Search results for "RETENTION"

Pressures, rewards and teacher retention: a comparative study of primary teaching in England and Finland

2004

The article presents some findings from the York‐Jyvaskyla Teacher Professionalism project. The project was a follow‐up study to earlier case‐study research in six schools in Finland and six schools in England on the impact of educational reforms on teachers' work. Data were collected by re‐interviewing a sample of teachers from the original schools six years later. The views of English and Finnish teachers concerning the ways in which changes in practice, pay and working conditions affected their perception of teaching as a profession are contrasted. The crucial factors discouraging teachers from remaining in teaching were work intensification, low pay, deteriorating pupil behaviour and a …

Discussion of “Soil Water Retention Characteristics of Vertisols and Pedotransfer Functions Based on Nearest Neighbor and Neural Networks Approaches …

2013

Sensitive Screening of New Psychoactive Substances in Serum Using Liquid Chromatography-Quadrupole Time-of-Flight Mass Spectrometry.

2021

Abstract Analysis of new psychoactive substances (NPS) still poses a challenge for many institutions due to the number of available substances and the constantly changing drug market. Both new and well-known substances keep appearing and disappearing on the market, making it hard to adapt analytical methods in a timely manner. In this study we developed a qualitative screening approach for serum samples by means of liquid chromatography--quadrupole time-of-flight mass spectrometry. Samples were measured in data-dependent auto tandem mass spectrometry mode and identified by fragment spectra comparison, retention time and accurate mass. Approximately 500 NPS, including 195 synthetic cannabino…

Optimising an outdoor membrane photobioreactor for tertiary sewage treatment

2019

[EN] The operation of an outdoor membrane photobioreactor plant which treated the effluent of an anaerobic membrane bioreactor was optimised. Biomass retention times of 4.5, 6, and 9 days were tested. At a biomass retention time of 4.5 days, maximum nitrogen recovery rate:light irradiance ratios, photosynthetic efficiencies and carbon biofixations of 51.7¿±¿14.3¿mg¿N·mol¿1, 4.4¿±¿1.6% and 0.50¿±¿0.05¿kg CO2·m3influent, respectively, were attained. Minimum membrane fouling rates were achieved when operating at the shortest biomass retention time because of the lower solid concentration and the negligible amount of cyanobacteria and protozoa. Hydraulic retention times of 3.5, 2, and 1.5 days …

Comparison of Activated Sludge Processes at Different Temperatures: 35°C, 27–55°C, and 55°C

2002

The performance of mesophilic (35°C; referred to as R1) and thermophilic (55°C; R3) laboratory activated sludge processes (ASPs) as well as ASP with a fluctuating temperature (27-56°C; R2) was compared. During the 124-day runs, in R1 and R3 hydraulic retention time was gradually reduced from 18 h to 3 h, corresponding to an increase in volumetric loading rate from 2 to 10 kg soluble COD m−3d−1; in R2 hydraulic retention time was gradually reduced from 18 to 4.5 h, corresponding to an increase in volumetric loading rate from 2 to 7.5 kg soluble COD m−3d−1. R1 removed on average 85% of soluble COD (GF50-filtered) that was approximately 10% more than R3. In R2 SCOD removal was dependent on the…

Gas-lift anaerobic dynamic membrane bioreactors for high strength synthetic wastewater treatment: Effect of biogas sparging velocity and HRT on treat…

2016

Abstract A laboratory scale external anaerobic dynamic membrane bioreactor (AnDMBR) treating high strength wastewater (influent COD ≈ 20 g/L) was operated to assess the effect of biogas sparging velocity (GSV) and hydraulic retention time (HRT) on removal efficiency and dynamic membrane (DM) filtration characteristics. An increase in GSV resulted in a decrease in DM filtration resistance. DM or cake layer was identified as the main contributor to the total filtration resistance. The external AnDMBR achieved over 99% COD removal efficiency irrespective of the GSV. The results showed that the DM formation process proceeded until a stable cake layer was reached. Reducing of HRT resulted in an …

Biomethane production from maize and liquid cow manure – Effect of share of maize, post-methanation potential and digestate characteristics

2013

Abstract This study investigates the co-digestion of liquid cow manure and maize with different share of maize in continuously stirred tank reactors (CSTRs). The objective was to determine the methane yield of reactor and the post-methanation potential of the digestate from different reactor trials. The highest specific methane yield (259 Nl CH 4 /kg volatile solids (VSs)) was obtained when the share of maize in the feedstock was 40% (VS) and the second highest specific methane yield was when the proportion of maize was 60% (VS) (234 Nl CH 4 /kg VS). The post-methanation potential of the digestate was determined in batch assays. The minimum value (maize 40%, 75 ± 1 Nl CH 4 /kg VS feed ) occ…

Long-term thermophilic mono-digestion of rendering wastes and co-digestion with potato pulp

2014

In this study, mono-digestion of rendering wastes and co-digestion of rendering wastes with potato pulp were studied for the first time in continuous stirred tank reactor (CSTR) experiments at 55°C. Rendering wastes have high protein and lipid contents and are considered good substrates for methane production. However, accumulation of digestion intermediate products viz., volatile fatty acids (VFAs), long chain fatty acids (LCFAs) and ammonia nitrogen (NH4-N and/or free NH3) can cause process imbalance during the digestion. Mono-digestion of rendering wastes at an organic loading rate (OLR) of 1.5 kg volatile solids (VS)/m(3)d and hydraulic retention time (HRT) of 50 d was unstable and resu…

Hydrogen and methane production in extreme thermophilic conditions in two-stage (upflow anaerobic sludge bed) UASB reactor system

2013

Abstract Two-stage hydrogen and methane production in extreme thermophilic (70 °C) conditions was demonstrated for the first time in UASB-reactor system. Inoculum used in hydrogen and methane reactors was granular sludge from mesophilic internal circulation reactor and was first acclimated for extreme thermophilic conditions. In hydrogen reactor, operated with hydraulic retention time (HRT) of 5 h and organic loading rate (OLR) of 25.1 kg COD/m 3 /d, hydrogen yield was 0.73 mol/mol glucose added . Methane was produced in second stage from hydrogen reactor effluent. In methane reactor operated with HRT of 13 h and OLR of 7.8 kg COD/m 3 /d, methane yield was 117.5 ml/g COD added . These resul…

Using Static and Dynamic Indicators to Evaluate Soil Physical Quality in a Sicilian Area

2013

Both capacitive indicators derived from the water retention curve and dynamic measurements of the flow-weighted mean pore radius, R0, were used to assess the soil physical quality of two agricultural areas (cropland and olive orchard) and two natural areas (grassland and managed woodlot plantation) potentially subject to soil degradation. The overall idea of the study was to investigate whether a dynamic indicator quantitatively derived from hydraulic conductivity measurements could be used to supplement the traditionally applied capacitive indicators retrieved from water retention measurements. According to the available criteria, only the surface layer of the cropland site showed optimal …