Occurrence and removal of N-nitrosamines in wastewater treatment plants

The presence of nitrosamines in wastewater might pose a risk to water resources even in countries where chlorination or chloramination are hardly used for water disinfection. We studied the variation of concentrations and removal efficiencies of eight N-nitrosamines among 21 full-scale sewage treatment plants (STPs) in Switzerland and temporal variations at one of these plants. N-nitrosodimethylamine (NDMA) was the predominant compound in STP primary effluents with median concentrations in the range of 5-20 ng/L, but peak concentrations up to 1 μg/L. N-nitrosomorpholine (NMOR) was abundant in all plants at concentrations of 5-30 ng/L, other nitrosamines occurred at a lower number of plants at similar levels. From concentrations in urine samples and domestic wastewater we estimated that human excretion accounted for levels of <5 ng/L of NDMA and <1 ng/L of the other nitrosamines in municipal wastewater, additional domestic sources for <5 ng/L of NMOR. Levels above this domestic background are probably caused by industrial or commercial discharges, which results in highly variable concentrations in sewage. Aqueous removal efficiencies in activated sludge treatment were in general above 40% for NMOR and above 60% for the other nitrosamines, but could be lower if concentrations were below 8-15 ng/L in primary effluent. We hypothesize that substrate competition in the cometabolic degradation explains the occurrence of such threshold concentrations. An additional sand filtration step resulted in a further removal of nitrosamines from secondary effluents even at low concentrations. Concentrations released to surface waters were largely below 10 ng/L, suggesting a low impact on Swiss water resources and drinking water generation considering the generally high environmental dilution and possible degradation. However, local impacts in case a larger fraction of wastewater is present cannot be ruled out.     

Bis(trifluoromethyl)carbinol polynorbornene as a pseudo-polyelectrolyte in multilayered films

Using weak, opposed to strong polyelectrolytes in multilayer polymer systems provides a convenient means of altering some of the physico-chemical properties of these thin films. Recently, we pushed the limits of the weak polyacids by the introduction of an additional class of polyelectrolytes, the pseudo-polyelectrolytes (pPE). This paper focuses on another pPE, poly[5-(2-trifluoromethyl-1,1,1-trifluoro-2-hydroxypropyl)-2-norbornene] (PNBHFA). As, with poly(4-vinylphenol), multilayer assembly with both a weak and a strong polycation was accomplished from aqueous media. However, this was achieved only at a high pH value of 12.0. The films that were produced were exceptionally thick, > 1.25 μm after only 30 total layers for the poly(allylamine hydrochloride)/PNBHFA system. The films were very hydrophobic with the contact angle of water increasing with the layer number; reaching a maximum of ~ 123° after 50 total layers of poly(diallyldimethylammonium chloride)/PNBHFA.     

Improved technique for measuring the ball volume removed in a ball-on-disk test

The volume removed from a ball as it slides against an abrasive surface is usually estimated by assuming that the wear scar formed on the ball is flat and circular and that the ball undergoes no plastic deformation. We show that these assumptions can lead to large errors. A simple alternative, in which we integrate the surface profile of the ball after wear, is demonstrated. This approach gives accurate results for wear scars that are not flat or circular, and it distinguishes plastic deformation from material removal.     

Extinction limits and associated uncertainties of nonpremixed counterflow flames of methane,ethylene, propylene and n-butane in air

Fundamental flame characteristics derived from counterflow flames are routinely used in chemical kinetic model optimization and validation. This paper reports an experimental and computational investigation aimed at understanding and quantifying the source of uncertainties associated with such characterization of extinction limits of fuel–air mixtures, ranging from low extinction strain rate methane–air flames to high-extinction strain rate ethylene–air flames. In the experiments, two pairs of convergent nozzles with exit diameters of 7.9 mm and 14.5 mm were used to introduce opposed jets of nonpremixed fuel and air to establish a planar flame in the counterflow mixing region. Velocity profiles and extinction data were measured using both LV and PIV setups. Experiments were conducted at various nozzle separation distances to investigate potential differences in axial velocity profiles along the axial and radial directions and the corresponding local extinction strain rates. The slope of axial velocity in the axial and radial directions at the air outlet boundary was found to increase with decreasing nozzle separation distance. The variation of local extinction strain rate with changes in separation distance was within the uncertainty of experimental data. Using a C1–C4 chemical kinetic model, quasi one-dimensional computations have been performed to quantify the experimentally determined boundary condition effects on the predicted extinction strain rate of counterflow flames.     

Obituary: Benjamin B. Wolman (1908-2000).

