A titrimetric respirometer measuring the nitrifiable nitrogen in wastewater using in-sensor-experiment

Measurement of nitrifiable nitrogen contained in wastewater by combining the existing respirometric and titrimetric principles is reported. During an in-sensor-experiment using nitrifying activated sludge. both the dissolved oxygen (DO) and pH in the mixed liquor were measured, and the FH was controlled at a set-point through titration of base or acid. A combination of the oxygen uptake rate (OUR), which was obtained from the measured DO signal, and the titration data allowed calculation of the nitrifiable nitrogen and the short-term biological oxygen demand (BOD) of the wastewater sample that was initially added to the sludge. The calculation was based solely on stoichiometric relationships. The approach was preliminarily tested with two types of wastewaters using a prototype sensor. Good correlation was obtained. (C) 2000 Elsevier Science Ltd. All rights reserved.

Development of a novel titration and off-gas analysis (TOGA) sensor for study of biological processes in wastewater treatment systems

The development of the new TOGA (titration and off-gas analysis) sensor for the detailed study of biological processes in wastewater treatment systems is outlined. The main innovation of the sensor is the amalgamation of titrimetric and off-gas measurement techniques. The resulting measured signals are: hydrogen ion production rate (HPR), oxygen transfer rate (OTR), nitrogen transfer rate (NTR), and carbon dioxide transfer rate (CTR). While OTR and NTR are applicable to aerobic and anoxic conditions, respectively, HPR and CTR are useful signals under all of the conditions found in biological wastewater treatment systems, namely, aerobic, anoxic and anaerobic. The sensor is therefore a powerful tool for studying the key biological processes under all these conditions. A major benefit from the integration of the titrimetric and off-gas analysis methods is that the acid/base buffering systems, in particular the bicarbonate system, are properly accounted for. Experimental data resulting from the TOGA sensor in aerobic, anoxic, and anaerobic conditions demonstrates the strength of the new sensor. In the aerobic environment, carbon oxidation (using acetate as an example carbon source) and nitrification are studied. Both the carbon and ammonia removal rates measured by the sensor compare very well with those obtained from off-line chemical analysis. Further, the aerobic acetate removal process is examined at a fundamental level using the metabolic pathway and stoichiometry established in the literature, whereby the rate of formation of storage products is identified. Under anoxic conditions, the denitrification process is monitored and, again, the measured rate of nitrogen gas transfer (NTR) matches well with the removal of the oxidised nitrogen compounds (measured chemically). In the anaerobic environment, the enhanced biological phosphorus process was investigated. In this case, the measured sensor signals (HPR and CTR) resulting from acetate uptake were used to determine the ratio of the rates of carbon dioxide production by competing groups of microorganisms, which consequently is a measure of the activity of these organisms. The sensor involves the use of expensive equipment such as a mass spectrometer and requires special gases to operate, thus incurring significant capital and operational costs. This makes the sensor more an advanced laboratory tool than an on-line sensor. (C) 2003 Wiley Periodicals, Inc.

Clinicians' evaluations of fetal oximetry sensor placement in a multicentre randomised trial (the FOREMOST trial)

Background: Fetal pulse oximetry (FPO) may improve the assessment of the fetal well-being in labour. Reports of health-care provider's evaluations of new technology are important in the overall evaluation of that technology. Aims: To determine doctors' and midwives' perceptions of their experience placing FPO sensors. Methods: We surveyed clinicians (midwives and doctors) following placement of a FPO sensor during the FOREMOST trial (multicentre randomised trial of fetal pulse oximetry). Clinicians rated ease of sensor placement (poor, fair, good and excellent). Potential influences on ease of sensor placement (staff category, prior experience in Birth Suite, prior experience in placing sensors, epidural analgesia, cervical dilatation and fetal station) were examined by ordinal regression. Results: There were 281 surveys returned for the 294 sensor placement attempts (response rate 96%). Sensors were placed by midwives (29%), research midwives (48%), registrars (22%) and obstetricians (1%). The majority of clinicians had 1 or more years' Birth Suite experience, had placed six or more sensors previously, and rated ease of sensor placement as good. Advancing fetal station (P < 0.001) and the presence of epidural analgesia prior to sensor placement (P = 0.029) predicted improved ease of sensor placement. Having a clinician placing a sensor for the first time predicted a lower rating for ease of sensor placement (P = 0.001), compared to having placed one or more sensors previously. Conclusions: Clinicians with varying levels of Birth Suite experience successfully placed fetal oxygen saturation sensors, with the majority rating ease of sensor placement as good.