Phosphate removal in a fluidized bed—II. Process optimization

The aggregation of fine primarily formed calcium phosphate particles with sand grains in a fluidized bed for phosphate removal was studied experimentally by means of a set-up which isolated aggregation from other processes during calcium phosphate precipitation, as well as through experiments under normal operation of the fluidized bed. The net aggregation process was described by means of a mathematical model which takes into account two competing mechanisms: orthokinetic aggregation and breakage. The net aggregation process was found to account for ∼ 60% of the phosphate removed by the fluidized bed. It was found that the orthokinetic aggregation can be improved by spreading the supersaturation more evenly throughout the reactor, and breakage can be diminished by a low energy dissipation rate in the bed. Optimization of the phosphate removal efficiency was therefore achieved by selecting sand grains of small sizes (0.1–0.3 mm) and a low superficial velocity (7·10⁻³ m/s), and by spreading the addition of the NaOH solution (reactant) over two dosage points. Under these conditions the phosphate removal efficiency was ∼ 80%.     

Performance,reliability and uncertainty of total phosphorus models for lakes—II. Stochastic analyses

Water quality problems in lakes are frequently analyzed with the assistance of models that simulate the dynamic behavior of total phosphorus. Part I of this series used deterministic methods to evaluate the performance and reliability of models with different formulations and mechanisms. Complex models are often amenable to accurate calibration but may be sensitive to uncertainties in the model coefficients and errors in measured lake data. This paper uses stochastic methods (Monto Carlo) to examine the supposition that the appropriate level of model complexity depends on the accuracy of measured data and the uncertainty associated with model coefficients. Three total phosphorus models are used to test the methodology for Shagawa Lake.     

On the use of the FluoroProbe®, a phytoplankton quantification method based on fluorescence excitation spectra for large-scale surveys of lakes and reservoirs

Although microscope analysis is very useful for studying phytoplankton community composition, it does not allow for high frequency (spatial and/or temporal) data acquisition. In an attempt to overcome this issue, fluorescence-based approaches that use selective excitation of pigment antennae have spread rapidly. However, the ability of spectral fluorescence to provide accurate estimates of phytoplankton biomass and composition is still debated, and only a few datasets have been tested to date.In this study, we sampled of a wide range of water bodies (n = 50) in the Ile-de-France region (North Central France). We used the resulting extensive dataset to assess the ability of the bbe-Moldaenke FluoroProbe II (FP) to estimate phytoplankton community composition in lakes and reservoirs.We demonstrated that FP data yields better estimates of total phytoplankton biovolume than do spectrophotometric chlorophyll a measures and that FP data can be further corrected using the average chlorophyll a to biovolume ratio among phytoplankton groups. Overall, group-specific relationships between FP and biovolume data were consistent. However, we identified a number of cases where caution is required. We found that Euglenophytes are expected to depart from the global FP vs. biovolume relationship of the ‘green’ group due to varying Fv/Fm and pigment content in response to environmental conditions (photoautotrophic vs. photoheterotrophic growth). Then, it appears necessary to consider the composition of the Chromophytes community in order to obtain a good agreement between both biomass estimation methods. Finally, we confirmed the misattribution toward the ‘red’ group of phycoerythrin-containing cyanobacteria and the occurrence of a strong scattering in the relationship between the FP vs. biovolume of the ‘blue’ group that can be partly attributed to the occurrence of large colony-forming cyanobacteria (e.g., Microcystis spp, Aphanizomenon flos-aquae).We propose correcting procedures to improve the quality of data obtained from spectral fluorescence tools in the context of large-scale sampling of lakes and reservoirs.     

Factors affecting the coprecipitation of inorganic phosphate with calcite in hardwaters—II Recirculating experimental stream system

Calcite precipitation and phosphate coprecipitation on calcite observed in experimental stream systems has been studied in detail and the results analysed using chemical kinetic models. Two series of experiments were done in the experimental stream systems, both under dark conditions, one without sediment and the other with a flint gravel substrate. The major effect of the gravel was to release inorganic phosphate into the water and so replace a fraction of the phosphate which had been coprecipitated. Under laboratory conditions this release was enough to lead to an increase in phosphate concentration and eventually completely inhibit calcite growth.     

Project management and burnout: Implications of the Demand–Control–Support model on project-based work

Project-based work has long been characterized as frenetic, fast-paced, and dynamic. The often competing constraints imposed by schedules, stakeholders, and budgetary restrictions make project activities conflict-laden and highly conducive to work-related stress. Stress is not an end unto itself but instead, is often a precursor for burnout. Burnout is a psychological syndrome of emotional exhaustion, cynicism, and reduced personal accomplishment. This paper reports on the results of a study of burnout among project management personnel. Using the Demand–Control–Support model as our conceptual framework, we analyzed a sample of respondents from four project-intensive organizations. Our findings demonstrated that women tend to experience emotional exhaustion to a greater extent than their male counterparts. Further, control and social support do serve as moderators for the burnout dimensions of emotional exhaustion and cynicism, suggesting limited support for the Demand–Control–Support model. Implications of this study for project management and workplace burnout are discussed.     