Memorializes Benjamin B. Wolman for his many contributions to psychology. He was proudest of a modification of psychoanalysis that he called the interactional approach. Wolman founded the International Organization for the Study of Group Tensions and the International Journal of Group Tensions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bilinear approach to multiuser second-order statistics-based blindchannel estimation

We present a bilinear approach to multiple-input multiple-output (MIMO) blind channel estimation where products of the channel parameters are first estimated from the covariance of the received data. The channel parameters are then obtained as the dominant eigenvectors of the outer-product estimate. Necessary and sufficient identifiability conditions are presented for a single channel and extended to the multichannel case. It is found that this technique can identify the channel to within a subspace ambiguity, as long as the basis functions for the channel satisfy certain constraints, regardless of the left invertability of the channel matrix. One important requirement for identifiability is that the number of channel parameters is small compared with the channel length; advantageously, this is exactly the situation in which this algorithm has significantly lower complexity than competing (parametric, multiuser) blind algorithms. Simulations show that the technique is applicable in situations where typical identifiability conditions fail: common nulls, a single symbol-spaced channel, and more users than channels. These simulations are for the “almost flat” faded situation when the propagation delay spread is a fraction of the transmission pulse duration (as might be found in current TDMA systems). Comparisons are made, when possible, to a subspace method incorporating knowledge of the basis functions. The bilinear approach requires significantly less computation but performs better than the subspace method at low SNR, especially for multiple users     

Compact Slanted Grating Couplers Between Optical Fiber and InP–InGaAsP Waveguides

We present theoretical and experimental results for compact slanted gratings for vertical coupling between single-mode fiber and InP-InGaAsP waveguides. The maximum calculated coupling efficiency is 59%. We have measured a coupling efficiency of 16% for a 10-mum-long slanted grating     

Knowledge management as a decision support method: a diagnostic workup strategy application

We have explored the potential of a computer-based approach called "knowledge management" to aid in clinical problem solving and education. The major features of the approach are its ability to support flexible and immediate access by a user to relevant knowledge and annotation and organization of the knowledge for personal use and subsequent retrieval. We illustrate this approach with its application to diagnostic workup strategy problems. In this application, knowledge may be in the form of static narrative text, diagrams, pictures, graphs, tables, flow charts, or bibliographic citations. Other more dynamic forms of knowledge may be the result of simulations, "what if" analyses or modeling, quantitative mathematical or statistical calculation, or heuristic inference. User assessment has demonstrated the system's ease of use and user perception of its desirability, but underscores the need for a "critical mass" of knowledge before such an approach will be widely utilized.     

Kinetic assessment and modeling of an ozonation step for full-scale municipal wastewater treatment: Micropollutant oxidation, by-product formation and disinfection

The kinetics of oxidation and disinfection processes during ozonation in a full-scale reactor treating secondary wastewater effluent were investigated for seven ozone doses ranging from 0.21 to 1.24 g O₃ g⁻¹ dissolved organic carbon (DOC). Substances reacting fast with ozone, such as diclofenac or carbamazepine (kP,O₃ > 10⁴ M⁻¹ s⁻¹), were eliminated within the gas bubble column, except for the lowest ozone dose of 0.21 g O₃ g⁻¹ DOC. For this low dose, this could be attributed to short-circuiting within the reactor. Substances with lower ozone reactivity (kP,O₃ < 10⁴ M⁻¹ s⁻¹) were only fully eliminated for higher ozone doses.The predictions of micropollutant oxidation based on coupling reactor hydraulics with ozone chemistry and reaction kinetics were up to a factor of 2.5 higher than full-scale measurements. Monte Carlo simulations showed that the observed differences were higher than model uncertainties. The overestimation of micropollutant oxidation was attributed to a protection of micropollutants from ozone attack by the interaction with aquatic colloids. Laboratory-scale batch experiments using wastewater from the same full-scale treatment plant could predict the oxidation of slowly-reacting micropollutants on the full-scale level within a factor of 1.5. The Rct value, the experimentally determined ratio of the concentrations of hydroxyl radicals and ozone, was identified as a major contribution to this difference.An increase in the formation of bromate, a potential human carcinogen, was observed with increasing ozone doses. The final concentration for the highest ozone dose of 1.24 g O₃ g⁻¹ DOC was 7.5 μg L⁻¹, which is below the drinking water standard of 10 μg L⁻¹. N-Nitrosodimethylamine (NDMA) formation of up to 15 ng L⁻¹ was observed in the first compartment of the reactor, followed by a slight elimination during sand filtration. Assimilable organic carbon (AOC) increased up to 740 μg AOC L⁻¹, with no clear trend when correlated to the ozone dose, and decreased by up to 50% during post-sand filtration. The disinfection capacity of the ozone reactor was assessed to be 1-4.5 log units in terms of total cell counts (TCC) and 0.5 to 2.5 log units for Escherichia coli (E. coli). Regrowth of up to 2.5 log units during sand filtration was observed for TCC while no regrowth occurred for E. coli. E. coli inactivation could not be accurately predicted by the model approach, most likely due to shielding of E. coli by flocs.