Inorganic nitrogen transformations in the treatment of landfill leachate with a high ammonium load: A case study

The inorganic nitrogen transformations occurring at a municipal waste leachate treatment facility were investigated. The treatment facility consisted of a collection well and an artificial wetland between two aeration ponds. The first aeration pond showed a decrease in ammonium (from 3480 (± 120) to 630(± 90) mg ⋅ L⁻¹), a reduction in inorganic nitrogen load (3480 to 1680 mg N ⋅ L⁻¹), and an accumulation of nitrite (< 1.3 mg-N ⋅ L⁻¹ in the collection well, to 1030 mg-N ⋅ L⁻¹). Incomplete ammonium oxidation was presumably the result of the low concentration of carbonate alkalinity (∼2 mg ⋅ L⁻¹), which may cause a limitation in the ammonium oxidation rate of nitrifiers. Low carbonate alkalinity levels may have been the result of stripping of CO₂ from the first aeration pond at the high aeration rates and low pH. Various chemodenitrification mechanisms are discussed as the reason for the reduction in the inorganic nitrogen load, including; the reduction of nitrite by iron (II) (producing various forms of gaseous nitrogen); and reactions involving nitrous acid. It is suggested that the accumulation of nitrite may be the result of inhibition of nitrite oxidizers by nitrous acid and low temperatures. Relative to the first aeration pond, the speciation and concentration of inorganic nitrogen was stable in the wetlands and 2nd aeration pond. The limited denitrification in the wetlands most probably occurred due to low concentrations of organic carbon, and short retention times.     

Demonstration,using Desulfobacter sp., of two pools of acetate with different biological availabilities in marine pore water

Desulfobacter sp. (Strain 3ac10), an acetate-utilizing sulphatereducing bacteria, was added to sterile marine pore water spiked with ¹⁴C-acetate, and changes in both the natural acetate pool and the added ¹⁴C-acetate were measured over time. Initially, both the added ¹⁴C-acetate and the chemically measured acetate were rapidly mineralized, but then the rate of removal decreased and a significant amount (approximately 20%) of both ¹⁴C-acetate and chemically measured acetate remained unmetabolised. In a replicate experiment, approximately 50% of the acetate was not metabolised. Kinetic analysis of the data indicated that there were two pools of acetate in the original pore water, a biologically available pool (which is rapidly metabolised) and a recalcitrant pool (which is only very slowly metabolised). Addition of ¹⁴C-acetate after the biologically available acetate had been removed resulted in rapid removal of the added acetate but no change in the recalcitrant acetate pool. The implications of this data to radiolabelled techniques of measuring in situ acetate turnover are discussed.     

Shift schedules on North Sea oil/gas installations: A systematic review of their impact on performance,safety and health

Continuous production processes on North Sea installations necessitate extended work schedules; 2-week offshore tours (alternating with shore breaks), 12 h shifts and rapid day/night shift changes are inherent features of offshore work. These intensive rosters, worked in a demanding physical and psychosocial environment, are potential sources of fatigue and impaired performance among offshore personnel. This article focuses on offshore working time arrangements, and presents a systematic review of studies which examine offshore day/night shift patterns in relation to operational safety and individual health risks. Of the 53 studies retrieved, 24 met the review criteria.Field study findings are generally consistent in showing that sleep, alertness and performance are relatively stable across day-shift tours; initial night shifts are adversely affected by circadian disruption, but full physiological and psychological adaptation occurs within 5–6 days; re-adaptation to day shifts is slower, and varies widely across individuals; the offshore environment is conducive to night-shift adaptation, but interventions to facilitate re-adaptation have proved only modestly effective. Analyses of survey data and accident/sickness records identify offshore night work as a risk factor for impaired sleep, health problems, and injuries, but little is known about the long-term health effects of different offshore shift rotations.In conclusion, research methodology and findings, and working time issues of current concern to the offshore oil/gas industry, are discussed. Aspects of offshore work schedules that have been not been widely studied (e.g. overtime, irregular work patterns) are also highlighted, and research areas that would merit further attention are noted.     

The effects of transition stress: a relocation study

Survey participants (N=175) were drawn from six branches of a major British supermarket chain. Employees from three branches, who had been selected for transfer to new stores, were surveyed before and after relocation to examine the impact of this transition on individual well‐being. A comparison sample of employees, drawn from similar stores but not involved in relocation, was also surveyed. Cross‐sectional multiple regression analyses found that psychological distress was related to both work demands and personal characteristics (gender, neuroticism, locus of control, and social desirability response). Furthermore, path analysis revealed that after controlling for prior symptom levels, distress during the relocation period was predicted independently by the relocation and by work demands. Although in the present study it was not possible to account for differences in outcomes between new and comparison store employees in terms of changes in measured work characteristics, the negative impact of relocation was found to be buffered by perceptions of control and social support. Additionally, the impact of high work demands was buffered by Type B personal characteristics. Copyright © 1999 John Wiley & Sons, Ltd.     

Analysis of volatile fatty acids by ion-exclusion chromatography,with special reference to marine pore water

A method for measuring volatile fatty acids using ion-exclusion chromatography is presented. The system was found to be applicable to samples with high salt concentrations (e.g. seawater and marine pore water) when coupled with a vacuum distillation procedure. The method is straightforward, with no sample preconcentration and no introduction of external contamination. Calibration was found to be linear, with good reproducibility (coefficient of variation normally less than 5%) and the system was sufficiently sensitive to operate at the sub-ppm level (minimum detection limit for acetate and propionate was approximately 0.02 and 0.05 ppm, respectively). This technique was used to investigate the distribution of volatile fatty acids with sediment depth at Station E70 in Loch Eil, Scotland (sample was collected in March, 1983) and the results were in good agreement with recent publications. Although the system, at present, is limited in marine pore water to acetate and propionate, it has certain advantages over alternative systems and these are described.