Pilot plant demonstration of stable and efficient high rate biological nutrient removal with low dissolved oxygen conditions.

Aeration in biological nutrient removal (BNR) processes accounts for nearly half of the total electricity costs at many wastewater treatment plants. Even though conventional BNR processes are usually operated to have aerated zones with high dissolved oxygen (DO) concentrations, recent research has shown that nitrification can be maintained using very low-DO concentrations (e.g., below 0.2 mg O2/L), and therefore, it may be possible to reduce energy use and costs in BNR facilities by decreasing aeration. However, the effect of reduced aeration on enhanced biological phosphorus removal (EBPR) is not understood. In this study, we investigated, at the pilot-scale level, the effect of using minimal aeration on the performance of an EBPR process. Over a 16-month operational period, we performed stepwise decreases in aeration, reaching an average DO concentration of 0.33 mg O2/L with stable operation and nearly 90% phosphorus removal. Under these low-DO conditions, nitrification efficiency was maintained, and nearly 70% of the nitrogen was denitrified, without the need for internal recycling of high nitrate aeration basin effluent to the anoxic zone. At the lowest DO conditions used, we estimate a 25% reduction in energy use for aeration compared to conventional BNR operation. Our improved understanding of the efficiency of low-DO BNR contributes to the global goal of reducing energy consumption during wastewater treatment operations.

Investigating the pharmacodynamics of ketamine in children.

BACKGROUND: The aim of this study was to describe ketamine pharmacodynamics (PD) in children. Adult ketamine concentrations during recovery are reported as 0.74 mg.l(-1) (sd 0.24 mg.l(-1)) with an EC(50) for anesthesia of 2 mg.l(-1) (sd 0.5 mg.l(-1)), but pediatric data are few. METHODS: Children presenting for painful procedures in an Emergency Department were given ketamine 1-1.5 mg.kg(-1) i.v. Blood was assayed for ketamine on three to six occasions (median 3) over the subsequent 14-152 min (median 28.5). Procedures were videotaped. Level of sedation (0-5; unresponsive - spontaneously awake without stimulus) and a test of memory were recorded. PD was investigated using a variable slope E(max) model (sedation) or logistic regression (arousal time, memory) with nonlinear mixed effects models. RESULTS: In total 60 children were enrolled. Pharmacokinetic data were collected in 54 of these children and there were 43 children available for PD study. The mean age was 8.15 years (sd 3.5 years) and weight was 34.9 kg (sd 15.8 kg). The half-time describing equilibration between the effect compartment and central compartment was 11 s (95% CI 0.07-20 s). The EC(50) for arousal was 0.52 (90% CI 0.22-1.17) mg.l(-1). The E(max) model with a baseline (E(0)) of five (spontaneously awake without stimulus) yielded a fractional E(max) 0.939 [coefficient of variability (CV) 24%], an EC(50) 0.56 (CV 136%) mg.l(-1) and a Hill coefficient 3.71. The EC(50) for recall memory was 0.44 (90% CI 0.09-1.70) mg.l(-1). The EC(50) for remembering was 0.38 (90% CI 0.12-1.75) mg.l(-1). CONCLUSIONS: Concentrations associated with arousal in children are analogous to adults. The ability to recall and remember occurs at similar concentrations to those associated with arousal. A concentration of 1 mg.l(-1) was associated with a sedation level of three or less (arouses to consciousness with moderate tactile or loud verbal stimulus) in 95% of children while 1.5 mg.l(-1) was associated with a sedation level of two or less (rouses slowly to consciousness with sustained painful stimulus) in 95% of children. These concentrations can be attained for 3-4 min after 1 mg.kg(-1) and 1.5 mg.kg(-1) ketamine IV bolus, respectively. The mean arousal time can be anticipated at approximately 10 min (1 mg.kg(-1)) and 15 min (1.5 mg.kg(-1)).

Conscious sedation reduces distress in children undergoing voiding cystourethrography and does not interfere with the diagnosis of vesicoureteric reflux: a randomized controlled study.

OBJECTIVE: Voiding cystourethrography (VCU) is a distressing procedure for children. Conscious sedation using oral midazolam may reduce this distress, but its use may also alter the ability of the VCU to show vesicoureteric reflux (VUR). The objectives of our study were to assess the effectiveness of conscious sedation using oral midazolam when administered routinely in children undergoing VCU and to ensure that conscious sedation using oral midazolam does not alter the ability of VCU to show VUR. SUBJECTS AND METHODS: Our study was a randomized double-blind controlled trial performed at a university teaching hospital; our study group consisted of children over the age of 1 year who been referred for their first VCU examination from July 2001 to July 2003. Participants were randomized to receive a placebo or midazolam syrup (0.5 mg/kg) before the examination. The primary outcome measures were the Groningen Distress Rating Scale (GDRS) and grading of VUR, as defined by the international grading system established by the International Reflux Study Group. RESULTS: There were no serious adverse events. One hundred thirty-nine children were randomized in the study, and 117 underwent complete assessment. Eight who underwent VCU after the study day were included in a "complete case" intention-to-treat analysis. In the placebo group, 34 children (61%) experienced serious distress or severe distress (GDRS score, 3 or 4). In the midazolam group, 16 children (26%) experienced the same degree of distress. There was a significant difference between the GDRS scores (nonlinear mixed-model analysis, p < 0.001) of the two study groups. The number needed to treat to reduce serious or severe distress in one child was 2.9 (95% CI, 1.9-5.5). VUR was identified in 16% of all children. There was no difference in VUR grading between the groups (nonlinear mixed-model analysis, p = 0.31). CONCLUSION: Routine use of oral midazolam (0.5 mg/kg) for conscious sedation of children undergoing VCU reduces distress and does not alter the ability of VCU to show VUR well enough to allow diagnosis.