Downflow fixed-film anaerobic reactors stability studies under organic and hydraulic overloading at different working volume

Four downflow fixed-film anaerobic reactors were used in this study. The effect of organic and hydraulic overloading on the reactors performance was studied. Initially, the reactors were operated at different working volumes and fed with a synthetic medium during start-up and after reaching a steady organic loading with deproteinized cheese whey. Reactors operated fully flooded (DSFF mode) had higher levels of acetic and butyric acids than reactors operated half flooded (ATF mode) during organic overloading. During hydraulic overloading, propionic and butyric acids rose to much higher levels within DSFF reactors than within ATF reactors. Systems operated in an ATF mode produced slightly higher amounts of methane as well as giving higher conversion at lower HRT than DSFF reactors. ATF reactors had a thin though very active biofilm, since biofilm thickness was controlled by shear and gravity forces as well as fluid recycle. In an ATF, inhibition occurred at a maximum of 2000 mg l⁻¹ of acetic, 3000 mg l⁻¹ of propionic and 400 mg l⁻¹ of butyric acid after a sharp overloading.     

Lecane tenuiseta rotifers improves activated sludge settleability in laboratory scale SBR system at 13°C and 20°C

Two experiments at different temperatures were conducted in five laboratory‐scale bioreactors with enhanced nutrient removal simulating the work of sequencing batch reactors (SBRs). The process was operated in three 8‐hour cycles. The oxygen concentration, pH and temperature were controlled and maintained at 1 mg of O₂/L, 7 and 13°C, respectively, throughout the first two weeks and at 20°C for the next 10 days. The introduction of Lecane tenuiseta improved the settling properties of the activated sludge dominated by Microthrix parvicella at both temperatures tested. L. tenuiseta rotifers led to a reduction in filamentous bacteria abundance and did not negatively affect the chemical parameters of the effluent. For each temperature, there were no differences in COD, N_tot, N‐NH₄ or P‐PO₄ values between the treatment and control bioreactors. The results have shown that the application of L. tenuiseta is a promising biological tool for bulking prevention especially in a cold season.     

Survival of the House Dust Mite,Dermatophagoides farinae,at High Temperatures (40–80°C)

Abstract Experiments were conducted to evaluate the survival time of randomly selected female D. farinae exposed to temperatures from 40 to 80°C and relative humidities (RHs) between 10 and 90%. Significant temperature effects were found on the length of time mites can survive under those conditions. The time needed to induce 100% mortality for female D. farinae held at 40°C varied between 39 and 84 h. At 70 and 80°C, all mites died within 5 minutes. At 50°C and above, RH had little influence and temperature alone was the determining factor for mite survival. The length of survival time decreased precipitously between 40 and 50°C, suggesting that a loss of physiological integrity of female D. farinae probably occurred in this range. The results of this study indicated that the technique of raising temperatures to above 40°C for a short duration can be used to reduce living house dust mite populations in homes significantly.     

In situ control of sulfide emissions during the thermophilic (55°C) anaerobic digestion process

Sulfide volatilization was found to be sensitive to the pH variations expected during normal anaerobic digester operation. As digester pH levels increased from 6.7 to 8.2, gaseous sulfide concentrations decreased from 2900 to 100 ppm H₂S(g). Although gaseous sulfide control through pH adjustment was technically feasible, its practical use was limited by the resulting increase in soluble sulfide concentration. pH adjustment for biogas sulfide control was recommended only under conditions in which the influent sulfur level was well below sulfide inhibitory concentrations.

Control of gaseous sulfide levels through insoluble iron (3+) phosphate addition was an efficient gaseous sulfide control process with no adverse effects on digester performance. By varying the influent FePO₄-Fe:SO₄²⁻-S input ratio from 0.0 to 3.5, gaseous sulfide levels decreased from 2400 to 100 ppm. The availability of iron under anaerobic conditions from an aerobically insoluble compound has been termed reductive solubilization.

Using results from this investigation, a unique anaerobic digestion system is outlined to treat sulfur rich wastes in which sulfide inhibition is minimized while maximizing energy recovery.     

Schweißen unter Betriebsbeanspruchung – Werkstoffkennwerte für einen S 355 J2G3 unter Temperaturen bis 1200 °C

Welding under service conditions – Material properties of S 355 J2G3 at temperatures of up to 1200 °C. Measures for rehabilitation, revitalisation of buildings are important future tasks to reduce costs. If reinforcements or changes of the system are necessary, welding is often the simplest way. If the structure, e.g. a bridge, a mast, an offshore platform, is exposed to varying load conditions, the question arises if it is possible to weld even under these service load conditions, which cause harmonic or repeated displacements of the weld seam. Systematic tests of welding under different load conditions as well as numerical simulations are described. An important task in this field is the determination of the material parameters under temperatures which approach the smelting point. Results showing the mechanical behaviour of construction steel S 355 J2G3 are presented in the paper.     

