A benchmark simulation to verify an inhibition model on decay stage for nitrification.

Activated Sludge Models (ASMs) are widely used for biological wastewater treatment plant design, optimisation and operation. In commonly used ASMs, the nitrification process is modelled as a one-step process. However, in some process configurations, it is desirable to model the concentration of nitrite nitrogen through a two-step nitrification process. In this study, the benchmark datasets published by the Water Environment Research Foundation (WERF) were used to develop a two-step nitrification model considering the kinetics of Ammonium Oxidising Bacteria (AOB) and Nitrite Oxidising Bacteria (NOB). The WERF datasets were collected from a chemostat reactor fed about 1,000 mg-NH3-N/L synthetic influent with at different sludge retention times of 20, 10 and 5-d, whereas the pH in the reactor varied in the range of 5.8 and 8.8. Supplemental laboratory batch experiments were conducted to assess the toxicity of nitrite-N on nitrifying bacteria. These tests suggested that 500 mg-N/L of nitrite at pH 7.3 was toxic to NOB and resulted in continuous decrease in bulk oxygen uptake rate. To model this phenomenon, a poisoning model was used instead of the traditional Haldane-type inhibition model. The poisoning model for NOB and AOB with different threshold poisonings for unionised NO2-N and NH3-N concentrations could successfully reproduce the three WERF datasets.

Abiotic reduction of nitroaromatic contaminants by iron(II) complexes with organothiol ligands.

Complexation of Fe(II) by dissolved and surface-bound ligands can significantly modify the metal's redox reactivity, and recent work reveals that Fe(II) complexes with selected classes of organic ligands are potent reductants that may contribute to the natural attenuation of subsurface contaminants. In the present study, we investigated the reactivity of Fe(II)-organothiol ligand complexes with nitroaromatic contaminants (NACs; ArNO(2)). Experimental results show that NACs are unreactive in Fe(2+)-only and ligand-only solutions but are reduced to the corresponding aniline compounds (ArNH(2)) in solutions containing both Fe(II) and a number of organothiol ligands. Observed reaction rates are highly dependent on the structure of the Fe(II)-complexing ligand, solution composition, Fe(II) speciation, and NAC structure. For two model ligands, cysteine and thioglycolic acid, observed pseudo-first order rate constants for 4-chloronitrobenzene reduction (k(obs); 1/s) are linearly correlated with the concentration of the respective 1:2 Fe(II)- organothiol complexes (FeL(2)(2-)), and k(obs) measurements are accurately predicted by k(obs) = k(FeL(2-)(2))[FeL(2-)(2)], where k(FeL(2-)(2)) = 1.70 (+/-0.59) 1/M/s and 26.0 (+/-4.8) 1/M/s for cysteine and thioglycolic acid, respectively. The high reactivity of these Fe(II) complexes is attributed to a lowering of the standard one-electron reduction potential of the Fe(III)/Fe(II) redox couple on complexation by organothiol ligands. The relative reactivity of a series of substituted NACs with individual Fe(II) complexes can be described by linear free-energy relationships with the apparent one-electron reduction potentials of the NACs. Tests also show that organothiol ligands can further promote NAC reduction indirectly by re-reducing the Fe(III) that forms when Fe(II) complexes are oxidized by reactions with the NACs.

[Carotid artery stenting via a transbrachial artery: techniques and problems].

Recently, carotid artery stenting (CAS) has been reported to be an alternative of carotid endarterectomy (CEA) for internal carotid artery (ICA) stenosis due to the improvement of protection devices. In general, the transfemoral approach has been chosen for CAS because of the sizes of the devices. However, the transfemoral route seems to be unavailable or at high risk, in cases of severe atherosclerotic changes or aneurysm of the femoral, iliac artery or aorta, or after bypass graft placement. In this report, we presented 5 patients who underwent CAS using the transbrachial approach. The mean stenotic rate of 84% before treatment was reduced to 14% after the procedures. The 30-day morbidity and mortality were both 0%. Major local complications at the puncture site were not encountered. There has been no stroke nor death during a mean follow-up period of 6 months. We suggest that CAS via transbrachial route is an effective and safe treatment for ICA stenosis, by use of low-profile devices and bi-plane DSA equipment, especially in patients who are not eligible for the transfemoral access.

