Comparison of nitrification rates in conventional and membrane-assisted biological nutrient removal processes

A membrane-assisted and a conventional activated sludge system, both operated in an enhanced biological phosphorus removal (EBPR) mode and under identical operating conditions, were studied to investigate the effect of the membrane solids-liquid separation on nitrification activity. Both the membrane EBPR (MEBPR) and conventional EBPR (CEBPR) processes achieved stable and complete removal of ammonium-nitrogen from the influent wastewater. However, when the intrinsic nitrification activity was assessed in offline batch tests, the CEBPR mixed liquor exhibited 15 to 75% greater nitrification potential than the MEBPR counterpart. These results were further validated by monitoring nitrification rates of conventional mixed liquor as it evolved toward a membrane mixed liquor. It was also demonstrated that the larger aerobic mass fraction of the MEBPR system could not be the only factor influencing the reduced intrinsic nitrification rate. The present study strongly suggests that the presence of a membrane solids-liquid separation per se may be sufficient to alter the nitrification kinetics of an EBPR mixed liquor and that this possibility should be considered in arriving at an appropriate process design.     

Eulerian and Lagrangian time scales of the turbulence above staggered arrays of cubical obstacles

Environmental Fluid Mechanics - We present results from water-channel experiments on neutrally-stable turbulent flows over staggered arrays of cubical obstacles modelling idealised urban canopies....     

A stochastic Lagrangian micromixing model for the dispersion of reactive scalars in turbulent flows: role of concentration fluctuations and improvements to the conserved scalar theory under non-homogeneous conditions

Several reaction schemes, based on the conserved scalar theory, are implemented within a stochastic Lagrangian micromixing model to simulate the dispersion of reactive scalars in turbulent flows. In particular, the formulation of the reaction-dominated limit (RDL) reaction scheme is here extended to improve the model performance under non-homogeneous conditions (NHRDL scheme). The validation of the stochastic model is obtained by comparison with the available measurements of reactive pollutant concentrations in a grid-generated turbulent flow. This test case describes the dispersion of two atmospheric reactant species (NO and O₃) and their reaction product (NO₂) in an unbounded turbulent flow. Model inter-comparisons are also assessed, by considering the results of state-of-the-art models for pollutant dispersion. The present validation shows that RDL reaction scheme provides a systematic overestimation (relative error of ca. 85% around the centreline) in computing the local reactant consumption/production rate, whereas the NHRDL scheme drastically reduces this gap (relative error lower than 5% around the centreline). In terms of NO₂ production (or reactant consumption), neglecting concentration fluctuations determines overestimations of the product mean of around 100% and a NO₂ local production of one order of magnitude higher than the reference simulation. In terms of standard deviations, the concentration fluctuations of both the passive and reactive scalars are generally of the same order of magnitude or up to 1 or 2 orders of magnitudes higher than the corresponding ensemble mean values, except for the background reactant close to the plume edges. The study highlights the importance of modelling pollutant reactions depending on the instantaneous instead of the mean concentrations of the reactants, thus quantifying the role of the turbulent fluctuations of concentration, in terms of scalar statistics (mean, standard deviation, intensity of fluctuations, skewness and kurtosis of concentration, segregation coefficient, simulated reaction rate). This stochastic particle method represents an efficient numerical technique to solve the convection–diffusion equation for reactive scalars and involves several application fields: micro-scale air quality (urban and street-canyon scales), accidental releases, impact of odours, water quality and fluid flow industrial processes (e.g. combustion).     