Reliability and residual service life of the steampipe welded joints at the temperature of 540°C

In this paper the influence is described of the 1/2Cr-1/2Mo-1/4V steel pipe joints, welded with electrodes of the same composition (with long-term exposure to the temperature of 540°C and the pressure of 14MPa), on life decreases of steampipe with 273 mm in diameter and 32 mm wall thickness. To the prediction of welded joint lifetimes the model of separated diffusion and fatigue failure was applied. The results show that the prolongation of intervals between the putting out of operation tends to welded joints lifetime elongation. It is also indicated that in lower weld structural stability values for fatigue processes are predominant being caused by a weld failure, and in higher structural stability values the failure is caused by creep processed.     

Long-term (1243 days), low-temperature (4-15 °C), anaerobic biotreatment of acidified wastewaters: Bioprocess performance and physiological characteristics

The feasibility of long-term (>3 years), low-temperature (4-15 °C) and anaerobic bioreactor operation, for the treatment of acidified wastewater, was investigated. A hybrid, expanded granular sludge bed-anaerobic filter bioreactor was seeded with a mesophilic inoculum and employed for the mineralization of moderate-strength (3.75-10 kg chemical oxygen demand (COD) m⁻³) volatile fatty acid-based wastewaters at 4-15 °C. Bioprocess performance was assessed in terms of COD removal efficiency (CODRE), methane biogas concentration, and yield, and biomass retention. Batch specific methanogenic activity assays were performed to physiologically characterise reactor biomass.Despite transient disimprovements, CODRE and methane biogas concentrations exceeded 80% and 65%, respectively, at an applied organic loading rate (OLR) of 10 kg COD m⁻³ d⁻¹ between 9.5 and 15 °C (sludge loading rate (SLR), 0.6 kg COD kg[VSS]⁻¹ d⁻¹). Over 50% of the granular sludge bed was lost to disintegration during operation at 9.5 °C, warranting a reduction in the applied OLR to 3.75-5 kg COD m⁻³ d⁻¹ (SLR, c. 0.4-0.5 kg COD kg[VSS]⁻¹ d⁻¹). From that point forward, remarkably stable and efficient performance was observed during operation at 4-10 °C, with respect to CODRE (≥82%), methane biogas concentration (>70%) and methane yields (>4 l_Methane d⁻¹), suggesting the adaptation of our mesophilic inoculum to psychrophilic operating conditions.Physiological activity assays indicated the development of psychroactive syntrophic and methanogenic populations, including the emergence of putatively psychrophilic propionate-oxidising and hydrogenotrophic methanogenic activity. The data suggest that mesophilic inocula can physiologically adapt to sub-optimal operational temperatures: treatment efficiencies and sludge loading rates at 4 °C (day, 1243) were comparable to those achieved at 15 °C (day 0). Furthermore, long-term, low-temperature bioreactor operation may act as a selective enrichment for psychrophilic methanogenic activity from mesophilic inocula. The observed efficient and stable bioprocess performance highlights the potential for long-term, low-temperature bioreactor operation.     

Effects of hydraulic retention time and proteins on sludge toxicity for 4‐chlorophenol wastewater treatment in sequencing batch reactors

Due to the higher uncertainty of environmental risk for pollutants’ treatment by activated sludge, 10 mg/L influent 4‐chlorophenol (4‐CP) treated via a sequencing batch reactor (SBR) was used as acclimated SBR. Another SBR was used as control SBR without 4‐CP. The effects of hydraulic retention time (HRT) and proteins on sludge toxicity for 4‐CP treatment were analysed, and compared to the control SBR. Results showed that the sludge toxicity in acclimated SBR was significantly higher than that of the control SBR. Shortening HRT from 12 to 8 hours was beneficial to degrade 4‐CP and lower sludge toxicity. The identified highly expressed protein of ABC transporter co‐existed in control and acclimated SBRs, while other proteins of TonB‐dependent receptor, heat shock 70 kDa protein and superoxide dismutase in acclimated sludge were overexpressed relative to the control sludge, which played an important function in degrading 4‐CP, resisting 4‐CP toxicity and eliminating sludge toxicity.     