Sensory perception during sleep in humans: a magnetoencephalograhic study.

We reported the changes of brain responses during sleep following auditory, visual, somatosensory and painful somatosensory stimulation by using magnetoencephalography (MEG). Surprisingly, very large changes were found under all conditions, although the changes in each were not the same. However, there are some common findings. Short-latency components, reflecting the primary cortical activities generated in the primary sensory cortex for each stimulus kind, show no significant change, or are slightly prolonged in latency and decreased in amplitude. These findings indicate that the neuronal activities in the primary sensory cortex are not affected or are only slightly inhibited during sleep. By contrast, middle- and long-latency components, probably reflecting secondary activities, are much affected during sleep. Since the dipole location is changed (auditory stimulation), unchanged (somatosensory stimulation) or vague (visual stimulation) between the state of being awake and asleep, different regions responsible for such changes of activity may be one explanation, although the activated regions are very close to each other. The enhancement of activities probably indicates two possibilities, an increase in the activity of excitatory systems during sleep, or a decrease in the activity of some inhibitory systems, which are active in the awake state. We have no evidence to support either, but we prefer the latter, since it is difficult to consider why neuronal activities would be increased during sleep.

Microvascular decompression of cranial nerves using sheets of a dural substitute--technical note.

Several types of prosthesis are used for microvascular decompression (MVD) surgery for neurovascular compression syndrome. However, most prostheses adhere to the surrounding neuronal structures and occasionally cause granulomas. The present study evaluated a dural substitute made of expanded polytetrafluoroethylene, the Gore-Tex EPTFE patch, as a prosthesis for MVD. Twelve patients with trigeminal neuralgia, 19 patients with hemifacial spasm (HFS), and two patients with glossopharyngeal neuralgia underwent MVD using the dural substitute. In most cases, one or two sheets of the dural substitute were inserted between the offending artery and the compression site covering the cranial nerve and the brainstem. Thirty of the 33 patients experienced complete relief of the symptoms that lasted for at least 10-75 months after the surgery. HFS recurred one month post-surgery in a patient who underwent MVD using two small sheets. Varied grades of hearing disturbance were observed in three patients with HFS. MVD using dural substitute is an easy and efficient method because it is not necessary to move the offending arteries away from the compression site. Large sheets should be positioned over the compression site for sufficient decompression. However, this technique needs to be improved so that the prosthesis does not affect cranial nerve VIII, as three of 19 patients with HFS showed hearing disturbances despite intraoperative monitoring of the auditory brainstem response.

Abiotic reduction of nitroaromatic compounds by aqueous iron(ll)-catechol complexes.

Complexation of iron(ll) by catechol and thiol ligands leads to the formation of aqueous species that are capable of reducing substituted nitroaromatic compounds (NACs) to the corresponding anilines. No reactions of NACs are observed in FelI-only or ligand-only solutions. In solutions containing FeII and tiron, a model catechol, rates of NAC reduction are heavily dependent on pH, ligand concentration, and ionic strength. Observed pseudo-first-order rate constants (k(obs)) for 4-chloronitrobenzene reduction vary by more than 6 orders of magnitude, and the variability is well described by the expression k(obs) = k(FeL2)(6-) [FeL2(6-)], where [FeL2(6-)] is the concentration of the 1:2 FeII-tiron complex and kFeL2(6-) is the bimolecular rate constant for 4-chloronitrobenzene reaction with this species. The high reactivity of this FeII species is attributed to the low standard one-electron reduction potential of the corresponding FeIII/FeII redox couple (EH0 = -0.509 V vs NHE). The relative reactivity of different NACs can be described by a linear free-energy relationship (LFER) with the one-electron reduction potentials of the NACs, EH1'(ArNO2). The experimentally derived slope of the LFER indicates that electron transfer is rate determining. These findings suggest that FeII-organic complexes may play an important, previously unrecognized, role in the reductive transformation of persistent organic contaminants.