Solar energy absorption by acrylic coatings—II: the effect of alternating environmental conditions

Atmospheric corrosion of building materials is an enormously complex and interdisciplinary process. It affects not only the ability of building to perform over the prolonged period of time but also the overall energy consumption. The presented paper is a part of a larger study on application of acrylic plasters in passive solar systems. Absorption characteristics as well as microstructural features of acrylic plasters subjected to alternating climatic conditions have been analysed. In order to simulate the real conditions, samples were exposed to the variations of temperature and humidity, near-daylight radiation (xenon lamp) and subjected to acid and alkaline environments.     

Investigation into the effects of grain size on strength and failure behaviors of granites using a breakable polygonal grain–based model

Bulletin of Engineering Geology and the Environment - The microstructure of rock is one of the most important factors that affect its mechanical behaviors. In order to study the effects of grain...     

Interactions of resin acids with aerobic and anaerobic biomass—II. Partitioning on biosolids

Solutions of five resin acids were contacted with suspensions of non-acclimated, inactivated anaerobic and aerobic biomass to assess the contribution of partitioning on biosolids to the overall removal of resin acids in batch assays. Both types of biomass exhibited resin acid partitioning rates that were significantly greater than the rate of removal by degradation. With non-acclimated anaerobic biomass, partitioning was found to be the sole mechanism of resin acid removal. Partitioning on anaerobic biomass could not be described as a reversible adsorption process. Instead, it was found that a constant fraction of each resin acid partitioned into the biomass phase. With non-acclimated inactivated aerobic biomass, the partitioning of resin acids could be adequately described by a linear partitioning model. Dehydroabietic acid was the resin acid least strongly associated with biomass in both the anaerobic and aerobic experiments.     

Sorption removal of Fe(CN)6 3− ion impurities from water and evaluation of water quality by the biotesting method

The sorption removal of Fe(CN)₆ ^3? ion impurities from water was investigated. A specially synthesized magnesium-aluminum double hydroxide with the hydrotalcite-type structure was used as a sorbent. The biotesting method used for various test objects proved the efficiency of sorption removal of Fe(CN)₆ ^3? from water.     

Population description of the non-methanogenic phase of anaerobic digestion—III. Non-hierarchical classification of isolates by principal component analysis

Non-hierarchical classification of 92 non-methanogenic bacterial isolates obtained from anaerobic digesters yielded an ecologically valuable classification since: (a) interrelationships between characteristics were demonstrated, (b) these interrelations could be interpreted ecologically, (c) the interrelations showed marked similarity to those determined from an agglomerative-polythetic classification and (d) a marked similarity existed between the classifications by means of agglomerative-polythetic procedures and by means of principal component analysis. Principal component analysis was a valuable classification method in this study as in other microbial ecological studies.     

Interactions of resin acids with aerobic and anaerobic biomass—I. Degradation by non-acclimated inocula

The fate and effects of resin acids in anaerobic and aerobic biological treatment systems were compared under batch reactor test conditions. With a non-acclimated anaerobic biomass inoculum, no degradation of resin acids was observed under anaerobic conditions after exposure times of up to 24 d. Inhibition of methanogenic activity of the anaerobic consortium was noted at initial resin acid/biomass ratios exceeding 0.0031 mg resin acids/mg VSS. Inhibited methanogenic populations were capable of acclimation to high concentrations of resin acids after 7–13 d of exposure. Under aerobic batch conditions with a non-acclimated activated sludge inoculum, high initial resin acid concentrations were reduced to detection limits in 2–3 d. The highest specific removal rate of 109 mg resin acids/g VSS · d measured in this study with non-acclimated aerobic biomass, was much higher than comparable values reported by others for acclimated aerobic biomass. The time required for removal appeared to be independent of the batch reactor biomass concentration. No evidence was found to suggest that high concentrations of resin acids resulted in inhibition under aerobic conditions.     

The ecology and chemistry of sandy beaches and nearshore submarine sediments of Natal— II: Pollution criteria for nearshore sediments of the Natal coast

Measurements have been made of some chemical and faunal parameters in nearshore submarine sediments off the Natal coast. Some variations depending on the type of sediment, the depth of water, and the season were detected. Comparisons between polluted and unpolluted areas showed that considerably increased levels of chemical parameters and high faunal densities were associated with organic pollution. The species Capitella capitata was specifically associated with organic pollution. Monitoring control levels are suggested which if exceeded, will indicate the existence of pollution with organic material in the area.