Waves and turbulence in katabatic winds

The measurements taken during the Vertical Transport and Mixing Experiment (VTMX, October, 2000) on a northeastern slope of Salt Lake Valley, Utah, were used to calculate the statistics of velocity fluctuations in a katabatic gravity current in the absence of synoptic forcing. The data from ultrasonic anemometer-thermometers placed at elevations 4.5 and 13.9 m were used. The contributions of small-scale turbulence and waves were isolated by applying a high-pass digital (Elliptical) filter, whereupon the filtered quantities were identified as small-scale turbulence and the rest as internal gravity waves. Internal waves were found to play a role not only at canonical large gradient Richardson numbers $(\overline{\hbox {Ri}_\mathrm{g} } >1)$ , but sometimes at smaller values $(0.1 < \overline{\hbox {Ri}_\mathrm{g}}<1)$ , in contrast to typical observations in flat-terrain stable boundary layers. This may be attributed, at least partly, to (critical) internal waves on the slope, identified by Princevac et al. [1], which degenerate into turbulence and help maintain an active internal wave field. The applicability of both Monin-Obukhov (MO) similarity theory and local scaling to filtered and unfiltered data was tested by analyzing rms velocity fluctuations as a function of the stability parameter z/L, where L is the Obukhov length and z the height above the ground. For weaker stabilities, $\hbox {z/L}<1$ , the MO similarity and local scaling were valid for both filtered and unfiltered data. Conversely, when $\hbox {z/L}>1$ , the use of both scaling types is questionable, although filtered data showed a tendency to follow local scaling. A relationship between z/L and $\overline{\hbox {Ri}_\mathrm{g} }$ was identified. Eddy diffusivities of momentum $\hbox {K}_\mathrm{M}$ and heat $\hbox {K}_\mathrm{H}$ were dependent on wave activities, notably when $\overline{\hbox {Ri}_\mathrm{g} } > 1$ . The ratio $\hbox {K}_{\mathrm{H}}/\hbox {K}_{\mathrm{M}}$ dropped well below unity at high $\overline{\hbox {Ri}_\mathrm{g} }$ , in consonance with previous laboratory stratified shear layer measurements as well as other field observations.     

Armaments and ornaments in the rock sparrow: a possible dual utility of a carotenoid-based feather signal

Females often base their mating preferences on male sexual secondary traits that are used to settle contests among males. Such traits are likely to be honest indicators of male quality if they are constantly used during costly male–male agonistic interactions. Carotenoid signals have been shown to work as a handicap because they are costly to produce. However, the role of carotenoids as “honest” signals during male contests is less clear, and it is not known whether a carotenoid-based trait can serve in both male–male competition and female choice. In this study, we studied the dual function of a carotenoid feather ornament in the rock sparrow (Petronia petronia), a bird species in which both sexes have a yellow throat patch whose size positively correlates with phenotypic measures. First, we investigated, in a field study, whether the size of a male’s yellow patch correlates with his ability to acquire a territory. Second, we tested the signal function of the yellow patch in two male–male interaction in captivity experiments. Finally, we measured female preference for males differing in throat patch size in a mate choice experiment. Our experiments revealed that the size of a male’s throat patch positively correlated with the number of nest boxes he was able to defend. Moreover, in controlled conditions, males with relatively large yellow patches had earlier access to food than those with small patches. Also, in an experiment in which a dummy rock sparrow with an experimentally manipulated yellow patch was positioned near a feeder, latency to feed by focal birds positively correlated with dummy patch size. Lastly, in a dichotomous mate choice experiment, females showed a proximity preference for males whose patch was experimentally enlarged. Taken together, these results suggest that the same carotenoid feather signal may be used in both male–male competition and female choice in this passerine bird.     

Toward a high-rate enhanced biological phosphorus removal process in a membrane-assisted bioreactor.

A membrane enhanced biological phosphorus removal (MEBPR) process was studied to determine the impact of hydraulic retention time (HRT) and solids retention time (SRT) on the removal of chemical oxygen demand (COD), nitrogen, and phosphorus from municipal wastewater. The MEBPR process was capable of delivering complete nitrification independent of the prevailing operating conditions, whereas a significant improvement in COD removal efficiency was observed at longer SRTs. In the absence of carbon-limiting conditions, the MEBPR process was able to achieve low phosphorus concentrations in the effluent at increasingly higher hydraulic loads, with the lowest HRT being 5 hours. The MEBPR process was also able to maintain optimal phosphorus removal when the SRT was increased from 12 to 20 days. However, at higher suspended solids concentrations, a substantial increase was observed in carbon utilization per unit mass of phosphorus removed from the influent. These results offer critical insights to the application of membrane technology for biological nutrient removal systems.     