Full‐scale maturation ponds working below a latitude of 43°S in a semiarid area: seasonal performance and removal mechanisms

Stabilisation ponds are the most frequently used wastewater treatment technology in Argentina. This study focuses on the performance of two maturation ponds (MPs) that are part of the full‐scale sewage treatment system of Puerto Madryn. Seventy‐seven shots of surface water were analysed for organic matter, inorganic nitrogen, phytoplankton dynamics and bacterial removal. The system presented a clear evolution with respect to oxygenation and phytoplankton development. The treated wastewater reached values above 8 mg‐O₂/L, an important organic matter removal, and this was accompanied by a strong increase in pH. removal and oxidation, was active even during winter in the MPs, with average concentrations below 10 mg ‐ /L. Bacteriological removal resulted in a liquid that approached the WHO recommendations for unrestricted irrigation. These results show that is possible to generate treated wastewater in stabilisation ponds working in a semiarid and temperate region, with bacterial content and conductivity suitable for irrigation.     

The effect of slightly warm temperature on work performance and comfort in open‐plan offices – a laboratory study

The aim of the study was to determine the effect of a temperature of 29°C on performance in tasks involving different cognitive demands and to assess the effect on perceived performance, subjective workload, thermal comfort, perceived working conditions, cognitive fatigue, and somatic symptoms in a laboratory with realistic office environment. A comparison was made with a temperature of 23°C. Performance was measured on the basis of six different tasks that reflect different stages of cognitive performance. Thirty‐three students participated in the experiment. The exposure time was 3.5 h in both thermal conditions. Performance was negatively affected by slightly warm temperature in the N‐back working memory task. Temperature had no effect on performance in other tasks focusing on psychomotor, working memory, attention, or long‐term memory capabilities. Temperature had no effect on perceived performance. However, slightly warm temperature caused concentration difficulties. Throat symptoms were found to increase over time at 29°C, but no temporal change was seen at 23°C. No effect of temperature on other symptoms was found. As expected, the differences in thermal comfort were significant. Women perceived a temperature of 23°C colder than men.     

Decolourization performance and mechanism of leachate secondary effluent using Poly‐aluminium(III)–magnesium(II) sulphate

Poly‐aluminium(III)–magnesium(II) sulphate (PMAS) was used to remove the colour from the secondary effluent of landfill leachate and the decolourization mechanism was researched. The results indicated that the decolourization efficiency using PMAS was better than the decolourization that occurred using other traditional coagulants, with a colour removal >90%. X‐ray diffraction and infrared spectrometry showed that PMAS was probably a type of macromolecular composite polymer of aluminium and magnesium that was based on –OH bonds. The coagulation mechanism of PMAS was primarily charge neutralization and coprecipitation netting, with charge neutralization being the dominant mechanism at low doses. In addition, the flocculation behaviour differed in response to various pH values of wastewater at high doses. Specifically, flocculation was primarily driven by charge neutralization at a low pH and coprecipitation netting at a high pH, while it occurred via a combination of these procedures under neutral conditions.     

PVC flooring at home and development of asthma among young children in Sweden,a 10‐year follow‐up

The incidence of asthma and allergy has increased throughout the developed world over the past decades. During the same period of time, the use of industrial chemicals such as phthalates, commonly used as plasticizers in polyvinylchloride (PVC) flooring material, has increased. The aim of this study was to investigate whether PVC flooring in the home of children in the age of 1–5 years is associated with the development of asthma in 5‐ and 10‐year follow‐up investigations (n = 3228). Dampness in Buildings and Health Study (DBH Study) commenced in 2000 in Värmland, Sweden. The current analyses included subjects who answered all baseline and follow‐up questionnaires. Logistic regression analyses were applied to questionnaire results. Children who had PVC floorings in the bedroom at baseline were more likely to develop doctor‐diagnosed asthma during the following 10‐year period when compared with children living without. There were indications that PVC flooring in the parents' bedrooms was strongly associated with the new cases of doctor‐diagnosed asthma when compared with child′s bedroom. Our results suggest that PVC flooring exposure during pregnancy could be a critical period in the development of asthma in children at a later time; prenatal exposure and measurements of phthalate metabolites should be included in the future.     

Electricity consumers under the state and the private sector: comparing the price performance of the French and UK electricity industries 1990–2000

Particularly because a preoccupation with process has tended to dominate the debate about electricity privatisation and liberalisation, this paper focuses on price outcomes by comparing the relative price performance of the French and UK electricity industries between 1990 and 2000. The main conclusion is that in 1990 the state-owned French electricity industry was performing better for most consumers than the state-owned UK industry, and a decade later it was still doing so with respect to the privately-owned UK industry. While this conclusion could be qualified by saying that, heavily prompted or assisted by the Regulator, the UK privately-owned industry has shown itself capable of achieving faster reductions in prices to close the gap between itself and the French, this achievement has been concentrated in the industrial market and even there the very significant gains were mainly restricted to the very largest consumers. In the context of the European Union the UK is shown to have performed relatively poorly for the smallest domestic consumers and, while both countries did much better in the rankings of industrial prices, they were still a long way behind the top performers.