‐DNT and 2,6‐DNT removal using a mechanistic mathematical biofilm model and a routine that minimized the sum of the squared residuals (RSS). Estimated kinetic parameters varied slightly for each steady‐state; retrieved parameters for qm were 0.83 to 0.98 g DNT/g XCOD d for 2,4‐DNT removal and 0.14 to 0.33 g DNT/g XCOD d for 2,6‐DNT removal. Ks values for 2,4‐DNT removal (0.029 to 0.36 g DNT/m3) were consistently lower than Ks values for 2,6‐DNT removal (0.21 to 0.84 g DNT/m3). A new approach was introduced to estimate the fundamental biofilm kinetic parameter S *italicb,min from steady‐state performance information. Values of S *italicb,min indicated that the FBBR performance was limited by growth potential. Adequate performance of the examined FBBR technology at higher loading rates will depend on an improvement in the growth potential. The obtained kinetic parameters, qm, Ks, and S *italicb,min, can be used to aid in the design of aerobic FBBRs treating waters containing DNT mixtures. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 63: 642–653, 1999.