Assessment of the rangelands of southwestern Santiago del Estero, Argentina, for grazing management and research

Native rangelands of the southwest part of the province of Santiago del Estero, Argentina, are a key source of forage for cow-calf operations. The objectives of this study were to delineate the ecosystem units of the area, to describe the associated plant communities and to interpret the role that physical factors and disturbances such as fire and grazing have had in the changes of the structure of these plant communities. This information is needed for developing recommendations for grazing management, for prescribing appropriate improvement practices (e.g. shrub control, prescribed fire) and as guidelines for future research. The ecosystem was divided into smaller units using a hierarchical method, the categories of practical importance being 'range unit' and 'range site'. They represent the catchment and hillslope scale of the water runoff-runon phenomenon, respectively. Vegetation was sampled using a block and cluster sampling design, registering tree, shrub, forb and grass species frequency, and the standing aerial biomass of the herbaceous layer in a sampling unit=1 ha. Environmental data (topographic position, fire frequency, current and past use, and tree and shrub cover) were also registered for each sampling unit. Indirect ordination of sampling units classified according to range units and range sites, and correlation with environmental variables were performed using multidimensional scaling (MDS) as well as the vector fitting technique. Standing forage and stocking rate were estimated from biomass data. Results indicate that 'range site' is the ecosystem unit that should be considered for management purposes since it correlates well with plant communities: tall, hardwood forests are located on upland sites, woodlands are located on midland sites and savannas are located on lowland sites. Dense shrub thickets dominate in areas rated in poor condition, irrespective of range site. Disturbances such as fire and current and past use have a significant positive and negative correlation with range condition, respectively, suggesting that a state and transition model would explain vegetation dynamics better than the succession model. The estimated stocking rate in lowland sites in good condition was 2 ha UG(-1), while in upland sites in poor condition the stocking rate was 90 ha UG(-1). Active (fire, mechanical treatments) rather than passive (grazing management) methods should be used for range improvement in order to achieve the full potential of the ecosystem.     

Soy production and certification: the case of Argentinean soy-based biodiesel

With the rising emphasis on biofuels as a potential solution to climate change, this paper asks whether certification schemes, developed to promote sustainable feedstock production, are able to deliver genuine sustainability benefits. The Round Table on Responsible Soy (RTRS) is a certification scheme that aims to promote responsible soy production through the development of principles and criteria. However, can and does this initiative address the negative impacts associated with the intensive production of soy? Taking the example of soy biodiesel produced in Argentina, this paper asks whether the social and environmental impacts of soybean production can be mitigated by the RTRS. It concludes that at present certification schemes are unlikely to be able to address either the institutional challenges associated with their implementation or the detrimental impacts of the additional demand generated by biofuels.     

Some characteristics of the urban boundary layer above Rome, Italy, and applicability of Monin–Obukhov similarity

Air temperature and wind speed profiles measured during one year by means of a SODAR-RASS system located within a large park were examined for the urban boundary layer (UBL) over Rome, Italy. These data, combined with velocity and temperature measurements performed near the ground were used to analyze the vertical structure of the boundary layer and to estimate some turbulence parameters characterizing the surface layer. About 52,000 vertical profiles of wind speed and temperature were used for the analysis, allowing investigation for a large variety of stability conditions. First, friction velocity and Obukhov length were examined, showing clearly their dependence on the time of day and season. Second, the applicability of the Monin–Obukhov (MO) similarity theory—developed over rural terrain—was tested up to 200?m above ground level. For the wind speed profiles, the performance of the MO similarity degrades with both increasing height and stability, with maximum errors that are on the order of 300?% at 200?m for the most stable case. In contrast, for the air temperature the error always remains below 50?%.